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A random thought on plane flattening

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CHJ

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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:
 

engineer one

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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:
 

Pete W

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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 :)
 

CHJ

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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.
 
A

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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 :p

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.

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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waterhead37":30hlihuo said:
Alf":30hlihuo said:
MikeW":30hlihuo 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.

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

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

Pete W

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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 :oops:.

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

Alf

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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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'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
 

Noel

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andy king":glikv5jt said:
'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:

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

Noel
 

bugbear

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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
 

bugbear

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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.
 

Alf

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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
 

bugbear

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Alf":2xboaq4f said:
bugbear":2xboaq4f 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

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

It *is* a metal working book, IIRC :)

BugBear
 

Alf

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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
 

Alf

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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-[
 

bugbear

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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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