Rack and Pinion Challenge

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Rack and Pinion Challenge

Postby evil2002usna » Sun Jun 29, 2014 2:45 am

So it has been a couple of months since I completed my leadscrew upgrade to my x-axis and so far it is still working good. I was going to do a similar leadscrew upgrade to my Y-Axis, but my leadscrew supplier, Trinity Labs, has closed their doors. As a result I have decided to try another method that has been interesting me for a couple of months after seeing some positive results on thingiverse. Recently I purchased a small 12' acetal rack and spur gear from SDP/SI. The idea is to hard mount the Y-Axis motor directly underneath the heated bed and design a way to hard mount the rack to the aluminum plate. Then i will use the motor and spur gear to drive the build plate. Does anyone have any experience with this kind of drive mechanism. I have attached a mock-up of my concept. The yellow parts are printed. Basically a mount for the rack I purchased. I plan on using tension pins to hold the rack in the mount. The mount will use the same screws I used to attach the heated build platform.
Attachments
Rack and Pinion Drive.JPG
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Re: Rack and Pinion Challenge

Postby orcinus » Mon Jun 30, 2014 3:43 pm

I'd advise against doing this or at least in this way.

The force vector from the rack will not be coincident with the linear slide, causing the Y table to skew this way and that during operation.
It will probably not have too big an effect near the center of the build platform, but it will rise as you get away from the center.

On top of that, the rack and pinion will likely have greater backlash than a (proper) belt.
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Re: Rack and Pinion Challenge

Postby evil2002usna » Tue Jul 01, 2014 4:39 am

Well here are the results http://youtu.be/pcQ9hYwiU5A. I am very happy with my first test cube. I still have the mount being held by only two screws as opposed to the six it was designed for, but it appears very sturdy. I also want to get some longer screws so that I can attach some nuts to the bottom of the rack mount. This is actually the best test cube I have ever printed if that is saying anything. I still want to do some larger prints. I will probably design a new foot since I no longer need the belts and pulleys.

If anyone is interested in the parts I used, here is the list from SDP/SI.


Part Number Description Sell Unit Price
S10Z05M028T0505 Module 0.5, 28 Teeth, 20° Pressure Angle, Acetal / Stainless Steel Hub Spur Gear Each $22.93
A1M12MYZ0525A Module 0.5, 20 (Deg) Pressure Angle, Acetal (Molded) Rack Each $3.38
Attachments
IMG_0005.JPG
IMG_0004.JPG
IMG_0008.JPG
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Re: Rack and Pinion Challenge

Postby orcinus » Tue Jul 01, 2014 6:19 pm

Ha! Looks pretty nice (in spite of my skepticism)! :)

Did you have to tighten the V-wheels more or is it stable as is?
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Re: Rack and Pinion Challenge

Postby evil2002usna » Tue Jul 01, 2014 7:28 pm

I didn't have to change anything with my printer except the extruder steps and I barely had to change it. I was only off by 1mm on my initial test cube dimensions. I still need to actually fasten the rack mount to the Y-Carriage with nuts. Right now it seems stable though. I want to see how the rack wears over time to see if i start to develop greater backlash as you predicted, but you can see that this was a really easy design to build and implement. It only took me a day and a half once I had the parts. Right now i just have the motor cables running outside of the aluminum, but I eventually want to get everything wired up nice and neat.
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Re: Rack and Pinion Challenge

Postby greenvandan » Wed Jul 02, 2014 1:42 am

Had you considered SDP/SI's Flexirack at all? At one point I had looked at it and it seemed there was a size, maybe the 1.5 module, that would fit inside of the slots on Misumi extrusion, or makerslide for that matter.
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