Spindle Motor Recommendations

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jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

martyscncgarage wrote: Mon Mar 29, 2021 10:10 am If you had more head weight you either counter balance it or use a stronger motor on the Z axis.
I would like to hear/see more success stories shared about users replacing their spindle motors successfully with Servos and their experience.
I think the motor on the z axis is going to be powerful enough for the 27 lbs servo motor (especially once I loose the BLDC driver and control panel). In finding used motors I bought very powerful ones for fairly cheap (I got three of these motors for about 250 each: https://www.teknic.com/model-info/CPM-SDHP-3421P-ELN/). Got lucky there. Right now with everything as it is the z axis motor on rapid moves is using about 30% of available power according to the clearpath software. If the motor isn't up to the task, I could replace it with a more powerful one without too much trouble. I would prefer not to go counterbalancing just for space behind the mill, but could if needed.

(edit: after looking at the available motors I think I would actually just build a belt drive reduction if I needed more torque. The motor I have can spin at 3k rpm and I am using nowhere near that. I could belt reduce it to 3:1 or even 4:1 and still get the rapids speeds I have now (3000 mm/min - 118 ipm)

Doing more and more research into this I think I am going to go the servo route. It seems that it will be about the same amount of money, slightly more constant power, way more peak power, all in a smaller, lighter form factor.

I am still waiting to hear back from Teknic (most of this research happened over the weekend), but if I do decide to go this route I will be sure to document it well and report back!
jlchapman
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Re: Spindle Motor Recommendations

Post by jlchapman »

Jpmsteadi,

Here is the ultimate extreme high dollar solution. https://www.youtube.com/watch?v=WagTkJSxt3c&t=2070s

Jerry
jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

I have watched his videos and love the idea of that larger spindle. a) quite expensive, b) I would have to get all new tooling holders. Not a huge deal, but certainly not ideal. and c) I like the idea of being able to belt the motor up or down depending on if I am doing aluminum or steel. I would love to try doing some titanium as well at some point. having all that big torque down low for those materials would be nice.

I had initially considered it, but I am trying to keep the value proposition down some. At some point it would just make sense to sell the machine and get a better base for a conversion or a proper cnc machine. Knowing what I know now and knowing how much I have enjoyed getting into cnc and the parts I want to make, if I could go back in time I wouldn't have bought this machine. But thats how learning works! I am also super pressed for space in my current setup, so the small size is useful.
jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

I was falling asleep last night my mind wandering on this upgrade. I knew I had to be missing something. I was. I don't think there is enough room in the top of the head to allow a large enough pulley to get the RPMs I want from the servo motor. Given that I would like 10k rpm and that motor only spins at 2400 on single phase that ends up being a 1:4 ratio pulley. Given that there is a quill and drawbar and whatnot I think it would be hard to get a smaller pulley than 2" on the spindle. That gives me an 8in pulley on the motor. No way is that going to fit up there.

That got me thinking on the whole spindle conversion as well. As with many projects I start I want to "do it right" (or as right as I know how at the time) and so it snowballs into being more expensive that I initially had hoped. I think for this mill the least investment that will do the job is the right move. I have found a new old stock teco VFD for under 100 dollars and a suitable light-ish 2 hp motor for about 250. I think I am going to go that route and save my money for other things.

I will still post about the upgrade and whatnot on this thread. I know there are quite a few PM-728VT owners out there and I imagine many of them will run into the same spindle issues I have.
tblough
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Re: Spindle Motor Recommendations

Post by tblough »

Baldor Inverter-rated motors have a 6000 rpm max rating. I have a IDNM3661T 3.0 Hp on my lathe and a IDNM3587T 2.0Hp on my mill. I'm actually under-driving both (lathe spindle 4K, mill spindle 5K) for a little more low-speed torque.
Cheers,

Tom
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I have CDO. It's like OCD, but the letters are where they should be.
martyscncgarage
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Re: Spindle Motor Recommendations

Post by martyscncgarage »

I used motors from TVT America http://www.tvtamerica.com/Metric-AC-Mot ... e-atex.htm
They are good quality. Their support is good. They will answer your questions.
You MUST ask as Tom pointed out, WHAT is the MAX RPM the motor is rated for. Then you will know how much you can overdrive the motor.
Most motors can have their RPM doubled, but you need to check with the motor manufacturer.
If you went with 240V input, and you really want a servo motor, DYN4 will drive their servos to about 5K RPM, you could then use a 1:2 drive belt system. (Personally, I didn't have much luck using an AC servo motor as a spindle, but it could have been my lack of further testing and tuning)

If you want to put an encoder on said spindle, you will be hard pressed to find an inexpensive one. Tom can point you to his sources.

You mentioned you bought new bearings, what RPM are they rated for? There might be a little more at play to a 10Krpm spindle cartridge, like clearances etc.

You will want to consider a VFD with SVC control too to help with low rpm torque too.

My .02 fwiw
Marty
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jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

Thank you both for so much data! I appreciate it!

The bearings I got are all rated between 12k-18k, and P4 precision

I am by no means tied to a servo on the spindle, just a route I was checking out. I just want it to be better and work, which I think means going the route of least resistance: VFD with a 3 phase drive.

It seems based on most of my research that the motor will generate its peak power at the 60hz (in the US) speed, so for a 4 pole motor generally around 1750 and for a 2 pole generally around 3600. Given that I want such higher spindle speeds and that 90% of my work is in aluminum, my thought is to go with the 2 pole at a 1:2 reduction pulley ratio, giving me right at 6-7k max power which is in the roughing range I am looking for in aluminum and being able to easily go up to 10k for the smaller tooling. My thought would be to also have a 2:1 pulley as well when doing steel or the like to be be able to get that max power at 1750 rpm and still be able to spin up to 5K.

It seems like going with a 4 pole motor while it would give me more toque down low, would start to taper off at the high end sooner (or require a bigger pully ratio)

Thoughts on my logic here?
jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

I just got back home this past Saturday and I was excited to dive into the spindle motor upgrade. I had seached eBay for quite a bit while I was away for work and ended up with a used like new marathon 2hp motor and an FM50 2hp single phase VFD.

Thankfully I got quite lucky with the motor and the pulley that came with the PM 728VT: the key was the same width and the shaft was only about 1.5mm bigger. A very easy job to just bore out the pulley to the right size.

I made two adaptor plates for the motor to use the same mounting bracket for the stock motor. Fairly simple as well.
IMG_20210531_162903_01.jpg
I also 3d printed a top fan shroud for a 22w 120v fan for cooling. It is the blue thing in the picture:
PXL_20210602_174537330.jpg
The new motor makes a WORLD of difference. I can actually get cuts that actually take enough cut and doesn't just rub. Literally cutting twice as fast. And drilling is actually doable without a ton of really tiny pecks.

I went from doing a 3/8" three flute YG1 end mill running a fusion adaptive at 10mm depth of cut, 1.8mm width of cut, and about 800 mm/min speed and the motor was audibly bogging down. With the new motor I am doing the same width and depth, but at 1600mm/min and the motor doesn't even seem to care.

The old motor also topped out at 4250 rpm while the new one can get me 7000 rpm, so much nicer for smaller end mills.

Overall very happy with the conversion and by waiting and shopping around I was able to do it for not too much.
martyscncgarage
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Re: Spindle Motor Recommendations

Post by martyscncgarage »

Nice work.
Just make sure the motor is rated for the RPM. Is that 7Krpm name plate or what you are running it at now?
There is a physical design RPM.

Marty
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Re: Spindle Motor Recommendations

Post by tblough »

That's a 3450 nameplate motor. I'd be careful running it much more than that. 1800 rpm motors can usually get away with running double the nameplate because manufacturers usually make a 3400 rpm motor with the same components.
Cheers,

Tom
Confidence is the feeling you have before you fully understand the situation.
I have CDO. It's like OCD, but the letters are where they should be.
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