MY BELT DRIVE CONVERSION STARTS

[small_toys]

I have begun my belt drive conversion. (parts ordered) I have some concerns about the low end grunt and overspeeding the motor, but will test it after assembly. This is what I have gone with.

Timing pulleys that mount without modification to the shafts.

34 Tooth on Motor and a 28 Tooth on spindle.
Motor is a 3HP 3450 RPM 56C face Baldor 3PH
Drive is a Hitachi SJ200

I would like to see @ 6000 RPM at the spindle, which requires @5000 RPM motor speed.

[Cruiser]

Basically you'll have a speed potential of 6300 driving vfd at 60hz and 12600 at 120hz. I think you will find that your drive ratio might be better reversed. You will find that the spindle probably won't survive that high of speed even with good bearings and your low end torque will be nearly non existent. Too bad you already ordered parts.

[small_toys]

Cruiser,

Not sure I follow you.

Motor Pulley is a 34 Tooth, and Spindle Pulley is a 28 tooth. That will give me a 0.8235 : 1 gear ratio.

At 60Hz Motor RPM will be 3450, spindle will be 4189 RPM.
At @90Hz (+/- 2) Motor RPM will be 5000, spindle will be 6070RPM.

If I understand correctly, Torque is constant below rated motor RPM so that sould be, Motor Torque = 4.57 ft-lbs, Spindle Torque = 3.76 ft-lbs.

The bearings I have ordered are good upto 11,000 or 12,000 RPM in grease if I remember right.

[BobWarfield]

Your VFD will tell you how slow the motor can go and still have it maintain torque. If it's slow enough, you may have some cooling problems if you don't have an additional fan on the motor.

If you haven't bought the VFD yet, look for a sensorless vector--they carry a broader torque range.

Cheers,

BW

[small_toys]

I have the VFD on hand already and it is a sensorless vector model. As for coolingthe motor, I plan to monitor the temps after its up and running and see if I need to replace the motor driven fan with an electric fan to help cool it for slower speeds.

I also plan on looking into buidling an ATC for this with index positioning so the drive dogs will work. Not sure if I will attempt to use the VFD or not. I know its not likely to work with my current setup, but I will see what is possible once its up and running.

[Cruiser]

Motor 34
Spindle 28
Motor turns once, spindle turns 1.2142857 turns
This is then an induced ratio @ 1/1.2143 ratio
Recalc your speeds now

If your pulleys were reversed then your ratio calc would be correct

And, your right, I did appear to botch my calc in previous post

[small_toys]

Cruiser,
My math is correct, and so is my ratio.

0.8235 : 1 is the same as 1 : 1.214

0.8235 is the inverse of 1.214

For every turn of the spindle the motor will turn 0.8235.

Its just another way of stating the ratio.

So @ 90 Hz the motor will be at 5000 RPM and the Spindle will be at 6070 RPM.

5000 * 1.214 = 6070

[small_toys]

I found out why the gearbox was so noisy. Some of the casting sand was still left in the gearbox! It turned the oil to a sludge and the bearings where rough. Some sand must have gotten in them as well.
Here are some pics.

[small_toys]

The pulleys and belt came in so I decided to check to see if the calculation for belt size was correct. Everything look good. I did have to turn the ID of the motor shaft down to fit my 15/16" bushing.

One issue I see is the motor pulley diameter as it stands now will hit the back wall of the gearbox. I will need to modify one or the other to correct this. Its about 1/4" overlap.

On the spindle side I will have to leave the seal and mount off where the spindle drive slides through. The bushing bolts stick below the mounting surface about a 1/16".

Overall I am pleased with it so far. I need to finish the motor adapter plate and bushing to run it.

[Bubba]

Hard to tell in the pictures, but maybe you can simply remove the flanges on the interfering pulley as you really only need them on the smaller of the two!

[small_toys]

I checked on removing the flanges on the pulley but they seem to be welded on. So I clamped the mill head to my other mill and just barely had room to clean up the area where the pulley would hit. Also chucked the pulley up and removed a little material from the flange.

Looks good.

[philbur]

Have you considered spindle bearing type, configuration and preload? These will all have an influence on whether you can reliably sustain 6000 rpm.

Just a thought.

Phil

I would like to see @ 6000 RPM at the spindle, which requires @5000 RPM motor speed.