Martini Cadet trigger screw problem UPDATE 2

[awp101]

Well, I thought I had the major problems licked when I got the original barrel installed (finally) on the project Cadet. I was wrong.

The trigger wouldn't set when the lever was worked even though nothing appeared to be altered. Finally figured out I didn't have the trigger spring and trigger mated properly. Once I did that I found the trigger screw wouldn't screw in more than a couple of turns. I tried the screw in my other Cadet and it was a no go. Tried the known good screw in the problem child and it wouldn't go either so I figure both the screw and threads in the trigger guard are galled or otherwise damaged.

Does anyone happen to know the thread used and if it could be re-tapped or cleaned up? Is there another option if they can't be? I don't have a lathe so this is something that would have to be handled with hand tools...

Thanks!

[Mescalero]

I think a milling machine would be appropriate.

[awp101]

I think a milling machine would be appropriate.

Oh boy, I love it when someone volunteers!

Here's the info I got at the ASSRA forum:

I measured the Cadet trigger screw and found the thread pitch is 36 TPI. The diameter is a couple thousands larger than a No. 6 screw.

Now I need to figure out my options. No budget for machine work and it's too close to being operational to stop now...

[Mescalero]

I have a lathe and a milling machine, they are in N.M.
I am in Phoenix.

[Mescalero]

Standard screws are available in increments of .001, .002,.003..... over and under from mean.

[awp101]

Fastenal was suggested as a source for a tap and there's a location not far from me. I may take the screw and the (empty) trigger guard in and see what they say.

Too bad your stuff is in NM but neither one of us is!

[Mescalero]

You should look into AN/AS aircraft fasteners, I think you would find what you need.

[bsaride]

You could chase the thread with a triangular needle file on the screw.

[awp101]

bsa, I'm going to give that a shot this weekend!

Under high magnification I can see where the first couple of threads of the screw might be bunged. Not sure how I did that but it may have happened when I assembled the trigger and trigger spring incorrectly and the screw got cross threaded.

[awp101]

Well, it's certainly in the trigger guard. I tried chasing the screw threads with no success so since it was just the first couple of threads on the screw I filed them down then tried again. Got to same number of turns before it locked up and the clean threads were now bad.

At least now I know for sure where the problem lies (and it's not the operator ). For the time being I've swapped the entire assembly between the two Cadets since the .310 will probably be done before the Bee.

[Mescalero]

Buy a tap 6-36 / .003 over and chase those threads.
Then buy an AN/AS 6-36 /. 003 over bolt of correct length with a nylock feature, and go with life.

[awp101]

That may be just the ticket my friend.

Not being a machinist type, they .003 over won't require re-drilling the hole?

[Mescalero]

No,
When are going to learn to trust me?

[awp101]

It's not that I don't trust you, I go for clarification so I don't make assumptions.

Over the years they've gotten me into trouble. And not the fun kind of trouble either...

[Mescalero]

It is a hole, 360 degrees.
You will be cutting a maximum of .0015, be sure you get a good start on the original thread.

[Chuck 100 yd]

It sounds like the screws thread pitch does not match the holes thread pitch.
Same size ,different thread pitch? Modify ,if any,the screw not the gun.

[Mescalero]

He said it was 36 TPI?

[awp101]

Got it Mescalero, thanks!

It sounds like the screws thread pitch does not match the holes thread pitch.
Same size ,different thread pitch? Modify ,if any,the screw not the gun.

Nope. It's the original screw. Somehow or another the trigger guard threads got messed up and buggered the screw when I tried to re-install it.

[Mescalero]

Trust me awp101.

[awp101]

Took the trigger guard, trigger and screw to the local Fastenal today and explained my situation. He tried the screw in his gage but thought it was too big to be a #6 and too small for a #8. We went over and tried a 6-32 just for giggles and sure enough it screwed right in!

Settled on a 6-32x1" (to have some extra to work with) hexhead cap screw as the solution. He asked if I needed two so I'd have a spare.

Sure!

"OK, here's two and have a good weekend!"

So what's the damage?

"Nope, have a good weekend!"

Well how 'bout them apples! I had to turn down the diameter of the cap for it to screw in (drill press and file) to about where it needs to be and I might have to see if I can take some off the thread end of the cap to get it to screw in a little closer to how the original sat.

Now all I need to do is fab a forearm hanger and forearm for the .310, figure out what screw is needed to get the .218 Bee forearm attached, source another Weaver 68 mount for the Bee and refinish them both. WOOHOO!

[Chuck 100 yd]

So it was the wrong thread pitch for the hole??

[Mescalero]

Apparently, wonder how he made that mistake.
He told me 36 TPI

[Chuck 100 yd]

I am wondering also if it could have been metric??? Some sizes are very close but no cigar.

[awp101]

I got the screw size information second hand from another forum. I don't know if the poster measured his own or had the information stashed somewhere. I need to pick up one of those size gauges and what ever is used to measure threads (never had to do it before so I don't know).

The clerk said they didn't have 6-36 and I explained I wasn't 100% on that measurement, it was just what I had been told so he did the size measuring, we tried the 32tpi to see how close it might be and we got lucky.

[Mescalero]

Yeah, you need a TPI comparetor.