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Cut vs Roll Forming Thread Question

 
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PokerpB9R
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Joined: 17 Apr 2007
Posts: 5
Location: Bay City, MI

PostPosted: Tue Apr 17, 2007 2:34 pm    Post subject: Cut vs Roll Forming Thread Question Reply with quote

I'm experiencing a problem with a custom 8-32UNC-2A jack screw made from AISI 416 stainless.

Were running the screw into a stainless nylon locking PEM insert and experience intermittent binding. We start the screw by hand & then use a higher speed air driver to set it.

I've checked the thread dimensions & it appears to be acceptable; have also had the supplier 100% sort the screws using a threaded ring gage.

I know running stainless threads against each other can sometimes create binding problems without using a lubricant; but was wondering if the thread manufacturing process had an impact.

The screws we're using are made via roll forming; the previous supplier may have been using a cutting process. Are there surface roughness or friction differences? Any feedback would be greatly appreciated.

Thanks.
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BIGmiralli
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Joined: 17 Apr 2007
Posts: 38
Location: Boston, Massachusetts

PostPosted: Tue Apr 17, 2007 2:35 pm    Post subject: Reply with quote

The finish from the rolling process should be near perfect, no chatter/tear/etc. If there are any imperfections, they would be from spalling due to excess pressure and be readily visible.

The only difference in profile would be on the major diameter. The cut thread major will be the same as the rough stock. In rolling, however, the major is the resultant of the blank size and the displacement of material upwards. It's form will look a bit like a rounded "M". And this may be your problem, you say the vendor checked the parts with a thread ring... thread ring gages do not check the major diameter. If the preroll blank size is slightly oversize, the excess amterial goes into the major.
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