Shopsmith Forums

I brought my digital tach home from the boat the other day to check speeds I was getting with my Mark VII cam arrangement and since it was there I checked some speeds on my 510 with link belt and with vee belt. I was surprised to see numbers well above the stated 5200 max rpm. So much so in fact that I checked my 3Hp Unisaw to verify the accuracy of the tachometer. The saw runs at 4300rpm and the tach gave it almost exactly that so I have to believe it is accurate.
My numbers for the 510 were:
With link belt (which gets well outside the motor sheaves, see pic)
Slow…..950rpm
Fast ….6340rpm
With the vee belt (worn, barely 1/2”)
Slow …. 730rpm
Fast ….7360rpm

Anyone able to explain what’s going on?

SS speed are very much dependent on belt width. New V belt vs worn V belt vs how wide is the link belt. Speed vs letter setting on the dial is not a precise thing. A link belt is not a substitute for a V belt in this application.

I’ve used link belts before as have some of the real gurus of ShopSmith. I have no problem with them and I know the belt width affects the speeds. My question is whether anyone can explain to me why in getting 2000rpm over the advertised max. That’s not a few percent.

Is there a low speed speed adjustment on the Mark VII like on the Mark V?

You mean high speed? Yes

shipwright wrote: Tue Oct 10, 2023 7:56 pm You mean high speed? Yes

Have you done the adjustment? Has the exchange of the V pulleys for the VII pulleys changed the geometry?

This is on the 510, not the Mark VII. The MkVII is currently waiting for a new (eBay) Mk V control sheave. I have proven that will work by trying a control sheave out of my Mk 5 but it needs 1/4” cut off to reach full speed. I’ll do that to the new one, not the Mk 5 one. It goes back where it came from.

So yes, the Mk V/5 sheave does change the geometry a bit because the spigot on the Mk VII sheave is a bit shorter.
I can fix that!

The link belt riding so high on the motor pulley definitely explains the higher speed.

Where does the v-belt ride at 'high'?

BTW belt length also affects this in addition to belt width.

I think thy link belt is too long. Make it shorter and the spindle speed will decrease as the belt rides lower into the motor pulley.

I agree that the link belt is one too long but the worn, barely 1/2” vee belt ran the machine at 1000 rpm higher.
I really don’t get it.

I think I would reexamine the 1/2" belt data/procedure. Those results do not make sense! I there is something else going on(multiple reflections if using an optical tach).