Rethread screw socket in PR chassis....

[JJP]

Greetings, once again, Sage experts.

I decided to take a peak inside the chassis of my Custom '64 hand wired PR to see how neat (or not) the wiring was done. I have to say, I was impressed, but I'm not an amp tech. However, while removing the four screws that hold the chassis to the cabinet, it became apparent that the front left screw was having severe difficulty being removed. I decided to add a shot of WD40 to the exposed screw tip and that helped a bit. I was finally able to get it out, and noticed that the threads that go through the fixed bolt on the chassis did not look so great. I tried running a couple of the other screws through the same hole and met the same resistance.

Me thinks that it needs to be tapped to smooth out the threads. My question is, what size tap do I need to do this? I realize I could just leave it alone, replace the nearly stripped screw head, tighten it up and be done with it. Or, I could just drill it out and replace the screw with a bolt and nut with a locking washer. I'm more inclined to try to tap it first to see if that doesn't smooth out the threads.

Regards, Jared.

[xtian]

I have had success cutting a cross-threaded nut with the same sized tap. I think Fender uses #8-24.

[JJP]

I have had success cutting a cross-threaded nut with the same sized tap. I think Fender uses #8-24.

Thanks.

[tedmich]

Most every imperial thread would be 8-32, 6-32 and 10-32 (32 threads per inch) it would be best to get a few fresh nuts or bolts to check these!

[Tom Phillips]

My best guess would be 8-32. To confirm the size you could use one of the other undamaged machine screws as a test sample. Just try to screw it into known size nuts to find out what size is an easy fit.

[g1]

Do you have a tap & die set, or are you needing to go buy a tap? Many tap & die sets have a gauge to check the thread pitch. A number 8 screw is .164" dia., (~ 5/32).

[eschertron]

I take my suspect component in hand (well.. pocket, actually) to the nearest big box hardware store and use the gauges they have hanging at the screw display. Or, I may take it to the nearest family-owned hardware store and politely ask the person there for assistance. Either way works, and I just happen to be in the very place where I can get any replacement parts or repair tools that I need

[52 Bill]

The correct thread size is 8-32. I get cross-threaded chassis nut inserts from time to time, even directly from the Fender factory. Too much use of powered screwdrivers.

I will rethread the insert with a hand tap and then start all chassis bolts by hand until I know that they are correctly threaded and then use my powered screwdriver to finish up.

Just for the record, the chassis bolts are 8-32 X 3", Phillips oval head.

[JJP]

The correct thread size is 8-32. I get cross-threaded chassis nut inserts from time to time, even directly from the Fender factory. Too much use of powered screwdrivers.

I will rethread the insert with a hand tap and then start all chassis bolts by hand until I know that they are correctly threaded and then use my powered screwdriver to finish up.

Just for the record, the chassis bolts are 8-32 X 3", Phillips oval head.

Do you use a 8-32NC tap, or 8-32NF tap? I'm thinking that the Fender screws and fixed nuts are fine thread as when I tried to thread the 8-32NC tap into the three other good fixed nuts, it wouldn't go. Total resistance, so I just left it. The threads on the Fender screws look to my eyes (with the aid of a magnifying class) to be deeper than the threads on the 8-32 tap.

[eschertron]

If you compare the removed screw to the tap ... I thought there was a post here about laying the two pisces-like against each other to compare the pitch? I wonder were I saw that? ... If the screw is 8-32, then the threads will mesh perfectly. If the screws are 8-36 (NF thread) then the two thread pitches will interfere and not mesh.

[drewl]

You can also pop the nut out and use a regular nut, or replace the cage nut, we have those cage nuts of various sizes here at work.

[52 Bill]

I'm not all that smart enough to tell you the differences, but I thought that the fine thread was an 8-36 and the coarse thread was an 8-32.

Take one of your original screws and hold it up next to the tap that you have. If they are the same, the threads will mesh with each other and fit like a glove. If they don't align, then the threads per inch are different.

[g1]

I thought that the fine thread was an 8-36 and the coarse thread was an 8-32.

That is correct. And the ones used in Fender are 8-32 so NC.

One thing I was not clear about from the first post was whether this is a vintage unit or some custom shop or re-issue. If it's not vintage, I suppose it's possible that for some bizarre reason, Fender did not use their standard screws.

[The Dude]

......or someone already replaced the cage nut with a different thread and tried to use the original screw.

[g1]

He did say that the tap wouldn't thread into the other nuts either. Maybe it's just the cheap Chinese hardware we sometimes see with very shallow threads.