Can I get some help with speeds and feed rates for steel?

[slashmaster]

I was just trying to cut a groove in same angle iron with a 4 flute bit and one of the tips of a flute chipped off. I guess this must mean my feed rate was too high right? I was spraying liquid wrench on it to lubricate it but it was smoking in low gear at moderate rpm so guess I can't mill steel fast without coolant can I?

[Geof]

Can you be a bit more precise than 'moderate rpm', 'feedrate too high', can't mill steel fast'.

What is your cutter diameter, what was the rpm, what was the feedrate, is this a manual machine?

[slashmaster]

Originally Posted by Geof Can you be a bit more precise than 'moderate rpm', 'feedrate too high', can't mill steel fast'. What is your cutter diameter, what was the rpm, what was the feedrate, is this a manual machine?

It was 1/4" diameter, don't know exact rpm but was maybe 200-400 when it chipped. Yes it is a manual mill right now.

[Geof]

I forgot to ask what type of cutter, HSS or carbide but I suspect carbide if you chipped it.

Mild steel can be machined at 400 fpm, or faster, with carbide and for a 1/4" cutter this is around 5000 rpm. Using HSS the speed can be up to 200 fpm so obviously you were well below the maximum cutting speed.

It is possible you were cutting a bit deep, you don't mention what depth you were cutting and it is likely you were feeding too fast and not evenly enough. It is very difficult to keep an even feed with a manual machine and it is easy to chip carbide tools because you are feeding jerkily.

Some guide lines are do not go deeper than around 40% of the tool diameter, try to feed so your cut per tooth is around .001" and try to get the speed up close to what the cutter can be run at. Coolant is not always helpful because it can thermally shock the tool when it is only applied intermittently, sometimes it is better to use a compressed air blast to clear chips and give some cooling.

[slashmaster]

Thanks Geof! The endmills are Titanium coated HSS. So I guess that would mean this particular bit could go 2500 rpm but only if I have flood coolant?

I don't believe I was cutting too deep, I had planned to cut through that 1/4" steel with several passes but maybe one of the passes was deeper than I thought? I just realized something though, one of the T nut bolts for the vice was loose so maybe the vice jerked up from the table? Is it only carbide I have to worry about spinning the cranks jerky like that? Now when you say to try to get the speed close to what the cutter can be run at you mean only if it isn't smoking the oil I'm spraying on it? Because that's why I turned it down.

Originally Posted by Geof I forgot to ask what type of cutter, HSS or carbide but I suspect carbide if you chipped it. Mild steel can be machined at 400 fpm, or faster, with carbide and for a 1/4" cutter this is around 5000 rpm. Using HSS the speed can be up to 200 fpm so obviously you were well below the maximum cutting speed. It is possible you were cutting a bit deep, you don't mention what depth you were cutting and it is likely you were feeding too fast and not evenly enough. It is very difficult to keep an even feed with a manual machine and it is easy to chip carbide tools because you are feeding jerkily. Some guide lines are do not go deeper than around 40% of the tool diameter, try to feed so your cut per tooth is around .001" and try to get the speed up close to what the cutter can be run at. Coolant is not always helpful because it can thermally shock the tool when it is only applied intermittently, sometimes it is better to use a compressed air blast to clear chips and give some cooling.

[DareBee]

Observation of speed really has nothing to do with your smoking of oil LiquidWrench penetrant really is not a decent choice for cutting fluid/oil - get some TapMagic. I will also say that jerky is not a preferred feed style.

You should be able to plunge that cutter through (like a drill) and mill your slot. A nice speed to run at for manual mill is 1200 - 1500RPM and you are going to have to figure feedrate by feel.
So... 4flute at 1200 x .001 per tooth = 4.8 inches per minute.
You could try and time yourself while cutting air to get an idea of the feedrate. Time yourself for 15seconds while cranking and get it to work out to 1.2 inches of travel (4.8/4=1.2).

[slashmaster]

Originally Posted by DareBee Observation of speed really has nothing to do with your smoking of oil LiquidWrench penetrant really is not a decent choice for cutting fluid/oil - get some TapMagic. I will also say that jerky is not a preferred feed style. You should be able to plunge that cutter through (like a drill) and mill your slot. A nice speed to run at for manual mill is 1200 - 1500RPM and you are going to have to figure feedrate by feel. So... 4flute at 1200 x .001 per tooth = 4.8 inches per minute. You could try and time yourself while cutting air to get an idea of the feedrate. Time yourself for 15seconds while cranking and get it to work out to 1.2 inches of travel (4.8/4=1.2).

Thanks DareBee,

Yeah I was thinking Liquid Wrench might not be the best choice.

If I'm not supposed to crank jerky I guess I'd better ask how tight my gibs should be? I kept making them tighter thinking more rigidity is always better. The Cranks spin about a half a turn when I try to spin them as hard as I can. Is that too tight?

[DMF_TomB]

I have found with carbide tooling and sometimes with HSS using the recommended feeds and speeds sometimes the flutes get packed with chips too much overheating the cutter and even melting the cutter.

On a machine where flood coolant is not practical, then a compressed air stream with manual applied cutting fluid might help with chip packing.

When cutting SS sheet metal I found sometimes a 2 flute endmill works better than one with more teeth especially using a small endmill to cutout a piece. Especially with slot cutting when 180 degrees of the cutter is cutting.

This is based on experience which sometimes the "book" may not mention chip packing of flutes.