I would like to contribute to the design for some of the larger format CNC Routers out there. My plan is to build a minimum 2ft x 4ft router and be able to index sheets across the 4ft x axis. I have seen multiple builds bolting together 20x80 extrusion but thought this may be of value to some. My Idea is to have a vertical 20x80 and then horizontal 20x60 extrusions on the top and bottom. I would drill and counter bore the 20x60 in the center slot, flat position and then run M5 cap screws to t-nuts on the vertical ends of the 20x80. This would create a fairly strong "I" Beam profile. I'm a machinist and have a full shop at my disposal, so building it isn't a problem for me. Right now I am looking at using the extreme mini v-wheels. There will be more than the 8 wheels on the picture, probably at least 4 more to lock in the inside of the I Beam. What are peoples thoughts on the Mini V? Would it be better to go with the standard V Wheel? The ratings on the larger bearings are several times higher but does it matter? Let me know what peoples thoughts are on doing it this way. I plan to start a build log as soon as I get some more drawn up but would like to know what others think of it first. Carl
Hi, sorry if i get you wrong (not a native english speaker). but if you drill all the way through, you are atually going to perforate the whole setup right along centerline and thus i doubt a gain in strenth. If you drill just the top / bottom "chamber" and screw into there i doubt the material to be strong enough to actually carry the screws once the machine runs. Without - you know "wiggling" out / working lose..from vibration /accel/ decel. Just thinking loud Flo
You will find the interface between the extrusions lacks proper mating surfaces and the screw between the pieces will be passing through a lot of air between the pieces allowing them to slide relative to one another and subsequently not providing a lot of stiffness. You may be able to prevent some of this slippage using J-B Weld in the joint but I'm not sure if anyone has ever tried that. Overall you would probably be better off just creating a I-beam out of a couple C-Beams placed back to back or by using a box section made from a 20x80 faced up against a C-Beam. There is a design for 3D printed V-Slot connectors in the reference section which would be helpful in the alignment process.
Florian, Rick Thanks for the replies. Josh I had seen the thread on the I-Beam Concept earlier in my searches and that is part of my inspiration on this design. My image may not have conveyed how I had envisioned the beam. I have attached an end view to show the concept better. I see where there could be some alignment issues tightening everything down. Even if I drilled the 5mm hole to the exact diameter of the bolt I would still have the slop in the T-nut to contend with. I may have to double up 2 20x80 vertically and go with 20x80 on the horizontal. It would add some strength and better mating surfaces. Possibly clamp everything down to the table on my Mill for tightening to keep surfaces parallel.
You might be better off drilling 4mm hex key access holes from above and doing the connections internally. With long lengths you may still have difficulty getting the sections perfectly aligned and keeping the connections from slipping lengthwise. I would still suggest the 3d printed connectors to set alignment and J-B Weld to keep it from slipping.
If your intrest lies in a much stronger beam than Cbeam why not simply get a different kind of extrusion? Bosch and ITEM come to mind. My heavy extrusion (90x90mm strong-variant) on the x (long) axis weight somthing like 15 kg/m and may carry an elefant with ease greets Flo
s This is what I use. It is strong but it's also heavy. My 1500mm gantry has twin lengths of this with I'd say an extra 30kg in each end plate assembly onto y. The y was initially one of these either side, unfortunately it wasn't enough to support the wieght with 0.1mm flex over 2ft. Had to run 90x90x5mm steel under each y profile to get rid of it. But it is super rigid if you keep in mind it's own weight can compromise rigidity in supporting lengths. Not cheap tho around £100 per meter here
