Rack and Pinion
I'm building a 3 axis 4' X 4' machine mainly for hardwood cutting but perhaps some aluminum as well. I'm using 8020 rail with linear rail guides and a rack and pinion driver. For the rack and pinion driver, I've looked at Standard Rack and Pinion Drive, NEMA 34 | CNCRouterParts . Instead of using this part, can I directly driver the rack from a Nema 23 or 34. I realize there may be some load issues, speed issues and gear wear issues but I was hoping folks could offer practical guidance for my application. If there are other alternatives for driving the rack, pls let me know as well.
Also are helical racks better than std racks? For example KHK KRHGF2 1000R Steel Ground Helical Rack 1005 31mm Total Length 160 Teeth | eBay
Thx in advance.
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Re: Rack and Pinion
Helical can be harder to align, but they run quitter with increased teeth contact.
There are a few reasons not to run a pinion directly on a stepper - increased wear on the stepper motor bearings (which you cannot change), decreased resolution, increased chance of resonance issues...
Re: Rack and Pinion
The simple answer here is no. Can a big enough stepper drive the pinion directly, most likely you can find a big enough stepper to do so. The problem is you aren't likely to get good performance and resolution might suck.Originally Posted by adda
I would suggest getting the performance specs for the steppers you want to use and figure out a gear box ratio based upon where in their torque curves you want to operate. At the same time you need to keep an eye on your steps per mm of travel. Here is the thing you want each step of the motor to create the required resolution that you need at the axis. Most likely direct connection of the pinion to the rack would result in suboptimal resolution so you have to use a gear reduction anyways. You task then is to find a gear reduction that gives you better than desired resolution and keep the motor operating in an ideal place on its torque curve.
One piece of advice. Don't assume that you have to use gears for a speed reduction!!!! Timing belts and pulleys work perfectly well and are very reliable. The primary problem with gear boxes is that they are not cheap in servo grades.
I realize there may be some load issues, speed issues and gear wear issues but I was hoping folks could offer practical guidance for my application. If there are other alternatives for driving the rack, pls let me know as well.
Maybe. To be honest I'm not a big fan of racks especially on smaller machines like this. I tend to think of racks as something you use when you have nothing better to cover the distance. That is probably a biased way to look at things.
Also are helical racks better than std racks?
Here is the thing with steppers, you basically have a fixed amount of resolution per revolution of the stepper. Usually this is 1.8 degrees per step or in some cases 0.9 degrees. You can enhance that a bit with micro stepping but there are diminishing returns on its effectiveness. 1.8 degrees can be a lot in a rack and pinion system, thus if your goal is to run them from steppers you are pretty much compelled to use a reduction drive of some sort.
Thx in advance.
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