Mark VII Caster Design
Posted: Fri May 14, 2021 3:30 pm
Hi all, I have been searching for a set of MarkVII retractable casters for a while and finally decided to just design my own. Although I don't know how useful this will be to others, I am pretty proud of it, and thought I'd share in case someone is in the same situation with their MarkVII. There are many caster options that bolt on, step lock, all kinds of different ways, but I really wanted something similar to the original design, and I didn't want to see them, have them stick out, or modify the MarkVII base in any way, just in case I ever find a real set.
I started out by designing a basic concept in 3D CAD. Then made a prototype. See the pictures below.
There are existing stiffner plates in the bottom channel about 13 inches from the ends, with holes already punched in them. I used this plate to attach a cleat (I think its called a cleat). This cleat acts a my hinge, or pivot point. I then made a base plate out of hard board as it had enough flex to bend where I need it to. I topped the base plate with a stiffner plate of 1/4 inch plywood to stiffen the hardboard almost to the hinge point. The weight on the wheel causes a rotational moment which wants to arch the hard board in the middle. The plywood stops this arching. Anyway, the rest is fairly self explained from the pictures. Added a block to attach the wheel to, added a blocking bar on a wooden dowel which when rotated into position locks (or blocks) the wheel into the down position. Getting the thicknesses of the blocks was done on the computer. It had to be thick enough to hold the machine off the floor, but thin enough to allow the wheel to retract up into the channel.
It's not perfect, I still have to manually lift the machine, and then lock the wheel as it is not a cam, and not made of steel. But this is much better than jamming my kids old skateboard under one side and carrying the other.
I haven't yet learned how to order pictures and add text in between them so they are all clumped together at the end here.
Thanks for looking at my project.
Mike -
I started out by designing a basic concept in 3D CAD. Then made a prototype. See the pictures below.
There are existing stiffner plates in the bottom channel about 13 inches from the ends, with holes already punched in them. I used this plate to attach a cleat (I think its called a cleat). This cleat acts a my hinge, or pivot point. I then made a base plate out of hard board as it had enough flex to bend where I need it to. I topped the base plate with a stiffner plate of 1/4 inch plywood to stiffen the hardboard almost to the hinge point. The weight on the wheel causes a rotational moment which wants to arch the hard board in the middle. The plywood stops this arching. Anyway, the rest is fairly self explained from the pictures. Added a block to attach the wheel to, added a blocking bar on a wooden dowel which when rotated into position locks (or blocks) the wheel into the down position. Getting the thicknesses of the blocks was done on the computer. It had to be thick enough to hold the machine off the floor, but thin enough to allow the wheel to retract up into the channel.
It's not perfect, I still have to manually lift the machine, and then lock the wheel as it is not a cam, and not made of steel. But this is much better than jamming my kids old skateboard under one side and carrying the other.
I haven't yet learned how to order pictures and add text in between them so they are all clumped together at the end here.
Thanks for looking at my project.
Mike -