View Full Version : Tiny tool feedrates

Robin Hewitt
06-09-2010, 10:56 PM
Just musing on trying to use tiny tooling in my mill. Feel free to chip in and explain why I'm bonkers, won't worry me if nobody does :smile:

I want to play at making injection moulds in aluminium, I want a nice clean finishing pass with cutter diameters down to around the 1mm mark. Unfortunately, 200 ft/minute then requires 19404 rpm :eek:

I can wind my poor old mill up to 2000 rpm but I can't say it enjoys it. Ten times that is cloud cuckoo land. The best I can offer in my comfort zone for a long cut is 1200 rpm.

Too slow a feed rate invites chatter, I think the tool rounds out the cut entry, rubs for a few teeth then suddenly takes a biggy so vibration can set in. Too fast and the tool will bend leaving an unremoveable excess. Have to do some test pocketing.

Gut says rough it out to 0.25mm under with a 3mm cutter, then finish with the 1mm and a feed rate of 1 mm/second giving a cut depth of 25 microns per tooth. When it reaches a 3mm corner the tool will suddenly start removing 0.45 rather than 0.25, so probably best to get in a good supply of votive candles.

I will spiral down on the finishing pass so there are no plunges to leave marks.

There's a 2 degree draft angle. I can either use a 2 degree tool and let it rub, which could introduce chatter, or use a ball nose and accept a scallop. A 0.25mm descent per lap would leave a 12 micron scallop which is right on the tolerance of the machine and hopefully easy to polish out.

06-09-2010, 11:22 PM
I can wind my poor old mill up to 2000 rpm but I can't say it enjoys it. Ten times that is cloud cuckoo land. The best I can offer in my comfort zone for a long cut is 1200 rpm.

That's interesting...I'm pretty sure we both have the same milling machine (I posted a picture of mine recently in my build log) and I've had mine on the maximum, 2150rpm iirc, for the past few months! So am I damaging the machine, or are the bearings in mine better (it's not overly noisy)?

1mm cutter, how many flutes? If it's 3 flute carbide then I also make it 57mm/min..so yes 1mm/s when cutting a slot. However if you're only taking 0.25mm off then you can up that to 2mm/s (again assuming it's 3 flute) because it's less than half the width of the cutter etc. Still going to take forever...

Where are you getting these small cutters out of interest? Why do you need such a small cutter...it must be a REALLY fine mould?

Robin Hewitt
07-09-2010, 12:08 AM
2 flute is more rigid than 3 flute so easier to find in small sizes.

Drill Service have slot drills in silly sizes and good prices. I have to start somewhere in my quest, might as well be budget tooling. They may be crap, I'll let you know.


Also sampling their small fishtail point slot drills, never tried fishtail, sounds like a way around the centre cutting scrape line.

I did put the mill on top speed once and started winding the spindle up towards 4000 rpm but chickened out at around 3000. It could probably do it, but not in my comfort zone for a long haul, I am not very brave. Besides, the faster you spin them the faster they wear out.

Robin Hewitt
07-09-2010, 12:19 AM
Why do you need such a small cutter...it must be a REALLY fine mould?

Not really, I'm trying to recreate a couple of moulds I already have that are showing signs of wear. I don't want to spark erode 90 degree corners and a 0.5mm radius looks like a credible approximation on the drawings. I can hand grind 0.5 to square if it looks naff but I'd rather not.

07-09-2010, 10:25 PM
I use a lot of these disposables for drilling http://www.mscjlindustrial.co.uk/CGI/INPDFF?PMCTLG=13 Page 9 FC3 Hertel longs cheap 2.2 each region and last surprisingly well compared to more expensive 6 to 7 ones up to 6mm.
1mm scary but used to use the 1.5mm longs ground away at shank on Dickson round action tumblers, Robin will know what i mean tool steels.

Robin Hewitt
07-09-2010, 11:18 PM
Robin will know what i mean tool steels.

Don't overestimate me, just found that drill service do 1mm in 2, 3, and 4 flute, all at the same price. Shows how much I know :rofl:

If you think 1mm is scary, howabout this in 1.2mm?

08-09-2010, 01:43 PM
Cutwell Tools have an offer on a the moment for 3 flute K2 coated carbide throwaways. - http://www.cutweltools.co.uk/home/milling-cutters/k2-coated-micrograin-solid-carbide

They rang me yesterday to see if I wanted any, I am sure she said something like 1.80 each any size from 1mm-6mm.

If you do call them then whatever you do don't give them your phone number as they keep ringing you all the bloody time.....

Robin Hewitt
08-09-2010, 02:48 PM
Bravo Steve :smile:

Effectively stub length rib cutters at around the 15-25 mark, about half normal price, conventional or ball nose.

That opens up new worlds of possibility, have to get me some of those :smile: :smile: :smile: