Shopsmith Mark VII plastic cam

[redleg]

I pulled this from a headstock that I picked up in the hills of northern Virginia. The bearing had disintegrated. Was the cam really as much a problem as it was made out to be? I think it was just poor operator maintenance.
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I made a prototype in wood from some templates with the Mark 7 in router mode. One template was cut with a bandsaw and sanded to match the outside dimension of the cam. The other cut 1/4 inch less than the inside rim of the cam to allow use of 1/4" straight router bit and 1/4" pin.
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You can find my sketchup file of the cam at

https://3dwarehouse.sketchup.com/model.html?id=u514b3f30-2b3c-4062-9f59-fb86f6028752

I know most hate this item in plastic but I have some delrin that I will use to make one. I have a price list from 1976 when Shopsmith was still selling the cam. It cost $2.76. Forgot a pdf with screen shots of the sketchup file and one sheet of the template cutouts that could be scaled for printing.
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[JPG]

Velly Intelesting!

Velly goot ingenuity!:)

I believe lack of lubrication and a resultant hot bearing/follower caused that damage. i.e. agree!!!;)

Do keep us posted re your progress.

[redleg]

Installed the newly fabricated Delrin cam today. I don't remember if the speed dial had to be completely removed to install the cam but with this design it does. The Delrin I had was 1 1/16 inches. One and a quarter would have made my day. I had to add a 5/32" turned spacer to the shaft area of the cam for proper alignment.

I used a cross slide vise to remove the excess material. No picture but I put a bolt in the vise 3/4" from the edge of the router bit and spun the cam by hand to make the raised center. Using a 1/8" bit instead of the 1/4" would have been a better choice turning the circle.
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Finished cam. Note that I also did not remove the half moon area around the shaft. This might have been an indexing point in Magna's machining process but maybe someone will know if it had any other purpose.
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Here's the cam installed in the machine. I did not remove the material on the side away from the operator.

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I replaced the bearing and the sheave. I used a sheave from a Mark 500.

[rcplaneguy]

Wow, good job!

[JPG]

This illustrates the reason for the hub relief. IIUC, you made the entire hub the 'shorter height'. If so it should work a-ok.

Nicely done!!!!!

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[redleg]

Thanks for the followup JPG. Sometimes I get so involved in the (how to make) that I miss some of the overall picture. It did function. Did you ever figure out the belt size? I tried a 29.5 from NAPA. It worked but I couldn't get the full range of speed so I put the used Shopsmith belt back on. Nice looking cam that you have.

[zenman]

Great job on the cam !!!!!!!!

The sketchup was awesome.

The bearing on the follower on my Mark VII was bad on two Mark VII I got. I tried to press it out of the sheave and the follower broke, because the bearing was staked into the sheave. Now I have to mill the follower out of 5/8 Delrin. There is a little 3 degree bevel for the shoulder. I think I will do a few more out of 5/8" Delrin stock.

Ideas?

Where did you get your delrin? McMaster???

great job - again.

[rcplaneguy]

Great job on the cam !!!!!!!!

The sketchup was awesome.

The bearing on the follower on my Mark VII was bad on two Mark VII I got. I tried to press it out of the sheave and the follower broke, because the bearing was staked into the sheave. Now I have to mill the follower out of 5/8 Delrin. There is a little 3 degree bevel for the shoulder. I think I will do a few more out of 5/8" Delrin stock.

Ideas?

Where did you get your delrin? McMaster???

great job - again.

There is quite a good selection on Ebay,
E.G.:
http://www.ebay.com/itm/Delrin-Virgin-white-sheet-1-25-x-2-5-x-6-5-Made-in-USA-CNC-1X-/400501545913?pt=LH_DefaultDomain_0&hash=item5d3fc09bb9

[redleg]

Great job on the cam !!!!!!!!

The sketchup was awesome.

The bearing on the follower on my Mark VII was bad on two Mark VII I got. I tried to press it out of the sheave and the follower broke, because the bearing was staked into the sheave. Now I have to mill the follower out of 5/8 Delrin. There is a little 3 degree bevel for the shoulder. I think I will do a few more out of 5/8" Delrin stock.

Ideas?

Where did you get your delrin? McMaster???

great job - again.

Will go back to Sketchup when I have a little more time and group it in layers.

I got my Delrin from ebay (surplusdealdude). Same link as rcplaneguy in previous thread. I bought a 2' long piece to use for other things also. The 1.25" would be better. Buy a little extra. At first if you don't fricassee fry fry a hen.

I would try Delrin but remember that's even closer to the bearing that sometimes gets warm. The shaft to seat the bearing on might be an issue due to the small size. Your original follower couldn't be welded back together?

Thanks all!

[JPG]

Thanks for the followup JPG. Sometimes I get so involved in the (how to make) that I miss some of the overall picture. It did function. Did you ever figure out the belt size? I tried a 29.5 from NAPA. It worked but I couldn't get the full range of speed so I put the used Shopsmith belt back on. Nice looking cam that you have.

Does that mean you have an 'original' Mark VII belt from Magna American? If so measure it! Please! I am am about to continue pursueing the 'correct' size. I have measured what I think is relevant on the MVII and will do the same on a M5 and determine the belt size from that 'input'.

That cam is a cnc milled aluminum cam courtesy of hdoilcan(and about $80!)]may[/B] still have 'extras'.

What 'bit' did you use to mill the cam?