Cutting 28TPI internal threads

[finsruskw]

What kind of tooling do I need to cut 28 TPI internal threads?
I have a switch I need to mount in a dash panel however the panel is too thick for the threaded stem to protrude enough to thread the nut onto.
was thinking making a nut that was long enough to catch enough of the threads to secure the switch in the panel, but I lack the tooling to do so.

I have never cut female threads before, but I did manage to cut 28 tpi on a test bar (see pic) and the nut screwed on just fine so I am fairly confident I can do this providing I have the right tooling.

The stem is .4950" x .3035" long.
I estimate I will need the nut to be about the same internal threaded length with one end a larger OD than the barrel. which I can turn to .625 once threaded.
Can someone steer me in the right direction for the tooling I need to do this task correctly as it probably won't be the last time I need to do so.
Thanks !

 

[Ischgl99]

I recently started using Micro100 threading bars for small stuff that I don’t have a tap for. I thread away from the chuck using left hand tools, makes internal threading very easy. If you are doing through threading, it doesn’t matter so much if you use right hand conventually, or left hand and away from the chuck, but if you do anything up to a shoulder in the future, away from the chuck would be my choice.

I have an ITL-230 tool that can do the smaller thread pitches, and a bigger one for 10-32 tpi I believe on the way.

Threading Tools

www.micro100.com

If you decide to thread using lefthand tools away from the chuck, you need to make sure your lathe does not have a threaded spindle, or you have a way to ensure it won’t unscrew while threading.

 

[Jim F]

I use one of these.

Tool Bit, 1/4" HSS Internal Threading 1895

Lathe Threading 1895 This 1/4" square high speed steel tool bit is pre-sharpened for internal threading. An internal threading lathe cutting bit is a...

littlemachineshop.com

I have a SB 9C and thread in reverse on a regular basis, if your chuck is seated well, there is not enough force to cause it to loosen while threading.

 

[Huub Buis]

If you only need to make one nut, you could taper the threaded bar (3 threads) and grind 3 cutting edges. Than make the nut from brass or aluminum. You find the drilling depth in most threading tables.
Place the threaded bar in the tail stock, press it firmly against the workpiece and turn the chuck by hand. Don't chamfer the hole.
If it is an UN 1/2 28TPI thread, I would drill the hole 12.82 (11.8) mm or 0.465"
If you have an internal threading tool, maybe it's time for internal threading.

 

[mksj]

You could buy a tap for around $10, would think that would be less expensive than a something like a Micro100 internal threading bar which are $50-60. I do use a Micro100 carbide internal threader for smaller odd internal threads that I do not have a tap for.

1/2"-28 Tap RH Thread Stainless Steel Titanium Tap =LIFETIME WARRANTY= 300 | eBay

This Tap creates a right hand thread, and is made of high quality High Speed Steel. 1/2"-28 Premium Quality Tap. A new 1/2-28 UNEF Tap for threading.

www.ebay.com

 

[mattthemuppet2]

I have a 1/2-28RH tap you can borrow somewhere if you want to go that route

 

[francist]

And of course there’s always the long way around…

Take a thrashed up tap that’s kind of close to the thread size you want, grind all the teeth off ‘cept one and you’ve got yourself an internal threading tool to single point. I’ve done this a few times now and while I wouldn’t suggest it for trying to hit a class fit on tight tolerance it’s a great way to get a tool up and happening within the hour.

-frank

 

[tq60]

Or buy a deep throat switch.

Sent from my SM-G781V using Tapatalk

 

[RJSakowski]

Five years ago, I needed a 4-48 nut so I made a threading tool and made one.

So what's a Machinist to Do?

Persuant to completing the lathe tool height gage made last week (, I needed a 4-48 jam nut to lock my custom dial indicator tip. I could buy a box of nuts from McMaster but what would I do with the other 99? Fastenal has them as well but I would feel foolish walking in for just one nut...

www.hobby-machinist.com

 

[GeneT45]

Make a small boring bar - take a bit of 3/8" rod, cross drill near one end for something like 1/8" HSS tool. Drill and tap the end for a set screw. Now grind a tiny threading cutter - it won't take long at all with 1/8" HSS. et voila! You're ready to thread your hole. This is a pretty non-critical application, so a great opportunity to experiment with something like this.

GsT