Mark VII “Project Machine”

algale · Post by **algale** » Sat Oct 14, 2023 8:07 pm

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 · Post by **shipwright** » Sat Oct 14, 2023 8:10 pm

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 · Post by **shipwright** » Fri Oct 20, 2023 8:13 pm

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.

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

https://youtu.be/A1rk_usD49g?si=ZCGf4g5U94ryCZyE

https://youtu.be/mLi8US8ZYdg?si=X1ekpxdbju9J2NUw

lahola1 · Post by **lahola1** » Sat Oct 21, 2023 11:51 am

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 · Post by **shipwright** » Sat Oct 21, 2023 12:13 pm

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 · Post by **shipwright** » Sat Oct 21, 2023 1:57 pm

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.

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shipwright · Post by **shipwright** » Sat Oct 21, 2023 7:24 pm

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.

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shipwright · Post by **shipwright** » Tue Oct 24, 2023 8:02 pm

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?

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JPG · Post by **JPG** » Tue Oct 24, 2023 9:05 pm

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 · Post by **shipwright** » Tue Oct 24, 2023 9:23 pm

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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