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View Full Version : Major upgrade to my CNC mill



Evan
04-15-2009, 08:09 AM
I recently burned out the motor of my mill. I have been making do with a makeshift arrangement using a small induction motor hung on the side with a step pulley. Bleh.

In the meantime I had been on the lookout for a suitable replacement motor. Last week I found just the item. At the local surplus store was one (1) small NOS series wound motor rated for 110AC. Knowing that it will also run on DC I bought it for $20. It has turned out to be absolutely perfect. Small with plenty of power and capable of very high rpm, at least 20K and probably a lot more. I geared it down 6 to 1 with a cog belt although I don't recommend cog belts for spindle drive because a little slip can be you friend. In this case a cog belt was the only option. The motor is smooth as silk with much less vibration and no hum as I had with the treadmill motor. It has a built in fan and doesn't seem to heat at all.

When I built the mill I designed the head so that it could pivot. All that it needed was a motor that could mount on the head, which I did not have when I comissioned it. To convert to a swivel head required only machining a circular cast iron mounting plate. I still need to make the clamping system and engrave the back plate with degree marks.

The motor performs beautifully and works perfectly with the controller that ran the now dead treadmill motor. Even with a six to one ratio it is capable of overspeeding the spindle so I am going to servo the spindle with a motor shaft encoder to give full torque at any speed and to limit rpm to a safe value.

http://ixian.ca/pics6/cncmill1.jpg

http://ixian.ca/pics6/cncmill2.jpg

wierdscience
04-15-2009, 08:46 AM
Nice upgrade,maybe the next upgrade could be turning the tilt feature into a 6th axis:)

Refresh my memory,did you use plastic for the leadscrew nuts,or bronze?If plastic how are they working out so far?

Evan
04-15-2009, 09:17 AM
The bottom level X axis uses bronze linear bearings and a pair of commercial bronze lead screw nuts. What a pain. I have to readjust them on a regular basis to eliminate backlash. The Y axis uses PTFE linear bearings, zero clearance and the lead screw nut is a 2" long acetal nut that I made, zero clearance. It has loosened with use to the point that it now has about 0.0005" backlash and that seems to be where it is staying.

The bronze linear bearings are causing very noticable wear on the X axis shafts. Fortunately replacing the shafts is a trivial exercise but it costs money. The PTFE linear bearings seem to cause no wear at all on the shafts and I am not using way wipers either. When I replace the X axis bearings and shafts I will go with PTFE bearings and an acetal nut. They are superior.

Dawai
04-15-2009, 11:44 AM
What a big chunk of aluminum.. The meth heads stole all the aluminum wheels from the cars at the shop.. they were bringing $20 a piece at scrap.

I went around knocking on doors and the thefts stopped.

SO?? what kind of motor? nameplate? no information other than I got one and you should envy it?? come on now Evan...

I watched a video of a guy with a cnc'ed torch.. made from late model auto window motors and drives.. no information on how to copy it.. just here it is..

camdigger
04-15-2009, 03:49 PM
I watched a video of a guy with a cnc'ed torch.. made from late model auto window motors and drives.. no information on how to copy it.. just here it is..

For CNC to work with motors other than steppers, there'd have to be closed loop positional feedback from an encoder of some kind? Aka "servo control"? I dunno, it's been 20 years since I had anything to do with position sensitive stuff, and all that stuff was sychronization issues....:o

Evan
04-15-2009, 04:40 PM
The nameplate information is singularly sparse. All it gives is the voltage as far as I can figure out.

http://ixian.ca/pics6/motor.jpg

John Stevenson
04-15-2009, 05:01 PM
The bronze linear bearings are causing very noticable wear on the X axis shafts. Fortunately replacing the shafts is a trivial exercise but it costs money. The PTFE linear bearings seem to cause no wear at all on the shafts and I am not using way wipers either. When I replace the X axis bearings and shafts I will go with PTFE bearings and an acetal nut. They are superior.

Fully agree with this.
A few years ago when I had to maintain 5 large laser cutting machines the gantry mounted Y axis which ran on linear shafts and ball bushings used to stick every 6 months or so.
This was caused by the fumes from cutting coating the linear rods with crud, Simple repair, remove the ball bushings, clean and soak in solvent and clean the rails with solvent then polish with fine scotsbrite pads, re-lube and reassemble.

Occasionally the ball bushings got replaced because of wear / lumpiness and a local bearing company kept spare bushing on stock to be called off.
One day I called to pick some up and they had failed to restock, only thing I could get at short notice was some solid dry-line bearings so these were fitted whilst new ball bushings were ordered.

It was then found that these didn't stick like the ball bushings, instead they wiped the rails and kept themselves and the rails clean with minimum lubrication.

Eventually all 5 machines were swapped over and no more bushings got changed until these machines were scrapped.

We also did the same at a local woodworking company on the routers, the fine dust from the MDF was clogging normal linear bearings, the dry line, which are like the PTFE ones, will not allow dust inside as there is no space to go.

.

madman
04-15-2009, 05:27 PM
I really Like youre Mill. Very nice. When you build a new improved model maybe i could buy youre old one. thanx Mike

JCHannum
04-15-2009, 05:58 PM
Amatek Lamb motors are principally used in vacuum cleaners, which are typically high RPM universal motors.

Evan
04-15-2009, 06:06 PM
It must be from one of the larger vacuums as it has a lot of torque. The treadmill controller uses back EMF feedback to regulate motor speed. It's pretty loose regulation but it does work well enough that even when turned down to 60 rpm I cannot stall the motor by gripping the spindle. Once I build a proper servo drive it will have full torque at all speeds with very good speed regulation. I may also gear it down further to take full advantage of the top end. A good thing about a vacuum cleaner motor is that it is designed for continuous duty. I stopped in today to buy another and this was the only one they had. Drat.

JCHannum
04-15-2009, 06:15 PM
They make about a jillion different models from disposable, sleeve bearing models to heavy duty, ball bearing motors. If it is the latter, it should give you good service as they are rated for continuous duty.

camdigger
04-15-2009, 07:15 PM
Product # not found on Amatek / Lamb motor site. Sounds like it has been discontinued...

japcas
04-15-2009, 07:33 PM
That looks real neat. Say you needed to run off some parts with holes drilled in at an angle and you couldn't fixture up the part on the angle you needed but you were able to bolt it down flat to the table. You could then tilt the head over and use z and x axis moves to drill holes on an angle. How hard would it be to change the software settings to drill holes on an angle with the head tilted over like in the second picture? Or would you have to trig it to figure out how much to move the z and x axis to drill at the angle the head is set at?

Evan
04-15-2009, 08:06 PM
To tell the truth I'm not sure. I will have to look at the options in the controller codes. I have figured out a number of ways to make Mach 3 do certain things that it isn't capable of doing.

BTW, I can also mount the spindle/motor assembly under the head with the motor on one side and with the spindle pointing out. Then I have a CNC horizontal mill. :D

japcas
04-15-2009, 08:15 PM
I wasn't sure if you could mess with the software to get it to do that or if you would have to manually write the code to do such an operation. I've seen full size vmc's do this but thought it would be handy on a small machine also.

wierdscience
04-15-2009, 10:52 PM
The bottom level X axis uses bronze linear bearings and a pair of commercial bronze lead screw nuts. What a pain. I have to readjust them on a regular basis to eliminate backlash. The Y axis uses PTFE linear bearings, zero clearance and the lead screw nut is a 2" long acetal nut that I made, zero clearance. It has loosened with use to the point that it now has about 0.0005" backlash and that seems to be where it is staying.

The bronze linear bearings are causing very noticable wear on the X axis shafts. Fortunately replacing the shafts is a trivial exercise but it costs money. The PTFE linear bearings seem to cause no wear at all on the shafts and I am not using way wipers either. When I replace the X axis bearings and shafts I will go with PTFE bearings and an acetal nut. They are superior.

Thank you for confirming my suspicions.I'm building a small desktop CNC router gantry and bronze nuts are out.I have some graphite filled PTFE left over from a job,I will try that.

Going to be using 1/2-10 x 5 start acme leadscrews,so making my own tap is in the cards.

+1 for the dry polymer linear bearings.I've used a bunch of these,too cheap to make at these prices.

http://www.igus.com/dryr/dryrjm.asp

Bruce Griffing
04-17-2009, 01:07 PM
Evan-
Did you make or buy your PTFE linear slides? If made, what version of teflon did you use? If bought - what brand? Tnx.