Swapping Step Pulley For Vari-Speed...

[HimyKabibble]

Is it possible to swap just the top part of the head, to go from step pulleys to vari-speed? If so, how hard is it to come by a good used Vari-Speed?

Regards,
Ray L.

[gus]

freq drive would be cheaper and quieter and easier

[TOTALLYRC]

Originally Posted by gus freq drive would be cheaper and quieter and easier

A good sensorless vector drive will cost far less than the varispeed prices I have seen on ebay.
It will give torque down to a very low speed and if you need extra torque, then all you have to do is shift into low gear..Even the varispeed head has a high and low range.

The pot an a vfd can be setup on a remote location to make it easier to change speeds.
If it is on a cnc machine it can be controled by mach3 and other programs with maybee a little extra hardware depending on the vfd.

I have also seen guys swap out a dc motor and speed control instead of ac and vfd.

[Al_The_Man]

This is a 1:1 timing belt conversion of Varispeed on Excello with 2 speed gearbox.
Using a VFD for 3 phase motor control.
Ignore the toothed wheel, I am experimenting with true spindle rpm indication.
Al.

[HimyKabibble]

A VFD, by itself, cannot give the range of speeds you need for working with 1/16" through 3/4" endmills. I have a VFD, controlled by Mach3, but that is only half the solution. I need to be able to go from a few hundred RPM to 8K+ RPM, without changing belts.

Regards,
Ray L.

[Al_The_Man]

Then I would think you will need to look at a high speed spindle for 8k+.
I would not want to run a BP or XLO knee mill spindle at that rpm.
Al.

[HimyKabibble]

Originally Posted by Al_The_Man Then I would think you will need to look at a high speed spindle for 8k+. I would not want to run a BP or XLO knee mill spindle at that rpm. Al.

Al,

I do it all the time. It seems perfectly happy. I let it cool down every couple of hours, but it certainly does not get hot enough to do any harm whatsoever. The design speed for this machine is 5440 RPM (two-speed motor), so I'm only over-speeding the motor 50% with the VFD to get up to 8200. The motor doesn't even get warm, and the head gets just warm to the touch, not at all hot, after perhaps two hours of constant running.

Regards,
Ray L.

[TOTALLYRC]

Originally Posted by HimyKabibble Al, I do it all the time. It seems perfectly happy. I let it cool down every couple of hours, but it certainly does not get hot enough to do any harm whatsoever. The design speed for this machine is 5440 RPM (two-speed motor), so I'm only over-speeding the motor 50% with the VFD to get up to 8200. The motor doesn't even get warm, and the head gets just warm to the touch, not at all hot, after perhaps two hours of constant running. Regards, Ray L.

Since I do not know exactly how the head of your mill is designed, I will tell you how mine works and see if it applies to yours.

I leave the belts in one position. I use the vfd for most of the speed control.
When using large cutters/taking heavy cuts, I just shift the 2 speed into low range. Even bport varispeed does it this way. They have a high and low range.
With a sensorless vector vfd, as opposed to a volts/hertz vfd, you get lots of torque way down low. how low I am not sure but running the spindle at 50 rpm in high gear, I couldn't even slow it down by hand, much less stop it.


Mike

[polaraligned]

Originally Posted by HimyKabibble A VFD, by itself, cannot give the range of speeds you need for working with 1/16" through 3/4" endmills. I have a VFD, controlled by Mach3, but that is only half the solution. I need to be able to go from a few hundred RPM to 8K+ RPM, without changing belts. Regards, Ray L.

That is what we all dream of Ray.
I just don't think you want to spin a varispeed head that fast. Problem is not the bearings but the varispeed pulleys are so sloppy, and engage the spindle shaft so high. The Varispeed heads sound like they are going to blow apart at 4500 rpm. I would wear an armored suit near that machine if it is going 8k rpm.
I am looking for a solution myself. I really have found none online.
I was thinking about putting a larger motor up top and using a vector drive, but I still think 3 gear ranges is probably necessary. With the backgear you only have 2 ranges (without using the varispeed).
I would love to hear other ideas.

Scott

[TOTALLYRC]

Originally Posted by polaraligned That is what we all dream of Ray. I just don't think you want to spin a varispeed head that fast. Problem is not the bearings but the varispeed pulleys are so sloppy, and engage the spindle shaft so high. The Varispeed heads sound like they are going to blow apart at 4500 rpm. I would wear an armored suit near that machine if it is going 8k rpm. I am looking for a solution myself. I really have found none online. I was thinking about putting a larger motor up top and using a vector drive, but I still think 3 gear ranges is probably necessary. With the backgear you only have 2 ranges (without using the varispeed). I would love to hear other ideas. Scott

My btc-1 has a stock 3hp motor and a 2 speed gear box 5000rpm in high and 1250 or something in low for max speeds. at 60 hz. I am using a sensorless vector drive.
If you were to raise the max freq on the vfd, you could go up to 8 or 10K depending on the motors ability to stay together and how long the bearings would last. The spindle is quiet at 5k and I have heard of somebody running the same spindle a 7k.

With the increased torque from the vector drive, you could change the spindle drive ratio to overdrive it and get more spindle speed with a lower max freq and still be able to run at low speeds in low gear.

I will be doing some real testing of the spindles and vfd power this week and I will let you know how I make out.
mike

[HimyKabibble]

Originally Posted by TOTALLYRC Since I do not know exactly how the head of your mill is designed, I will tell you how mine works and see if it applies to yours. I leave the belts in one position. I use the vfd for most of the speed control. When using large cutters/taking heavy cuts, I just shift the 2 speed into low range. Even bport varispeed does it this way. They have a high and low range. With a sensorless vector vfd, as opposed to a volts/hertz vfd, you get lots of torque way down low. how low I am not sure but running the spindle at 50 rpm in high gear, I couldn't even slow it down by hand, much less stop it. Mike

Mike,

If I try to do that, I end up with a giant hole betweem 1000 and 2000 RPM, even allowing the VFD to go to 120Hz. So, at *least* one pulley change is required to cover the whole range.

Regards,
Ray L.

[TOTALLYRC]

Originally Posted by HimyKabibble Mike, If I try to do that, I end up with a giant hole betweem 1000 and 2000 RPM, even allowing the VFD to go to 120Hz. So, at *least* one pulley change is required to cover the whole range. Regards, Ray L.

Hi Ray,
Forgive me for being thick, but I guess I am missing something.

I just checked the manual on my sj200 hitachi , sensorless vector 3hp vfd.

It will give %100 torque down to about 6 hz or so. seems like it will cover the gap nicely. Even if you had to make a set of 1:1 pulleys to get rid of the step pulleys, it sounds like it will work.

1000rpm is 120hz in low and 2000 is 60hz in high.
If I am understanding the rpm numbers you gave correctly

You could go 90 hz in low (750rpm) and then you would just need to run it down to 15hz in high (750rpm)to cover the gap without really revving the poor motor in low speed.

I would make sure and use a seperate motor cooling fan if the motor is currently cooled with a shaft mounted fan. The motor mounted fan will not cool the motor sufficently at significantly reduced speeds.

Mike