New Guy, New Lathe, need a little help.



Ok I have a question on the variable-drive. I’ve looked over many threads and haven’t found an answer to my question so here it goes.
First I bled this thing every way I could find Instructions too. I gave up and ordered new seals and packing. It has the newer, I think, unit with the square master cylinder not the round one. After the new seals and bleeding it again I think I finally got it working good.
However I can not get the dial to match the speed of the belt. After a couple of days looking at it I decided to take the top of the variable-drive apart and try to figure it out.
So I found the push rod that rides on the cam is adjustable with a set screw in the end. (See pictures) I’m not sure if this is a stock piece. Seems kinda hokey that the set screw would push on the piston. The Manuel I have shows the old style round master and it looks like the pushrod is not adjustable. Is this the right piece?
Anyway, when I adjust the push rod so that the cam runs the full distance around, it will push the drive too far. It will go so far on the high speed side the belt will run off the pulley.
I bought a tach to check the rpm and I have adjust the low speed nut on the variable drive pulley to 42 RPMs and then adjusted the push rod until I get 230 RPMs. This is great however the dial does not match up to the RPMs. When I set the dial to 42 RPS at the slow speed it tops out about 210 RPM on the dial.
Am I missing something? The only thing I can think of is that the cam is wrong and ramping up too fast and pushing the rod too far too soon. But I can’t imaging anyone changing the cam, but who knows.

Thanks for any help.94BEAAD5-658F-4662-B445-7DD215F44C99.jpeg4F0FC413-2295-4083-8604-0F6CB1A748A8.jpeg2E92A3B7-4C81-47E3-AE2F-4996EAC8EA21.jpeg4B4D5338-5938-4FAA-902B-3A6FFD41660A.jpeg6FD71271-446A-435C-A755-17B196017F3F.jpeg
 
Well I guess no one here has dealt with this problem before, or maybe it just doesn’t matter. The dial seems to be just a pretty rough estimate of speed anyway. Sense I only have the high speed due to the motor change. I’m thinking I might just make sticker with new graduations to match the speeds and call it a day. Anyone see a problem with this?
 
I don't have a Clausing so I have no clue on that drive, but is it possible the speed of the new motor is different than
the OEM motor? Is the difference between actual speed and dial speed consistent across the speed range of the
machine?
 
I've got a 6913 with a similar variable but it was disconnected before I got it so I never used it. I do have the old parts still. I could look at them and photo them if you think it might help you in any way. Just let me know. Not sure if they are the same either, but they LOOK similar.
 
It would be interesting to hear from some any other guys out there who own the same lathe if their speed ranges correspond closely to the dial increments or not.

I have two variable speed drive systems here, one on my power hacksaw and one on my shaper. And in my experience with these things, the transition between the low-high limits is not necessarily a straight line. I suspect mathematically it should be, but when push comes to shove there are nuances and tipping points in the physical system that causes some slight inconsistencies in the transition.

The lathe in question though is not a mickey-mouse machine, and I figure a good deal of engineering went into making things right. When I look at the speed range and the increment spacing on the dial, it would seem to me that there should be tighter accuracy. I mean, we're not talking about 20 rpm on a 42-2300 range, we're talking 20 rpm on a 42-230 range.

Back to my experiences with less than linear transition, if some of those might be inherent to design (as opposed to being induced by wear) an ideal way to compensate would be through the lobe shape on a cam. Right now the OP has set the low speed limit of 42 and notes the discrepancy at the high end of the range. Are the results consistent if the cam/pusher are set up to achieve a correct top end speed of 230, does the low end then suffer by the same amount? Where I'm going is does the lobe shape on the cam maybe compensate on one end more than the other?

The other thing I know can be a little tricky is getting the belt tension right to produce the desired range. It can be a bit of back forth to set the limits on the variable drive, check the range, tweak the tension, reset the limits, check again, etc. At least that has been my experience with the two I've played with. Is it the correct belt both in profile and size to match the variable drive pulley?

I really like variable drives, they're cool to run. But they can be fiddly to get set up and even harder once a few of pieces start to get changed. Good luck with it. Oh yeah, and I don't like the looks of the set screw bearing on the cam either. That seems less than ideal, but it may have been a factory compromise at one time. Again it would be nice to hear from someone else who has the same machine.

-frank
 
I believe the original motor to be 1800/900 RPM from a sales brochure I found. The motor in there now has a data plate that reads 1735 RPM so it’s pretty close. If anything I think would need more travel on the Variable Drive to make up the 65 more RPM. Not less travel.

Dhector if you had a picture of the push rod and the master cylinder that might show me if this is the right part. Thanks.

The old belt was shredded so I put on a brand new belt from Clausing. The pulleys on the drive are really smooth (no groves from running in at one RPM it’s whole life) so I think the speed stays pretty consistent threw the range.
The cam would seem to be the obvious choice to me, that is just ramps up too fast. With so many owners over the years the cam could have been changed out to a different one, but I wouldn’t think it is a wear item that would be replaced. But who knows.
Does anyone know if Clausing made multiple different cams? Maybe some one along the way swapped a different one in.
In an endless search on the web about this I have seen a few people talking about RPM discrepancy’s on their lathe but no responses or follow up on how to change it.


 
Iron-Iceberg said:


Dhector if you had a picture of the push rod and the master cylinder that might show me if this is the right part. Thanks
Click to expand...

I'll get pics for you next time I go to the shop. Might be today, if not, I HAVE to be at work tomorrow and I'll get some then.
 
Iceberg -- have you seen this video series by Randy Richard? Again, not the exact same lathe as yours -- his is a 6903 -- but maybe something there that can help. I also understand he's a pretty good guy, so maybe a comment on his channel might get a helpful response. The link below is for part 1 of three, I only watched a portion of Part 3 where he puts it all back together.

 
Dhector said:
I'll get pics for you next time I go to the shop. Might be today, if not, I HAVE to be at work tomorrow and I'll get some then.
Click to expand...
That would be great to eliminate one variable. Thanks For the help.
 
francist, yes I have watched his videos. He sure has done a lot of work to get his lathe working. His lathe has the older round master cylinder and he doesn’t take it apart on the video to see much. I might have to shoot him an email to see if he has any ideas.
 
You must log in or register to reply here.
Back
Top