Discussion on Small CNC Mill Spindle and Axis Motor Performance

[Yukonjack]

I agree with your assessment after talking with CNCDepot about that spindle.
I'm at a crossroads. I want to CNC a PM940. PM has some 940M's inbound but no 940V's until the end of the year.
I was considering buying the 940M and making a new head.
However, the "most flexible spindle arrangement" you show above, seems like a 2-yr project with no trailblazing from anyone.
Makes me come back to why bother and just start looking for a Fadal.

Hard to believe there isn't more available to address your "most flexible spindle arrangement". Maybe because the ratio of home router to home mill guys seems to be 1000:1.

 

[spumco]

Trailblazing is underway right now.

Im working on the "drive a BT30 to 8krpm with a 2.2kw BLDC using surplus servo amp and cheap encoder" phase.

The "2 speed Pozi-drive via BLDC and OEM drive" also appears to be underway.

I've actually spun & servoed my BLDC with this drive, just not made chips on anger yet. It will be another month or so before I can report on actual in-cut performance as I've switched to LinuxCNC and the learning curve is very painful (for me).

Phase 3, depending on my BLDC performance, will be a guide to shopping for surplus (or cheap) servo/drive combos that will work with each other and various controls. I've already failed with those Siemens due to the voltage mismatch, but there are plenty of other candidates.

 

[spumco]

Makes me come back to why bother and just start looking for a Fadal.

If you've got the room, power, and concrete thickness, that's not a bad idea. But even a small Fadal 2016 is not in the same league as a G0704, PM940, or my mill. Different animal.

Given the limitations of the dovetail ways and overall stiffness, I don't understand why folks are so keen on CNC'ing the RF45's and similar. They're very good 'hobby' sized manual mills, but seem to me like a sub-optimal cost-to-potential performance choice once they are converted to CNC.

I guess it's difficult to find used 'real' CNC mills in some locations, whereas it's easy to get a PM940 delivered to your house.

 

[Reddinr]

I know it's not optimal but I've made many parts and have earned a good living in part due to the capabilities of the IH RF-45-like mill with CNC conversion kit. Not sure what is available that is significantly better for anywhere near the low price I paid for it. The larger than standard envelope of this mill has been very useful. On the other hand, if price, weight and space were no object I would like something a bit larger that I don't have to baby as much. I may start a new thread on that subject.

 

[spumco]

Not sure what is available that is significantly better for anywhere near the low price I paid for it.

That right there is a good answer to my earlier speculation/rambling. In some parts of the country you can't swing a dead cat without hitting old CNC machines - almost get them for the cost of hauling them away.

In other places, not so much. And I shouldn't have discounted the somewhat sequential budget impact of a DIY conversion.

 

[Reddinr]

Interestingly (maddeningly), my mill X axis started missing steps today. I ran 24 parts with some simple profiled holes and about half of the holes on some of the boxes were off in X by about 20 mil. Fortunately, that didn't ruin them because they were just conduit holes in plastic cabinets. Looks like I have to troubleshoot that. This is the first problem I've had with the electronics even though it is a Mach 3 lash-up of 3 or so breakout boards on two parallel ports.

It might be time to upgrade my controls.

 

[spumco]

In conclusion, I see no advantage to using a servo or BLDC motor for a spindle drive when a standard induction motor is less expensive and easier to control with inexpensive hardware.

Duh, I should have listened to Jim.

I'm abandoning my attempts to use a servo drive and BLDC as a spindle motor. Long story short... I want my mill back and while fiddling with various combinations of motors and drives has been educational, I can't say it's been productive.

I'm quite sure there are AC servos and BLDC motors out there that would work fine, but everything I've got on hand (or returned) isn't doing it for me. And everything I know will work is too expensive to justify.

So... back to a VFD and an induction motor. I'm thinking an induction motor is better for a spindle due to the inertia mismatch issue with PM servos - but I could be wrong.

Remember that Fanuc A06B-0851 I joked about earlier?

I stumbled across a unicorn on Friday. It fits, mostly, and eliminates the need for a reduction or overdrive.

Brand new, still in the Mitsubishi crate. It's a 2002 model (motor plate is from internet) but appears never to have been installed. Spins up fine (open-loop) with my 1.5kw VFD on the bench.

VFD is on the way, as is a normal encoder and QD bush to fit the shaft. Came with an oddball Tamagawa 15v magnetic encoder that simply looks too fussy to re-use.

Plenty of electrical enclosure work and rewiring to do, but I'll report back when I've got something interesting.

-Ralph

 

[macardoso]

My jaw is on the floor and my heart full of jealousy!

If you don't mind sharing, what did you pay for it.

 

[spumco]

There was this sale at HGR...
I think it was $112.00 after taxes.

You can work out for yourself how long I agonized over the decision.

 

[macardoso]

There was this sale at HGR...
I think it was $112.00 after taxes.

You can work out for yourself how long I agonized over the decision.

AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH jealous