I think we need something people can use to keep the work piece flat.
screw/clamp/nail to the plywood
I like @dlangâs design, but maybe with three A-frames (two near out edge and one in the middle)
remember that my design has a horzontal 2x4 across the top of the plywood, and
itâs trivial to add some blocks (or scraps of plywood) across the bottom. The
back of the plywood and the back of the bottom brace are flush with each other.
Can I also suggest that we incorporate a place to mount the electronics? like a cut piece of plywood that the boards can get mounted to?
I would put this under the top of the frame in the center (unless someone else
has a better idea), can it just attach to the bottom of the 2x4 or is more space
needed? (and if so, how much)
With the alternate1 frame above (with the fixed A frames), the plywood is
structure as there is not enough else controlling the A frames. switching from
2x4 to unistrut would not help (and may even hurt, bolts make great pivot
points)
I would strongly recommend against using unistrut for the bottom beam, you
want something there that wonât wreck you bit if you cut to low and get into it.
Itâs a lot better to replace a $5 2x4 that gets chewed up a bit than a more
expensive bit that sends parts all over your shop
Here is a sketch of my basic idea. My representation is gorked on scale.
David, perhaps you or anyone else could onshape this. if we could design a
2x4 to Unistrut mounting cap. It could be easy to put together and take apart
quickly.
Thatâs pretty easy to do. Especially if you plan for the top beam to move
forward and back, it should be easy to remove entirely
The design is based on making the Skirt out of 9 inch boarders cut
from a single 4 x 8 sheet first. Using 2x4 small pieces of 2x4 to hold the
skirt edges together. This frame creates a negative space to mount the
âworking sheetâ.
you need to adjust the skirts in and out to match your workpiece + wasteboard,
how would you adjust that? (also, you should only need 4-6", not 9" all around)
The 2 2x4âs 46 inches apart create the âWorking Sheetâ main
attachment. Two 46 inch braces between the uprights at the outer edges of the
skirts. The Unistrut sits on top of that. A diagonal brace between the 2
upright 2x4âs support itâs not racking.
thanks for the reminder, I didnât include a diagnal brace on mine
1 more 2x4 as a âlegâ to tilt back on.
I donât like a single leg, too tippy, and too easy to bend to the side
The motors are on a 12 foot long Unistrut 21 inches above the working top edge - ~7 foot 9 inches tall.
thatâs 93 inches, normal doors are 80, garage doors are commonly 7â (84")
now, you should be able to bring the top beam down, the stock design has the
motors ~18" above the top of the workpiece
By the way, I hope Iâm not coming off as someone pitching their own design at the expense of others. I have put a lot of time in it, and I think itâs a very solid contender for the new stock design, but I want to be sure that Iâm providing constructive feedback, not running down other designs.
They are stable as long as the center of gravity is within the triangle.
three legs make it easier for the CG to get outside of that footprint.
Iâve knocked over far too many easels over the years, or hung things from them
in ways that made them tilt.
The other problem is the question of the hinge, a single leg is much easier to
push sideways than a pair of legs (and the distortion of the support is much
higher)
I was trying to express the need to make sure the plywood is very flat and doesnât warp or cup. That way when someone clamps/screws/nails a work piece to it, its also flat.
I donât see a 2x4 spanning the top of the plywood sheet in your drawings. (I did not open it on onshape⌠just looked at what you posted.) The bottom can be handled as you said by blocks/scraps across the bottom. Just didnât see one up top.
Iâm doing something very similiar for my âhangs and folds flat against the wallâ planned setup, only I doubled the top 2x4 (and with that Iâm getting maybe an ~.125" deflection with a 200+ lbs unsupported in the middle, which I reckon exceeds the amount of force the motors can supply at max torque) because I already had and itâs cheaper than Unistrut. Iâm extending the vertical 2x4 arms up behind the beam and running a 1/4-20 lag through both; that way I can tighten it all down, or loosen it and put spacers behind it to push it out for thicker material.
My question is how much clearance do you have under the top beam support arms in your design when the chain is at the top of the opposite corner? I havenât done the math, but preliminary playing around makes me think itâs at least 9" (Iâm planning on making the support arms as plywood gussets on either side of the 2x4 uprights), but wanted a sanity check.
Unistrut isnât available in home depot equivalents over here, i donât know about the rest of Europe, but the first time i heard about it was when i was working as an elektrician in a seaport.
I wouldnât make it required in the stock build. Itâs a lot more expensive then a 2x4 over here if you manage to fibd it over here too.
I loved working with it though, when i didnât have to pay for it.
Maybe incorporate an option to replace top wood beam with unistrut and everything else being standard? So if someone wants to take the extra steps and can readily get the materials, they could. I only suggest because it seems that the top beam is the most important part of the build.
I agree it should not be a requirement, and it isnât.
The motor mounts are a little harder to attach to to unistrut, so the 'standardâ
design should probably be with wood, and as an option, use unistrut.
Not really, sorry if i wasnât clear. Iâm asking how much room you have under this support before chain angle becomes an issue:
Especially once you tack a brace on:
If thatâs 16" to begin with, would the chains clear the brace if the sled is at the top of the opposite corner?
@dlang, you extended your a-frame to the reach the top bar. Is this necessary? I donât see how to easily incorporate a 2x4 extending across the top of the plywood and yet stay flush with the a-frame. Can only the back leg of the a-frame be extended up (i.e., does it provide enough stiffness to handle the stresses?) Something like this:
Alternatively, can we incorporate a gap in the front leg of the a-frame for the top plywood stiffener to fit into as shown below? Itâs a bit more of a complicated build. I hope the picture relays the question.
Iâm not thrilled with the alternative, which is to add a beam above the top of the plywood as it is done on the bottom of the plywood because if someone has a workpiece slightly taller than 4-foot, theyâd have to trim it to fit it.
This is why I thought three legs (two near the edges and one near the middle) would give enough mounting points to ensure the base plywood is flat.
@madgrizzle
the top beam needs to be in the plane of the workpiece, so it canât be supported by the back legs, it needs to be supported by the front legs.
the A-frame version doesnât include a stiffener, the folding version does (itâs hard to see in those angles, obvious to me since I know whatâs there, but not so obvious otherwise)
good point, thatâs ~33 inches out from the brace, so that could be an issue (especially when not out all the way). let me tinker a bit.
The first thing to do is to pull the brace back, but it may be necessary to go with something thinner (put the 2x4 on itâs side??) to have everything clear.
The stiffener on the folding version just spans between the two legs? If so, same could be done for the a-frame, correct? and is that enough and that we donât need to worry about the edges (though bottom edge can be fully braced)
