Superstrut or MDF/ply over frame for Lowrider edges?

LowRider CNC Advice
21

Hi all - I’m back after a cold, windy and bumpy ride to Florida. And not only was the bandwidth insanely slow - the latency was >2 seconds! So nice to be back on broadband…

Here is my latest attempt at a table design. It is really taking advantage of the great work several of you have done and shared on the forums - using full size sheets on two torsion boxes, using superstrut for the edges that go to full length, and borrowing from some other ideas out there on folding tables, etc. I’m really just trying to pull this all together into a single design, and one that the Lowrider can print itself (using an insanely simple, inexpensive, initial frame made from 2 @ 10’ 2x4).

The joinery is mostly square-nuts with bolts (about 90 1-1/4" x 1/4"), plus a few T-nuts here and there (about 32). Everything bolts together (and therefore can be unbolted for upgrades/transport). The table has legs that fold in (secured using pins), and then the table folds up, allowing for a total floor space of 26" deep by 10’ long when stored, and can do full sheets when pulled out. The table simply rotates around two 3/4" 6-inch long pipe set into a floor flange. All parts easily commonly available in the US (design is parametric, so adjusting for other sizing should be doable).

Not done with the cut sheets, but this looks like a close fit for 4 sheets (2 @ 3/4", 2 @ 1/2"). Total price looks to be just under $150 - about $60 in lumber, $40 for the superstrut, $12 for bolts/nuts, $12 for four locking/swivel castors, $20 for pipes and flanges, and $8 for temporary 2x4 lumber for the initial frame. Anybody have an opinion on using the lower cost 3/4" sheathing ply for a top? For flatness, is it better to go to MDF or higher quality (veneered) ply? Note that this top is held on with a 18 bolts, per side (36 total) - so lots of support to maintain a flat top.

Fusion claims the weight (of the wood) is 110 lbs, which seems about right since the raw sheets would be 200 lbs and I’ve cut out a lot of holes to reduce weight.

Here is the table, in the setup and ready-to-use position:

[attachment file=76397]

Here I have removed the top to show the torsion box design. Notice the use of the flat-nut joinery throughout:

[attachment file=76398]

And here it is folded up. There is sufficient space for the Lowrider rails and gear to clear the ground.

[attachment file=76399]

If you want to look more closely at the design, here it is (sharing my current working version, which I continue to evolve and therefore may be different than these pictures): https://a360.co/2R1aeQ6

Appreciate any thoughts on this…

Chris

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That looks awesome. How do the temporary legs attach/remove?

That should be pretty darn tough. If you find it works well, I might suggest actually gluing the main table. The glue will resist any minor movements and make the top skin really stiff. How well you cut the frame pieces and how flat the surface is when you assemble is are going to be the big factors on how flat the top is (in my opinion (not a mechanical engineer :smiley: )).

I would be very tempted to try some movements with it at several angles to sort of give an idea of what’s possible. I would also be tempted to try to balance the whole assembly with nothing but the jog buttons moving the gantry back and forth (for fun). I would fail, so I would make sure it was on video. Oh, I just noticed it’s not centered. That would be impossible then. Darn.

For the rotating joint, you might want to look at how people have made flip top workbenches. I see lots of pipes used for that kind of thing (which seems overkill for a miter saw, but not for this).

You could also think about putting another rotating joint in the middle. You could also put another piece of wood as a strap along the bottom of the table, connecting the two rotating joints. That would mean the plywood would have to stretch to make the table bow down, and it’s hard to stretch plywood.

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They are held with a single 1/4" bolt/T-nut along the top of the leg, and then a hole is used to insert a 1/4" pin in either the down or up position.

Leg down, pin about to be inserted (note the open hole on the other side of the leg should have a bolt which acts as a hinge):

[attachment file=76408]

Leg down, pin inserted:

[attachment file=76409]

Leg up, held by the pin:

[attachment file=76410]

It isn’t a highly structural leg - much of the structural element comes from the center base, and the side legs are to handle the offset loads as the Lowrider moves around. I do wonder if those legs need adjustable feet, since so few floors are really level… And I also worry they will be too floppy and not provide sufficient support. Hmmm.

One could glue it for sure and significantly improve the stability! But, given my prior experience with 3D printing and MPCNC is that I’ll make many adjustments and changes to this before I’m happy, and glue makes that hard! Hoping that the bolts with square nuts will keep it solid enough. I think it will…? Hoping it will…?

Nor am I! But I do play one on TV (or at least in Fusion 360…) But my thought is that since these are being cut by the Lowrider itself, they should be pretty darn consistent (but maybe not square?) The biggest challenge is that you will be cutting edge-to-edge (along the 8’ length) on the sheets, so that accuracy of the cuts will be determined by the accuracy of your Lowrider setup (on the temporary frame) and how well you position the mill prior to starting the cut. Having only used the MPCNC, I do worry that getting that alignment dead-on may be challenging on the Lowrider??

My plan was a 3/4" pipe of ~3" in length, being cantilevered from the sides through the top pivot holes. Low cost, easy to install. Seems similar to what others have done on the web, though often people use full length pipe rather than short pieces of cantilevered but the cost goes up and I don’t think the extra metal provides any meaningful benefits.

Floor flange on pivoting center support:

[attachment file=76411]

Pipe passing through center hole on table:

[attachment file=76412]

What are you contemplating here? That the two large sides will bend given all the cantilevered force of that 8’ x 2.4’ torsion box simply being bolted on, making the top no longer flat? If so, I share that concern. I did look at spanning both torsion boxes with a few longer boards, but the design I was playing with ended up requiring an additional sheet of lumber (hoping to avoid that). But I really need to lay this out into a cut sheet and see what excess lumber (if any) I have to work with. And at some point go ahead and build one and see what happens! I’ve got all the Lowrider 3D parts printed, but I’m 90% of the way through upgrading my MPCNC (was a V1) to Burly and that needs to be done first!

Thanks!

Chris

Table-v2-pin-leg-down-pin-out.png

Table-v2-pin-leg-down.png

Table-v2-pin-leg-up.png

Table-v2-flange.png

Table-v2-pipe.png

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Sounds good to me!

Just make yourself a note to check the bolts after a few jobs, and see if they loosen up. Bolts in wood tend to open the holes up a little over time if there’s any wiggle, in my experience. Non locking nuts tend to come loose with vibrations. It might be nothing, but if it is, hopefully you can catch it early enough to glue it, and it will happen late enough that you can be pretty sure you’re done with tinkering on that part. If the top is your spoil board, that’s another reason to avoid glue.

That’s right. It should be easy to determine before you assemble the whole damn thing. If you just prop one end up on something, and put something heavy in the middle, you can measure the flex. It’s pretty thick, so it’s possible I’m over worried. This would be one of those things to figure out before you glue anything though :).

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Oh man!

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When I built mine, they did just that! I glued and stapled my boxes together and thought the long side pieces would keep everything flat. They actually bowed a tad along the length. Couldn’t figure out why the top skin was short, then realized the whole thing bowed down because I didn’t have enough support. I put them on the support frame in the shop upside down from the orientation I build them in, and it mostly canceled out the bow, but it’s still there. Luckily the unistrut is attached with a seperate plywood plate, and that is straight. I still haven’t gotten around to surfacing the spoil board, but with a large project I’m planning, I’m going to have to do that sooner than later.

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For longer lightweight tables have a look at placing your legs at Bessel points, 0.2203 L from each end.

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Now you’re just getting fancy!

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I felt fancy just typing it.

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Fancy was the largest word I could think of…I would have said “sophisticated” but I felt if I needed to spell check it maybe I should not use it.

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