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6-32 Helicoil: Is it really 8-32 or special

Hello.

I have stripped the plastic threads on the outlet box on my electric bicycle. It holds a dimmer. For more see sci.physics.

Jensen will install Heli-coils for $25, and maybe do up more than just the one, for me to use later.

I'd rather save $25.

Will an 8-32 tap properly prepare the worn threads for a Helicoil? The difference in size is about 1/40 inch, 0.025 or 0.026.

Or should I just put in #8 pan head sheet metal screws and be done with it?

I can file wide notches or flats into one screw to make it a tap. Then I can follow the hole. That way the screw won't split the plastic. I wish I had a self-tapping Plask screw. They don't have them at Home Depot.

But I like 6-32 best. After all it's the American standard for that function. Why complicate disassembly?

I guess I'll buy both. They're only a dollar.

Let me know about the Helicoil.

To read about my senior project at ODU, Go to Google Groups and enter dgoncz along with any or some of these words: ultracapacitor electric bicycle motor generator fluorescent energy display

Reply to
Doug Goncz
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It's also the weakest of the bunch. How about tapping up to 8-32, is there enough meat?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Reply to
jim rozen

Doug Goncz wrote: (clip)Will an 8-32 tap properly prepare the worn threads for a Helicoil? (clip) ^^^^^^^^^^^^^^ Helicoil taps do not match standard threads. By a huge coincidence, it is conceivable that the 8-32 might be close enough, but I wouldn't bet on it. Installing a Helicoil involves a special insertion tool which pulls the coil from the bottom, causing it to collapse slightly, so that it is slightly loose as it goes in. After insertion, it springs open, so it becomes secure. If the tap diameter is not perfect, the insertion will either be too loose, or else the finished thread diameter will be too small.

In order to install Helicoils, you would have to buy a kit, good for several threads, for about $25. This will include the insertion tool and the tap. I would opt for that before I would pay someone $25 to do just one.

There are other thread repair inserts, which look like set-screws, which can be installed using standard taps.

It is also possible to repair a stripped thread using an epoxy type material, available from Loc-tite (I think). You spray a screw with a release agent, smear on the plastic, and push it into the hole. After it is hardened, just unscrew the screw, and you have threads. It's not recommended for critical applications like connecting rods, but ought to be OK for what you're doing.

Reply to
Leo Lichtman

Or . . . fill the hole with JB Weld, re-tap after JB sets up - at least 12 hours.

You spray a screw with a

Reply to
Bob Swinney

Special insertion tool: take one bolt of correct thread, file a notch in the end to pick up the tang on the helicoil. Wind the insert onto the tool thus formed, and use it to wind the insert into place.

For one-off stuff, it makes sense to simply buy the tap and a couple of inserts.

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Reply to
jim rozen

Perhaps replacing the outlet box would be the easiest fix.

Reply to
Roger Shoaf

I ended up filing tap teeth grooves into the end of a #8 sheet metal screw and "tapping" the hole with this. This gives threads that fit best with plastic.

I did mention the box is plastic, didn't I?

Replacing the box is difficult. It gets sawed and milled to fit in the space available. I haven't optimized that process yet to make spares.

I can now remove and refit my "digital dashboard" any number of times. One is a voltmeter and ammeter, and a dimmer in the middle. The other, smaller, is my Pocket PC in its dock. Various configurations are possible.

To read about my senior project at ODU, Go to Google Groups and enter dgoncz along with any or some of these words: ultracapacitor electric bicycle motor generator fluorescent energy display

Reply to
Doug Goncz

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