Say you had a 1/2" thick sheet of plexiglass and needed to tap a hole that was drilled beginning on the edge and continuing in 3 in. What type of thread density would you choose, coarse or fine? The strain on the anchor will be fairly minimal.
Say you had a 1/2" thick sheet of plexiglass and needed to tap a hole that was drilled beginning on the edge and continuing in 3 in. What type of thread density would you choose, coarse or fine? The strain on the anchor will be fairly minimal.
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Brad, If the bolt screwing into the plexiglass is 3/8 inch or smaller I would use a coarse thread. 16 threads per inch or more would be sufficient. If the bolt is 1/2" or bigger I would use a fine thread size. 1/2" 20 tpi or 5/8" 16 tpi.
We have pieces at work that are threaded. We use heli-coils in them.
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"Design"? Possibly. "Intelligent"? Sure doesn't look like it from this angle.
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You are correct about OD pitch, but the improved bite is largely one of unintended consequences. Helicoil inserts are designed so the coil ‘wire’ cross section, pitch, and internal major/minor diameters meets the intended thread standard (i.e. 1/2-13). This leaves the ‘outside thread’ of the coil at something other than a (SAE) standard - same pitch, same difference in major/minor diameters, but larger OD. And this is why the Helicoil kit comes with a custom tap - to match this OD/pitch.
Upon further review of OP's post, I agree: he's threading a hole edgewise through the sheet, so 1/4" is pretty much the maximum. With 3" of thread, I'm pretty sure pull-out of the threads will not be an issue, so even smaller might be better, maybe 10-24 or 8-32, to maximize the overall structural strength around it.
Drilling that hole is probably harder than tapping it...DAMHIKT.
Last edited by Lee DeRaud; 03-25-2021 at 11:07 AM.
Yoga class makes me feel like a total stud, mostly because I'm about as flexible as a 2x4.
"Design"? Possibly. "Intelligent"? Sure doesn't look like it from this angle.
We used to be hunter gatherers. Now we're shopper borrowers.
The three most important words in the English language: "Front Towards Enemy".
The world makes a lot more sense when you remember that Butthead was the smart one.
You can never be too rich, too thin, or have too much ammo.
I considered <1/4", but unlike polyethylene family, plexiglass/acrylic/polycarbonate are not known for their lubricity :: they'll gall easily and the flute relief on #10 and/or #8 taps will just make this worse IMHO. I'd want all the 'gap' I can get on a tap. Brittle material will also chip more on finer threads.
Whose signature line is "Sharp fixes all manner of (problems)"? ...New tap may be the ticket here!
As for drilling, I have experienced the same beating. I'd sincerely hope Mr. Hays can rotate a DP table to 90deg and drill straight; maybe a doweling jig as plan B? Slow RPM; limit heat build-up; cut a hole, don't 'melt' it in.