# A random thought on plane flattening



## Pete W (7 Dec 2005)

I'm a lurker under the Porch; I have subscribed but haven't yet figured out how to post a message there, which is why I'm posting here  

Saw a post there from Bugbear on the dangers of the common method of plane-flattening (glass or other flat plate, wet'n'dry, etc) and realised that there's a body of evidence to support his opposition...

Among the other hobbies/interests I don't have time for, astronomy figures high on the list. From whence comes this bit of esoteric knowledge. If you want to make your own telescope mirror from scratch, you buy two round glass blanks (sort of like turning blanks), scatter appropriate abrasive material between them, and grind away in a circular fashion. After some time and effort you, rather miraculously, end up with one convex and one concave piece of glass (a parabolic, concave mirror being the ultimate aim).

So, as Bugbear argues, grinding your plane on abrasive paper is almost guaranteed to produce a concave (or convex) surface, if you do it enough (I don't have the experience to suggest how long is enough).

As an aside, the traditional final grit in the abrasive process of mirror-grinding is common talcum powder. Which always makes me smile when I read people recommending talc as a way of lubricating the surface of cast-iron tables.


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## Philly (7 Dec 2005)

Pete
You got it-the real knowledge is when to STOP flattening! :lol: 
Cheers
Philly


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## bugbear (7 Dec 2005)

Pete W":pdz60p8f said:


> So, as Bugbear argues, grinding your plane on abrasive paper is almost guaranteed to produce a concave (or convex) surface, if you do it enough (I don't have the experience to suggest how long is enough).



ATM practice uses loose abrasive between 2 workpieces. I forget which one (upper or lower) becomes convex, which concave. I know that if the process goes too far, you simply reverse the lower/upper workpieces, and the process drives the other way.

In "normal" plane flattening (ha!) the lower surface is fixed abrasive, glued on a hopefully flat (ha! again) and rigid (ha! a third time) reference.

The plane certainly cannot be worked concave but may well (IME) become convex _to some degree_.

BugBear


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## engineer one (7 Dec 2005)

but surely the point is where does it change?

DC suggests that concave is not a bad thing, as long as it
hits at the front and rear and around the mouth. indeed one
might think that those older planes with ribbed soles are 
trying to minimise this too.

surely the whole point about marking the sole with marker pen, and then 
only grinding until the marks have all gone uniformly will
answer the problem.

bugbear is right, it is a question of when to stop :?: :?: 

paul :wink:


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## andrewm (7 Dec 2005)

Pete W":5p3l4z4h said:


> Among the other hobbies/interests I don't have time for, astronomy figures high on the list. From whence comes this bit of esoteric knowledge. If you want to make your own telescope mirror from scratch, you buy two round glass blanks (sort of like turning blanks), scatter appropriate abrasive material between them, and grind away in a circular fashion. After some time and effort you, rather miraculously, end up with one convex and one concave piece of glass (a parabolic, concave mirror being the ultimate aim).



Totally off-topic I know but what is about this process that ensures you get a parabolic mirror? Common sense seems to suggest that what you get is curved (as in a portion of a circle) such that it is the same radius at each point. But this obviously doesn't happen if this technique is used to produce parabolic mirrors.

Andrew


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## bugbear (7 Dec 2005)

> Totally off-topic I know but what is about this process that ensures you get a parabolic mirror?



It doesn't. That's the "ultimate aim". A perfect curve of the desired radius is merely a stage in the process.

BugBear


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## bugbear (7 Dec 2005)

engineer one":1ck9jh3z said:


> but surely the point is where does it change?


Only in the context quoted - 2 workpieces with loose abrasives. This is NOT the context of "woodworker's lapping" on a plane.



engineer one":1ck9jh3z said:


> DC suggests that concave is not a bad thing



DC says that minor CONVEXITY is ok, because of the common tendency to plane the workpiece convex. A slight convexity in the plane provides a countering tendancy. C.F. Sprung joint, where one is aiming for a concave workpiece.[/quote]




engineer one":1ck9jh3z said:


> surely the whole point about marking the sole with marker pen, and then
> only grinding until the marks have all gone uniformly will
> answer the problem.



This merely guarantees that every part of the sole has been touched by abrasive - this can easily be the case for a convex sole.

BugBear


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## Anonymous (7 Dec 2005)

Pete W":3anp5flv said:


> After some time and effort you, rather miraculously, end up with one convex and one concave piece of glass (a parabolic, concave mirror being the ultimate aim).
> 
> So, as Bugbear argues, grinding your plane on abrasive paper is almost guaranteed to produce a concave (or convex) surface, if you do it enough (I don't have the experience to suggest how long is enough).



So if we put loose abrasive between two planes' soles, we can make compass planes! :lol: 

As BB pointed out, with the abrasive paper method only the plane sole is being abraded. However, abrasives break down and the backing compresses so there is a limit to the degree of flatness obtained. Of course, there are also limits to the flatness needed for woodworking.


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## bugbear (7 Dec 2005)

> However, abrasives break down and the backing compresses so there is a limit to the degree of flatness obtained.



You forgot swarf build up!

BugBear (who knows that Roger knows this)


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## ydb1md (7 Dec 2005)

Roger Nixon":2oatbo2o said:


> Pete W":2oatbo2o said:
> 
> 
> > After some time and effort you, rather miraculously, end up with one convex and one concave piece of glass (a parabolic, concave mirror being the ultimate aim).
> ...



So why do we rub waterstones together to flatten them? Mine don't come out dished. :-k


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## bugbear (7 Dec 2005)

> So why do we rub waterstones together to flatten them? Mine don't come out dished.



Actually, they may well be dished. The question is - what's the radius?

To expand - nothing is ever "straight" or "flat" or "true" or "square" - precision engineers (who come closest) never use those words; they always talk about "tolerance", and guaranteed minimum deviation from those concepts.

Only woodworkers (*) think their Starrett squares are "perfectly accurate"; Starret make no such claim 

BugBear

(*) yeah - I'm generalising


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## Alf (7 Dec 2005)

In November 1934 The Woodworker":3iro9aft said:


> It is probable that the new plane will have its sole planed perfectly true. Try this with a straight edge. Surely this is as it should be - the face of a plane should be perfectly true? Well, the aim in planing is to get the surface of your rail or board true. If the plane's sole is quite flat this is less easily accomplished than if the sole from end to end is slightly round. From the mouth to the heel take a few shavings off so that, when tried with a straight edge it is round to about 1/16". I always treat my planes so.



Cheers, Alf

Flat Sole Society? Just say "NO!" :wink: :lol:


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## bugbear (7 Dec 2005)

*In 1918 (or maybe 1928) The woodworker said*

(checked - it was 1918)



> Trueing Sole of Plane
> 
> E.S.W. (Henley) asks the correct method of trueing the
> sole of a plane
> ...



Maybe it's like the bible - you can find a quote in favour of anything!

BugBear


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## Alf (7 Dec 2005)

bugbear":3mpd020d said:


> Maybe it's like the bible - you can find a quote in favour of anything!


Ah ha...



Many said:


> Of course the Earth is flat, but I like a nice banana-shaped sole on my plane. Does a good job, eh? <indicates large ark containing all the creatures of the Earth therein> Never would have got it finished if I'd listened to Ham and his flaming nonsense about inventing a saw blade that goes round in a circle while held on a table, just so he could use the table to flatten his Nile Valley and Lea Nileson fancy wooden planes. And don't get me started on Shem's idea of putting the big cats next to the gazelle pens...



Cheers, Alf


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## MikeW (7 Dec 2005)

"Flat" soles on a medium that can "move" over time and conditions, being used to work a medium that itself changes seasonally--and sometimes within a single day.

I think that trying to obtain relative flatness is all thats needed--and probably more important is making sure the plane's sole is not twisted. Obsessing over a tolerance only measurable with feeler gauges or prussian blue on referance plates is futile. 

A plane flexes in use. The more the pressure, the more the flex. How does one "fix" that? Plan on covexity keyed to how much a particular person presses down on their plane? Different pressures and lengths of soles to account for resulting in lesser or greater amounts of convexity?

Well, gotta go out to the shop. Need to make room for...

Take care, Mike


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## Anonymous (7 Dec 2005)

bugbear":324qzjng said:


> Actually, they may well be dished. The question is - what's the radius?
> 
> To expand - nothing is ever "straight" or "flat" or "true" or "square" - precision engineers (who come closest) never use those words
> (*) yeah - I'm generalising



_The first thing we do is kill all the engineers!_ 
(Hey if Alf can rewrite the Bible, I can mess with Shakespeare :lol: Very funny, Alf! (hammer) )

Even a straight line can be described as an arc with a radius of infinity.


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## Alf (7 Dec 2005)

MikeW":1p28f81r said:


> Well, gotta go out to the shop. Need to make room for...


Yes...? I hate it when you do that. Of course that's _why_ you do it. ](*,) :lol:



Roger Nixon":1p28f81r said:


> _The first thing we do is kill all the engineers!_


You sure we're not related, Roger? :-k :lol: 

Cheers, Alf

Who likes engineers really. Some of my best friends are - actually, no, I tell a lie... :wink:


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## Chris Knight (7 Dec 2005)

Alf":2wb7anam said:


> MikeW":2wb7anam said:
> 
> 
> > Well, gotta go out to the shop. Need to make room for...



A Coordinate Measuring Machine of course. Everyone knows that a surface plate and prussian blue depend totally on smearing the right thickness of blue on the surface - a CMM has no such limitations - ask Tony.

Mike is only fooling about non-flat planes, his cabin in the woods could never have been built otherwise :wink:


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## Anonymous (7 Dec 2005)

MikeW":3c8850em said:


> "A plane flexes in use. The more the pressure, the more the flex. How does one "fix" that?
> Take care, Mike



I agree. This is a question I would like to see answered. It would seem though, that the plane couldn't flex more than the stock is out of flat. Or put another way, as the stock gets flatter the plane would flex less.

In any case, I have a simple test. If the plane performs as needed, I leave it alone. If not, I tune it until it does. Most of my planes have not been flattened at all. Some I have flattened on a sander belt on float glass until marker applied to the sole was removed and some I have spotted on a granite surface plate. Just enough to get the job done.


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## Anonymous (7 Dec 2005)

Alf":3ggu3bp4 said:


> You sure we're not related, Roger? :-k :lol:
> 
> Cheers, Alf
> 
> Who likes engineers really. Some of my best friends are - actually, no, I tell a lie... :wink:




Of course we are related, Cousin Alf!

Roger
Who has counts many engineers in his lists of "Most Admired" and "Most disliked"


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## CHJ (7 Dec 2005)

Alf":3iah5ah1 said:


> ...SNIP...
> Who likes engineers really. Some of my best friends are - actually, no, I tell a lie... :wink:



Hmmm.. MIGHT just go looking for some of those Show shots for the gallery after all :twisted:


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## engineer one (7 Dec 2005)

well without the engineers, who'd make the planes and chisels
anyway.
i say lets kill the accountants, but then i'm biased :evil: :-({|= 

alf you do not know what you are missing by slandering us
people who occassionally still work in metal.

paul :lol:


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## Pete W (8 Dec 2005)

Hmmm - didn't quite think things through... I hadn't considered the fact that using abrasive fixed to one surface would change the mechanics, but it's obvious now.

I should also own up to being firmly in Alf's camp - 'flat enough' is good enough for me, and I'd measure that flatness by the surface it leaves on wood


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## CHJ (8 Dec 2005)

waterhead37":1u46l876 said:


> ....SNIP...
> - a CMM has no such limitations -...snip..


*Chris*, You should know better,  even a CMM has zone tolerances; and the majority of them are a lot greater than many people realise. 

In my metrication room we had to spend a lot of time reminding people to take into account the limitations of the CMM when passing or rejecting components as at least 15% of items fell in a so called "failed tolerance range" which was very close to the margin of error of the machine. 

CMM's enable a consistent and programable way of checking the relationship of dimensions on complex items but they are still only a comparator that has the advantage of computer software to iron out some of the mechanical inaccuracies. 

Even when you get to THESE LEVELSof flatness checking, hand pressure can bend the glass enough to influence the interpretation of the surface. 

Now where is my coat.... 

Having had the pleasure of having to make surface plates by hand, (you need at least three by the way to avoid the dishing), I for the life of me cannot see where there is any relationship between their need for accuracy and that of the sole of a wood plane. I'm with *Alf* here despite her lapse into dangerous thinking.. [-X 

Open that bunker door please Gill.


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## Chris Knight (8 Dec 2005)

CHJ":1qc73lr3 said:


> waterhead37":1qc73lr3 said:
> 
> 
> > ....SNIP...
> ...



Properly chastened here


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## Anonymous (8 Dec 2005)

Pete W":1scd708q said:


> I'm a lurker under the Porch; I have subscribed but haven't yet figured out how to post a message there, which is why I'm posting here
> 
> Saw a post there from Bugbear on the dangers of the common method of plane-flattening (glass or other flat plate, wet'n'dry, etc) and realised that there's a body of evidence to support his opposition...
> 
> ...



Interesting point Pete but surely not the same for a plane as you describe a circular motion with the two pieces of glass whereas when flattening plane soles, one only moves forward with pressure on the abrasive and lifts it slightly (or apply no pressure) when retunring ot the start position. 

Also, if the two pieces of glass are the same size, then there must be overlap between them whereas with a plane sole flattening job I always ensure that the abrasive paper is longer ( 3 sheets long usually) than the plane sole


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## Anonymous (8 Dec 2005)

waterhead37":30hlihuo said:


> Alf":30hlihuo said:
> 
> 
> > MikeW":30hlihuo said:
> ...



:lol: Nice one Chris :wink: No limitations? You now the truth form your lotus days  

I think our current CMM (new one has been ordered at £160,000) has an envelope of 5um


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## Pete W (8 Dec 2005)

Tony":ej19gmuw said:


> surely not the same for a plane



You're right, as were the others who pointed out the error of my thinking .

Pete - always willing to learn (which is just as well #-o)


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## Alf (8 Dec 2005)

Engineers? Fine fellows. Love 'em all, every one. Wouldn't be without them. Bless their cotton socks, eh? Heck, I was even heard to murmur "clever fellows, these metal bashing types" while persuing "The Amateur's Lathe" last night. :shock: :wink:

Cheers, Alf

P.S. If that hasn't worked I may need to ask Gill about her bunker rates for long term stays... 8-[


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## Anonymous (8 Dec 2005)

> 'flat enough' is good enough for me, and I'd measure that flatness by the surface it leaves on wood



Absolutely!
I see little point in looking for flaws or discrepancies on any plane without first trying it. If I can plane timber flat, twist free and square with it, what is the point of flattening it when it already does what it is intended to do?
Seems like a pointless excercise to me! :shock: 

Andy


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## Noel (8 Dec 2005)

andy king":glikv5jt said:


> > 'flat enough' is good enough for me, and I'd measure that flatness by the surface it leaves on wood
> 
> 
> 
> ...



At last, the voice of reason and common sense. Waaay too much proctologic nonsense....

Noel


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## bugbear (8 Dec 2005)

Alf":2e2xs03g said:


> while perusing "The Amateur's Lathe" last night. :shock: :wink:



Took me ages to get a cheap, original copy of that - it's quite sought after, since it is still relevant to modern hobby practice.

Excellent book!

BugBear


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## bugbear (8 Dec 2005)

This argument has raged for YEARS, with considerable heat at times.

I make no comment on the _need_ for flatness, except to point out that a radically curved plane won't work well.

Having taken this on board (that a plane needs to be fairly flat (*)) my obessive compulsive personality led me to make many of my planes flat(*), and as flat(*) as possible to boot.

But I do continue to assert that the "mark with a surface plate and hack off the high points" method is not merely the only way to very high degrees of accuracy(*), but is (counter intuitively) a rapid and effective way to get lower levels of accuracy(*).

BugBear

(*) All uses of absolute terms like "flat", "straight", "accurate" are intended to interpreted as carrying a tolerance, hopefully made clear by context.


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## bugbear (8 Dec 2005)

MikeW":1qq0dcba said:


> A plane flexes in use.



I'm glad you mentioned that 

http://nika.frontier.iarc.uaf.edu/~cswi ... 20#message

I bet you're sorry now!

BugBear


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## Alf (8 Dec 2005)

bugbear":1tuoh18y said:


> Took me ages to get a cheap, original copy of that


How original original? And exactly how cheap? Just so I know the full horror right away... :roll: :lol: 

Cheers, Alf


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## bugbear (8 Dec 2005)

Alf":2xboaq4f said:


> bugbear":2xboaq4f said:
> 
> 
> > Took me ages to get a cheap, original copy of that
> ...



I'll only tell you if you tell my WHY you bought your copy :twisted:

It *is* a metal working book, IIRC 

BugBear


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## Alf (8 Dec 2005)

bugbear":l0dtauy0 said:


> I'll only tell you if you tell my WHY you bought your copy :twisted:


Ah.

Erm. Hum. Well. Erm. 8-[ The thing is... 

Periodically I get this recurring fever - sort of metal working malaria - where I muse over how useful it'd be to turn up the odd metal bit for a jig or replace a missing part from a tool. Take my Lewin for instance; I did something that works okay-ish using files and dangerous and illicit things on my proper, honest woodworking lathe, but they don't really look _right_... It's the result of one of these relapses - and reading it last night was the result of another one I'm currently undergoing. #-o It doesn't help that my old man's ears pop up like a rabbit that's heard a carrot growing in the vicinity every time I vaguely mention it. If we egg each other on just a tad more I fear the consequences... :-# 

Cheers, Alf


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## bugbear (8 Dec 2005)

Surely you can find room for...

http://www.lathes.co.uk/adept/index.html

BugBear (who saw a G+ one go for 60 quid, and didn't bid - FOOL!)


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## Alf (8 Dec 2005)

Room is not the issue so much; it's cost, availability and so forth. Round these parts you can't throw stones without hitting engineers - even if you're not trying to... :twisted: So secondhand isn't a cheap option.  And yes, you fool. :roll: :lol: 

Oh, and don't think I haven't noticed you've failed to answer the question, btw... [-X I told you mine, you tell me yours. :wink: 

Cheers, Alf

Incidentally, wasn't there a topic floating around here someplace? 8-[


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## bugbear (8 Dec 2005)

Alf":2fo74uos said:


> Oh, and don't think I haven't noticed you've failed to answer the question, btw... [-X I told you mine, you tell me yours. :wink:



IIRC it was 4.00 GPB + P&P from bookfinder. Still cheaper than the reprint, and with hard covers and better-than-reprint quality, especially on the photographs. 

If you were thinking I got it for 1.50 at a car boot, you can rest easy.



> Incidentally, wasn't there a topic floating around here someplace? 8-[



I saw one once, but it go away.

BugBear


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## Alf (8 Dec 2005)

bugbear":21z7f9sx said:


> Alf":21z7f9sx said:
> 
> 
> > Oh, and don't think I haven't noticed you've failed to answer the question, btw... [-X I told you mine, you tell me yours. :wink:
> ...


Big spender. Second edition, £3, local bookshop. See? It was lucky find; it's not like I _ordered_ it. 

Cheers, Alf


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## bugbear (8 Dec 2005)

Alf":1lciqwrk said:


> Big spender. Second edition, £3, local bookshop. See? It was lucky find; it's not like I _ordered_ it.
> 
> Cheers, Alf



Lucky indeed. Nice find.

BugBear (jealous)


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## Chris Knight (8 Dec 2005)

I think I shall ask Charley to set up a separate board for gloats and boasts..


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## Alf (8 Dec 2005)

waterhead37":t7y71vyg said:


> I think I shall ask Charley to set up a separate board for gloats and boasts..


Aww heck, just for once I beat him and you're gonna pull the plug on me? What's he paying you? :evil: It's 'cos I'm not Philly, isn't it... :roll: :lol:

Cheers, Alf


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## engineer one (9 Dec 2005)

bugbear said that DC talks about convex, and i say concave,
so i checked seems to me all the talk is about having
the front and rear, plus around the mouth, should be in line
in between it should be hollow like a japanese chisel.

with a convex sole, you are surely never going to get what you 
want.

paul


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## bugbear (12 Dec 2005)

> with a convex sole, you are surely never going to get what you
> want.



'tis all a question of degree. DC is not speaking of something like a compass planes, he's speaking of a uniform curve of around 2 thou sagitta max on a #5 1/2

BugBear


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