Anchors should be at least ~12" (30cm) out from the edges of the workpiece (24" suggested)
Anchors do not need to be level with the arms of the sled, but that may be a good idea if you have the anchors close
each belt can apply >14kg (30 lb) of force
Bar has two example ‘frames’
A sideways H frame of bolted together unistrut
We know that this is not stiff enough, the unistrut flexes which causes errors in the sled position
Anchors in his driveway
Very little feedback from this so far.
an obvious variant to Bar’s frame would be to build the same shape from 2x4 material.
one idea I have is that if you boxed in the ends of the H frame (i.e. vertical pieces between the tips of the H) it should stiffen it up significantly
I also have thoughts of building a torsion box table that’s large enough to have anchors at the corners (and possibly movable extensions to extend the anchors)
Another thought would be to get a couple 24" interior doors (80" tall), use those on the sides, with something (unistrut or 2x4s) between them, with a wasteboard in the middle. It should be possible to setup a wasteboard at the right thickness that the doors will act as skirts to allow you to cut right out to the edge. The doors are light and very stiff, and have wood around their edges that make it easy to fasten to
(something similar to https://www.homedepot.com/p/Masonite-24-in-x-80-in-No-Panel-Primed-White-Smooth-Flush-Hardboard-Hollow-Core-Composite-Interior-Door-Slab-13930/100086651 currently $62 for me locally)
I also like the idea of using t-nuts to make the frame something simple to break down and transport/store
What about aluminum channels like what you would typically see used on a 3d printer but just thicker like some of the material listed at https://8020.net
i was hoping to use a unistrut frame too. hope we can figure out why.
i wouldn’t think that 30lb would deflect unistrut, but i’ve never measured. specs are something like 1/8" at 3’ at 1000lb, so at 30 lbs, that might be 0.1mm, which i guess is enough to matter.
it might help to add some tension to the frame since unistrut is much stronger than necessary - a fast way to try it would be (2) ratchet straps at the diagonals would add hundreds of pounds of tensions and cost maybe $15 if you didn’t already have them. not a permanent solution, since the nylon will stretch and creep, but if it works, aircraft cable plus some turnbuckles aren’t expensive either.
You sound like you know what you’re talking about.
How about writing up a How To Build a Unistrut H-Frame for Maslow?
I’m sure many of us would like to be building in anticipation of getting our Maslow4.
The problem is that spec is under ideal conditions. Strut twists longitudinally pretty easy and when it does those deflection ratings go out the window. It doesn’t usually matter because normally it is either part of a frame or bolted to something that doesn’t twist but a single strut sticking out into space will move all over and a short arm at 90 degrees on the end will wave in an arc.
why not just make a regular maslow frame, add a 2x4 to the bottom and center the waste board in the middle? Pretty sure a cheap 2x4 is more stiff than unistrut channel which is missing a side.
travisgood - unistrut isn’t cheap, the benefits are that it is fast to build with and reusable/reconfigurable for when your first idea sucks. personally, i don’t have the room to keep it set up, which is why unistrut or floor mounting is of interest to me. if you do go with unistrut (brand name), you can easily source locally and build it in a couple of hours. just be aware it might cost nearly as much as the maslow4 and make sure you’re getting 12 gauge.
melvin - i guess you’re right, it isn’t that hard to twist unistrut at the end of a 3’ piece. but i think we’re only talking about a couple of ft-lb. load. still, if this is the issue, adding tension would reduce.
charlotte_nc - if you have the room to keep it set up and are sure the design gives you the results you want, i agree with you that stick built is cheapest.
dlang - for a torsion box bigger, cheaper and stronger than the doors, buy foam insulation board and sandwich it between two sheets of 1/4" ply, all stuck together with construction adhesive. to make it useful, frame it with 2x4 so you have somewhere strong to attach screws to.
2 doors, a wasteboard, 3 10’ 2x4s, a wasteboard that’s 35mm-thickness of your workpiece (and a piece of something to make a lip to rest the workpiece on that could double as a skirt)
This is relatively cheap (the doors are a bit pricy at ~$60 each, not too bad to store (either assembled or disassembled), is relatively stiff, and is easy to build in that you use the wasteboard to define the separation between the doors and the alignment of the 2x4s.If you are doing a permanent assembly, you can use screws or lag bolts and their position doesn’t matter much (as long as they get a good bite in the 2x4), if you want to disassemble it, you can drill holes at equal positions on the 2x4s so that all 3 are interchangeable.
If you are leaving this setup, it’s easy to add a couple legs on the ends that pivot out, and a couple non-swiveling castors on the bottom of the doors to roll it around on
that image shows the wasteboard centered vertically, with 16" offset to the motors rather than the suggested 24". This is what you would want if you are going to lay it flat. If you want it near vertical, it probably makes sense to lower it a bit so there is more offset on the top than the bottom. Have to do the math to see what offset would make the tension in the top center and bottom center even on all belts (will depend on the weight of the sled)
Any chance you have a construction diagram made with unistrut and with dimensions? It might cost almost as much as the Maslow4 in the end but for a 4x8 sheet fixture and for repeatable assembly/disassembly it might be worth it for me. If this already exists from someone else’ efforts then please just point me to it. Thanks!
I have a Vertical Panel Saw in my shop. I’m envisioning an attachment (two attachments?) that can be clamped onto the VPS for cnc cutting. Has anyone done that?
I quoted this only because its a good segway into talking about unistrut stiffness and application. I see a lot of use of unistrut here that is not to the design intent of the product and I think that is where a lot of problems people have with it originate from.
The natural tendency is to bolt things to the strut on the closed side of the form. However, unistrut was designed to have things attached to the open face of the form. Bolting to the open face will stiffen the form and reduce torisional weakness. It uses whatever gets bolted to it as a structual element. Furthermore, it was specificaly designed to have things bolted using the T-Nut accessories. You can through bolt things through it but that has the tendency to distort the cross section of the form and will weaken the structrure overall. The T-nuts are designed to “bite” into the underside of the open flange and are prevented from sliding under a load.
It is possible to create a hybrid frame that is part wood and part unistrut. Here is a picture of the backside of my Malsow:
The unistrut portion is made up of an “H” frame design with a double crossbar. The two vertical sections extend up above the worksurface and carry the horizontal section which is the top beam. The worksurface is bolted to the “H-frame” using unistrut T-nuts and bolts. This provides structural rigidity to the frame proper as the worksurface essentialy becomes the main structrual member.
However, take a look at the top beam. If you look carefully (its hard becasue it’s brown), you can see that I had to add sections of angle steel to the open face of the top beam in order to stiffen it and keeping it from deflecting under load. My modification for M4 include replacing the unistrut beams (because I have to add a bottom one) with something else.
My point is that unistrut can be a cost effective solution if employed correctly, where it matters. With Maslow3, having a frame design that allowed adjustment, geometric symetry, a nearly flat worksurface, all while being as stiff as posssible was incredibly important. With Maslow4 though, the only real property that is desired is stiffness and maybe flatness.
This is especially true if the something you bolt to the open side of the Unistrut extends to some other fixed part of the frame, as opposed to something hanging in space like the motors on the chain Maslows. “Closing the box” will reduce the torsional flex, but only locally. The open segments will still flex.
Very true, which is why these need to be minimized as much as possible in a frame design. In my case, my beam had long lengths of open C that needed to be closed to limit the torsion, hence the addition of the angle steel.
I am thinking of using EMT conduit in a box shape with about 4 inch spacing between legs. I think it would be strong yet light weight. So 4 lengths of conduit and a bunch of 1/4 " bolts. For conversion 1/4" us about 6mm. 1/2" is about 12mm ans spacing would be nearly 100mm.
Do others think this might be strong enough. Instead of H frame in middle i believe diagonally placed conduit would offer more strength.
