APT High speed, high hardness end mills - anyone used them?

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Originally Posted by Muzzer

Perhaps I'm missing something but it looks to me more like a job for the lathe (to make the fundamentally cylindrical body), followed by the mill (to position and drill 4 holes), then bang some pins in the holes. How were you planning to use the end mills?

304 isn't actually very hard (typically HRB 70 ie it doesn't even make the bottom of the HRC scale) - and being stainless you can't through harden it either. Machineability is different to hardness. Some form of carbon steel would be a better, allowing you to machine it easily and then harden it with a torch and a bucket of water. Then you'll get something nearer HRC60.

If it's an emergency and you are short of carbon steel, how about using an old cold chisel, crowbar etc as a donor. Cut a bit off with an angle grinder, heat it up to a cherry red and let it cool. Then you should find it easy to machine. It's easy enough to harden up again using the bucket of water etc. You can get tools like this at Aldi etc for peanuts if you don't have any.

While you are figuring this out, you could be letting some penetrating oil slowly do its business....

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Thanks for the input guys. Yes, I was looking to do the counterboring on the lathe, then start the 4 pin holes on the CNC, followed by drilling to full depth (cobalt drill, thankfully I have some from the previous project). The other task for the CNC is to cut a hex on the other end of the tool to put a spanner on. Sadly I don't have anything carbon steel of suitable diameter that could be sacrificed, about 18mm seems the biggest and it's far from straight. Normally it wouldn't be a problem, I'd go round to the local agri engineer and scrounge a bit - but of course things are not at all normal at the mo, and the nearest town is a bit away - not that I'd want to go there anyway. I do see one or two eBay metal traders still functioning though so if I can get by for a few more days of topping up the offending tyre that might be the way to go.

It would be interesting to know if anyone has experience of using these cutters anyway (they're 4 flute on a 1.8KW spindle Jazz
), they seem a bit of an oddity, but could be useful for other stuff as well. The high RPM is a bit unusual, and I know I'm going to have to keep on feeding steadily as discussed before; I might just do a test cut with a 0.5mm DOC (enough to undercut the hardened zone) and see how it goes.

don't think the body needs to be anything exotic, Mild steel would do and you could case harden the hex, make your pins out of silversteel then harden and temper. what diameter/length stock are you looking for ?

It would need to be 25mm/1" diameter to give enough meat around the pins and maybe 28....30mm long?

You have a PM
Mike

So I thought I'd do a test cut on an odd bit of steel to get a feel for what these cutters can do. The 6mm seems happy at 10mm/sec and 0.5mm DOC and gives a decent finish:
Attachment 27819
This means it'll take a few of minutes to cut the hex on the end of the piece, as I've only one cutter I might drop the feed back a bit - what's an extra minute on a one off job? It's not fast in the grand scheme of things, but it's interesting to know the machine will cut harder stuff, even if slowly.

Do you want it tonight ?

After a couple of delays due to other stuff I finally had the opportunity to have a go at it today, and I have to say I'm impressed with the APT cutters. Sequence of machining was:

1) Turn down outer of bar to size ont' lathe, spot drill either end for centering.
2) Peck drill pilot holes for the 4 pin holes on the CNC, 4mm cutter.
3) Transfer to drill press and drill pin holes to full depth.
4) Drill a 10mm centre hole for the recess (lathe) - this made the subsequent milling much less arduous.
5) Enlarge centre hole & machine counterbore on the CNC - I didn't do this with lathe as my boring tool was a bit shagged.
6) Flip it over and machine the hex at other end.

I had to quickly turn a couple of pointy things that fitted into the collets to achieve the centering, but they'll be useful in the future no doubt. Seems to have turned out OK, accuracy is fine (apart from a small centering error on the centre hole) and the finish is pretty good -not that it matters really, it's only a tool - but nice to know for future work.
Attachment 27866
Attachment 27867
Things that I've learned about the cutters are:

1) You need a good lot of coolant when using them on steel!!!. Thankfully the pump on my mister has quite a range and fairly gobs it out when you turn it up - just need to sort out some sort of drain/recirculation to avoid puddles on the floor now :whistle:
2) The stated RPMs on the APT site are OK for edging/shallow surfacing, but for anything deep & confined you need to take them down a fair bit: I ended up with 14K on the 4mm when drilling and it sounded fairly happy.
3) Although it seems to be possible to press on with a reasonable feed rate in X and Y, the Z plunge rate has to be far less.

But all in all these cutters are a useful thing - although you might have to take things gently, being able to machine steel on a DIY machine (made of aluminium!) is obviously useful. I'll get a few more next time I'm ordering from APT and maybe do some tests to see how hard they can be pushed.
PS thanks to Mike (Mekanik) for the bit of steel :-) )