O1 Steel For Internal Threading Tool

boostin53

boostin53

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I need to make an internal threading tool for a project I'm working on. My current internal threading tool I ground from 1/2" HSS is just shy of reaching to where I need to thread. So my thought was to make one from some 1/2" o1 tool steel. Drill a hole on one end to hold a tiny HSS bit hanging off the side. With a set screw holding the bit of course.

Does the o1 need to be hardened or can I just use it as is? My thoughts say harden it to reduce flex in the shank. But it's going to be used on aluminum, at least for this project. So, to harden or not to harden. That is the question.
 
I would not think so I use a 3/4" bar with a threading bit quite a bit. It works out well. I have 1/2" bars and would a threading bit in any one of them if I was threading a smaller hole. In answer to your question I would not harden.
 
I agree with David and would use the largest boring bar that would fit into the work with a HSS tool inserted in the end of the bar. Edit: The bar could be hardened or not. Hardened is stiffer, softer will have less vibration. Best would be a solid carbide bar.
 
Young's Modulus is a fairly stable property of steel, and does not change significantly during heat treatment. Therefore, little if anything is gained by heat treating (hardening) of the material.
 
3/4" is as big of a bar I can use for this project. I have 3/4" mystery steel, would it be acceptable to use some for this? I opted for the 1/2" o1 because I know what it is. I try to stay away from mystery metals as much as possible. I just dont have any 3/4" o1.
 
You can buy internal threading tools that will do an 8tpi thread and are much wimpier that a 1/2" O-1 round.
Unless your 3/4" mystery metal is some exotic alloy specifically intended to be soft and flexible, it should be beefier than the 1/2" O-1.
Use the 3/4" stuff and move on.
 
Mystery metal is fine (so long as you can cut it). Even a little larger, will be quite a bit stiffer. As Tony pointed out, stiffness is described by Young's modulus - it will be very similar, regarless exactly what type of steel, or whether it is heat treated. However, a larger diameter will really help (5/8" is a lot stiffer than 1/2" bar) - go as big as you can. With threading, you can take very small cuts (if you have problems only cut one flank at a time - reduces the load on that bar). Make sure your tool is honed and as keen as you can get it. Set the tool slightly above center, then when it flexes (and it will), then it will flex to a reduced load. If you set the bar on center, then it loads up more as the tool load pushes down, which increases the load and makes it flex more, . . .

Solid carbide bars are wonderful. Get yourself a real small one (say 1/4") - they are amazing.
 
joshua43214 said:
You can buy internal threading tools that will do an 8tpi thread and are much wimpier that a 1/2" O-1 round.
Unless your 3/4" mystery metal is some exotic alloy specifically intended to be soft and flexible, it should be beefier than the 1/2" O-1.
Use the 3/4" stuff and move on.
Click to expand...

Well then I guess I will use some of my mystery metal then. And save my o1 for what I purchased it for. Moving on now.
 
ditto ^, use the largest piece of steel round with the shortest stick out possible. ID threading is harder than OD threading because of the flex of the bar, especially when you're near to full thread depth. Working in alu should help.

I also use my ID bar for grooving, with a different bit
 
I've done very little internal threading. And what I have done has been at the end of the work. The ID threading I'm attempting tomorrow is about 2" in the bore. The actual thread is roughly one inch long. So I need a thread relief on both sides of the thread. Could I put my threading tool upside down and run the lathe in reverse? Possibly allowing me to see the end of the thread easier since it will be the closest to me?
 
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