Setting up a Mini Mill & Stuart 10V Machining

.

So, just to be clear: The set-up in the first picture produced the result in the second picture

... isthat correct ?

If so [and noting Andrew’s expert comment on the standard cutting behaviour], I agree that flexibility of the column mounting could be a contributing factor ... in addition to cutter sharpness & quality, speed & feed, and many more.

MichaelG.

If the debris on the table is what is coming off when cutting then you are feeding far too slowly. You should be getting long shavings from each flute on each revolution of the cutter. At about 0.125mm per flute with a 4 flute cutter that is 0.5mm per revolution. For 50mm of travel that is only 100 revolutions. At 1000rpm that works out at 6 seconds to travel 50mm to give the correct feed to cut not rub. These figures are picked for simple numbers for an example but should give some indication of how fast to turn the wheels to get a cutting action.

Shallow cuts with conventional milling are also problematic, you are trying to remove material with a starting depth of cut of zero. The chip also snaps off at the end of the cut and as a result can damage the cutting edge. This is guaranteed to start each cut with a rubbing rather than a cutting action which is why climb milling often gives a better finish and is always kinder to the cutting edge. Climb milling starts with a cut and ends with the zero thickness.

So trying to do a shallow edge cut with too slow a feed on a machine which may not be easy to do climb milling on leaves you in a dilemma. I would try pinching the gibs not enough to lock the machine but enough to give resistance to movement whilst still allowing you to turn the handwheel and try a cut using climb milling with a suitable feed rate and a small depth of cut, maybe 0.1mm.

Martin C

I could be wrong but I suspect the problem is the cutter, a bit of video below of my SX2P with some 8mm gauge plate and a 10mm 3 flute HSS cutter from the ARC premium range. With your comment about the sound of your machine I copied your 0.1mm cut for you to compare and then a 0.5mm cut followed by a 0.75mm final cut.

Speed 1500 rpm which I know is a bit fast but the mill and cutter seemed to like it, the sound and feel of the cut was better than at 1200 and with a very good finish I would have thought not much can be wrong.

Off camera I did try a basic 10mm 4 flute cutter which didnt sound too good on a 0.1mm cut though it left a half decent finish but a 0.5mm cut was a no go, sounded awful and part way into the cut is was struggling so I gave up.

Also note that Ron is cutting on the other side of the vice. I find this can often be more solid as the cutting forces push the head back down against the column in the same direction it would naturally hang. Working from the side you are can tend to lift it and if there is any slack in the dovetails you can get movement. This applies more to hobby mills with a moving head than industrial with sold heads and moving tables.

Tried again with the suggested changes.

No change though in noise and vibration. If anything the ploughed field effect is slightly worse.

I'm increasingly thinking it's a stiffness issue, so I will remove my column shims and repeat the test.







BTW it's a 12mm diameter cutter.

Cheers.

The chips are looking as they should.

I have done a quick experiment to see if I could see any difference between climb and conventional milling. This was done on a piece of 10x100mm gauge plate using a 16mm 3 flute M42 cutter with no name but says made in England on it. I used the Mach3 Mill speeds and feeds wizard to get recommended speeds and feeds. Depth of cut was 0.1mm and tooth load was 0.125mm. The result was that there is no real visible difference but the conventional milling finish was a bit rough as in it felt torn. It also had a slightly bigger burr on the top edge. The roughness felt like it would come off with a bit of rubbing with Scotchbrite.

Milling wizard page.

Climb milling in progress

Climb milling result

Conventional milling in progress

Conventional milling result

The swarf slivers are about 15mm long. The mill is a CNC mod on a round column RF45 type machine. You have to look closely to see the machined surface. The work took about 35 seconds to complete each pass.

Martin C

Time added at end.

Edited By Martin Connelly on 15/05/2020 15:08:08

Taking Martin's cutting speed that would equate to approx 630rpm for your 12mm cutter which would be worth trying as it looks like you have th emachine set at around 1200rpm.

OK. I'll try that now.

I want to do the drilling on my sole plate and box bed today, so I might leave the shim experiment until the weekend.

Cheers.

I was running my 10mm cutter at 1500 rpm and all seemed well.

This is with the lower spindle speed - it was worse than with the higher speed:

That finish is how I imagine it would look if the cause was vibration but I am guessing, I'm sure others will know.

The biggest unknown is still that bit of tool steel do you have any mild steel of known spec to try cutting? Better to eliminate that unknown before mucking about with the machine.

.

I agree ... Please see my comment on your spot-facing thread

MichaelG.
.

[ no experience of these Mills, but I did work 11 years in a vibration test-house ]

Edited By Michael Gilligan on 16/05/2020 07:29:57

I'd also suggest a sharp cutter, that one has several chips out of the edges

I’ll get some steel off EBay next week.

TBH it’s a simple job to remove the column shims and repeat the test. If it’s the same Ill just replace them.

Re. The cutter - I get exactly the same results with the brand new ARC cutter I got last week (similar spec to the ball nose), albeit that is 10mm not 12mm.

I suppose I’ll have to buy another set. Any recommendations?

Thanks.

Edited By Dr_GMJN on 16/05/2020 08:11:20

Can I suggest you go to M-machine for your steel just to be sure what you get is as ordered. Excellent service, good pricing and they carry a large selection of material. If you go to their website you can download the catalogue and you will see the various grades listed against the types of material.

The 10mm cutter I used in the video is from the ARC premium range HSS 3 flutes TIAIN coated £10.36.

Ron

Thanks Ron - I will do that.

For a test like this, on this machine, what grade and thickness of material should I get?

In other words, worst case - what should it be capable of?

I’ll get some ARC premium cutters too.

That little exercise will see my spending money for the month gone! But it’s all good fun.

+1 for M-Machine; they're one of my suppliers. Only use Ebay if you know what you're doing and are prepared for the metal quality to be poor, which may not matter for temporary fixtures.

I've had poor finishes like those shown. It's all down to the cutting tool, material and cutting parameters, especially feed rate. What it isn't down to is the rigidity of the machine. I got my poor finishes on a Bridgeport. While that isn't the most rigid of mills, it's much bigger and heavier than a SX2!

Andrew

Postscript: Get some bright steel flat (EN32B) or, if you want a slightly increased challenge and to save money, get some black (hot rolled) flat. Thickness and width aren't critical, but may be 6 to 8mm thick and whatever width will be useful. Note that bright flat will be to size, black is usually slightly over to allow for removal of the black mill scale. Learn to get a good finish on low carbon steel before worrying about testing the mill with more difficult materials like  gauge plate or stainless steel.

Edited By Andrew Johnston on 16/05/2020 09:51:27

This thread is a real education. Lots of pictures and suggestions for why certain results are achieved. For someone like me this is excellent reading, thanks all.

As for Cutters ARC's premium have been mentioned a few times in this thread and the standard length 3 flute that Ron mentions would be a good all rounder and just for risk of being called bias this 10mm 3-flute "disposable" is another alternative., I use both but would suggest you don't go at the iron castings with these until you know if there are any hard spots under the surface, keep the Tin ones for that.