Delta base size?

Another basic question for you helpful people! I'm (re)building my delta now, and I have a question about the positioning of the bed relative to the size of the horizontal rods. I'm using V-slot 2040 if that matters. Currently my bed is a 300mm circle and my horizontals are quite long, long enough that I can easily fit the bed inside the triangle without resting on the edges. I've seen many deltas where the bed is resting (overlapping) on the horizontals. This obviously brings my towers closer together, saves space in my apt etc. Is there any downside to shortening my horizontals? Originally I calculated an incircle of a triangle for a bed larger than the 300mm one I ended up with, but now I'm realizing that even using an incircle isn't necessary based on how many I see with the glass resting on the supports.

Further, could someone help me reverse engineer how they would set up their horizontals with the constraints I already have? I have magnetic rods that are 360mm from ball center to ball center. I believe this puts my radius somewhere around 170 tops, but I'm using a 300mm glass bed (for now!). How long should my horizontal supports be (ie how far apart should my towers be) and is there a problem with bringing the towers closer together generally (like I'd imagine resolution takes a big hit at moves very near a tower as those rods are very vertical).

Basically, I've got the software down, the brackets perfect etc just looking for help on how short I can make these supports to get the most out of my machine.

Thanks in advance.

What do you want to achieve? Maximize your build volume? Make the printer footprint smaller? Maximize quality?

I've always built them with "oversized" beds so I'm using 355 horizontals with a 330mm bed but I'm probably only reliably printing on 150mm radius. If I really needed to print something much larger in x than this I could, but as you point out the resolution takes a hit at the extremities probably more so if the arms are outside of the towers.

Maybe you should keep your frame the same and put a larger bed into it?

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

The disadvantages that I see of extending the print bed outside the base triangle are:

- The printer is less easy to transport, because you can't put it on its side on a non-padded surface (but other things like wheeled carriages may prevent you from putting it on its side anyway)
- It makes the printer harder to enclose
- For a given rod length, the closer together the towers are, the greater the angle of sideways motion required at the joints. So check that your joints have enough motion before you make the frame smaller.

My printer has 300mm print radius too. The rods are 350mm but if I were rebuilding it I would choose 360 or 370mm. The horizontals are 355mm and the corners are the Robotdigg ones for 2020 extrusion. The bed protrudes outside the horizontals See link in my signature for more details.

Personally, in your position I would probably keep the frame size and fit a larger bed, unless space for the printer is too big a problem.

Edited 1 time(s). Last edit at 12/05/2016 03:58AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Quote
dc42
The disadvantages that I see of extending the print bed outside the base triangle are:

- The printer is less easy to transport, because you can't put it on its side on a non-padded surface (but other things like wheeled carriages may prevent you from putting it on its side anyway)
- It makes the printer harder to enclose
- For a given rod length, the closer together the towers are, the greater the angle of sideways motion required at the joints. So check that your joints have enough motion before you make the frame smaller.

My printer has 300mm print radius too. The rods are 350mm but if I were rebuilding it I would choose 360 or 370mm. The horizontals are 355mm and the corners are the Robotdigg ones for 2020 extrusion. The bed protrudes outside the horizontals See link in my signature for more details.

Personally, in your position I would probably keep the frame size and fit a larger bed, unless space for the printer is too big a problem.

The bolded is genius! I would have completely overlooked that. Not to trouble you too much, but if I handed you 360mm mag rods, what would you do? I have the same alu Robotdigg corners but for 2040. I currently have a 300mm glass top and a 300mm silicone mains powered heated bed. That said, bigger is better. You also make a good point about enclosing, which is actually a future goal for me. Then it seems the ideal distance to get the most out of this rebuild is to figure out the maximum reach of my arms, assume that as my bed, then calculate the bottom horizontals such that the bed can rest on the horizontals without actually crossing them. That sound about right? By my own math, excluding the effector and carriage offset, 360mm rods should cover 338.29mm at a 20 degree angle. When I get the actual numbers together I'll post the plan here before I wreck my material haha.

DC on a side-note, thank you so much for your involvement here and in the community generally. As someone jumping from cartesian and Marlin to delta and Duet with your firmware, there are a lot of things I'm still figuring out and your repeated help (and firmware, and IR probe, and PanelDue haha) has been critical on getting this thing together. Thanks!