Disagreement about tolerance on print

Toolroomguy · Jun 10, 2017

We had some simple parts made by a local general machine shop because we are swamped.
5 1/2" by 4" with a print dimension of .375" thick.
Tapped holes, dowel holes, bolt holes, and some clearance cuts on the periphery.
The title block gives a +/- .005" on a three place decimal.
They were told they had to grind the thickness.

Parts come in .355" one end .364" other end.
They said they told the engineer they would come in undersize because they started with 3/8" cold rolled.
The print was never changed.
They claim the parts meet print because there is no parallelism call-out on the print.
Apparently we should use the center of the part as nominal, and one end is -.005 ,and the other end +.004, so it meets print.

Does anybody agree that a 5 1/2 " x 4" ground part can have .009" taper across it?
Is this a normal shop practice?
They want to be paid for these parts which we can not use.
We had to make them ourselves because there is no way I am giving the automation guys a part that would be scrapped out if we made it.

plastikdreams · Jun 10, 2017

thats a load of horse manure. anyone who would try to pass that off as good is a hack. no matter what the print says i always shoot for less than .001 runout tir (unless its less, but i havent seen that in quite a while) and square. knowing it had to be ground then it should have been dead nuts. i would send the parts back, and not pay them a cent.

Milland · Jun 10, 2017

I'd say the contracting company made some paperweights that are going to look great on their desks. Or table leg shims. But as they're grossly out of spec, nah, they eat it.

Centerline? That's a no-fly if I ever heard one.

cmccull166 · Jun 10, 2017

Toolroomguy said:
We had some simple parts made by a local general machine shop because we are swamped.
5 1/2" by 4" with a print dimension of .375" thick.
Tapped holes, dowel holes, bolt holes, and some clearance cuts on the periphery.
The title block gives a +/- .005" on a three place decimal.
They were told they had to grind the thickness.

Parts come in .355" one end .364" other end.
They said they told the engineer they would come in undersize because they started with 3/8" cold rolled.
The print was never changed.
They claim the parts meet print because there is no parallelism call-out on the print.
Apparently we should use the center of the part as nominal, and one end is -.005 ,and the other end +.004, so it meets print.

Does anybody agree that a 5 1/2 " x 4" ground part can have .009" taper across it?
Is this a normal shop practice?
They want to be paid for these parts which we can not use.
We had to make them ourselves because there is no way I am giving the automation guys a part that would be scrapped out if we made it.

You have to be making this up? there is no freakin way anyone would ok this, these should be in the scrap pile

Toolroomguy · Jun 10, 2017

cmccull166 said:
You have to be making this up? there is no freakin way anyone would ok this, these should be in the scrap pile

I wish I was making this up. The really screwy thing is we are talking to the owner of the shop. We could send him thousands of dollars of work, but not with this stuff going on.

Larry Dickman · Jun 10, 2017

Wishing something is in print doesn't make it so. Complete load of horse shit.

moonlight machine · Jun 10, 2017

Toolroomguy said:
I wish I was making this up. The really screwy thing is we are talking to the owner of the shop. We could send him thousands of dollars of work, but not with this stuff going on.

Not unless you want thousands of dollars worth of scrap.

gbent · Jun 10, 2017

Yes, the parts could have .009 taper and be in print. But they are not in print specifications. From your dimensions, the acceptable size is .370 to .380.

You do reference ANSI Y14.5 on your print, don't you?

extropic · Jun 10, 2017

Crap print. If you need parallelism better than the size tolerance allows, put it on the print.

"They were told they had to grind the thickness." Were they ground? How'd that work out for you?

Put it on the print! You're holding the reason "why" in your hand.

The "you know what I want" approach only works after the expectations have been well established via extensive interface.

Also crap parts and workmanship, no doubt.

Ask the engineer (small e intended) if .350 thick is acceptable and grind the parts in.

Better yet, hand the parts to him/her and ask if .009 parallelism is OK. Answer: NO! Reply: Fix the fucking drawing!

Malcolm Foster · Jun 10, 2017

Hi Toolroomguy.

The parts should not have been less than 0,370" thick so at 0,355", they are out of tolerance, scrap, their error.

Toolroomguy · Jun 10, 2017

gbent said:
Yes, the parts could have .009 taper and be in print. But they are not in print specifications. From your dimensions, the acceptable size is .370 to .380.

You do reference ANSI Y14.5 on your print, don't you?

I agree the print was a problem.
No, no reference to any standards on the print.
Prints are generated from solidworks models with only minimal dimensions on them.
We make the parts in house and they fit and work.
The other toolmaker in our shop repeatedly told engineering they were going to have problems.

Terry A · Jun 10, 2017

I have to agree with extropic your print did not call out for anything better than what you got.
Unfortunately you do need to have this specified on your print due to some shops carp work.
On the other hand would you want a shop doing work for you that can make a part that far out of parallel on a surface grinder.
Any machinist that has ran a grinder longer than a hour should have gave you a better job.

gnadoc · Jun 10, 2017

It sounds to me like some creative fellow went out of his way to make the most screwed up parts possible that were still within tolerance. Make sure the shop owner understands that if he wants paid for this kind of crap, he'll never again get any work from you.

Malcolm Foster · Jun 10, 2017

gbent. Agreed!

robert123 · Jun 10, 2017

gbent said:
Yes, the parts could have .009 taper and be in print. But they are not in print specifications. From your dimensions, the acceptable size is .370 to .380.

You do reference ANSI Y14.5 on your print, don't you?

I agree with this if the .375" is called out on the print. But I am curious about your reference to .375" cold rolled stock. Is that on the drawing? I'm assuming on the type of material used, but cold rolled 1018 flat bar stock has a tolerance of +.000/-.008" per ASTM A108 (assuming stock wider than 6" was not used). How did they manage to get down to .355" unless they machined it further?

Toolroomguy · Jun 10, 2017

robert123 said:
I agree with this if the .375" is called out on the print. But I am curious about your reference to .375" cold rolled stock. Is that on the drawing? I'm assuming on the type of material used, but cold rolled 1018 flat bar stock has a tolerance of +.000/-.008" per ASTM A108 (assuming stock wider than 6" was not used). How did they manage to get down to .355" unless they machined it further?

The material call-out on the drawing was "steel".
Again,I wish I was kidding.

They ground both top and bottom.
How they managed to get so much taper when they flipped over the part is unknown.

plastikdreams · Jun 10, 2017

Terry A said:
I have to agree with extropic your print did not call out for anything better than what you got.
Unfortunately you do need to have this specified on your print due to some shops carp work.
On the other hand would you want a shop doing work for you that can make a part that far out of parallel on a surface grinder.
Any machinist that has ran a grinder longer than a hour should have gave you a better job.

gnadoc said:
It sounds to me like some creative fellow went out of his way to make the most screwed up parts possible that were still within tolerance. Make sure the shop owner understands that if he wants paid for this kind of crap, he'll never again get any work from you.

Y'all are both insane...anyone who would let this out of their shop and then attempt to justify it is a jerkoff. The stock thickness I can see, I've run into it myself. They are garbage parts from a garbage "machinist" at a garbage shop...period

I don't personally know any machinist that would look the other way just based on astetics alone.

Toolroomguy · Jun 10, 2017

Malcolm Foster said:
Hi Toolroomguy.

The parts should not have been less than 0,370" thick so at 0,355", they are out of tolerance, scrap, their error.

This is where the vender said they told the engineer they would be undersize.
In my world, the number on the print would be red lined out, the new value written in, and the change initialed by both parties.

robert123 · Jun 10, 2017

You said that they told engineering they would be undersized. Did engineering OK this? If so, I might agree with them that they met the requirements.

They should have started with thicker stock if grinding to .375" though. If the thickness is not as important, could you not fix them by grinding some more to make them as parallel as needed?

ManualEd · Jun 10, 2017

Check the finish on your "ground" surfaces.

If they have grinding swirls or arc segments about 5" diameter, your parts were angle ground and maybe flashed over on a belt sander to hide it.

Disagreement about tolerance on print

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