Shopsmith Forums

So, on my Mark VII (with Mark V speed control) I have run into a problem. The control sheave busted where the bearing goes. It was becoming harder to go from High to Low speed, and then it broke. FYI, I was SLOWLY moving it to the slow position, so it wasn't because I was trying to move it to slow too quickly. I have the pieces where the bearing goes, so I believe I can repair the end using the copper coupler method. Either way I will be ordering a replacement to have on hand.

I'm trying to figure out why it broke in the first place. I have only had this machine for about 9 months, and it's only had about a total of 15 minutes of run time since then. I've been busy restoring it, so it hasn't been in actual use. I did apply the turbine oil, so I don't believe that was the problem. However, the previous owner may not have oiled it properly. I believe the key on the idler shaft is the problem. It has some wear on the end of it, and perhaps it is too short. I couldn't find a picture showing what it's supposed to look like, so maybe its length is ok.

Picture of what my current key looks like. So, with that... here are my questions.

1) Do you guys think the worn key is the reason the control sheave was sticking?

2) Is the key the right length, or did the end break off?

3) If the length is ok can I just gently file it down to clean it up?

4) If I need to replace the key are the Mark V keys and the Mark VII keys the same part?

Thank you very much for all the help you guys offer!

First off, which idler shaft is it?

Second, WHY are there set screw marks on the key?

IIRC, the 'snout' on the MVII sheave is shorter. However that could have been taken into account when the M5/V speed control was mounted. i.e. it needs to be checked.

I do not think the key needs to extend out to the end of the shaft keyway.

I assume you have a MVII idler shaft.

I would get a new M5/V key and compare it.(I think you need a new one anyway)

I almost would bet that key came off the motor shaft and does not have the kink in the opposite end.

You do need to know which parts are which 'vintage' for future reference.

I believe they are wear marks. How they got there I am not sure. My bet is the previous owner didn't have max speed set correctly on the control assembly, and was pulling the control sheave out too far causing it to "garf up" the key. Just a guess.

Here's a close up of the worn part.
Good idea on comparing the keys. I will order a key when I order the new sheave.

Yes, it is a Mark VII idler shaft.

IIRC so far the only parts I have noticed that aren't 'vintage' are the speed control assembly, the control sheave, and possibly the idler sheave too.

I tried filing down the worn spots on the key, and at least when I tried it by hand it seemed to be much better. I will try putting it back together tomorrow and see how the speed change feels (manually turning, not under power).

That key looks like it was intentionally 'dinged' perhaps an ill advised attempt to reduce slop.

IIRC, the idler sheave MUST be a MVII for the 14 rib belt to fit.

The control sheave needs to be loosey goosey with out wobble. That is why frequent oiling is required.

I wasn't sure on the idler sheave. That's good to know!

There isn't really any slop, and the control sheave slides easily now that I filed that spot. However, I will order the key when I order the control sheave. I can then compare it to my current one.