Discussion on Small CNC Mill Spindle and Axis Motor Performance

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.

Wow. I wish there was industrial surplus local to me like there is in the states - I'm jealous. Looking forward to seeing your progress.

On a side note, I'm still trying to work through some issues with my spindle. The good news: SKF TR bearings seem to be holding up so far. I've been running them pretty hard without seeing excess heat buildup (measuring 50-60C on average when running through programs). The bad news: I've seized the small bearings on the idler tensioner and as a result burned through a belt. At 8000rpm spindle speed, the idler is spinning at roughly 18krpm. The bearings I seized were rated to 45krpm but the dynamic load rating had essentially no factor of safety in my design. I'm in the process of redesigning the idlers with more capable bearings - small oversight on my part.
 
Any room for larger idlers? At that diameter even 1/2" larger would cut the bearing speed down a meaningful amount.
 
Any room for larger idlers? At that diameter even 1/2" larger would cut the bearing speed down a meaningful amount.

Yup, that's the plan. In addition I stepped the bearing sizes up to 26mm from a .75" which triples my dynamic load rating while maintaining the same reference speed limit.
 
Sounds like yer in bidness!

Don't know if you're using sealed or shielded, but shielded tend to run cooler as there's no shield contact with the inner race.
 
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.
1.2 seconds?
 
Wow, it's been a while since I've followed up with this thread! Been super busy, but my mill has been reliably trucking along making lots of parts with the new spindle configuration since I last posted. I have probably put over 100 hours on the machine with the new BLDC spindle motor and I haven't had many, if not any, issues.

I promised a video of my spindle motor on the PM25 mill and although I don't have a video specifically showing off the belt changer, I did manage to grab a video with my phone machining a new brake pedal when I was in the shop tonight. Thought I would post it here to show off the capabilities of these small mills with an 8000 rpm spindle. In retrospect, I probably could have pushed my 3/8" endmill harder without issue... My typical F360 settings for it is 8000 rpm at 0.5" DOC, 0.05" WOC and 100ipm. The part in the video is roughly 12"x4"x0.875".

Ignore the weird color hue of the video... the LED's in my enclosure appear purple in photos and videos for some reason.



PXL_20220124_021619194.MP.jpgPXL_20220124_022415386.MP (1).jpg

-Adam.
 
Ran across this guy today. Might be the lowest cost / highest HP AC servo that can do 5000 rpm in the hobby market.

$385 for motor, drive, and cables (1.5m). 5000 rpm, 3.2Nm continuous, 9.5Nm peak. 1000W or 1.34 HP.

This would be plenty sufficient for a PM25 or G0704 sized machine in a 1:1 belt configuration.

 
Interesting reading here guys. I have a Tormach (just a 440) and I sure wish I have a higher torque motor. Now I am not nearly as versed as you guys at CNC, only about 2.5 years. I run into the most issue with straight drilling. If I'm not short/slow pecks, I can stall my motor. I use yg-1 luma-power and altin coated yg-1 for steels. I really only run SS, A6, (probably more than my mill was sold as being able to handle, but since I don't KNOW that, it hasn't slowed me down. I feel my tool paths are really limited now that F360 has cut us cheap users ($400+ a year) I have sat through so many of their classes just to find at the end, that is an add on at another $1600 a year. I hope you guys continue your convo here as I'm sitting back and taking it all in.
Related note, anyone know if it possible (without extensive mods) to increase my motor setup? It does have a <5000 rpm pulley and a 5000~10K pulley. That drilling issue is really a huge problem for me, obviously on the slower/torquier pulley.
 
Interesting reading here guys. I have a Tormach (just a 440) and I sure wish I have a higher torque motor. Now I am not nearly as versed as you guys at CNC, only about 2.5 years. I run into the most issue with straight drilling. If I'm not short/slow pecks, I can stall my motor. I use yg-1 luma-power and altin coated yg-1 for steels. I really only run SS, A6, (probably more than my mill was sold as being able to handle, but since I don't KNOW that, it hasn't slowed me down. I feel my tool paths are really limited now that F360 has cut us cheap users ($400+ a year) I have sat through so many of their classes just to find at the end, that is an add on at another $1600 a year. I hope you guys continue your convo here as I'm sitting back and taking it all in.
Related note, anyone know if it possible (without extensive mods) to increase my motor setup? It does have a <5000 rpm pulley and a 5000~10K pulley. That drilling issue is really a huge problem for me, obviously on the slower/torquier pulley.

I do not use F360 and was thankful of that fact after they killed it off. I had a student license of Inventor that was still going strong until 2 years ago from when I was in college. I've since moved onto other CAD/CAM options.

I think you're going to be in a bit of a pickle with the 440 if only for the fact that you're working with a Tormach designed system, and I'm guessing they don't allow freely editing their software to deal with modded hardware configurations. I could be wrong about this of course.

One option, if there is room, is to swap the 0-5000 rpm pulley to a 0-2500 rpm. This would double your torque on the low end, but also create a gap in the 2500-5000 rpm speed band which would not be handled well by the upper pulley.

You could also swap in a motor with more horsepower/torque. Not sure what the 440 uses, but if it is an induction motor or a BLDC, then your only option would be a permanent magnet motor for the power density. You'd need to develop the drive interface and get it working with the software.

I'd also be concerned about the machine having the rigidity to use the extra oomph from a bigger motor.

Best of luck and do tell us what you try!
 
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