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Advice on belt path

Posted by nikker 
Advice on belt path
April 24, 2017 12:40AM
Hi all, I have been lurking on the forums for about a year and have slowly been prepping for a corexy build. I have all my motors, electronics and linear rails, etc. My next step is to get the 8020 extrusion and some .125" aluminum plate cut but i need my design finalized and would like any advice on how I have my belts crossing at the front of the printer. As you can see the belts are all on the same plane except at the front, where they cross and the maximum separation is 14mm, the angle in relation to the top/level plane is 0.8 deg. I will be using 3GT belt and smooth idlers with a 17.5mm diameter that have a small shoulder on them. Can anyone with some previous experience guide me on if this well make the belts wear excessively? I do plan on having the printer running non stop for quiet some time. Thanks for any input and feel free to ask any questions, I do plan on starting a build page shortly when things begin.
Attachments:
open | download - beltpath1.JPG (38.5 KB)
open | download - beltpath2.JPG (86.1 KB)
open | download - beltpath3.JPG (47.4 KB)
open | download - beltpath4.JPG (55.6 KB)
Re: Advice on belt path
April 24, 2017 07:38AM
You should consider using stacked belts instead:


NB: They don't have to line up where they meet the carriage:

Re: Advice on belt path
April 24, 2017 07:43AM
I would consider using a Stacked CoreXY arrangement like so:

I built my printer this way and my design is so much shoddier than yours. This prevents any risk of the belts slipping off the pulleys or other bad things.

Belt wear shouldn't be that much of an issue. What could hurt you though is belt stretch: if your printer is a certain size that 0.001 of strain might start to seem like a lot. Also, the longer the belt the more prone your belts are to vibrate and exhibit whiplash, but that might just be due to my poor design.
Re: Advice on belt path
April 24, 2017 07:44AM
If you're putting the belts on two z levels, why are they shifting up and down? If a belt meets a pulley at anything but 90 degrees relative to the pulley's axle, the belt is going to ride against the pulley's flange. That will add friction to the movement and tend to wear the belts. The path length along the top edge of the belt should be exactly the same as the length along the bottom edge of the belt.

1/8" aluminum is going to flex a lot when you tension the belts. I'd use 1/4" as the minimum.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Advice on belt path
April 24, 2017 09:18PM
Thanks for the help everyone. I will go for stacked belts. Digital dentist, do you think It wont be rigid enough when its mounted like the image? Extrusions are 4040 for the verticals and the rest 2040. I imaged the aluminum plate more as just a mounting surface to get everything square/aligned as best as I could and the strength coming from being bolted to the extruded aluminum.
Attachments:
open | download - Capture.JPG (223.5 KB)
Re: Advice on belt path
April 24, 2017 10:39PM
All the force- the torques created by the belt tension on the pulleys that are stood off the plate- is being applied to the 1/8" aluminum plate. It's going to flex quite a bit, I think. If one belt were above the aluminum plate and the other an equal distance below it, it might be OK, but with both belts on one side of the plate...

Edited 1 time(s). Last edit at 04/24/2017 10:41PM by the_digital_dentist.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Advice on belt path
April 24, 2017 11:28PM
Makes sense, I have a smaller plate of .125" aluminum plate from another project and it seems pretty stiff, but I may be under estimating the forces especially once they have some leverage on them. Either way I am deferring to your experience. I am on the fence about even going through the trouble of getting aluminum sheet fabricated now and just sticking to all 40x40 extrusion and some .25" thick square tubing for mounting the extrusion to the HiWin blocks, kind of like what you have done in your last build, it might be a cheaper route to go too. I do have access to very precise measuring instruments so getting the frame/rails square should be too hard (famous last words!).

Edited 1 time(s). Last edit at 04/24/2017 11:29PM by nikker.
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