First time cutting steel Taig lathe problems

[Tony P]

The added pressure may be causing flex in your tool post.

When cutting the post is pushed back into position "a", when you move back the pressure is still there but a little less so tool post now closer to work so it cuts again.

If it is cutting consistent across the work and using HSS, STOP when you get to left, then move back to right.

You also can look at the number on your dial and turn it 1/2 a turn back before moving then put it back on the number you started with.

You may need to optimize your angle on your cutter as well as lighter cuts.

Reduce stick out and tighten the gibs.

Sent from my SM-G781V using Tapatalk

only 3" stick out but I'm using the tailstock. Gibs are tight. the entire machine is at tight as possible,

 

[Tony P]

That means that there's more tool pressure than either the lathe, or the setup can handle. The work, the tool, or both are being deflected during the initial cut, and when you back out, they "spring back", and thereby continue cutting.



Why are you doing this? Does the dial not stay put, or are you doing it preemptively, in case that was a problem?



Same as above, there was deflection, so just like the cutting on the back cut, the tool continues to cut in one place. The deflection, and the nature of the situation to cause a pressure to return to it's original position, the work or the tool is feeding under spring pressure.



I dunno... You ground it. You need to have the rakes and clearances dialed in so it cuts well. Whatever angle you put on the cutting portion of the tool, that is what will determine the angle at which you present the tool. You're going to be in a pickle at first, because on a light lathe there are many variables that you can "get by" with a lot less concern for. But dialing in several variables at once can be pretty daunting at first, but with a little patience (and maybe a good sense of humor) you'll get it.

This approach from the Sherline lathe people helped me out a bunch getting going. They're easy, quick, and they're customizable without reinventing the wheel. Is that kinda how you have yours done?

https://sherline.com/wp-content/uploads/2015/01/grinding.pdf

Any chance you can get us a picture of the tool you ground, and how it was presented to the work? Also, what kind of tool post/holder are you using? There may be some more specific advice based on that.



Backlash shouldn't be an issue, as it's all taken up when you feed in to touch off, and dial in the depth of cut. Nothing is going to push the cross slide into the work.



Maybe. Too much or too little, either way can cause issues. I've never run a lathe such as yours, but I'd expect the nose radius is going to be quite small.


Speed can cause some issues, but if you're at or below anything recommended by calculations, or off of a chart or whatever, you're in the ballpark. I'd stay conservative, and save that one for later.



Well, mild steel (which that appears to be) isn't really that "hard", but yeah, it's tougher to cut than the stuff you've mentioned. It will tend to push back more, which will put the onus on you to keep your cutting tools as free cutting as they can possibly be. If you're using one of the "standard" grind patterns, like the Sherline page I linked, you're probably going to want ten to twenty degrees of side rake, and ten to fifteen degrees of back rake, and ten or so for the reliefs. Also, I suspect that your tool post is going to present the tool mostly if not exactly horizontally, in which case all of the grind angles can be ground in relation to the tool bit, however if your tool post presents the tool at an angle other than horizontal, you're going to have to accomodate that, as the angle that matters is not the angle relative to the tool, but the angle, as presented, relative to the work piece. So if your tool is angled upward from horizontal as it's presented, your rakes will be less and relief will have to be more to accommodate that.

Yes holding the knob because I don't trust it 100%, no reason for that i guess. In my alum work I thought it helped a lot. I mean the shank of the tool bit at 90. There's a huge amount of deflection. I can make 3 or 4 or 5 passes and it still cuts back and forth. I'm using the Taig toolpost which is a rectangular block with a center screw going down to the tee nut. Tools are 1/4". I've ground bits quite a bit but as I said not for steel, its simple enough. I'm going to regrind or make a new tool and try it again with lighter cuts and bare minimum tool length past the post. I've had this lathe for years and take care of it. Its tight and adjusted as much as it can be. I'll take pics of everything later when I do it. Thanks

 

[Tony P]

Reground the tools. Changed from live center to dead. Cuts great. Light passes are ok but still drags back. Surface finish is better but not ideal that’s for sure. I had added handles to the tool posts because using the Allen is a royal pain. I made bushings to sit on the hole on the post but it sure seems tighter with the normal set up with the Allen screws the handles add another 3/4” to the length and loss of yet more rigidity. Onward I’ll go. I have to get the 12L14 and try it. I maybe able to improve surface finish, etc etc and have to live with the dragging. Just don’t do it.

 

[WobblyHand]

Just don't drag on a finish pass. For non finish it doesn't matter I guess, but I always retract the cutter after a pass.

 

[ShagDog]

Tony, you mentioned "light passes" in your last post. What do you consider to be a light pass?

 

[Tony P]

Just don't drag on a finish pass. For non finish it doesn't matter I guess, but I always retract the cutter after a pass.

Yes just have to work on surface finish.

Tony, you mentioned "light passes" in your last post. What do you consider to be a light pass?

not measuring right now but 10-15 thou

 

[ShagDog]

...

not measuring right now but 10-15 thou

Is that 5 to 7.5 thou on the dial or 10-15 thou on the dial?

 

[Tony P]

Is that 5 to 7.5 thou on the dial or 10-15 thou on the dial?

Ha, 10-15 by my eye !