How much precision do we need in woodworking?

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Forum topic by b2rtch posted 08-23-2012 01:04 PM 2798 views 0 times favorited 61 replies Add to Favorites Watch
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4861 posts in 3044 days

08-23-2012 01:04 PM

Topic tags/keywords: question

I have posted again and again about my Powermatic 60 jointer.
Now I am still wanting to adjust the tables.
For that I need a good straigth edge, I have been borrowing a Starret from work but it is only 36”.
I would like 72 or 96” so that I can use it for other things but really good straigth edges are extremely expensive.
So, like may other people, I was thinking about buying a steel ruler or may be a carpenter level (I need a new one anyway).
Many time I have been wondering if we demand too much precision when doing wood working.
Do we really need to adjust a TS or jointer within a few thousand when we are working wood, a living materiel which will move again any way?

I understand why I need my jointer tables need to be co-planar and flat and so on but when do we become obsessive/compulsive about it?

What is acceptable and what is excessive and our quest for precision and accuracy?

(by the way, I work in the pharmaceutical industry and I daily check our equipment with an accuracy with a few 1/10 of a thousand of an inch and/or a few tens of a thousand of gram)

-- Bert

61 replies so far

View BrentNichols's profile


40 posts in 2944 days

#1 posted 08-23-2012 01:23 PM

Bert, My experience from this is that it does not need to be perfect. However it may seem that you are a little like me and we are perfectionists to a small degree. I do too put a dial indicator on my jointer blades when changing to get them within .001 of an inch, as i also do this to the tables. I also use this method align my tablesaw fence and miter track to the blade. My other friends tell me that i am way to picky when setting things up like this and as long as its close it will work fine. It would be perfectly fine without the precision we use but it would be the idea of knowing it was not close to perfect that would bug me to fix it. I hope this hepls a little.

-- BN in Indiana

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4861 posts in 3044 days

#2 posted 08-23-2012 01:44 PM

BrentNichols, I believe that this is a good explanation.

-- Bert

View CplSteel's profile


142 posts in 2160 days

#3 posted 08-23-2012 02:10 PM

I like it when things fit together well however, If you are asking if we need our tools dialed in percicesly the answer is no, precision can be had easily without exact error free tools. There are two different ways of working, machine precision and cutting to fit. Neither is right or wrong and they have different advantages. If you want every leg of a table the same length, you can dial in a saw to 1/100” a, measure, and cut each leg. Or you can cut one leg and use that to measure the others. In the first example, if your measurement is off between one leg and another, the variance is small, in the second because you are referencing off the piece, if you are off the variance is small. You can always go back and true them together, all four at the same time to ensure they are exactly the same length.

If you watch Roy under hill, he may measure a piece at 6” and cut it, but when he goes to drill the center of it he doesn’t measure in 3”, he uses dividers. That way even if 6” is 6 1/8”, center is still center.

Another example is door fronts. If you batch them out ahead of time then your measurements, on all the cuts, not just the drawer fronts, need to be percise because a 1/8” gap stands out. However, if you cut to the size you need, not the size you planned to need, the left drawer may be 1/8” wider than the right, but because you can cut it that way the gap between them will be uniform and unoticable.

Obviously if you are making many identical cuts in a production shop and you are using very stable material, like mdf, then taking the tIme and expense to dual in your tools will be money well spent. A home hobbiest working with real wood can just work a bit differently. After all do you need 4 legs all exactly 23” long or do you need four legs about 23” long and exactly all the same length. The latter is far easier to achieve than the former.

Most importantly is to work the way you enjoy. I am lucky enough not to own any machines made well enough to be dialed in with that kind of precision. When I do, I will probably try to get them exact as well.

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4861 posts in 3044 days

#4 posted 08-23-2012 02:23 PM

CplStee, thank you for your very good answer, I truly like the way you explain the way you achieve what you want to achieve.
This makes a lot of sense to me but my sequestration is more oriented toward how much precision do ewe need while adjusting our power tools.
I read review and read about people using, say, Incra miter gauge that they can dial in within 1/10 of degree or so, is this really necessary?

-- Bert

View Lee Barker's profile

Lee Barker

2170 posts in 2846 days

#5 posted 08-23-2012 02:24 PM

To find what is acceptable for you in terms of accuracy, improve things until you aren’t apologizing for your work.



-- " his brain, which is as dry as the remainder biscuit after a voyage, he hath strange places cramm'd with observation, the which he vents in mangled forms." --Shakespeare, "As You Like It"

View EPJartisan's profile


1118 posts in 3121 days

#6 posted 08-23-2012 02:40 PM

With an Industrial Design background.. I was taught to do the best you can at every stage of the process, because you can not be perfect and all those small imperfections add up at the end… BUT that was for manufacturing mass producible items.

To me, wood working is more like sculpture. I love being perfect, but i never let the tool determine the process nor the result. I gave up “perfection” a while ago, my tools move each season, blades go dull in the middle of a process… the wood a living material and if you don’t work with it… it will work against you. yet I work that there are places people see and feel and those places I make perfect, but the rest I just don’t stress about, so I say always do your best, and only focus on perfection for those few areas: joints and visible places. Thus I focus on beauty,, not perfection. Just take a serious look at Japanese cabinet makers… little spaces, uneven areas, plane marks.. they are about the beauty and efficiency… the perfection comes from the passion and repetition.

The other thing is.. people are far more amazed YOU actually made something from scratch.. people are kinda blind to the imperfections we beat ourselves up for.. and I only fear other woodworkers scrutiny.. LOL. There is a book titled, the structural properties of materials.. and they have a chart that explains how much you can be off before it is a) actually visible to the client… b) or will fail from stresses. and you know.. we get a lot of wiggle room.

-- " 'Truth' is like a beautiful flower, unique to each plant and to the season it blossoms ... 'Fact' is the root and leaf, allowing the plant grow and bloom again."

View b2rtch's profile


4861 posts in 3044 days

#7 posted 08-23-2012 02:46 PM

Lee and Eric, I truly appreciate what you write, I believe that these are good lessons.

-- Bert

View jdmaher's profile


427 posts in 2575 days

#8 posted 08-23-2012 02:54 PM

As CplSteel said, fit is easier to achieve. And remember, you ain’t gonna hit spec anyway.

I’m not doing production work with metal. I’m doing hobby work with wood. I thickness the boards to 3/4” – on an August day that’s 98 degrees and 87% humidity. Then I have to work for a living; and my wife insists on visting people and having guests over and taking a trip and replantting the gardens; and I have to work for a living. When I finally get to cutting the tenons on the end of those boards, it’s almost Halloween and 45 degrees with 45% humidity – and I mis-measured when I thicknessed anyway – so damned if those boards aren’t 11/16ths thick!

I try to keep my focus on making something that looks good and fits, not something that measures out exact.

-- Jim Maher, Illinois

View EPJartisan's profile


1118 posts in 3121 days

#9 posted 08-23-2012 02:58 PM

For my empathy.. I purchased a jet 6” jointer about 6 years ago. It was on sale and Rockler only had the floor model left. needless to say.. I will never buy the floor model again. The beds are not parallel, infact one has a slight bend to the bed as if it was dropped at some point. I was a naive to the tool at the time, but now I know more than I have ever wanted.. it is a great tool to have on hand.. but a total PITA to maintain and adjust. I moved on to make sleds for my table saw, but I still use it for pieces under 20”.. yet I still get angry at it and try to adjust it, shim it.. take it apart.. then give up! I only use it the best I can and move on with the desire to trash it and get a 8” grizzly or something.

-- " 'Truth' is like a beautiful flower, unique to each plant and to the season it blossoms ... 'Fact' is the root and leaf, allowing the plant grow and bloom again."

View WrathOfSocrus's profile


24 posts in 2448 days

#10 posted 08-23-2012 03:16 PM

I agree that changes in moisture can negate accuracy, particularly in humid climates like where I live. I also agree that woodworkers beat themselves up more than non woodworkers would care or notice in your projects.

One thing I would say is that I don’t think it matters to have that level of accuracy over 6 feet or more. The weight of the wood would lay itself down if the ends of your infeed and outfeed are off a few thousandths. I’m sure if you planed a piece of wood (say 4 feet long or more) perfectly flat and uniform in thickness, then clamp one end to a bench and let it hang off, it would sag more than just a few thousandths. If you can get the 18” – 24” on either side of the cutting head to a flatness you find acceptable, then you should be able to produce stock reliably within your tolerances. If the machine has long feed tables then I would just check each for flatness and then flatness and accuracy between tables at the cutter head. If you use add-on feed extensions I would just get it close without going crazy. If you are spending more time lining up extensions than u did building them then it probably isn’t worth the time.

-- "To do is to learn. A brilliant man once said that... I think he had a beard, too." - Joe Burns, HTML Goodies

View dbhost's profile


5710 posts in 3228 days

#11 posted 08-23-2012 03:21 PM

If we were working with highly refined alloyed metals with controlled expansion / contraction rates, and building components intended for high speed operation I could see tolerances in the thousandths or ten thousandths being the range we want to work in, but we aren’t, we are working with wood, a media that moves and flows on its own. While I don’t encourage anyone to be sloppy in their work, I don’t see the point in going to extremes for accuracy when there is no real benefit. If for example a piece of steel stock used as a straight edge is within .001” in an 8’ run, to consider that not straight for woodworking purposes is for all intents and purposes over concern with accuracy. I would however be concerned if there was variation at the .1” per 8’ level…

You say you have a 36” straight edge that is known good. You can check an 8 footer with your 3 footer. If 3 feet are good, then move down 2 feet so you are checking against a known good foot, and check, repeat until done…

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Mainiac Matt

8034 posts in 2324 days

#12 posted 08-23-2012 03:30 PM

I’ll add a couple thoughts….

In general, I think chasing thousandths in a woodshop can be misplaced effort. Because wood can be porous and has grain, variations of a few thou. are inherant to the material. Also, because wood “moves” a part that is spot on today, may not be tomorrow.

But the human eye and sense of touch can detect differences as subtle as .005” quite easilly… so you want to have “perfectly” matching surfaces…. but how you get there with wood is a different approach… one that reflects more “craft” than it does “math”. So little things like the sequence in which you cut… making the final pass for all your table top boards through the planer at the same time, without and changes to the settings (so the part to part variation is effectively zero) is more important than the ability to dial in 1.000 on a Wixley.

Woodworking craftsmenship has to take into account shrinking and swelling as well. So the better mortice and tennon joint isn’t necesarilly a 1.000” tennon in a 1.000” mortice. But rather, a slight interference fit achieved by lightly sanding a tennon that is intentionally cut slightly oversized untill it can be driven into the mortice, with relief cuts around the shoulder may yeild superior results.

I certainly like precision… but I’m finding that the absolute measurements are of lesser importance than the relative measurements between mating parts..

-- It’s the knowledge in your head, skill in your hands and motivation to create in you heart that makes you a woodworker. - Mainiac Matt

View Loren's profile


10381 posts in 3644 days

#13 posted 08-23-2012 03:34 PM

I think there is too much emphasis on making wood objects perfectly
right off the machine. Even if you square plywood good panels very
square, there will still often be a little twist in a plywood cabinet
due to distortion in the material. You can learn to make things
look good and function well anyway. Perfection of the geometry
of the box is not essential to its function and good appearance.

I know from experience my jointer doesn’t have to be perfect to
be mostly effective (I had a 12” machine with funky tables
and worked around it). Wood always moves and the process
of jointing and then flipping the board over and planing the other
side to thickness always results in the balance of tension in the
board changing. I check long boards with a 78” level and
winding sticks (though my eyes alone have got pretty good).
Corrections are done with hand planes. Sometimes the smart
thing is to take the tool to the work.

A reliable thickness planer is more of an asset to me than a
large jointer. Thickness consistency from part to part is
important to me… more important than surface finish off
the tool. This is why I use a Belsaw.

I recommend a 78” level as a most useful device for making
good boards. In millwork, the long level is essential to
the way I work.

A black lumber crayon and a white piece of chalk or grease
crayon are also very useful to mark flaws in board faces
and help keep track of which side was planed last.

View Dan Krager's profile

Dan Krager

4000 posts in 2230 days

#14 posted 08-23-2012 05:06 PM

I have learned that as you gain experience, there are many times you don’t want a board to be perfectly straight. For example, gluing up a panel with tension in it will help it last for lifetimes without splitting. A jointer set to get a perfectly straight edge most likely will not do it on a regular basis and the board will more likely than not have a convex curve in it. I used to adjust mine so a very slight concave curve resulted. Another example, A bit of curve on a hand plane blade is useful to speed removal of rough surfaces and slight (<.002> concave edge for edge gluing.
Agree with those above. Perfection is not needed everywhere, just in the critical areas. Like finishing a house…the only two places perfection is needed is in front of the toilet and around the front door!

BTW I’m happy if a 10” blade wobbles less than .005.

-- Dan Krager, Olney IL One should always prefer the probable impossible to the improbable possible.

View PurpLev's profile


8535 posts in 3644 days

#15 posted 08-23-2012 05:17 PM

I think people try to be too precise when it comes to woodworking many times when it comes to perfect joints and what not, but when it comes to straight/square cuts – small differences do show up in the finished product and yes, it does make a difference. to a few thou in the finished cut? definitely not, but definitely to 1/64th.

thats as far as cuts go, but when we discuss setting up machinery there is another aspect to it – safety.
setting up the blade parallel to the miter slot with too much variation can lead to pinching of the wood between blade and fence and can lead to kick back for example (there are more cases of course, but this is the most obvious). so when setting up machines – I would indeed use the 1/1000 scale

bear in mind – setting up machinery with precision is greatly different than using that machinery to cut wood precisely…. 2 different scales being used there.

-- ㊍ When in doubt - There is no doubt - Go the safer route.

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