I just had to Laugh

[Stevie]

I just got home from work (had a cash job)

Anyhow; I also made my 8 step pulleys; and when I got home I tried them out; I bought a 6" bench grinder for the Lathes power source; well I removed both grinding wheels and placed my shinny new pulley on the shaft and switched the grinder on; I had the 2L belt on the slowest setting 1,803 rpm and by golly the thing spun the spindle up to speed but it did seem to be having a problem getting it started; but after a few sec it did
Next the nighest speed 12,740 rpm; the grinder just sat and hummed; I feel it was saying out loud "You want me to do what"
I burst out laughing; what else could I do

Now for the question

I still want the spindle speeds as listed here 12,740-10,242-8,193-6,480-5.050-3,816-2,743-1,803 rpm's in 8 steps
But 1/4HP just wont cut the mustard; what would you recommend I really don't want to drop to 1700 rpm on the motor; I'd like to stick with a 3600 motor (most of the work for the lathe is under 1/4" dia and Alum or Brass)

please post some ideas for a still laughing motor ignorant machinest

[balsaman]

Grinders are meant for turning a grinding wheel, therefore they are not designed to start under load.

You can get motors that are designed for this, and will produce several times thier rated torque on startup. Look for a "Cap start" motor.

What sort of lathe? how large? what happened to the origianal motor, and what HP was it?

E

[Stevie]

this is my small self built lathe; there are some photos of it in the other thread; in fact you posted to that thread

[Stevie]

OK as the shaft hole in the new pulley is 0.500" I've just found a #48 cap start ac motor has a standard shaft of 0.500" so I guess just the HP ratings is to be determined; I've found a listing for 1/2hp and 3/4hp with the shaft needed; now do you think that will be enough power

heres a link to the page of the 3/4hp

http://www.aosmithmotors.com/concert...html?navApp=a2

[keithorr]

I have a Jet drill press (my shame, sorry) that has pulley speeds up to 4200rpm at the spindle. The 1.5 h.p. (can you really trust the label?) capacitor motor trips a 20 amp breaker before the spindle gets to speed.

The only way I can run at that speed is to loosen the tensioning lever and let the belts slip while the motor starts, then slowly tighten up and set the lever.

[balsaman]

Originally posted by Stevie
OK as the shaft hole in the new pulley is 0.500" I've just found a #48 cap start ac motor has a standard shaft of 0.500" so I guess just the HP ratings is to be determined; I've found a listing for 1/2hp and 3/4hp with the shaft needed; now do you think that will be enough power

heres a link to the page of the 3/4hp

http://www.aosmithmotors.com/concert...html?navApp=a2

When in doubt, go with the bigger motor...

E

[Stevie]

I do have a 1/2hp with the right shaft; it on my belt/disk sander; just looked at it; 3450rpm and cap start; I'm thinking if it can start that big belt 36X6 and the sisk with its belt drive it must start the lathe just dandy

edit edit; dang shaft is 0.625 with a keyway; I could change my pulley; but that would be over the coming week (I don't feel like going back to work again this weekend) I looked inside the belt cover and it looked like a 1/2"

[HuFlungDung]

12,000 rpm for a lathe spindle? I would estimate about 20hp should keep it turning as the bearings melt their way through the main casting

Seriously, you need force lubricated bearings (oil or oil mist) to cool them down. A lathe spindle has a decent preload for obvious reasons, and is reasonably stiff. You might want to actually reduce the preload a bit if you are serious about pursuing this kind of speed.

Also, make sure that your chucks are rated for whatever speed range you do manage to attain.

A variable frequency drive would do a nice job of providing a controlled acceleration ramp to prevent nuisance tripping of the overloads. For that you would need a 3 phase motor and a VFD, of course. The cost of the motor is soon forgotten, so get a 2 hp or so. Remember, a motor of adequate size will last longer and consume no more power than it needs to do the job at hand. There is little point in running the snot out of a dinky little motor.

[Stevie]

Hu

this lathe is very small; the bearings are 30mm ID; the spindle needs to be fast for the tiny parts it will make; most of the time I'll run it around the mid range; but to polish up a 1mm scale AA gun barrel I'd need 12,000rpm
while I'm using regular deep row bearings with a setable preload via the end nut; I expect to replace them about every 100hours

[HuFlungDung]

Stevie,

Why don't you rig up a small toolpost buffing wheel? Then you can run ordinary spindle speeds and let the SFM of the wheel get the speed you require?

[Stevie]

but I stil need very high speeds to turn tapers etc on sub 1/8" dia stuff; I don't know about you; but I find over 7,000 rpm works best on very small dia's

[Stevie]

Ok great news on the motor front; the beltsander motor works great; even up to top speed; it will be slightly lower as the motor is a 3450; not 3600 hence the speed is down to 12,206 with zero losses; I'm sure there will be some

The next job is to mount everything to a nice 1" thick Alum plate; I'll make the motor slide and fasten the lathe static; then add a belt guard; this puppy is really spinning; if it broke; I'd be wearing it
AS there is "no" 3 or 4 jaw chuck the spindle seems very smooth for the high rpm's it winging round at; but I'm sure my estimation of 100hours for a set of bearings will be close
They are standard SKF units and are rated to 10,000 in oil; as these are 2RS units; or sealed both sides; I'll pry off the inner seal and flush out the grease; then I'll 1/6 fill the head stock cavity; this will form a bath for the bearings; if i stay under 10,000 (really any speed other than highest) they should last the 100 hours