A new anti-intersection iteration of the CoreXY principle design.

[Chris Burger (Ubermeisters)]

https://www.dropbox.com/s/5n5vv74rz3w4nhe/Render.jpg  Same as attached image, not sure which works better, so .. posting both.

Here is my latest iteration of the design for my printer, thought you guys might enjoy it. Saw the post about issues at the twist with CoreXY designs, so i figured i would provide an additional alternative.

You can't see it in the rendering, but between the stacked pulleys, there is a M8 nut, as M8 threaded rod will be the post. this enables the bearings to spin free of each other.

I would love to hear some constructive criticism, I'm always looking for good ways to improve my design, and almost all my parts are in, so soon it will be time to finalize the design, and send out for plasma cutting etc, so soon it will be too late to make major modifications!

[Whosa whatsis]

Accidentally sent this off-list...

The runs of belt going to the Y pulleys (the ones that change length as the Y axis moves) need to be parallel to the Y axis, otherwise their geometry (and thus belt tensions) will change as the axis moves. Otherwise, yes, that’s how I always pictured building one, with one belt slightly higher than the other rather than trying to cross within the same plane.

BTW, if you’re using bearing idlers, you shouldn’t need a nut between the stacked pulleys. A washer will do.

[Chris Burger (Ubermeisters)]

Sage advice friend. I can't believe i didn't account for the geometry of the parts moving! Ok, so new iteration. the pitch circle remains concentric for all Y axis belt leads. it looks obtuse due to the belt run from the motor to stacked pulleys being acute.

I think i am going to keep the 4mm nut between, although you are correct, a washer would do just fine. i like the comfort of knowing that the belts are decently spaced apart from each other, i can always replace them with washers at a later date, i intend to make both the motor mounts and the carriage belt connections adjustable, so that i can accommodate minor changes in the Z level of the different assemblies.

[makertr...@gmail.com]

Nice design! 

The added height of the stacked idlers may be an issue, but only if you want to enclose the printer.  My build has motors,pulleys all within the frame for shipping protection and aesthetics.  Makes for a slightly larger frame, but at least the added cost is negligible.

[Chris Burger (Ubermeisters)]

I am not producing this commercially, this is a design specific to a single build, centered around some expensive motors i have kicking around, and don't want to go to waste. I have an old entertainment center piece that i will be using for an enclosure, there will be plenty of room within for the printer, regardless of configuration. I am also working with a set amount of 80/20 extrusion, that i got for cheap on ebay, from 80/20 inc's "garage sale" (great way to get it cheap!)

[Jim Niehues]

If you simply move the two stacked pulleys closer together instead of moving the Y-pulleys, mounting to the Y-Carriage should be easier. The belt going between the stacked pulleys and the motor does not need to be parallel.

[Jim Niehues]

If belt clearance becomes an issue you may have to unstack the stacked pulleys and only move the ones furthest from the motors

[Chris Burger (Ubermeisters)]

Yeah, I wanted to do that, but i have already sent the DWG to my brother for plasma cutting the brackets, and i dont want to bother him (free service is best left simple!), so i will tailor the design around the plates, its easy enough, since everything else is still raw material.

[Spongman s]

very nice.

i'm not sure if it's a good idea. but a half twist in the two long Y sections would eliminate the need for toothed idlers.

[Chris Welch]

VERY INTERESTED!

Following design!

[Eugene Lee]

Awesome idea Chris Burger! I have a few questions though.

What is the point of having toothed idlers at all? Wouldn't flanged bearings work just as well? Is there a problem with running the toothed side on bearings?

[Jean-François Talbot]

Chris,

I used simple spacers and did offset the pulleys, like in the original CoreXY design (both of the cloth).

See it there

Jeff

[frank...@gmail.com]

Chris

I'm working on a UConduit variant and I would like to incorporate this belt routing in the design.
I'm not a mechanical engineer, and have no experience with belt drives. So forgive this 'stupid' question.
The machined idler pulleys that I can find are smooth - don't have slots for the belt teeth. In your
pictures you show the idlers that contact the tooth side of the drive belt with slots just like
drive pulleys. Is it possible to substitute smooth pulleys for those? [maintaining belt alignment, naturally]
or will they cause problems by deforming the belt teeth?

Frank Pirz
Media Conversions

[Chris Burger]

You can find them at SDP/SI i suspect, but smooth idlers would work just as well, een a simple bearing with washers on top and bottom (to trap the belt) would work just fine.

[David Shepherd]

Chris,

Did you ever release source files or stl's? I've looked over a few Corexy based designs recently, and this one looks like the ideal combination of 'simple and solid' (which is the ideal in engineering I imagine), and the only downside is I'd have to design the parts myself...  the others are printable, yet don't satisfy my desire for a 'great' design.

Did I miss a github release somewhere in here?

Thanks for the great design, really.

David 

[William Cook]

I looked into this once, but concluded that offsetting the idlers on the carriage introduced a moment on the bearings, which is what you're trying to avoid. Offsetting the fixed-position idlers in the corners and allowing the belts to cross in the back does not have this problem.

Really, this design still intersects - it just does so a little less obviously.

[Ryan Carlyle]

I've tried both on the same machine, there's no practical difference whatsoever.

[Alex Borro]

William, I could not get your point.. What bearing could be damaged and why??

Cheers.

Alex

2015-10-11 9:18 GMT-03:00 William Cook <william...@gmail.com>:

Racking not racing. I hate autocorrect.

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Alex Borro

[William Cook]

CoreXY was designed to solve the issue of racking which plagues the standard H-bot design. H-bots tend to wear out their bearings due to this moment, see the discussion here.

This "non-intersecting" design (which still intersects) introduces a much smaller moment on the gantry than a typical H-bot because the moment arm is roughly the width of one of the idler bearings instead of the entire width of the gantry. Still, the moment is there, and as Ryan Carlyle says the design provides no practical advantage whatsoever, so why do it?

If the aesthetics of having the belts cross visibly really bother you then go ahead, but the fact remains that it is an unnecessary engineering compromise which at best provides no advantage and at worst puts pressure on the bearings which could easily be avoided.

[DonaldJ]

FWIW, I'm muddling through a build of my own design, and I have the belts only a few mm apart, directly above the V-wheels of the Makerslide I'm using.

Racking should not be an issue...

[Kirk Blum]

Has anyone gotten this to work?  This looks like a much simpler routing scheme than getting the geometry correct for the crossing belts of the original coreXY design.  

 Thanks.

[Ryan Carlyle]

There are lots of different CoreXY arrangements now. The easiest is to put one belt in one plane and the other belt in another plane and shift the pulleys and attachment points up and down as needed.

Crossing belts was never really a problem in the first place though. People put way too much energy into solving a non-issue. Just let the belts touch. The contact pressures are too low to cause any wear.

[William Cook]

The only issue I have with some of the crossing-belt arrangements is the way they go around the idlers off-axis, which causes things to be noisy among other problems. I much prefer the simple two-plane arrangement you describe with each belt in its own plane.

[Whosawhatsis]

I agree, the interaction between the belt and pulleys when the belts cross is probably a bigger issue than the belt-belt contact. This issue is, of course, more significant on smaller printers, as the longer belt runs make the bending more gentle.

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[Ryan Carlyle]

What you can do to fix the pulley angle issue is rotate the axis of the idlers a bit so both belt legs are perpendicular to the pulley axis of rotation. That puts a small amount of twist in one of the belt runs, but not enough to be a problem.