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Adjust variable speed mechanism on Powermatic by Logan lathe.

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daveog

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#1
Hey guys,

I'm in the process of cleaning up this lathe and just put the headstock and belts back together. It all runs just fine, but the variable speed mechanism doesn't seem to be calibrated. It stops slowing down before it gets to the lowest setting and isn't as slow as listed, and peaks out before getting to the high end of the dial. I emailed Logan and was told they don't have any more information than what is in the manual, which is confusing. I've attached what the manual says and the drawing included. I also attached a photo of my drive, which looks different than the manual.

Has anyone successfully adjusted this?

Thanks guys,
Dave



Screenshot 2018-09-17 09.12.02.png Screenshot 2018-09-17 09.12.12.png IMG_1133.jpg IMG_1132.jpg
 

markba633csi

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#2
I read the belt adjustment procedure and it makes sense. It doesn't look like there is any adjustment on the dial mechanism itself.
I'm guessing the dial was not intended to be truly accurate by design.
Nice looking lathe BTW- I like the Houdaille versions
Mark
 

francist

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#3
I would first make sure that the belt is indeed the proper belt, both in length and in width. The variable speeds to the machine depend on how far apart the sides of the pulleys are in relation to each other. That's why they're saying in the manual to have the belt bottomed on the countershaft hub and then adjust the motor bracket so that the belt is at the extreme outside edge of the motor pulley. That position would establish a maximum setting. As for the belt width, if the belt is not wide enough it may not be spreading he pulley sheaves apart enough to affect the proper changes in diameter. I have a Roto-Cone variable pulley on my shaper that takes a 1" (or maybe even a bit wider) belt.

-frank

Oh yeah, and nice lathe! :encourage:
 

daveog

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#4
Thanks for the compliments guys! Well, I think I understand what you're saying Frank. The belt in there fits the width of the sheave by my eye. The walls of the sheave are so darn tall that I can't see inside to see what's happening with the pulley or the belt, especially not while it's running. What I did manage to do was find the lowest setting on the dial and set the spindle to it with my eyeball. I ran the speed down until my eye counted the start of the spindle thread go around 40 times in a minute. Then I slipped the dial for the speed control to match. That took about 5 or 6 times going back and forth, but it's currently at about 38-39 RPM at the 40 setting. I counted about 98 at the 100 setting and 150 was as fast as I could keep up with and it was about right on. In direct drive, it runs up to the high end of 2,000 but sounds a little screechy there. Just a tad off of it sounds good though. Given it is working and the dial seems to be about right, I don't think I'm going to mess with it anymore. One of my future steps is to install a VFD, so I shouldn't have to be changing the speed mechanically too much. I wanted to make sure it was at least functioning correctly first though. It's probably not as good as it was from the factory 40 or so years ago, but neither am I so I think we'll get along just wonderfully.

Thanks!
Dave
 

francist

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#5
Whoa, if you're only two rpm's off I'd take that as as good as it gets! I really like the variable pulley setups, I have two, but it seems there's always a bit of variance with them. Maybe that's why they call them variable speed... ;)

If you start dropping one or two hundred rpm you might look at it again, but until then you seem to have it figured.

-frank
 

markba633csi

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#6
Yeah I thought you were much further off than that- sounds pretty darn good as is- better than I even expected
mark
 

daveog

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#7
It was off significantly until I slipped the dial. I was concerned it would take more than just slipping it, but thankfully it didn't. Thanks for the support guys!!
 
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