I had an epiphany last night... My model now allows for 400mm of travel in X/Y/Z (Y may be a few mm short). All I had to do was invert the Z steppers and all of the holes lined up using standard brackets (though I did have to move the upper rail in a bit). This also let me change the lower side rails to doubles instead of triples. This also allows more freedom in the bottom space for mounting the power supply, control board, etc. I plan on mounting the whole unit on rubber feet so I will be getting at least another 1/2 inch of Z space (which I think I need for the PS) - If I need the space for electronics, I can change it to triples all around. I also changed the mount plates for both the main and middle carriage to simple 3 hole joining plates. Adding double hole tee nuts to mount them should keep them from moving without issue.

Anyone see any gotcha's?

 

I wonder if the acceleration of the X/Y movements could cause z-wobble? I would think if the z carriages are tensioned well it'll be ok?

 

Yes, that is my greatest concern and why I did my best with the CG and lengthened the moment arm of the main gantry wheels. I had originally started with a design with 4 Z leadscrews but didn't like the added complexity of another belt/pulley assembly under the chassis. I figured I would test it first and if it didn't pass muster, then I have already thought of a different way to go to four leadscrews (but would like to save $60-70 if I can - I'm already at about an $1,100 estimate for the build). If someone can state with authority that it absolutely won't work without going to four leadscrews let me know....

 

I think it'll depend more on the play in the z-axis carriages. If the towers are rigid, and the wheels are tensioned well to the towers , you should be fine with two screws, but won't know until tested. I appreciate your research if you decide to go through with building!

 

Exactly. Though I'm fairly confident that the rigidity will be sufficient for the mass it will need to constrain. And I am going to proceed with building. I'm completing my BOM right now. If needed in the future, adding two additional leadscrews would be a simple mod. As you can see, it is easy to enclose for a heat controlled space if desired. I think I am going to mount my control and display electronics on the top front (now the back in the pic above; I am going to switch the hot ends around - and of course the front can be whichever face you desire). This way my control line lengths to the steppers, etc., will be shortened, reducing wire resistance (it is easier to run one larger gauge wire up to the control board). I will use a DC/DC relay for the heat bed to keep the high power line lengths to a minimum (also much simpler with a fixed bed). I moved the X/Y steppers to the opposite side, improving belt placement and reducing belt length (though requiring two more pulleys). I also found that cutting a universal OB v-slot gantry plate in two will yield a gantry plate with the holes lining up perfectly for OB mini wheels.

 

Here's a shot of the other side (doesn't reflect new belt routing around the pulleys) with a cut-in-half V-slot plate which makes a perfect gantry plate with room at top for bowden tube and wiring attachment/relief.

 

That looks like a great implementation for the core x/y! I have been shying away from this type of build because of the belt overlap and never thought to move the motors to the other side. I am highly considering this now. I do have a couple questions if you don't mind. The first is for the firmware does this need a customized solution for the core x/y or can you use say marlin? My next question is as to what the power requirements for this size heat bed? Might I suggest starting your own build page I would definitely like to keep tabs on this and possibly "borrow" some of your ideas. Thank you in advance.

 

Thank you! I keep thinking about what if's (I just may invert the belt assembly to gain more Z height - need to play with it again)... This should work with any core x/y capable control software. Marlin is core x/y configurable. A 360W heater should heat a 400mm x 400mm aluminum spreader plate and glass bed to 60C in 1 minute and 100C in about 4 minutes (higher for shorter heat-up time/lower for longer heat-up time - your choice). I didn't mean to hijack this thread, I'll see if I can ask someone to move my posts to a new thread....

 

Good night Giuliano

That´s a great project. I am looking for XY Extended Idler part STLs in the build files. Have you removed it ?

Thanks
Reinaldo

 

Forking to a new thread to not interfere with Guiliano's build:

http://www.openbuilds.com/threads/h-bot-corexy-cube-with-fixed-build-plate.1528/

 

Guiliano,

Did you see my mini (20mm) v-slot gantry plate configuration? Have you worked on a similar floating carriage adaptation? Are you still set on the replicape? Did you see this review (www.youtube.com/results?search_query=replicape)?

I went ahead with the Fastbot BBP(1S) kickstarter. I had also looked at the replicape but if the Fastbot hadn't come out I think I would have gone with a CRAMPS/BBB (which you could probably still do and use your manga screen). Have you looked at the CRAMPS (http://reprap.org/wiki/CRAMPS, http://blog.machinekit.io/, http://pico-systems.com/osc2.5/catalog/index.php?cPath=5)? Looks like a pretty sweet setup with machinekit...

Please have another look at my current config and let me know if you see any issues or have come up with a better idea for yours. I'm getting ready to freeze my BOM and order parts to begin construction...

Thanks!!!

 

In your last gantry depiction (in post 9445) your side rails were vertical whereas this H bar rail appears to require horizontal side rails or 20x20's to ride on. Did you change your gantry side rails as well?

 

Your belt routing seems problematic in this configuration. Didn't your printed stepper mounts work as is? Couldn't you do the same thing by mounting the single 20x20 gantry rail like you did previously and modify your pulley mounts while utilizing your originally printed stepper mounts? A single pulley mount could then be used to hold both front and rear pulleys and you wouldn't need to cut the gantry rail.

 

Seems like you are giving up a lot of X travel in this config. Also, make sure you do your very best to minimize any belt offset from pulley to pulley or pulley to gantry as this will (however minutely) change the distance your belt travels across the span and vary the tension on your belt. Offset is fine between fixed pulleys - just not ones that move in a way that changes their offset angle as a function of their travel...

 

Let me know your thoughts about the CRAMPS after you fire it up with a BBB and check it out... I'm now waiting for the arrival of my BBP 1S:
https://www.kickstarter.com/projects/1177488680/bbp-making-your-3d-printer-faster/description

I'm hoping that it comes in early vs late June. I have quite a lot of work to do before then so I probably won't be ready much before it arrives anyway. It is nearly identical in specs to a CRAMPS/BBB or Replicape/BBB but as in everything the proof will be in the pudding - the LCD and expansion board are still in the works though so it will be wait and see if servo support ensues. If the BBP doesn't deliver on its promises, I may just get this since the CRAMPS doesn't have servo outputs:

http://www.ebay.com/itm/RAMPS-FD-Du...148?pt=LH_DefaultDomain_0&hash=item339a915634

I'm really hoping the BBP works out though because it looks like most of the RAMPS-FD boards out there are still v1 and I'd rather avoid the requirement to rework the board to make the v2 changes...(http://forums.reprap.org/read.php?219,424146)

UPDATE: I found out that the supplier who said they were selling v1.2 boards [GEETECH] were actually v1.A boards - explains the cheap price - really hoping my BBP1S works as advertised...

 

I would be afraid of belt stretching effects introducing Z height error. However, I would avoid belt crossover regardless; I see no way of doing this that wouldn't require some belt offset that would introduce Z height variation as a matter of height (however small) even without belt elongation effects. If you are set on testing the efficacy of belts, I would suggest you use separate belts for each side with the stepper in the center. This would increase overall belt strength/reduce elongation potential and obviate the need to cross belts, though it would require a couple of extra idlers.