M6 thread repair

[Innovate1]

Have an M6 thumb screw (actually the head has a bigger handle than a thumbscrew but that's the general idea) on a string trimmer for changing the attachments. It no longer tightens up. I suspect on of the yard help backed the screw all the way out and the end looks to be slightly mushroomed in manufacture as it never needs to come out - and that enlarged the female threads. The female looks to be a flanged insert spot welded to the sheet metal clamp. I could just add a wing nut - that would be the easiest and not too bad for use after I remove the mushroomed end of the bolt. I don't think the metal is thick enough for a helicoil. Maybe epoxy a nut on - the bolt is long enough. Or maybe put some JBweld in the threads and retap them - that seems sketchy and haven't every done anything like that. Any suggestions besides firing the help?

 

[grissom]

If you are talking about this clamp I would just buy a new one

 

[CJM8515]

new clamp. www.ereplacementparts.com

 

[Innovate1]

The clamp is not loose. I will have to look at how it is attached to see if it can easily be detached. It is a Ryobi 40V power head.

 

[BillK]

Are you talking about the large winged part ? Cant tell from your picture but maybe a Rivnut ?

 

[no704]

Tie a couple or more strings of dental floss thru the hole. Will need replacement periodically but will tighten up the hole.

 

[Innovate1]

The clamp ring has a dimple that sits in a hole in the tube. Loosening the bolt and spreading the ears slightly allows it to come off the hole. It can then be rotated to clear another raised portion on the end of the tube (a ramp for the button that latches the attachment into the motor end) so it can be removed. Now to look for a compatible replacement or take it to someone that can tack weld on a nut.

 

[racecougar]

Pictures of what portion is actually damaged?

 

[CraigStu]

I think attaching a nut is your best bet. W/ thin metal either silver solder or brazing might be better than welding.

 

[rust in the eye]

Run a 1/4"-20 tap through the hole and replace the thumbscrew with a 1/4" -20 one.

 

[MoonRise]

Riv-nut.

Or weld or braze on a replacement nut or threaded piece.

Or use a wingnut. Which will probably get lost.

Or replace the existing thumbscrew item with a bicycle-type quick-release clamp.

Or source a replacement clamp.

Any of these can work.

Check to make sure that the male threads on the end of the thumbscrew item aren't buggered up, so that they don't chew up the new female threaded item.

 

[WildBill]

I just fixed something like that on my 8" chainsaw on a stick with a rivet nut.

 

[Innovate1]

Thanks for the suggestions. Looks like my options in order of increasing difficulty so I am going to try them in order...

See if a clamp off an older non-functional trimmer will fit.

Tap to 1/4". Seems to be enough material for that.

Attach a nut with brazing or some such.

 

[racecougar]

Running a 1/4-20 tap through a M6x1 thread isn't going to produce a good thread. The minor diameter of a 1/4-20 thread is 0.1960"; 6mm equals 0.2362". No bueno.

A rivnut is super easy to install, provided what you're installing it on can accept it. Hence the request for a photo of what we're actually working on.

 

[Innovate1]

Running a 1/4-20 tap through a M6x1 thread isn't going to produce a good thread. The minor diameter of a 1/4-20 thread is 0.1960"; 6mm equals 0.2362". No bueno.

A rivnut is super easy to install, provided what you're installing it on can accept it. Hence the request for a photo of what we're actually working on.

1/4-28 has a larger minor diameter (0.220") but still marginal and with the hole wallowed out probably not workable. Here's some photos...

 

[racecougar]

Yeah, that wouldn't be a good candidate for a rivnut. I'd stick with either replacing the clamp or tacking a nut on it.

 

[MoonRise]

In true GJ form, you need to fabricate a billet aluminum clamp block.

With lightening holes (aka 'speed holes').

And bang his wife.

(which would actually work, well the fabrication part anyway. The bang wife part may be optional. )

I think a riv-nut could work here. Drill out to the correct installation diameter for the riv-nut and install, done.

Welding 'something' there could probably also work, but involves some more steps. Drill out the old, clean paint and crud to get to clean shiny steel (the bracket part IS steel, right? Otherwise, welding a steel nut to a non-steel bracket ain't gonna work too well.), hold nut in place (clamp, NOT your fingers! ), weld nut to bracket and not blow a hole through the bracket or distort the threads of the nut so much that the male threads can no longer be installed (put a bolt with the correct threads INTO the nut before attempting to weld it to the bracket, but coat well with never-seize or anti-spatter first).