Parting Practice Chatter

[Dranreb]

Instead of trying to see what's happening while you part off, how about gripping the biggest bar you can get in a tool holder locked in the tool post and just giving it a bit of leverage in all directions, look at the gibs, the tool post, the top and cross slides and anything else you can get your finger tip to. You should be able to feel even the slightest movement that way.

Bernard

 

[Wreck™Wreck]

Power feed the cross slide when parting, .003-.001" per revolution (on metals) or so depending on setup and material.
Feeding by hand is inconsistent at best, the worst that can happen is that you ruin a test specimen or blow up a $10.00 parting blade.

Experience is priceless.

I run lathes every day for a living, haven't used a HHS parting tool in 20+ years of course. I was parting 1" round solid Thompson linear guide rails on Friday using a hard turning insert to get through the RC60 case down to 7/8" Dia., then a generic wedge insert carbide parting tool until parted.

530 RPM, .002" per rev., flood coolant, I would have run it faster but I had to catch the 6" cutoff part by hand, they came off very nicely. Didn't require a good surface finish because there were more operations to be performed on the ends afterwards, (one end is welded into a hub, the other has a .6256 +.0005 -.0000 diameter bore by .203 deep)

Good luck and keep practicing.

 

[rick9345]

I think I'm getting it. Practice is helping me a lot as well as the suggestions. Thanks All!

i think I could benefit from a bit better cutter. I'm using a cheap T style from Grizzly and I can see it loose the nice edge on a single pass on a piece of 1018 CR 1".

i am still of the belief that I can learn how to use the machine with inexpensive tooling and as I get better I can get some tooling that fits my level of skill.

what else is popular for parting? So far all of my tooling is hand ground HSS except for one threading tool I bought just to see if I was grinding mine like the factory stuff.

thanks again everyone!

inexpensive tooling is a joke. Maddeningly frustrating is not a good learning method.
After the skill and confidence is aquired, then it is time to go back to the make do tooling

 

[deyve]

Jibs - gibs - how loose are they

 

[RVJimD]

I just ordered some better tooling. And, I am still looking at way to tighten up the toolpost, compound and cross slide. I worked with it most of the day today and I have identified some issue with the tooling. I don't think the HSS is holding up well. It get along just fine and then instantly the chip changes and it is due to a chipped cutting edge. I think the tool does not take well to the heat during grinding. I was able to swap out a different sharpened cutter and it would continue from the same spot until it suffered the same fate.

im trying to make some notes as I push thru the learning process and hope to post some of my findings when I get to the point of being able to part off consistently.

jim

 

[mattthemuppet2]

coming from someone with, I think, the smallest most flexible lathe on this site (well, until this weekend) here's what I've found.

Parting sucks. You're jabbing an enormously wide cutting edge into the work perpendicular to the direction the lathe is strongest in.

Things that make it better

- a less enormously wide cutting edge. going from 2.5 to 1.2mm wide made an enormous difference in chatter, but also limited the depth of parting.

- side rake, back rake and front rake and front to back clearance. My grooving tools (bit much to call them parting tools) are ground with a sniff of side rake, so that the sides of the tool doesn't touch the work. They're also ground with a sniff of relief from front to back (ie. looking down at the top of the tool it appears slightly tapered) for the same reason. Front rake is as little as possible, 5deg at most (less than on the ends of HSS blanks). Back rake is fairly steep and ground to form a chip roller. This makes the tip "slice" rather than push, plus it helps roll the chips and push them out of the cut.

- heavy feed. Feed is as hard as you can, you should be getting constant cutting and chips. If it chatters, push harder!

- if that doesn't help, sometimes you can take a small cut, retract the tool, move it over and cut to the same depth. That way you get more clearance and half the cuts will be on half the cutting edge, so they'll be smoother.

That said, I can't part with my current lathe as the whole compound/ carriage/ headstock/ spindle flexes enough that the work rides up onto the blade when the diameter gets too small.

 

[bpratl]

I eliminated all parting chatter by replacing the upper compound with a solid aluminum block, on my G0602, after converting to electronic lead screw. Bob

 

[Dranreb]

I think the tool does not take well to the heat during grinding. I was able to swap out a different sharpened cutter and it would continue from the same spot until it suffered the same fate.
jim

To hopefully eliminate another worry for you, unlike carbon steel wood chisels and plane blades, HSS lathe tooling will still cut even when dull red hot, it has to be towards white hot to soften it.

Grinding shouldn't soften it unless you're very heavy handed, or your tip is much too pointed, more damage can be done by dip cooling it in cold water whilst grinding due to thermal shock causing micro cracks.

The very tip of the tool can become white hot momentarily when cutting the workpiece if your setup isn't right, and this is what does the damage and ruins the tip, the split second that happens you're done.

Bernard

 

[caster]

T-nuts describes their shape, they behave just like nuts. The space below the nut is irrelevant, the bolt should pull the t-nut up and its upper sides should be firm and flush with the top of the t-slot. The bolts or posts I use don't exit the bottom of the t-nuts, the last thread in the t-nut stops them. The holding / clamping pressure is applied from the top pulling the t-nuts up. If you can rock the tool post then it has not been properly installed. Rigidity is your friend, lock the carriage and the compound, make sure the gibs on the cross slide are snug. Make sure the parting blade is tight in the holder, it can slide. Be square and centered to the work and use cutting oil or coolant where applicable.

good luck and keep trying.

Caster

 

[RVJimD]

Big Gain Made Today!

Big thanks to everyone for all the tips! And, a special thanks to Bpratl for the tip about the upper compound mod. I have seen a lot of G0602 owners doing a four bolt mod to the compound and I had already added one more bold to the front right to turn the stock mount into a three bolt. This helped but I think the root of the problem is the small round surface area of the protractor in the mount design. You will see this in the photos. I got some 1/2" aluminum and made a rough non rotatable mount. I hope it is 29.5 degrees so I can leave it in place for turning and threading and parting! :talktogod: I'm not real optimistic though!

So I got the new mount bolted down with only the two in line studies and it works BETTER than the stock mount! The larger surface area prevents the post from flexing forward. I can really see the difference if I push it too hard and stick the blade during a cut. I did five more parts like the stuff I had been practicing on and had great success!

here are the pics of the mod. I think I will design a bit better version and see if I can make it positionable. At the very least, I plan to make one from steel and a bit bigger to take advantage of the space available on the top surface of the cross slide.