My coreXY design is progressing to the build stage

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the_digital_dentist
Yup, keyed shaft. I didn't have the tooling to do it, so I contacted a guy on ebay who sells short keyed shafts for Rinos and paid him about $20 (IRIC) to make a long one. The keyed shaft can still slide out of the gearbox, so I used lock rings on either side of it, though placement of the pulleys and pillow blocks at the ends of the shaft could also keep the shaft from sliding out. In my build there is space between the pillow blocks and the pulleys, so the lock rings help. There aren't any forces along the length of the shaft, so it probably wouldn't move anyway, but why take the chance? You can either print lock rings to fit at the gearbox or spacers to fit between the pulleys and pillow block bearings. Either way does the job.

When I made the heater for the enclosure I thought I might just move the gearbox toward the left side of the shaft, but then I realized the shaft key is centered so I can't move the gearbox more than about 1 cm.

If everything is lined up right, the shaft should stay put without the lock collars. Doesn't hurt, though. We had some new conveyors installed where I work (I'm an industrial mechanic) and the bargain bin contractors we use did a terrible job building them. Long story short, gearboxes aren't mounted rigidly enough so the shafts are always walking out. I could rant about contractors (Looks good from the house!) all day.

Anyway, if your gearbox has a solid mount and your bearings are lined up, you shouldn't have any problems.

The kinematic mount for the bed is genius but the ball head screws seem to be a little difficult to source. Has anyone considered using ball studs for gas springs? They're widely available and as cheap as can be. Also, if the ebay guy gets tired of machining shafts for everyone copying DD's build (such as myself), MMC sells keyed drive shafts at pretty reasonable prices. Gotta love Mcmaster-Carr.

They aren't that hard to get: [www.amazon.com]

Amazon has a lot of ball stud listings, too, but you need to be able to adjust them by getting a wrench on them from under the bed plate, so be sure to leave room. The threads are pretty coarse, too, but manageable.

I don't think there are a lot of people copying the design, but maybe there will be a few more once I get the printed gear box finished and tested. That $100+ part is about half of a lot of people's printer budget.

Edited 2 time(s). Last edit at 02/23/2018 10:54AM by the_digital_dentist.

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

Quote
the_digital_dentist
They aren't that hard to get: [www.amazon.com]

Amazon has a lot of ball stud listings, too, but you need to be able to adjust them by getting a wrench on them from under the bed plate, so be sure to leave room. The threads are pretty coarse, too, but manageable.

I don't think there are a lot of people copying the design, but maybe there will be a few more once I get the printed gear box finished and tested. That $100+ part is about half of a lot of people's printer budget.

Yeah, that amazon listing kinda put me off since it doesn't seem to have a quantity listed. Surely they aren't $10/each. I ordered from these but it's going to take them over a month to get here. The ball studs also come attached to brackets which I though could be useful so I snagged some of those since they're like $1 each.

The Rino gearbox is my favorite part of your design. When I got mine in the mail, I took it to work and showed it off to all my friends (we're mechanics). Scored a nice set of THK rails for $100. Pretty excited about those since I saw a video clip of how smoothly your bed travels. Also, just got a message from the guy selling the short output shafts for the Rino's saying he/they can't make a shaft the length I need so MMC it is. Which is no biggie. I want to get my own green and yellow book one day.

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[www.wildbot3d.com]

It came with at least 6 of the screws, but maybe as many as 8. I don't recall, but I have 2 on the machine, and 4 in a box. The screws are chrome plated soft steel, so the hex sockets on top of the heads can be stripped if you apply too much torque to the wrench. It doesn't say anywhere, but the ball is 8.88 mm in diameter.

That was a good deal on the THK rails. I scored two new 470 mm long 12mm IKO rails for $68, shipped, a couple weeks ago. They are almost as cheap as HiWin knockoffs, but unlike the knockoffs, there's no doubt about their quality.

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

Nice. THK makes quality parts, no doubt. You've done an excellent job with this build/design. You used quality parts where it was important but didn't waste money on non-critical stuff. I'm having a ball sourcing the parts. Feels good to build an industrial grade machine as opposed to the poorly designed plywood knockoff that's sitting next to me at the moment.

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[www.wildbot3d.com]

Ouch! $28 + shipping for a drive shaft with a 2mm keyway.. that seems like a very small key. Is it really 2mm?

I've also started a similar setup... really like the design @the_digital_dentist

Z movement seems to be my biggest problem.

ampapa,

Gotta make it worth the dudes time..... he is probably making about $15 for 20 minutes of work, not crazy.

Yeah, 2 mm key.

The new worm drive I'm working on uses an unkeyed 8mm shaft- grub screw(s) on the disc gear lock it in place. That will save a few more bucks over using a Rino.

I'm hoping the gears match the drawing/description, are of adequate quality, and that I can design a gearbox/mount that won't flex enough to cause any print quality problems.

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

@the_digital-dentist... can't wait to see this new worm drive concept.

Is this base don the garage door opener I remembered reading something about?

ampapa,

That one used plastic gears, 16:1, and was going to use a NEMA-23 motor, but the shaft and bearing sizes were a problem, so that project has been abandoned.

The new one is much smaller, uses 40:1metal gears, NEMA-17 motor, 8mm output shaft, F608zz bearings:



This is rev 3 mounted on a piece of 40 mm square t-slot. It also fits on 1.5" square t-slot. A single carriage bolt secures it to the frame, but I may be changing the mounting method.

Edited 2 time(s). Last edit at 02/23/2018 10:43PM by the_digital_dentist.

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

Quote
ampapa
Ouch! $28 + shipping for a drive shaft with a 2mm keyway..
ampapa,

Looks like MMC has pretty much the best price. I'd make it myself but I only have standard end mills so the cost of the shaft material plus $10-15 for a 2mm end mill is going to be well over $40. So $28+shipping from MMC knowing it'll be here in just a couple days and be well made seems reasonable to me. Let me know if you come across a better source, though.

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[www.wildbot3d.com]

Looking good @the_digital_dentist! Maybe I'll test your design instead... hmmm.

@hayseed_byte, I agree with you, 8mm shafts are easy to find but slotted ones however are another story. I have some small end mills but not a 2mm.

ampapa,

@the_digital_dentist how's that new design coming on the worm drive...?

The gears finally shipped from China. Still waiting...

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

The worm gear set finally arrived and they do not match the drawing that was on the manufacturer's web page, so I am redesigning and reprinting the gear box. The good news is they look like reasonably high quality gears. Stay tuned for updates...

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

Progress:

The gears were quite different from the manufacturer's drawing, but like their web page said "drawing for reference only- goods prevail".

They appear to be new gears- there's no wear on the slightly rough tooth surfaces, and there were some burs in the worm's bore hole where the grub screw hole was tapped.

I tweaked the design a bit (and still have a few more tweaks to apply), printed it last night, and got it assembled this morning.





There is no play in the shaft at all.

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

The images didn't post to the page.. but it looks awesome!

No backlash is incredible...

ampapa,

Thanks for (planning to) sharing, looks clean and efficient.
I will slowly be building a semi-large CoreXY with 2x 750mm linear rails for Z axis, and this should come in very handy.

Edited 2 time(s). Last edit at 03/26/2018 10:29PM by orea.

I've been making a lot of tweaks and reprinting and believe I have the final design for the worm gearbox ready for testing. I tried testing the last version and found that the assembly was too tight and the gears were binding. In this version I spaced the gears about 0.4 mm farther apart which has created a tiny bit of rotational play in the shaft but it shouldn't matter as it will always be loaded in one direction (thank gravity!) if used in a Z axis. I also bumped out one side of the box a few mm to stiffen up the bearing mount on that side. The whole gearbox is a little wider than the motor now. In previous designs I used 9mm thick ears on the end of the box to mount the whole assembly to the t-slot. I found that was too flexible, so in this version I thickened the mount to 25 mm and added a screw to clamp the two halves of the box at that point.

The asymmetry of the disc gear requires a specific assembly sequence. First put the worm gear on the motor shaft, then put the bearings, washers, and disc gear on the shaft.

subassemblies

Then you mount half of the gearbox (the half on the left side of the photo, above) on the motor.

The reason you have to assemble it this way is because disc gear and bearing flange interfere with tool access to the motor mount screw.

Then you slide in the shaft, gear, and bearing assembly and apply some lithium grease to the gears.

Then close up the gearbox by screwing the two halves of the gearbox together.

Finally, you screw the second half of the gearbox to the motor.

It looks extra beefy because I don't want it to flex. I printed this with 40% infill using the grid pattern in slic3r, 4 perimeters (2mm thick) and 6 top/bottom layers. Each half of the box uses about 54 g of filament. I used plastic thread rolling anchor screws to hold the two halves of the gearbox together, but you can easily put bolts all the way through the assembly. It is designed to mount on 1" square t-slot using a single 1/4" carriage bolt, but it should also work fine on 25 mm t-slot with a 6mm carriage bolt. I'll make another version or two to fit on 40 mm square and 1.5" square t-slot. I'll post CAD and/or STL files once I have verified satisfactory performance.

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

Nice thing to wait this. I'm going to copy this and my printer is starting to be ready to start ordering parts.

I didnt see link at where did you ordered those gears? Are you going to publish it?

Edited 1 time(s). Last edit at 03/29/2018 02:31PM by kapperi.

Here are the gears:

[www.aliexpress.com]

The gears I received do not match the drawing on their web page. I will post dimensions of the gears I received, but you may get something else...

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

Okey, thanks. Pretty decent price...

Your belt driven z-axis is pretty simple, low cost and should be fast enough. Compared to leadsscrews or ballscrews, its very simple.

@The_Digital_Dentist, is there no need for an extending post at the top of the worm gear, will it not flex?



Good stuff...

ampapa,

Edited 1 time(s). Last edit at 03/29/2018 06:00PM by ampapa.

It probably wouldn't hurt, but I don't think it will be necessary. The force on the motor shaft (and the plastic holding it all together) will be more or less constant. As print mass increases (slowly) the load will increase a bit, but it seems unlikely that it will be enough to matter. I'll be testing it for lifting capability, precision, and belt stretch/torsion. There's no grub screw at the far end of the gear to keep a 5mm shaft in place, so adding one would be sort of wonky. If you had a motor with a really long shaft it would be great, but I haven't see any motors like that.

Edited 2 time(s). Last edit at 03/29/2018 06:47PM by the_digital_dentist.

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

Initial test result: I connected it to a driver and ran it with different microstepping values and a range relative low speeds (<2.4k pps). I put two 40 mm pulleys on the shaft. At most settings is was pretty quiet, though a few excited some resonances. I tried to stop the rotation by grabbing the pulleys with both hands and was not able to keep it from rotating. I think it's going to work... More tests to come.

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

Good stuff! Looking forward to more test resultat!

OK, after a couple design errors, I believe I now have it in operational shape. I was trying to figure out a test fixture to build for it and decided that would be too much work to build something special, so the final design is essentially a drop-in replacement for the Rino in UMMD. I went back to the UMMD CAD file, measured the distance from the drive shaft to the cross bar at the bottom of the Z axis and duplicated that in Fusion360, then built the new box around them. Over the next couple evenings I will be pulling the Rino out of UMMD and installing the printed gearbox. Once it is in I'll run a bunch of tests and try a few prints. I have a couple different NEMA-17 motors to try depending on the results, but I'll start with the 40 mm long motor.

UMMD currently has HTD-3M belts that will be replaced with GT2 belts. I had to redesign and fabricate the upper pulley plates, the belt clamps, and the spacers for the pillow blocks. I'll check belt stretch vs load, positioning accuracy and precision (as well as my digital gauge can read), maximum load, and maximum speed.

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

After looking at it last night, I realized that thanks to my nifty DLPC side panels, it will be a major undertaking to put the new worm drive into UMMD. This may take a little longer than originally anticipated...

I've also run into an annoying problem with the Titan extruder. I had some problems with the screws loosening so I applied lock-tite. Problem solved, but I found that the screw that clamps the hot-end into the body of the extruder wasn't holding tight and the hot end is wobbling slightly when printing, creating less than stellar Z axis quality. I tried to take it apart to see if I could shim it and it seems that the brass insert (IRIC there's one in there) in the plastic base of the extruder is just spinning, so I can't back the screw out.

Upon further thought, I may be able to drill through the cover to get access to the 4th screw that goes into the motor and remove the whole extruder from the extruder carriage. Then I can attack the brass insert from the back side of the extruder. Ugh!

Now I'm starting to think I'm going to have to design my own extruder and mill it from a block of aluminum...

Edited 1 time(s). Last edit at 04/05/2018 10:44AM by the_digital_dentist.

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

I have thought that too, I think that titan extruder is good but groovemount + plastic casing is not.

I have same thoughts about making it from aluminium but instead of milling, Im thinking just drilling and some spacers. Of course the lid is going to have some milling to do for the v6 heatbreak.