My custom D-Bot
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@uncreative1 Are you planning on using a single motor to turn 3 screws, or one motor for each screw?
The screws you linked appear to have 8mm of travel per revolution which would be fairly steep in my arrangement and might require more torque to lift a heavy build platform than a single motor can reliably provide. This wouldn't be as much of an issue with one motor for each screw though.
For the pulleys I just chose 40 tooth GT2 pulleys to give the belt ample surface to grip. They are the same tooth count between the motor and the lead screws, which gives 1:1 ratio. 5mm bore for the motor and 8mm bore for the screws. The triangle arrangement ensures that the belt gets good contact and reduces the chance of slippage.
Here's a link to the pulleys I used. https://www.aliexpress.com/item/10pcs-New-GT2-Timing-Pulley-30-36-40-60-Tooth-Wheel-Bore-5mm-8mm-Aluminum-Gear/32822906054.html
In your case, you may want to change up your gear ratio between the motor and the screws to gain more torque. For instance, a 60 tooth pulley at the motor and 40 at the screws.
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This is a really pretty build, and it's made me pull the thread on building one. I just bought a kit and am looking at what other parts I'm going to need to buy. I definitely like some of the changes you've made and used, and plan to use some myself. Looking through your pictures and this thingiverse file you used (https://www.thingiverse.com/thing:2401504), and I'm not getting how the lead screws stay secure in the flange bearings. He said something about using 8mm clamping collars, but I'm not seeing how that would keep it any more secure than the toothed gear. Am I missing something? I looked through your pictures, but couldn't from the angles. Thanks for sharing your build!
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@ntgorilla Thanks for the compliment. I think you'll enjoy the build, it's a challenge, but pretty satisfying when it all comes together. Spauda01 did well on the design.
I took some more pictures of the lead screw mounts that show how I have used them. I didn't follow exactly the description from that original thingiverse mod. The pulleys I used have a body small enough to sit comfortably on the bearing, so the weight of the bed assembly holds it down onto the bearing. The lead screw protrudes from the bottom just enough for a lock collar to clamp on and keep the lead screw in place against any lifting forces. It doesn't do anything else other than let you clamp the lead screw into the bearing sandwich.
During installation I slide the lead screws into the bearing blocks and put the collar on so that the end of the lead screw is flush with the collar. Then I push down on the pulley and up on the collar and secure the set screws of the pulleys. That keeps the lead screws quite secure in the mounting block.
Before putting the belt on I rotate the lead screws so the tops are flush with the top of the nuts in the bed mount. Then carefully wrap the belt around the back pulley and then side pulleys without making them rotate to keep the in sync. Then into the tensioner. It really helps to have a second set of hands for this step. I try not to tension the belt too much or else it deflects the lead screws a bit which can cause binding when the bed is at the lowest extent.
Speaking of binding, it's also critical to get the lead screw bed mounts perfectly lined up with the screw mounts. The bed frame needs to be tightened in stages to allow for some wiggle room in the X or Y. The Z wheels need to be aligned on the V slots before being tightened. Everything needs to be done in stages otherwise you will run into binding.
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@phaedrux Awesome! Thank you for the extra pictures and explanation! That makes a lot more sense now, and looks a lot sturdier! Thanks for the tips too! I'm looking forward to working on it!
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@ntgorilla If you have any other questions I'd be happy to answer.
A few other tips I wish I'd known when I started.
- Get T slot nuts and don't use square nuts. Get some hammerhead t slot nuts as well as they let you insert anywhere along the slot.
- Get aluminum spacers and precision shims for the wheels. Makes tightening without binding possible. Polycarbonate wheels are a nice touch too. The Delrin ones do wear down.
- Get aluminum corner brackets and plates. Much stiffer and really not expensive. Saves a lot of printing time too. Literally pennies more expensive than the filament.
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@phaedrux Thanks for the tips! I've definitely learned some of those the hard way building a couple deltas. I have a nice stash of t-nuts ready to go. I'm holding off on the PC wheels for now, because I have some extra linear rails I might try to see if I can work into it. That's good to know about the Delrin wheels though. I never had that issue on a delta when I was using wheels, but then again, I could see how this would stress them a lot more than a delta. And I definitely picked up bunch of the metal L and T plates, and the 90 degree corner brackets. Parts should start trickling in this week. I'm still waiting on a part for my delta to get here. I held off on installing one of my old extruders because I thought it would get here faster. But I've been pretty busy too, so I still have a lot of parts to print lol.
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Ref the Delrin wheels, I've not seen any sign of wear after many hundreds, if not thousands, of hours of printing and I'm throwing about 2kg of mass on each gantry. We're they the mini wheels or standard?
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@deckingman They were mini V wheels. The edges would eventually leave some black dust on the v slot. Perhaps they were low quality or perhaps over tensioned, but I don't think so. When they were too tight they became stiff to push, I had them still gliding effortlessly. Maybe they didn't match the extrusion profile, but I find that hard to believe as they come from the same source. Who knows. It's not like they fell away to nothing, just had some visible wear.
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I've seen one or two reports from people who have had problems with the mini V wheels. Can't remember the exact nature of those problems but it could well be wear due to the smaller diameter? Or as you say, maybe something to do with not being able to get the correct pre-load. Anyway, for whatever reason, the "standard size" Delrin wheels have been fine for me and my machine.
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I've had Delrin mini V's on my small printer for the last 3 years without any issues thus far. And it has tons of printing hours on it.
I tried running the new harder clear wheels on my large printer but ended up switching that one to Delrin wheels now. The harder wheels transfer vibrations that were showing up in my prints. Also 2 of the harder wheels had chipped at some point during the many hours of printing. I probably got some plastic or who knows what on one of the tracks to cause the damaged wheels.
The Delrin wheels don't transfer the vibrations and aren't as fragile so I'll stick with them. I never tried the larger wheels.
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@timcurtis67 that's interesting you mention vibration transfer. I wonder if I'm not seeing some of that now. At low layer heights I seem to have quite a bit of micro ghosting happening at anything other than a crawl speed.
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@phaedrux said in My custom D-Bot:
@timcurtis67 that's interesting you mention vibration transfer. I wonder if I'm not seeing some of that now. At low layer heights I seem to have quite a bit of micro ghosting happening at anything other than a crawl speed.
If you have a set of the Delrin wheels it's worth trying them. It helped on my large printer.
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@timcurtis67 yeah I still have the set of delrin wheels. I'll have to do some detailed before and after.
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It'd be interesting to see a comparison between the mini V and the "standard" wheels too. That'd probably mean a major re-design though. I think the mini V wheels are about 15mm diameter and the "standard" or non-mini V are about 24mm diameter.
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@deckingman I believe I've seen some mods to use the full size wheels, but I don't have any larger wheels and don't think I'm willing to go that far to test. At that point I might as well go to linear rails.
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@phaedrux said in My custom D-Bot:
@deckingman I believe I've seen some mods to use the full size wheels, but I don't have any larger wheels and don't think I'm willing to go that far to test. At that point I might as well go to linear rails.
Yes they are not cheap when you add in spacers (eccentric and otherwise), bearings, bolts etc. I had a fit when I worked out how much I'd spent on the 40 wheels sets that my machine has! Oh and I wasn't suggesting you try the larger ones - I just meant that it would be interesting to see a comparison.
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I've flat spotted some Delrin wheels. Swapped all 20 to the polycarbonate 'tyres' when I bought a further eight to add a second set of z-axis guides to the front of the machine. Had no problems that I am aware of since.
This was on a core-xy using four wheel guides as per standard build instructions. I think I'd pinched one pair up too tight against the rail.
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That would certainly do it (having them too tight). I have to say that before I started printing my own gantry plates, I bought a couple of OpenBuilds ones and found that even with the eccentric spacers backed fully off, the wheels were too tight on the rails. I got around it by opening up the smaller hole in the gantry plate which gave me a bit more adjustment.
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I think I've isolated the source of my micro vibration patterns showing most visibly on lower layer heights. It's hard to get a good picture of it, but it looks almost like ringing patterns, except that it doesn't follow the same edge pattern, it's more distributed and random looking.
Normal ringing pattern:
Vibration ringing pattern:
I have been trying to use the formula provided by @dc42 here to eliminate the ringing. I was able to clear up the X axis, but wasn't able to remove it from the Y axis direction.
Then I started to hear a rather loud cracking sound. What's that sound?
In the video you'll hear what sounds like intermittent snapping plastic. When this started I stopped trying to fix the vibrations and started to find out where the awful sound was coming from. I couldn't see anything broken in the carriage. The wire loom wasn't the source (I took it off).
Then I disconnected the belts and moved the carriage by hand. Movement on the X axis was definitely not smooth. I tested rolling each wheel and discovered that the top wheel was very stiff and when I moved the carriage quickly I could reproduce the sound. I swapped out the top wheel with one of the spares and the sound went away and movement feels smooth again. The bearing of the wheel had exploded and leaked black lubricant
However, the Y axis still has some vibration and I think one or more of the polycarbonate wheel bearings are also failing. I bought a few extra expecting some failures, but didn't expect them this soon.
X before:
X After:
But the Y side always looked something like this:
I'm now torn over whether I should just go back to the delrin wheels and let them deteriorate or get something like the openbuilds delrin wheels. https://openbuildspartstore.com/delrin-mini-v-wheel-kit/ If only they weren't so expensive! 7USD per wheel. The polycarbonate wheels on ali express were 40 for 16$!! Get what you pay for though I suppose.
At least now I know the source of the problem and can fix it.
EDIT: Found a couple more bad bearings. At least it was only one per wheel so I was able to combine the good bearings and reinstall. Who knows how long they will last. Also surprised by the wear on the wheel. The failed wheels were all directly on the tensioner side. I suppose it's possible I had them over tensioned, but it's just an M3 screw finger tightened.
Now to see if the vibrations are gone in the print. The movement definitely feels smoother.
