Anybody have a 3" - 12 tap?

rickseeman · Sep 1, 2020

I (and my friends) have a good selection of taps. But I'm trying to repair a cast aluminum electrical junction box and need a 3"-12 tap. I don't know if it's fixable but I want to try. I've tried ebay but I can't spend a lot since it's not a high value junction box. Anybody have one they want to sell on the cheap? Thanks. Rick

I'm not near good enough to pick up the very damaged ID threads with my lathe. But thanks for thinking I was.

Nmbmxer · Sep 1, 2020

I've made thread chasers before by cutting the male thread in a plug of steel and grooving it in a few places with a ball end mill such that the face had a little hook. I usually tapered the threads a bit for the first few threads. I'd think a mild steel chaser would be fine for one thread in aluminium.

BT Fabrication · Sep 1, 2020

find a bolt, or cut some threads in 4140 and improvise a tap.

Blazemaster · Sep 1, 2020

I had this same problem a few months ago, but with a 2" pip tap. I had a spare piece of 2" pipe with threads on the end so used a small endmill to cut some reliefs and it worked fine for aluminum.

MattiJ · Sep 1, 2020

BT Fabrication said:
find a bolt, or cut some threads in 4140 and improvise a tap.

I bet it's easier to find 3" 12 TPI tap than actual bolt :skep:

I'd use this as an excuse to work your skills to pick up the thread on lathe. Large taps with fine thread like that are not too easy to start straight in a mangled thread.

Milland · Sep 1, 2020

I'd find a 12 TPI threading insert and a chunk of 3" Delrin, and make my own tap. Have a minor-diameter pilot on the Delrin body to help keep things straight, then adjust pocket depth for the insert to match the female thread.

Or, spend the $375 to get the tap from Victor. For the next time you need to fix an electrical box, or chase the threads in your Ford Triton V-10...

reggie_obe · Sep 1, 2020

Get a 3" pipe nipple, turn it into thread chaser.
Borrow a tap from an Industrial Electrician

Garwood · Sep 1, 2020

Take whatever screws into it, hack some notches into the threads to make it "self tapping". Problem solved.

4GSR · Sep 1, 2020

reggie_obe said:
Get a 3" pipe nipple, turn it into thread chaser.
Borrow a tap from an Industrial Electrician

A 3" pipe nipple will have 8-threads per inch, not 12 TPI.

Cole2534 · Sep 1, 2020

4GSR said:
A 3" pipe nipple will have 8-threads per inch, not 12 TPI.

Nor will it be 3" in diameter.

Sent from my SM-G981V using Tapatalk

reggie_obe · Sep 2, 2020

4GSR said:
A 3" pipe nipple will have 8-threads per inch, not 12 TPI.

If its this, ".....cast aluminum electrical junction box and need ......", why would it be a screw thread and not a pipe thread?
I demand a (thread) recount.

Phil in Montana · Sep 2, 2020

Electrical stuff has its own standard, just make a tap on the lathe with slots, more of a thread rolling tap and a lot of wd 40...Phil

Joe Gwinn · Sep 2, 2020

Phil in Montana said:
Electrical stuff has its own standard, just make a tap on the lathe with slots, more of a thread rolling tap and a lot of wd 40...Phil

Electrical conduit threads descended from gas pipe threads.

cstrickland · Sep 2, 2020

do you have enough material around the thread to bore or circle mill it to say 3.5" ID, and then make a sleeve with a 3.5" OD and the desired internal thread ?? you could then cut it on the lathe and then press fit (not sure electrical code would allow) or weld into place

rickseeman · Sep 2, 2020

It's pretty thin there but I could try to sleeve it. Got a 3 day weekend coming up. The material is so thin there maybe I should use a less than normal press fit. Maybe .001" with super glue. Is that crazy?

reggie_obe · Sep 2, 2020

cstrickland said:
do you have enough material around the thread to bore or circle mill it to say 3.5" ID, and then make a sleeve with a 3.5" OD and the desired internal thread ?? you could then cut it on the lathe and then press fit (not sure electrical code would allow) or weld into place

Doing so will probably void the UL Listing for its intended purpose.

cstrickland · Sep 3, 2020

rickseeman said:
It's pretty thin there but I could try to sleeve it. Got a 3 day weekend coming up. The material is so thin there maybe I should use a less than normal press fit. Maybe .001" with super glue. Is that crazy?

yeah not sure I would use super glue, but a good epoxy I would feel would hold it without issue for what it is. Now again I can not speak to as if this causes issue with UL or anything like that so your on your own there. if you are just repairing to see if you can, and not using it then no harm.

cstrickland · Sep 3, 2020

reggie_obe said:
Doing so will probably void the UL Listing for its intended purpose.

that is a good question hence why I stated about the code. I am certainly not familiar enough with electrical codes or UL, but I have seen much crazier things that have passed inspection . Right or wrong.

Phil in Montana · Sep 3, 2020

I hate to ask, what is the fitting? explosion proof? I hope not...Phil

reggie_obe · Sep 4, 2020

Inquiring minds want to know.....
Is it pipe thread or not?
Why would an electrical enclosure be tapped for a 3" machine bolt?

Anybody have a 3" - 12 tap?

Cast Iron

Stainless

Titanium

Hot Rolled

Titanium

Diamond

Diamond

Diamond

Diamond

Diamond

Diamond

Stainless

Stainless

Aluminum

Cast Iron

Diamond

Aluminum

Aluminum

Stainless

Diamond

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