Consistency of measurement

[RogerS]

What prompted this was several posts and my own preconceptions...but challenged by a 'light-bulb' moment during an excellent days' outing to Jason (JFC). Jason was showing me the best way to make up some casement windows based on some original Georgian style that I needed replacing.

Now I am the first to admit that I tend to get anally fixated about absolute accuracy and consistency when it comes to measuring lengths. When I started to prepare the legs for my workbench, I went to huge pains to get them all to be the exact right length...and to square off the ends perfectly with the Woodrat....but my floor is nowhere near as level as the accuracy to which I was working!

Even if I had been tenoning these legs I would still have measured the length exactly before going anywhere near making the tenons. But working with Jason showed me that I'd got my perspective all wrong...you need accuracy but not at every point in the build. It was the engineering purist in me that wanted everything to be micrometre perfect at every stage of the process.

The same philosophy also became apparent to me when reading the various posts on sharpening and flattening. And posts that talk about fractions of a millimetre on bought in machines...

We need accuracy but I now realise that it needs to be in perspective and in the right place at the right time.

So...where do you guys focus your accuracy and, perhaps more to the point, where do you say 'that'll do for now'?

 

[Scrit]

Surely consistency is better than accuracy of measurement? That's why we make rods to hold dimensions - then a wonlky tape can't introduce inaccuracies.

But first things first. No two tape measures are the same..... I've proven this to my own satisfaction a couple of times by buying several Stanley tapes (all right on one occassion ten), pulling them out side by side and visually comparing. I'd say you'll get 3 or 5 out of a box of ten which are accurate - or consistent, which is probably more to the point. Secondly I have what I refer to as the "register" machine in my workshop. That happens to be my Altendorf panel saw which has laser etched scales which seem to match my digital calipers, so as that's the machine I do all the accurate panel cutting on that is the obvious candidate. To be useable any tape measure has to be reasonably close to the Alt's scale - if it's not it gets returned. I've teed off a number of the local ironmongers and tool stockists by returning tapes. Most consistent tapes to date seem to be the bright green CK 5 metre tapes, although even they do need the end hook adjusting almost every time I buy a new one. Lastly on any job pick out a tape and use that tape and that tape only for the job as your master tape. Use the same tape to check against your sawn pieces as well. Then even if it isn't accurate, it will be consistent and the job will still fit, all being well :?

Scrit

 

[Ian Dalziel]

Good question Roger,
I have gone a bit of a circle.....I started in engineering and still work in heavy engineering. I did woodwork as a hobby and always tried to keep my tolerancies low but having fitted a few hundred kitchens it wore off where it didnt matter.
I have been working with Karl Holtey on and off about 5 months and now its worse than ever....everything is now to be better than a thou if i can quarter of a thou is ideal. but it really has to be put into perspective. Toolmaking has to be extremly accurate.

Woodworking...accuracy...depends on what you are making and if the part is seen and if it has to work ie a drawer sliding.

After all real wood is a natural product and can move huge amounts...this is why you see a lot of veneered boards on large surfaces for stability

anything that catches the eye has to be virtually spot on as the eye is a very accurate tool at picking out mistakes. If it doesnt look plumb then 9 times out of ten it isnt

Take marquetry as an example...if its not right then it stands out.

I think perspective is the ideal word for what your asking....
I agree with Jason....

just my tuppence

Ian

 

[Scrit]

Ian

When you were fitting kitchens how many times did you put in a kitchen (or the first part at least) accurately, i.e. square according to the level or laser only to find is was visually a bit wrong? This is especially true of very old houses. This is a dilemma signmakers face all the time with old buildings.

Scrit

 

[Ian Dalziel]

Phew your quick at typing Scrit,

When i was doing kitchens i could only work to the best level i had (a brickies stabila) , after getting it right on all planes to the level i worked on from there. I must confess to never using a laser, i beleive sound levels and lasers are all the rage now but i liked the stabila.
I would say very few houses are square (if any)or have level floors even new builds so i used to work to a compromise of level and eye. I never had a single complaint though. as you well now if its drastically out the doors will eventually fall open and i havent heard of that happening yet

This is where perspective has to come into it.

signmakers will know this only 2 well

I

 

[RogerS]

i beleive sound levels and lasers are all the rage now but i liked the stabila.
I

I like my Stabila too... my useless Homebase spinning laser has a beam width of about 4mm ...useless for measuring..as indeed are all the other duff laser thingies I have bought and tried over the years. Might be OK for laying a course of bricks.

 

[Scrit]

When i was doing kitchens I could only work to the best level i had (a brickies Stabila) , after getting it right on all planes to the level I worked on from there.

Actually that's what I still use - despite the laser level I have I still find the Stabila more accuratte........ I've also had good reason to be thankful for the modern trend to put cover panels on the ends of runson more than one occassion - it means I can hide the amount of packing I sometimes have to resort to to get upper cabinets to hang "straight".

Scrit

 

[RogerS]

Surely consistency is better than accuracy of measurement? That's why we make rods to hold dimensions - then a wonlky tape can't introduce inaccuracies.

Scrit

I was thinking more along the lines of the philosophy of making everything right...for example, if you're going to make through tenons then I would have cut the wood to exactly the right length then made the tenons to exactly the right length when...I could have made the tenons oversize and trimmed them afterwards.

 

[Ian Dalziel]

it means I can hide the amount of packing I sometimes have to resort to to get upper cabinets to hang "straight".

ohh that brings back happy memories. :shock:


I saw your point eventually on sign makers on old buildings.

I fitted a UPVC front door and frame to an old cottage....across the width of 3 feet it was out 2 1/2" . Fitting a nice square frame in here was a nightmare...thats where compromise comes in.
I guess most old building have moved in one way or another and can sympathise with any tradesman trying to work on them.

was thinking more along the lines of the philosophy of making everything right...for example, if you're going to make through tenons then I would have cut the wood to exactly the right length then made the tenons to exactly the right length when...I could have made the tenons oversize and trimmed them afterwards.

Thats a bit risque :wink: :lol:

I

 

[Scrit]

I was thinking more along the lines of the philosophy of making everything right...for example, if you're going to make through tenons then I would have cut the wood to exactly the right length then made the tenons to exactly the right length when...I could have made the tenons oversize and trimmed them afterwards.

Sorry Roger - slightly crossed purposes

As for cutting the tenons dead to size as opposed to trimming, there are reasons why we do certain things - for example the "proper" way to make framed doors is to leave the horns long and cut to length when you get them to site, the reason being that it protects the top and bottom mortises from transit damage. It doesn't look right, but it does work well. The reason you cut a tenon slightly long is to get an exact fit by trimming - it tends to compensate for woods tendency to shrink and grow (awkward stuff, tree bits). Many traditional joinery and cabinetmaking techniques use this "fuzzy" factor to achieve an end, such as green oak frames being pegged together with dried pegs. An engineering perspective tends not to do this I feel, although that said an expert engineering machinist will argue that there is such a thing as "feel" when milling different materials....

I suppose this means that I feel that if it looks or feels right then it probably is - regardless of how accurate it actually is. That's how I approach hanging and trimming doors. In hand plane terms that probably puts me more in the Bill Carter camp than the Karl Holtey one - but as I can't afford eithers' wares that's really just an acedemic point! It's also why when I've gone out and hung signs I've invariably found myself hanging the things on a few screws and crossing the street to see if they look right or balanced. That's left a few of them hung on a slope and not centred on the building - but at least I never used to get told to go and move them. :lol:

Scrit

 

[JFC]

When making the windows Roger and i where working on i marked out the square stock and left 10mm each end of both styles , head and bottom rails . The glazing bars i also cut to roughly the right length . We then had to cut the moulding and rebate into the timber .
The marks for the right size pieces are marked on the timber but the 10mm will act as the horns when moving the windows and prevent damage to the corners aswell as giving some play on glue up if some tweaking to get square is required . The 10mm that will be on the end of the tenons is again to give some play at glue up and to get a perfect finish after glue up when they are cut off .
If im moulding timber i will cut it to a rough length first and then mark up properly later but sometimes its easier to mark up the square stock first .

Scrit , you type to fast :lol:

 

[woodbloke]

Scrit wrote:

I suppose this means that I feel that if it looks or feels right then it probably is

Generally this is I think a fair way, I think, to approach working with this wood stuff being tricky and awkward stuff at the best of times; there isn't the 'dead' feel to it which happens with metal working. For example, you can machine a piece of mild steel to exactly a set dimension and know that the following day it will still be the same. Not the same with a lump of timber as it may bow, move, twist or warp overnight depending on a number of conditions. Hence woodworkers take this into account and make allowances for it. My own view is that the fitting of a drawer requires a high degree of accuracy, make the opening just a tiny fraction smaller than the front than the back and it should fit; the other way round, and it won't......but then you say, 'how big is a tiny fraction?' :-k :-k Tricky stuff - Rob

 

[Paul Kierstead]

So, lets say I have to make a little notch in a piece A to fit piece B into. I hold piece B up to A and mark it with a pencil. I pull out my saw and saw to the line, maybe a little shy. I try fitting it. I trim it with a chisel a bit until it fits perfectly.

Nothing was 'measured', or calibrated, or ...

Is that accurate woodworking? No calipers were involved, no engineering, just plain old style woodworking.

Need 4 legs the exact same length? Cut-off stop on miter guage (or cross-cut sled). Hold one up to the height the table should be (use another table or your body), set the stop, cut all legs with the stop. They will be dead-on the same length as each other. Again, is this accurate?

I think where people go wrong is the belief that perfectly fitting and great looking work involves measurement and metrics; 'engineering'. Most of the time it does not.

Just my CAD$0.02

 

[engineer one]

as an engineer, you tend to get a kind of tunnel vision when it comes to
measurements and clearances, but then in principal, you know within
very defined limits how the metal will move.

for instance when we cast brass we allow one kind of tolerance in the mould whilst white metal needs another.

but wood then that is different.

if you want to be accurate, then you use machined boards.

but, if you want "style" thenyou use real wood, and you have to be
somewhat more flexible about measuring.

the problem about cutting your bits to exact lengths is that you may well
have to cut off a nice piece of wood, or end up with knots etc in the middle of a joint. so instead of 10-50 % waste you end up with 100%.

grain direction and joint formation are as important as anything else, making the best of the woods features is more important than measurement. that is why people use shadow lines and other techniques to both enhance and hide flaws on their work.

face frames were devised to cover the front of machined boards, or allow the use of cheaper wood where it could not be seen, and the best wood
in the visible surfaces.

i guess roger you have to learn to be more flexible with your dimensions.

i agree with scrit about tapes, even recent starret ones cannot be guaranteed.

lets have a better idea about using story sticks/rods, but rather like layers on cad programmes i get confused if i have too much information
in a particular place.

certainly i can see the importance of making the distance between the start of two tenons on the same piece of wood being the same for the
whole job, but unless they are closed tenons the length should not
be of any concern until after assembly. :shock:

my 2p

paul :wink:

 

[Scrit]

As an engineer, you tend to get a kind of tunnel vision when it comes to measurements and clearances, but then in principal, you know within very defined limits how the metal will move.

And every time a "woodie" mentions rods and dividers we can see it! :wink:

Lets have a better idea about using story sticks/rods, but rather like layers on cad programmes. I get confused if I have too much information in a particular place.

I see we'll need to introduce you to the concepts of a double sided rods (that's 4 edges......) and coloured pencils. :wink: Levity apart that's how I tackle it, although to date it's all gone on one side, albeit on two edges and in 3 colours (red, blue, grey-black - that's the limit as I can't get any more colours for my clutch pencil )

Scrit

PS I'm still wondering whether we need to review the concept of using "Bobs" (any one remember them) and "smidgeons" instead of 1/64ths.....

 

[Sgian Dubh]

PS I'm still wondering whether we need to review the concept of using "Bobs" (any one remember them) and "smidgeons" instead of 1/64ths.....

Well, if it's down to smidgeons and "Bobs", I think I'll stick to bo'hairs, red ones, blonde ones, and black ones. Slainte.

 

[engineer one]

so where have we all used "full inches" or " short 1/4s"

or even a "full millimeter" or was that only us metal workers?? :twisted:

scrit, can't you buy a newer 4 colour pencil?? :lol: :lol:

i think the major thought is how big do you make the rod/stick/ pole or perch? surely past a certain size they become unwieldy and difficult to use.

i can see the value around say a window in a kitchen to centre or make prettier the layout of the kitchen, or for a single cabinet, but a whole room,
that's where i get confused. i guess if you mark a point halfway along a wall and then you can "mirror" the images on the rod, but do you really
use 16 feet rods?

going back to the original question of roger's i would suggest that if you are making some kind of say ladder frame held apart by tenonned cross shafts, you need all the tenon shoulders to be in the same place on all the pieces, but the tenon lengths are not relevant until the mortises have been made, and the need is to adjust the shoulder fit.

of course you could always now use tenons with dowels to pull them in. :lol: :lol:

paul :wink:

 

[Scrit]

I think the major thought is how big do you make the rod/stick/ pole or perch?

Answer: as big as you need it to be, but preferably not so big you can't use it at the bench when laying out.

Surely past a certain size they become unwieldy and difficult to use.

Yes, but for most doors, pieces of furniture, windows, etc they aren't all that big.

I can see the value around say a window in a kitchen to centre or make prettier the layout of the kitchen, or for a single cabinet, but a whole room, that's where i get confused. I guess if you mark a point halfway along a wall and then you can "mirror" the images on the rod, but do you really use 16 feet rods?.

No, but I have been known to use 2 x 6 feet, as that's the longest I can comfortably carry in the car. I think there's a difference between the type of rod you need to build a cabinet and the type you would use to lay out a kitchen which would only have the cabinet overall sizes, window and plumbing positions marked. For those purposes I don't thing they need to be wonderfully accurate, mainly because buildings settle and plasterwork is never flat...... But being able to assemble a wall of cabinets in the shop and check that they will fit by offering up the rod can save you some costly mistakes. I get the feeling from the way you are talking that you've never used one.

Going back to the original question of Roger's I would suggest that if you are making some kind of say ladder frame held apart by tenonned cross shafts, you need all the tenon shoulders to be in the same place on all the pieces, but the tenon lengths are not relevant until the mortises have been made, and the need is to adjust the shoulder fit.

True enough, but it gets really confusing when you start to look at the way single end tenoning machines are made - with a cut off saw to allow you to saw the tenon dead to length if you want to.

Scrit

 

[engineer one]

ok i confess scrit you are right i have never used one.

wasn't taught is my excuse.

but also like some people who have not had full formal training
i find that i build the outside and work back in so wonder at the
real value, but am pleased to be taught.

paul :wink:

 

[Jake]

ok i confess scrit you are right i have never used one.

wasn't taught is my excuse.

Me either.

Anyone know of where I could find a good description of how to go about setting out a rod?