What tolerances needed for woodworking?

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The simple answer to your question is because there is no need! Seriously, it depends on a number of factors: type and expense of wood being used, type of project, type of finish, how exposed part is going to be, etc. For example, if pine is being used for say a distressed pine table with a faux finish, there is plenty of leeway. On the other hand, if I'm building a hardwood table with a clear or stained finish, I will be very careful and precise.
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If the part fits, it is in tolerance. Seriously, there is no need for a one off item that most of us make to have a tolerance. If a table top is 36" long or 35 63/64" or 36 1/8" does it make a difference? No. If a bench is 1/4" short of the plans, can your ass tell when you sit down? If you cut one part wrong you usually can cut the fitting or mating part to the size needed to mate properly.
If your factory is making bearings to fit crankshafts made by a different factory, different story. Oh, those pistons better fit the block too. Mortise and tenon joints are made to slip fit, but if they are all a little over or under you adjust as needed.
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"Edwin Pawlowski" wrote:

The advent of close tolerance manufacturing revolutionized, among other thing, the manufacture of rifles/arms as well as ammunition for them.
Made life lot easier for the army.
Way back when, a FoMoCo engine plant was one of my customers.
Worked on a project that involved measuring both pistons and block bores, correlating the data, then selecting specific pistons in specific bores based on that data.
Since it had to be done at high speed, it was one of the early applications of solid state logic.
By comparison with today's control hardware, that stuff was pure buggy whip, but it got the job done.
Lew
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spaco wrote:

As others have said, tolerances aren't that important. What *is* important is that the various pieces that define a given dimension in the finished piece be identical in that dimension.
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dadiOH
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Eggggzacktly. Piece A goes into Hole B, there should be minimal error. But, as Ed said, who gives a rat's ass if the over-all project is out by as much as a quarter inch. As Angela's dad used to say...and I never had the pleasure to meet that man (A WW2 Vet), "A man sometimes has to chose the hill he's gonna die on."
If you're making a bench out of twigs, nobody cares (or knows) if you're out an inch. But....now mount a Soss hinge....
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They really SHOULD give similar tolerances. Weekend woodworkers (who cut the wood in week 1 and fit it together in week 3) can't easily hold tight fits due to the wood movement between operations. That would make the (printed) tolerances useless (in week 1, you cut it, and it's within specs; in week 3, a perfectly cut tenon doesn't fit because the mortise shrunk). I've also cut dozens of oak sticks, then (actually planning this time) gave them a half month to relax before hand-planing to make 'em straight again.
There are some joints (sliding dovetail) I have gaged carefully with feeler gages, then readjusted a jig to make 'em tight. That time, the slot was the exact same size as the tongue, +/-.002" tolerance (it took linseed oil and mallets to assemble). If I was using water-based glue (white glue, or yellow) I'd open the gap to about .010" and glue with confidence.
When I made my doweling jig, I measured from a dowel in the first drillguide hole to a dowel in the drill press chuck, and tweaked the hole/hole spacing to +/- .001". The jig is in hard (filled) plastic with steel bushings, so that's not exactly a woodworking tolerance...
Another tight-tolerance situation is cutting and fitting plugs; a plug-cutter and boring bit have to match (hole +.002" to .006" oversize) or the plug doesn't look right when finished. That, or the plug doesn't fit in.
It is said that old turned chairs were made with dry wood crossmembers fitted to green uprights, and the uprights shrank to make a tight joint, even with no glue. My sister has some such chairs, probably about 200 years old, and still strong. The tolerance for such fitting, assuming .005" compression of the crossmembers in a 0.600" hole, tangential to grain, is about .030" (six percent shrinkage when drying), so old craftsmen were definitely doing better than 1/32 inch tolerance to get that kind of joint to work.
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Wood breathes, and expands and contracts with changes in moisture. Precision depends upon the amount of compensation needed to adjust to these changes, whcih depends on the size and length of each piece of wood involved. And how well the joint will hold, and the quality of construction.
Doll house miniatures versus timber framing has completely different requirements for precision/accuracy.
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spaco wrote:

In general, woodworking isn't dependent upon absolute measurements so much as relative measurements. When jointing boards, 1/32 would be unacceptable since one wants the joints "light-tight". On the other hand, 1/32 is way ridiculous in overall project dimension tolerance. For joints, the absolute dimensions don't make near as much difference as the dimension of the joint components (mortise to tenon,etc.) relative to one another.
The nature of the material seems to drive this -- wood moves and changes with humidity. It's better to work to relative fits than absolute dimensions.
--
If you're going to be dumb, you better be tough

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spaco wrote:

Tolerances are most important in the area of joints. I think as long as you hammer the nails to below the wood surface, that's fine. Paint can fill small hammer dings, bondo fills the bigger ones, but they won't hide protruding nail heads very well. Silicone caulk smooths out the joints where the board ends don't match up well or aren't square.
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On Mon, 15 Sep 2008 09:02:02 -0500, spaco wrote:

Leaving the "my tolerances are smaller than yours" brigade to carry on measuring each other! in practice, the tolerances are about the width of a pencil line. You can sharpen (or not) your point if you really need better than 1/2 mm or so. Most people just tighten the clamps a bit more if the tolerances don't work in their favour.
Just my 2p worth.
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One of the beauties of specializing in Shaker style pieces is that being off a little can be chalked up to aging and all those boogers in the finish lend character to the distressed look.
I like it when a new piece looks 60 years old.
People always say I must be rally skilled to get that look. They don't know it is due to a limited skillset.

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Hmmm... sounds like my marketing line when I tell them that each turning is unique.. lol
mac
Please remove splinters before emailing
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wrote:

Metal and wood are very different. Wood changes shape so tolerances don't make sense. Understanding wood movement is crucial when making larger projects if you want good results.
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Tolerances usually are included when drawings are submitted in an industrial environment. You won't see tolerances in any hobbyist magazines or books. The topic is "beyond their scope". But, if a cabinet shop gets a set of drawings from an architect, there is generally a definition of tolerances. Sometimes it is implied and sometimes it is explicit. In general, tolerances are as follows unless otherwise specified:
- Dimensions in fractions: +/- 1/64" - Dimensions with one decimal place (X.X) +/- 0.10" - Dimensions with two decimal places (X.XX) +/- 0.01" - Dimensions with three decimal places (X.XXX) +/- 0.005" - Dimensions with four decimal places (X.XXXX) +/- 0.003" - Angles +/-0.5 degrees
You'll find drawings with tolerances in furniture factories (even for the cheapie knock-down furniture). They will even have inspection stations with SPC data collection and control charts. Just about any environment where interchangeable parts are being made you'll see drawings with tolerances. Ask Henry Ford why it doesn't pay to run a factory full of "artisans" who insist on custom fitting everything.
If you can't read prints and build something to spec (with tolerances like these), then you're probably better off working with designers and consumers. Drawings from designers rarely include dimensions, let alone tolerances. It's usually up to the craftsman to engineer the solution from a sketch. And consumers want you to come up with the drawings based on an idea in their head or pictures from magazines, etc. In these cases you're on your own to figure out how much accuracy is needed to produce the desired results.
The hobbyist making something from plans out of a magazine or book usually gets dimensions but is pretty much on their own for everything else. You learn by experience what needs to be accurate and what doesn't.
Unique skills are required for success with all of these disciplines. But, I wouldn't want to confuse "trial and error" with any of these skills. It's better classified as a coping mechanism used by those who need to develop some skills. It usually comes from having no idea what accuracy is needed or how to produce it. You just try something and see if it works. If it doesn't, you try again. You keep trying until you get it right or you get fed up with getting it wrong so often.
Ed Bennett http://www.tablesawalignment.com
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On Tue, 16 Sep 2008 19:45:41 -0700 (PDT), Ed Bennett

Interesting.
Just for comparison, the standard (implied) tolerances on engineering drawings at the aerospace firms I was associated with throughout my career was X.XX +/- .03, and X.XXX +/- .010. Any tolerances other than those, looser or tighter, had to be explicitly specified in the dimension callout. Often those non-standard tolerances, and virtually all 4 place dimensions, had to be justified to the group leader or project engineer and, unless the need was obvious, would frequently be questioned by the manufacturing engineers or planners.
Tom Veatch Wichita, KS USA
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On Sep 17, 1:27am, Tom Veatch wrote:

Hi Tom,
Different industries, different customers, different vendors, different tolerances. In some areas a particular company dominates the market and their standards tend to prevail. For example, here in Boise it's Micron. Just about every machine shop in town does something for Micron. I'm sure in Seattle it's Boeing. I'd bet that Detroit is dominated by automotive needs. And, some companies have a formal review process (sounds like your experience) while others let engineers run open loop. It's always uncomfortable questioning tolerances from one of these open loop guys. I've met a few who have never built anything in their entire life.
Ed Bennett snipped-for-privacy@tablesawalignment.com
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Thanks to all who replied. I get the picture. I reverse engineer (metal)components for a no longer-produced all terrain vehicle for my son. I have to create drawings for myself when I make the parts and for others when he farms things out (higher volume than I want to deal with). Particularly for the outside stuff, I am the only guy alive (probably) who knows what fits with what, so I have to figure and apply tolerances as needed. The game I play with myself is to make the drawings good enough that the vendors are happy, my son's costs are minimized and the parts NEVER fail to fit and function.
Pete Stanaitis ------------------------
spaco wrote:

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