[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.

[small_toys]

Yes,
I have purchased angular contact bearings for top and bottom on the spindle.
Bearing numbers are the ones Cruiser had listed. I have them greased with some Kluber Isoflex NBU 15.

[philbur]

You need to consider the bearing configuration/layout as well as the bearing type. A spindle running at 6.000 rpm is going to get very warm, this temperature rise will increase the spindle length and potentially reduce/remove the preload from the bearings unless you have a bearing layout or other strategy to compensate.

Will the original configuration with AC's run at 6,000 rpm, probably. Will it be a good machine tool spindle, probably not.

Phil

Yes,
I have purchased angular contact bearings for top and bottom on the spindle.
Bearing numbers are the ones Cruiser had listed. I have them greased with some Kluber Isoflex NBU 15.

[small_toys]

phil,

Yes it might not be the best solution, but without seriously machining the spindle housing to accomodate 2 AC bearings at the bottom (if that is possible) this seems the best solution.

I am open to ideas?

On the other not. I have completed the motor adapter plate and need to make a coupling adapter to mate the motor shaft to the bore on the drive pulley shaft. Pictures to follow.

[philbur]

You might want to down grade your target of 6,000 rpm to something around 4,000, if 6000 rpm turns out to be unusable then you have sacrificed low end grunt for no purpose. Also you could look at ways of achieving a more accurate preload setting, to minimise temperature rise.

You might want to consider a two belt drive to give you a "high" and "low" range, as per the Tormach. This would also help greatly with low end grunt.

Just a thought
Phil

phil,

Yes it might not be the best solution, but without seriously machining the spindle housing to accomodate 2 AC bearings at the bottom (if that is possible) this seems the best solution.

I am open to ideas?

On the other not. I have completed the motor adapter plate and need to make a coupling adapter to mate the motor shaft to the bore on the drive pulley shaft. Pictures to follow.

[philbur]

Just because you use bearings with a maximum speed rating higher than your intended use it doesn't mean that they will survive at the lower rpm under the prevailing conditions. There are many factors related to spindle design and installation that down rate the maximum rpm capability, not least of which are preload and spindle housing and shaft tolerances and concentricity. To at least understand the issues you should do a read up on application from one of the major bearing manufacturers.

Just another thought
Phil

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

[Cruiser]

I have run mine at 6,000 rpm for many hours cutting aluminum and it only gets warm, which is normal. If good grease is used it will stay put on the bearings for quite some time. The only real concideration is implementing an appropriate maintenance schedule to redo the greasing of the bearings. This greasing maint. should be used for any spindle. I've been into mine a number of times and found that the grease will burn and vaporize out, leaving minimal clean lube behind with time. I started with approx 100 hrs for checking it and it could have gone longer, but not too much longer. It is fortunate that our IH quil can be dropped and serviced and back to work in an hour. I tried a grease that smelled like amonia that only lasted an hour and was done. Good grease should last for a long while, and resist migrating as well as vaporizing. If it is an unknown then drop quil and check it out.

[small_toys]

Well, I have my conversion assembled, only the gearbox and motor, no spindle. I ran it at roughly 6000 RPM and the bearing on the spindle gear side get really hot. No temp gun to read it but I cant keep my fingers on it because it's so hot.

Cruiser, did you replace this bearing? I did not. Maybe because the spindle is out I have less support for the bearing and that's why its so hot!

phil, I want to make 6000 RPM. I will run this and see how it works. If it fails or does not work like I want I will look into spindle bearing arrangment and modifications. I have looked at the SKF catalog on bearings and spindles, this gave me an understanding of what should be done. But again, I am trying to work with what I have with as little mods as possible.

I have pictures but need to upload them first. Maybe tomorrow.

[arizonavideo]

Your going to have a lot more side loading using a belt over a gear so I would not be surprised if it runs hotter. I don't think the drive shaft fits tight enough to lessen the side loading either.

My top bearing ran hot with the stock setup when new but cooled down over time so it could be just the bearing. It's a low cost part so you might just put in a better one.
My machine also made a racket when running it without the spindle installed.

Installing the spindle may help with side loading so you need to put it in to find out. A looser bearing may allow the pressure to transfer to the shaft and lower the side loading too but I won't bet on that, it is a fairly loose fit.

The belt will also break in quite a bit in the first 20 or so hours, perhaps a long run in at a lower speed might do the trick too but to reduce the side loading you may have to cut off the drive gear and mount the pulley closer to the center bearing axes if you have room.

BTW, I like the idea of putting the belt drive inside the head better than having it on top if the low speed torque is satisfactory I will do the same thing. I have a new motor and a VFD sitting here.