Woodworking Machine Tolerances

[Greg Quenneville]

For 90 years the book “Testing Machine Tools” by Dr. George Schlessinger has been the bible for accuracy standards in precision machines. It defined what was acceptable for industry.

The book has a chapter for woodworking tools…the screenshots are below.

A friend also has a PDF on his website: http://www.etech.net.au/Testing%20Machine%20Tools.pdf

Metric measurements…0.1mm is about 0.004”

Several times I have read posters asking about what others would accept when it comes to warped tables etc. This book at least provides reference values.

Greg

[Maurice Mcmurry]

I Love data! One of Dr. Gorge Schlessinger's modern counter parts Is Dan Gelbart. I refer to him often. I am trying to stop ragging on H.F. . Hopefully others will do some reading and research.

[Greg Quenneville]

Thanks Maurice, never heard of him. Now there goes my morning watching videos.

Greg

[Bill Dufour]

My standard response is the human eye can see a mismatch of 0.001" in a flat plane surface joint. No need for any more accurate then that. Wood seasonal movement is more then the 0.001 by far. ).002-5" is probably as good as needed before a quick sanding.
BilL D

[Maurice Mcmurry]

His videos are worth the time required! He invented the air bearing that is the center of disk drives!

[Edward Weber]

My standard response is the human eye can see a mismatch of 0.001" in a flat plane surface joint. No need for any more accurate then that. Wood seasonal movement is more then the 0.001 by far. ).002-5" is probably as good as needed before a quick sanding.
BilL D

I'm pretty much in the same camp.

While I like things to be square, flat, accurate, etc., it is woodworking after all and the tolerances, for the most part, simply don't need to be as accurate as metal working tools.
Everyone has their own level of acceptable accuracy, some eyeball it while some obsesses over it.

Thanks for the link, it looks interesting.

[Greg Quenneville]

I think if you read the first picture's text he does state that the tolerances are different between machine tools and woodworking tools. That’s not the point.

I posted this because we sometimes read of guys astonished to find huge variances in new jointer beds, for example. And read that manufacturers are cagey about printing acceptable tolerances.

The fact that wood moves is germane how? We build things from accurately machined pieces so that they mate properly. Once assembled the wood is going to move in concert (more or less). No one is going to take a vernier calliper to a finished piece to check overall dimensions but you sure can easily detect small mismatches in components.

By the same token metal moves with temperature too, often by a lot. That does not stop me from wanting to achieve accuracy with my parts no matter what they are made from.

[Jacques Gagnon]

Greg,

Thanks for sharing; as Maurice said, data is good!

When looking quickly at the tolerances shown in the tables, it is easy to understand why so many people are looking for old iron. If those machines met the tolerances back then, it is no surprise that they were (and may very well continue to be) good performers.

Regards,

Jacques

[Warren Lake]

thanks Greg

reality is some machines can be out so much it affects there use. Try and set up a sliding table at some amount above the table when the table is not straight. Its been interesting to read about new stuff and tolelrances. Same time its made me look and see my old stuff is so good.

[Maurice Mcmurry]

Wood is not a machine. Wood Working tools are machines. The better our woodworking machines are, the better our results with woodworking will be.

[Bill Dufour]

Read about setting up machine tools and learn that you must wear cloth gloves and no sunny windows as the heat can cause things to move too much. I bet no woodworkers worries about the wood temperature off the saw before measuring it.
Bill D

[Ken Fitzgerald]

I'd suggest while precision is great, in reality, you have to consider the material you are working. Wood is much more dynamic than most metals or plastics for example.

[Greg Quenneville]

Read about setting up machine tools and learn that you must wear cloth gloves and no sunny windows as the heat can cause things to move too much. I bet no woodworkers worries about the wood temperature off the saw before measuring it.
Bill D

Yup. My metal lathe sits on a 24” thick bed of concrete. If the shop was a constant 70° with no drafts, and if I crank up the preload on the spindle bearings, and I hold my tongue right, and the neighbour doesn’t start his truck, then I should, in theory, be able to hold 50 millionths accuracy. Beats me how I'd measure that without in date calibrated micrometers. Can’t imagine needing to either.

But I really do want good manufacturing standards in my machines. I am not trained in either field, and I don’t have the skills to work around crap equipment.

[Brian Holcombe]

Ken, I agree with Greg and the others who’ve stated that the machines themselves need be accurate for many reasons. Aluminum, steel and plastics move but I’ve never heard that logic expanded to metalworking machines.

The critical reason for accuracy in my opinion is setup, as example it is hard to square a fence or set a cutter to a table that is not flat.

Inaccuracy in the machinery just makes your work less accurate or your assemblies more difficult.

[Randy Heinemann]

What is generally most important to me is that, when you cut multiple pieces that must be the same length or width or when you need parts to fit together you make sure that all multiples are cut the same and the parts fit together as you want them to. If you try to match lengths but cutting to a line on each, the parts most likely won't be completely identical. Measurements are great but stops for cutting the same length or width and actual fitting of pieces are more productive to getting a piece to fit together than making measurements. We all like accurate, precise tools. In fact, I've spent my whole woodworking experience (40 years) trying to be accurate and precise. In the end, though, measuring can only get you so close. Using stops, "story sticks", and ripping/jointing boards with an identical set of steps is the way to get parts to fit properly. Flat jointer, router, and saw tables, straight rip fences, etc. are the way to get the results you want.