Rigid vs Flexible Couplers for Trapezoidal Leadscrews?
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I mostly go for the higher precision to be able to print at any 10 micron step interval and not having to remember to do 20 micron steps (or 40 micron steps as before the gearing). Gearing was only to get higher precision not because of missing torque.
For me personally I don't see a need for 5 micron full steps. I only use manual leveling, not even mesh bed leveling anymore and everything is fine - already was at 8mm lead. This is just for convenience.
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I have a novel approach. I use rigid couplers, but I use a solid petg plate to attach the brass lead nut. It's 1-2mm thick. The plate doesn't move, but it can flex a little, so the lead screw doesn't bind if you get a little wobble. The plate sits atop The bed frame which has a large hole cut and the petg plate is like a patch over the hole. The nut is under the bed, screwed up into the plate that sits on top of the bed.
I also use VHB gel tape to mount the motors to the floor of my enclosure. I can fine tune the position and gel works amazing well.
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@gnydick said in Rigid vs Flexible Couplers for Trapezoidal Leadscrews?:
I have a novel approach. I use rigid couplers, but I use a solid petg plate to attach the brass lead nut. It's 1-2mm thick. The plate doesn't move, but it can flex a little, so the lead screw doesn't bind if you get a little wobble. The plate sits atop The bed frame which has a large hole cut and the petg plate is like a patch over the hole. The nut is under the bed, screwed up into the plate that sits on top of the bed.
I also use VHB gel tape to mount the motors to the floor of my enclosure. I can fine tune the position and gel works amazing well.
Pics please?
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@gnydick You have a nice rigid frame, and using rivets is a nice idea. That's an option I did not think of yet.
I wonder however whether using the VHB gel is good, because your stepper could rotate around a bit, if you say, you can correct the position easily. Maybe you can fix the stepper after you have found the best position.
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Today I swapped the three flexible couplers on my D-Bot for these plum couplers.
They are much quieter and I can get the steppers up to much higher speeds. Previously I was limited to about 5mm/s otherwise I got binding. I can now get 10mm/s.
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you might want to look into some from of thrust bearing/washer between the motor face and the bottom of the coupler so you don't put to much strain on the motor bearings or the spring plate that is fitted at the rear of the motor to take up any end float.
just a suggestion!
Doug
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@dougal1957 I'll look into that, thanks.
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Here's a question for you guys.
My lead screws are not mounted to a motor. They rest in a double bearing block, and are belted to a single motor. This means no flexible coupler to give the alignment some degree of play. If my bearing blocks and lead screw nuts aren't perfectly aligned, I am prone to getting binding. When they are aligned it's no problem, but it's tricky.
I've seen some people replace the leadscrew nut hard mount to the bed with a gimballed Oldham style rocking mount. But these are 3D printed, and there's not much information on how they should mount or go together.
So my question, then, is something like this readily available? Are there other options that do the same thing?
Printed example of what I'm talking about:
https://www.thingiverse.com/thing:1814061
https://www.thingiverse.com/thing:1812507 -
@joergs5 That's exactly right. The VHB tape is VERRRY strong. The steppers don't move AT-ALL once you've got them in their final position and you're happy. Just leave them alone and they'll get firmer and firmer in place.
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@kraegar said in Rigid vs Flexible Couplers for Trapezoidal Leadscrews?:
Oldham - Best of the "common" couplers, quiet with the least artifacts transmitted. Cheap ones separate easily.
Do you know a source for these couplers for 5 to 8mm? Couldn't find anbnything.
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@MartinNYHC Misumi do them about 12$ each
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I'm a fan of the diaphragm couplers myself and use them on both my corexy printers. They allow for some flex but don't have the spring to them like the standard flexible couplers. https://www.amazon.com/gp/product/B078VT1QCK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
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one way to stop the cheaper plum couplers from separating is to mount a pillow block on top of them.
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@kraegar the ‘slop’ in the z-axis/vertical artifacts is/are now the biggest ‘issue’ that I have in my RailCore after having spent a lot of time massaging all the other bits (of course I still have artifacts from the belt teeth, but best I can tell a big design change would be needed to fix this & unfortunately 2GT belts have the same pattern as any other GT series like GT3. As per distributor & personal inspection).
Now I will admit that one of the z-axis motors could be aligned a little bit better with the corresponding leadscrew/rail/extrusion, but after having done a bit of research a while back on flex couplings & seeing how expensive they can be I figured I’d see what I can come up with.
So I did some searching and shopping and today I received 3 Gerwah DKN 15 bellows flexcouplings. These are very quality German couplings that are clamp style (rather than using set screws which are tricky to center), have aluminum hubs with a stainless steel bellows that I believe is of the edge welded variety, & supposed to have effectively no backlash while also being one of the most misalignment forgiving styles. Downside is bellows can’t take much torque, but size 15 seems to be able to handle considerably more than what I need I believe.
They are quite lightly used, some minor superficial scuffing on the finish, but other than that in great condition - and I paid under $60 total for them on eBay!
Definitely not nothing & more than the 10/12 dollars for the Misumis (but with tax & shipping the difference is prolly almost negligible), but these guys generally have a 3 figure price tag. Per coupling.There were a bunch of other options on eBay too so I figured I’d throw this out there as an alternative option for sourcing flex couplings
