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How much precision do you need in woodworking?

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Forum topic by StumpyNubs posted 03-22-2011 09:10 PM 3621 views 2 times favorited 142 replies Add to Favorites Watch
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StumpyNubs

6259 posts in 1519 days


03-22-2011 09:10 PM

Topic tags/keywords: jig question tablesaw plane jointer milling traditional

This morning GarageWoodWorks and I had a good natured debate about Starrett combination squares and it led to a question that I think is very interesting. So I thought I’d post it here…

How much precision do you really need in woodworking, and how much of it is just overkill?

From what I can see, there are two schools of thought. One applies the ultra-precision of the machine shop to woodworking. Tolerances beyond the thousandth of an inch. Using devices like a micrometer to achieve precise thicknesses way beyond what can be detected with the naked eye. In the past (in fact for hundreds of years) these level of precision were not applied to woodworking. But today’s ultra high end tools and jigs are designed to these levels.

The other side of the issue is that woodworking is not THAT exacting. You want your materials flat, your cuts square. But if it is off a tiny amount, less than can be seen with the naked eye, will you really ever know it? For example, if you make a mark with an absolutely perfect machinist’s square on a board, can you even make a cut that perfect anyway? Not if you’re sawing it by hand, and probably not even with a well tuned table saw because even a solid fence deflects a couple thousands of an inch. And if you get your material to an absolutely precise thickness, what happens when you sand it? Is it still perfectly flat? Does it matter?

We’re talking thousandths of an inch here. Nobody is saying a crooked crosscut or twisted board is acceptable for woodworking. But when you’re working with a material that moves, swells, twists and contracts back and forth with the humidity level, can you expect (of should you strive for) the same perfect tolerances of a machine shop?

What’s your opinion?

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com


142 replies so far

View Greedo's profile

Greedo

468 posts in 1679 days


#1 posted 03-22-2011 09:20 PM

in my case when i adjust a ruler or a fence on a machine i try to get it right with a tolerance of max 0.2mm.
thats about the smallest measure my eyes can make.

precision is verry important to me in the first stages of a project, when planing, length cuts, marking the mortises and tenons etc… because when you assemble different parts together and each part has a small error, then the errors add up!
once its’ assembled then precision doesn’t really matter that much, the sanding completely changes the dimesions and thicknesses

View Bertha's profile

Bertha

12951 posts in 1412 days


#2 posted 03-22-2011 09:23 PM

This is my favorite ruler:

I think that should dispell any myths that there’s any kind of precision in my shop!

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View Cosmicsniper's profile

Cosmicsniper

2199 posts in 1877 days


#3 posted 03-22-2011 09:26 PM

My opinion is that until you’ve ever used a precision device (like my Incra TS-LS positioning fence), then you probably don’t know how important precision is. I know I didn’t realize just how those minute errors actually compound into larger issues. It is very easy to assemble something when you KNOW that your cuts are perfectly square.

Whereas I’ve heard people argue that precision isn’t important because “wood moves anyway,” you’d kinda like it to hold off a while UNTIL you get the project finiished!

But I think anybody who has ever mitered a picture frame can tell you how difficult it is to get good miters…it takes a while to dial in your miter gauge to that perfect setting. Tenths of a degree, in that case, only gets you partly there.

Or how difficult is getting an invisible glue joint? Doesn’t take a whole lot to make that seam stand out like a sort thumb.

So, ultimately, it probably comes down to your degree of satisfaction in the finished product or the type of projects you tackle, but for me, I get a little upset when I do something a little bit “off” than it could be…and it’s usually a very fine line.

-- jay, www.allaboutastro.com

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StumpyNubs

6259 posts in 1519 days


#4 posted 03-22-2011 09:28 PM

Bertha- I love those vintage tools! I have a similar folding rule.

I don’t believe the Greene bros. created their masterpieces 100 years ago with a micrometer and a .0001 microadjuster on their table saw fence! Hand work is the heart and soul of great woodworking and it is not a precise process!

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

View Bertha's profile

Bertha

12951 posts in 1412 days


#5 posted 03-22-2011 09:32 PM

I recently started a project using mostly hand tools (http://lumberjocks.com/Bertha/blog/21738). If you follow along, you’ll see a few joints that are dead on & a bunch of joints with some slop. I leave all my marking lines and I overcut my saw lines. I do this because I like the appearance & the imprecision doesn’t bother me. That being said, I think everyone’s right! If you’re happy with your work, it’s precise enough.

And Stumps, I’m a big lover of vintage tools. That Preston rule is off about 1/8” on it’s length but I still can’t resist using it!

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

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StumpyNubs

6259 posts in 1519 days


#6 posted 03-22-2011 09:34 PM

Cosmic- I think Incra makes some of the best tools around. But if it’s off 1/1,000 of an inch, will you ever even notice? If so, why does their fence system have 1/32” adjustments? Wouldn’t you want to adjust it far finer if it really mattered at that level?

If my miter is off by a degree, I’ll notice. If it’s off by a thousandth of a degree, there’s really no way anyone would know it unless they use a precision measuring device to check it.

How did the great craftsman of the past do it?

BTW- I am not saying absolute precision is BAD. I’m just saying there comes a point that it’s just overkill. However, I think the incra system’s 1/32” is not overkill.

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

View brtech's profile

brtech

695 posts in 1642 days


#7 posted 03-22-2011 09:37 PM

The thing to remember about accuracy is that it always goes downhill.

An easy example is if your ruler is 1/16” accurate, and you are reading a 1/16 scale, the most accurate results you are going to get is 1/8”. If you measure from an end of a board, place a mark, and shift your ruler down to put the zero on that mark, and them measure 10” from that, the second measurement is going to be as much as 1/4” off relative to your starting point. That’s why you want your tools to be MUCH more accurate than your results need to be.

Sure, you can compensate for errors later, but it’s better to not have the error in the first place.

View BigTiny's profile

BigTiny

1664 posts in 1607 days


#8 posted 03-22-2011 09:47 PM

I think accuracy is important, as the errors do add up. That having been said, you have to make up your own mind what your definition of “accurate” is.

For most things, plus or minus 1/32 is close enough, but in some cases even that is too much, like in fitting drawer fronts in a case. If one differs from its neighbor by that much it will show to the naked eye. 1/64 would be the most you’d want in that situation.

One source of error many people are unaware of is the difference between measuring tools. If you measure a gap with a tape measure, them measure the board to fill that gap with a steel rule, there’s a good chance they won’t be the same. Check your measuring tools against each other. You can find as much as 1/8 inch to the foot difference from one to another. You should always use the same tool to measure everything in a project for safety’s sake.

I like to use a “story pole” for most projects. I measure the line I want carefully on the stick, mark it across with a square, and label it with the length and what it’s for. After that, every time I want that measuement, it’s right there, as accurate as you please.

-- The nicer the nice, the higher the price!

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StumpyNubs

6259 posts in 1519 days


#9 posted 03-22-2011 09:50 PM

brtech- That’s correct. But 1/16” off is a lot. That is not precision and it will add up like you said.

The question arose when I said my vintage Miller’s Falls combination square was perfect based on the tried and true test of drawing a line, flipping the square and seeing if it still lined up. The other person said my eyes can deceive me, it may not be “perfect”. I say that kind of absolute perfection is neither necessary, nor possible in woodworking.

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

View CharlieM1958's profile

CharlieM1958

15712 posts in 2937 days


#10 posted 03-22-2011 10:05 PM

Generally, I fall into the camp of “close enough”. As others have said, precision is more important in some situations than others… like making a mitered frame or a box with mitered corners. In other cases, it’s just not that big a deal. Who cares if the table legs are 18” or 18 1/8? What’s important is that they match each other.

-- Charlie M. "Woodworking - patience = firewood"

View Cosmicsniper's profile

Cosmicsniper

2199 posts in 1877 days


#11 posted 03-22-2011 10:07 PM

“Cosmic- I think Incra makes some of the best tools around. But if it’s off 1/1,000 of an inch, will you ever even notice? If so, why does their fence system have 1/32” adjustments? Wouldn’t you want to adjust it far finer if it really mattered at that level?”

__

The Incra is pitched at 32 tpi (hence 1/32”), but it can be quickly micro-adjusted within this pitch…and it really comes in handy.

Trust me, the difference of perfectly fitting an inlayed strip into a groove is measured in plus or minus a couple of thousandths…with the Incra, I can do it the first cut.

People get good miters with shooting boards and get invisible glue joints with a hand plane…but just because they are “hand tools” doesn’t mean there isn’t precision involved. In those cases, it’s a degree of precision that can be measured in small fractions.

When you smooth a board, it seems like you sand off a ton? But are you really? The peak to peak difference in smoothness can actually be measured in very small amounts. This is why you can run a smoothing plane over a board just once in lieu of actual sanding. How thin is that curl of wood? Pretty darn thin, IMHO…you could probably read your favorite woodworking magazine right through it.

That single curl is probably the difference of a board properly fitting in a dado; a tenon fitting properly in a mortise.

I just think there’s a misconception that handtools aren’t precise. I disagree…that’s why it takes years to learn how to get good fitting, hand-cut dovetails…the tools are capable, but the technique must be refined. This is why I gave up and went with a jig! :)

By the way, if you are building boxes for cabinets, precision isn’t important. If you are building decorative, mitered boxes or doing marquetry…I think you’d better be pretty darn precise!

-- jay, www.allaboutastro.com

View Bertha's profile

Bertha

12951 posts in 1412 days


#12 posted 03-22-2011 10:13 PM

^ I honestly hadn’t considered the demands of inlay work. I imagine that to be quite demanding in terms of precision. I shoot miters with a handplane, so I guess I AM interested in superb precision on occasion.

-- My dad and I built a 65 chev pick up.I killed trannys in that thing for some reason-Hog

View drewnahant's profile

drewnahant

222 posts in 1808 days


#13 posted 03-22-2011 10:32 PM

I think that striving for accuracy is important, having tools with precise increments, because once you go with the theory that 1/32 is good enough, you can start adding up the errors, you get tools that are only that accurate, then you let your cuts be within that accuracy without remembering that your rule is already off, and so on. also remember that just because a ruler, tape measure, fence, whatever it may be, is only marked at every 32nd doesnt mean that it is only that accurate, it just means that you can only use those measurements. a ruler with markings every inch can give you perfect results as long as your cuts are at even inches, just dont estimate what’s in between.

View richgreer's profile

richgreer

4524 posts in 1793 days


#14 posted 03-22-2011 10:37 PM

It seems like it is often more important that various pieces be exactly the same length or thickness or angle as opposed to being exactly X inches or Y degrees. Example 1 – I really don’t care if the legs of a table are exactly 32” long, but I really do care that they are all exactly the same length. That’s where stops on miter saws and table saws and good jigs come into play. Example 2 – when running an edge along a jointer to prepare the edge for a glue up it is not essential that my fence be at exactly 90 degrees if I flip the boards so any error is cancelled out when I glue up. I could offer more examples, but you get the idea.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View StumpyNubs's profile

StumpyNubs

6259 posts in 1519 days


#15 posted 03-22-2011 10:39 PM

drewnahant- Again, we’re not arguing about precision to the 32nd of an inch being overkill. (That was just the Incra adjustment question). We’re talking about machine shop precision to the thousandth of an inch.

I think it depends on the situation. But crosscutting or ripping to the 64th on an inch is “perfect” enough in even small pieces. Inlay is different, but even then much more than 1/64” is not detectable by the human eye.

I suppose on a piece with many segments that make up an overall measurement it can add up. But unless you have a hundred segments, absolute perfection beyond the thousandth of an inch is overkill in my opinion.

-- It's the best woodworking show since the invention of wood... New episodes at: http://www.stumpynubs.com

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