Prototype Frame Assembly: Part 3

Well I ended up taking down the upper frame. It proved too expensive to source a chevron mounted bearing, after Fastenal failed to deliver on the one in their catalog, which would have been ideal. So I drilled some new holes in the frame rail and started to use a hole saw to expand the hole around the shaft, to suit a different bearing.

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New bearing mount holes to the sides of the shaft, and my damage to the rail using a hole saw.

I found out 2 things from this: using a hole saw without a solid pilot hole (I used a chunk of wood for the pilot) to guide it doesn’t work well. And it is DEFINITELY loud enough to wake a sleeping toddler. I could clamp some aluminum behind it to provide a better pilot but to save time, and be lazy, I am going to leave the hole as it is and just space out the bearing. Also I think I would need to scrounge up a better hole saw. The blade I was using had some serious wobble and has little left for teeth.

I then reassembled the upper frame and did a little bounce testing.

From this testing I found that the lower frame isn’t quite as stiff as I would like. The back right hand corner will lift a little (about 1/8″, maybe less) when you really bounce your weight away from the wall. It doesn’t feel flimsy or like it’s going to tip but it is a little off-putting when you can see and hear it lift. With the planks on I doubt you will be able to see it, their weight should hold it down more, but I would still like to do something to stiffen up the frame. The wall frame feels super stiff.

Since only the one side lifts I am inclined to think that the diagonal strap on in the lower frame (the one that runs along the floor) is keeping the other corner from lifting. If this is the case it will be easy enough to stiffen things by adding an additional diagonal strap, making the lower frame symmetric. It could also be that the one brace running diagonally from the top to the bottom shown below has a stiffening, bent flange, while the other does not. This can be checked by simply swapping the braces and seeing if it has any effect.

(Note: I swapped the braces after writing this post and it did change things a bit but the difference seems to come primarily from the lower strap.)

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The lower frame may benefit from adding a second cross brace to the bottom, making the stuff on the floor symmetric.

I will run some additional FEA and verify that this change will improve things.

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Prototype Frame Assembly: Part 2

There was a bit of a learning curve involve with getting the main frame rails in place. I had to sit them on blocks and balance them in place against the lower frame while I then slid the main shaft into place. The thought of knocking them over while inserting the shaft made it slightly nerve wracking.

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Frame rails in place. This thing is enormous!

Then before bolting the bearings to the frame rails I had to carefully block the rails up so that the pin hole on the rail was centered on the hole in the pin plate. This would be a totally unnecessary step if I used bearings like this which would be piloted into place on the rail. They are slightly more expensive but I think this would have been worth it.

Putting the little brackets on the cross brace pieces I noted 2 problems. First Princess Auto had nothing but 3.5″ bolts in the 3″ bolt bin. And the mounting faces of the brackets are not flush with the end of the square tube. Next time I would use slotted holes in the brackets to allow for some variance in the bent parts.

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Bolt is too long, gotta make another trip to princess auto, ug. and brackets aren’t flush with the end of the tube so my wall will be about 1/4″ wider than I had intended.

I don’t think this will cause any major problems, but we will find out.

 

Prototype Frame Assembly: Part 1

I didn’t get quite as much done on the weekend as I had hoped, as I was briefly sidelined by a stomach flu. But on Sunday, with the help of my father, we managed to get the lower frame assembled.

First we assembled the two outer frames:

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Lyle kicking the tires on the lower frame.
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The outer portions on the lower frame assembled… and a Honda product placement?

We then stood them upright and put in the cross bracing. This was a bit of a chore and it would have been a pain on my own. It might have been easier to assemble the lower part of the frame and build up from there.

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The lower frame. This thing seems both large and heavy, though the footprint is no larger than a big treadmill.

Next we managed the only bit of real metal working that should be necessary in this project. We drilled and tapped holes in the ends of the main support shaft that the wall frame pivots on. This allows you to bolt the shaft to the frame. (This might not be the only metal working. I will need to do something similar to get the motor driven angle adjustment working. If I bother.)

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The hole drilled and tapped in one end of the shaft. Not perfectly on centre but close enough.

I kinda anticipated this being a pain and it was, but it went much better than I expected thanks to Lyle “the human lathe” once we found a sharp bit. It was still a two person job to drill and keep the drill aligned well. If I do another one of these I will make a point of buying the softest steel I can reasonably get to ease this step, rather than whatever cold-rolled material was on sale.

The biggest surprise was how big (and HEAVY) this thing is. Sure I designed it, but I didn’t really envision it taking up half my garage. I kinda thought we might be able to park on that side if I trimmed my work bench. Oh well, at least summer is coming up and parking outside won’t be a hassle.

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Frame with the shaft in place. I tested it with a couple chin ups and it feels pretty solid.