Machining accuracy
Machining accuracy
(OP)
Hello,
I recently had a tight toleranced dwg where I had called out a +/- 0.00025 on distance between two holes and the same tolerance on the height of the block.
Now the machines I know (like typical bridgeport and other conventional mills) can do tolerances like +/- 0.0005 or lesser, however am not sure about the precision below half a thousand.
I have a company who claims they can do this, but am not sure if they are going to do it exactly.
I have this question
Are there machines that can do +/- quarter of a thousand ? (exactly without rounding off to .0003 or .0002?)
If so can you give me some names/websites where I can read more about them?
Thanks
I recently had a tight toleranced dwg where I had called out a +/- 0.00025 on distance between two holes and the same tolerance on the height of the block.
Now the machines I know (like typical bridgeport and other conventional mills) can do tolerances like +/- 0.0005 or lesser, however am not sure about the precision below half a thousand.
I have a company who claims they can do this, but am not sure if they are going to do it exactly.
I have this question
Are there machines that can do +/- quarter of a thousand ? (exactly without rounding off to .0003 or .0002?)
If so can you give me some names/websites where I can read more about them?
Thanks





RE: Machining accuracy
Hole position is more difficult, good accurate VMC (Bostomatic BD12) can position to 1/3 this but may tool doesn't start exactly right. Look also at sink EDM or jig bore (Moore tool still makes jig borer IIRC.)
How many parts you make? Dedicated multi drill head can do this but costs too much unless you are making autos.
RE: Machining accuracy
http://www.mooretool.com/
Mike Halloran
Pembroke Pines, FL, USA
RE: Machining accuracy
RE: Machining accuracy
Most CNC machines have a tolerance of +/- .003. Is this part you making going to be for huge production runs or a one of? I would try not to use that kind of tolerance on huge production runs. If this was a mold to make other parts but this is still hard to achieve little lone to measure with your average hand held calibers, maybe you should request a CofC (Certificate of Compliance) with this part.
Tofflemire
RE: Machining accuracy
RE: Machining accuracy
A traditional jig grinder is similar, but the spindle orbits and translates a high speed grinding spindle to enlarge an existing hole. This was also commonly done with an attachment to the jig borer.
The jig borer has been made obsolete by super- precise CNC mills, which can run autonomously. I get the impression that jig grinders are still operated manually. I don't know if they still use gage blocks, or super- precise DROs.
Mike Halloran
Pembroke Pines, FL, USA
RE: Machining accuracy
(Although really precise/accurate old school equipment is awesome. We had an XRD machine (Scintag?) in college that had a tube powersupply and a chart recorder. The staffperson that ran the X-ray labs said it was better than the newer Siemens machine by far.) Teh goniometer gears were springloaded I think to reduce lash.
RE: Machining accuracy
The distance between the holes is more problematic, you do not mention the distance, if it is say .500” okay if it is 20 feet you will have your work cut out.
You stand next to no chance in doing it on a Bridgeport or any other similar turret mill, get your self a nice “tenths” clock bore a hole undo the locks move away in two axis go back to zero do the locks up, is it within 0.0002”? No I thought not.
Even CNC or jig borers that have had a “hard life” will struggle with this. To have any degree of certainty I would say you need someone who has at the least a temperature controlled shop if not an environmentally controlled shop.
Ask to see the calibration records for the machines and there inspection equipment, if they don’t have them the chances are you will get some paper weights to put on your desk.
RE: Machining accuracy
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Machining accuracy
... and ...
At micron tolerances, beyond the temperature controlled room, you have to do anal stuff like let the spindle run for a couple of hours so its temperature distribution, and dimensions, will stabilize.
Mike Halloran
Pembroke Pines, FL, USA
RE: Machining accuracy
And yeah has to be temp stablized. So why is it so important to have that particular tolerance? It must be a gage? Or for micro electronics?
RE: Machining accuracy
What is the size of the part to be machined?
What size are the holes and precision required on same, assuming C/L dimensions?
RE: Machining accuracy
The real question to ask is: Why do I think I need that tight tolerance? One which dimensions?
Truck