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Drawing call out - SAE straight thread

by Q_Goest
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Q_Goest
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Dec8-08, 09:52 AM
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Just for fun, thought I’d throw this out for discussion. What do you think is the best way to call out an SAE straight thread port on a drawing? For example, you could call out all the individual dimensions so that every machine shop would be able to machine it even if they’re not familiar with it. In addition, a general note could be added to mention that a form tool (ex: roughing and finishing tool) is advisable so the shop doesn’t waste time trying to cut the port on a mill or lathe with conventional tooling. The only problem with calling out all the individual dimensions is that it’s really a waste of time. You’d think a shop could simply pick up the spec or locate the dimensions off the network such as is found here:
http://www.inserta.com/PDF/AI-STR-THD-PORT-DIM.pdf

When I was working in aerospace, we’d always use the MS equivalent and simply call out MS33649-06 for example. So I wonder if there’s an equivalent way of calling out an SAE straight thread port, such as SAE J1926-06. Have you ever seen SAE straight thread ports called out on drawings without having to dimension every feature? How have they done it?
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FredGarvin
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Dec8-08, 11:55 AM
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To this day I still call out MS33649 and/or MS16142. Technically they are not the same thing however in practice I have not had one problem interchanging the two (for the record, NOT on flight hardware).

Both MS33649 and J1926 have special reaming tools that the mill hands can use to take all of this into account. This negates the need for a overly detailed drawing by adding a callout for using the tool.

Here is one for the J1926/MS16142:
http://www.newmantools.com/cutters/ms16142r.htm
Q_Goest
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Dec8-08, 12:09 PM
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Hi Fred,
Knew I could count on you to respond! MS16142 as you probably already kinow, has the same dimensions as the SAE port. The MS33649 is more of an aerospace thing equivalent to the old AND10050 spec (going by memory here). Both work. So yea, I could call out the MS16142 spec and get the same dimensions as the SAE spec.

So do you just call out the spec and leave it without dimensions? Do you ever have machine shops calling up and saying, “We can’t find this, what the hell is it?” I called one of my favorite machine shops and they weren’t familiar with either of them unfortunately. It’s like you have to spoon feed these guys the entire set up, including tooling plus dimensions and tolerances. Kinda frustrating when it’s so easy really.

FredGarvin
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Dec8-08, 12:48 PM
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Drawing call out - SAE straight thread

The few times I have had that happen I gave them a copy of the spec and went about our business. I guess if your local shops aren't used to it, then that's a bit of a different story. I can't really see the benefit of doing a completely detailed drawing for a spec'd out port. It kind of negates the whole purpose, doesn't it?

The only time I have ever dimensioned a print is when I have modified a depth on one of the call outs.

I guess I would look at your drawing. If you only have one size port (yeah, right) and I was worried about my machinists messing things up, then I would do a detail. I would try to save the time though and just use a call out. To me, there is no difference between a port call out and a standard thread call out.

One other aspect of this that you may want to think about...What is the purpose of your print? If it is simply to get the thing machined properly, then what we're talking about here is OK. However, if the print is used for inspection purposes, then you may want to think twice about throwing a bunch of dimensions on your print. It can really add up time to the tail end for your inspection department. By calling out the spec, you are allowing the QC guys at either end to use accepted inspection gauges, etc...If you have a bunch of the dimensions called out on your print, it may take a month of Sundays to get your parts through inspection and with poor results.
Q_Goest
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Dec8-08, 02:51 PM
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All good points Fred, thanks. I think I'll take your advise and just call out the MS port (instead of the SAE equivalent) since at least I have that spec in hand. I can then add a note because we have a half dozen different machine shops that handle our work so it's best to clarify when at least one machine shop is sure not to know what MS16142 means.


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