Need Tool For Internal Threading

rwm

rwm

Robert
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Mar 25, 2013
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This will be my first adventure into internal threading. I need to purchase a tool for internal threads 3/4 x 16. I would like to be able to do as small as 1/2" . I prefer indexable carbide. My lathe (Asian 9 x 20) accepts 1/2' tooling. The toolpost will fit 0.750" but that would put me above center at the tool tip.
I was looking at something like this:

http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=7908975&PMAKA=422-3038

The shank looks to be too large and would put my tool above center? I do not see any with 1/2" shanks? How are these tools typically held in the tool post? Any advice would be helpful.

Another thought. Should I just take a piece of 1/2" CRS and machine my own holder to fit that insert?
R
 
Unless there are aspects of the part design that will not allow it why would you not tap the part? 3/4-16 is a small thread and a tap would cost much less then an inserted threading bar and be much faster.

Use single point threading for Dia./Pitch combinations that are large or uncommon where a tap is unavailable or prohibitively expensive for the job.

A tap is $38.00 from McMaster which means that it can be had for 1/2 of that price elsewhere, you won't touch a threading bar and inserts for that price.
 
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Good thought. In this application, I need the threads to be precisely centered. I have not had good results with taps in this regard even threading on the lathe. I feel like this is one piece of tooling I should have for versatility anyway.
R
 
rwm said:
Good thought. In this application, I need the threads to be precisely centered. I have not had good results with taps in this regard even threading on the lathe. I feel like this is one piece of tooling I should have for versatility anyway.
R
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How do you measure the concentricity between the part and the internal thread PD where you determined that it was off?
 
I have made some threads that were visibly off center if I put a screw into the hole and locked it with a jamb nut. I realize that this is not the most precise way to measure concentricity but these were way off. My understanding is that taps give less accurate concentricity than single point cut threads. Am I wrong about this?

Having said that, I may take your suggestion and tap these.

I would still like to know about tool holders for internal threading if any has a product suggestion or other input.
R
 
It might be the initial drilling to size that wandered off line or was the hole bored?

Stuart
 
rwm said:
My understanding is that taps give less accurate concentricity than single point cut threads. Am I wrong about this?



R
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You are correct, however how concentric do they need to be in order to work in a given application? You could spend the rest of your adult life measuring generally meaningless dimensions and gain nothing from the experience aside from practice, which is not a bad thing I suppose.
 
I have one of those Mesa threading tools with the 1/2" shank. Works pretty good is soft steel or aluminum. I used it 4 times and ended up having to order some more inserts as the originals kept chipping. The replacement inserts are not cheap either and are proprietary to that tool only.
If you are going to purchase a new threading tool, I would look for something that uses more common inserts, that are easier on the pocket.
 
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