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Mark VII “Project Machine”

shipwright

No, it’s because the best deal on Amazon was for a five pack of the bearing that fits the single bearing quill. I have a Mark 5, a mark V 510, and the Mark VII. I figured I’d do them all just for fun. That leaves me with two lonely bearings so I thought if it fits, I would replace both in the 510. AFIK the second bearing doesn’t do much and seldom wears so if these don’t fit I’ll just leave that one.

JPG

So you have a two bearing quill on the 510? I do not know if the two bearing(there are multiple variations) quill uses the same bearing as the M5/MVII.

i.e. you may have 3 orphans.

shipwright

We will find out tomorrow or the next day. I think I read that the main one is the same but the second one may not be.

I’ll keep you posted.

shipwright

JPG wrote
I consider the pinned follower to serve the same purpose as the wire loop on the m5. IMHO the pins only become relevant with sluggish response of the floating sheave due to either too fast adjustment of the speed dial or inadequate lubrication of the floating sheave. Main purpose is non-rotation of the inner race of the control sheave bearing.

While I’m waiting for my new eBay sheave and my new printed cam to arrive I’ve been giving this some thought.

For the first part, sluggish return to high speed would be a good indicator that it’s past time for lubrication. That makes it actually more of a good thing than a bad one.

The second part made more sense to me. You do want to prevent the inner race from rotating so I thought I’d try a spring between the button bearing’s bail and the headstock case. The one I have in the pics is very light and may need some tweaking but I think the concept works. The idea is enough tension to prevent spinning but not enough to create an axial pulling force on the bearing. I think it can be quite light as I don’t think it would take much to prevent spinning if the bearing is good.

JPG

Sluggish movement towards slow creates wear pressure on the quadrant(MV) or cam(MVII). The increased speed dial indication remains a mystery???

shipwright

But sluggish movement toward slow would be no different from MkVII follower to button bearing.

In either case, time to lubricate.

JPG

The problem with sluggish response to adjusting towards slow is the control sheave is squeezing the belt. That squeeze is relieved only by the floating sheave response(opening and creating less tension).

shipwright

I get that but it’s the same for either the follower or the button, is it not?

JPG

Yep. Control sheave butting against whatever is trying to move it.

shipwright

Good news / bad news. I got the 3D printed cam and immediately broke it while fitting the shaft.

So on to another angle of attack. I decided that the cam could be solid and much more robust if I was going to use a button bearing and have no need for a flanged edge. When you discard the U shaped follower and its roll pins the cam design becomes much simpler to reproduce. I decided to try some Purpleheart I had around and it only took maybe an hour all together to make what I think will work well. Time will tell. I’m still waiting for the eBay sheaves to arrive.

The finished cam is pictured here and a detailed step by step to make one is here.

https://photos.app.goo.gl/mV1QkEDC9PVcD54C6

algale

I have been waiting for you to go to the wooden cam solution. But I expected lignum vitae -- if it was good enough to make a strut bearing for the first nuclear powered submarine, it should hold up on the Mark VII.

shipwright

I would have Al, but I didn’t have any. It was down to Purpleheart and Tubi aka Queen Ebony. I had more Purpleheart.

When I had my shipyard my big 36” bandsaw had Lignum Vitae bearings.

shipwright

I finally got the Mark V control sheave assembly from my eBay order. Pressing the sleeve through the sheave, cutting 1/4” off, and pressing it back went quite easily in my veneer press. Unfortunately the process damaged the button bearing so I didn’t get to prove it would work. I punched it out and replaced it with the Mark VII follower and reassembled everything. It took a little adjusting with custom spacers and washers but I’m happy with the results so far.

My rpm range is about 830 on the low end to 5200 on the top end, measured with an optical tachometer. Not sure why it won’t get down to 700 but I’m not too worried about that. The only glitch at the moment seems to be that the detent bumps seem to lose their power toward the high end. I think a tiny modification to my custom spacer inside between the cam and the control shaft housing might tighten it up.

A couple of short videos of the machine running up and down.

lahola1

Looks like a good, simple solution for MKVII's with bad speed cams. Let us know when/if it fails. Hopefully it's a permanent fix.

shipwright

Thanks.

I used the Purpleheart because it was what I had that was strong enough. I’ll let it go a while to prove the fix and then likely make one out of 1/2” aluminium plate. I really see no need for the roll pins is the follower. They just make the cam 10X harder to make.

shipwright

So, I got the speed control working perfectly but ....... when I tried a little turning the spur quickly got hot. ...too hot to touch.

There also appears to be runout on the quill. My thoughts are:

1) I have the wrong bearing. (same as single bearing Mark V?) It was a very hard press but it went on.

2) I have the right bearing but I damaged it when I pressed it on.

3) Can you bend a quill shaft?!!

Just as a check, I ran the chuck on my other two machines and it is not the problem.

shipwright

Okay, moving along then….

I replaced the bearing and used the lathe for another hour. Nothing got even warm! There was a little runout when working at the end of my piece beyond the chuck but fine between centres. I was able to produce a chevalet part so I guess the Mark VII is officially a worker.

shipwright

I glued part of the offcut from the cam back on and recut it 1/16” bigger at the slow end. Now I get 680 rpm to 5249. Most numbers on the dial are within 100 of the actual speed.

The dial is quite hard to turn to get to the very lowest. Can anyone tell me if that is normal even with the factory cam?

JPG

My VII is not operational at the moment, but IIRC it did get stiff as approaching slow. That stands to reason since the leverage greatly decreases as the cam profile increases. Also the increasing radius of the control sheave belt position again manifests itself as resisting 'more'.

Increased friction between the cam and the follower also increases tactile feedback. Graphite ????

shipwright

That's about what I thought. I'm very pleased with what I've got now. It's no great hardship but it is stiff. The mechanical advantage can't be what the worm and quadrant produces.

I'm going to try some lubrication.

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