Chipload and DOC for small endmills

[M250cnc]

dont let that intimidate you jonathan, in this country it could easy mean spending 15 years with a cup o tea in one hand and a fag in the other and wondering which hand to scratch your arse

Probably true in your case Mark

Phil



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[Jonathan]

Probably true in your case Mark

:rofl:

I haven't found sub 3mm tooling in high helix with a rebate on the flutes and the carbide tinies tend to be coated with other than aluminium nitride so that helps not a lot.

That sentence took me a bit of time to decipher!

Even so, I wouldn't step drill it. Presumably you've turned a blank for the pulley and removed any surface hardening from the extrusion, if it isn't cast, and there is no oxide layer to wear an inconvenient slot in the flutes. Personally I'd go for around 2000 rpm, feed it at 1 -> 1.5 mm/s on a 3 flute, start with .25mm DOC, increasing if it seems good to go.

Yes I'm using aluminum bar, not cast. I wasn't aware of surface hardening being an issue with aluminum (iron yes), however now you mention it it makes sense. One anodises aluminum to make the surface harder (or prettier), so it follows logically that the natural layer of aluminum oxide will wear the tool.

42T pulley with 0.25mm DOC and 1.5mm/s will take 170 mins. Maybe a little less if I get rid of some rapids in Gcode, but not much.
Chip thinning may enable me to run the cutter a bit faster for the same chipload a significant amount of the time. I can quite easily add that to my program.

I'm warming to the make a tailstock (anyone got a spare!) and just use slitting saw idea. I can stop the 63mm slitting saw bending by machining some 50mm steel disks and sandwiching it between those on the arbor.

Standing over it with a blow gun, a pot of Rocol RTD and a brush could be an exceptionally good idea even if this temporarily suspends tea, fags and scratching

Who says I can't drink tea whilst doing that!

[Robin Hewitt]

That sentence took me a bit of time to decipher!

At risk of sounding patronising, I suppose it would be sociable on an open forum to explain that there is a difference when it comes to aluminium :naughty:

I've just taken a picture, two 3mm cutters designed for aluminium, one ordinary, 1mm, 3 flute carbide slot drill

[blackburn mark]

indeed... i speak from experience :)

[Robin Hewitt]

Since the advent of CNC there is a lot more fag smoking, tea drinking and arse scratching time available and you probably aren't encumbered by leather gloves set in a permanent clench. You can even smoke real fags instead of rollies because you aren't depending on it going out when you suddenly get busy with monotonous regularity.

We aren't newbies, we all know the problems with aluminium are it's bad habit of clagging the cutting edge and extruding when you want it to cut.

When faced with a tiny tool we also start to get nagging doubts about being able to transfer enough power to the tip. Watts = radians/second * Nm and the more Watts the more it is going to bend and once it starts to bend significantly, the more the chance of overloading it with a dig in.

I haven't found sub 3mm tooling in high helix with a rebate on the flutes and the carbide tinies tend to be coated with other than aluminium nitride so that helps not a lot.

Add to that the impossibility of getting anywhere near the correct cutting speed. If you could do 50k rpm the enormous feed rates required to maintain a cut above collet/tool eccentricity means you know that ain't going to work.

Even so, I wouldn't step drill it. Presumably you've turned a blank for the pulley and removed any surface hardening from the extrusion, if it isn't cast, and there is no oxide layer to wear an inconvenient slot in the flutes. Personally I'd go for around 2000 rpm, feed it at 1 -> 1.5 mm/s on a 3 flute, start with .25mm DOC, increasing if it seems good to go.

Standing over it with a blow gun, a pot of Rocol RTD and a brush could be an exceptionally good idea even if this temporarily suspends tea, fags and scratching

[blackburn mark]

leather gloves set in a permanent clench

hahahahahaha!!!! i remember them
they where cold and uggly first thing on a winters a morning and you had to curl your fingers to get them in but it was allways heart breaking when you had to trade them in for a new pair :)
everyone seems to be using latex now, not the same (i must be getting old)