Thanks very much! Much for me to learn, so I really appreciate this!

Quote Originally Posted by MrIdaho View Post
At 340 lbs I would suggest going with at least 2 inch box, .065 or thicker material.
No real reason to go with the cast pillow blocks as the stamped steel are more than adequate. Suggest go with a 3/4" axle.
For a good source of axles, sprockets and bearings
they carry the axles but are not listed on their site.
yes put some gussets on the 45 miter corners. The underside is really all that is needed as the stress is pushing up on the joints.
To avoid having to insert spacers or ?? to prevent the box tubing from getting crushed if you use 3 1/2"bolts to mount your pillow blocks, use some 1 3/4" bolts welded to a short bar stock that have holes for mounting the pillow blocks. Drill mounting holes on underside of frame, insert the bar stock w/ bolts. No need for two wrenches and no bolt head on top.
I have a thread somewhere on here on this method as well as fabricating the needed freewheel adapters etc.
good luck and post lots of pics