Speeds, Feeds, and Strategies for Bench Top Mills

I had a guy turn the pulley to fit both the spindle and motor shaft. I use a Gates 5m belt, a rather small V belt. It's always worked really well for me. If I had to do it again, which I plan to do myself this time, I will use the same V belt but will use two of them on each pulley. A single belt has been very reliable and can stand up to way more load than I would have expected, but i does show some wear. Also, it would provide redundancy, so if one belt would fail I know I can keep working with one.

Well good news. Got all the parts in yesterday. Today I installed the new bearings, good grease, set preload to what I think is about right.

Also made a 3D printed spacer that takes out ALL the slack from the spline. It's functionally a direct drive now.

Got it all back togehter. Did the bearing break in and it ended up around 140*F.

Did some test cuts and it seems happy. Was running 0.3 cubic in/min in some 4340 with a 1/2" end mill and it was working good, quiet, great surface finish for roughing. Looks like getting rid of that slack in the spline made all the difference!

Looking pretty good! 140F sounds manageable. I'd say my spindle gets to there or even a spot hotter, though I am not sure what RPM you are running.

That's a healthy looking chip from such a small machine, so I'd say you are doing very well.

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Originally Posted by CL_MotoTech

Looking pretty good! 140F sounds manageable. I'd say my spindle gets to there or even a spot hotter, though I am not sure what RPM you are running.

That's a healthy looking chip from such a small machine, so I'd say you are doing very well.

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This was running 1800 RPM. I did see it get to 158*F after about I finished machining. So it went up some but that would be expected.

Yeah I'm pretty happy with it now.

Question for ya. What do you think of putting this motor on the PM25? : https://www.teknic.com/model-info/CP...tage=230VAC3ph

I was thinking of using that, and then pulley it say 3:1 from the motor the to the spindle. I have 220V single phase power, and may be able to get a 3phase rotary converter as well.

The hope with that motor would be that I could spin higher RPM to increase speed and no longer worry about stalling the spindle all the time.

Quote:

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Originally Posted by patrick31

This was running 1800 RPM. I did see it get to 158*F after about I finished machining. So it went up some but that would be expected.

Yeah I'm pretty happy with it now.

Question for ya. What do you think of putting this motor on the PM25? : https://www.teknic.com/model-info/CP...tage=230VAC3ph

I was thinking of using that, and then pulley it say 3:1 from the motor the to the spindle. I have 220V single phase power, and may be able to get a 3phase rotary converter as well.

The hope with that motor would be that I could spin higher RPM to increase speed and no longer worry about stalling the spindle all the time.

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I have this one sat in a box waiting to go onto mine:
https://www.aliexpress.com/item/4000981806107.html

Quote:

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Originally Posted by patrick31

This was running 1800 RPM. I did see it get to 158*F after about I finished machining. So it went up some but that would be expected.

Yeah I'm pretty happy with it now.

Question for ya. What do you think of putting this motor on the PM25? : https://www.teknic.com/model-info/CP...tage=230VAC3ph

I was thinking of using that, and then pulley it say 3:1 from the motor the to the spindle. I have 220V single phase power, and may be able to get a 3phase rotary converter as well.

The hope with that motor would be that I could spin higher RPM to increase speed and no longer worry about stalling the spindle all the time.

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If you get into any serious RPM that temp is only going to climb. Your preload is probably fine for your current speeds, but the spindle will overheat pretty quickly if you push towards even 4k I would think.

That servo is a lot of motor, probably overkill for the 25, at least as far as shear power is concerned. Keep in mind that servo probably has a better power curve than my BLDC, which is 2.2kw. It runs at 1:1 (max RPM 6k) and is more horsepower than the G0704 really likes at times, and in fact is probably overkill by 15% or so (just guessing). Suffice it to say, the spindle motor is no longer the limiting factor, and rigidity truly is a concern. It will break 3/8" carbide way before it ever stalls. This is why I never pushed much past like 5.5 cu/in/min in aluminum, and really only run it at like 4.7cu/in/min on the regular. My steppers just can't keep up, and rigidity is questionable at those feeds and cutting forces. TTS also tends to peter out for me at around 5.5 cu/in/min. Not an issue if you aren't use TTS, of course.

Also, I am not sure you gain with the indexing/positioning of the servo? I have a small rotary encoder and can rigid tap with my BLDC, not that I ever do, but it's cheaper to buy a BLDC and encoder than it is to get a servo together. Especially when you are looking at three phase and rotary converters. This arrangement is less tidy than a servo, but the results are nearly the same. If you were going for BT30 or something that required indexing for tool changes, then I could see the need for a proper servo.

That said, it would be cool to watch you try it! I didn't look at the motor size, but be careful with the amount of space on the head. It can get a bit tight on there depending on how much junk you add. PDB being the prime example.

Quote:

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Originally Posted by CL_MotoTech

If you get into any serious RPM that temp is only going to climb. Your preload is probably fine for your current speeds, but the spindle will overheat pretty quickly if you push towards even 4k I would think.

That servo is a lot of motor, probably overkill for the 25, at least as far as shear power is concerned. Keep in mind that servo probably has a better power curve than my BLDC, which is 2.2kw. It runs at 1:1 (max RPM 6k) and is more horsepower than the G0704 really likes at times, and in fact is probably overkill by 15% or so (just guessing). Suffice it to say, the spindle motor is no longer the limiting factor, and rigidity truly is a concern. It will break 3/8" carbide way before it ever stalls. This is why I never pushed much past like 5.5 cu/in/min in aluminum, and really only run it at like 4.7cu/in/min on the regular. My steppers just can't keep up, and rigidity is questionable at those feeds and cutting forces. TTS also tends to peter out for me at around 5.5 cu/in/min. Not an issue if you aren't use TTS, of course.

Also, I am not sure you gain with the indexing/positioning of the servo? I have a small rotary encoder and can rigid tap with my BLDC, not that I ever do, but it's cheaper to buy a BLDC and encoder than it is to get a servo together. Especially when you are looking at three phase and rotary converters. This arrangement is less tidy than a servo, but the results are nearly the same. If you were going for BT30 or something that required indexing for tool changes, then I could see the need for a proper servo.

That said, it would be cool to watch you try it! I didn't look at the motor size, but be careful with the amount of space on the head. It can get a bit tight on there depending on how much junk you add. PDB being the prime example.

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Good point. I will keep an eye on it if I go any higher on the RPM.

How did you setup the oiler on yours for the spindle bearings? Do you circuilate oil to the bearings? Mist? How does it work?

The oiling system is total loss. I don't have any pictures but it's a very simple setup.

I took a piece of aluminum sheet metal, cut a hole in it with a hole saw that was large enough to fit over the spindles splined section (it's actually a fairly tight fit) without touching. The piece fits inside the head above the spindle housing, I simply glued the piece in place with silicone sealant. Drilling and tapping holes inside the head seemed like a chore so silicone it was. On the plate is an oil fitting that drips oil via the automatic oiler feed. Gravity carries the oil from the top of the spindle down to the bottom. When the machine is off, I get some oil collecting below the spindle.

To do it right, there would be two oil feeds, one high for the top bearing, and one low for the bottom bearing. Then likely a proper seal on the bottom of the spindle (Chris with another build here has spent some time on that). As is, on really long runs, I feel the lower bearing is under oiled as I think the top bearing tends to churn the oil and keep it up high. That leads to over oiling in an attempt to force oil to the lower bearing. The lower bearing also tends to force it's oil out the bottom on account of the taper direction and gravity. Additionally, the lower bearing is also subject to coolant washout. I have fitted a fat oring over the spindle that rests against the spindle "seal", this helps sling coolant away and hold some oil in. Again, it is basically total loss.

Wear is good, performance is good, but oil use could be lower by adding that second lower oiler. I have no plans to add a lower oiling port. I'd rather just buy a better machine... Not that I am complaining, I machined some parts at +/-.001" the other day, pretty sweet for the home conversion of a junk machine. That said, the only bearing failures I have had since adding the oiler were a result of either running out of oil (the control is not aware if the oiler is working) or having too much preload on the bearings and overheating them. My current bearings have been run hundreds of hours at this point. I am doing more and more steel, and it's not been an issue.

CL_MotoTech, do you happen to know the shaft size of the factory PM-25 pulley that goes on the 1HP motor? Is it 12mm by chance?

Thinking of setting up my 3KW spindle to just spin a pulley that then drives the original headstock.

I don't have any idea. Maybe give PM a call? I would think somebody here could help you out, but since I never have had a PM25 I am of no help.

I cannot get this 3 flute 45 degree Shars Carbide end mill to run in aluminum without ungodly chatter. Great looking end mills for the price, but damn near worthless in aluminum on my machine. All the feeds and speeds numbers line up with recommendations from FS Wizards Pro. I have tried moving feed and speed all over the place and it only get's worse outside the recommended F&Ss.


https://www.shars.com/products/cutti...rbide-end-mill

I guess that chatter is the least of my worries. I haven't yet gotten the Clearpaths on, and have just been chugging along with the steppers. I ran the machine until about midnight last night, today I go out and now the Z axis is hanging up in both down and up movement. It won't move an inch without losing steps. I have no idea what changed overnight. My shop is somewhat climate controlled, so ambient temps haven't really changed in there. I'll have to take it apart. It isn't going to be fun. The odd thing is that none of the Z wiring moves, so why it would go bad I don't know... It could be the driver I guess. I sure hope not. I've scaled back all my orders over the past month so I could finish off customer work and switch to the clearpath servos, but I have one order left to complete...

Quote:

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Originally Posted by CL_MotoTech

If you get into any serious RPM that temp is only going to climb. Your preload is probably fine for your current speeds, but the spindle will overheat pretty quickly if you push towards even 4k I would think.

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You..... were right!

I got it setup with the 3KW to drive the original headstock/spindle with a 2:1 pulley so I can go up to 6K. Well, like you said, temps took off. I was careful and watched it but it went to 160 pretty quick.

Tried backing off preload which helped some, but wasn't enough. I think I had the bearings at 50% or so grease fill.

Anyway, planning to do an oiling system now. Plan is to use an oiler for pnuematic tools on a timer to periodically oil the bearings. Going to take modding the headstock and spindle thing so oil can get in/out. But this will be an air/oil mist going in so it should travel up to top bearing and down to bottom. Just need to mod it so there is a flow path in the center and out the ends.

Check out this video! Got it going up to 0.5 cubic in/min in 4340 with a 5/8 indexable end mill. Pretty sure once I get the bearing situation done, I'll be able to go even faster.

https://youtu.be/xJrATTRVkZc

Depending on how tight the race is on the spindle shaft, simply decreasing preload on the nut may not actually decrease the preload on the bearing. I hit the top of the spindle with a dead blow hammer to reseat the race with less preload. Bearings with less of an interference fit are desirable for this reason. They are just easier to adjust.

Looks like you got nice results there!

Yeah I read that on there from either you or someone else. Mine sticks too so I've been doing as you say to loosen it.

Right now I'm setting it up to use an air blast with oil mist to lubricate the bearings. I drilled and tapped the headstock today and installed fittings for supply and vent for the upper bearing, drilled the spindle thing as well so it can flow in between the bearings. Waiting on oil and other things to set it all up. In the end, the plan is to have an air/oil mist fire every few minutes to deliver oil to the bearings.

That's sounds like a very comprehensive plan you have there. I look forward to seeing your results. I run my auto oiler at 1cc per 10 minutes, but that's for all the ways, ball nuts, and the spindle.

Here's some updates on the machine. Includes extensive temperature testing, development of oil system, and test cuts to 1.2 cubic in/min in alloy steel!

https://youtu.be/LpvvsgencPw

https://youtu.be/GlWnMDQe9HE

https://youtu.be/Uys5PujjFBs

Awesome! Hopefully you see good bearing life as well.

How much air pressure are you using?

I got off easy for once, the bottom gib screw fell out of the Z carriage and the gib was way too tight. Managed to get the gib driven back up into the carriage using a drill bit against the base and then gib, then lowering Z and forcing the gib back up into the carriage. Then it was just a matter of putting the gib screw back. It still took 45 minutes of messing around. Lot's of sweat. Even with the AC at full blast my shop is like 80 degrees currently. I am however relieved that I won't have to buy anything. Now it's time to get back to work!

What are you trying to do?

Stuart