Chip Welding

[Tyro 001]

Had an occasion to turn a spacer for my wood shaper spindle. I was turning the O.D. on an expanding mandrel. I used HSS & carbide insert tooling as a back to back test. The turning conditions were the same for both the HSS and carbide; 300rpm, .20" DOC, and feed was the slowest the lathe has to offer. The carbide gave a better finish,but kept building up a chip which appeared to weld itself to the spacer, catching on the lathe tool which caused the spacer to stall while the mandrel kept turning.This happened repeatedly until I gave up and switched back to the HSS. As nearly as I can tell, the carbide insert had a tip radius of 1/64 - 1/32. The HSS had sharp tip. Both were positive rake. Any ideas why the carbide seemed to be welding the chips? Anybody have experience turning on a mandrel? What kind of DOC can have? I'm assuming one should use light cuts on a mandrel. Thanks.

[winchman]

The .20" DOC might be a bit much.

I think you need to tell us the material you're working with, too.

[BigBoy1]

Cutting Speed

If one consults the speed/feed tables, the cutting speeds and feeds for HSS and carbide tools are different with the higher speed/feed for the carbide tools. I looking a table, the recommended speeds for the carbide tools are about twice that of HSS. This is just a general observation with some being more or less depending upon the material being cut.

Perhaps if you tried your test again using the proper speed for the cutting tool used and used a smaller DOC, chip build-up will probably go away.

[MuellerNick]

Chip welding on carbide -> Increase cutting speed

Nick

[KiddZimaHater]

300 RPM for a Carbide cutter seems a bit slow.

[MuellerNick]

300 RPM for a Carbide cutter seems a bit slow.

Depends on the diameter.

and feed was the slowest the lathe has to offer.

Minimum feed (and DOC) depend on the tip radius. Roughly speaking, both DOC and feed should be as big or bigger than the tip radius. Feed can go down to 50% of radius, but that depends on DOC and the alloy and coating of the insert.


Nick

[oldtiffie]

Take it easy

Had an occasion to turn a spacer for my wood shaper spindle. I was turning the O.D. on an expanding mandrel. I used HSS & carbide insert tooling as a back to back test. The turning conditions were the same for both the HSS and carbide; 300rpm, .20" DOC, and feed was the slowest the lathe has to offer. The carbide gave a better finish,but kept building up a chip which appeared to weld itself to the spacer, catching on the lathe tool which caused the spacer to stall while the mandrel kept turning.This happened repeatedly until I gave up and switched back to the HSS. As nearly as I can tell, the carbide insert had a tip radius of 1/64 - 1/32. The HSS had sharp tip. Both were positive rake. Any ideas why the carbide seemed to be welding the chips? Anybody have experience turning on a mandrel? What kind of DOC can have? I'm assuming one should use light cuts on a mandrel. Thanks.

I think you were a bit optimistic too as regards taking what are heavy cuts on a mandrel or anything of a friction-driven nature. The heavier the cut and feed and the larger the diameter more the effect will be seen.

Friction-driven jobs are meant to be finishing or lighter cuts on a lathe.

If I were doing it, I'd use a spigot and a clamping nut and washer to force the job onto a flat (turned) face and take it easy.

Roughing work - as a general statement - should be done with the job in a chuck.

[beanbag]

There are many different kinds of carbide inserts. Which one do you have?

[winchman]

We need some of these:



Without more info from Tyro, we're really shooting in the dark.

[Tyro 001]

As usual, thanks for the replies. I don't get on here very often, in fact I haven't been able to get on since I made the original post. When I was typing the original post, I accidently deleted part of it and didn't get it all typed back in. The DOC was .020" not .20". The steel in question was 1018. The part was so short there was no way to chuck it to do the heavy machining. The weight of the holding device I was using to turn the lathe dog was enough that at 300 rpm there was just enough vibration I didn't want to go any faster. In the future I hope to use something like Tiffie's suggestion of a spigot or something similar. I'm still tooling up and trying to get a critical mass of materials and tools so I can get something done without having to acquire everything first like I did this time.