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Screw size to mount MB-6582 PCB to bottom of PT-10 case?


fussylizard
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I haven't seen a spec on what screws to use for this.  The hole is ~ .089" diameter x .250" deep, plus maybe .125" thickness for the PCB.  I doubt that's a common screw size so I thought I'd ask what others have used.  I couldn't find anything on the Pac-Tec site, the mechanical drawing, the intertubes, or the forum.  Suggestions before I just wing it?

TIA,

C

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I haven't seen a spec on what screws to use for this.  The hole is ~ .089" diameter x .250" deep, plus maybe .125" thickness for the PCB.  I doubt that's a common screw size so I thought I'd ask what others have used.  I couldn't find anything on the Pac-Tec site, the mechanical drawing, the intertubes, or the forum.  Suggestions before I just wing it?

TIA,

C

Didn't your case come with those screws? Mine did.

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Didn't your case come with those screws? Mine did.

Really? Mine didn't.

I asked the PacTec people about this a long time ago, their reply:

I spoke with an engineer and there are also 4 type B thread forming screws in the PT-10.

Not much help for me, though... I just found some wood screws about the right size.

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@strophlex - I just got 4 screws to connect the two halves of the case together, plus the 4 screws to secure the stock front panel to the metal tabs on the top part of the case.  That was it.  If you got the correct screws with yours, I'm jealous!

@Wilba - Not the most helpful engineering team at Pac-Tec, eh?  I looked up "thread forming screws" at McMaster-Carr and they seem to call them "tapping screws". Their drawings look similar to other screws I've seen going into plastic cases.  Maybe I'll order some "correct" screws from them, but that would be my third order on this project from them which is getting pretty bad from a planning perspective. :-) I may just take the wood screw or sheet metal screw route if I can find some that will fit.  Thx for passing along the "official" answer, such as it is...

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Further perusing the McMaster-Carr web site makes me think I would try something like item #92525A205.  It's a #4-24 3/8" tapping screw.  It recommends using a #41 - #44 drill bit for the hole, and the hole in the case appears to be about a #43 (.089").  Not sure if the 1/4" or 3/8" length would be better...

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The old fashioned term is 'self-tapping' screws... They're not for everything, and my PT10 is not handy right now to compare, so be sure that the PT10 is designed to have these particular screws, as using the wrong size/thread/etc on the wrong materials will cause them to explode from the screwhole outwards  :(

I'd cover my *ss by emailing pactec and saying "Is this one going to work?" so I could get a refund if it didn't.... The good news is that, so long as they aren't too wide, you have a lot of room for error :)

OT: If you've ever done a lot of manual tapping (like our resident furniture experts will tell you), you'll know why it's a nice feature - two turns in, one turn out... two in... one out... two in... one out... omg...this is boring... two out... one in... two out... one in.... wait... i'm going backwards.... two in... one out... two in................................zZzZzzzZzZzZzzzzzz

It's like uncorking wine, on acid, with no tasty juice at the end. No fun.

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I have done a moderate amount of tapping aluminum by hand.  After the first few successfully threaded holes the charm and wonder wears off. :-)  Cutting large-diameter threads with a cutting tool on a lathe is still pretty fun though...

For a minute I was thinking I could use my regular taps for the PT-10, but then I realized my regular taps would probably not work in the plastic since I think the thread pitch for plastic is much larger than for metal (i.e. threads are farther apart for plastic than metal).

I'm doing OK without the PCB screwed into place for now so I'm not too concerned about it...

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  • 2 weeks later...

I'm taking my MB-6582 on a trip with me in a week and a half, so I figured I'd better actually screw down the base PCB.  I used 5/16", 4-20 "thread forming" screws for ABS plastic (p/n 90380A107 at mcmaster.com).  These are different than the "type B" thread-forming screws that PacTec support told Wilba to use.  Per the McMaster web site type B is for metal, so I got ones they said were for ABS plastic (like the case).  At any rate, they work perfectly.

In the attached pic you can see a thread-forming screw compared to one of the screws to connect the top and bottom parts of the case.

tapping-screws-comparison-IMG_3897.JPG

tapping-screws-comparison-IMG_3897.JPG

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