How to apply the right tolerances of forms for this part ?

[LCform]

Hi All

I would like to know the most correct way to apply the tolerances of form in this part, since it is gonna be cut in a wire cut machine. Since the part is not round, I have some doubts.

I appreciate your attention

 

[drawoh]

LCForm,

What is the part supposed to do?

--
JHG

 

[3DDave]

Doubts = think this is not true
Question = don't understand and want to know

 

[LCform]

@drawoh, I don't think the application is important in how to apply the tolerances of form, thepiece is supposed to hold some parts in it, and through being bolted in the two holes should stay straight at its position

 

[drawoh]

LCform,

If this was my drawing, I would start it by applying datums. Good practice is for the datum features to be your mounting features. Your fabricator and inspector must be able to clamp the part using those features. I apply my tolerances and feature control frame on everything else, based on my requirements. I need to understand your fabrication processes. For example, an as-cast diameter makes a very poor feature-of-size datum.

There are all sorts of ways to fixture your part and attach dimensions and tolerances. For any given functionality, most of those ways are wrong.

--
JHG

 

[KENAT]

LCform, end function is critical to how to apply correct tolerances, don't think otherwise.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[LCform]

I have explained the function, it's just a grip, I need to know how and where to position the datum planes at the first place and then decide the tolerance, for which it would be so appreciable ifsomeone could let me know about a standard table of acceptable tolerances of form or position of they exist, I really wish actually they do

 

[JNieman]

I haven't come across, and strongly doubt you will find, a standard table of tolerances of form - that's why many of us have jobs.

If that's a jaw for something like a scroll chuck, it depends on the usage. We can tell you how to set up a logical datum reference frame but there's no way we could be expected to tell you how much tolerance is ok. We don't know what it's holding, what it's mounted to, what's being done to the workpiece, how accurate the next action must be, etc etc ad infinitum...

I would set Primary Datum as the mating face. I would set the hole nearer the grip-face as secondary datum and the hole to the rear as tertiary. Unless that jaw sits inside a precision slot, like a key in a keyway, the outside periphery likely doesn't matter. I assume that gripping surface at the tapered end does. But that's on you.

Profile-of-a-Surface is logical and you can either provide sufficient basic dims or a 3D model to define it.

Do the 'teeth' have to be critical or are they just there for some kind of serrated gripping improvement? If so, then I suppose the arc of the gripping face is all that matters, and your tolerance zone should be applied accordingly, leaving the 'teeth' to be constrained less.

This post has a lot of assumptions in it and my advise may be relevant or not. It's a crap shoot when you go out of your way to minimize the information you give us.

 

[LCform]

Thank you very much

That's true that I might not be prefer to explain the application, but I think it has the solution : the teeth have or not have a important role. I would like to know the solution in both cases. I think that would be perfect


Also : which book has explained the composite tolerance of form well and complete?

 

[JNieman]

People will probably be more prone to help you if you make it easy for them to answer. Ask direct questions, not open ended ambiguous questions. You're more likely to turn people away than to get answers for 2-3 scenarios, when one is all that's required. Don't make more work than necessary for those you're asking help of.

 

[LCform]

JNieman

Thank you for your both answers, no I am not willing to make it too boring

ok let's go back to your first answer, I am very sorry , but I had a hard time understanding what did you mean by the mating face, which one is it ? also how do I put a hole as a reference ? on the axis ?

shall I please if someone would sketch this for me ?

Thank you so much

 

[JNieman]

By mating face, I meant that _IF_ it is a chuck jaw; the face that mates to the chuck.

I don't know what it is though because you have refused to expand after multiple requests for information, so I'm not going to waste time with back-and-forth discussion based on assumptions that may or may not be anywhere close to reality. Without knowing what it _IS_, we can't even communicate clearly by referring to certain features specifically by name.

 

[LCform]

Sorry , the part is supposed to have a small interaction with its mate. meaning that it should penetrate in the other piece.

this is the functioning