Why don't they give tolerances on wooodworking projects and plans like they do for metalworking? Are there some tolerances that are so "standard" that everyone but me automatically knows them?
Pete Stanaitis
Len "
I disagree Leonard. I constantly keep things down to 1/32 or 1/64. Angularly, I certainly maintain =B1 0-degrees on angular measurements.. at least I try.
Most important, IMHO, is learning to tolerate neighbors borrowing tools.. lol
Other than that, "If it fits and looks ok" works well for me..
mac
Please remove splinters before emailing
I think you meant 1/16th, no?
Even that is quite a lot for many projects. For some even 1/32 is too much.
Are you serious?
I usually work in thousandths of an inch and try to keep most work within five thousandths for cabinet making work. Most everything I use is equipped with Digital Readouts attached to my Planer and other tools.
Tolerances in wood depend on wood type, grain, moisture content, and even how the particular part is used...
I'm still kidded by people in one of the CNC forums for my 1-hour,
2-hour, and same-day joint designs because if the joint wasn't assembled within a particular timeframe, it could probably /never/ be assembled.My brag was that I didn't need the glue to hold the parts together, but to lubricate the assembly. :-)
(And I did build my own CNC joinery machine to improve the accuracy of the cutting - photos at the link below.)
Hand tools (planes, chisels, scrapers) allow you to remove a thousandth of an inch. This isn't usually important in overall dimensioning, but can be useful for fitting joints.
Often people will assemble items and then plane/sand/scrape them afterwards to ensure that everything that should be flush actually is.
Of course wood also moves, so some parts of joints are less critical because you know that in a few weeks or months they won't be flush anymore anyways.
Chris
Woodworkers don't generally work with tolerances like that, and would be surprised at what sort of tolerances they are actually achieving - they just don't get there the same way. If it's critical then it's much more likely going to be done by cutting it long and sneaking up on it or test cuts in scrap than with careful setup of the machines. Probably because the materials are a lot cheaper and easier to machine.
I make every cut as accurately as I can, but I don't cut all the parts ahead of time and then expect it all to just fit together. It doesn't really matter how accurately the space the drawer fits into matches what the plan says if you haven't made the drawer yet and you mark it from the actual opening.
Just my Opinion, and nothing more!
Tolerances are something from interchangeable parts, production lines, and factory production. If your wood part drawing is for / from a manufacturing or assembly line plant, you can be sure there should be tolerances and QC inspections notations.
If you are a hobbyist then most of your work is going to be one of a kind type of project making. You apply your own tolerances to be with in the limits of YOUR measurement equipment and skill level.
There are two separate tolerances you need to be aware of: As a hobby woodworker, the most common measurement device is most likely the yo-yo measurement tape. Please don't get this group started on the errors induced by the printing of the marks on metal backing on your measuring tape. I still think the best is a story stick for a project, where all measurements needed are recorded (marked) on a single stick at one time, by one person.
The second error is in your transferring the mark(s) from the ruler (or story stick) to the work piece. This should be very small, about one half of the smallest marking on the ruler used. For example a ruler with 1/16" markings, tolerances should be +/- 1/32", like wise a steel machinist ruler with 1/64 engraved markings, we at the wreck will expect you to be +/-
1/128"As another posted, way before interchangeable parts and the Auto Industry, one would make the cuts a small amount fat, and then use hand tools to sneak up on it from both sides fitting together.
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.
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.
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
What kind of cabinet needs 1/200 tolerance? Heck, I wave a piece of sandpaper at wood and it loses more than that :)
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.
If you have edging on plywood that is 1/200" proud of the plywood, you can easily feel it with your fingers. But you can also easily sand or plane it flush.
The key with woodworking is not so much that individual pieces be dimensioned that precisely, but that *matching* pieces be dimensioned precisely. And this can be done post assembly, or by trial and error.
Chris
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....
You thickness plane to .005"?
Cool!
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.
Wonder how much different it is two hours later, what more the next morning???
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