Rough Threads Single Point Threading

Sailplane Driver

Sailplane Driver

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I've never had good luck single point treading. I can get good threads with the correct pitch diameter but they look like they've been chewed out with an axe. My latest attempt was on 12L14 with a brand new carbide threading insert appropriate for the TPI. For scale, the picture is showing a 3/4-16 thread. I was feeding in using the cross slide rather than the compound. I went in with about 8 steps, larger at the beginning, decreasing as I got close to the correct dimension, and a couple of spring passes to final dimension. I run at a pretty low RPM and was feeding towards the headstock as opposed to Joe Pie's revese feed. Anyone have any suggestions on what I may be doing wrong?

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It sure does look rough; I don't have any suggestions but I'm going to hang out and see what the experts have to say.
 
I'm no expert, but it almost looks like you're tearing the material rather than cutting it. And you probably have a lot of chatter since you are cutting on both sides of the tool.

For starters, use the compound. Set it at 29.5 degrees and feed in with it. That keeps the cut on the forward edge, reducing chatter. I rarely have issues with cutting threads this way. I typically put an indicator on the back of my tool post to help me keep track of the total depth of cut, which avoids me having to to the math. Plus, by using the compound, you get some increased sensitivity. It's easier for me to dial in a .001" cut using the compound and a dial on the tool post.
 
so please, lets start with the basics.
  1. Cutting oil, dry or coolant?
  2. Compound set to 29.5 , 30 ? I know you said you are using the x slide, but still curious.
  3. What is the insert? Does it match a 16tpi thread?
  4. What do your threads look like when using HSS?
  5. Are you squaring the thread to the piece? (using a fishtail?)
  6. How much are you taking on each bite?
  7. Are you using a threading dial? Or backing up?
  8. Do you back out after taking a pass?
12L14 is so easy to cut. So it has to be something very basic.
 
woodchucker said:
so please, lets start with the basics.
  1. Cutting oil, dry or coolant?
  2. Compound set to 29.5 , 30 ? I know you said you are using the x slide, but still curious.
  3. What is the insert? Does it match a 16tpi thread?
  4. What do your threads look like when using HSS?
  5. Are you squaring the thread to the piece? (using a fishtail?)
  6. How much are you taking on each bite?
  7. Are you using a threading dial? Or backing up?
  8. Do you back out after taking a pass?
12L14 is so easy to cut. So it has to be something very basic.
Click to expand...
Last time I ran our Haas, we were threading 12L14 at .020 per pass, 1500 rpm.
Programmer screwed up and started it at .00003 per pass........
Took 50 passes to thread m16x1.
 
Is the tool on center? Is the insert sharp? carbide will not perform well using slow rpms. I do not thread with carbide, HSS works just fine with the speeds that can be done on manual lathes and is way cheaper and durable than carbide,
If you are like most hobbyists, perhaps you use inserts to avoid grinding tools. I use Aloris threading tools, they are sharpened on top and last for many years with regular use. use of cutting oil is a must for anything but brass, I use TapMagic for nearly all shop work where cutting fluids are appropriate.
 
Definitely go to using the compound at 29.x* for infeed. Make sure your tool is on the centerline, and perhaps reduce your infeed depth - experiment as you start and try to find an infeed that gives a good result *before* you get to your final pass(es). And I dispute that you need HSS. I like HSS, but I've had good luck with all kinds of carbide threading inserts at slow speeds as well.

GsT
 
Carbide doesn't like low speeds. Use a SHARP high-speed steel cutter or raise the RPM.
Also feeding straight in usually results in rougher threads than feeding in at 29 or 30 degrees.
 
Sailplane Driver said:
I've never had good luck single point treading. I can get good threads with the correct pitch diameter but they look like they've been chewed out with an axe. My latest attempt was on 12L14 with a brand new carbide threading insert appropriate for the TPI. For scale, the picture is showing a 3/4-16 thread. I was feeding in using the cross slide rather than the compound. I went in with about 8 steps, larger at the beginning, decreasing as I got close to the correct dimension, and a couple of spring passes to final dimension. I run at a pretty low RPM and was feeding towards the headstock as opposed to Joe Pie's revese feed. Anyone have any suggestions on what I may be doing wrong?

View attachment 456634
Click to expand...
What is the specific toolholder & insert you are using? What is the machine you are on?
 
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