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5th November 2012, 06:28 PM #1
Hand Plane fettlers should read this
A little while ago pmcgee posted a video of Paul Sellers flattening a plane sole, in fact it was this one. While I don't flatten plane soles in the way Paul shows, one particular piece of advise caught my attention and that is not to hold the plane by handle and knob while you lap and certainly if you do be careful to not 'bulldog it' (whatever that means) as it will twist the sole with obvious bad consequence to the lapping- if it were actually possible to twist a cast iron plane. One member on here suggested it was a laughable suggestion that you could twist a plane sole just by applying a twist to the handle and knob. Well is it or not? It just happens that I have just done an hour or two scraping on my brother's old Stanley #4 made in England. It's now at the stage where the spotting done on my granite surface plate is starting to spread across the middle of the sole and I have most of the toe and heel in contact (just been hogging not refining yet) as you can see in pic 1.
planetwist1.jpg
Now when I cleaned it and respotted by holding some twisting pressure, and not very much at all mind you, the spotting pattern appeared in pic 2. So I've registered it on the toe so you can see contact all across the front, but at the back it's twisted so only that one small area is in contact.
planetwist2.jpg
Then I cleaned it and respotted twisting the other way. This time it happened that the heel was what registered, you can see the spread of contact points, but at the toe, just one little contact point.
planetwist3.jpg
Conclusion, This plane is a run-of-the-mill Stanley #4, nothing odd about it and no repairs ever. Clearly it is possible to twist this sole by application of a twisting force through the knob and tote. I would have to say qualitatively it wasn't very much force at all and from my distant memory of lapping I would guess that it is entirely possible in the fatigue and impatience of lapping to apply that sort of force if you don't remain present in the task. So my recommendation is as Paul suggests, if you lap, be careful how you hold the plane, it may not be much twist but errors can grow large with the number of iterations involved in lapping. Perhaps I'll pull out some of my other scraped planes and do a similar test just to provide a larger sample size.
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5th November 2012, 09:44 PM #2Jim
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Is it possible that what you are seeing is not the result of the body of the plane flexing but merely you putting selective pressure on one part or another resulting in an uneven lapping?
Cheers,
JimCheers,
Jim
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5th November 2012, 09:55 PM #3
Michael, according to Newton, you would be twisting the plane body a bit, but the millimicron amount would be most unlikely to be measureble by the comparatively crude method of a try-plate & dye. My first guess is that your 'twisted grip' is applying a little more pressure to one side, and amplifying dye deposition in the highlighted areas. The differences you are highlighting must be in the thousandths to sub-thousandths range, & I suspect this would settle as you proceed & approaach closer to a flat sole. So hopefully, your previously scraped soles will all be pretty true, but I suggest it is precisely the reason that lapping on abrasives almost never gives a truly flat sole, because you constanly rock the body ever so slightly when lapping, & this is exacerbated by a higher grip........
Well, tht's my take, anyways, and besides, even if those soles of yours aren't flat to molecular-distance tolerances, they sure feel good enough for anything I would want to throw at 'em!
Cheers,IW
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5th November 2012, 09:56 PM #4
Jim beat me to it!
IW
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5th November 2012, 10:22 PM #5
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5th November 2012, 11:01 PM #6
You're missing the point Ian, I am not making a comment about how I spot before scraping, nor am I worried that my scraped planes are not flat. What I am showing is that I can twist the sole and I use my surface plate to demonstrate the point. This shows up as the two spottings in pic 2 and 3. What I am doing is supporting Paul Sellers statement with visual evidence. I am not saying that this is the total reason why lapping sucks, I agree with what you say about rocking. All I am trying to do by this post is show the photos that support that the plane sole can be twisted vis a vis' Paul Sellers point.
Edit. In photo 1, which is a true spotting there is spotting on both sides of the heel and toe. In pic 2 and 3 there is spotting on both sides of the toe and heel respectively, while the other end has only one side spotted. It is only possible to do this by holding a twist in the sole..
To say it another way, the relaxed spotting pic 1, you could pick four points, toe left and right and heel left and right. It is not possible to make only three of those spots touch the dye and not the fourth as in pic 2 and 3 without twisting the plane. I am not saying it is a great twist (and it does not stay btw) the spotting returns to normal when relaxed) nor I think is Paul. But if it happens a bit, it will add to the uneven wear when lapping which will then make rocking even easier...
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6th November 2012, 12:01 AM #7
You might also conclude that if it is pretty easy with hand pressure to twist the body of a metal plan a few thou, then ordinary or hard use could have it moving around like a trampoline - at a very low scale.
My question then would be ... is it all that important to worry about the flatness of the sole to such an extent (other than as an exercise)?
It might also explain the performance expected from infill planes - I'm guessing they have a larger heft and rigidity.
And what about the woodies?
Cheers,
Paul
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6th November 2012, 08:23 AM #8
I haven't quantified the level of twist but it is most certainly pretty small (a rebate plane like a #10 1/2 is even more flexible) and I think the flex is likely mostly to occur through the shoulders at the line of the mouth. I think it is small enough to be meaningless when planing and anyhow you, er well I, don't have a death grip on the plane when planing. But with lapping it is cumulative. I don't know about woodies and infills. I didn't want to associate the act of planing with anything I'm talking about in this post however.
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6th November 2012, 08:37 AM #9Jim
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6th November 2012, 04:27 PM #10Senior Member
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Since we rarely go don to thousandths when working wood, just how significant is this perceived problem? How much time did Malouf, Krenov or Nakashima put into getting their planes perfectly flat? I'm no metal machinist and hardly a woodworker, just a part-time rust collector but I am interested in just how flat does flat have to be?
Cheerio,
Virg.
PS Paul Sellers then puts what to me is almost a mild splay on the edges of his plane. How does this effect flatness?
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6th November 2012, 04:44 PM #11
Hi Virg, this may sound short, but I don't want this thread to become a discussion about plane flatness, it's been done to death on here before and I've said a fair bit about what I think if you want to do a search. This thread is about answering the question, 'can you twist a plane as Paul Sellers says in that video?' that's it. 'Cause, can't stop others telling you what they think
That small bevel Paul puts on the perimeter of his plane does nothing to upset the 'flatness' It would still bear on the majority of the rest of the sole...
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6th November 2012, 05:51 PM #12SENIOR MEMBER
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If people were really really interested in quantifiable differences in the deflection//twist of the different types of planes in use (ie wood/infill/stanley etc.) I could be convinced to test it with the laser interferometer (it's good to 0.00001mm or 0.0004 thou). I doubt the usefulness of such tests but it might be interesting and or surprising to have the data.
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6th November 2012, 07:41 PM #13
Well I will express an interest! I'd like to see how much hand pressure can twist a plane body, and if it is an amount measureable by less sophisticated means . I know Michael says it can, according to the dye distribution method, but I have my private doubts that it is really measuring twist in the body, and not reflecting the way pressure is applied. If your gear has that sort of sensitivity, and you can rig up a suitable test bed, it ought to be able to put the matter beyond doubt. Be nice if your setup can measure the trorque applied as well as the deflection of the plane body.......
cheers,IW
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6th November 2012, 07:59 PM #14
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6th November 2012, 08:01 PM #15Jim
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me too lol
Cheers,
Jim
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