Paralelism

[Leandro]

I get a part 100" x 60" x 3" for milling.

The part had some grooves but mainly is a flat milled plate.

I have some paralism problems because the part bend or deform when i mill on both sides.

Did somebody have any experience what are normal tolerances for this paralelism.

I mean parcial and total paralelism.

Or were cann I found information about paralelism standards.

Thanks

[Jim at Gentex]

Leandro,

 

Do you have a drawing for this part?

If so, a parallelism callout should be on there.

 

If there is no parallelism requirement specified on the drawing, then it is what it is.

[Leandro]

Jim:

Thanks for your answer.

Actually I have got a drawing.

My question is if there is a standard like DIN 7168 T1 for lenght.

DIN 7168 T1 is a standard for length, there you can see different Klasses, for example f,m,g and sg.

f (fein)

m (mittel)

g (grob)

sg(sehr grob)

 

And according to my job I decide what toleranz klass did I take.

[strabe]

Can you check with your material supplier? They should have some specs for the raw material. Are you trying to keep it the same as it came in the door?

[Dave.L]

Many materials contain internal stresses based on the production method. 2024, 7075 and 6061 aluminum all contain stresses due to the temper. So does cold rolled steel products. So, when you mill one side or both, you remove so stresses that cuase the part to twist and curl. In many cases you will need to rough the part, remove from clamps, re-fixture and finish machine. Stress relieving helps but you need to be sure you don't change the material properties.

 

HTH

[Leandro]

I know about this deformations and also do this procedure (rough, turn the machining side, rough again and final finish, in this case I done this two times)

Actually the part has been Tempered treated before machining.

My question is if anybody has got any allowance.

How did you decide if the part is ok or not?

Which criterium did you use for take this decision

[Dave.L]

The print specifications

[Philcott]

Leandro,

 

I have not heard of a general tolerance on parallelism that would say something like "unless otherwise stated parallelism is to be .005 and flatness to be .003 per foot".

 

One may exist but I have never seen it.

[shazam/TPP]

On your print you should have a general spec called out like ANSI Y14.5M-1982 or something like that, then google the spec or machinist hand book. hth

[TheePres]

Most of our customers do specify the "general machining practices and tolerances allowances".

Some are based on ANSI Y14.5 as stated above.

But Print will say which spec to refer to.

 

Our current customer specs lists as such:

"Machined surfaces shall not deviate from flatness, straightness, or contour by more than (.010 per ft)".

"Parts may be deflected to meet specified tolerance...." then goes on to state amount of pressure (weights) allowed and at what intervals you may place these weights.

I can send you this spec thru email if you would like, just remember that your customers general practices are the ones to go by.

We are currently producing wing panels (pretzels), so have become well versed in these flatness requirements.

[Leandro]

Thee Pres:

 

This spec that you offer me is that what I need.

I send you an e-mail

 

Thanks