Did you ever wanted to print a Kajak? I did 
I got inspired by the Hangprinter to print bigger things and was very close to build one but was a little held back by all the strings attached to it.
So I went into a little more classic approach with a framed printer but with very minimal part count and without classic linear guides. Almost all parts are very basic tubes and printables. I had a delta printer in mind but that āwastedā to much vertical space with the arms. I found the polar approach previously done done on the R360 and while it has some limitations it should work well with larger and hull type prints, hence the current name āHullkā.
It bascially is a crossbreed between Ryan Zellars MPCNC and the R360 by Kory also using that firmware at the moment but not using any parts from them, just the principles.
It is in a early stage where I build the whole machine and currently IĀ“m at the first print to see where it needs improvement. The general motion concept works and I will add a counterweight to reduce motor loads.
So Summer is getting closer, hope I can pull this up in time to get in my Kajak 
Print volume ca 600 x 1500 mm on the proto
Made a Communitie for it so if you are interested feel free to join https://plus.google.com/communities/115891306925383228109?sqinv=OGNZZ0hjYjZJTjZjaUpvbmxyalBBUGFMSmRYWnhR
I agree that too much space is wasted on delta style printers. About half of the wasted space between the delta arms at the top of the printer can be used be electronics or extruders, but people usually do not use the space. The slicers most likely will not let you safely determine if the print is within the pointed area at the top of the print zone as opposed to being to the side of it. Too much space is used up by arms in the first place.
I like your design. I imagine you could use the high pound fishing line for a balanced Z lift or use 3 threaded rods. I think your radius motor needs to move on Z but that will probably not be a problem for anything but Z hops.
@NathanielStenzel Would have lost too much space with delta or it would be like 3 meters high. The mechanics stay also very simple that way. Delta gives a better print quality for sure but I can live with that. It is meat for printing hull shapes anyway so the centre of the table is mostly left out and printing with the larger nozzles will mot likely hide imperfections close to the centre as wel.
@NathanielStenzel The Z lift currently works with steel HTD belts with the motors climbing on them. That works to lift the middle assembly safely but I will integrate a counterweight system so the motors don have to work too hard and In case of a power loss it is not going to just fall down. Fishing lines should work great for that.
Leadscrews would have been a good option of course but I went with the belt as they may apply force in random directions at lenghts of 1,50m + and are more difficult to ship. (The conduit is meant to be sourced locally)
Well, thatās novel 
You should consider constant force springs instead of counterweights. That will give you the Z load balance without adding mass and wobbly hanging bits banging around.
@Ryan_Carlyle Hmm constant force springs, I must admit that I havenāt heard of them yet but they seem a good idea. To keep it ābuildable from sourceā I may keep them optional with a neatly hidden counterweight system as standard.
Just to understand how it moves, is it a sort of āpolarā 3d printer?
If you can buy belts, motors, wiring, and pulleys, you can buy springs https://www.mcmaster.com/#constant-force-springs/
@Ryan_Carlyle Sadly we donĀ“t have such a place of mechanical goodness over here but IĀ“m sure I can find a similar easy accessible source.
@shauki IĀ“ve seen that approach recently, canĀ“t remember where it popped up. It didnĀ“t looked finished from the group. The mechanics are pretty simple and very much reduced to a minimum, I knew that It would be more complicated on the software side thats why IĀ“m building on the R360 concept and thats what I mentioned.
I just thought about printing big vertical parts and this is what came out. I can still switch easily to coreXY or something more common but I liked that polar concept and it really fits for printing hulls.
Will see if it works out well, Mechanics look good, the frame is stable the linear parts move freely with almost no play , all good so far
@shauki I will share the progress inculding videos in the Hullk community so I got everything in one place
Iām just curious - you complain about wasted space at the top of a delta - which is fair, though it largely depends on the length of the rods in relation to the bedās diameter.
With your current design though, arenāt you limited to printing in a prismatic volume? (triangular base)
Whatās the point of your round bed in this case? Youāre increasing X/Y precision as you go towards the pivot point (on the near tower in this image) significantly, but youāre also getting to a point where you have a whole lot of wasted volume compared to the dimensions of the printerā¦ Because the useable volume in that prism is going to be located at a minimum distance away from the pivot tower, given that you need a movement thatās at least a nozzle width away.
Iām curious to see how far you can go with the concept, and whether or not youāll be affected by frame torsion as you reach higher above the build plate. (common problem with a large delta frame)
Iād suggest using rectangular extrusions as the towers, with the long side of the cross-section tangent to the bed to protect against such torsion of the chassis.
@Jon_Charnas With delta IĀ“m loosing around 600mm in vertical build volume at the given 600mm bed.
IĀ“m not sure if I understand you right but the build volume nearly uses all of the machines intended build volume. You can print a vase with max diameter from bottom to top.
The frame torsion is compensated by two points at the top where it is mounted to the wall. At the moment even that doensĀ“t seems to be necessary The tubes are harwarestore (baumarkt) sourcable, so that way the parts are less specific. It doensĀ“t even use any linear rails components so it should be buildable anywhere.
@Thomas_Herrmann What I mean is that your frame is basically pivoting around one of the towers. Your maximum frame movements are limited to a triangular shape, instead of a full circle.
@Jon_Charnas It is a polar printer so the X-Axis is only moving in one direction while the table turns. So you got only one direction of moving mass there and the rotational forces at the bottom = not much force on the frame especially when wall mounted at two points at the top. Trust me
Oh, I misunderstood the kinematics then! That makes more sense, and I can see how that would work out quite efficiently now. How are you controlling vertical motion? Lead screws or belts with counterweights?
Very nice! Makes me want to rethink my Delta design. But first want to implement the right kinematics in redeem
