When did woodworkers become machinists??

I actually came across a situation where a few thousandths of an inch became important. A friend emailed me and asked me to check the width of the tongue created by my old Stanley #48 T & G plane as he found that his was making a tongue several thousandths inches wider (maybe .007) than the replacement blades he had gotten for his. For those unfamiliar with the #48, it uses two blades to cut away either sides of the edge of a board leaving a tongue in the middle. To cut the groove the fence pivots 180 degrees on an offset pin which moves the registering edge of the fence over so that one of the two blades is in position to cut the groove while the other is buried behind the fence edge. The inside edges to which the blades index is cast and machined at the factory so is not adjustable so the width of the tongue created is fixed. When he made a joint using his plane, the tongue would split the edges of the groove out when it was forced into place. Mine is a relatively new plane to me, so I had only tried it out a bit when I got it and hadn't gotten around to cleaning it. So happens that mine has replacement blades from the same source as his. When I tried mine out, I noticed that the tongue fit quite tightly into the groove, but it didn't split the sides out like he was experiencing.

Anyway, I broke out the dial calipers, cut a tongue onto a piece of scrap and measured it. Amazingly, to me anyway, was that the tongue I created was, with a couple thousandths variance over the length, the same exact width as he was getting, and yep, the blades were about 7 thousandths narrower than that tongue. The remedy to the situation is to tip one or both blades out about 1/2 hair at the top so that they are tilted ever so slightly inward at the bottom making a tongue that is a few thousandths narrower. Or maybe just intentionally kant the plane a bit or use a side rabbet to take a shaving off of one side.

But, truth be told, that is about the only time where I have found that a few thousandths made any difference what-so-ever in woodworking. I've done some segmented turnings on the lathe and used a large plastic adjustable protractor from a hobby shop to set the bevel angle for cutting segments along with a stop block and found that I could squeeze out the accumulated error over 24 cuts using large hose clamps in even very hard wood.

There's a difference between worrying about a few thousandths in dimension of your workpiece, and trying to get machines set up with that sort of accuracy. Machinist precision might sometimes be warranted in setting up machines.

The woodnet query was from someone who was setting up an expensive new cabinet saw, and found that the cuts were not as good as those of his old contractor saw. He checked for possible causes and found this small fence deviation as a possible culprit, and asked if it was plausibly significant.

There is risk of getting carried away in striving for precision, but there is also some risk of piling on in belittling attempts at precision. If someone measures a deviation and does not know if it is significant, isn't asking about it a reasonable thing to do?

M Toupin said:

A long long time ago, a finish carpenter taught me the secret to good looking work, "it's not about the accuracy, it's about the fit". He showed me how to use a story stick and my 'fit" immediately improved along with the appearance of my work.

Mike

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I have always used story sticks. Mom always said, "If the shoe "Fits".....



DT

Alan Schwabacher said:

There's a difference between worrying about a few thousandths in dimension of your workpiece, and trying to get machines set up with that sort of accuracy. Machinist precision might sometimes be warranted in setting up machines.

The woodnet query was from someone who was setting up an expensive new cabinet saw, and found that the cuts were not as good as those of his old contractor saw. He checked for possible causes and found this small fence deviation as a possible culprit, and asked if it was plausibly significant.

There is risk of getting carried away in striving for precision, but there is also some risk of piling on in belittling attempts at precision. If someone measures a deviation and does not know if it is significant, isn't asking about it a reasonable thing to do?

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I am guilty as charged. As a machinist in my other life, I find it almost impossible to change my ways, but here is a quote I lifted from another thread:

A lot of people thing you don't need precision in woodworking but when they run their fingers across a surface and feel a mismatch they sand or scrap it out. That mismatch may only be 0.002" to 0.004". They are working closer than they realize


Keedy

Keedy

Gary Keedwell said:

I am guilty as charged. As a machinist in my other life, I find it almost impossible to change my ways, but here is a quote I lifted from another thread:

A lot of people thing you don't need precision in woodworking but when they run their fingers across a surface and feel a mismatch they sand or scrap it out. That mismatch may only be 0.002" to 0.004". They are working closer than they realize


Keedy

Keedy

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I agree, but they are doing it by feel not by measurement. Feathering two mating edges so that they feel smooth is a long way away from trying to persuade wood to submit to measurement to that level of accuracy which is almost as pointless as it is difficult.

Ian Barley said:

I agree, but they are doing it by feel not by measurement. Feathering two mating edges so that they feel smooth is a long way away from trying to persuade wood to submit to measurement to that level of accuracy which is almost as pointless as it is difficult.

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And I agree with you also, but using good techniques and accurate cuts can sure as heck cut out alot of excess scraping and sanding.
Keedy

Chuck Thoits said:

I would also have to add. They/we are sanding out the inaccuracy of our equipment and the movement of the wood.
Did it just today one piece 8 feet long ripped on the table saw. Cut it into four side of a frame.Glued and nailed the frame up. When dry I sanded the front surface smooth. Each joint was just a little thicker on one side. All where flat on the back.
And never did I take out the dial indicators.

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I guess I'm spoiled. My equipment cuts accurately (thanks to indicators) and I have been using alot of quartersawn white oak, which seems to keep it's shape consistently.
I did have alot of trouble with wood movement last fall when I was doing a project in maple. Granted, wood is not constant, but it bugs the heck out of me to go-over my work because of shoddy and careless habits. But I did ease the pain recently with the purchase of a new sander and vacuum that help keep the dust down.
Keedy

Gary Keedwell said:

A lot of people thing you don't need precision in woodworking but when they run their fingers across a surface and feel a mismatch they sand or scrap it out. That mismatch may only be 0.002" to 0.004". They are working closer than they realize

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I'd disagree Gary, that's not working to precision, that's working to "fit". Those .002 or .004 out doesn't matter one bit once you swipe it with a scraper or plane and "fit" the part to a flush "fit". Actually it wouldn't matter if the cut was off an inch as long as the end result is a smooth "fit". Granted, it will take a lot longer, but the end result is the same. Conversely, spending 15 min setting up for that perfect cut to .001" is a bit of a waste (IMO) when you still need to hit it with a scraper to take it to the final "perfect baby butt smooth "fit".

My point is, if two woodworkers make an identical item and they both come out looking identical, the road there doesn't really matter. In the end, both items are still identical.

Mike

The funny thing is, is that even with all that accuracy of their machines, I can intentionally remove less than .002 inche increments with my 75 or 80 year old hand plane if the need arises. With all of their tweaking, they would be pressed to intentionally shave increments of .005 inches.

Very fortuitous that this tread started about the same time we received word that the incredible penmaker, Eagle, had died. When the compilation of some of his work is posted, you simply will not believe that what he did was possible. Even while you are looking at it. Then, to fathom that he made his cuts on an inexpensive table saw, with a cheap blade goes beyond our normal frame of reference. Ripping hair thin pieces for his inlays is what I'm referring to. Unreal. Maybe machining and woodworking aren't different worlds after all. Not debating, just thinking out loud.

There are many times after a dry fit that I will put wood back in machine and take a few thousands off. I do alot of straight Arts and Crafts furniture and I use very hard wood and if they don't go together right it would be a major pain to sand or srape them down and it would not look very good, either. The naked eye can pick-up all those little dips that trying to fix a lousy joint can cause. Not trying to be argumentative but thats the way I like to work.....that's all.
Keedy

I used to be on the geometric dimensioning and tolerancing team for the C5 Corvette (back in 1994). I designed cars here in Detroit and Europe and used metrics all the time. It's refreshing to just look at the wood and SEE where it needs to be corrected rather than micing everything. A tape measure, and some kind of depth gauge (for router table and saw blade heights) is good enough... IMHO.

Leave the anal-retentiveness to the engineers; I prefer the human element and artisanship - otherwise, where is the pleasure in getting a headache over crunching numbers?