What tolerances can I expect from a local machine shop?
What tolerances can I expect from a local machine shop?
(OP)
Hi all,
I'm having simple fixtures made for some material testing. They are essentially plates with through holes to insert precision dowel pins. The center to center spacing for these holes must be accurate, and my design allows for no more than a +/-0.001" tolerance. My question is, is it safe to assume that a normal machine shop can hit these this tolerance no problem? Also, what type of tolerance can I typically expect for the overall width of the plate? (both faces will be end milled). From what I remember working at my uncle's machine shop as a kid, it wasn't uncommon for us to hit +/-0.0005. I just want to make sure that I'm not making some absurd request.
Thanks,
M
I'm having simple fixtures made for some material testing. They are essentially plates with through holes to insert precision dowel pins. The center to center spacing for these holes must be accurate, and my design allows for no more than a +/-0.001" tolerance. My question is, is it safe to assume that a normal machine shop can hit these this tolerance no problem? Also, what type of tolerance can I typically expect for the overall width of the plate? (both faces will be end milled). From what I remember working at my uncle's machine shop as a kid, it wasn't uncommon for us to hit +/-0.0005. I just want to make sure that I'm not making some absurd request.
Thanks,
M





RE: What tolerances can I expect from a local machine shop?
Did you ask the machine shop that is making your fixtures if they could deliver your tolerances before you gave them the job?
Ted
RE: What tolerances can I expect from a local machine shop?
RE: What tolerances can I expect from a local machine shop?
There have been threads about 'typical tolerances' before, maybe you can find them with a search.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What tolerances can I expect from a local machine shop?
Then send them out for quotes. The machine shop will make your decision, and answer your question.
If you don't really require tight tolerance, then don't put them on the print; ask for what you need.
If you really need the tolerances that you are asking about; then it really does not matter what to expect.
Charlie
www.facsco.com
RE: What tolerances can I expect from a local machine shop?
all of the advice given is very good & are very good suggestions.
These are my thoughts. for your FYI only.
The fixture tolerance should be approximately 1/3 max of the tolerance of the production parts. rough rule of thumb.
for very tight tolerance. .001" x .333 = .00033 max, it's more complicated than this but this works.
+/-.001 is a very reasonable tolerance, but may be not adequate enough.
if these test are one time only, then the tools can be made pre hardened tool steel. available from Mcmaster carr. p-20 tool steel, apply your dim's &
get your quotes & ask for the cost saving suggestions from the manufacture. I would use a shop that has grinding abilities. but not necessary for your tolerancing.
if this a test that is to be rerun for production, have instructions on your print tool surfaces to be heat treated to 60 min HRc then ground.
depending the steel used. (if it's heat treatable)
If a more accurate requirement are needed. the holes & plate surfaces will require to have stock left for finish grinding.
this will prevent the tool from wearing out prematurely & have a very accurate tolerance.
As I seen the other senior members point out on other post, you only have to apply your requirements on the print.
and the manufacture has figure it out. but I like to advise what is involved.
send out three quotes & see who is of more help, as well as cost sensitive.
good luck
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: What tolerances can I expect from a local machine shop?
RE: What tolerances can I expect from a local machine shop?
the cost is base on the Time & Material,"tolerance, Labor, cost of machining, cost of material, heat treating & process required",
HTH
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: What tolerances can I expect from a local machine shop?
RE: What tolerances can I expect from a local machine shop?
I have always thought all dimensions should be at 20 degree C. If you start specifying a different temperature that would add a huge cost to the part as all machines and inspection equipment I am aware of are calibrated at 20 degrees.
Personally I would go down the route of changing the part to be functional at whatever temperature is required but inspected and machined at 20 degrees not insist that all production machines and inspection equipment are calibrated at a one off temperature.
RE: What tolerances can I expect from a local machine shop?
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: What tolerances can I expect from a local machine shop?
Mike Halloran
Pembroke Pines, FL, USA
RE: What tolerances can I expect from a local machine shop?
My point was not to use an oddball temperature for machining, but to machine and inspect at the same temperature. Depending on the distances involved, a few degrees of temperature difference between machining and inspection can result in out-of-tolerance results.
RE: What tolerances can I expect from a local machine shop?
agreed, just that who ever is machining must be smart enough to make the correct adjustments.
I know many areas in the world requires air conditioning & or heat depending if it's winter or summer.
I live in southern California which has Mediterranean weather, which is 70 deg F most of the year.
I forget other parts of the world are not the same.
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: What tolerances can I expect from a local machine shop?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What tolerances can I expect from a local machine shop?
RE: What tolerances can I expect from a local machine shop?
thread281-280471: spec for machining tolerances
thread1103-287585: Machining Tolerance Standards and General Notes
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What tolerances can I expect from a local machine shop?
I am in agreement with you
It depends the the level quality required & what is required by your customers which now is a more complicated answer.
certification to ISO & so on.
as a supplier it should be audited to make sure the machine shop is qualified to make the parts. yes
With the correct quality procedures Inspection & manufacturing equipment, that traces back to the bureau of standards ect ect. or depending where it is situated in the world.
Kenat
It it not part of being certified to AS9100 or ISO 9100?
and as for U.O.S. I prefer a tolerancing block for untoleranced dimensions.
but I believe it is better to use ASME/ANSI and directly dimension all attributes.
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: What tolerances can I expect from a local machine shop?
What tolerance can and should be held 'It depends'
RE: What tolerances can I expect from a local machine shop?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What tolerances can I expect from a local machine shop?
I guess I must have just been lucky over the years and nothing should be taken for granted, but it does leave me wondering what exactly you could take as a given.
RE: What tolerances can I expect from a local machine shop?
your post are always very helpful. & I agree.
Bill
The OP as I interpreted it, is for a small testing fixture for the lab. but size & complexity does make a difference.
I to worked with large equipment & parts. up to 10' diameters, & longerons that the starting material was aluminum plate.
that specially fabricated, it was approximately 20-30 ft lengths. I am guessing now. because it has been years.
These were machined on plank mills. the 10 ft dia was machined on & with a 20 ft bed VTL.
it was all verified optically. except the dia was verified with a pie tape, I believe the tolerance was +/- .010"
in the restrained condition.
it may have been closer.
Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.
RE: What tolerances can I expect from a local machine shop?
My recollection was that the philosophy in the UK was similar, though not quite as hardcore on the legalese aspect.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: What tolerances can I expect from a local machine shop?
CNC, yes, manual, not likely. What normal?
RE: What tolerances can I expect from a local machine shop?
I would argue (based on several years of working with local machine shops and +/- .0005" tolerance, is that your past experience in a shop is missing the point. The point is that shop machines routinely read out to the .0005" or better, and will repeat to .0005", but rarely are *accurate* to .0005". In my experience, unless the shop has a robust CMM system they simply have never learned the difference between repeatability and accuracy.
It gets much worse when you include the fact that the z axis of travel is usually not exactly at 90 degrees to x and y, so that if you machine features at different depths, the perpendicularity error will throw off locations by up to a .0005 to .001" per inch of z.
Then don't forget clamped condition vs. as-used and as-measured condition.
Certainly in the environment of local job shops, you may succeed with this part but IME you won't have a chance of success unless that vendor or your company has appropriate CMM equipment to prove it.