Mark VII Low Speed Too Fast

[miken]

Hi all, hoping to get some advice on my Mark VII speed control. FYI, I measured my RPM using a vintage Starrett 104 RPM meter, so it is not a precise RPM measurement. I have tried to verify accuracy some by testing it against my metal lathe at a known RPM of 805 and I read 815 or so. The lowest RPM of my Shopsmith is around 810. I am in the process of putting my second headstock back together so I can test against that as well.

I am trying to figure out if the plastic speed cam looks like it is set properly for the lowest speed, or if the end of the cam (largest diameter) should be closer to the button bearing thing in the pictures below. Also note that I have one detent left on the speed dial, but it wont stay in that position and clicks to the second to last detent automatically. That is to say, the bottoming out roll pin is not in contact in the slot behind the speed dial. I am also attaching pictures of the V-belt at 700 RPM in the top sheave. I don't think it can really go any higher in the sheave as the bottom (motor) sheave spring is pretty much fully compressed. Also, I have two v-belts that appear original and they both measure 30" O.D. I have read that 29.5" is supposed to be correct for Mark 5's, but I assumed the same for Mark VII's, mine may be stretched? Not sure if they can stretch 1/2" though, or if a longer belt equates to higher or lower RPM.

I am not really sure where to start on this other than if the speed cam does not look right (I think rotating it further (clockwise in the photo) towards the end of the cam would cause a reduction in speed) I could try to loosen the 3 screws on the speed dial and turn it a bit. However, I really think I am limited by the compressed motor sheave spring?

Thanks for looking, any help is greatly appreciated.
Mike -

[wa2crk]

Miken
Absolute speed is really not extremely important. Close should be good enough. Within 100 RPM or so should be good. 800 RPM on the bandsaw is about 2400feet per minute. Most bandsaw speeds are about 700 to 750 FPM so I do not consider your readings to be a problem. The speed can de affected by the width of the belt and how far the sheeves are moving. If they are not moving far enough along the motor shaft or the speed control shaft then minor variations in speed can be expected. Minor rpm readings can be expected.
This is all my opinion, but then, I am an opinionated old guy
Bill V

[miken]

Miken
. . . Absolute speed is really not extremely important. . . .
Bill V

Thanks Bill, that's basically what I thought before I got any SPT's and only used the SS to saw and drill, but I think it just feels way too fast for the jig saw and would like to see if I can get it closer to 700 RPM. I suppose it's not a huge problem if it stays the way it is, but I am a "tinkerer" by nature.

Thanks, Mike -

[JPG]

Have you tried to rotate the entire speed control? The three screws/slots allow doing that. The bullet detents IIRC do not cover the entire range(may have only one detented at the extreme(700/5200)speed settings).

The high speed setting procedure is completely different from the mark 5/V.

What is the part # on the two OEM belts? How wide are they at the widest? Narrow belts will cause higher speeds.

My MVII headstock is currently not accessible.

[miken]

Have you tried to rotate the entire speed control? The three screws/slots allow doing that. The bullet detents IIRC do not cover the entire range(may have only one detented at the extreme(700/5200)speed settings).

The high speed setting procedure is completely different from the mark 5/V.

What is the part # on the two OEM belts? How wide are they at the widest? Narrow belts will cause higher speeds.

My MVII headstock is currently not accessible.

No, I haven't tried any adjustment of the speed dial yet, was hoping for confirmation the speed cam didn't look rotated enough. Can you explain the MarkVII high speed adjustment to me? The OEM (I am only assuming OEM) belt number is 501330 and it appears to measure 1/32 under 1/2 inch wide (15/32 inch).
Thanks, Mike

[JPG]

I think the cam needs to be rotated more.

I think the "high speed stop" on the Mark VII is essentially a dial movement stop.

The true limit is the internal parts(cam follower, speed control shaft interfering).

The adjustment is a sliding 'stop' secured by a screw in a slot. IIRC a pin on the back of the knob travels in a groove stopped by the 'stop'.

15/32 is a too narrow belt. Makes speeds slightly high. Makes belt seat further into the pulleys.

OEM belt is 507490

P.S. According to my MVII journey thread, the oem belt is 29.5.

A longer belt will make it run faster.(I added an idler to make the belt effectively shorter)

IIWM, I would try a 29 inch "1/2" belt. (1/2" makes it run faster)(shorter makes it run slower)

A top cog belt may be desirable.

I have not yet tried the OEM belt(507490)

[miken]

I think the cam needs to be rotated more.

I think the "high speed stop" on the Mark VII is essentially a dial movement stop.

The true limit is the internal parts(cam follower, speed control shaft interfering).

The adjustment is a sliding 'stop' secured by a screw in a slot. IIRC a pin on the back of the knob travels in a groove stopped by the 'stop'.

15/32 is a too narrow belt. Makes speeds slightly high. Makes belt seat further into the pulleys.

OEM belt is 507490

P.S. According to my MVII journey thread, the oem belt is 29.5.

A longer belt will make it run faster.(I added an idler to make the belt effectively shorter)

IIWM, I would try a 29 inch "1/2" belt. (1/2" makes it run faster)(shorter makes it run slower)

A top cog belt may be desirable.

I have not yet tried the OEM belt(507490)

Well, I threw the backup headstock back together, and even though the dial reads 700 and the speed cam is clearly rotated more (I would say that's scary max'ed out), my reading was actually 10 RPM faster at 820. So, it is very possible my RPM meter is way off, it is likely older than the Shopsmiths I am measuring. Or as you mentioned, maybe it's more about the V-belt. I do find it odd that both machines have matching 30" belts.

I have had this D&D PowerDrive 29.5" in my Amazon cart and think it was the one recommended in a past post. https://www.amazon.com/gp/product/B01AG ... 0DER&psc=1

Shorter equals slower so that's a place to start. I will try the 29.5" first and see what happens. I don't think there is much I can do about the belt width as you know from past posts, they advertise 1/2" wide, but fall under that. I wonder what style the OEM belts are, 3L, 4L etc. Did you finally land on a belt that you thought was best? I know you were trying a bunch of them. Were you testing for RPM or just fit?

This isn't a huge problem for me, was just hoping to slow down the jig saw a little. I don't think it's really worth chasing 100 rpm's down a rabbit hole, but it's worth trying a 1/2" shorter belt to see what happens. Sad that Shopsmith basically abandoned these machines and their owners to only the similar Mark 5 parts, but that's business for ya.

As always, really appreciate your help.
Mike -

[lahola1]

I could never get my mkVII to go below 800RPM either. I believe I have an OEM belt (29.5" ,IIRC.505" wide). I also tried the exact top cog belt that JPG recommended; it made it worse (it was slightly less than .500" wide).
I don't remember if I tried adjusting to sliding stop (can't find my notes anymore).
I think one possibility (being a plastic guy) is that over 50 years the plastic nylon cam has shrunk (especially if it was molded in a cold mold which it probably was). that causes nylon to shrink over time. This would not push the sheave as far as before ; not being able to slow to 700RPM. Again, I don't know this has happened; just a possibility.

[JPG]

My trying different belts was an attempt to get the correct one. Had I originally had a correct OEM belt I would not have had to do that.

Imagine my chagrin when I originally tried to put a M5 belt on it!

The oem belts were non standard and slightly wider than a 4L belt.

Trying to get a predictable result with all the current varying belt designs is a z00.

[miken]

I could never get my mkVII to go below 800RPM either.

Thanks for adding that. Good to know I'm not the only one.
Mike