I remixed this and made some small adjustments to make it easier to assemble and a larger handle for comfort.
The "L" shaped part needs adjusted. I moved 1 of the supports away from the slot to make room for the knob but it seems I forgot to move the other one.
Changes I made:
Handle: I changed the handle to be a little more comfortable and added counter-bored holes to allow the bolt to be adjusted from the top of the handle. The handle could use some fine tuning.
Sides: I added hex-holes to the sides to hold the bolts and increased the hole size on the nut end to allow a socket to tighten.
Center Support: I slightly modified the 'tooth' on one end to fit a little more loosely for smoother movement.
Knobs: I redesigned the knobs to accommodate a nut.
Lastly I created a nut sleeve to add to the 1/4-20 nuts so they would catch in the slots without resizing them.
Bolts that attach the sides to the main body are 5/16" x 4" long. They stick out about 1/4" so they will need trimmed.
The bolts for the handle are 1/4-20 Phillips head x 1" with sleeves over the nuts.
The nob bolts are 1/4-20 x 1" with sleeves over the bolt heads.
At .03 resolution and 20% infill this was pretty solid.
I used supports where needed (handle, side support)
Printed in PLA
Print speed was 60mm/sec
Bed temp 60º
Extruder temp. 210º
You could print with a better resolution and more infill to achieve a better finish and heavier body but this thing feels solid.
I added a couple washers under the handle to allow it to tighten using 3/4" long bolts.
I used a little 3-in-one lock dry lube to make all of the parts slide pretty smoothly.
I used peel and stick craft foam for the bottom grip.