Turning A Lot of Material

[ddickey]

I've got into a habit of using cheap carbide bits to take off lots of material then finish with HSS. For example I have 1.75" 12l14 round stock and needed to turn down a section to .875" I put in the cheap carbide bit and went at it taking a few >.125" DOC's. I don't care about the tool bit but I do care bout my lathe.
Am I doing any damage or abusing my lathe by doing this?
It doesn't bog down at all but I'm wondering if I'm stressing it more than I should.

 

[4GSR]

Probably not.

It all depends on the lathe you have, how big it is or how small it is. Didn't mention feed rate. 12L14 machines like butter, you can almost cut it with a butter knife. I'm used to some what larger lathes taking cut .250" plus on depth of cut and feed rates up around .015-.025" per revolution.
One key thing to taking heavy cuts on smaller lathes is using tooling that does not use high cutting forces. If that means grinding your own tool, that what you have to do. Make sure the ways are well oiled when taking heavy cuts and wipe down often and re-oil. This will add life to your lathe.

Ken

 

[echesak]

If the lathe is chattering with the heavy cuts, you might want to take a look at either tooling or the cuts. That's my main worry on my less-than-tight old Clausing. It doesn't mind properly tooled heavy cuts. But I work to minimize the chatter.

my 2 cents...

Eric

 

[intjonmiller]

A 16" lathe with a 3+HP 3 phase motor and heavy tooling won't mind a .125" cut at all. My 10 Logan with worn drive belt (such that it doesn't matter how much power the motor puts out; I can't bring myself to spend money on a new one when the plan is to put a continuous belt on before long) would audibly laugh at me for trying that, regardless of the tooling.

If your lathe is sufficiently stout and transfers enough power to the spindle then there shouldn't be any problem with your approach, though it's likely unnecessary with 12L14.

 

[mikey]

This is a very good question in a way - how do I know if I'm overloading my lathe? In the old days, the idea was that a lathe should work as hard as it could; push it until it groans and then back off a tad. On your lathe, a 0.125" cut in 12L14 isn't even approaching the groaning stage (I know which lathe you own); in fact, with the right tool you could double that cut and still be okay with this material. But for guys with smaller lathes, how do you tell when you're pushing it?

I don't know what other guys do. I'm of the mindset that you should listen to and feel your lathe as it cuts; this tells me how happy or unhappy the lathe is as it cuts. On a heavy cut, my motor doesn't slow down and my hand on the compound only feels the cutter engage in the cut; after that, there is no more movement under my hand. I hear a hissing as the tool cuts and the finish of the cut is appropriate for the material. The lathe is loaded but it is handling the load and is cutting as it should. My 11" Emco with a good HSS tool will take a 0.250" cut in 12L14 without complaint and my little Sherline will take a 0.050" cut in 12L14 without even slowing down.

When I get too ambitious, the lathe will tell me. The motor slows, and I can feel the compound rise as the power feed tries to push the carriage through the cut. I hear the tone of the cut change; it now sounds raspy and rough, with a lower pitch. The finish gets coarse and my lathe just feels and sounds like its laboring. It may not chatter but its getting close to it. If you know your lathe, you'll see/hear/feel this within a few seconds of engaging the cut.

The only way to know how your lathe reacts to a cut that is too big for it is to push it until you reach it. Trust me; you'll know it when you get there.

I also happen to agree with Ken - the tools you use make a big difference in how aggressive you can get with a cut. If I need to maximize my depth of cut, I reach for a HSS tool ground to reduce cutting forces in the material I'm working with and I reduce my lead angle to keep those forces as low as I can. I'm sure others have their preferences and approaches.

 

[ddickey]

Thanks guys.

 

[4GSR]

This is a very good question in a way - how do I know if I'm overloading my lathe? In the old days, the idea was that a lathe should work as hard as it could; push it until it groans and then back off a tad. ......snip.......

Back in my earlier days of metalcutting, if the lathe was not groaning, you weren't taking enough of a cut! But I got wiser over the years too, back off a little on speeds and feeds and depths of cut and the machines seem to last much longer too.

 

[mikey]

I agree ... too much moaning and groaning and the next sound you might hear is SNAP! To be honest, I would rather use the right diameter stock to begin with when possible so I'm not roughing so much off. Sometimes you have what you have, though.

 

[Wreck™Wreck]

I agree ... too much moaning and groaning and the next sound you might hear is SNAP! To be honest, I would rather use the right diameter stock to begin with when possible so I'm not roughing so much off. Sometimes you have what you have, though.

Can't be done if a single part has 8" and 1" diameters, if the machine does not have CSS then start slow and increase the spindle speed between passes as diameter decreases and somewhere in the middle for finishing, use as heavy a DOC as the machine and tooling will allow. If a stout machine the tooling will fail first.

 

[Downunder Bob]

I've got into a habit of using cheap carbide bits to take off lots of material then finish with HSS. For example I have 1.75" 12l14 round stock and needed to turn down a section to .875" I put in the cheap carbide bit and went at it taking a few >.125" DOC's. I don't care about the tool bit but I do care bout my lathe.
Am I doing any damage or abusing my lathe by doing this?
It doesn't bog down at all but I'm wondering if I'm stressing it more than I should.

Without knowing what lathe and motor what RPM. You say it doesn't bog down but if you are in a fairly low gear it won't bog down. At high spindle speeds that is a fairly good indicator if the machine is not complaining then it's probably ok, but at low speeds it may still overload something. You could wire your power supply through an amp meter and read the max amps on the motor plate. mark a red line on the amp meter, and don't exceed it, this will work well in your top 3 or 4 speeds,, but at the lower speeds is not so reliable..

If the machine is complaining you are probably doing some damage.