Tolerance for Moulding Dimensions

Moulding manufacturers discuss the limits of perfection in wood machining. January 13, 2006

I was told that AWI standards allow for 1/32" tolerance in the width or height on mouldings. Is this much tolerance really okay to millwork buyers? I spoke with one guy who consistently machines his material 15/1000" undersize because it increases his yield and it falls within the 1/32" tolerance. However, I've approached the subject with certain customers of mine who expressed the importance of precise material sizes. I would like to know what other millwork producers consider acceptable when producing accent mouldings.

Forum Responses
(Solid Wood Machining Forum)
From contributor T:
This may sound dumb to some, but I have 0 tolerance. Everything off our moulder is checked with calipers and is exactly to size. I know it won't stay that way, being wood, but I feel the closer to perfect when it leaves my shop, the better it will be when it's done shrinking or swelling.

From contributor F:
If you sell enough moulding that milling it .015" undersized would make a difference in your bottom line, go for it. .015 is, in layman's terms, a sixty fourth of an inch. I doubt if most customers can discern a thirty second of an inch, much less half of it. The only place to be really concerned is when adding to an order where someone ran short in the middle of a job. In that case, they will be possibly mitering two pieces from different runs together and though doubtful, .015" might be seen.

From contributor T:
I'm wondering if I'm missing out on something here. Just curious what you might gain by milling .015 undersize? The only thing I can come up with is a slightly bigger ripping off the last piece of the board.

From contributor G:
I agree with contributor T. Nail it to the thousandth every time, and guys will swear by
your moulding, not at it. Wood expansion and contraction will not need to be considered as long as you use good kiln dried lumber.

From contributor J:
We machine mouldings to .005" tolerance. I may be wrong on this, but I believe the AWI industry standard is .007". It is easy to get that close, and the customers never complain when they have to reorder more material that the first run does not match up with the second. Expansion and contraction will still happen, but as long as your MC is good for your area, it should all even out.

From the original questioner:
Thanks for the advice. We rip a lot of small mouldings out of 4/4 random width stock. .015 doesn't make much difference in yield unless you're gang ripping 1/2" strips or smaller. I think I will take the safe route and just mill to the exact sizes. I have checked some of the smaller mouldings sold at retail outlets such as Lowes and sure enough, they do measure slightly less than what the specified sizes are. They also leave saw marks on the back side of the mouldings. Of course I always think it's a good idea to be a notch better.

From contributor G:
You're right on the money. If you keep it within .005, you are a man who takes pride in his work. I have no doubt that your customers are very satisfied with your moulding. Keep up the good work.

From contributor Y:
I once worked for one of the largest wood window and door manufacturers in the Northwest. Tolerances were almost always +/- .015". That is plenty good for most wood products. If your moulder will machine dead on, then go for it, but there isn't much profit in dinking with a 30 year old worn out moulder trying to hit a +/-.005 tolerance on a piece of casing. There will always be some variation. My father in law works in the aircraft industry manufacturing tail sections for big airplanes. He says most structural parts are +/- .005.