# Internal thread



## rzw0wr (Oct 25, 2019)

I need to turn an internal thread.

It is a 1/2" thread. The tpi are not standard so I can not use a tap.

I made a boring bar for threading but it keeps flexing. The hole is 1" deep.

I can not find a boring bar small enough to fit into the hole.

Any ideas on how to thread this hole.


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## mmcmdl (Oct 25, 2019)

They do make insert bars that would fit into that bore . If it was a blind bore , I'de be threading out .


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## rzw0wr (Oct 25, 2019)

It is not a blind hole. Who make a bar that will fit the minor dia. of a 1/2" thread?


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## MontanaLon (Oct 25, 2019)

What material are you threading? You can make a threading tool out of HSS pretty easily. I have had good luck using broken drills as long as I am not working with anything really hard. You can get as fancy as you want or need to make it work. 

Turn it, grind it, whatever it takes to get there.


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## mikey (Oct 25, 2019)

rzw0wr said:


> It is not a blind hole. Who make a bar that will fit the minor dia. of a 1/2" thread?



Much depends on the depth of the hole so you need to give us that. For a 1/2" deep hole, I would personally use a3/8" diameter inserted carbide tool with a carbide shank that will let me go 3.75" deep. Micro 100 also makes solid carbide threading tools that will work really well. You can also turn down a piece of tool steel with a 60 degree profile on the end and grind half of the tip off to make your own tool. You can harden and temper it easily in your home shop.


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## francist (Oct 25, 2019)

Here’s one I made in a pinch from an old tap. Obviously the plus-side is that the 60 degree point profile is already done for you, you just need to make the rest of the teeth disappear and give a bit of clearance. Lots of ways to do it, pick your poison.

-frank


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## mmcmdl (Oct 25, 2019)

I have a boat load of them from Manchester , TopNotch etc . I just located them down the basement looking for something else .



rzw0wr said:


> t is not a blind hole. Who make a bar that will fit the minor dia. of a 1/2" thread?



That's a big one !


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## darkzero (Oct 25, 2019)

My Carmex 3/8" internal bar that uses 11IR inserts will thread a 1/2 hole. 1/2" hole is the smallest I thread with it. But the clearance is tight so have to be careful when backing it out. I use my DRO to keep track of it so luckily I've never had a mishap with it. There are better options though for more comfort. As MIke suggested, Micro100 is a good choice. They make quality tools & I like them.

(Yeah I know my bar is mounted upside down, don't mind that, that's just how I use internal threading bars  )


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## mmcmdl (Oct 25, 2019)

darkzero said:


> (Yeah I know my bar is mounted upside down, don't mind that, that's just how I use internal threading bars  )



Back in my cnc days , I always ran the slants upside down . The machines were limited to the distance over spindle center . The machines didn't mind at all . Just a M3 code vs. an M4 code !


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## darkzero (Oct 25, 2019)

mmcmdl said:


> Back in my cnc days , I always ran the slants upside down . The machines were limited to the distance over spindle center . The machines didn't mind at all . Just a M3 code vs. an M4 code !



Wudda wudda wuh? I'm still CNC illiterate.


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## mmcmdl (Oct 25, 2019)

Easiest machines to run and program were the Leblond Makino slant lathes . Conversational programming was a snap . I wish I still had the use of one , I would get rid of everything else .


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## darkzero (Oct 25, 2019)

mmcmdl said:


> Easiest machines to run and program were the Leblond Makino slant lathes . Conversational programming was a snap . I wish I still had the use of one , I would get rid of everything else .



I wish you still had access to one too & lived closer.... so you could teach me & hopefully let me use it sometimes.


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## RobertB (Oct 25, 2019)

Since it is a non-standard thread make sure that it is a 60° angle before buying an insert tool.


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## BGHansen (Oct 25, 2019)

darkzero said:


> Wudda wudda wuh? I'm still CNC illiterate.


M03 is clockwise rotation, M04 is counter-clockwise.  That'd be about as exciting as not putting the lathe in back gear when firing up the motor with the half nut already engaged.  Ask me how I know (thank goodness for a foot brake . . .).

Bruce


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## ericc (Oct 25, 2019)

rzw0wr said:


> ...
> I made a boring bar for threading but it keeps flexing. The hole is 1" deep.
> ^^^^^
> ...



What did you make it from? what does the cutting end look like.  How thick is it.  Is it flexing because you are trying to "bully" the cut?  Could it be dull?

I just cut a 1/2-20 internal thread for my Craftsman 109 lathe faceplate with a 3/8" diameter mild steel bar with a 1/8" broken drill bit as a cutter, and it worked just fine.


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## MrWhoopee (Oct 25, 2019)

If you have the time, order a set of bars with inserts. For $20 with free shipping you can't go wrong.








						37.28US $ |New 3 Set SNR0008K11+SNR0010K11+SNR0012M11 Lathe Boring Bar Stainless Steel 3Pcs wrench+ 10x 11IR A60 Insert Wrench|Turning Tool|   - AliExpress
					

Smarter Shopping, Better Living!  Aliexpress.com




					www.aliexpress.com
				




Yes, I bought a set and they do the job.


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## Jimsehr (Oct 25, 2019)

Victor machinery has special pitch taps . 1/2 inch taps run from about 11 bucks to 20 bucks. I don’t think I would fight threading one for that cheap of price. Plus you have the tap for the next time you need it.


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## Mitch Alsup (Oct 25, 2019)

MrWhoopee said:


> If you have the time, order a set of bars with inserts. For $20 with free shipping you can't go wrong.
> 
> 
> 
> ...



I have the same set.


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## epanzella (Oct 25, 2019)

I make my own internal threading tools out of 01 tool steel to suit the job at hand. I like square blanks so the rake angle can be easily maintained. I use a 60 degree carbide bit to turn the tooth profile then mill off a little more than half the  diameter to provide clearance. This leaves you with two perfect cutting teeth. One in the front and one in the back. Grind off the one you don't need. Heat cherry red and then dunk in motor oil. I don't bother tempering. Sharpen by stoning the flat on top so the tooth profile remains unchanged. You can make these as big or small as you want and they can go quite a while between sharpenings.


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## rzw0wr (Oct 27, 2019)

I finally got it threaded.
I made a new tool from a 5/16 lathe bit.
Worked great.

Thanks for the replies


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