[crazy_mike]

Hey Everyone,

I've been planning this machine / collecting parts for about a year now. I got the kit from the CNC Building Blocks Kickstarter last year. Luckily the building blocks were not made in plastic, and he had the parts machined from aluminum, except the shaft supports which were machined from delrin.

All of the axises will ride unsupported 3/4" case hardened linear shafts with oil impregnated bronze bearings. The kit came with 3/8" acme anti backlash nuts so I ordered some lengths of 3/8" acme threaded rod. Along with that I've got 3 200oz nema 23's with anti backlash couplers for the threaded rod.

I really want to be able to mill PCB's, cut aluminum and obviously wood. Milling PCB's calls for some very good resolution and aluminum will need good rigidity from the frame. After looking around, I really like the idea of using aluminum extrusions so that the machine can "grow" with me as I get deeper into this "hobby" .

I would really appreciate some feedback on my design. All frame pieces are 80/20 (love the cad files on their site) 3030 except one section of 3015. The X axis rails are 20" long with 19" of travel. The Y axis rails are 30" long with 29" of travel, but the Y table is 8" wide so the effective travel is 21". The Y table is tall enough so that anything mounted to it will clear the frame when traveling. I want to put some sort of t-slot layer on top of the table that will provide mounting points and also enlarge my machinable area. I'm concerned about flex etc when cutting not directly over the Y table. Also I'm pretty sure I have too many plates, but like I said I want this thing to be very rigid.

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[Spk64]

Your frame construction looks good but I think you will be disappointed with the un-supported rails. These will reduce the rigidity of the machine considerably.
You have a nice fixed bridge with a floating table but the cutting forces will be flexing the un-supported rails unless you take really light cuts.
If there is anyway to add supported rails your machine will be much better.


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[crazy_mike]

I appreciate the insight. I agree with you on the unsupported rails, however my z-axis is already purchased, assembled and working with that configuration. I'm thinking that I will add supported square rails down the road after I get the machine up and running, 80/20 is the "adult erector set" after all

I've got a bit of a chicken and egg problem right now, I need those inner mounting plates to be machined, but I have no access to a mill and locally I'm coming up short. I've looked at protolabs.com and emachineshop.com but quoted prices are pretty ridiculous (~$180 per plate).

[dmalicky]

Unsupported rails for a Z axis are much less of a problem than for X and Y -- Z rails are much shorter, and flex goes by L^3. Check out ebay SBR20 for X and Y -- not much more $ than unsupported. I'd also suggest more vertical separation between the gantry rails: at least as much as the Z clearance.