Internal Threading Problems: Carriage Moves

Anybody feel like doing a couple of photos for the respective setups above to help clarify any ambiguities?
A picture is worth a thousand words.
 
Jeff M said:
I forgot to mention that (and it is probably obvious) the tool will be facing the back of the part if you thread in reverse from the inside coming out. the compound should be 29º to your left. 1/2 degree into the trailing edge.
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Not sure if I can do this with a 9A. With a threaded chuck won't the chuck unscrew? Or am I thinking about it backwards?
 
You are absolutely right, it would be unwise to run a thread mount chuck in reverse. Too many people have learned that the hard way. Unless you can use a collet you should only run forward. If this is the case you can't use the reverse method. Glad you made that point.
 
You can still thread on the backside, just flip the tool upside down, run like normal. I did this on my Sheldon that has a 2-1/4" -8 thread.


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the cutting tip of the threading tool is pointing down when threading the inside and far side of the bore. . . . . . you do not run the machine backwards and you thread fro the right to the left, as normal outside threading or turning for that matter, is done
 
Yes, I agree that you could cut the thread from the back side with the tool upside down but that would be the same as running in on the front side with the tool right side up. You still have to feed in to a hole that you cannot see. I am only saying that it is much easier to thread internally coming from the inside out. I would not do it with a thread mount, but with any other mount (D, L, A, or Hardinge nose) I find it much easier.
 
It's all personal preference I suppose. I find that threading on the back side, the compound slide handle is in a more comfortable place.


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I tried this last night, along with tightening my carriage brake (is that the right name for it?) just enough to let things keep moving but hopefully take up the vertical slack. The movement was much less, but I still had issues. I'm thinking my threading tool is getting dull very quickly, maybe due to improper setup? After a few passes it appears the tool is just riding the existing thread, and not cutting any new material away.

I set up the tool with the top of the cutting face dead level, and the nose of the tool (round V shape HSS, I assume) seemed to be what was gettig dull as if it were rubbing instead of cutting. Should the top flat face be angled downward slightly to give more clearance to the nose underneath?

I can't find a pic online of my threading tool, so maybe it's an oddball thing and/or I'm using it wrong. I'll try to take one tonight to make this more clear.

TomS said:
Are you cutting a right hand or left hand thread? If you are cutting a right hand thread and the compound is set the same as an external thread your tool is cutting, or trying to cut, on the trailing edge. What's happening is the tool pressure is taking up the slack in your half nut and pushing your carriage forward.

Tom S
Click to expand...
 
4130 should cut fine with no top rake. Check the clearance angle on the leading edge of your tool. 4130 only needs 3-5º clearance but you have to add the helical angle of the thread to that 3-5º. The helical angle changes with thread pitch and diameter. If you have adequate clearance, you may try some top rake. With the higher shear angle, it will machine a little more freely. The trade-off with top rake is quicker edge wear. The trailing angle probably doesn't need any clearance as the clearance will be generated by the helical angle of the thread.
A good cutting oil can also make quite a bit of difference. What are you using?
 
Something that works for me, is to hold a little tension on the carriage hand wheel while it's threading. This keeps the threading tool from "tracking" and messing up the thread. But as others have said, get your clearance angles correct on your cutting tool, this plays an affect on how it cuts or not cut as it should.
Ken
 
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