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September 2013

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Subject:
From:
"Stadem, Richard D." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard D.
Date:
Mon, 23 Sep 2013 17:12:08 +0000
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text/plain (113 lines)
Would a nylon screw work? Even if it touches the board it won't short out anything.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, September 23, 2013 11:22 AM
To: [log in to unmask]
Subject: Re: [TN] Does anybody know where I can get a 5/16" long 4-40 wafer head machine screw?

Hi Ed,

Yeah, I know that it may come down to something like that....CRAP!!
Here's what I'm dealing with. This board we're building has these high power NPN transistors that get screwed down to a heatsink and then the board mounts to stand-offs on the heat-sink:

http://stevezeva.homestead.com/Screwhead.jpg

You can see the offending part in the photo. The photo is my first proposal to our customer with a button head cap screw, I wanted to put some .050" thick washers on the stand-offs to raise the board a little bit. But NOOO, the board has a 15-pin D-Sub connector that straddle-mounts to the end of the board and then goes through a chassis opening that doesn't allow for any slop at all...not even .050"!!!

What happened is that the part used to be a On Semiconductor TO-218 with a metal tab (PN# TIP35CG) , but they did a PCN last year http://www.onsemi.com/pub/docs/pcn/FPCN16827.pdf that changed it to a TO-274....

So here I are....

Steve 


-----Original Message-----
From: Ed Popielarski [mailto:[log in to unmask]]
Sent: Monday, September 23, 2013 10:01 AM
To: TechNet E-Mail Forum; Steve Gregory
Subject: RE: [TN] Does anybody know where I can get a 5/16" long 4-40 wafer head machine screw?

Steve,

You could probably modify these
http://www.mcmaster.com/#90910a714/=omte40 by making a block with 4-40 D&T holes on a matrix (20X20?) and fly cut it in one pass. With 2 blocks and an electric screw gun you could probably do a few hundred per hour. 

If you need "lots", I know a guy with a CNC screw machine that could make custom screws reasonably.

Ed Popielarski
Engineering Manager


                               970 NE 21st Ct.
                              Oak Harbor, Wa. 98277

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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, September 23, 2013 8:45 AM
To: [log in to unmask]
Subject: Re: [TN] Does anybody know where I can get a 5/16" long 4-40 wafer head machine screw?

Hi Richard!

Thanks! But do you have a link to the vendor where that has the ones that have a head height of only .030" ? All the ones I'm finding have a head height of at .059" which is too tall...

Steve 

-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Monday, September 23, 2013 9:34 AM
To: TechNet E-Mail Forum; Steve Gregory
Subject: RE: [TN] Does anybody know where I can get a 5/16" long 4-40 wafer head machine screw?

You can use a 5/16" 4-40 cap head screw. Same length but the head is only .030" thick. I have attached a picture. It won't show up on the posting, Steve, but you should get it directly.
dean

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, September 23, 2013 10:19 AM
To: [log in to unmask]
Subject: [TN] Does anybody know where I can get a 5/16" long 4-40 wafer head machine screw?

Morning all,

 

Looking to find a 5/16" long 4-40 thread wafer head machine screw. It's to fasten down a TO-247 Power Transistor...don't have any clearance for the screw head. That's why I'm looking for a thin head. I only have about .053" clearance for the head of the screw.

 

Any help would be appreciated...

 

Steve 

 


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