I'm doing some relatively fine work (0.25mm holes for example) and so I've built a high speed milling spindle for my mill. By high speed, I mean up to 19,000 rpm. It has an ER11 collet.

So far I've tried to use two types of (carbide) end mills. There's one sort readily available on Amazon which has a 1/8th barrel and quite a long cutting part (so perhaps 1mmx 20mm or so). It's not always clear if these are meant to mill metal, but some seem to be.

The other is a more clearly metal oriented end mill from APT (who very kindly suggest speeds and feeds on their site – a 1mm end mill should run at 20,000 in steel, but I guess 19,000 is close enough). The cutting part in this case is around 5mm.

I've had the joy of breaking a number of the amazon end mills and one of my two APT mills.

I can't quite work out what is the trigger for breaking and end mill. In one test I made a slot in steel 3mm deep, 1mm across and 15mm long with no problems (about 0.3mm DOC). In other tests I am less aggressive (so I think) and 'sping|' away goes the cutter.

Best success so far (relatively speaking) was cutting a 0.4mm deep slot across about 30mm of aluminium (1mm wide) with the APT cutter. This went fine (see later), but right at the end of the slot as it immerged from the metal,'Sping!', the APT one went.

One thing what was disturbing with APT one was a strong signing. If I move the bed slowly it would be intermittent (so contacting the metal, rebounding, contacting and so on). going faster the singing was consistent.

I think that this was mainly due to the stick out of the mill. The barrel is very long and hits the end of the collet internal bore. With my next one I will shorten the barrel.

I'm really looking for general advice on this. Are the cheap cutters really going to work on steel? Should I just buy lots of mills as they will break?

I should say that the mill is substantial (for a hobby – a VM32L, around 240KG) but manual, so my irregular handle turning may be a factor.

Hope this makes some sense.

Iain

Firstly, many thanks for the various answers, which were helpful.

My main take-aways were to lower the speed and DOC a bit and to avoid slot milling!

I set to and did my first attempt at what I'm (ultimately) trying to make. that being watch hands. the image below is the result.,

I ended up using a 2mm cutter for this item. The first step was to thin it down from 1mm to about 0.25 except around the boss you can see. Then to finish the rough square on the rotary table down to 2.5mm and drill the centre to 1.9mm.

Although the thickness is ended up at about 0.3mm, I@m more than happy for this as a first attempt. I had expected to use the smaller cutter to actual carve out the hand shape (which is essentially a rectangle with arcs where the boss is) but I realised I'd not got all the measurements I need on my drawing. Plus, I definitely felt that I should quite whilst I was ahead.

For those interested, I started by squaring (well two faces) some 6mm ally on the mill, then bolted it to the rotary table more or less in the middle. Then mill the centre to ensure that it was still square.

Next to make some slots to absorb any excess superglue (initially with the 1mm slot drills, but that turned out not work so well – see earlier posts!).

Deburr, clean and then stick a piece of 1mm thick 5×10 carbon steel in roughly the centre. You can see that I was quite a bit out!. Add some weights and leave till the next day.

Trim round the central boss .02mm or so oversize and down to 0.25 mm (target is 0.22, but will need polishing etc), then turn round the boss using the rotary table and finally centre and drill the boss to 1.9mm.

Given that the mill end diameter is 2mm you can see how small this is!

All in all this has gone much better than I expected. Probably next step is cut out and file to shape (with VERY fine blades) and if it's not broken by then, polish and heat treat. I suspect, however that this will not end up being the final hand – I have so MANY mistakes to make yet!

Iain

A couple of reasons. One is that a larger cutter has more force and is likely to take the piece off the superglue chuck fixture. At least it has for me in the past.

Second, the intent was (and perhaps is) to take the remainder of the metal away leaving the hand in place. Shaping this will require a finer cut than a bigger mill will do (the hand is narrower than the boss). As per the above, I've not got to that part yet

However, at least the thinning is tedious and it would be worth experimenting with a larger cutter, though previous attempts have not gone well.

Iain

HI, John.

I'm using Carbon steel from Cousins. It's available in sizes from 0.8mm and up. Carbon steel of course so it can be hardened and blues.

The actual hand is around 2mm across and 13 or so mm long. the piece I milled was about 10×20 mm for exactly that reason.

Not entirely sure how you are milling pinions with a slot drill – would that not be an incorrect profile?

Cheers!

Iain

Thanks Vic.

My last attempt (with superglue and a 4mm cutter per Jason) failed. Sping! went the part.

I'm now looking at adding some bolt downs on the piece (also per Jason). After thinking about using the centre hole as a securing point, I've decided not to as it (probably) wouldn't end up exactly centred on the bore and tolerances are tight.

Instead, I will extend the piece and bolt both ends, leaving enough clearance for the cutter (I'm going to try most of it with a 4mm and finish off with a 1mm). Oh and superglue as well. I'm nervous about using shellec (though I have some) as I would imagine that the layer of stick would be thicker than superglue and not flat. Also not sure if it would stick better than superglue.

I've re-measured the run out of my current spindle. Depending on the collet (cheap from china and AA purchased recently) and the test bar, I get unacceptable levels. 0.06mm for example near the collect and over .12 at 20mm or so.

The bearings in the spindle are current 'budget' and I've ordered some ABEC-9 ones from China. I'm trying to find some more accurate 8mm straight shank ER11 spindles (extension bars they are called), but all I can find are 0.008 mm ones. I'm unclear how this is measured – Aliexpress is NOT good at technical detail for the main part!

.005 and .003 spindles start at 10mm shanks and that won't work with my design without reworking everything (and spending more money). If anyone knows a source I would be grateful.

So the test today (if all goes well) will be with the straight mill at 2200 rpm. See how it goes!

Iain

The results of my test were not encouraging. I had bolted the raw material (roughly 30x8x1 mm) down to an aluminium fixture at each end with M3 bolts. Also with superglue underneath.

I took 0.25mm cuts with a 4mm carbide cutter at 2200rpm, thinning it down to 0.25 mm apart from a 3mm dia boss where the pivot will go (watch hand remember). Then trimmed down the sides to give a 2mm wide hand.

By the time I'd finished the trimming, the metal had lifted off the fixture (though still bolted down). I suspect that this actually happened on the thinning, not the trimming, but hard to tell with burs and suchlike.

I noted that the superglue tends to stick to the aluminium fixture and not the carbon steel material. The material has been polished flat (down to 2000 grit) and I wonder if I should score it up a bit more.

Experiments to try include less aggressive depth of cut, roughing up the surface of the steel or trying an HSS cutter and/or retrying the smaller cutters when I've improved the runout. Would shellac be a better choice?

Or anything else that you guys can suggest!

Iain