Setting up a Mini Mill & Stuart 10V Machining

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ron Laden on 12/05/2020 05:37:54:

This morning just as a quick test I put up a piece of 8mm gauge plate on my SX2P and tried a 0.5 mm deep edge cut using a 10 mm 3 flute HSS TIAIN cutter from the ARC premium range.

No issues at all the mill sounded and felt fine which is something I always go by. I went with 1250 rpm and a steady not too fast feed. I tried it at slower speeds but it was best at 1250. A picture below of the finish which I can't detect with my finger nail so good enough I think.

p. s. I forgot to say going by the hanwheels my machine has 0.2 mm backlash which never gives me any problems and with the DRO, s I am lazy and tend to ignore it. Also I sometimes climb mill for a better finish but nothing too heavy. I guess I really should try to reduce the backlash before it catches me out.

Edited By Ron Laden on 12/05/2020 05:58:51

Edited By Ron Laden on 12/05/2020 05:59:52

Thanks Ron. Looks good. I'll do some further tests when I get my new end mills. They've not arrived yet.

[JasonBModerator @jasonb]

Yes thanks for posting that Ron, goes to show that the Premium cutters are worth that bit extra both in the finish they give and the ability to remove a bit more metal on each pass without the mill complaining. When I did those videos I deliberately used a budget cutter as that is what a lot of new people to the hobby tend to buy.

[Dr_GMJNParticipant @dr_gmjn]

So the small fly cutter holder arrived today. I put my Sandvik 8mm left hand tool holder in it, fitted with a DCMT 070208 insert for steel, and had a go at fly cutting for the first time. Must say I was really happy with the results, finally a bit of progress. Workpiece was the same mild steel I've been using for the vice clamps. I went up to 0.5 mm cut depth with no issues.

The only slight problem was vibration due to the tool holder being long. I ground it down a bit and that resolved that. The grub screws in the holder appear to be made of cheese, so having got the tool well and truly stuck, I spent a good 30 minutes drilling them out and replacing with caphead screws, which was fun.

Missed the postman due to work, so the milling cutter test will have to wait, but in the meantime, for the 10V castings, what do folks recommend for facing: milling or fly cutting? I did get some DCMT070208 inserts for iron too.

Thanks.

[JasonBModerator @jasonb]

I usually use a multi tooth cutter to surface cast iron bit the insert won't know that it's on its own so why not give that a try, at least if there are ant hard spots you won't blunt your HSS cutters when they arrive

[Dr_GMJNParticipant @dr_gmjn]

Posted by Dr_GMJN on 12/05/2020 13:22:37:

Posted by Ron Laden on 12/05/2020 05:37:54:

This morning just as a quick test I put up a piece of 8mm gauge plate on my SX2P and tried a 0.5 mm deep edge cut using a 10 mm 3 flute HSS TIAIN cutter from the ARC premium range.

No issues at all the mill sounded and felt fine which is something I always go by. I went with 1250 rpm and a steady not too fast feed. I tried it at slower speeds but it was best at 1250. A picture below of the finish which I can't detect with my finger nail so good enough I think.

p. s. I forgot to say going by the hanwheels my machine has 0.2 mm backlash which never gives me any problems and with the DRO, s I am lazy and tend to ignore it. Also I sometimes climb mill for a better finish but nothing too heavy. I guess I really should try to reduce the backlash before it catches me out.

Edited By Ron Laden on 12/05/2020 05:58:51

Edited By Ron Laden on 12/05/2020 05:59:52

Thanks Ron. Looks good. I'll do some further tests when I get my new end mills. They've not arrived yet.

So I got the new end mills from ARC today. Again, face milling is fine, but there's no way side milling is right. even a 0.1mm cut in 15mm thick steel is hopeless – noise, vibration, terrible surface finish. I tried it again with a Sandvik cutter, and it's the same. I'm wondering if it's the material I'm trying to cut. Pretty sure it's mild steel – I've made 4 vice clamps now, with no real issues with fly cutting, face milling or drilling. As soon as I switch to side milling, there's just no way it's having it. All axes are locked apart from, in this case, y. Tried changind speeds and feed rates, to no avail.

Thanks.

[Martin ConnellyParticipant @martinconnelly55370]

You need to have the quill locked and the spindle bearings properly adjusted to make these type of cuts. The head should be as low as possible with minimal quill extension.

Martin C

[Dr_GMJNParticipant @dr_gmjn]

Posted by Martin Connelly on 14/05/2020 12:45:11:

You need to have the quill locked and the spindle bearings properly adjusted to make these type of cuts. The head should be as low as possible with minimal quill extension.

Martin C

Thanks Martin, but there is no quill extension to lock on the SX2P. As I said, the head (z-axis) was locked, as was the x-axis.

I was using an ER25/R8 collet chuck, with the cutter inserted as far as possible. The workpiece was in a vice, so head height was also minimised.

Spindle bearings? No idea. There is no discernable play in the spindle, but I think there could be an issue with them judging by the noises now coming from that area. Something tells me it's not that though. It's not rough, but I think rather some plastic part is rubbing somewhere.

I can't find any strip-down guides to the SX2P, but I'm sure it's not rocket science. Since it's only been used a few times, I've contacted ARC, so we'll see what they say.

[Ron LadenParticipant @ronladen17547]

Just out of interest clock the taper on the inside of the spindle, my SX2P has 0.01mm runout and its done a lot more work than yours. You should be seeing similar or even better, though I suspect 0.01mm is pretty darn good for a small hobby mill and probably wouldnt get any better.

Ron

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ron Laden on 14/05/2020 16:58:50:

Just out of interest clock the taper on the inside of the spindle, my SX2P has 0.01mm runout and its done a lot more work than yours. You should be seeing similar or even better, though I suspect 0.01mm is pretty darn good for a small hobby mill and probably wouldnt get any better.

Ron

Ron,

This is the maximum runout on the inside taper of the ER25 collet holder (not the spindle):

Call it 0.02mm?

Again, I tried side milling. This is the setup – everything tapped down and tightened:

Again, the result of a 0.1mm cut is akin to a very loud tuning fork. The vibration/chatter results in a swirly pattern on the workpiece (not too obvious here TBH):

This sample was marked "unhardened tool steel", and was fine for face milling, drilling, fly cutting etc.

Anything deeper than 0.1mm is unbearable – at least for anyone with a shred of mechanical sympathy.

Anything less than 0.1mm and I might as well use sandaper.

I'm wondering now if I've somehow changed the resonant frequency of the column by shimming it. To be fair, the shims are pretty narrow, and some are just in the corners. The deflection under hand load doesn't seem excessive compared with what other folks have said though. Then again I'm running out of ideas.

[JasonBModerator @jasonb]

As I said earlier lower the tool so you are cutting towards the top of the flutes as that will help,

What diameter is that cutter?

Try some mild steel as that tool steel could be part of the problem.

What is the runout of the tool close to the collet?

[Anonymous]

I very much doubt the problem is anything to do with resonance. Chatter is all to do with the cutting process, not the resonant frequencies of the machine tool. Chatter does not imply resonance of the tool or workpiece, but unstable cutting conditions.

I'd agree with JasonB. The cutter looks blunt to me. A shallow cut with conventional milling on unknown material with a blunt cutter will almost certainly lead to rubbing and then cutting, and back to rubbing. A slow feedrate will make matters worse.

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Dr_GMJN on 14/05/2020 22:42:34:

[…]

Again, I tried side milling. This is the setup – everything tapped down and tightened:

Again, the result of a 0.1mm cut is akin to a very loud tuning fork. The vibration/chatter results in a swirly pattern on the workpiece (not too obvious here TBH):

This sample was marked "unhardened tool steel", and was fine for face milling, drilling, fly cutting etc.

[…]

.

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.

[Martin ConnellyParticipant @martinconnelly55370]

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

[Ron LadenParticipant @ronladen17547]

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.

[JasonBModerator @jasonb]

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.

[Dr_GMJNParticipant @dr_gmjn]

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.

[Martin ConnellyParticipant @martinconnelly55370]

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

[JasonBModerator @jasonb]

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.

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 15/05/2020 16:11:52:

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.

[Ron LadenParticipant @ronladen17547]

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

[Dr_GMJNParticipant @dr_gmjn]

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

[Ron LadenParticipant @ronladen17547]

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

[JasonBModerator @jasonb]

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.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Dr_GMJN on 15/05/2020 14:43:46:

[…]

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

.

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

[JasonBModerator @jasonb]

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

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