Shopsmith Forums

Just turned on my 1982 Mark V 500 for first time. I acquired from a friend and rebuilt headstock. I have 4 belts to try, Jacob A belt, SS new, Kevlar belt and a 32 link belt form HF. Link belt is on now. I have a calibrated RPM gauge and the slowest speed I get is 1080 rpm. The motor is running at 3580 rpm. My questions are:

What is the motor rpm supposed to be and will a longer or shorter belt slow it down?
I can't go any slower or the belt hits the casting.
Sorry about the pics, for some reason they rotated when I inserted.

Low RPM should be in the 700 range. Your speed is most likely a result of having the wrong belt length.
My suggestion would be to put on the Shopsmith branded V belt and try again.
Bill V

Motor RPM is 3450. IIRC that is at 100% rated power/load. Theoretical no load speed is 3600, never reached in practice. So the useful range is from 3450 to a bit less than 3600 from full load to no load. You are in a low load condition, so your motor speed seems reasonable to me.
A longer than nominal belt will cause the machine to run at higher RPM by allowing the motor sheaves to move closer together. You might try removing a link, but I have no experience with link belts in headstocks. Your closest to nominal speed results will probably occur with the new SS belt. (IIRC the Jacob belt is metric and slightly longer and wider than nominal. The others are unknowns to me.)

- David

Both the width and length of the belt effect the speed, Also, the tabs on the link belt make it deeper through and will limit how far the belt can go in the sheaves.

Got some results:

SS Belt 700 rpm
32 link belt 1080 rpm
30 link belt 760 rpm
Jacob A Belt 767 rpm

32 link belt is a no no
The rest appear to be OK and close to spec.
Bill V

A longer belt will cause higher speeds since the floating(motor) sheave must compress(close) more to maintain tension and that results in the belt riding further out on the motor pulley.

A shorter belt will invert that. The belt will ride further IN on the motor pulley causing slower speed range.

The control sheave range is fairly consistent with a properly set high speed stop.

A narrower belt will cause faster speeds since it will be riding further INTO the idler pulley and further OUT on the motor pulley.(wear can create that)

The 32 link belt started same size as SS and is a little wider. But after running for a few minutes, it stretched so I removed 2 links to make it same size as SS. Since it is a little wider, it hits the casting when trying to get below 760 rpm. I went back to the SS belt.

Gio800 wrote: Mon Feb 01, 2021 8:33 am The 32 link belt started same size as SS and is a little wider. But after running for a few minutes, it stretched so I removed 2 links to make it same size as SS. Since it is a little wider, it hits the casting when trying to get below 760 rpm. I went back to the SS belt.

Check out what 29 links will give you.(is odd link count possible?)

Ok, I'll bite on this one. What are the advantages of using a link belt on a Mark V? As I understand it, the marketing for link belts promote lower vibration from their use. However, I have seen woodworking discussions on them on other forums and the conclusion often is that they only offer a benefit when the motor mount is a gravity type design. Vibration is much lower for a link belt, e.g. when used on a table saw where the motor weight holds belt tension due to gravity. When the motor is a fixed mount it is my understanding that they offer no less vibration than the equivalent V belt. The Mark V would be this latter case and presumably has no less vibration with a link belt. Disadvantages are that links do break, but repairs are easy. Also, they can be noisier than an equivalent V belt. Of course when a V belt replacement isn't handy, etc. I get that link belts offer an advantage. Just surprised to see discussion of link belts from time to time on this forum. IMHO I don't see much benefit to using them on a Mark V. Comments?