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Yet another workbench #6: Mobile base

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Blog entry by JonasB posted 07-22-2019 12:17 AM 669 reads 2 times favorited 1 comment Add to Favorites Watch
« Part 5: Hardware 2 and Wrap Up Part 6 of Yet another workbench series no next part

So after five years, I finally decided to build a mobile base for my workbench. Prior to this, I have experimented with bases for some of the other equipment in my workroom and always found something I did not like with most of the traditional designs that are out there. This was my justification for coming up with my own over-engineered approach for my beloved workbench.

My goals were fairly basic.

About an inch of lift
Table stands on its own legs when not mobile
Easy lifting
Stable in both stationary and mobile configurations.
KISS
Strong
Minimal mod to bench
Installed without having to move my bench (since I am adding it to a heavy, already in place item)

After letting my brain work on this while sleeping for many years, I finally decided to go with a cam mechanism attached to the bench for the lifting, and an independent dolly base to support the wheels.

The Dolly

The dolly base can be anything from a sheet of plywood to welded iron. I decided to go with two plywood platforms for attaching the wheels and two ¾ pipes connecting the two and providing a metal surface for the cam to slide against. The dolly can surround the object to be lifted or be inside of it. I decided for clamping clearance and less tripping issues to have the dolly inside the bench legs. The bench was big enough that this still gave enough separation for the wheels to prevent tipping. To keep the dolly from sliding out of alignment, the plywood platforms have rectangular cutouts at the corners that register on the legs and keep it loosely contained. The wheels are attached with 5/16 bolts and the pipes are drilled and attached to the plywood platforms using ¼ bolts. Here is what I came up with. Ignore the paint aesthetics. Since it is mostly invisible I used up left overs and was concerned with rust presentation more then looks.

The Cam Mechanism

The cam is a rotating ¾ pipe with 2 inch pipe sections attached off center to provide the lift. Hubs are attached to the legs with lag bolts to support the ¾ pipe. This configuration is not optimized to even out the lifting forces, but does make it easy to find the parts and to make it. The 2” pipe gives the desired 1 inch of lift and does not require much strength to operate with my 300 lb table.

I found the hubs at a big box store, its a 3/4 in Silver Galvanized Steel Structural Pipe Fitting Swivel Socket.I think it’s used for fences. I had to shorten one leg to fit my bench.

I cut the pipes to size with a cut off wheel on my angle grinder (No threads needed for this) I did not want anything to stick out from under the bench, so I found a pair of ½ inch drive sockets that fit snugly inside the ¾ inch pipe (watch out for that welded ridge). Every manufacturer makes wrenches somewhat different, so I grabbed a piece of pipe and went to the tool section to find the right fit. In my case the 14mm wrench was just right. I ground away the welded pipe ridge and then pounded the socket into one end of the pipe with the drive side sticking out. Finally I drilled a 5/16 hole through the pipe and wrench (carbide drill, cutting fluid and crossed fingers for the wrench section), put a mild steel pin in and cold pounded the pin until it deformed to keep everything locked in place. I had to file things down since the pin wound up inside the hub.

The ¾ pipe is attached to the 2” pipe segments using 5/16 bolts and one nut on the inside to keep things off center and one nut on the outside to keep everything together. Since the cam rides on the dolly pipe there is enough clearance for the bolt heads. I also added a stop block on the 2” pipes to stop the rotation. The block is adjusted so that the rotation is past the unstable max lift point and is resting in a stable configuration without losing much lift. While nothing is guaranteed, I do not expect the cam to rotate loose when moving the bench around.

Assembly

This can get a little tricky. I had to attach and detach things a number of times till I got everything fitted. Sequencing was also an issue, since one step usually blocked some aspect of my next planned step. Luckily I had a reasonable amount of clearance under my bench to work with, so I was able to sort things out without having to lift the bench.

To setup the dolly, I had to assemble one of the wheel platforms to the rest of the dolly while everything was positioned under the table. It would not fit otherwise. The dolly was then used to set the height of the hubs with the cams in the lowered position. I allowed about ¼ inch of clearance for uneven floors and debris under the wheels. You want the dolly loose when the bench is not up on its wheels. I used lag bolts to attach the hubs to the bench. Of course the dolly blocked the holes for the lag bolts, so unassemble, shift, reassemble and repeat. The lag bolts for the hubs was the only change required to the bench.

Conclusion

I used a 15 inch ½ inch T-handle to rotate the cam and it did not require a lot of force to raise the bench about ¾ of inch into a stable position for rolling the bench around. DO NOT USE A RATCHETING HANDLE FOR THIS. WHEN LOWERING THE TABLE A RATCHET WILL ALLOW THE BENCH TO CRASH DOWN.


This approach is fairly flexible. It can be installed under or around an object to be lifted. The cam can be attached to the dolly or the item to be raised. If built under the object to be lifted, this requires clearance for the cams to rotate and to allow room under the assembly for the wheels. The drilling of the axis pipe for the cams requires some care to keep the offsets aligned at both ends. The socket wrench is overkill. Much simpler alternatives can be used. Great care must be taken to avoid interference issues when choosing the locations for the various bolts and brackets. All the metal parts attract each other and want to be placed where they can cause the most problems.

This worked out very well for me. I can now get at the sawdust that has been hiding under my bench with ease and the ability to create more space where needed is sooooo nice.

-- Jonas



1 comment so far

View brandongb's profile

brandongb

3 posts in 2425 days


#1 posted 07-22-2019 01:32 PM

This is really cool. It would never occur to me to use half of what you did as parts for this project; hats off to you, sir!

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