Mark VII Gear Rack Replacement

[robinson46176]

Food for thought...
Many years ago back in "Ye Olden Days" of Yahoo email lists I proposed a couple of possible modifications to the old Mark VII speed control cam problem to make one functional. The choice would make it work but would not look at all original... Just a hack but you could use the machine for anything.
This was long long ago and I have forgotten a huge amount of details since then. I never tried them since my Mark VII has a good (so far) speed control and one of my 2 "donor" Mark VII's also has a good cam.
Both possibilities involved forgetting the dial and concentrating on moving the sheave thingy in or out.
The first notion requires thinking a bit out of the box. You have to visualize "unrolling" the snail shaped original cam which we already know is at best "tricky" to duplicate. "Unrolled" it becomes a simple inclined plane, straight on the backside and a straight but angled plane toward the "pusher thingy"... Damn, I would kill to have my "names of things" memory back... This wedge shaped piece, now with all straight lines would be quite easy to make in your choice of suitable materials. Visualize this inclined plane piece mounted on a piece of about 1/2" "all-thread", say maybe with 2 nuts welded to the back of the wedge shaped cam. The threaded rod would be mounted through the headstock case using the hole from the original dial and any number of possible mountings at the back. The threaded rod could be turned with a knob, small crank or several possibilities.
The second possibility is a bit similar but would use no cam A simple rod would mount through and have a small lever attached inside with a link to the "pusher thingy". Outside it could have a simple quadrant with maybe a friction surface or a position clamp or think in terms of a small index wheel with places to stick in a position lock pin etc. The best way to visualize this one is to find an old farm tractor and look at how the linkage between the hand throttle and the engine governor operates. No need to reinvent the wheel...
There are a lot of other possibilities like cable controls etc. too.


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[RFGuy]

I don't know about the gear rack, but I believe you can get replacements for the cam. I think someone is 3D printing them:

https://www.shapeways.com/product/ENZED ... _tquWfmkN4

From this thread, you might be able to make a new gear rack:

https://www.shopsmith.com/ss_forum/main ... 0jRTCR8Z8E

https://www.shopsmith.com/ss_forum/view ... hp?t=17064

[WLKuhns]

Thanks Iahola1, I’ll give it a try! It can only be learning experience

[WLKuhns]

Thanks Mr. Robinson, these are doable too!
I’ll keep these I the packet for when my cam finally goes. You can see in the picture that I placed 2 small screws in it to set the limits; that was the only thing giving me trouble. I adjust speeds real slowly so as not to stress the cam. So far it’s working well!

[WLKuhns]

Now I’m really inspired! I’ll have fun fabricating...recently retired.

[chapmanruss]

There is a Mark VII being parted out and the parts sold on ebay. They started showing up yesterday. Another Mark VII lost but may help others keep working. With less than 11,000 made their number are shrinking faster than the other Shopsmith Models except maybe the Mark 2.

Farmer, an interesting idea on a replacement option for the speed control. I can even picture it in my mind from your description.

[lahola1]

RFGUY, nice links to great threads on making your own rack. I haven't seen those before.
Farmer, yes, I agree those are great "thinking outside the box" ideas for keeping a mark VII running when parts aren't available.