spindle control on harbor freight 7x10

[tkbot47]

"Very" accurate isn't a true statement in retrospect; sorry for that. That implies close to dead-on accuracy. I should've used "fairly" or "reasonably". Very close speed control would need a servo motor or VFD.

Having said that I am getting better results than you are. I'll check mine later today & get back to you. I recently took some stuff back apart on it for some improvements but it won't take a minute to put a couple things back together enough to check spindle speed. I don't see surging with my setup. That sounds like an adjustment on the 125 board. The manual covers adjustments pretty well.

I wouldn't worry about 100 rpm since you won't get enough torque for useful work on the large diameter stock that would need that low a speed... unless you're cutting wax or marshmallows.

Thanks for checking - let me know what you find out. I'll be cutting mostly aluminum and nylon or hdpe plastic......no marshmallows for me - they don't stay in the chuck very well Not having experience with cutting threads, I'm not sure how slow the lathe needs to go to do either threading or hard tapping. The on/braking/reversing works very well.

I wonder which trim pot needs adjustment on the 125R to minimize surging, especially when it's marginal and comes and goes. I suspect that the DC motor on my lathe is not that sophisticated - it's only a brush type 3/4 hp. Do you have a suggestion for a better one, like a brushless DC? It would be nice to not have to switch low and high ranges mechanically.....I know some higher torque brushless DC motors have that capability.

[DICKEYBIRD]

I'd forgotten about the Mini Lathe having a hi/lo gear box. That'll help with low speed torque. The surging is most likely the max speed and/or accel pots set too high.

I didn't realize Mini Lathes came with 3/4 hp. I have a Baldor 3/4 hp dc motor on the ORAC & it's huge compared to the pictures I've run across of motors on Mini Lathes. Chinese horses I guess.

Small CNC lathes & threading are a skill that I'm still learning. The ORAC had Mach 3 previously & it was a PAIN to get decent threads in steel of any size with its single-pulse indexing. That's the main reason for switching to Acorn & an encoder. That should help a lot but WILL NOT turn it into a 10 hp brute lathe. I feel sure it will still be a juggling act of whether to use HSS at slower speeds or use carbide & hope everything tracks the higher speeds accurately. I'll find out if I ever get time to get back on it. The "side" jobs are eating up all my spare time!

[tkbot47]

Something else is going on. I disconnected the acorn analog output from the 240d, and ran some mdi commands and the voltage out is rock solid and dead on. When I connect it back to the 240D inputs 5 and 6, about 600mv gets added to the volts measured, and when surging is going on, the voltage varies +/- 0.1 v or so. When I switch to manual input from the pot, it is dead on again, varying from a few mv to something like 11.1 vdc. I've fiddled with the min, max, accel, CL, and IR pots, with little or no effect. Then, all of a sudden, the surging will go away and everything is solid again.

There must be some sort of coupling or interference or something going on, but right now I'm stumped. I have grounded foil shielding on all the interconnect wiring (except 110V and the motor armature wiring), and I've kept the runs of signal and power separate in the box with the 240D and 125R.

Any ideas? I don't know that it will cause issues when running, but it's irritating to say the least.

The switchable low range is indeed great for torque increase, but I can't tell CNC12 to switch the lever in the back That's why I mentioned about the brushless DC motor with a single variable range, like the slightly larger mini lathes. Supposedly they have better low speed torque without mechanical advantage.

I've dressed the wires up as well as I can, so I think I'll run for a while and try it out. I air cut some of the sample programs in CNC12, and they ran fine, switching the motor off and on when required for tool changes, etc.

BTW, in your experience, what max rpm would you think would be OK for mini lathe spindle bearings? They are standard sealed ball bearings, not tapered roller bearings. I bought a set of Timken RB's for it, but haven't tackled taking the headstock apart yet. The 240D/125R combo will drive the spindle faster than Grizzly's original controller if I want, and the motor is rated for 5000 rpm.

[ScotY]

I have a DMM servo motor and Dyn4 drive running the spindle on my mini mill. I’m still trying to get it all set up but it works well. The Dyn4 outputs an encoder signal so that makes it a little more convenient. It’s a Nema 34 frame motor and is about 1hp. The only catch (aside from the price) is the motor needs to be geared 1:1 in order to utilize the encoder output. You could use a less expensive Dyn2 drive, gear it however you want, and use an external encoder. I thought about adding one to my mini lathe but I’ve got too many projects as it is and the motor mount would take some thought.

[DICKEYBIRD]

I'm not getting that sort of speed accuracy on my G0765. I have acorn set for 100 min and 2300 max. Low speeds below 1000 are too low and high speeds are too high, ie setting 200 gives about 160 and setting 2300 gives about 2600. How can I get this more linear with acorn and 125R/240d trimpot adjustments?

Finally got a chance to play with mine a bit & check the speed accuracy. Mine is setup for 250 on the low end & 1650 on the high. It does (what I consider) pretty good. M3 S250 gets me 220 to 250 & 1650 gets 1610 to 1650. I tried a few medium speeds & they look good too. If I switch directions, the speeds are a bit higher for some reason. Not enough to worry about though.

It's really hard to pin down the exact speed since (I guess) the screen refresh rate/encoder output shows the speed numbers bouncing around in a 30 to 50 rpm or so window. I guess the XL belt drive on my encoder pulleys isn't as smooth as a GT2 or GT3 would be so my readout may be a bit jumpy. I'm re-thinking my whole encoder mounting system & when I settle on something, it'll get new GT3 pulleys & belt.

I can't Imagine why yours is doing weird things. Mine is more accurate than It has to be really. If I had to guess I'd say you're having a ground or noise issue. Come to think about it someone else was having weird voltage readings with their Acorn but I think it turned out to be a VFD connection problem??

Keep slugging, you'll get it!

[tkbot47]

Your speed range is quite a bit lower than mine, that may help. I believe Acorn divides the full 10V between the low and high set speeds, so you're getting better resolution in mv/rpm than me, however, switching from CW to CCW doesn't have an effect on the speed. My encoder jumps around a bit also, but it is gear driven off the main spindle gear - no belt.

The volts coming out of the acorn up to the switch are rock solid unloaded, but then lose something once connected to and before they get to the 240D. I'll have to relook at my connections. Like I said, it the variability effect isn't repeatable, but the low low and high high correlation is. Isn't this fun?

[tkbot47]

Update: I think I finally got it! The key was adjusting both the min and max pots back and forth on the 240D, rather than just the max pot. I was focused on keeping the min pot at exactly zero volts, but it turns out that really small changes in the lower voltage make pretty significant differences in the lower rpms. Now I get +/- 5% actual vs set rpms from about 100rpm to 2K rpm. Thanks for all the advice, guys.

[DICKEYBIRD]

Great news; thanks for the update!:D The problems you were having really had me doubting the recommendations I've made to you and others through the years. I've "turned on" quite a few fellows on various forums about using KB products for their projects using brushed DC motors. "MaxHeadRoom" on the HSM forum educated me about them originally. Thanks Max!

[tkbot47]

Great news; thanks for the update!:D The problems you were having really had me doubting the recommendations I've made to you and others through the years. I've "turned on" quite a few fellows on various forums about using KB products for their projects using brushed DC motors. "MaxHeadRoom" on the HSM forum educated me about them originally. Thanks Max!

I agree....the KB stuff seems to be good quality. Like you, I can go back and forth from CW to CCW without a hitch. The motor brakes, then reverses without any issues. I've tried some CSS turning and it works quite well. I think I've gotten the little Grizzly motor working as well as it can right now, and the encoder feedback controls the Acorn output quite nicely. On to other things!