• If you like antique engines, vintage tractors or old iron, please register and join us. When you register on Smokstak, give complete answers and fill in all blanks. Be Considerate, this is an application to JOIN Smokstak, therefore it becomes part of a decision to open the door to you or send you off to the dropout file. Place your City, State, Country in the location box and it will be compared to where the internet lookup utilities say that you are. Don't give me a zip code to look up, the Eject button is much easier. We get hundreds of applications, so there is not time for monkey business.

Parting off my Lathe

cobbadog

Registered
Hi guys,
I am looking for some more advise on parting off in my lathe. For no reason at all the carbide tips have been snapping off. I have checked that the cutting tip is at centre height as shown with my metal rule between the job and cutting tip. You can see how the tip is just shattering and I have posted a new tip which appears to have clearance behind the cutting edge. I have tried a chuck speed of 115 rpm and 350 rpm and both have the same end result no matter how slow I insert the tool or even putting it in and then stopping and then some more weight.
I am parting off a lot of short pieces of 12mm/1/2" round rod of mild steel construction so it's not as though it is a high tensile steel. Hopefully you can set me straight as I have been doing alright in the past once I had the height set right and set the tool holder in close to the tool post.
Thanks in advance,
Cobba20200207_140910.jpg20200207_140943.jpg20200207_141335.jpg20200207_154026.jpg20200207_154115.jpg20200207_154115.jpg
 

Joel Sanderson

Registered
Here's what I would do, Cobba, but understand I'm a blacksmith and only a machinist at the other end of the shop. ;)

Set your toolholder farther out so you do get a little flex, then set the tool slightly below center so that the tool flexes downwards, away from the work. This makes it more of a scraping action and less a gouging action, if that makes sense. Carefully hand feed it, slowly, and use lots of oil. I use lard oil, but I don't think that's anything magical. I also use HSS cut-off tools that can be ground with a little hook on the tip for a chip-curler. Yours look too flat to me. Make sure your cross slide is tight.

I hope this helps. I'm sure there are folks here with more experience than I have.

Joel
 

Rob Charles

Sponsor
Last Subscription Date
04/05/2017
Looking at your 2nd picture your toolholder appears to have some of the area under the parting bit broke away. With carbide you need maximum support. I suspect that when cutting the bit is jumping and chipping the tip
 

Lumbersawyer

Registered
Looking at your 2nd picture your toolholder appears to have some of the area under the parting bit broke away. With carbide you need maximum support. I suspect that when cutting the bit is jumping and chipping the tip
Your tool does not look square to the part. It could be just the angle of your camera, but the tool has to be perfectly perpendicular to the part.
 

I like oldstuff

Registered
Last Subscription Date
11/09/2015
I don' t have experience with the carbide insert cut off tools but they're the real deal these days. Does the cut chatter then snap the edge? Or does it cut well then suddenly dig in and stall/snap. One thing I find is that parting requires a flood of oil to keep it from sticking in the work. Try that and hopefully you won't snap another $5 tip.
 

DwayneClark

Registered
I don' t have experience with the carbide insert cut off tools but they're the real deal these days. Does the cut chatter then snap the edge? Or does it cut well then suddenly dig in and stall/snap. One thing I find is that parting requires a flood of oil to keep it from sticking in the work. Try that and hopefully you won't snap another $5 tip.
Your tool holder does appear to be broken under where the insert sits. Also, carbide parting tools like to run fast and wet.
When you replace your tool holder, try bumping your speed up up to at least 100 sfpm.
 

Tanner Remillard

Subscriber
Age
36
Last Subscription Date
02/05/2020
As stated, the bottom of your holder looks busted off below the insert, which will cause problems. Also, run it fast. If I was doing that, I'd turn 1/2" rod at least 800+ RPM. Carbides don't like slow, and as also stated, its good to have part off tools like this a touch below centerline when you get to the smaller diameter, its trying to push the material out of the way rather than cut it because inserts don't have a sharp edge like HSS, and it will snap off like your experiencing.

Fast RPM, below centerline. I use carbide part off inserts like this a lot at work.
 

Pete Spaco

Registered
What everyone else has said.
I don't use carbide for cutting off but I do use HSS.
The one thing I can add that hasn't been covered so far:
The chip is exactly the width of the cutter, right?
Okay, so that faster you go, the hotter the chip gets and, of course it expands. Now it is WIDER that the slot that it's coming out of.
I use a tiny, but constant, stream of oil when I am cutting off to keep the chips cool enough so the don't get stuck in the slot. A little bit of oil or coolant isn't going to do the job because the chips can heat up real fast.
If you are going pretty fast with carbide, I suspect that the chip build up happens all at once so you may not even be able to see exactly what is happening until it's all over.
I guess there's one more thing: Keep the tool cutting continuously.

When I first started to use a cut off tool (I'm just a hobbyist) many years ago, I read my "how to run a lathe" book and used back gear at about 50 rpms and still had problems. Now (still with HSS tooling) I run at 300 to 400 rpms on stuff like you showed and have no problems at all.

Pete Stanaitis
--------------
 

OTTO-Sawyer

Subscriber
Age
57
Last Subscription Date
07/15/2019
How much play do you have in the cross slide gibs, and/or feed screw ?

Sounds like it's maybe diving in and breaking due to too much play on one or the other or both.

Gibs can/should be adjusted, but if they're worn in one spot there's only so much you can do there before it binds up in other areas.

Excess Play in the screw threads can only be fixed by replacing both the screw and the nut, as a worn out unit will allow it to build up tool pressure and then finally start to cut again at which point it dives in by however much play there is in the threads. . . but you can get around that by Grabbing on to the tool post and pulling back on it as you slowly feed the tool in to keep it from diving in .005-.015 or more as it builds & releases pressure.

Since you're using a Quick-Change Tool Post that offsets everything way off the side of the cross-slide the Gib where it creates a Lot More of a problem (especially with cut-off tools) than the old lantern style did which kept the tools somewhat Centered on the cross-slide. Hanging off the side like that makes them want rock around on the Ways, as the tool gets pulled down it raises up the opposite side if the gibs aren't tight.

Here's a youtube video a guy made a while back showing a support block he made up to go under the cut-off tool to help with the loose gib situation, eliminating the chatter and tool breakage from that.

Jump Ahead to around the 3:30 minute mark. . .

:salute:
 
Last edited:

L Spies

Registered
Hi guys,
I am looking for some more advise on parting off in my lathe. For no reason at all the carbide tips have been snapping off. I have checked that the cutting tip is at centre height as shown with my metal rule between the job and cutting tip. You can see how the tip is just shattering and I have posted a new tip which appears to have clearance behind the cutting edge. I have tried a chuck speed of 115 rpm and 350 rpm and both have the same end result no matter how slow I insert the tool or even putting it in and then stopping and then some more weight.
I am parting off a lot of short pieces of 12mm/1/2" round rod of mild steel construction so it's not as though it is a high tensile steel. Hopefully you can set me straight as I have been doing alright in the past once I had the height set right and set the tool holder in close to the tool post.
Thanks in advance,
CobbaView attachment 379191View attachment 379192View attachment 379193View attachment 379194View attachment 379195View attachment 379195
I don' t have experience with the carbide insert cut off tools but they're the real deal these days. Does the cut chatter then snap the edge? Or does it cut well then suddenly dig in and stall/snap. One thing I find is that parting requires a flood of oil to keep it from sticking in the work. Try that and hopefully you won't snap another $5 tip.
looks like your chuck jaws are worn bell mouth and the material is flexing lynmn
 

cobbadog

Registered
thank you very much to everyone who has made a comment and offered a solution. The lathe is one of those "Best Chinese" models but in general is in pretty fair condition to my way of thinking and bear in mind I am a learner driver on this thing with next to no experience. When I set it up in the shed there was some movement on the cross slide and saddle. I found some small adjusting bolts with lock nuts that apply pressure tot eh slide and saddle in the dovetail section. This took out the wobbles from it but still allows me to operate the slide and saddle, any tighter it started to be stiff to move. I also lubricated it at every point that had the ball bearing set in a brass plug so it got a drink that it probably had not had in along time. As far as I can tell the spindle bearing feels good and I am not too sure on how to check it properly but I did put a short bar under it to see if I could detect any movement and I could not.
I too can now see the part of my tooling that appears to be missing and now will look at either replacing it with the same tool or updating to something a bit more substantial, I will research this option. I will also drop the tool height a bit to see how that goes, lift the speed up and have another go with those settings. I also tend to agree that maybe the tool is diving down and is what may have cased the damage to the tool holder. That was an interesting video. I watched it from the start and does point out the need to make the cutting edge as solid as possible and is why I have mounted the tool holder so close to the post. I will go out and have a play again making some adjustments. If there is no joy I will look at different parting off tools. I will let you know what I do and the results, again I thank everyone for the replies.
 

Duey C

Subscriber
Age
55
Last Subscription Date
12/08/2019
Good discussion! cobba, ya beat me with your typing! :)
Hehehe, I've done much of the same: Held on to the tool post/lantern wrench to hinder/or slow the flex, moved the compound as far back as I can get away with, centered the tool over the carriage best I can, fiddled with heights, figured out little ways to get the minimum of cutting edge hanging out on this ancient tooling here and would love to try some exotic/modern parting on a 109 year old lathe! :) I THINK the parting blade itself may be high speed steel... Re-sharpens like it is.
The little chinaman behind me is worse and he's only 15 years old!
Parting is the big challenge with a lathe. ?
You guys are right, steady feed IN. Too fast and it slugs. Too slow and it chatters. Some days it still gives a fella the finger! :unsure:
OIL! Constant as ya can.
:)
Red Green said: "We're all in this together."
cobba, could you rebuild that lower section of the tool holder to better support the carbide? Weld up, grind down to width etc?
 
Last edited:

cobbadog

Registered
I forgot to add earlier that this very basic lathe does not have a wet lubrication system but I use some stuff and brush it on as in the photo.
Well after some messing around with adjusting the height to being only just below centre going by the point on my 'live centre' I now have nice cutting off tool again. I will still look at the part that appears to have broken off and replace it if necessary but at the moment it is actually working well. I dont know why they make the cutting tip double ended as once it has broken you cannot hold the shorter tip in the holder as it gets pushed back, but that is not a problem.
It now makes 'chippies" like it is suppose to, I think!

I can't thank you guys enough for being so kind as to help me out in a very informative way and for me to get a good result in the end. Thank you.
 

Attachments

cobbadog

Registered
Thanks Tracey, I'm dull but not double ended.
With all the help I can now fly through cutting the rod to be spokes in my new trasporter wheels for my next stationary engine projec, try to resurect an old McDonald Super Imperial Diesel engine. I made a jig, had some 65mm wide flat bar rolled to 250mm od and using water pipe as the hub and the 12mm rod as spokes. If only I could weld better than I am at the moment. It is a bit tricky using the mig in a tight space but it is what it is and it will stay this way. I'm sure it wont fall apart, well mI hope not other wise this will happen. :hitfan:
 
Last edited:

Sonny Reese

Registered
Don't feel bad! -- I am still trying to get my SB set up! --- NEVER was around a metal lathe, Have done tons of wood lathe stuff.
As for mig welding, ---- I still fight that!-- getting a little better, BUT-------
 

cobbadog

Registered
Well I got all my wheels made after help with the parting off of the 12mm rod issue. As for the cockyshit weld I have managed to improve a bit probably up to Budgerigar Poop so I went over the first one. The easiest way to describe my problem was lack of Voltage to get penetration. The timber particle board jig stood up far better than expected.
The wheels are for an engine transporter once I fix the engine.
 

Attachments

Top