Currently restoring a 618 I found a few months back. I got it mostly complete aside from a motor and related counter shafts. My question is what direction should I go with powering this lathe. I have a new 1/2 hp motor laying around but I do not have the counter shaft. Should I get a counter shaft on ebay or possibly go with an entirely different motor powered with a VFD and is it feasible to not use the counter shaft with a VFD setup? I could even do a 90 VDC though the motors are more expensive. The reason I ask is the counter shafts are pricey and I could go with the other options for nearly the same price, but keep in mind I do have the 1/2hp motor and a nice drum switch to go with it. Just looking for some ideas as I really cant decide. Thanks.
-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
Powering my 618?
- Thread starter BrianT
- Start date
- Joined
- Feb 1, 2015
- Messages
- 9,988
I have had a 3/4 hp 3450 rpm motor on my Craftsman 6x18 for forty years with no issue. For 23 years, I used the lathe almost daily for production. I do run the belt tension on the driven belt low enough that it will slip if the lathe is overloaded though. I run a 1-1/4" pulley on the motor with the OEM counter-shaft.
One data point.
One data point.
Maybe Im making this confusing after rereading my original post. From what Ive read 1/4 to 1/2hp is recommended for the lathe. What Im thinking Id like to go w/ a VFD set up, running a 3ph motor off 110v VFD, so would I still want the counter shaft to change or adjust belts. Im guessing that even with a VFD I would want to change speed pulleys at some time. I dont know that I can have the speed range of the VFD and get the speeds I want off the lathe with out a pulley change at some point. Is it still worth having the counter shaft to do this? Possibly a step pulley on motor would suffice?
- Joined
- Feb 1, 2015
- Messages
- 9,988
The OEM counter shaft gives an 8 to 1 range in speed, not including the back gears. Going to a vfd and eliminating the countershaft may cause some torque limitations at the lower end of the speed range. The back gears will help, giving a 6.6 to 1 reduction in speed and a 6.6 to 1 torque multiplication. The OEM top end is 3050 rpm so 1 to 2 pulley arrangement will get you the equivalent with a 1725 rpm motor.
If I remember correctly, torque on a vfd motor drops off fairly dramatically when you get down in the 10 - 20% range. The minimum OEM speed in back gear mode is 55 rpm. This would require a driven pulley speed of 360 rpm. with a 1:2 pulley setup, this would be 180 rpm for the motor or about 10% of rated speed. (there is some rounding so numbers aren't axact, but you get the idea)
A step pulley will help. If you had a 3 to 1 arrangement, you should have reasonable torque at the low end.
If I remember correctly, torque on a vfd motor drops off fairly dramatically when you get down in the 10 - 20% range. The minimum OEM speed in back gear mode is 55 rpm. This would require a driven pulley speed of 360 rpm. with a 1:2 pulley setup, this would be 180 rpm for the motor or about 10% of rated speed. (there is some rounding so numbers aren't axact, but you get the idea)
A step pulley will help. If you had a 3 to 1 arrangement, you should have reasonable torque at the low end.
- Joined
- Oct 18, 2016
- Messages
- 2,872
The spindle speed chart for my 618 shows a range of speeds in direct drive from 365 to 3225 rpm and 54 to 481 in back gear. I'm not sure that's feasible with a VFD.
Keep in mind that running some motors at very low speeds with VFD's overheats the motor since the fan turns so slowly, so there are practical limits to their use.
The OEM countershaft seems like the way to go.
Keep in mind that running some motors at very low speeds with VFD's overheats the motor since the fan turns so slowly, so there are practical limits to their use.
The OEM countershaft seems like the way to go.
- Joined
- Feb 14, 2016
- Messages
- 623
3,450 RPM that's interesting RJ are you running the stock counter shaft set up ? I think the motor originally used is 1,750 RPM . I'm using the stock counter shaft , but I don't have the correct pulley on the motor . At first when I got my 101.07301 6" Craftsman the motor (1,750 1/3 HP) would not start by it's self , but now that I have it all oiled up and have been using it it starts up fine now . At first I was thinking of different set ups and a different motors , the tread mill motor came to mind and I think (?) there is a guy on HM that documented the whole thing and he runs it direct drive . I might do that down the line . Another thing I was thinking about was to put the counter shaft and motor under the lathe and go straight down through the middle of the lathe with the belt that way you would not see anything the lathe would just be sitting there with everything underneath . I had a few sleepless nights thinking of that set up ! But it just was not practical for me . One of the reasons I wanted to do that was because I have space constraints . I think I came up with a good alternative I got the counter shaft as close to the lathe as possible and mounted the motor on a shelf underneath .
Last edited:
- Joined
- Feb 1, 2015
- Messages
- 9,988
No I'm not running the stock counter shaft I replaced the OEM step pulley with a 6" pulley for about a 4:1 speed reduction. The driven pulley is stock. I bought my lathe used and I believe that the motor was 1/2 hp. I happened to have the 3/4 hp 3450 rpm motor at hand so that is what I put on the lathe. Like the bumble bee not knowing it couldn't fly , I had no information about the recommended hp so the 3/4 hp motor worked and continues to do so. No internet forty years ago, don'tchaknow.
As to running the drive belt to a counter shaft below, there are several reasons that could be problematic. One is that it would be more difficult to change belt positions and engage/disengage the belts. Another is that area tends to be fairly dirty, collecting swarf and oil which could foul the belt and/or counter shaft pulleys. A barrier could be put up to minimize that though. Finally, it appears on my lathe that the belt may rub in the casting.
I have an OEM table for mine and the counter shaft extends 17" in back of the centerline of the lathe at its furthest point. It could have been mounted about 2.5" closer or, if mounted on an angled block, possibly as much as 6 or 8" closer.