# Top quality Engineer's Square



## whiteant (25 Aug 2007)

Hi, Looking for a good quality Engineer's Square.
Can anyone recommend a maker and an online shop to purchase one?

TIA


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## Mike.C (25 Aug 2007)

I have this Incra and it is spot on.

http://www.rutlands.co.uk/cgi-bin/psProdDet.cgi/GSQR7

Cheers

Mike


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## woodbloke (25 Aug 2007)

I use the engineers squares from Axminster, made from steel. I always worry a bit that when I use an aluminium square with a very sharp knife I'm going to shave a little bit of the side of it, probably never happen. The Axminster squares are quite good, I use a 150mm one for general use but have smaller 100 and 50mm M&W squares as well - Rob


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## Mike.C (25 Aug 2007)

I also use a very sharp marking knife and I have never had any problems.

Cheers

Mike


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## Dan Clark (26 Aug 2007)

I have the same Incra square and like it a bunch. Actually, I bought the large and small one, which was a probably a mistake. The small one just sits in the box. 

Althought they are very accurate, the biggest advantage (IMO) is the thickness of the metal. It makes them easy to hold and easy to get lined up. I have some steel engineer squares that are the traditional thin ones. Now they just sit in their nice pretty wood box.

Dan.


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## DomValente (26 Aug 2007)

Mitutoyo make very good engineers squares.

Dom


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## jasonB (26 Aug 2007)

Moore & Wright also make decent squares, an grade B (workshop) one should be fine for woodworking purposes. Just hope you don't want a big one as they go upto £650 :!: for a 24".

You can buy them here, jump to page 584

Jason

PS I still use the one I made at school.


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## engineer one (26 Aug 2007)

the obvious question that has not been asked is what do you want to do with it???

unless you intend to use it as a reference item, then it is often better to use a combination square, which gives you the chance to draw 45degree lines too.

axminster do a decent one, but if you can find an engineers square, then look for m&w or starrett, or as dom says mitotoyu

paul :wink:


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## Paul Chapman (26 Aug 2007)

engineer one":1mixphv6 said:


> then it is often better to use a combination square, which gives you the chance to draw 45degree lines too.



In my experience, these are probably the most inaccurate "squares" of all. I have a couple which I use for a lot of things, but never as squares, because they are simply not square.

Cheers :wink: 

Paul


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## engineer one (26 Aug 2007)

interesting paul, i never have any trouble with their being square :roll: 

a lot depends upon the quality and the tightening mechanism i guess.

also depends upon the maker too i would think.

actually for woodworking, i use the winged square that trend now sell,
i think it is 3m's is very accurate, and adjustable, plus the wings mean you can go round 3 corners which is pretty useful.

another way to go is one of the veritas saddle squares, the go round two corners, which minimises errors.

will go and check my combination square again, but am pretty happy. :lol: 

paul :wink:


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## Woody Alan (26 Aug 2007)

Paul I have had the same and opposite experience. My Starret combo is as accurate as could be wanted certainly as accurate as the axminster engineers square but more importantly it's easier to use being a bit lighter. I have a rabone combo which was slightly out but like anything else it was fettled to be good enough to use, a bit of draw filing on the blade and polish on a stone. I agree Paul (eng 1) combo for the woodshop with engineers square for ref if needed. I bought a japanese small square form CHT wasn't impressed out of the box, It's square now,I think you get what you pay for. 

cheers Alan


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## engineer one (26 Aug 2007)

being a pessimist, and typical of anyone using their tools, i think the other problem with an engineers square, is what happens when you drop them  

somehow the over long thin arm can be dinged out of accuracy quite easily if you manage to drop it. in my experience, the combination square is more able to handle the day to day abuse.

when bought, or even in the store, check that it is square, it ain't difficult.

get your favourite cut edge, mdf works well enough and draw a line along the long arm. then reverse the square and draw another line, if in the same place, it is square, if not well now you know. :roll: 

paul :wink:


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## Paul Chapman (26 Aug 2007)

woodbloke":3tg387r6 said:


> I always worry a bit that when I use an aluminium square with a very sharp knife I'm going to shave a little bit of the side of it, probably never happen.



I've found that, if you are not careful, you can sometimes shave a thin sliver off a steel square or straight edge if the knife is very sharp :shock: 

Cheers :wink: 

Paul


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## engineer one (26 Aug 2007)

ok, just checked a couple of things.

i actually have 3 combination squares too. a short one taiwanese/general make, which i use for checking on my tormek in sharpening. only 3inches long,it has very small error possibilities.

i also have two longer 12inch ones(boasting i know  )
one is a cheap and cheerful ally one. checking that i have found it is about 0.5mm out over 10 inches, which is not too bad.

i have also checked the axminster one i had bought some time ago. 
that is i would say pretty spot on. interestingly of course, if you try to get the whole length of the ruler in use, you build up the inaccuracy since it has to be lined up with the ruler along the whole of the slot. so in fact you only get about 10 inches of useable ruler.

actually, i rarely use my combination for checking square, but i do use it as a marking gauge, much more accurate than a tape. and unless you make your own "proper gauge" rarely do they come in sizes of more than about 6 inches. so the combination square is a quick and dirty way of marking out, and with the square part, you can run along a board and get a pretty accurate line.

another useful tool is also a veritas one, which is an attachment that screws on to a steel ruler of standard 25mm width, so far i have found it too to be pretty accurate and square. the also do an adaptor which screws on to a rafter square which allows you to rest the edge of the square against a board edge.

you could also buy one of the plaster board 1200 squares, i am amazed how accurate they are and stay. 8) 

finally you need both a 3,4,5 square and a set of pinch rods to ensure that things are square. and you can make the 3,4,5 out of a piece of mdf or ply, whilst the pinch rods are also easily made at home from strips of 3/4 wide by 1/2inch thick hard wood clamped in the middle, and extendible.

paul :wink:


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## Paul Chapman (26 Aug 2007)

engineer one":1ljhtn4g said:


> which is not too bad.



Well it is, actually - it's either accurate or it's not :wink: It's all about compound errors. A little bit out might seem OK but those little bits add up. When you come to put several pieces together, and they are all a little bit out, you find that the whole job is p****d. And with combination squares, if you want to use the outside edges, you have to have the blade fully extended, which is when its accuracy is at its worst.

If you are happy with the accuracy of yours, Paul, that's fine but I certainly no longer use mine to check squareness - but they are very handy for depth measurements; checking distances, say, from the router base plate to the edge of the cutter; making parallel pencil lines along boards, etc.

Cheers :wink: 

Paul


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## engineer one (26 Aug 2007)

i do agree paul, and i think the really important thing is to be happy with whatever tool you use.

when i trained all those years ago, we used two squares one for laying out, and the other to check. i do however think that we have a little more flexibility in wood than we used to have with metal.

the most important thing is to minimise the compounding of errors.

by that i mean make for instance one "h" frame, and ensure that is square
then make the other etc. 

i think that when one starts one is so determined to finish that one does not dry assemble prior to final assembly, ( i know that is a no no with 
dovetails :roll: ), and then you can i think reduce the accumulated errors to some extent.

of course the really strange thing is how accurate your eye is once you get it back into practice, so often, the square is only a guide anyway.

if you are not using man made boards, then wood movement will impact on your squareness, and your ideas thereof too i think.
anyway that's another can of worms. :lol: 

if you look at how devon woody builds his boxes, he seems to use a lot of jigs to ensure flatness and square. i think many of us tend not to use jigs for "normal" work which may also exacerbate the angularity.

thank good for bessey clamps i say :lol: :twisted: 

paul :wink:


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## woodbloke (26 Aug 2007)

Paul Chapman":sio14prg said:


> engineer one":sio14prg said:
> 
> 
> > which is not too bad.
> ...


I also have a decent enough R&C combo square but I only use it for a bit of 'rough' work, eg if I want to put a pencil line across a board for cross cutting to size then this sort of square is very handy. For accurate work tho' it stays on the 'Tool Wall' and something else is used instead :wink: - Rob


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## Mike.C (26 Aug 2007)

The thing I like about the Incra is they guarantee that it is square when you receive it, and it will stay that way even if you drop it.

Cheers

Mike


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## DomValente (26 Aug 2007)

Mike.C":oh6lb5ul said:


> The thing I like about the Incra is they guarantee that it is square when you receive it, and it will stay that way even if you drop it.
> 
> Cheers
> 
> Mike



Uhuh  I'm not a cynic, honest.

Paul I agree with Paul, anything that is inaccurate gets chucked out, as he says, those little bits add up.

Dom


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## engineer one (26 Aug 2007)

interesting i have been following this thread today whilst doing some cad work for a book i am involved in.

i am re-drawing gear for working a water scoop on an old 19th century locomotive tender. so accuracy has been high in my mind.

however i keep getting told that woodwork can never be as accurate as metal work, so the dichotomy is interesting :lol: 

i agree that your tools that are intended to be square should be square, but i wonder how many of us actually re check the scms, table saw, band saw EVERY time we make an adjustment :? 

truly errors accumulate, but that is why you use only one measuring tool on any one job, and only one square or type of square.

the question that was asked, was without a reason, since we do not know what he intends to do with the tool. so whilst it is good to aim for complete accuracy, it may not actually be what is required. :roll: 

as i have said, you can obviously make some adjustments in assembly, and if you make sub assemblies, and each is square and the correct length, the whole will also be square.

now back to turning 2d engineering drawings into what i want in 3d  

paul :wink:


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## DomValente (26 Aug 2007)

*Engineer one wrote:*


> the question that was asked, was without a reason, since we do not know what he intends to do with the tool. so whilst it is good to aim for complete accuracy, it may not actually be what is required.



Surely Paul, the fact that he asked for an engineers square was a clue.
 
Dom


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## whiteant (26 Aug 2007)

Yes, it is needed as an accurate reference square.
I will buy an Incra and see how it goes.
Many thanks for comments.


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## AndyBoyd (26 Aug 2007)

I use the GROZ ones from Dick, I check it every now and again and it it's been knocked out I bin it and get another they are as cheap as chips.

To check it I drawer a line flip it draw the line again and see if they deviate


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## David C (26 Aug 2007)

This 'woodworkers don't need accuracy because wood is always moving' thing, is one of the most misleading old or new wives tales available, and demonstrates a complete lack of understanding of fine cabinetmaking skills..

A one thou gap looks and feels like a one thou gap.

A four thou gap in an edge joint probably means it will fall apart.

My second dvd demonstrates that it is perfectly simple to plane up a piece of wood to a tolerance of plus or minus about 2 thou without undue difficulty. The sample is usually about 15" long, 4" wide and 3/4" thick. This marvel is done with a hand tool and needs nothing more than a setsquare, winding sticks and a marking gauge.
What's more we can be achieve this a great deal more quickly than an engineer could with a lump of metal and hand tools. Stanley laterly failed to do this with machinery.

The straight edge is not necessary if using a well tuned jack plane.

I get beginners to achieve plus or minus 4 thou" in a matter of days.

The errors of squareness relative to a bench grade engineers square are significantly less than 1 thou".

best wishes,
David Charlesworth


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## Dan Clark (26 Aug 2007)

Paul Chapman":2oi8pjb5 said:


> engineer one":2oi8pjb5 said:
> 
> 
> > then it is often better to use a combination square, which gives you the chance to draw 45degree lines too.
> ...



When I posted about buying an Incra square, what I didn't say was WHY I bought it...

I have a Starrett combo square. Since Starrett is a (or was) a top name here in the states, I always assumed that it was *SQUARE*. Hah! Wrongo!

For several weeks, I kept having problems with cuts that were square according to the Starrett square, but were not. So I finally checked it against my cheapo engineer squares. Arrgh! Then I checked it against my Swanson Speed Square (which is supposed to be construction-grade). The Speed Square was more square!!!

It turns out that my Starrett combo square would change squareness depending on where it was set. I still use it occasionally where accuracy isn't critical.

OTOH, my Incra is used constantly. It's only weeks old and it's starting to show wear marks from all the use. It seems expensive, but on a per-use basis, it's dirt cheap!

Dan.


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## Woody Alan (26 Aug 2007)

> It's only weeks old and it's starting to show wear marks from all the use


Is it possibly how the starrett became inaccurate through lots of use and needed replacing? 

Alan


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## MikeW (26 Aug 2007)

I would be one person chanting the mantra that woodworking does not need to be to the accuracy as metal work--but what I mean by that may not be what another means.

Accuracy is needed in top work. Accuracy to the best of one's ability is reality. Trying to achieve accuracy beyond one's ability is simply improvement. _*Trying to achieve metal working tolerances is insanely unrealistic.*_ 

Using accurate layout tools that are beyond one's ability to achieve in performance eliminates them as a source of error. Error will creep in during marking out and processing. Dealing with that error is simply experience.

The two materials (wood/metal) are so different. If you think you can see a 1 thou gap in wood, try metal. It looks/feels even more acutely wrong. I would reckon no one here on this forum can make a set of DTs to 1 thou accuracy across the width of a single corner, much less 4 corners. And one doesn't need to, either. Wood has a different level of compressibility. I think that for some of these really nice DTs that have been pictured here, that there actually is a degree of "too" tight a fit. Which works out wonderful in wood--not so in metal.

So too with tenons. If I am a few thou off cutting a shoulder line I can assure you it will close under average clamping pressure. A metal version simply would not.

So, nope. I don't think woodworking is anything like the level of precision needed to the average metal work done at a machine shop. The machine shop I worked at in the 1970s worked at fairly sloppy tolerances for most work. 3 zeros before significant digits.

I also think there is in woodworking a tendancy for especially new workers to fret that their work needs to be as accurate as what they may see pictured, or aspire it to be. So when someone like myself suggest they relax, finish and move on because "woodworking doesn't need accuracy to multiple decimal point" it can be interpreted as "it doesn't matter." (Nor do they actually understand what it really was like prior to the nice picture that was taken--the during building and following glue up.)

I have built fairly OK furniture for rather good commission fees. I have never, ever cared if a rail was within 2 thou of the adjoining stile before glue up. Nor did I care if it was that all 'round a door after glue up. Could I do it? I don't know. I've never tried. In all likelihood I never will try.

So there it is. My "standards" or lack thereof.

Take care, Mike "The Heretic" Wenzloff


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## engineer one (27 Aug 2007)

having thrown down the gauntlet, a couple of points.

i think mike w is absolutely right. experience gives you the ability to 
make things more accurately in wood particularly, whether you or even i can plane a piece of wood accurately to within 1-2thou, and i have been lucky enough to do it when i had my last practice, it does not make the assembly any more accurate. what makes the assembly accurate is 
that the diagonals are the same. :twisted: 

whilst gaps can be seen, in many designs i have seen, the gaps are actually made something of, and people tend to use "shadow lines" to divert the eye.

i think if you use modern glues, it is easier to adjust for the gaps, and still get decent glue up.

you can only make to the best of your ability, and as you finish one thing,
you find where you want to improve, and become more accurate on the next job. at which point you may want additionally accurate tools, but as we have seen rather like cutting tools, you cannot assume your so called square tools are all properly square.

dom, i actually do use an engineers square in my woodworking too,
so it was a valid question, even for me :roll: :? mainly to set up machine tools. 

surely when you make mortices and tenons, for instance, the value of shoulders is in the hiding any errors in the mortice, but not of course any errors in the cutting of the shoulders and their bottoms.

paul :wink:


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## Dan Clark (27 Aug 2007)

Woody Alan":uk3y4ydm said:


> > It's only weeks old and it's starting to show wear marks from all the use
> 
> 
> Is it possibly how the starrett became inaccurate through lots of use and needed replacing?
> ...


Alan,

Perhaps, but the Incra is still perfectly accurate and the Starrett is not. 8) Starrett still makes nice stuff, but I'm not buying much of it these days.

Dan.


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## David C (27 Aug 2007)

Mike,

For a heretic the fit of the spine of your dovetail saw to the handle is awesome ~;-)# The top of the range Pax I was loaned recently is flapping about in the breeze.

Though I agree that there is no point trying to exceed one's ability and that accuracy is only needed in a few specific instances it does matter.

The fact that most bench grade engineers squares are off by a thou" or more has little impact if one has a consistent technique for using them. 

The compressibility of many timbers can be helpful, but the hand sliding fit of a tennon requires good tolerances.

Dovetails in dense brittle timbers need accurate work as well.

best wishes,
David


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## engineer one (27 Aug 2007)

once again david you coat the sour pill lower down in your responce.

"even if an engineers square is off by a few thou, if used consistently it will suffice" (sorry if i have slightly overstated the fact) :? 

any time you move a measuring or layout item, you are bound to accumulate errors, since every time you move, you move your stance, and thus the way in which you hold the scribing instrument,pencil, knife etc,
and the pressure you put on it. :? 

also it is often awkward to stand properly over the whole piece of a board, or sheet. you have to use a position or stance which is comfortable and yet enables you to see the whole item. :roll: 

for instance the standard square check of flopping the item and drawing along both sides depends to some extent on where you stand, and how you angle the scriber and whether it has one bevel or many.

one of the reasons that many experts suggest using a single sided marking knife, and then marking the struck line with a pencil to highlight.
but unless you hold the knife upright, (which may be very uncomfortable)
you still can build in some errors in marking.

unless you are making furniture to specifically fill a space, without framing to fit it, you have some room for manouvre, and the important thing is the "LOOK".

i appreciate that more of you are expert than me and have more finished items to your scrap book than me, but i spend a fair amount of time converting items into models, and i know that often when something is perfectly scaled and made into a model, it just does not look "right"

the eye is a strange instrument, and the accuracy it offers is more important than mere measurement.

as i have agreed in another thread about levelling tables/chairs it is important to start out as accurately as possible, but unless we then make everything on a cnc machine, errors WILL creep in, it is inevitable with any hand work. every time you saw by hand you cut to a different part of the line, every chisel stroke or plane stroke does the same. it is inevitable that every time you move, you do not return to EXACTLY the same place, thus you input is slightly different. :-k 

more worrying is that often something is perfectly correct, and still LOOKS wrong, and no amount of accurate layout, making etc will change that.  

so i guess the answer to the original question is someone like Shesto,
Tilgear, or Chronos, and buy the best you can afford, then use it only for checking your other measuring equipment or squares. 

also check out the trend 3 way square, it is a neat piece of kit, but of course it won't lay flat on the workbench :? 

paul :wink:


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## woodbloke (27 Aug 2007)

I read somewhere (can't remember where :?) that the levels of accuracy needed in good quality work, for example, on a carcass lets say with a diagonal of 1000mm, ought to be 1/2 or 1mm out in the diagonal is acceptable. It's also a requirement to know *which* measurements are critical to get right and those that are not so important. As has been said before on other threads, perfection can't be achieved 'cos we're all human beans with all that implies, but it's relatively easy to be* very* precise when working with timber which goes someway to achieving perfection. Any work we do will *always* have accumulated faults no matter how skilful and careful the maker, the important thing is to realize what and where those faults are, why they were made and to try :roll: to ensure that they aren't repeated in the next project - Rob


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## Paul Chapman (27 Aug 2007)

woodbloke":2sicbyg8 said:


> It's also a requirement to know *which* measurements are critical to get right and those that are not so important.



I think a good example is something like a picture frame, where there are eight 45 degree cuts to make. Each one may only be out by one degree but the whole lot together come to eight degrees, which is a lot and would be very noticeable in the finished job.

Cheers :wink: 

Paul


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## engineer one (27 Aug 2007)

yes, but paul, there are actually two arguments there. :roll: 

one is actually you will only get 4 angles with the same error, since you then turn the wood around, or the jig, or the mitre block, so often they can cancel themselves out. technically you are right, but :? 

the other thing we are always told that sawing to an angled line may not bee too accurate anyway, so back to the shooting boards :lol: :lol: :twisted: with birds' nests to ensure you get the angle right.

the other thing is you can always fiddle the joint once you have cut all 8 angles. pin the pieces in the jig, and then cut through the joint to ensure accuracy.

paul :wink:


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## MikeW (27 Aug 2007)

Hi David--thank you...

I think there's a difference in reality and goals. The reality is I cannot exceed my own abilities, often changing abilities within a single piece of furniture. My goal is (nearly) always to try and exceed my abilities.

What I can do is use accurate tools and rely on my eye. I must confess I do not have engineers squares. My most used try square for larger layouts is a 16" long Disston from about the 1875 period, for moderate sized layout, an 8" General bought for $5 (new), and for general joint layout a pair of Stanley 4" try squares from the end of the 1800s. For depth marking or even smaller layout, an old 4" B&S double square. For a combination square I rely on my 1950s era 12" Tumico. 

Steel rules generally come from Woodcraft or LV, none of which have I bothered to true. I may mark a "straight" line with them, but rely on the plane or chisel to actually make the stuff "true." How do I know it is true? If it fits <g>.

Take care, Mike


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## MikeW (27 Aug 2007)

engineer one":3dg0xrl0 said:


> ...the other thing is you can always fiddle the joint once you have cut all 8 angles. *pin the pieces in the jig, and then cut through the joint to ensure accuracy*.


Or rather, complimentary inaccuracy :lol: 

Done that more than once, Paul. It can work if the stuff is such that it can be joined straight away from the saw. In the case of something always exposed, like a picture frame, a box to be seen and handled, I will still opt to shoot it or lightly plane it freehand.

Take care, time for work at my end...Mike


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## David C (27 Aug 2007)

I used to read Model Engineer magazine, to while away Prep time at school. Also because I was attempting to machine Stuart Turner kits of castings in the excellent machine shop.

Live steam scale models are fascinating, and I seem to remember that they could not be made to work well because in a half scale model;

dimensions are halved,
areas are quartered,
and volumes are divided by 8.

therefore steam passageway crossectional areas and cylinder volumes had to be increased to get the things to work??

I am fond of stating this as a reason why scale models of furniture do not quite give the feel of a full sized piece. Hope there is some truth in this?

David C


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## engineer one (27 Aug 2007)

i do agree with both those comments david, but the other thing is that it is actually difficult to visualise how a model will look in real size.

all models of full size things can do is to allow for placement and getting a feel, to really see it needs to be the size you intend to create.

one of the reasons so many smaller steam engines use high pressure steam is because of the problems you highlight. one of the important things to remember is that as air/steam gets nearer to the surface, it is more affected by the laminar flow layers, and thus needs more speed and 
pressure to achieve a similar effect.

mike, i bow to your comments about frames i was just putting forward an alternative to that of the other paul. :? 

paul :wink:


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## bugbear (28 Aug 2007)

whiteant":2n2ikjeg said:


> Hi, Looking for a good quality Engineer's Square.



Can you be more specific as to your requirments? 

Some square are so "good" that they are easily damaged, and have to be used in temperature controlled rooms!!!

BugBear


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## David C (28 Aug 2007)

Yes,
Tolerances are more useful than descriptive words. Good is a bit vague......

I have some remarkable straight edges from Dick fine tools where tolerance is quoted;

such as 500mm long tolerance 0.004 mm.

Now 0.1 mm is almost exactly 0.004 inches (4 thou")

So I think this means + or - 0.00016 inches or plus or minus less than a couple of ten thousandths of an inch! 
At 21.60 euros this has to be the bargain of the century.

I'm sure someone wise will correct my maths if I have got this wrong?

The item mentioned, cat no 707292 on page 88 of the 06/08 catalogue, has a plastic or rubber hand grip so that body heat does not warm and distort the precision edge.

There are various firms who ought to know better who sell "straight" edges with no tolerance. The one thing you can be certain of is that these are not straight enough to be much use...... specially for testing plane soles (a subject which is of great interest to me), as you can't plane a straight edge with a fine shaving if the plane sole is significantly hollow in length.

Sorry if you have heard this rant before but some manufacturers seem to ignore this inconvenient fact.

David Charlesworth


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## lurker (29 Aug 2007)

I think too many of you are trying to crawl up yourselves a bit here. :lol: 

The adge that you only get what you pay for does not always work.

ie a £100 square is not 10 times as accurate as a £10 one and even if it was then marking out is likely to negate that. And its just as likely to get damaged as a cheapo one.

I'm fortunate enough to have access to measuring equipment that fills a building and as BB says has to be temperature controlled. I bought a 10" cheap engineers square and got "the lads" to check it out for me. They say its as accurate as any other in the company's machine shops (most are M&W costing eyewatering sums and kept in there own boxes). I use this as a reference for my other squares and don't bash it about.

The big issue IMHO is the square is square enough, but importantly is stays that way (and you check it frequently).

My problem is (being a rubbish woodworker) is I can mark out accurately (thanks to my engineering apprenticeship) but can't cut to the line


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## bugbear (29 Aug 2007)

Dan Clark":1669y70m said:


> I have a Starrett combo square. Since Starrett is a (or was) a top name here in the states, I always assumed that it was *SQUARE*. Hah! Wrongo!



Assumign that tools from any manufacturer, including Starrett, Mitutoyo, Moore & Wright etc are "absolutely accurate" is a mistake.

All these manufacturers makeq a wide range of tools, at different prices, and for different requirements.

AFAIK they ALL make toolroom grade reference squares. These are guarenteed accurate to quite remarkable tolerances.

They can only be used to this degree of accuracy under highly controlled circumstances. They are so accurate that thermal expansion of the square or workpiece caused by a 1 degree change in temperature is greater than their tolerance, and (clearly) what would be a tiny "ding" on a roofing square is a disaster on a square of this tolerance, so handling and storage must be done with care.

Fortunately, less accurate squares are also made, requiring less care in use, and at a lower price.

It is (I hope) obvious that a combination square will never be as accurate as a fixed "engineer's square" since the bearing surfaces in a combo square are quite small, and subject to frictional wear.

In short (as I've said before) there's no such thing as "dead accurate"; just "close (r)tolerances"

BugBear


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## bugbear (29 Aug 2007)

David C":6f1j9x04 said:


> Yes,
> Tolerances are more useful than descriptive words. Good is a bit vague......
> 
> I have some remarkable straight edges from Dick fine tools where tolerance is quoted;
> ...



That would be a _remarkable_ bargain; I suspect the tolerance is probably 0.004mm per <some>; perhaps you could check, since I can't find the information on their web site.

BugBear


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## engineer one (29 Aug 2007)

this has certainly grown into an interesting and informative thread.

what is certain is that a "truly accurate" square cannot be used outside a clean room which is temperature controlled, and actually touching it may well throw it out. :? 

so we have to accept a certain level of inaccuracy to be able to use the item in day to day life. obviously 89 or 91 degrees are no good, but where in the range of 90+- 0.3 degrees are we prepared to accept things?

as for bugbears comment about the bearing surface on a combination square in part i would suggest he is wrong. on most engineers squares i have (3, 6,9 and 12inch at least) the actual area of the stock which encloses the blade is quite small, being approximately 70% of the interface. also the way many people use their squares is going to cause major problems because the number of people who hold the square by the blade is amazing  

certainly on my combination squares the bearing surface is quite a lot longer. obviously wear takes its toll, but you do need to check all things measuring on a regular basis. 

my final thought is we all spend a considerable amount of money 
and time using tapes which have moveable ends and we all accept that accuracy. :roll: 

paul :wink:


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## David C (29 Aug 2007)

BB,

I also cannot find the + or - tolerance per ?? except on a European standards website where you have to pay to read the information ;-(

Perhaps an e mail to Doktor Rudolf will supply the answer ...

best wishes,
David


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## bugbear (29 Aug 2007)

engineer one":1yvswjyl said:


> certainly on my combination squares the bearing surface is quite a lot longer. obviously wear takes its toll, but you do need to check all things measuring on a regular basis.



In all (not that many...) combination square I've seen, the blade runs on small bearing surfaces at each end of the slot it sits in, not even the full length of the slot. There is no attachement to the "face" of the rule.

BugBear


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## Racers (29 Aug 2007)

Hi, Bugbear

Yes combination squares rules only ride on a small area at each end of the slot that is so you can adjust them by filing, I have done mine both the 90 and 45 deg angles are quite good now (temperature depending)and it didn't take long.


Pete


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## Paul Kierstead (29 Aug 2007)

Luckily for me, my shop is temperature controlled so I'll never have to worry about any project not being square.


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## bugbear (29 Aug 2007)

Racers":376vshw6 said:


> Hi, Bugbear
> 
> Yes combination squares rules only ride on a small area at each end of the slot that is so you can adjust them by filing, I have done mine both the 90 and 45 deg angles are quite good now (temperature depending)and it didn't take long.
> 
> ...



Heh. I've done that. But only after I'd taken out the 1/32" bow that had been worn into the edges of the rule, and made the edges parallel (*) (**) !!

I guess it was a fairly well used combination square  

BugBear

(*) actually filed one edge with reference to my surface plate
(**) actually filed the second edge in reference to the first edge, checking every 1/2" with a micrometer across the width of the rule


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## Harbo (29 Aug 2007)

The tolerances of Dick's tools are stated in their catalogue (hard copy).
The precision knife edge rules are Grade 00 to DIN 874 - the 500mm Tolerance is 0.004mm Cost 54.50 Euros plus VAT.
The 300mm one is tolerance 0.003mm and costs 26.50 Euros.

They also do knife edge squares to similar tolerances. Because of their thickness and bevel edge not much good for marking out but good for checking edges and other squares.

Rod


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## David C (29 Aug 2007)

Harbo,

I did quote that tolerance about ten posts back....

However as it is stated in the catalogue the meaning escapes me.

Are we talking +or- 0.004 mm overall or +or- 0.004mm per 100 mm? for the 500 mm precision straight edge.

David


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## woodbloke (29 Aug 2007)

David C":7uxm8ozd said:


> Harbo,
> 
> I did quote that tolerance about ten posts back....
> 
> ...


.....we're talking about _woodwork_, and after a bottle of red vino, it's off to bed.....zzzzzzzzzzzzzzzzzzzzzzzzzzzzzz - Rob


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## PaulO (29 Aug 2007)

David C":oh5ls5xl said:


> Live steam scale models are fascinating, and I seem to remember that they could not be made to work well because in a half scale model.......
> 
> David C



You need to scale according to Reynold's number.


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## Harbo (29 Aug 2007)

Sorry David C - I have been away for a few days and have been only quickly scanning the threads.

As the tolerances are quoted differently for each of the three rules - increasing with the length - I would read it 0.004mm per 500mm.

It also quotes that a square 0.5degree out of true, gives an error of 8.7mm per m. 

Rod


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## PaulO (29 Aug 2007)

Paul Chapman":53xbwl2f said:


> engineer one":53xbwl2f said:
> 
> 
> > which is not too bad.
> ...



Accuracy depends on the scale that you are using. An engineers surface plate prepared using the three surfaces and scraping/frosting is generally considered "flat", but the surface finish is actually quite poor. So over (very) small distances, it can't be considered "flat". In the same way an engineers square with a (small) bow across any of the dimensions may be square for certain dimensions, but not for others.

Sorry if I have missed similar comments on other pages of the thread, but I have short attention span, and can't read more than 1 page at a time :roll:


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## David C (30 Aug 2007)

Harbo,

No worries. That is what I assume though it is not stated absolutely explicitly.

Anyway it is the best most affordable testing st edge that I have ever owned and I am very pleased with it. 

The small version is fantastic for testing chisel and blade backs to see how much work they will take to flatten or minutely hollow! 

Also very pleased indeed with the lifetimes supply of plastic engineering shim stock that a kind reader from USA sent me.

David C


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## newt (30 Aug 2007)

Just a thought. If you have what you think is a straight edge (SE) could you check it as follows. Flat piece of MDF longer than the S E, drive a small panel pin at each end, place SE against both pins, mark the centre of the SE then draw a line against the SE for the full length. Now place the straight on the other side of the pins, line up the centre mark and again draw a line. If the SE is true the 2 lines should be parallel spaced apart by the thickness of the pins. I checked my 1 meter rule and it was concave on one side and not surprisingly convex on the other, I thought it was straight. The really sad thing is I was thinking about this when I woke up at 3 in the morning. I accept this is very very crude.


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## Paul Kierstead (30 Aug 2007)

newt":2kr73u0d said:


> I accept this is very very crude.



Crude? I think not. It is quite elegant and -- AFAIK -- is more or less (sans pins usually) the accepted way to check a straight edge that doesn't have to be to laboratory standards.


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## David C (30 Aug 2007)

Newt,

This is a good method, but not quite sure why you would assume a ruler to be straight? Generally they are not.

Now in the past workshops had wooden straight edges which they made and checked.

Three edges which agree with each other must be straight.

Sounds like a good planing exercise to me.

David Charlesworth


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## Karl (3 Sep 2007)

Hi Whiteant

Not sure if you've purchased your Incra yet, but I have just ordered a set of squares from Aminster. http://www.axminster.co.uk/product-Axminster-Three-Piece-Precision-Square-Set-649978.htm

In terms of squareness they seem to be more than upto the task, and you get 3 for pretty much half the price of the Incra. The longest isn't quite as long as the Incra though.

Mine should be arriving in the next day or two - I will let you know the outcome if you'd like.

Cheers

Karl


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## MooreToolsPlease (3 Sep 2007)

That seems like a simple and easy method newt, 
When I buy straight edges and squares, as long as they comply with the relevant british standard I am happy enough.
I have a Master square that they get checked by when new and thats usually it unless the square gets dropped


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## bugbear (4 Sep 2007)

newt":v2hf62fe said:


> Just a thought. If you have what you think is a straight edge (SE) could you check it as follows. Flat piece of MDF longer than the S E, drive a small panel pin at each end, place SE against both pins, mark the centre of the SE then draw a line against the SE for the full length. Now place the straight on the other side of the pins, line up the centre mark and again draw a line. If the SE is true the 2 lines should be parallel spaced apart by the thickness of the pins. I checked my 1 meter rule and it was concave on one side and not surprisingly convex on the other, I thought it was straight. The really sad thing is I was thinking about this when I woke up at 3 in the morning. I accept this is very very crude.



It's a fine, and well accepted technique. It (clearly) is limited by the fineness of the line you can draw, and your eyesight in judging parallelness.

Within these tolerances (that word again) it's a thoroughly reasonable test.

BugBear


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## NeilO (4 Sep 2007)

Engineer one wrote,


> what is certain is that a "truly accurate" square cannot be used outside a clean room which is temperature controlled, and actually touching it may well throw it out.



Didnt realise you`d seen my workshop , Paul  :lol:  :lol:  :lol: 


I wish..........



So, why that in mind does anyone want to come and collect all my tools, because there is no way I`m working to tolerances like that... :shock: :lol: 

put your perfect square down , and if youve not already bu**ered it up by touching it, a nice .5 micron of dust falls on it and bends it like a `kin banana :lol: :lol: 



I know accuracy means a lot , but surely the fact wood moves gives you a small amount lee way, im not talking huge gaps like 2-3 mm, but even a tight fit would .25-.50 mm for glueup ?


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## Neil A (9 Sep 2007)

Harbo":2jopesb9 said:


> The tolerances of Dick's tools are stated in their catalogue (hard copy).
> The precision knife edge rules are Grade 00 to DIN 874 - the 500mm Tolerance is 0.004mm Cost 54.50 Euros plus VAT.
> The 300mm one is tolerance 0.003mm and costs 26.50 Euros.
> 
> ...




The DIN standard of tolerance on Dick's straight edges has caused a little discussion. Whilst I havent been able to lay my hands on the standard, I found a couple of papers about it.
Essentially, the tolerance appears to be over the entire length of the edge.
The documentation I found is for edges of 500mm and upwards.

Anyway, DIN 874 covers a number of separate standards exist:
DIN 874/2 -- where the tolerance is 22 micro meters (0.0008 inches)
DIN 874/1 -- where the tolerance is 12 micro meters (0.0005 inches)
DIN 874/0 -- where the tolerance is 7 micro meters (0.0003 inches)

My Dick edges are 300mm and 100mm and marked DIN 874/00 ....
so I assume that these are for shorter edges than 500mm; and will have lower tolerances still.
Perhaps those with a 500mm edge could check if it is marked DIN 874/0 or 874/00?

My conclusion -
Dicks edges are far more accurate than my woodwork!


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## DaveL (9 Sep 2007)

Hi Neil,

Welcome to the forum.

Good first post, your link to the source of the information has been caught by our spam trap, this will stop once you have a few more posts to your name, in the mean time here it is.

Source: http://www.lineartools.co.uk/files/data%201042.pdf


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## David C (13 Sep 2007)

Have a look at the spec on the new Axminster set of three engineers squares 2" 4" & 6" for £21-74. Page 365 of the autumn winter 07/08 catalogue.

Squareness within 0.00063" , 16 microns, or in plain speak just over half a thou".

I have just ordered two sets for two of my September students and so far have checked one.

It looks very good, and a huge improvement on previous stuff from this particular manufacturer. I am much happier to see this spec stated than the rather vague, "good level of accuracy" stated for the range above this new set......

David Charlesworth


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## Newbie_Neil (13 Sep 2007)

Hi Neil A

Welcome to the forum.

Cheers,
Neil


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## Neil A (13 Sep 2007)

David C":2df971sp said:


> Have a look at the spec on the new Axminster set of three engineers squares 2" 4" & 6" for £21-74. Page 365 of the autumn winter 07/08 catalogue.
> 
> Squareness within 0.00063" , 16 microns, or in plain speak just over half a thou".
> 
> David Charlesworth



That is quite impressive. The square (100mm x 70mm) sold by Dick
is to DIN 875/00.
I havent been able to find much about this standard but it would appear
that this equates to a squareness tolerance of 0.004mm, or 0.0001574inch.

However, I am not sure what a linear distance (ie mm) means when assessing squareness, which is afterall an angle ...


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## bugbear (14 Sep 2007)

Neil A":3ok0b00p said:


> David C":3ok0b00p said:
> 
> 
> > Have a look at the spec on the new Axminster set of three engineers squares 2" 4" & 6" for £21-74. Page 365 of the autumn winter 07/08 catalogue.
> ...



At a guess, the linear divergence of the blade from the theoretical position of an ideal blade (i.e. perfectly straigh @ 90 degrees)

BugBear


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