Possibly upgrading a motor on a mill, what do I need to know?

I've got a PM-30MV (2HP brushless DC) and it will do the same thing at slow speeds. I was using it a few days ago and using a socket head countersink and if not really careful on downfeed, it would stall easily. That was on low speed belt position as well.
 
xr650rRider said:
I've got a PM-30MV (2HP brushless DC) and it will do the same thing at slow speeds. I was using it a few days ago and using a socket head countersink and if not really careful on downfeed, it would stall easily. That was on low speed belt position as well.
Click to expand...
Hmm, that's discouraging. How slow was the RPM?
 
A 4" is even a bit big for my full size knee, I usually run 2.5-3". You have to factor in the increased torque required as the diameter increases of the cutter. Finer teeth with decreased feed would improve things, as well as teeth that cut some relief so there is less binding. As you mentioned, some form of light lubrication also helps. An issue with belt drives with one or two speeds covering very wide speed ranges, is you just need a dam big motor to get any decent performance at low speeds. So first step would be pulley ratio changes, but you are probably already pushing the diameters that can be fitted in the head. FYI, I use to have a BF-30 with 3 speeds covering 50-3000 RPM with a 3 Hp BLDC motor and did stall it on a few occasions cutting too aggressively. I still think a heavier mill is required to push a 4" blade with what you have.
 
mksj said:
A 4" is even a bit big for my full size knee, I usually run 2.5-3". You have to factor in the increased torque required as the diameter increases of the cutter. Finer teeth with decreased feed would improve things, as well as teeth that cut some relief so there is less binding. As you mentioned, some form of light lubrication also helps. An issue with belt drives with one or two speeds covering very wide speed ranges, is you just need a dam big motor to get any decent performance at low speeds. So first step would be pulley ratio changes, but you are probably already pushing the diameters that can be fitted in the head. FYI, I use to have a BF-30 with 3 speeds covering 50-3000 RPM with a 3 Hp BLDC motor and did stall it on a few occasions cutting too aggressively. I still think a heavier mill is required to push a 4" blade with what you have.
Click to expand...
You are right, this mill isn't really suited for this. Seems this kind of motor doesn't have torque at low RPM.

It took me 2 hours to make 3 cuts 1" deep through 30mm diameter stock. That's an average cut of 1" in 40 minutes. That's an equivalent feed rate of 0.04"/minute, which to my inexperienced self, seems slow. My 4" diameter, 1/16" thick Niagara staggered tooth saw has 36 teeth.

I bought the saw blade before I knew better. It was listed on evilBay for an attractive price. But, even so, it has proved to be useful, although slow cutting steel. I see there are 3" saws called jeweler's that have a lot more teeth, 168. Another possibility is to use a carbide blade, although they are brittle and more expensive.

Still looking a machining a pulley, maybe I can improve the ratio a little.
 
xr650rRider said:
Around 150 RPM. Had to speed up > 600 and peck at it to get to depth. The point was, slow speed, no torque.
Click to expand...
Seems to be the torque characteristics of these motors. Wonder if there are better choices for this application. Going to read about motors.
 
Last edited:
a gearbox with torque multiplication but not in these mills future. The Chinese 2HP rating is probably closer to 3/4 HP in US. They are just small mills and you have to live within the limitations or spend the money for a real mill. If you installed a pulley drive system with around 5 belt positions like a drill press, you could probably get decent torque at 100 RPM but not with variable speed that can go from 50-1500 RPM.

It's a baby mill, so use baby cutting tools.
 
xr650rRider said:
a gearbox with torque multiplication but not in these mills future. The Chinese 2HP rating is probably closer to 3/4 HP in US. They are just small mills and you have to live within the limitations or spend the money for a real mill.
Click to expand...
Yeah, I know. Becoming obvious to me now.
 
Took some measurements of the pulleys and how much room there is.

Spindle 60mm, 80mm, 45mm bore, 28mm height
Motor 60mm, 40mm, 12mm bore, 28mm height

For low range, the ratio is 1:1, for high range, the ratio is 2:1. Makes sense.
High range is 1:1, Low range is 1/2:1. In low range the spindle rotates at 1/2 the speed.

If I don't modify the motor mount bracket, there is room, just barely for a 75mm pulley with a belt on it. (I measured 77mm.) Might need to slightly relieve the bracket if there is any rubbing.

On the spindle, since there is a bore of 45mm, AND a key, I might be able to make a 50mm pulley. Let's say it is 52mm. That would be a speed reduction of 52/75 = 0.693, or about 70%. If I understand correctly, the motor will be spinning 1.44 times faster than before - if the motor speed is measured at the spindle, which I think is true. This should make low speed cutting a little easier. I think this might be worth doing, sounds like a fun little lathe project.

The little belt on the pulleys is a 160J. I have been able to find the tooth pitch and depth (2.34mm, 1.60mm) but not the belt vee angles. Does anyone know what the angle is? I don't have anything to measure it with. On my machine, the spindle pulley wasn't machined correctly, as the vee is oriented as a 7, not as a >. The motor pulley looks like a proper vee.

Making this pulley will leave a hole in the speed range. It would be better to have 3 stacked pulleys, but I'm willing to try this out. It only takes a couple of minutes to change the pulleys, so if it saves me even 30% of my time, it would be well worth it.
 
Last edited:
Don’t you want a small motor pulley and large spindle pulley for a slower spindle speed?
 
You must log in or register to reply here.
Back
Top