Draft dimensioning 1

[urkson]

Are there any hard rules concerning the dimensioning of draft angles on castings and forgings. We (QC) find our engineers seem to have their own rules on how to apply draft. They have a dimension that will say
+dft. and one that will say -dft. They will have in the notes; Dft. angle 1 degree max. or Dft. to be within tolerance, usually meaning the box tolerance. Although they do not specify they usually mean per side but not always.

Thanks

 

[CheckerHater]

Read ASME Y14.8-2009 and if you like it, demand your engineers to follow it.

 

[urkson]

Unfortunately we do not have Y14.8. We have Y14.5. To get Y14.8 I will have to put a req. in and it will end up taking 2-3 weeks. I will do that but I was looking for some guidance on draft that I could use now to solve an immediate problem.

 

[CheckerHater]

OK, I’ll bite.
According to the standard dimensions affected by draft are specified using the following technique:
Specifying “DRAFT ADDS MATERIAL” or “DRAFT REDUCES MATERIAL” in general notes.
Specifying “+DFT” when the dimensions may increase due to the draft.
Specifying “-DFT” when the dimensions may decrease due to the draft.
Specifying “DFTINCL” when the draft must be contained within the given tolerance.
The standard also suggests using such technique preferably for non-critical dimensions
For more detailed explanations you still need to refer to actual standard. It has a lot of good stuff besides draft.

 

[KENAT]

If you are doing any significant amount of castings (or similar processes) then 14.8 is really helpful.

Posting guidelines faq731-376

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

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

 

[ctopher]

May not answer your question, but thought I would share the other "draft" thread. It may be a little helpful.
thread1103-275160

Chris, CSWA
SolidWorks 14
ctopher's home
SolidWorks Legion

 

[urkson]

Thanks everyone. Standard has been ordered should receive in 2 weeks.

We are dealing with a .065 wide slot in a casting. My immediate concern was the Note "Draft included in tolerances". The box tolerance is +/-.005.
Since Dft. is per side we (QC) interpreted this as adding a max. of .0025 per side to the dim. (ID Dim). We rejected it because it was + .004
per side. Engineer says we got it wrong and the draft, as called out, is max. .005 per side.

 

[KENAT]

I'm wanting to say you both may have it wrong.

I'm thinking that all the way through the slot the width has to be .065+-.005.

There is no implication that the draft has to be equally divided between the sides. The effect of the draft on slot overal width needs to be within the +-.005 boundary.

I'm not sure why you're even directly measuring the draft.

Posting guidelines faq731-376

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

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

 

[urkson]

Obviously the draft in castings and forgings is to ease the manufacturing process as parts are removed from the dies and molds.
We do not start by measuring the draft angle we measure the feature.In this case we rejected the part because the slot went out of tolerance
because of the draft. We then had to accept the engineers view even though we did not agree with his interpretation of the draft callout.
Since we are getting different call-outs and interpretations I wanted to see if there was a rule within GD&T for the dimensioning of Draft.

 

[CheckerHater]

Providing that you purchased your copy of 14.8 here is a little present for you

 

[dgallup]

I agree with Kenat & CH. If the feature dimension is 0.065+/-0.005 DRAFT INCLUDED then the feature has to measure 0.065+/-0.005. So you were correct to reject the part. If engineering wants to accept .005 draft per side then they need to change the drawing.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[urkson]

So is the default call-out for draft per feature and not per side?

 

[dgallup]

I think that draft per side is more common, I certainly use it far more often. However, in your example, the draft itself is not dimensioned, the draft has to fall within the feature tolerance which you indicated was .065+/-0.005. It makes no difference how it is drafted, just that the feature including draft must meet the dimension.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[CheckerHater]

The important part is, if the drawing says "draft included", the feature has to stay within specified tolerance, draft or no draft.

 

[racookpe1978]

Since Dft. is per side we (QC) interpreted this as adding a max. of .0025 per side to the dim. (ID Dim). We rejected it because it was + .004
per side. Engineer says we got it wrong and the draft, as called out, is max. .005 per side.

I think you're bloody lucky to be in a position where you CAN argue about 0.001 difference in a cast part! More often, it is a 1/16 or more.

 

[urkson]

It's not a matter of luck mate. First of all these are precision castings and there are mating parts involved. Second we do not design the parts or produce the prints.
Our job is to inspect the part to the relevant prints and report what we find. While we are not into arguing with the engineers we will question ambiguous call-outs. The
biggest problem we have of course is that the engineers start their 'Notes' with "Interpret Drawing Per ASME Y14.5-1994" and then go on to prove that that they don't have
a clue what GD&T involves and they don't want to hear it because they are the 'Engineers'.