Yes, in the original H-Bot design I used all cantilevered V-wheels with the M5 bolts that come with the mini V-wheel kit (no back plates at all). I found that this setup had too much flex due to the flexibility of the plastic parts the wheels were mounted to and contributed to the "H-Bar Torsion / racking" issue people talk about. It tried pre-loading them a bit but found it produced a slight angle to the V-wheel contact area. Using metal plates would do the trick, but not facilitate the belt runs.

Using a back and front plate the wheels are well constrained and kept square in the V-Slot as they are supported from both sides. This setup is much more rigid and might make my original design feasible...

The Z axis the V-wheels are still cantilevered. I didn't switch this as I already compensated for the cantilevered forces by constraining more bolt length in the plastic support to make it more rigid. I also wanted to keep the far side of the extrusion open to mount the extruder to. It could be done though. If you do go with a 12"x12" bed and think there is an issue then this area could be converted as well.

Aside: The plates in the current design are overkill- I can shave some plastic out of them and they will function just as well.

 

I used 40% honeycomb infill, but with my forced perimeter count only a few areas had infill

 

I've seen some setups that do this, but having had the issues with the H-Bot rigidity I didn't want to skimp. I think with some part redesign it would work fine and be rigid enough for the CoreXY setup.

 

The blue circled hex holes serve no purpose, they are just holes so that less plastic is used during printing.
The red ones are for bolts to the V-slot extrusion end holes, which I drilled out to 4.5mm before assembly. The hole is countersunk so the same hex head M5x10mm bolts used elsewhere will work.

If you don't have a 4.5mm drill bit, a 3/16" might work but leave less material to bite.

 

You're right, there really isn't much of a savings in plastic. It really isn't a critical stress area so I don't think there are any structural issues with these. Easy to remove though once I finally post the 123D files.

As for the red holes above, they are fully printed in the idlers. There is a 0.2mm membrane layer designed in to facilitate bridging over the countersunk hole, but otherwise no drilling needed. The hole that needs to be drilled/tapped is in the end of the aluminum extrusion itself. They are about 4mm when you get the V-slot and needs to be enlarged to fit a M5 bolt. It can be tapped to M5 size or if drilled close enough, the bolt can cut threads for itself.

 

I got mine custom cut from Voxel factory. It is 3mm borosilicate, which is nice for it's low thermal expansion and thermal shock resistance but expensive. The biggest thing is getting a nice flat piece of glass. You can't level a curved plane of glass!
My friend prints on 2mm thick picture pane glass and while he has broken 2-3 pieces of it, it is only $3-4 a piece.

 

Looks good. I see you are going with a 20x20 on the vertical legs. I think this a good modification to enable the use of a two plate setup for the Z axis.
I don't think the bolt holes you added where the hexagons once were will be usable as the belt needs to run through that section of extrusion. However, I think your version is printed most easily from the left hand side of your first picture being down on the bed, which would enable you to add a support on the inside of the extrusion if you wanted.

How is the prusa build going? A coworker of mine just ordered a Prusa 10" i3v Kit from Maker Farm.

Do you think think I should put a word document together detailing some assembly steps for the C-Bot or do you think it is unnecessary/obvious?

 

It is under the "files" tab of the build

 

None taken, though I am not sure what you mean, is that an openbuilds site discussion status? This thread is new as I've just posted the build on this site less than 2 weeks ago (and just last night on thingiverse).

I'd consider it live and is producing excellent prints as is (it is printing right now actually and I am not home). I could change the build status to complete. I'd love if people were interested in building this printer and add their improvements/twists to the design like John is above. He is working on some modifications to accommodate a larger bed (12"x12" I think) and enhance the Z axis to a two plate setup instead of a cantilever.

The BOM has two versions but they are identical. One is an xls and the other is a xlsx to enable folks with older versions of excel to open it.

 

I can't really make that comparison as I have never seen an Ultimaker in person.
The V-slot is very smooth and vibration free in my experience. I haven't attempted to push this printer to it's limits. I have been up to 200+% default reprap speeds temporarily (10 sec) but haven't left it there for a full print. Proper tuning of the stepper drivers is of course important and at this point I am able to run all motor and my drivers with no active cooling. Motors only get warm. I suspect my direct drive filament feed motor will end up being a limiting factor at some point and either active cooling/increased nozzle temps or orifice size/switching to a geared setup would be required. Alternatively, at some point sharp changes in direction with high acceleration will create belt stretch and reduce the print quality.
I am focusing more on quality over quantity at this point, but with larger bed sizes higher print rates do become important. Something to stress down the road.

 

Excellent mod. You said you were using sketch up for them?
Two things to note:
-V-Slot has pretty sharp corners. You are going to have to greatly reduce or remove the corner rounds from the inner extrusion profiles.
-regarding the second support web for the 20x20 extrusion, do you think it will bridge at an angle? I guess it depends on the intelligence of your slicing program!

 

Here are some prints in black ABS.
http://www.thingiverse.com/thing:482043

The little guy figure below was printed with pillar support, unfortunately I broke the spear bottom off with the needle nose pliers. The spear top is intact and printed wasn't supported. 0.15mm layer height. Source:
http://www.thingiverse.com/thing:182618

You will notice some cracking in the tower. I am new to printing in ABS and am not sure what caused this. Just a large part? If anything it is my printing settings or a need for an enclosure. 0.2mm layer height. None-the-less you can see the layer alignment is excellent and the fill is balanced and parallel (maybe a touch overextruded, but that is just tuning).