My adventures while making a motorized x-axis feed for my Rong Fu mill

[ARC-170]

My cheap Vevor Chinesium x-axis feed motor has died for the second and last time. I've been researching making one and found one that I think I can make. I thought I would document it here and ask questions and post the answers in one place.

WHAT I'M MAKING
Here's the link to it:

It's a guy that goes by MrPragmaticLee.




He has another video that goes over the wiring for the speed control and motor:

Here's a follow-up video with the limit switches:

COMPONENTS
Power supply: Power supply #1

Motor: Motor #1
It has 10 kg-cm of torque, which is about 0.7 ft-lbs. Doesn't seem like enough. This is the style motor I'm using.

Maybe this one is better: Motor #2
70 kg-cm of torque, 5 lb-ft.

Speed Control: Speed Control #1
This is the style I'd like. It has a readout that gives the percentage.

Limit Switches: Limit Switch #1 these have 2 wires, which might mean they won't work for my application. Anyone know?

This style (I think). Note the 3 connectors. This is the kind used in the video:



QUESTIONS:
1. The motor he references is from a company that no longer exists. I can find similar ones, but need to know what RPM to get. I'm thinking about 200 max speed?
2. How much torque would I need to move the table while taking 0.025" cuts in steel?
3. The limit switches have 3 connectors. What wires go where? A more detailed wiring diagram would be helpful and appreciated.
4. The design uses 2 sockets. Are impact sockets easier to machine than the standard chrome ones? I might need to drill and tap a hole for a set screw in them.

More to follow! I'm in the preliminary design stages of the parts and layout for my mill. I will post when that's ready.

@markba633csi Do you have any insight?

 

[RJSakowski]

The first motor seems light. The drive motors on my Tormach CNC are 700 oz-in which is 3.6 lb.ft and they are driving ball screws. But it depends on any gearing you have in the drive train as it will multiply your torque.

You can measure the torque needed to move your x axis by replacing the crank with a pulley, wrapping a cord around the pulley and attaching a scale to it. The scales used for measuring luggage weight work nicely. The torque will be the pull reading multiplied by the radius of the pulley. I would look for a motor at least twice what you are reading.

Remember that you will be working against the cutting forces if you are climb cutting so take that into account. Also, running a motor at reduced speed will also usually reduce the available torque. A more sophisticated speed control will provide feedback to increase drive current under load but simple speed controls are lacking. The conditions requiring the most torque will also be the ones requiring the slowest speed so take that into account as well.

 

[ARC-170]

The first motor seems light. The drive motors on my Tormach CNC are 700 oz-in which is 3.6 lb.ft and they are driving ball screws. But it depends on any gearing you have in the drive train as it will multiply your torque.

You can measure the torque needed to move your x axis by replacing the crank with a pulley, wrapping a cord around the pulley and attaching a scale to it. The scales used for measuring luggage weight work nicely. The torque will be the pull reading multiplied by the radius of the pulley. I would look for a motor at least twice what you are reading.

Remember that you will be working against the cutting forces if you are climb cutting so take that into account. Also, running a motor at reduced speed will also usually reduce the available torque. A more sophisticated speed control will provide feedback to increase drive current under load but simple speed controls are lacking. The conditions requiring the most torque will also be the ones requiring the slowest speed so take that into account as well.

Motor Torque
Thanks! I measured 5 lbs of pull over 1.75", max was 8 lbs. So, a 10.1 kg-cm to 16.2 kg-cm motor should work. Going your recommended 2X that would be 20.2-32.4 kg-cm (1.4 to 2.3 lb-ft). This was under a load of 0.050" cut in steel with a 1" diameter bit.

Motor RPM
I rotated the handle 3 times in 15 seconds (12 RPM) under the same load as above. I rotated it 20 times in 10 seconds (120 RPM) with no load. Is the given motor RPM in the specs the max speed? I assume it is. Would slowing to motor down by, say half, yield half the torque? Not sure how this works. It's probably more complex than that, but I'd like a rule of thumb or general guidelines. Or, point me to some education.

 

[RJSakowski]

Motor Torque
Thanks! I measured 5 lbs of pull over 1.75", max was 8 lbs. So, a 10.1 kg-cm to 16.2 kg-cm motor should work. Going your recommended 2X that would be 20.2-32.4 kg-cm (1.4 to 2.3 lb-ft). This was under a load of 0.050" cut in steel with a 1" diameter bit.

Motor RPM
I rotated the handle 3 times in 15 seconds (12 RPM) under the same load as above. I rotated it 20 times in 10 seconds (120 RPM) with no load. Is the given motor RPM in the specs the max speed? I assume it is. Would slowing to motor down by, say half, yield half the torque? Not sure how this works. It's probably more complex than that, but I'd like a rule of thumb or general guidelines. Or, point me to some education.

Brushed DC have notoriously low torque when average voltage is reduced, whether it be by lowering the voltage or changing the average voltage by means of pulse width modulation. I encountered this when I replaced the OEM motor on my G0602 lathe with a 2.5 hp. brushed DC motor. I wondered why we don't see this when using a drill and I realized that we use biofeedback via the trigger. If the motor starts to stall, we squeeze harder to keep it turning. What I ended up doing was using a rotary encoder to sense motor speed and when the motor started to slow down, I increased the pulse width, effectively increasing the average voltage. The result was that I have usable torque over a 50:1 range in motor speed and can effectively use my lathe at spindle speeds down to 10rpm.

If your drive motor is large enough, the decrease in torque may not be an issue and it is the easiest solution. Gearing is also a good way to increase low end toque although it will reduce your top speed accordingly. If the pitch of your lead screw is .1" and you are looking at 100 ipm for a rapid traverse, , the input to the lead screw will be 1000rpm. If you have a 5,000rpm motor, 5:1 gearing will achieve that. That would increase the torque available to the lead screw 5x.

 

[markba633csi]

On each limit microswitch in the sketch above you would use two of the three contacts: common and normally closed.
They are usually marked on the switch case.

 

[ARC-170]

On each limit microswitch in the sketch above you would use two of the three contacts: common and normally closed.
They are usually marked on the switch case.

What's the other one for?

 

[markba633csi]

Normally open- you push the switch lever to close the contact
Normally closed you push the lever to open the contact

 

[Charles scozzari]

Just wondering, have you considered mating a mill table as used on the Bridgeports.

 

[ARC-170]

Just wondering, have you considered mating a mill table as used on the Bridgeports.

What do you mean?

 

[ARC-170]

PRELIMINARY DESIGN
Here's the very rough CAD drawing to give me some idea of scale and sizes for everything:

The whole assembly is about 7" long without the motor. If you watch the video I linked you can get an idea of how this works. Briefly, the shifter assembly moves the clutch disc/socket assembly back and forth to engage/disengage the sockets from the hex nuts. It only moves about 1/2".

The milling machine x-axis shaft sticks out 2.5". I already have the mill mounting plate made and would like to use it again.

I need to figure out which motor to get so I can draw the motor mounting plate and motor shaft sleeve. The ones shown are best guess.