Im getting ready to move my 10R onto a bench for a 9A. Im really low on space behind the machine so im tempted to get rid of the countershaft and drive the spindle directly from the motor using a inside-out poly-vee belt. I have a 1 hp 1750rpm motor with a 110V to 230V VFD that I could use. I consider to gear it 1:3 and use the motor in field weakening mode (over speed it at constant voltage) to get the higher speeds.
The power from a motor is acutally quite constant above its name plate speed so you dont loose anything by over speeding it vs gearing it.
Have anyone documented this in the past? Im hoping to see some elegant motor mounts:-)
How fast can a 10R cast iron spindle run?
I don't really see where you are gaining here. If you keep the standard horizontal cone pulley drive you are stuck with 18 to 20" bench width to fit the cone, useable belt length and adjuster in. Given that its probably easier simply to dump the standard Vee to flat countershaft drive, with its irreducibly big driven pulley, and either use a polly Vee (serpentine) or a two stage plain Vee belt drive. Single or two speed, all new or modify the existing casting, to taste. Either way the large step of the cone pretty much defines the bench depth. I've done the two stage, two speed Vee drive several times over the years on both SB and other breeds, works well and is easy to include a jockey pulley type clutch. Can do you a suggestions PDF if you like. Nowadays I'd seriously look at the poly Vee drive, still with a jockey pulley clutch, even if you don't exploit the clutch the spring loaded jockey pulley tensioner gets you out of the matched pulley & belt length trap. especially as you plan to use a VFD so speed trimming is easy.
From your reference to over-speeding I guess you are looking to replicate a two speed system with a simpler drive. Standard SB countershafts tend to run in the 390 to 410 rpm range so a 4, or 4.4 to 1 reduction would be a better fit. 1400 rpm is about as fast as I'd care to run a segmented type cast iron bearing without a bit of attention to lubrication. Push to 1,600 maybe if the wicks and all are on top line. Only reason for seeking such speeds is real tiddly work or to properly exploit carbide tooling neither of which is really 10" SB forte. To get this sort of speed you will need to double or more the standard motor RPM using the VFD. Do-able if you have a designed for VFD motor and its matching drive but risky with a standard motor. If you are expecting constant output power you are in drive systems engineering territory. Most VFD units have input power draw limits but how much actually gets through to the shaft is a different matter.
There are very good reasons why the "always safe" variation on a reasonably modern motor is considered to be around the ± 30% region and on older ones ± 25 or even ± 20% is more prudent. VFD units tend to supply the power needed so at part load the safe operating area extends considerably. The problem is that motor efficiency drops badly once you go too far beyond the design rpm, depending on about a million constructional and design factors, and Home Shop Guy has no way of measuring what is actually going on. Falling efficiency means higher current draw for the same torque. Higher current means more heat inside. Too much heat evaporates the magic smoke!
I've done it on a small Atlas lathe in the past to conserve space and there is no reason why it won't work on a South Bend as well. South Bend made lathes with speeds up to 1800rpm. The only difference appears to be the pulley sizes. If you're lathe is in good shape, properly adjusted and lubricated, you should be fine. Watch the bearing temps at the higher speeds just to be safe.
Use the VFD for a direct drive speed range of 300-1800rpm (20-120Hz) and the back gears for the lower range (I don't remember the rpm range). You'll lose torque and/or hp at the extremes but I assume that you're not in a production facility and taking a smaller DOC won't be a big deal.
Many motors weren't designed for varying speeds but that doesn't necessarily mean that they can't handle it. Assuming it's a fan cooled motor, it will probably be fine. If not, get a new one. They aren't that expensive. I've used non-VFD rated motors with VFD's for years without a single failure. Your mileage may vary.
NOTE: I see that you mention a cast iron spindle. You may have to adjust your speed range down on the high end if you don't have bronze bearings.
Ulf, I'll be interested in seeing how you go about this. I need to tackle the same problem as soon as my 10L is cleaned up. It didn't come with a stand, though I do have the counter shaft I would rather not use it and maybe do a direct drive with a servo motor. My thought is to weld up a stand and tray but have the servo direct connected and just limit the top end speed with pulley selection (~2.5:1). I will get 100% torque at 0 rpm so I shouldn't need the back gears unless I really take a hogging cut. If my calculations are correct, the motor I've selected should give me about 4hp to the spindle from 0-1400 rpm without the back gear.
Cliff, VFD rated motors typically have thicker insulation systems. It does not matter much for short wire runs. When you are up in the 30ft range you can start to build higher voltage.
If I gear 1:4 or 1:3 or their inbetween I can put the motor right behind the back gear. I win about 1 ft.
Im thinking of making a simple plate to mount the motor on from some 5/8 Aluminium and clamp it to the V on the bed like the collet rack. I should be able to support the weight with a 1/2 threaded rod to the table.
I did this (eliminated the countershaft) on a benchtop pratt and whitney milling machine,
which is V-belt driven. The results for that machine, were outstanding. Check
to see what spindle speeds you want, and work the numbers for the given pulley
Your options include the 3~ motor nameplate speed, 1200 or 1800 rpm, the motor
hp rating (size up if you think you need hp at below nameplate speed) and the belt
type. Avoid leather belts as they will slip, the serpentine belt is the way to go.
Don't forget you will effectively gain some hp at the spindle by removing one set
of belts and the countershaft.
Im tempted to try to find an old cone pully and machine in the vee grooves. I dont view the 10R as very collectable and there are a few that is parted out now and then so I dont feel to bad over modifying a pulley.
(I do feel bad over not having a P&W miller, I think one of those make you a better person, kind of like a Hermann Schmidth edge finder ;-)
I have considered doing something similar for my bench-mount 9 JR, if the current mechanical variable speed drive ever quits.
My plan is to mount two small diameter long rollers off the rear of the bed behind the cone pulley. They will look like a winch fairlead. These will turn the belt down thru a hole in the table, to a motor underneath. A lever running under the table to the operator will control tension on the serpentine belt, probably using the fairlead. I have no plans to groove the cone pulley.
The only question then becomes the drive itself. The thin Poly-V belts allow very tight turns, so my current plan is to use a small diameter cone pulley directly on the output shaft of a low RPM motor, and drive it with a VFD. I routinely drive the motor on my mill from 30hz to 90hz, without problems. So if I do that with an 850rpm motor on the lathe, I would get 425 to 1275 rpm. I would use only a 1/4 to 1/2 HP motor, since it will have twice the torque of a 1725rpm motor.
So, being a computer programmer, I wrote a quick script that applies the Rankine belt formula to my cone pulley diameters and RPM range, and produces a suitable motor cone pulley to keep the belt length constant. This does not account for the deflection of the fairleads, but it might still work:
HS Motor Min Max
Diam Diam Rpm Rpm
2.625 3.315 535.5 1606.5
3.751 2.181 246.5 739.5
4.875 1.001 89.25 267.75
Give me the diameters of your cone pulley steps, and I'll run it for you.
Last edited by kitno455; 11-23-2010 at 04:58 AM.
Reason: Grr- tables are disabled here....
Mentioned your space problem this morning whilst chewing the fat with Mike the Pilot and he made what seems a good suggestion :-
"Assuming the basic problem is that there is a wall, not a window, behind the bench and limited space in front why not hang the motor and any countershaft or drive gubbins on the wall behind and above the lathe so the belt drive goes straight down. Make a sort of cupboard type enclosure to keep the dust out with the door on the front coming down far enough to make a belt guard. If he sticks a whiteboard on front of the door he'll have something to scribble on to keep track of the cuts."
Sounded promising to me and probably wouldn't look at all bad if you made a matching rake of cupboards to go along side it running above the lathe with the bottom 5 ft or so off the floor. I have three shelves arranged thusly (8 ft ceiling) and find the arrangement good.
No good if you are under a window tho', a position I loathe with passion.
Although the capabilities of a well set-up VFD drive vary from wonderful to jaw dropping amazing (check out the so called servo replacement integrated motor drive systems) I've met enough disappointments not to take their capabilities for granted. Uprated insulation, basically to let the motor coil innards run hotter, is one of the smaller differences between a modern "designed for VFD" use motor and a good classic 1950's to 1980's machine. Most decent VFD boxes have a long list of parameters which the user can adjust. Optimum for the job rather than general can make a huge difference. Not wishing to be involved in that side of engineering a VFD, to me, is an easy way of getting 3 phase and closing the gaps in the standard drive steps. In practice leave the belt on middle 90 % of the time. But each to their own.
I thought about the same thing, but my serpentine belt is running so good that I thought it would be a waste of time. Also these belts are very critical about the alignment. I have seen serpentine belts disintegrate in the first few seconds, because of misalignment. considering the low horsepower needed, I don't think you would gain enough to make it worth while.
Originally Posted by tribologist
Not sure why a poly-Vee belt would blow up? I been abusing them whay past their design load for various reason and they hold up well. Look how many hours you get from them in a car.
I saw a 900 dollar Goodyear poly vee driving a wood chipper come apart. And the guy that owned it just stuck another new 900 dollar belt on it and it came apart. I asked if he thought it was time to find the alignment problem? So he sold the chipper minus the belt...Bob
Originally Posted by tribologist
Bob Wright Metal Master Fab
Salem, Ohio Birthplace of the Silver and Deming Drill, all others are copies.
That would be the equivalent of expecting the belt holding up when ramming the tool into the chuck :-) I cant imagine a more demanding application than a wood chipper. A set of V belts are probably more forgiving.
Originally Posted by aametalmaster