Taping a fixed nut on a Fender Custom '64 hand wired chassis...

[JJP]

Greetings,

I posted a question a couple of days ago pertaining to the size of the bolt that is used to attach the PR chassis to the cabinet, and several of you chimed in. Thanks for that, and it is indeed an 8-32. I took one of the bolts to Home Depot and matched it up with a nut and it threaded perfectly. However, it was apparent that one of the bolts (front left) was so resistant to being removed, that I nearly stripped the screw head. With the one bolt being damaged, I decided to pick up a new set of "Vintage Fender" replacement bolts (which comes with a set of nuts and lock washers and cabinet straps).

I decided at that point that rather than drilling the fixed bolt out and using a nut and lock washer, I'd attempt a tap it to fix the misaligned threads. I bought a small, DeWalt tool and tap set and it had the requisite 8-32 tap. I first tried to insert the correct tap into the problematic fixed nut, and it simply would not go in. It was very rough. I tried the rest of the fixed nuts, and had the same results. I then tried to screw the nut (that comes with the "Vintage Fender" replacement screws and straps) onto the tap, and it simply would not thread either. I'm assuming, perhaps incorrectly(?) that the correct sized nut, such as an 8/32 should thread on the 8-32 tap with out any resistance, and similarly, the 8-32 tap, should easily screw into the three other properly threaded fixed nuts, no?

I'm at a loss here. I think the problematic fixed nut is not aligned properly on the chassis and the best way to fix it is to tap it. The tap kit consists of 6-32, 8-32 10-32 and one other tap, as well as corresponding drill bits. The 6-32 tap is way to loose. The 8-32, which would appear to be the correct one, will not go in to the existing fixed nuts, and will not thread the nuts that come with the new screws/bolts - which are 8-32. Any suggestions?

Cheers, Jared

[Greg Robinson]

It's common for nuts to not freely thread onto a tap. Modern nuts are mass manufactured with a cold rolling process, which leaves a blunt crest and root in the formed thread, unlike a tap which - as a cutting tool - has a sharp crest and root. If you're second guessing the markings on the tap, so long as the the tap "threads" mate with the threads on the screws (place them side by side from opposite directions to allow clearance for the head of the screw and the shank of the tap and mesh their threads together - any thread pitch differences will be immediately apparent), and the outer diameter is close (tap will have a slightly larger diameter than the screws to allow for clearance), then it is correct. Thread the tap in 180° steps, turning backwards 90° after each step to break the chip, and make sure to use tap oil/cutting oil. Hope that makes sense.

[JJP]

It's common for nuts to not freely thread onto a tap. Modern nuts are mass manufactured with a cold rolling process, which leaves a blunt crest and root in the formed thread, unlike a tap which - as a cutting tool - has a sharp crest and root. If you're second guessing the markings on the tap, so long as the the tap "threads" mate with the threads on the screws (place them side by side from opposite directions to allow clearance for the head of the screw and the shank of the tap and mesh their threads together - any thread pitch differences will be immediately apparent), and the outer diameter is close (tap will have a slightly larger diameter than the screws to allow for clearance), then it is correct. Thread the tap in 180° steps, turning backwards 90° after each step to break the chip, and make sure to use tap oil/cutting oil. Hope that makes sense.

Thanks, I'll give that a shot. I'll try it on the already misaligned fixed nut, that way if it's not right, I can at least use the nut and lock washer that comes with the chassis bolts. JP

[eschertron]

As mentioned, be sure to verify the thread pitch by comparing the tap (8-32) against the screws that came out of the unit. It's possible that one of them is 'national fine' thread instead of the 8-32 'coarse' thread. Not likely a problem, but as Enzo said, "never think up a reason NOT to test something".

I learned the difference between NC and NF thread pitch the hard way when I bought some machine screws for a rack unit. D'oh!

[JJP]

As mentioned, be sure to verify the thread pitch by comparing the tap (8-32) against the screws that came out of the unit. It's possible that one of them is 'national fine' thread instead of the 8-32 'coarse' thread. Not likely a problem, but as Enzo said, "never think up a reason NOT to test something".

I learned the difference between NC and NF thread pitch the hard way when I bought some machine screws for a rack unit. D'oh!

Hmm, on the packaging for the tap set if has the letters "NC". To my eyes (using a magnifying glass) the threats on the Fender screws look deeper than the threads on the tap. What might that suggest?

[52 Bill]

If the original bolt fit the 8-32 tester at the store, then I would think that the difference is with the tap set. Does it have any instructions or specifications?

[Greg Robinson]

Hmm, on the packaging for the tap set if has the letters "NC". To my eyes (using a magnifying glass) the threats on the Fender screws look deeper than the threads on the tap. What might that suggest?

NC 8 would be National Course, or 32TPI.

[JJP]

NC 8 would be National Course, or 32TPI.

I'm thinking that the Fender screw is fine thread. When I was at the Home Depot checking which nut fit the Fender screw, the box that I pulled a nut from read "machine screws", which I'm assuming to mean fine thread, not course.

[JJP]

NC 8 would be National Course, or 32TPI.

I'm thinking that the Fender chassis screws are fine thread, not coarse. I'm currently on hold with Fender hoping to get an answer. The nut that I tested the screw with at the Home Depot came from a box marked "machine screws" which I'm assuming to be fine thread, not coarse.