Knowledge You Can Build On — Est. 1998
Need opinions
Spence in Rhode Island
>I'm looking at a job right now. Lots of very small pieces to be made out of mahogany, walnut and maple. Very very tight toleranses though. 1/100 of a millimeter which converts to 0.0003937. Here's my question: Would the wood expand or contract more than that with changes of humidity? I've worked with a + or - of 0.005" before but 0.0003937 doesn't seem very realalistic to me. What do you think?
TIA
Spence
Re: Need opinions
Ace Foster in Ben Lomond 95005
>What does this .01 mm work out to as a fraction of the size of your object? It seems extremely optimistic to me to imagine that you could reliably and repeatably a) machine wood to such a tolerance and b) measure the result.
Ace
Re: Need opinions
John Trant (DC/Baltimore Corridor)
>No way. Wood will change far more than that with changes in humidity and temperature. This is assuming that the wooden part is of some reasonable (workable) size. I would think metal would be equally unreasonable as a substrate for this job.
John
Re: Need opinions
Gary Evans, Tallassee, TN
>Spence,
According to the shrinkage equation in Bruce Hoadley's "Understanding Wood", mahogany pieces 1/2" wide, flatsawn, would shrink or expand .018" in width with a change in MC from 10% to 8% or vice-versa.
I don't see how anyone with any knowledge of wood as a material would write a specification to those tolerances. Working to 4 ten-thousandths would be difficult if the material was metal or plastic. I used to rebuild, align and balance two-stroke crankshafts which had tolerances in the ten-thousandths. I wouldn't volunteer to hold that kind of precision again if I didn't have to.
Good luck,
Gary
Re: Need opinions
Chuck Nickerson
>This sounds very much like a scam. Do they want a preprocessing or instruction/material fee? I have a friend who answered an ad for simple toy assembly. She sent a $100 material fee, only to discover that the toys could NOT be assembled.
Re: Need opinions
Pete in Holland, MI
>I assume you have a metal lathe-type machine with a machine mounted tool. That type of tolerance would be impossible to hold by hand, especially in quantity. 0.003" is a normal human hair. It is very tough to hold that tolerance on a good metal lathe. That type of tolerance is usually left to grinding. Are you sure the customer who needs the parts didn't accidently give you standard metal tolerances without knowing that wood changes with the seasons? Curious to know what type of wood product would need tolerances that tight. Good luck !
Wood is wrong material !
Brad Vietje
>
Re: Need opinions
Tom Mullane
>NO WAY NO HOW are you going to be able to keep wood at that tolerance... I don't care if it is Lignum Vitae which barely moves at all.. it aint gonna happen... especially turning it on a wood lathe
Thanks Folks!!!
Spence in Rhode Island
>Thanks for all the info. I didn't see how wood could be held to that tight a tolerence myself but wanted a second opinion to back my thoughts up. To be honest I never even progressed to the point of how I would measure it. I've written back double checking that its not a typo. I don't see how it could be a scam as so far I'm not asked to put out any cash. As far as how realalistic the job will be I'll just have to wait and see. These will be about the size of pegs for a cribbage board I think and I've made quite a few of those. Its that 1/100mm stuff thats the killer.
Thanks again!
Spence
