[cadguy247]

I'm new to running a lathe and had a question concerning DOC & Speeds. I have a PM10-20G lathe and I'm turning down a piece of Ø1.25 12L14 steel. RPM is set at 1990 and I'm taking a .025 DOC and I'm hand feeding it, and I'd say I'm feeding it at about 1"/min using cheap carbide inserts from CDCO Tools.

If I pushing it just a little faster, the motor bogs down.

Question is, is this normal, seems to me I should be able to get more out of this machine. Or do my numbers look incorrect? if so, any suggestions?

Thanks
Kyle

[hanermo]

Yes, and no.
You are running way too fast and feeding way too slow for 1.25", about 30 mm.
Your DOC is 0.75 mm.

I would use about 1.5 mm DOC, 800 rpm, with CCTM inserts.
My feed speed would be until the chips are turning color, and the motor starts to slow down for 1.5 kW power.

Calculate your material removal rate.
This calculator suggest 800 rpm,
SFM=315, IPT=0.00729, RPM=803, FEED=5.85

FSWizard - Free Advanced CNC Speed and Feed Calculator

I suggest your insert is negative rake, and you lathe is not big and rigid enough.
Change inserts and increase results 300-600%.

What inserts and holders ?

[Fastest1]

I do know that beginning machinists gravitate towards higher rpms than necessary to cut. In some cases work hardening the part during the cut. Try slowing down. I am not familiar with your lathe, but gear down too if possible. Should lessen the bogging.

[cadguy247]

for my numbers I used the calculator on the LMS website, but when I use the FSwizard I also get different numbers then stated above so I'm obviously punching in some incorrect numbers

However I did try 800 rpm and .040 DOC and that was definitely going to bog down if I pushed it just slightly more than I was, I highly doubt I could do .060

Could be the inserts I'm using, like I said they are these cheap inserts that came with this set I bought from CDCO Tools

When you say "gear down" do you mean change the gears in the gear box? wouldn't this do the same as changing the quick change speeds? and I would make my quick change numbers incorrect, so I wouldn't really know how fast I was running. Or am I missing something?

Thanks
Kyle

[Fastest1]

I use a 3 phase motor and a VFD along with the stock gear train. I can achieve the same rpm in many different gears. I was merely referring to using a lower gear so the motor can spin at a higher rpm where there is more available torque.