My Core XY Build

Hey All,

New to this forum.
I recently finished my first build. I have a bunch of wire clean-up to do but it's just about there. I used Misumi 2020 extrusions and rods. Most of the bearings and pulleys are from AliExpress.

I've been having issues with belt tension, belts slipping off the flanged bearings, and some poor prints. Here's the build as it sits today.





When I first completed the build, I had no issues and could print some really nice prints. I printed a Marvin as a test that was very good, and even printed one at 1000% scale which came out great. This was with an e3d genuine hot end and 0.4mm nozzle.

A month later I swapped to a 0.6mm Volcano (genuine) and moved my printer to another room (carefully). I haven't been able to print a flawless print since. I've used known good slicing profiles from others with the same printer and same setup

I've calibrated the extruder steps, aligning belts with my calipers to make sure heights were even all the way across, remeasured my frame and tightened everything up, I've tried tightening belts (no scientific way to make sure I have even tension)

I guess I'm just asking for some general maintenance items or other things I can check to help bring this printer up to spec from some Core XY guys. How do you guys tension belts evenly? I've just been measuring the distance between the x-ends and idler blocks to make sure they were even.

Edited 2 time(s). Last edit at 02/14/2017 02:19PM by theory.

Push on the belt and get them both to have the same tension.

Your belt paths don't look like they are parallel, so the path they travel changes length.

Edited 1 time(s). Last edit at 02/14/2017 04:08PM by stephenrc.

Hi theory
Nice machine, well done. To achieve equal belt tension I use pitch (musical). Choose the 2 shortest equal length belt runs and ping them, adjust the tension of one of them till the pitch is the same. Much easier if you have screw adjustment. If you are tone deaf use a guitar tuning app on your phone. Check to make sure your belt runs are co-linear parallel and perpendicular, if not tension may vary.
I have had problems with belts riding up flanged bearing pulleys on the bed of my cartesian printer. Solved with smooth wide flange pulleys (cheap Chinese ones).
I'm also running genuine volcano 0.8mm nozzle. Early days yet and only using PLA. I'm having trouble getting a really nice first layer, but some experimentation should sort it out.

The belt connection to the extruder carriage will have to be redone. Those belt segments must be made parallel to the X axis, otherwise prints will be distorted and you'll probably have trouble keeping the belts on the pulleys because the tension will change depending on where the extruder is in XY space. I can't tell from the picture, but the variable length belt segments along the Y axis rails have to be parallel to those rails for the same reason.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Thanks for the tips guys. I'll take some close ups of the belt path tonight so you can see.

Quote
the_digital_dentist
The belt connection to the extruder carriage will have to be redone. Those belt segments must be made parallel to the X axis, otherwise prints will be distorted and you'll probably have trouble keeping the belts on the pulleys because the tension will change depending on where the extruder is in XY space. I can't tell from the picture, but the variable length belt segments along the Y axis rails have to be parallel to those rails for the same reason.

So essentially all belt paths need to be as straight and parallel to the x and y axis as possible?

The variable length segments have to be parallel to their respective guide rails. The segments that are fixed length (the ones that run between fixed pulleys or between the motor and a fixed pulley) don't matter.

This is what it should look like:

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
theory

So essentially all belt paths need to be as straight and parallel to the x and y axis as possible?

If a section of belt goes to a pulley that moves it needs to be parallel. Otherwise the belt gets tighter as the gantry moves closer to the pulleys. Belt that goes from the motors to stationary pulleys, or between the two stationary pulleys at the top do not have to be. Many corexy designs use this as an advantage (crossing belt designs).

Would it help to use bigger OD idlers on the H-beam? That way you only have to print a sleeve that fits over the actual bearings.

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o_lampe
Would it help to use bigger OD idlers on the H-beam? That way you only have to print a sleeve that fits over the actual bearings.

Don't forget that the shafts for the pulleys are mounted in a plastic piece. L Chances are it has warped a bit and the shaft is no longer perpendicular to the mount, so a bigger pulley may just cause the belt to slip more.

I think if there's actual belt slipping (not motor slip) it's probably due to the fact that the tension of the belt varies with XY position. If he initially tensioned the belts when the carriage was in a "tight" position, when it moves away from that position the belts get looser, maybe loose enough to slip. Once the belt routing problems are fixed I'd bet the belt will stop slipping.

Based on what I've seen posted here in the last year or so, it seems that one common problem with setting up coreXY printers is motor slip when the printer starts printing solid infill on the first layer. That's typically printed at 45 or 135 degrees relative to X or Y axis and only one motor is moving the entire X axis and extruder carriage. You have to set the motor current, acceleration, print speed, and jerk to allow for that.

Using plastic parts to hold the pulleys is a bad idea- it's hard enough to keep them upright in all-metal construction. The way most people design them, plastic parts will flex and cause problems.

Edited 1 time(s). Last edit at 02/15/2017 10:11AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
the_digital_dentist
The variable length segments have to be parallel to their respective guide rails. The segments that are fixed length (the ones that run between fixed pulleys or between the motor and a fixed pulley) don't matter.

This is what it should look like:

08080006.jpg

I can't stop staring at this photo. Everything just looks so good.

I will edit the extruder carriage so that belts are parallel and straight on the variable length side.

I do agree that plastic parts have flex and after further investigation I think that's what is causing the belts to slip. If I over tension on the top belt it will bend the idler bolt causing the lower belt to slip up like it does.

I need to research and see what, if any CNC parts are available that I could use to replace plastic pieces.

I still need to re-design the idler blocks for the belts, but here's the new hot end carriage. Belts are straight and parallel and it's working out ok

They are not parallel to the movement axis.

oops! missed a couple...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Those are the idler blocks I referred to in my post that I still need to redesign They are next on my list

I think I'm there

Something is definitely up with the new setup I installed.

Without the belts on, everything moves freely, when I install the belts, and they aren't very tight, the x y gantry is difficult to move.

It's a slow and frustrating process.

Edited 1 time(s). Last edit at 04/05/2017 02:58PM by theory.

Nvm

Edited 1 time(s). Last edit at 04/05/2017 02:56PM by Qdeathstar.

It looks like you're got the belts arranged properly now.

I question the value of those "thermal pads" under the glass. The thermal pads conduct heat better than air, but not as well as having the glass right on the metal surface. If you put glass right on the unflat metal plate, you get warm areas where the glass touches the metal and cool spots where it doesn't. Now you throw thermal pads in there and you're lifting the glass off the bed, and inserting a thermal resistance between the glass and the metal. You're going to end up with heat islands around the thermal pads and cool areas everywhere else.

I really don't understand the 3D printing community's love of glass and all the silly stuff that has to be done to make it work. Just get a piece of cast tooling plate, put a thin layer of PEI on it and you're done -no problems with parts letting go before the print finishes, and no need to put gooey stuff on the bed. Yeah, it costs a few $ more up front, but in the long run it's probably cheaper than any other option, because you won't waste so much time and material on failed prints, and you won't have to keep "feeding it" with glue and other crap, and replace broken glass plates.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Do the X axis guide rails have solid endstops inside the bearing blocks at their ends? If not, the belt tension is probably pulling those blocks inward which will flex the Y axis guide rails. That will lead to problems moving the X axis assembly along the Y axis rails. Another possibility is that the X axis rails are flexing due to the belt tension, which allows the Y axis rails to flex inward, causing the same problem. If the belt tension isn't pretty close to matched, the X axis may tilt relative to the Y axis and put a lot of pressure on the Y axis bearings. End supported rails can be a b**ch...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

I read the recommendation for the cast aluminum build plate with PEI and gave it a try. It solved many frustrating issues. I found ATP 5 to more more affordable than MIC6, and very good.

[www.midweststeelsupply.com]

Quote
the_digital_dentist
I really don't understand the 3D printing community's love of glass and all the silly stuff that has to be done to make it work. Just get a piece of cast tooling plate, put a thin layer of PEI on it and you're done -no problems with parts letting go before the print finishes, and no need to put gooey stuff on the bed. Yeah, it costs a few $ more up front, but in the long run it's probably cheaper than any other option, because you won't waste so much time and material on failed prints, and you won't have to keep "feeding it" with glue and other crap, and replace broken glass plates.

The thermal pads are there to raise the glass as my cheap aluminum plate has a slight bow in the centre. When budget permits I plan to upgrade to a better plate, but until that time glass and hairspray will have to suffice. The tooling plate and pei sheet sounds like a great solution.

Edited 1 time(s). Last edit at 04/06/2017 12:17AM by theory.

Quote
the_digital_dentist
Do the X axis guide rails have solid endstops inside the bearing blocks at their ends? If not, the belt tension is probably pulling those blocks inward which will flex the Y axis guide rails. That will lead to problems moving the X axis assembly along the Y axis rails. Another possibility is that the X axis rails are flexing due to the belt tension, which allows the Y axis rails to flex inward, causing the same problem. If the belt tension isn't pretty close to matched, the X axis may tilt relative to the Y axis and put a lot of pressure on the Y axis bearings. End supported rails can be a b**ch...

The end blocks just have a printed flat surface that butt up against the end of the 10mm rod in a groove.



Now that you mention the flex of the x rails due to tension that does make sense. Not sure why it's more pronounced at this point, my stepper motors are skipping in the prints whereas prior to my modifications I could at least print. I'll measure the distance between rod and the extrusions tomorrow with belt on and off to see how much flex exists. I'll loosen the belts a touch more to see if it helps.

Thank you

The Y axis rails need to be parallel to each other, and the Y axis bearing blocks need to be spaced exactly the same as those rails, and they need to be aligned so the Y axis rails have a parallel path through the blocks.

Those end stops for the X axis rails assume that everything is measured, cut, and printed perfectly. If the rails are short of the end stops, the blocks can slide on the X axis rails and pull the Y axis rails inward toward each other. If the X axis rails are a little too long, the Y axis bearing blocks will be further apart and may not match the spacing of the Y axis rails, flexing them outward and apart when the X axis is in the middle of the Y axis, and jamming it up at either end of the Y axis. If one X axis rail is shorter than the other it could cause one or both of the Y axis bearing blocks to tilt (no longer parallel),

I would have designed those blocks with screws in the ends of one of the blocks to allow adjustment of the stops to match the spacing of the Y axis guide rails, and to compensate for different length X axis rails, then cut the X axis rails to be a few mm short so that the screws would set the exact spacing between the Y axis blocks to match the spacing of the Y axis rails.

The problem you're going to have with a redesign is that the X and Y axis guide rails are coplanar which means you won't be able to access the screw heads to adjust them while the whole thing is assembled.

The more I think about it, the more I like linear guides screwed to a flat plate. It simplifies the design and alignment more than I fully appreciated.

Edited 2 time(s). Last edit at 04/06/2017 08:25AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

What I did was measured the distance from the outside of the 2020 extrusions to the outside edge of the 10mm rods on the y axis and adjusted the y rod end blocks to get a parallel path through the blocks on both sides. There are still many flaws due to a variety of small variances that I'm sure exist between the printed parts and cut parts though.. I was able to print very well previously, and something that I introduced has caused the belt slippage, and binding i'm experiencing now, I just can't figure out what it is.

I measured an inward deflection of ~0.4mm per side from when the belts were loose to when they were tensioned. I loosened the belts and the printer is useable. I'm looking into linear guides now to replace my xy gantry.

I would think you could rescue the existing stuff by redesigning the Y axis bearing blocks to allow for adjustable end stops for the X axis guide rails. That way you could ensure that the Y axis rails don't flex when belt tension is applied. You could move the X axis rails up or down so they aren't coplanar with the Y axis rails, and add a couple screws to one block that are coaxial with the X axis rails. Turning the screws would adjust the distance between the Y axis bearing blocks to exactly match the Y axis guide rails.

Edited 1 time(s). Last edit at 04/09/2017 10:23AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]