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Thread: SB dc motor pulley or no pulley
03-11-2017, 02:59 PM #1
SB dc motor pulley or no pulley
I'm trying to set up a dc variable speed motor on my model 9c SB. Here is the dilemma I have, can I just set up a motor without using existing pulley system? What I mean is can I just use one belt from motor to the chuck shaft or using pulley (2 belts) is a must?
My current motor is 1/4 hp and new DC motor is 1.5HP, so I think I will have enough torque, maybe?
03-11-2017, 03:49 PM #2
Monarchist, thank you for reply, but I'm new to lathes and I have no idea what you just explained.
Here is the reasons I want to convert. 1/4 is ac NOT variable speed, new dc motor is higher hp and variable speed(it is a treadmill motor, baldor and it works).
I would like to eliminate pulley system to save space, but I don't know if eliminating that big pulley wheel and one belt would bring up issues. To me it seems that getting rid of pulleys would not make much difference especially since I'm adding a stronger motor.
03-11-2017, 04:33 PM #3
right to the motor. Oh, and a means to tension the belt of course.
You'll probably find it does not work well, predicted by looking at the relative sizes of the motor pulley you are using
right now, vs the size of the large diameter pulley on your countershaft assembly. Figure out the speed reduction from
that setup, and then figure out how fast the spindle wants to be going, based on the motor speed and that reduction,
figuring the countershaft speed is about the same as the spindle speed. On the center set of cone pulley steps, it's more
or less one-to-one.
You'll find that you probably need to restrict your dc motor to less than 1/4 speed to make it all work out, even with
a pretty small dc motor pulley. Also be aware that flat leather belts don't like to be driven by really small pulleys,
you'll find a fair amount of slippage there.
In my case I deleted the countershaft from a small milling machine, but most of the speed reduction was betwen the
pulley on the countershaft and the pulley on the spindle. Truly the countershaft eats a lot of power that is better off
delivered to the cutting tool. In my case I used a four pole 3 phase motor and can run it between 10 percent of nameplate
speed, and 150 percent.
03-11-2017, 04:55 PM #4
Thank you Jim for the answer.
Morarchist, I think you completely missed my question and just decided to point out my lack of knowledge in that matter in a humiliating way. Anyway, the question was "Are pulleys necessary or not in my case ?" please stay on topic if you have useful information. Thank you.
03-11-2017, 05:08 PM #5
You must be careful not to overspeed the spindle, but since you did not tell us which lathe you have, and what year, it is very hard for us to say what that speed might be.
03-11-2017, 05:14 PM #6
03-11-2017, 05:36 PM #7
1929? No, the SB 9C did not come out until 1935 or so. Give us the serial number.
03-11-2017, 05:42 PM #8
I think the speed reduction from smallest driving sheave to the large sheave on the spindle is about 2.5:1
As such, you would need a range of 0 to 3500 rpm to cover 0-1400 rpm on your lathe. this is pretty typical for treadmill motors.
This seems reasonable to me. if you are driving that motor with an SCR drive, its very likely you need an inductor. A microwave oven transformer (with secondary removed), and a paper thin gap in the core should be about the right capacity and inductance.
if you can use an uncut serpentine belt and make a pulley for it, you won't have a lack of friction problem on the motor shaft side.
some serpentine belts have grooves cut just like v belts to help with small diameters pulleys. you could probably get away with just a 1.25 inch diameter pulley on the motor side, that would give you about a 4:1 ratio to the cone pulley on the spindle. some treadmill motors are 4500 rpm.
415-AC is the catalog number. Popular Mechanics - Google Books
there should be a serial number at the end of the lathe between the tailstock flat way and the front v way.
post was edited.
03-11-2017, 05:46 PM #9
The only number that I see is 415AC
03-11-2017, 05:51 PM #10
Top of the bed, right side front, near the screws where the leadscrew hanger attaches.
03-11-2017, 05:58 PM #11
looks like it is 162076
03-11-2017, 06:01 PM #12
by using a calculator and formula the year should be 1944 if my math is right
03-11-2017, 07:58 PM #13
Around May 1945: http://wswells.com/serial_number.html
Assuming your bearings are in good shape, and the oiling system is working properly, I'd run a segmented cast iron bearing 9" up to a max sustained speed of maybe 1000 RPM, with brief excursions to 1200 RPM. For a smooth cast iron bearing, probably 200 RPM less for both numbers. If you can set your pulley up to have the motor speed max out at around that spindle speed, you should be fine on the top end. You will have to try it out, and see if you can still move metal without stalling or overheating the motor at lower speeds, however.
Monarchist liked this post
03-12-2017, 08:50 AM #14
"if you can use an uncut serpentine belt and make a pulley for it, you won't have a lack of friction problem on the motor shaft side. "
This is of course the way to go. Much more flexibility and grip. Could be spliced or laced to go around the headstock
cone pulley too!
The entire thing could be tested for about 20 bucks or so.
03-12-2017, 06:18 PM #15
Spindle oil was previously flushed out, I was using a mix of heating oil and 5w-30 in a 50-50 mix calculated to match the viscosity of what you're supposed to use.
I replaced it with green ATF that a friend of mine mistakenly drained out of a 2013 suv. I can't remember what he drives, but its one of those vehicles you have to tow to the dealership if you do that because there is no fill port, only a drain port. i can't remember exactly what vehicle it is, can find out later though and update once i find some information on this atf. but its thinner than 5w-30 oil.
The spindle warmed up, my guess about 20F. bearing clearance is about .0015"
03-13-2017, 05:31 PM #16
I'd suggest keeping the countershaft. I've done a small lathe and a drill press with DC treadmill motors and on both the countershaft has given a more usable range of speeds. At low speeds they have little torque and at top speed they're pretty loud.
03-16-2017, 02:47 PM #17
Some of this may/not apply to your exact machine but:
I use a KB electronics PWM adjustable DC drive with a 1HP Boston gear PMDC motor 1725rpm @90V(BG says its good for up to 50:1 speed reduction with full torque). I dont know if a treadmill motor has anywhere near equivalent specs. I limit top speed to 1400 at the lathe spindle with the drive. My SB is newer, has bronze spindle bearings and a 4 groove V-belt pulley on the spindle, I use ~3" V-pulley on the motor and the largest of the 4 grooves on the spindle. I use a segmented V belt to reduce vibration. It is fairly quiet (new bearings and brushes well seated). Im waiting on a spindle tach module to make it easy to adjust.
IMHO you are going to need some flat pulley on the motor, just the belt on shaft will allow too much slippage. Belts have a minimum bending radius which limits the minimum pulley size.
03-20-2017, 03:41 PM #18
biggest issue with treadmill DC motors is the 4000rpm speed that most of them have (your Boston gear one is much more ideal). It's hard to drop the speed down to a usable range direct drive (say 400-2000rpm) or back geared (50-400rpm) without a countershaft.
One of the better things I did for my lathe was use a polyV belt from motor to countershaft (actually the original pulleys from the treadmill) which allowed a bigger step down as the polyV can run off a much smaller driven pulley without slipping. That shifted the usable speed range down further, although I still need to make a countershaft to spindle polyV pulley as the little 3/8 v belt on there slips like crazy.
03-21-2017, 02:12 PM #19