Powder Hopper Thread Size

[fc60]

Greetings,

A friend wrote to me and asked the thread size of items #32 (Powder Magazine) and #70 (Powder Slide Housing Cover). Since I have never machined any of  these parts I went to the shop to measure them. At first, it appeared to be a 9/16-27 thread. Bastard size, of course, to stay with Star tradition. Closer examination of a Powder magazine revealed that the thread is actually tapered, not straight. Aha, I thought. A pipe thread. Consulting my Machinery's Handbook I found no such thread in the National Pipe Thread section. Further reading lead me to a section on Dryseal Pipe Threads. Two days later of searching the Internet, I found what I think is the answer. It is a Dryseal Taper Pipe Thread, Fine, F-PTF. The actual size appears to be a 1/4-27.

Source: SAE J476a Revised Jun61

http://wenku.baidu.com/view/ee8be83143323968011c927b.html

I have no idea what language the link is written. However, the PDF for J476 is in English. You will find the specifications near the very end of the document.

My next adventure is to locate a tap of this size. So far my Internet search has been null. I will resort to contacting the various tap manufactures for a source. I dread finding out what such a specialized tap will cost.

The quest continues....

Cheers,

Dave Wilson

[askimball (Doc)]

Dave
Since 'maurilew' make powder cut-off's, his replay to me was   9/16"- 27 TPI
for the #70

Also, Do you really think the Star shop would have used such a ODD-BALL Thread

I DON'T THINK SO...

[varmintpopper]

Doc
I must side with Dave , I measured all Five of mine and the thread appears to taper about 12 thousands over the length of the thread and under magnification has
the threads flattend as per the spec's for dry seal pipe thread. I also think Star may have chosen this thread to make it easy to start the threads when replacing the
powder measure, Also the threads seal without having to bottom out on a flange or other device.  That's My Two Cents,, Hope it made since.

Good Shooting

Lindy

[askimball (Doc)]

OK, I will reevaluate.... Just going by what I was told...

I went to MSC which has a store here in Shreveport, I had them search for makers of a several dies I needed,
and they (MSC) had them made for me.......Little pricey, don't remember the costs, but, $50 + dollars

[angus6]

Doc hit VME up for odd ball dies ans taps, I've found them much better then MSC,McMaster Carr or Grainger
and  Dave is correct it's a pipe thread

[fc60]

Greetings,

I found a tap on eBay for $4.50. I will report back once it arrives. Hopefully it is the correct one.

Cheers,

Dave

[tony barone]

I wonder if Star used that particular size in that it might have also been used in their primary sprinkler business. I guess its what makes Stars special.

[askimball (Doc)]

Angus6

VME WHAT..?
Couldn't find anything listed under VME...

OK, I've bought from them, BUT, for AK's, they didn't have left hand threaded dies so MSC helped out....

[angus6]

Angus6

VME WHAT..?
Couldn't find anything listed under VME...

http://tinyurl.com/62lub6f

[fc60]

Greetings,

I got my 1/4-27 Pipe Tap in the mail. It does not fit the housing properly. The tap is marked NPT and I suspect I need the F-PTF series.

When time allows, I will try to cut off the one I have and have the cutting leades reground and make my own custom Star Tap.

Cheers,

Dave

[Rolling Stone]

Dave,
I don't know if you have run into this but the size of the hole before tapping makes a big difference as to how far into the hole the tap goes easily. I was told there should always be 4 to 5 threads remaining on the tap when you quit tapping in order for it to seal correctly. If you have some stock to try a couple of different tap drill sizes,perhaps that is why it appears to not be correct. Or maybe measure the minor diameter of a powder housing thread. I notice all my housings and reservoirs fit differently. As in some screw in almost all the way and others only a few threads. But then the aluminum bronze or red reservoirs are the only parts I am 100% sure, are Star mfg.
RS

[fc60]

Greetings,

The 1/4 NPT tap I bought "drops into" the hole easily. I need to cut off about 3/4" and resharpen it. The taper is the same either way.

Currently, it is not a priority project. Too busy machining dies for the forum members.

When I had a "real job" I had the shop supervisor order a set of gauges to machine the tapered threads. Much better than the "looks good enough" process used prior.

Cheers,

Dave