Dowel Hole Location Tolerance

[Dave Ball]

Just looking for input, this is part of a new line of hydraulic workholding for us. In the picture the center jaw is secured by SHCS and located by two .5005/.5009 dowel holes. What do you think the true position between the two locations "NEEDS" to be?

 

[YoDoug®]

GD & T should be used for design intent, meaning fit and function. So that leads to ask, what do you need from those holes? Are you simply concerned over fit of mating components (center jaw) or do you need to hold positional tolerance of the mating components as well?

[kh012]

it shouldn't be any greater then the differance between the largest dowl pin size and

the smallest hole size for a basic true position call out. then you can add maximum

or min. mat'l modifiers to the GDT block for the hole size and dowl pin size.

 

HTH Ken,

[Dave Ball]

Positional tolerance isnt critical as they just locate the jaws, however the axis between the two holes must be perpendicular to the vise length. I guess a simpler way of asking this would be What should the tolerance be between two dowel holes used for alingment? How far "out" of perfect location will allow a slip fit?

 

 

[Del.]

Positional tolerance isnt critical as they just locate the jaws, however the axis between the two holes must be perpendicular to the vise length. I guess a simpler way of asking this would be What should the tolerance be between two dowel holes used for alingment? How far "out" of perfect location will allow a slip fit?

 

 

 

I would say about .0002 using the .5009 Dia. hole. You need about .0003 fo a slip.

[JAMMAN]

Leave stock and send it to the jig grinder?

[EX-wccprogrammer]

Can you modify the design to allow thru holes on the jaw? If so, leave the diameters undersize on jaw and body, assemble, and line ream both pieces. End of tolerance issues.

[EX-wccprogrammer]

For production, you can use a jig with bushings as a master guide. This also would eliminate deviation.

[taperlength]

The simple answer, make one hole a slot which is in line with the other hole.

 

Or, two holes, one round pin and one diamond pin.

[crazy^millman]

I would give it a .0005 True Position with a Max Material condition calling out the .5003/.5009 dia. That will keep everything under .0008 for location. You want it tighter then just think about the increase in cost. What I just called out increased the cost 5 fold IMHO. IF you could do a .004 True Position with a Max Material condition on the .5003/.5009 then I think you put it most shops ability to manufacture. Using my first call you then start increasing cost and quality, and limits the amount of companies able to do that work.

 

Sorry late to the topic.

[Newbeeee™]

As Taper said, go for a full dia and a diamond (correctly installed of course )

As they are location only, I'd go for the simple way and wouldn't beat yourself up too much.

[JAMMAN]

So Dave.... what happened? What did you do?

[Dave Ball]

A group decision was made to go with .001 true position.

[crazy^millman]

That is cool .0005 X and Y should be doable. Did you guys decide to use MMC or not?

[Newbeeee™]

That is cool .0005 X and Y should be doable. Did you guys decide to use MMC or not?

According the the 'ol true posn calculator, .0005 error in x + y = an actual true posn of 0.00141.

To get a true posn of .001 and have *some* error in both axes, then .0004 off in both x + y = your max limit (.001).

True posn is always a whole lot tighter than it looks.

[crazy^millman]

Yes, but you are assuming RFS and I am assuming MMC on a .0004 tolerance on the hole. So with the .0004 bonus I would be okay. With RFS then no I would not.

[K2csq7]

I have a pretty easy formula for true position, how much you can be off in X and Y.

 

take the true position call out and square it.

divide by 2

take square root

divide by 2 again.

 

For .001 you are allowed ±.00035 in X and Y (then you take MMC into account)

[K2csq7]

Works backwards too.

if your hole is off .002 in X and Y

 

.002 *2

^2

*2

Sq. rt.

=

.0056 (true position)

 

(I made this up so correct me if I'm wrong)

[robk]

True Position Calculator for some of us lazy programmers.

[Newbeeee™]

Thanks Rob - more detailed than the one I have

[Mr. M]

Thanks for that link Rob!

[crazy^millman]

Hum what does it say?

 

Without MMC it is .0014 with the MMC and a hole size of .5009 you fall into the tolerance.