Cutoff Tool

Mork said:
Reversing with a inverted tool would be a great way to part off but I'd also be worried about my screw on chuck.
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If you are running the parting tool inverted on the back side of the chuck, directional rotation will be the same as right-side-up on the front.
 
You're right planeflyer, I messed up.... got turned around.

I tried the inverted tool (standard rotation of course) as Mikey suggested but I had some of the same problem. I then sharpened the parting tool an at a very slight angle and tried it again. It did work better and even better yet at higher speeds (except for it slinging oil and chips everywhere). Still some chatter however but I can see where some fine tuning might make it a better method. Be sure to stand to one side tho... oil and chips sling everywhere. I'm thinking a thinner blade would be better... I think mine is 1/8"

Mikey said he used a .040 blade... that is very thin but this would require much less force and stress on the lathe. I'll have to experiment.
 
Something isn't right. There should not be oil and chips slung about when parting from the rear - the oil generally stops at the blade and the chips simply pile up on top. I guess it can happen but I've never seen it.

If you're chattering I would check to see if you're on center height and perpendicular to the work. If I had to guess I would bet the tool is not centered.

Once you are, don't be afraid to crank up your speed. The tool will cut easier. You should feel a slight positive resistance to feed all the way through the cut.

I think for a lathe of your size a P2 (about 3/32" wide) or a P2N (5/64" wide) would work well.
 
I don't think anyone's asked this yet, but what material are you trying to part? I'd suggest getting a piece of delrin or plastic tubing and starting with that, then work up to aluminium and then steel. As Mikey says, something isn't quite right here, so start with the most forgiving material and work up from there. Could be that you're not feeding hard enough, so the tool rubs and chatters. You should be getting nice curls.
 
I went through my lathe and tightened everything up today. It wasn't in terrible need but there are a few area on my Logan lathe that in my opinion are very poorly designed. This area is where you adjust the carriage to the bed of the lathe. Both the front and back are basically snugging screws to remove excessive clearances. A much better method would be to install shims and tighten the saddle securely with .0001 slop. Its been a while since I have had the saddle apart so there may be a method of shimming and securing the operator side but on the back side there is no way to do this (not with the original design anyway).

Mikey... the back side of my saddle might be what is creating a problem. I used lock washers on the bolts holding the lip that catches the underside of the bed. This works fine while working from the front but the washers acted like springs when parting from the back side.

Now that things are all tightened up parting from the front is better than it was... even if my adjustments are all a little stiff now. I plan on trying a thinner parting tool with an insert next. I think parting from the back side is a great idea but its a bit awkward without T slots. I may explore this more in the future.

I agree "Big Bore"... solid solid solid. The thing is, the Logan 200 is not extremely solid. I may explore some modifications for tightening the saddle to the bed but there are limits as to how much I can solidify.
 
Parting from the rear causes the forces on the blade to push the tool holder down. This usually takes up play in the supporting structures and improves rigidity. I checked this once with a tenths-reading indicator. When parting from the front I could see upward movement on the cross slide as the tool entered the work. From the rear ... nothing. Regardless of which way you go - front or rear - as long as you pay attention to the basics you should do okay.
 
I am following this thread. I have hit and miss parting. For me hardest is larger diameter and harder steel. I like to have my parting blade ground to face the fallen part.
Jack

Sent from my SGH-I337M using Tapatalk
 
Interesting... I would think parting from the back would raise the back of the carriage although I can see how the force could transfer to the front. Maybe taking the play out of the carriage in front will help parting from the back. I'll probably try this again in the future.
 
Parting is its own anomaly. Personally I don't like HSS blades as a whole. When a youngster in this trade I would pucker when parting off more than anything else. I have learned enough tricks to get by just about any problem. Love the carbide replaceable inserts, but at home I still use a HSS cutter. Usual problem is in the rigidity of set up. I still pucker a bit. In fact when teaching at the Vo-Tech last year I was explaining the woes of parting off, then gave a demo. BANG! Snapped the HSS tool off. The guys jumped. "See, no matter how much experience you have __it still happens!"
 
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