[sneakrz]

We bought a two year old Patriot and we are interested increasing the speed of the mill. The goal is to increase the cutting speed and decrease the time needed to cut a part.
We want to avoid overclocking the motors.

Our first thought is to cut our own over/undersized pullies. Does anyone have any experience with this? Any other input is greatly appreciated.
Thanks in advance,
Jeff

[sharpshooter90]

There are several options depending on what RPM you are looking for. You can probably get up to 5-6000 with the current setup with some slight mods, but if you want 10-20,000 speeds you will need to go to a high speed motor/spindle combination.
Your motor will run reliably at 120 Hz, so that puts a 1400 rpm motor up to about 2800. By using a larger motor pulley to get 2-1 drive it will spin your spindle to 5600. However, the spindle bearings will probably need to be upgraded to a higher quality tapered roller, or even a set of double angular thrust rollers like the new Mill Turn uses.
If you are looking for the really high speed, look on E-Bay for those Chinese spindle motor sets- find one that is a 2HP rating so it will work with your inverter and then manufacture a mount to attach to your quill.

[xjdubber]

Kind of wondering what types of motors these mills have that they will run at 120hz reliably? a regular 60hz motor will have no torque left anymore at that speed.

[sharpshooter90]

Our machine had 4 pole inverter duty motors wired for STAR configuration. We did not find any significant loss of power throughout the RPM range. I have read some of the theory, but unless you are an electrical engineer it gets pretty confusing. However from what basic I could understand, the inverter keeps a balance between Hz and Current, and also supplies torque boost under startup and load conditions. There are some differences in the torque curves between STAR and DELTA configurations, so most machine tools use the STAR. There are also motors wired to run either STAR or DELTA.

[xjdubber]

if its a 4 pole motor the base speed is 1800 rpm wye or delta wiring is going to determine your voltage input Delta would be 240 3phase and wye 460v.Where do you find differences in torque going from y to delta?

[sharpshooter90]

Sounds like you are familiar with the subject. I can only speak from experience. Maybe try over on this forum for better answers.
http://www.cnczone.com/forums/phase-converters/

[hanermo]

Complex in many ways.
Increase spindle rpm = easy.

But that wont make the machine run faster,
Increase acceleration on axis drives, speed on axis drives, speed on controller = very complex.
Budget ??

[smallblock]

Hanermo,
You are right about increasing the overall speed of the mill, as it requires a lot of other things. However, I think the original poster was referring to the spindle speed only. The older Patriot machines had good feed rates on X,Y and Z, but the mill spindle speed was limited to about 3000RPM. By doubling the spindle speeds it could essentially double the overall cutting rates of the machine like the new Mill Turn.

[sneakrz]

Thank you all for the input..
As some of you know, we had several issues with our mill. One was a pretty nasty wobble (.030 to .045 depending on the day). Ill post here how we fixed that. http://www.cnczone.com/forums/shopma...dle-nut-2.html
We are running a very small end mill on aluminum and having issues breaking and clogging flutes. I have a very experienced machinist running it and we have tried various speeds, feed speeds and cut depths (as well as other solutions). The problem is that most of the solutions create run times measured in hundreds of hours- there has to be a better way right?
So we also installed a 10.4 inch pulley on the motor and have run it to 3000 RPM (it is theoretically capable of 3700RPM or so). We made each pass shallower and faster reducing our total run time to 45 hours (made some other tool path optimization that helped as well).
To install the pulley, we had to bore the ID (the motor has a metric shaft). We also had to move the mount for the safety cover and change the way the speed sensor is mounted. Of course they are metric threads too (cant get that at Home Depot). It was a long day.
We have been cautioned about the bearings and we plan to drop the quill and re-grease the bearings after each piece (I can do that in less than an hour). When the bearings finally do fail, does anyone have a good source for a solid high speed bearing that we could run at just under 4000 RMP without the need to constantly rebuild?
In case anyone is interested, we looked at a 12.5 in dia pulley but we had a lot of clearance issues with the other motor and would have had to make some very significant changes in the motor mounts (move it out farther on the arm).
Im no engineer but I really don’t think this machine is capable of much more than 5-6k RPM. The pulleys would be have to be pretty big, the motors upgraded and the machine rewired (we decided we would go to a 3 phase system if we needed that much speed). If you are willing to do all that, I think you are going to run into issues with the overall stability of the machine. It will be even more top heavy and with all that rotating mass/energy…..
Now that is not a professional opinion or fact… I have simply watched it run at 3k…
Ill post more after we get a few pieces under our belt and let you know what else we gave up to get what we got..
Jeff
Attachment 307618
Attachment 307620

[BlackICE1]

I'm curious about why you needed such a large drive pulley for 4000 rpm. Mine does about 2450 stock, with that big of a pulley it would probably do over 7000.

[sneakrz]

We are trying to avoid overclocking the motor because we have some very long runtime projects (the final project may be upwards of 100 hours even with tweaks and tricks)

I agree, it would be theoretically possible. We calculated that at the rated motor speed of 1400 RPM we could get about 3800 RPM (If I remember the conversation correctly) using the bigger pulley.

What is the longest time you have run the mill at speeds over, say, 2300 or so?
Jeff

[hanermo]

Motors can run reliably at high speed.
They have more cooling, because the fan pushes more air past it, and for eth same hp, there is less torque = stress.

CHANGE THE GREASE (spindle and motor, if possible).
Kluber Isoflex 15.
Google it.

With the right grease, bearings can run reliably at 12.000 - 15.000 rpm.
Several reports of much lower temps with better grease.

[BlackICE1]

Only run about 30 mins max at a time.

How hard is it to remove the pulleys from the motor's shaft and the one at the top of the spindle. It would be nice to mod it to take a step pulley increase the range of rpms over what the VFD gives you.

These sheave bushing would come in handy for making different sized pulleys for the motor. I measured the shaft to be 24mm and the keyway width at 8mm. Does anyone know how and pulley is mounted to the mill spindle and what the dimensions are?

https://www.grainger.com/category/ta...FN-apzZ1z0cp49