I am looking for some advice.

3D Printing
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I am looking for some advice. I am building the prototype sub assemblies for my printer design. I have never owned a 3D printer before. So building my own design from scratch is a bit ambitious. I am hoping I didn’t bite off more than I can chew.

My question is for anyone who has built a corexy or h-bot style printer before. After viewing the video, can you let me know if I am in for trouble in regaurds to the racking forces. Will the smooth idlers on the printed X/Y gantry pieces distribute the forces evenly enough? The PBC Linear Frelon/Aluminum bearings seem to be prone to binding if they get side load. I think this is because of the tight tolerances they hold to the ceramic coated shafts. I made the plate of plywood for now because I want to get things dialed in before paying to have it waterjet cut from 1/4" aluminum.

For reference I posted all my 3D model files a little while ago for anyone to use, review, and improve upon.

Thanks in advance for any help the community can provide.
https://www.youtube.com/watch?v=KKH9FBdm_Xo&feature=youtube_gdata_player

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Below is a picture of the assembly, and a diagram of my concern about the forces if A and B are not equal (evenly distributed).

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Really nice looking bot - equally nice looking shafting/bearings.

I know it’s not quite the answers to your question, but have you considered using the cablebot type layout?

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I have thought about it. How painful is the tensioning setup? What it the best cable to use in higher load applications?

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@Sanjay_Mortimer
That is very interesting to me, any other links to the creator of that one ? That cabling arrangement, T-slot and your Kraken would be awesome. I wonder about the Z-stage crashing down as @Tim_Rastall is dealing with. Perhaps a brake that releases with Z-motor step current …

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AFAIK, the racking becomes an issue due to the not only lack of rigidity in the stages, but also the long belt stretching, which causes tension on one side of the end effector and slack on the other. The core xy has shorter runs and has the tensile loads laid out in force couples so that there is less twisting on the end effector carriage.

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I could switch to Corexy with some standoff spacers and a slight change to the extruder cart mount. Do you think it would be worth a redesign? It wouldn’t take long.

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Honestly, I’m not sure, as I’m looking to deisgn a core xy as well. The h-bot has less parts, but I’ve read quite a bit about the racking issues. I’d personally do the core xy, but I haven’t actually seen any documented core xy printer designs out there, but there seems to be a handful of h-bots. I’d love to see what your results are, as I’m sure to be draggin my feet for a while on my design… although my extruder just crapped out so now might be the time for me to design as well.

Good luck

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I have built multiple H bots and core xy too all different sizes. A couple were quite large. The results I got on the h bot didn’t impress, so I’d recommend the core xy. At the size you have, I think you will be ok.
My $.02
Brook

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@Brook_Drumm thanks

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I was just messing around a bit before I go to sleep. Looks like I can make a pretty easy conversion over to CoreXY without changing the aluminum plate. I just need to utilize an existing rod support mounting hole, use longer bolts, and add some printed standoffs.

But I will have to redo my extruder cart to add 2 more belt attach points, and stagger the attachment heights. That way it can be swappable for Hbot to Corexy.

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Good plan. The proof is in the prints of course, but I don’t think either will be a problem with racking. Make those pulleys beefy and the belts tight!

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@Brook_Drumm thanks. I just got my openbuilds pullys and belts today. No binding turning the steppers by hand. The idlers balance forces pretty well actually. Now I think I will design a turnbuckle tensioner for the extruder cart :slight_smile: