Yes – We joined 2 pcs. together at 90 degrees to make an L-shaped cross section to resist flexing in both planes – Because we’re a woodworking shop, we had rippings of clear dry hardwood to use – Construction lumber might be prone to warp and twist as it dries – Perhaps use 4" x 8’ rips of 3/4 ply – one plane using 2 - 8’ pcs glued end to end (maybe with a short pc. spanning the joint for re-inforcement, and the other plane with a 4’ pc. each end with an 8’ in the middle, to stagger the seams – Strong, light, and stable – We used a similar assembly for a cross piece supportinga the top edge of the 4x8 work sheet – The flat horizontal board also makes a nice shelf to put the cotter pins on when you’re measuring the chain lengths!
once you put in another 2x4 connecting the top of the arms, you have reinvented the “top beam” design
The ‘wing’ frame gives the motors a lot of leverage (it puts the motors several inches out from the arms, and the arms 18 inches above the plywood, and it’s the plywood and all the screws that need to resist flexing)
You want to give the chains/motors as small a lever arm as possible against the pull of the chains towards each other.
Ideally, you do this by mounting the bracket so that it’s flush with the front of a solid beam (wood or unistrut) that connects the motors (unistrut is not quite as common as 2x, but it’s not far behind, I think the design should support both)
- Chain positioning
The ‘wing’ frame forces you to compromise between the chain being parallel to the workpiece, and it being at the balance point of the sled. The stock motor mounts put it at a reasonable place for working on 1/4"-1" material, but beyond that (including thick waste boards), you want to move the motors out.
It would be good to eliminate the wood motor mounts entirely and mount the metal motor mounts directly to the top beam. This requires having some ability to move the beam out from the back. Making this adjustable is pretty easy once you have it out at all.
- Plywood quality
The ‘wing’ frame uses the plywood as a structural element. The ‘top beam’ approach eliminates most of the stress, but you still have the legs attaching to the plywood. With just a little framing, the plywood can cease to be a structural element. I can be the wasteboard directly, or at least be shrunk down to a 1/2 cheap plywood
I posted a new idea for the chain takeup a couple days ago chain take up idea
This takes the idea of the plywood chain guide (two layers of plywood where the chain rides against the back of one and the side of the other) and extends it to take up the chain, not just passively guide it
Well summarized @dlang !!!
I posted a new shape for the metal motor mount brackets a couple days ago new motor mount suggestion This has holes to mount it to wood or unistrut, and has a tab to keep it from sliding down the beam.
It also replaces the slots with holes so it’s less likely to twist (although, especially for unistrut, it depends on the back and end flaps to keep it from twisting more than the screws/bolts)
I saw that and it looks really cool! Unfortunately we had to put in the order for the motor mounts quite a while back to get them on time so we can’t change them for this version
This is how I built my frame actually, so that the front plywood is not structural. I haven’t put my front plywood piece on yet because my kit is still coming, so I could snap some pics too.
Pictures would be great! They are worth 1,000 words
I have been working on a folding design for a while, and earlier on did an A-frame top-beam design. The A-frame design doesn’t have all the refinements of the folding one.
The A-frame design enlarges the A-frames from the stock maslow and still uses the plywood as structure.
The folding version I like a lot more, it’s built almost entirely out of 2x4s (with one potentially being a piece of unistrut) and the only thing it uses plywood for is the sled and brick mounts
The 2x4 cut list is pretty simple:
well, you did ask for pictures
For the folding version, I put wheels under it so that when it’s folded, I can wheel it into the garage on edge. It would be pretty trivial to add fixed legs and fixed braces to convert it from a mobile design to one that’s fixed. There’s enough wood left in the last 2x4 to do this sort of thing
I’m a little bit worried about this connection here:
I guess that the forces there won’t change as we move up or down, but joining lumber like that could be tough, right?
the whole thing is in onhape at https://cad.onshape.com/documents/e635c24e358635f51da4b399/w/5a63b67113542f248fbe6d7b/e/7cf092bea21763650fb0c54c
that point is a 12" piece of 2x4 that has the flat of the top 2x4 across the top, and the flat of the side 2x4 on the side.
With a couple screws (or lag bolts) through this from each direction, it would be pretty stable. There aren’t a lot of vertical forces here, it just needs to support the sled + top beam out to ~8" in front of the frame
If needed, it’s pretty easy to add a triangular brace below this. It would be toenailed into the 12" parts and then screws through it to the side of the frame.
Here are a few that I quickly snapped just now. I’m not completely finished, but all the major pieces are there. I was going to make a separate thread that goes in more depth of why I did some things, but the short story is I just had time to kill before my kit gets here.
normally I hate toenailed joints, but in this case, they are merely providing vertical support to prevent the supports from twisting.
All fasteners are going into the face grain of the wood (no end grain joints). If I was building it, I would use lag bolts instead of screws, but I’ve been known to overbuild things
What a gorgeous build! I really like how you did the angle 4x4s to push the motors forwards. It’s probably a little too advanced for the new stock design but love it!
@rjon17469 I second that, a beautiful build. I like massive overkill, which this is. But you won’t have problems with flex