Problem- Temperature

[rjsmith]

Has anyone ever had tolerances be affected by room temperature? If so how many degrees to make a difference. I turn A/C up at night 6 degrees and am getting part variation, is it possible that temperature difference would affect parts.Tolerance we are looking for is plus or minus .001. We have a Citizen L20 and just trying to let it run for 2 hours after we leave..

TIA

[ImanCarrot]

1. Assuming your talking 0.001", not mm?
2. Assuming you're talking deg F, not deg C?

Could be possible, but unlikely at those toloerances. +/- 0.001" is quite lose.

To give you an idea how temperature affects stuff, a 100mm iron rod will change in length by 0.012mm at a temperature change of 10 dec C. (source= Mitutoyo Engineers Reference Book, page 11).

The Machinery's Handbook gives a more detailed analysis (page 405) the thermal co-efficient of expansion affects it too.

I would suspect the spindle changing length as it warms up (you do perform a warmup cylce with the coolant running?)

Could also be coolant changing temperature, if used. All these can be monitored and managed.

I run the aircon 24/7 in my lab so that the machine can temperature soak. My compressor also runs 24/7 for the same reason. My spindle is liquid cooled again to stop temperature effects.

Temperature is my enemy. Don't even get me started on humidity lol

Oh, also, remember that if you're cutting a hole, say for example boring a hole, the hole will expand as it heats exactly as if the hole were a disk of the same material.

[ProProcess]

You did not mention material, I've had issue with Plastic parts with variances exceeding .001".

Here's the thing, everything expands and contracts with temperature/humidity; simple physics tell us that.
The key is to have the part being measured and the instrument doing the measuring at the same/stable temperature/humidity for some period of time (at least an hour).
This is refered to as "Normalization".
Often times people see the effects of temperature/humidity change as it effects the measurement, not so much the part.
This then causes a false reaction(offset) when in fact your just measuring and un-stable condition (part/gage not normalized).

HTH
Good Luck!

[rjsmith]

We run all day 8 to 10 hours, and then want to run for a couple hours unattended. We turn A/C up 5 to 8 degrees , run for a couple hours and parts grow out of tolerance.

[ProProcess]

If you are sure that the out of spec parts are caused by the change in room temperature while you are machining...
I would advise you to spend a few hundred dollars and invest in a programmable thermostat.
Have it adjust the temperature for you once your few hours of unattended running has completed.
Presumably you'd be able to justify the cost of the thermostat with the gain of not producing parts that are out of spec.
HTH.
Good Luck!

[hacdlux]

on my tsugami we typically note .0003 growth between morning and afternoon, no a/c in my shop, depending on time of year we are talkin 20-30 deg temp swing

this is after running the machine about 16 hour to get the coolant uo to temp(no chiller or hpc) we will typically see another .0003 from cold machine to warm machine.

we run 15 hours unattended during the week and 22 on weekends

iron thermal expansion
1 - 6.5 microinch per inch per deg F.

avg. casting thickness x temp swing x .0000065= close aproximation of change

hmmm im going to try this on the boss and see if i can get some ac

[SWISS20]

i have 4 swiss's we run 24/7 with exception of tool changes, setup and maint. I run them unintended from 1am to 5am holding .0004 or .001 tolerances running 1018, 1141, 17-4. and i can tell you 2 hours can be no problem holding .001 as long as program and tool changes are proved out, room temp does have a minor factor but the two biggest factors will be your coolant temp, make sure its nice and warm and consistent with the last 4 hours of running machine and 2nd your tool life, as an example I have a part we have to hold +or- .0002 on the od, we get approx 500pcs of a 5010 insert. when doing a tool change shortly after the dia will rise .0004 in the first 45 mins and stay consistent for the next 6 hours and approx another .0001 every 2 hours after that, so i do a tool change 2 hours before closing up shop and adjust my offset so my dia .0001 below nominal knowing it will stay consistent and possible grow .0001 or .0002 at most overnight still leaving me .0001 under the high limit

also if the machine will be doing bar changes, make sure next bar sizes are consistent with current bar, if your bars a much larger or smaller it could change your od or lengths

For anyone having sudden issues holding consistent sizes in L20 we came across a few jobs where the sizes were bouncing around more than usual, and found out our wedges in the tool holder were worn, we machined new ones and it fixed our problem, keep this in mind if you come across this problem