lathe feed?

hi so this is a question that might seem realy stuped but for the life of me i can't figuer it out. pritty much i have looked up some feeds and speeds online and for this task it says somthing like 500 rpm and 80 mpm but my issue is i dont know what 80 mpm (meters per minute) is on my lathe. the lathe is a colchester master mk 2 (flat top) it has a threading box on it but it gives my the unites in ether pitch or tip and i can't figuer out how to convert that to a feed.

hopefully that make some sense im realy confused so wording it all is hard.

p.s sorry for any spelling mastakes

Start by assuming it's Imperial. The gearbox will tell you the feed in inches per rev. Multiply inches per rev by spindle speed and you get inches per minute. Divide by 39.37 (40 would be near enough) to get metres per minute. Actually inches per rev is more sensible. A reasonable starter for10 is 0.004 in/rev, or 0.1 mm/rev in metric. Your quoted figures must be mm per min, not metres per min, and give 80/500 = 0.16 mm/rev, just over 0.006"/rev which is a bit heavier cut, but still sensible

m/min is usually taken as the cutting speed of the metal and has nothing to do with feed rates, you will need to divide the circumference of your work ( in meters) into 80 to get the rpm.

Feed rates on a lathe are given as mm/rev or thousandths of an inch/rev

Edited By JasonB on 23/08/2020 19:47:35

I don't know what mpm is, but 80m/min is never going to be a sensible feedrate on a lathe, or even a mill for that matter.

My advice would be to ignore information online, a lot of it is worthless and/or just plain wrong. Tell us what you want to do (material/diameter as a minimum) and I expect we can come up with some sensible spindle speeds and feeds. I would think that the gearbox on your lathe will list distance per rev in some positions, as well as tpi.

Andrew

ok i think i see i couldn't see what all the diffrent numbers ment as a metric guy i just assume all the other numbers are some form of saying a inch. i am only trying to machine some steel. but if im understanding it correctly if i have a figuer of 500 rpm and 5 ipm then i would need to set my lathe to 0.01 and for a more normal feed a 500 at 3ipm would be 0.006

It sounds like you have been looking a milling feed rates as they are given in ipm (inch per min)

What is the diameter of your steel, What grade would help, what tool ar eyou using HSS or Carbide

20mm steel and i was using caebide but i think i would like to try some hss to see if i can get a better finish

So for HSS tools a cutting speed at the surface of the metal would be in the region of 30m/min divide this by the circumference of the work ( 0.02m x 3.142) which gives 30/0.063 = 476rpm so your speed was about right had you been using HSS but was too slow for carbide that could easily take 2 to 3 times that speed.

As for feeds I tend to use quite a conservative feed and for finishing would be using about 0.06mm per rev or 0.0025" per rev and double that for roughing out. I would use the same feeds for either HSS or Carbide. Andrew would tend to go a bit more but he has a heavier duty lathe than me.

You need to make sure you use the feed lever on your lathe not the thread cutting lever as the carriage will tend to move too fast if you do

Edited By JasonB on 23/08/2020 20:56:06

ok thanks for all the help i realy couldn't figuer that out. ill give that feed a go and see how it turns out but now i under stand the maths a bit so many thanks for that. one last thing what would you recomend if it was aluminum and not stee; (same size)

Of course it depends upon the exact type of steel, but as a starter, with insert tooling, I'd be running at 1200rpm and 0.1mm/rev for finishing and 0.2mm/rev roughing.

Andrew

Postscript: My lathe doesn't run fast enough to use recommended surface speeds on 20mm diameter aluminium. I might up the speed to 1700rpm but keep the same feeds. I would change the insert to a CCGT aluminium specific one.

Edited By Andrew Johnston on 23/08/2020 21:35:42