Spindle Motor Recommendations

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martyscncgarage
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Re: Spindle Motor Recommendations

Post by martyscncgarage »

tblough wrote: Sat Jun 05, 2021 8:14 am 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.
Exactly. Consult with the manufacturer to see what the MAX RPM rating of the motor is. Let them know you are using it with a Variable Frequency Drive and wish to increase its speed.
It "looks" like a standard duty motor, not an inverter duty rated one.
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jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

For sure! It is a 3450 nameplate RPM motor. It is inverter rated, I am running it at like 78hz to get that 7k rpm. It has a 1.62 ratio pulley on it, so when the spindle is at 7k the motor is only spinning 4350 rpm, so not too much over the nameplate. When I bought it the ebay ad said it was rated for 5400 rpm, but on the motor I can't find that anywhere. I didn't pay much for it. I am hoping by keeping it cool and only barely running it over the rated RPM I will be okay. If it ends up dying Ill replace it with a more proper motor.

It does say its inverter rated though. 10:1 VT 2:1 CT.
martyscncgarage
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Re: Spindle Motor Recommendations

Post by martyscncgarage »

Call Marathon with the model number and ask the rated RPM.
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jlchapman
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Re: Spindle Motor Recommendations

Post by jlchapman »

Hi Jim,

I really like your 2hp mod. The PM motor is really disappointing where it bogs down so much.

Are you still liking the conversion to 2hp? What about the fitment of a power drawbar, still enough room?

I'm pricing out doing the conversion to 2hp. Can you send me the part numbers of the bearings you bought?

Thanks,

Jerry
jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

Hey Jerry,

I am enjoying the new motor. It is night and day from the old one. I would say that as long as you aren't pushing the new spindle much faster than the 4250 rpm rated stock the stock bearings are probably fine. I ran them for a bit, but on longer ops at slightly higher RPMs they were getting toasty.

I just looked at the exploded view on the manual for the mill that PM provides and searched ebay for new old stock bearings of the right numbers from good manufactures (NSK, SKF, etc). Found some good deals. One thing I did do is change the deep row ball bearing on the top of the spindle (not the ones in the head, but the one the nut tightens onto to preload the main bearings) to a high precision angular contact bearing.

I haven't done a power drawbar yet, but I imagine it would be tight. Doable, but maybe not with a kit; might be some custom stuff.

If I did it again I would make a motor choice that aligns with what marty and the like are saying: make sure it is rated for the RPM you are spinning. this motor was cheap enough that I will just keep it running til it dies, but for peace of mind I think it makes sense to get a proper one (and keep it cool!)

I would also say: the head weights probably 1.5-1.75x as much as it did stock. Be sure your Z axis motor can handle it. Thankfully my motors are very strong (stronger than needed for this size mill), but steppers might have problems loosing steps if you get aggressive with rapids.

Please let me know if you have any other questions!
SpacedmanSpiff
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Re: Spindle Motor Recommendations

Post by SpacedmanSpiff »

I cannot recommend the DMM dyn4 as a spindle motor. They do not have the required tourque to be a spindle and there seems to be a quality control issue with the encoders being out of calibration. I could not get mine to run consistantly foreward and backwards with accurate rpm. GREAT customer service however.
I am now using a 3phse from automation direct with a vfd. Seems to be ace at this point.
jpmsteadi
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Re: Spindle Motor Recommendations

Post by jpmsteadi »

A bit of a 6 month update:

The motor is still going strong. Working perfectly. Been machining a ton and having the more power makes such a difference. I’ve figured I can push it even a bit more than I was. A 3/8” 3ft carbide end mill doing 7k rpm with a 2.25mm stepover and 19mm doc at 1500mm/min feed. No industrial mill, but pushing along pretty good!

I added a power drawbar a couple of weeks ago. Had to design and make a custom lever style one to work with how big the motor is, but boy it’s nice to have!

Next on the list I want to try and figure out rigid tapping. Just have to find an encoder than will withstand 7k rpm without exploding that isn’t crazy expensive.
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