Powermatic 90 Speed Adjustment Question

[doug kawallski]

I just got finished rebuilding a Powermatic Model 90. Not having any experience with this lathe before my question is what is the normal effort and time taken to adjust the speed? Let me elaborate some. The lathe starts fine and can be brought up to the 2100 RPM range quickly and smoothly. The issue, if there is one, is in the deceleration back to stop. I can go from 2100 to about 1300 with relative ease but then it requires more effort if I continue on without stopping. If I pause at 1300 then I can more easily resume the deceleration but the same issue will recur at around 700 RPM. Everything has been cleaned, oiled, adjusted and moves very nicely otherwise. My only reference to how this should be is a video on Youtube but in that video the author does pause and appears to exert some extra effort for the final leg down. I have tried a new belt as well as the old belt and although the old belt (not seriously worn) is somewhat better it is not an appreciable amount. I have seen other videos with other Reeves drives and they seem to be able to move max to min quite fast. After experimenting with numerous ideas I only have one semi reaching theory. I am wondering if on the way down to the slow speed the outer corner edges of the belt are getting just slightly rolled under the sides of the belt as the belt is being forced to the outside of the upper sheeve. Letting it pause briefly allows the belt to normalize and the deceleration can continue. One reason for this theory is that some Reeves sheeves have radial slots or depressions that may allow the edges to normalize quicker or possibly not roll under. I welcome your thoughts on this and your experience with this machine. While I have experimented with belt tension I would really like to hear your experience with this. Thanks

[Curt Fuller]

When you are accelerating (speeding up), the centrifugal force of the belt on the drive pulley is aiding in the speed increase along with the spring that's pushing the two halves of the pulley together. When you're slowing down the opposite is happening. The belt is being pushed into the pulley, spreading it back apart against the pressure of spring and centrifugal force. I don't have a PM but on my Oliver which is very similar, it is much easier to speed up than slow down. You mentioned that everything is cleaned and oiled, but on the Oliver the expanding pulley has a grease zerk to lube the sliding half of the pulley. It's kind of a messy thing if you over grease it but it does need a pump now and then to keep it sliding smootly.

[Roy Turbett]

I have three PM90's and agree with Curt - its easier to speed up than slow down a reeves drive. This is a link to an excellent thread titled "PM 90 Spindle Woes" at OWWM.org. Roy Wall discusses all of the potential areas that could be affecting performance and how to fix them. Search the website and you'll find alot of other posts on the PM90.

http://www.owwm.org/viewtopic.php?f=1&t=128234&start=15

[Mike Cruz]

Roy's link is probably your best bet. I had a PM90 that I restored. I have to say, that I didn't have any issues speeding up or slowing down. That said, it is a "manual" speed control, so there is "some" amount of force necessary compared to an electrical knob. Hey, how about some pics of her!

[Mike Cruz]

Doug, I'm sure you've already done this, but just in case you haven't... Take the belt cover off, and see what it is doing as you are slowing down the lathe. When you rotate the handle, the one pulley should expand. The second one reacts (with a spring). So, as you move the handle, the upper pulley out to be moving smoothly in and out. When you are slowing down the lathe, IIRC the upper pulley moves in closer (pinches together to, in essence, make a larger diameter pulley). If you can pull the handle smoothly, changing the upper pulley's diameter, but the spindle speed isn't reacting, that would tell me that maybe the lower spring isn't reacting to the change in the upper pulley somehow. If you are saying that you physically "can't" pull it unless you stop, wait, then try again, then maybe you are on to something that the belt is somehow catching. Is the inside of the upper pulley (the left and right halves that contact the belt) smooth (worn shiny), or is it rough (maybe slightly rusted)? It should, IIRC, be shiny so the belt can move back and forth smoothly. If it is rough, you might be able to smooth it down with sand paper...

[doug kawallski]

I appreciate the feedback I have gotten so far and I welcome other thoughts. I have experimented with some of the input I've gathered but so far it hasn't changed much. It really isn't a big deal it just seemed like maybe it wasn't quite right. For now I am content to run it and see if some time improves things. If not, that's okay too. I will add some pictures in a following post as I had some difficulty including them with the text in a previous attempt. I should have taken some before pics for comparison sake. When I got it was a very flat gold color top to bottom. Not original Powermatic gold, someone had repainted it. The bed was rusted and a few parts, like the tool rest locking screw were missing. The speed dial band was also damaged beyond repair so I had to get creative there. All in all a bigger project than I anticipated but quite happy with the end result. Doug

[doug kawallski]

IMG_0225.jpgIMG_0227.jpgIMG_0228.jpg

[Mike Cruz]

Very nice job, Doug! I really like your color choices...well, sorry, not so much for the base, but for the rest of it, that looks really sharp! Thanks for posting them.

Yeah, the restorations do take longer than you'd think. My PM90 restoration took extra long since I did risers, VFD, and variable speed switches, etc. But it was certainly worth it.