Frame integrity: Hexagon vs. delta vs Y-style construction

Hello everybody!

I have been following reprap forum for a while now anonymously, but now at last I decided to join because I wanted to start conversation about a topic that I haven't really been able to find so much information about.

Namely, is there so much difference between different delta printer designs when it comes to rigidity, and do they REALLY translate into higher accuracy and speed? I assume good enough _resolution_ is already achieved with good belts and rails/rods (because limits in FDM tech itself)
Also, are you already maxing out the speed because of limits inherent to plastic itself (faster for PLA and slower for ABS and PETG of course), if we would like to print say, 10x10x10 cm part with 0.1-0.2 mm accuracy? Lets assume middle sized delta printers, print area of 250-300mm diameter, 350-450mm height). Or is it anyway the sharp angles and corner speed that slow printing most and thus the need for rigid frame?

First, theres the basic delta style (Kossel, Rostock) printers. If I've understood correctly, as long as they are symmetrically constructed and properly calibrated, good accuracy can be attained. And if printed parts are replaced with metal ones, then high speeds are also possible (lets assume the motors, drivers and hardware are not limiting factors).

Then there's the Y-style construction (like Delta Tower), where horizontal bars are connected in the middle in Y-form instead of delta style horizontal side bars on the outside. That thing is a 135cm tall 22kg metal monster, but I haven't seen any specs on speed and accuracy. Does the Y-shape really make it more rigid or is it just a fashion statement?

Lastly, there's the hexagon style construction. I think one of the few available printers of this category is the Hexagon V2, It looks pretty HQ construction, although the parts are PET printed plastic. Also the build diameter (200mm) is smaller than in many other non-Kossel mini printers. There are no english reviews, but with my Google Translator skills it seems that the germans are quite happy with it.
The on-going construction by Aussiephil here of his hexagon printer also looks very interesting, but it's not yet finished so there are no results yet.

I'm mainly interested in the hexagonal style not only because it (supposedly) could make bigger frames more rigid and allow higher speeds (although 260-280mm diameter x 350-400 height would be enough for me) but also because it could be enclosed more easily. Also the "motorized flying Bowden extruder" (suggested by dc42) possible with these extra towers sounds intriguing. However I'm not completely sold when it comes to the question of rigidity. Here the 3 main towers are not connected directly, but via other towers in the middle (so it's 120 angle between towers instead of straight line). Doesn't this actually weaken the structural integrity? Also isn't it harder to construct the main towers to be at equal length from each other, and so accuracy is compromised?

The towers do not need to be exactly equidistant from each other, because the differences can be calibrated out. But almost everything else does need to be accurate.

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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].

I dont think a hexagonal is that much more rigid that a Y delta , the triangle is one of the best structure and also cost less on materials side... take my design for example " the imp all metal" my corner are so wide (11 inch long and 3 inch deep sitting on top of the side frame ) its giving lever effect to stabilize the tower pretty much like a hexagonal minus the multiple tower. It can be very solid when the right corner and extrusion is selected. My top frame is quite heavy too cause its still the same corner as my bottom so 1/4 inch and 3 tower is plenty to support that.

Its not that hard to put the 3 tower in the place, it just take time to do it right.

Edited 1 time(s). Last edit at 04/11/2016 08:16PM by GroupB.

I have built a wood boxed printer using an (irregular) hexagonal frame. [rouzeau.net] [github.com] . The hexagonal frame is not stiffer than a triangular one, but required to let room for moving parts when there is panels or bracing.
Whats makes the ensemble stiff is the panels, which add shear resistance between the "towers", which are in my case the panels themselves. The overall stiffness of this closed box is much higher than any simple tower structure could achieve.
This is equivalent to a structure with diagonal double bracing, possible with hexagon, but not quite with triangular frame for clearance reasons.
So, hexagon is a good structure, but only if associated with structural shear panels or double (cross) bracing.
The stiffness approach the one of a tube of a diameter equivalent to the printer.

"Y" foot/top does not make sense on a structural viewpoint. It is done only because it (slightly) helps attaching accessories. Not worth [edit] the loss of stiffness [/edit], in my opinion.

Also, stiff structure is only of interest if other element are on par with the structure quality. The mechanics of the Lily come from Fisher delta and while the Lily structure is an order of magnitude stiffer than the Fisher, there is no noticeable improvement in the print quality (which was good, anyway), because of the intrisic weaknesses of a rod-based printer. The advantages are elsewhere, in the closed envelope.



Edited 5 time(s). Last edit at 04/12/2016 10:05PM by PRZ.

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Pierre

- Safety [reprap.org]
- Embedded help system for Duet and RepRap Firmware [forums.reprap.org]
- Enclosed delta printers Lily [rouzeau.net] and Lily Big [rouzeau.net]
- OpenScad delta printer simulator [github.com]
- 3D printing on my site [www.rouzeau.net]

I'll start some comments with a follow on from GroupB.....
I personally think the Hex frame is potentially less rigid when built with the same items due to the additional joints involved in the hexagon shape. Add to that the lack of metal corners for a hexagon and your in questionable territory.
So why did I go that way, well a hexagon is far easier to enclose with panels and if you make those panels structural reinforcement at the same time you end up a remarkable strong, rigid and stable frame with no impact to your printable area.

Random thoughts:

Y Delta designs seem to be pure metal framed and hence should be rigid because of that, but will, like all delta frames potential suffer from twist of the parallelogram vertical structures unless those structures also encompass bracing to stop the twist.

Personally i think that designs that have the carriage structure and the frame structure as the same thing can again potentially suffer the most from frame ringing/vibrations/ distortions.

I have a Flashforge Pro that I'm using to print all the parts i need and one thing i found early on was that despite it having a very rigid frame setup any and i mean any vibration that resulted from carriage movement that transferred to a table then got reflected back to the printer and became evident in the print in the form of ripples.
I found this when I moved it from the 80mm thick router table that never moved to another work bench that wasn't as solid..... needed to bolt the workbench to the garage framing to get rid of ripples in the print.

My frame design is big and ultimately HEAVY for a reason, it's not meant as a portable printer and may even be solidly bolted to the garage concrete floor to remove as many movement factors as possible.

Like for Like at the same speeds the more rigid/solid printer should have less resonances to affect print quality and therefore be able to then attain higher speeds subject to motors/extruders/plastic.

Having rambled on, maybe making some sense, any design that is solidly constructed should provide good quality prints, the trade offs between price - speed - quality will ultimately print output.

Wrote this then spotted PRZ's comments, that largely echo mine in different terminology

When I think about it my printer is not a Y delta but a hybrid Y/ Hexagonal, I may have only 3 tower but my corner extend so much I got a hexagonal shape the goal was to enclose it for extra rigidity and its easier that way, no need to curve the panel just 6 flat panel will do the trick.

Group B, in your posts, isn't there a mix between 'Y' (or star) and Triangle (or delta) structure ?
The link given by OP for the 'Y' structure is clear about what is meant.
Your build is indeed, hexagonal, and you can directly add panels or cross-braces

Edited 1 time(s). Last edit at 04/12/2016 10:27PM by PRZ.

Ya triangle not Y sorry, I was thinking Y as tower position because some T position exist too. Y is so fragile I dont understand why ppl consider this at all. My build is triangle / hexagonal hybrid then