convert rf45 type to belt variable speed and some cnc info?

can anyone point me to how to convert a rong fu type gear mill to belt drive with variable speed
and what type of stepper would i need to convert it to cnc, not really brand but more like in/oz info and also the same type of info for controller and driver like vdc and amp
one last thing how, if possible, do you calculate the in/oz from a stepper if all you have are voltage, ampering and ohms
i tryed to search for it a BIT i now have a vague idea about the stepper but none about the conversion to belt and variable speed, again if possible

ok foud this about the gear to belt conversion but i havent read it yet
http://www.cnczone.com/forums/showth...ting+gear+belt

about the motor i am not able to find the torque of those motor so does anybody know if they are any good for a small bench mill x2 or x3 type of bench mill or there not worth snit

VEXTA 2-PHASE, 7.4, V 1A STEPPING MOTOR PK266-01A-C23

or this

103-770-0194 Step-Syn - Sanyo Denki Stepping motor
Nominal Voltage 5.1
Current 1
Wires 6
Condition pulled
Steps / Revolution 200
Step Size (degrees) 1.8
NEMA frame size 23

I have been doing some preliminary work on a rf 45 and have determined that servos with 600 in/oz. are about the minimum power needed if using ball screws. The problem is due to the table weight and acceleration requirements. If using a 5 tpi ball screw, I would use a 3:1 reduction minimum and possibly a bit more. If the motors can do 3000 rpm, this gives you a 200 ipm table speed. possibly a bit to fast for the motor power limitation. 4:1 gives a respectable 150 ipm. I also would advise lapping all x & y axis ways to minimize friction.

Anyone with machinist abilities working with one of these machines quickly realises the need for spindle speed when working with aluminum and small diameter cutters. I have an older RF-45 with the 3 phase / 2 speed motor. This gives a max spindle speed of 3000 rpm. Almost all my work is done using high helix end mills at max speed. This machine is really noisy at high rpm and does it ever generate heat. After a few hours use, you feel like you are standing next to a woodburning stove. Changing to a timing belt drive with an inverter speed controlled 3 phase motor is the way to go. Doing so would reduce noise by probably 75% and cut power consumption and associated heat by a huge amount. Can anyone help with any design info already available???

thx for those info i would also appreciate plan or info on how to convert one to belt drive for the same reason as you belt also offer the advantage having variable speed wich help when cncing

I may desigh a kit in the near future.

why you change a gear box to belt,i think gear box is good enough ,except the noise a bit loud,gear can given your high torque! belt can not .

I would prefer to see a belt or VFD drive as multiple or step pulleys would be ble to whichever is needed. Current gear on clone seem too limited. Just my 2 cents. I will be following this closely.
Scott

When you do a belt conversion on one of these, you remove all gears and oil from the head casting, install a timing belt pulley on the motor, machine another pully to replace the spindle drive gear, then install motor setup with pilleys and belt inside the gear box housing. A friend of mine builds printing equipment transmitting 20 HP with timing belts no problem. I believe the sound may be reduced by 30db, that is a lot. each 3db is a 50% reduction in sound pressure level so we are talking 10X quieter than stock without heat buildup.

Only problem is that you can not have both worlds. Either speed or torque. If it is setup for speed and you need to do something slow you may not have the torque to do it. If you set it up for torque then you will not have the speed. The reason Tormach has a two speed belt drive. If I absolutely had to I think that I could set it up for speed and deal with the low end torque since 90%+ of my work is at speed. Been thinking about belt drive. You would also have to figure out a way to lock the spindle for tool change out. Now I just select the lowest gear and all is well.

I have done a couple of things to fight the heat build up. They are on my photopage at: RF-45 info and ideas To include a lower spindle bearing cooler and a gear head cooler.

Thomas

I agree that you can't have both worlds. The best power solution I can think of is to install a 3 phase 2 speed motor that is inverter rated and run with a 1:1 or lower belt ratio. This gives a spindle rpm of lets say 300 to 2500 low speed and 600 to 5000 high speed. So far as torque is concerned. By reducing the ratio to 1 : .75 you can still get around 4000 rpm high with improved torque. Even when using a 3/4" end mill you still want at least 1500 in aluminum and 750 in steel for optimum material removal. The only application I can think of requiring high torque / very low speed is when drilling very large diameter holes ( 5/8" + ) with a drill bit. If its CNC, you can mill them. My RF-45 came with a 2 speed motor from the factory so I am set to experiment when I get around to it.

Hi TPPJR,

I really enjoyed the photos. Attached is my solution which took 1/2 hour to build and install. I used 90lb. gas springs which give an effective zero head weight at the angle shown.

Guys,
Any ideas what the spindle bearing are rated at, as far as rpm, for the rf45 clones and the IH?

Ron

Quote:

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Originally Posted by dcprecision

I agree that you can't have both worlds. The best power solution I can think of is to install a 3 phase 2 speed motor that is inverter rated and run with a 1:1 or lower belt ratio. This gives a spindle rpm of lets say 300 to 2500 low speed and 600 to 5000 high speed. So far as torque is concerned. By reducing the ratio to 1 : .75 you can still get around 4000 rpm high with improved torque. Even when using a 3/4" end mill you still want at least 1500 in aluminum and 750 in steel for optimum material removal. The only application I can think of requiring high torque / very low speed is when drilling very large diameter holes ( 5/8" + ) with a drill bit. If its CNC, you can mill them. My RF-45 came with a 2 speed motor from the factory so I am set to experiment when I get around to it.

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Looks like we have the same machine. I don't think I would go over 4000 rpm, probably stay about 3k. I think that is around the limit for the type of bearings the RF has. Wish it had "real" spindle bearings. I would want to do the conversion mainly to get away from the head noise and heat.

Thomas

Quote:

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Originally Posted by dcprecision

Hi TPPJR,

I really enjoyed the photos. Attached is my solution which took 1/2 hour to build and install. I used 90lb. gas springs which give an effective zero head weight at the angle shown.

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Looks good. I am still waiting for my 150lb spring to come in to replace the 200lb. I will be done with the counter balance then. Did you loose any travel?

Thomas

I would run it faster, at least 4500 rpm. If the bearings give up the ghost, so what, you can always replace them with quality units. I am more concerned with the motor itself. A motor designed for inverter use has an armature that is resin impregnated and bonded and is criyically balanced. This keeps it from flying apart under the high "G" force loads encountered at high rpm. One other point!!!! I estimate that the RF type gear drive system is probably loosing at least 40% of its power and possibly more at high speeds due to heat production. A belt is going to be 95% + efficient. Just think of all the power you gain vs. gears. This is power where it counts on a cnc and far offsets the torque lost at very low spindle speeds.

Quote:

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Originally Posted by dcprecision

I would run it faster, at least 4500 rpm. If the bearings give up the ghost, so what, you can always replace them with quality units. I am more concerned with the motor itself. A motor designed for inverter use has an armature that is resin impregnated and bonded and is criyically balanced. This keeps it from flying apart under the high "G" force loads encountered at high rpm. One other point!!!! I estimate that the RF type gear drive system is probably loosing at least 40% of its power and possibly more at high speeds due to heat production. A belt is going to be 95% + efficient. Just think of all the power you gain vs. gears. This is power where it counts on a cnc and far offsets the torque lost at very low spindle speeds.

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Remember I am not shooting this down. I like the idea. Actually the bearings are quality from the factory at least mine were. When I did my rebuild I replaced them anyway with good ones again. The problem is that they are the wrong kind of bearing for that kind of speed. The best will not hold up. If you go belt drive why do you have to over speed the motor to get 4500? Just adjust the pullies that you use to give you the rpm you want without seriously over speeding the motor.

Another thing is that the gear box lube is what helps carry away the heat from the upper bearing. Once that is gone the bearing will run hotter still.

Thomas

Thomas,

I understand what you are saying. I think that the vast majority of heat is being produced by lubricating fluid displacement by the gears themselves not spindle bearing friction. Just like a car engine, the vast majority of heat is not from combustion or bearing friction but by oil friction between the cylinder walls and pistons. I think that the bearing temps would be substantially lower without the gear system. I have not disassembled the RF head so I can not say definitively what type of bearings are employed. There is no bearing cooling needed on drill presses or knee milling machines, so why on a RF spindle.

I was under the impression that a belt drive conversion is going to fit internally within the gear box using a timing belt. No access for belt changes. If a ratio of .8 : 1 were used for improved low speed torque, a motor rpm of 5625 is needed for 4500 spindle rpm. I think that 1:1 ratio is more practicle with a 2 speed motor. This gives a good power range of 1000 to 5000 rpm considering gains in transmission efficiency.

The bearings are conical bearings, about the worst you could use. The preload changes with changes in spindle temp etc, etc. The bearings produce a ton of heat. Try this, run your spindle (not the head) to the lowest positon then run the mill full speed for 20 minutes. Then feel where the lower bearing is, (where your quil stop is attached) it will be quite hot, you may not even be able to keep your hand on it. Then feel up the spindle from there, the temps will drop but you are getting closer to the gearbox. The gearbox does produce a bunch of heat, most of the heat you feel when you touch the gearbox is from gear friction but the upper bearing runs hotter than that and the oil is on the outside of the casting the spindle slides up and down so the heat is getting transfered to the oil from the bearing too. You would just loosse this heat transfer if you go to belt drive.

What benifit would there be to having a two speed motor if you went belt drive? I have a two speed motor now but have the VFD wired to the high side only. Two speed is not needed.

The worst thing I feel in this whole process is not having the mill to make the modifications that I would need to make. I would have to take the mill down to do the work then would not have a mill to do it with. I would love to do some tinkering around with this without any permanent mods if that is possible.

Thomas