Correct way to interface braided line with stepper motor?

Hi guys,

It's been a while since I've been active but I've been keeping an eye out occasionally. Moved a couple of times but now I'm settled in a good home and ready to start making again. To start off, last week, I made a pen plotter from old DVD drives which works flawlessly. Now I started making a bigger one using braided PE fishing line instead of belts. Why? Because it saves space and makes up for a very small form factor. I like the idea of using the smallest printed parts possible and moving from GT2 belt to braided line is one of the design choices that will help me achieve this goal.

However.. I have been thinking what would be the best way to have the stepper motor and the braided line interact with each other.

The mechanics I will be using are that of a CoreXY type:


And I must admit that when I started working on how the string connects to the motors.. I realized that I hadn't thought of how the string would actually interface with the wheel/knob/gear that I still have to design.

Now I have come up with something like this:


But honestly I don't think that I need to have the spiraling indentation, plus with a CoreXY setup, the motor will spin more centimeters than there is available on the spiral which will cause the line to bump into it, causing all kinds of artefacts on the print in a circle on the print surface.

So, what I am wondering, since I haven't been able to find anything clear about this, what kind of wheel would be best to use on the motor end to drive the braided line without having slippage and would a simple thick round knob be enough as long as the line is tightened enough?

Edited 2 time(s). Last edit at 07/04/2018 09:51AM by Ohmarinus.

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http://www.marinusdebeer.nl/

I was recently looking into the same topic. The problem with spiraling the that the cable will walk up and down the pulley, changing the angle of the cable relative to the guide rails. The solution is not to use a spiral groove, but multiple parallel grooves and another nearby pulley that shifts the cable between the grooves on the main pulley:

polygonhell figured it out: [3dprinterhell.blogspot.com]

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

Wow, that looks very good. Would this also work with a CoreXY setup? I have sketched a new pulley without grooves because indeed I realized that the line would just walk off the pulley..



But that system with the nearby pulley looks even better. I do not have access to a mill so I might have to figure out how to print a part like that. The concept is well thought out. The lines do not need to walk because the grooves on both pulleys are already offset so they are never in contact with the pulley for a full 360 degrees and can never roll over each other this way.

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http://www.marinusdebeer.nl/

It should work with corexy. You just need to allow space for the extra pulley at each motor. They should be easy to print, but make sure the diameters of the two pulleys are exactly the same or you'll have problems. There's no way to know how long printed pulleys will last- probably long enough to make sure the concept is going to work and get some proper pulleys turned on a lathe.

Edited 1 time(s). Last edit at 07/04/2018 02:56PM by the_digital_dentist.

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

I've published a fixed line pulley with no slippage. It works best on Deltas or Cartesian, where no idler pulleys are in the path. But for a Penplotter it might work good enough.

The major issue for me would be the walking of the line up and down on the wheel. I have designed everything in such a way that there is only a little space for the line to move through.

I am starting to think my idea of having the machine as I had it in my head isn't the best way to make it. Maybe I'll ditch the idea of using 2020 extrusions as linear guides and go back to timed belts instead of braided line. It's not like I don't have any parts left over (like a couple of extrusions and some nicely hard chrome rods with bronze sintered bushings).

Maybe I'm just trying to make it all too cheap and easy. I'll take a more traditional route with the linear guides and will invest some time into trying to make the idea by polygonhell work.

Update:
For now I've redesigned my frame to work as a CoreXY with belts.



Edited 1 time(s). Last edit at 07/07/2018 01:54PM by Ohmarinus.

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http://www.marinusdebeer.nl/

Hello, I am interested in wire solutions also ...

If you take a 8 mm shaft for wiring you have a perimeter of about 24 mm, so with a 0.2 mm wire you need at a 300 mm printer about 14 rounds and need 3 mm for the line moving, this should be small enough to build into your printer.

Edited 2 time(s). Last edit at 07/09/2018 08:52AM by JoergS5.

Designing the coreXY with linear guides and extrusions tell me that you are interested in quality. Please let me give you the hint to support your pulleys from top, otherwise they will tend to bend.

Quote
Ohmarinus
For now I've redesigned my frame to work as a CoreXY with belts.

You can't design printed parts as if they're made of steel. I think that as soon as you apply tension to the belts, everything is going to tilt.

If you must use printed parts, they need to be beefy. Instead of steel sheet metal, think about them as if the parts were being carved out of solid billets of steel. If you were doing that, you'd do as little cutting of the metal as possible to let the parts do what they are supposed to, because otherwise it would be a lot of extra work and/or would cost a lot more. The result would be big and chunky, but it would be extremely strong.

The image below illustrates the idea- that's your motor mount on the left, and a block type mount on the right. Which do you think is less likely to bend when you tension the belt?



You can do the same for the pulley mounts. Don't stick the pulley's axles into the air like fence posts. Fit the pulleys into slots in the plastic, and make sure both ends of the axles are locked in one piece of plastic.

Edited 1 time(s). Last edit at 07/07/2018 09:06PM by the_digital_dentist.

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

Don't worry, I have made some parts that cover it, it's just for the render that I show it without I have already made 2 printers and 1 laser cutter and the laser cutter uses the same kind of setup with a little roof over the bearings.

Also, I'm not using bolts to support the bearings but pressure-fit brass stock. It works like a charm.

Edited 1 time(s). Last edit at 07/07/2018 03:24PM by Ohmarinus.

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http://www.marinusdebeer.nl/

So we commented something that you do not plan ...

So good luck with your construction, CoreXY is a very successful construction and you can achieve good printing results.

It's okay, thanks for the heads up, imagine if I had indeed just let them the way they are. My poor PLA prints would eventually bend and break It's good to know people are still thinking with you over here.

Edit:
Got around to finishing the parts


Edit 2:
Gawd, it turns out that the seller of the 2020 extrusions has sold me the 'A' type with 5mm wide slots. And all the T-nuts I can find for 2020 extrusions I can find are for the 6mm wide slots. I'm going to completely ditch all of this stuff and just go full-VSLOT on this build. Back to the drawing board.

Edited 3 time(s). Last edit at 07/15/2018 07:29AM by Ohmarinus.

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http://www.marinusdebeer.nl/