Sunday, 21 October 2018

Rack & Pinion or Leadscrew? - episode 221

Dan Zanotti asked me a little while ago a series of questions about my opinion on Rack & Pinion versus Leadscrew. While I'm happy to tell What I have and why I decided to go one way or the other I'm not usually happy to inflict my opinion on them. In this video I try and explain why I moved to Rack & Pinion and why I think that for my machine the combination of R&P on the X Y axis with Leadscrew on the Z is a good combination. I don't claim to be an expert on drive systems, I'm just a hobbyist like you.
In this video I start to explore Backlash which by my reckoning is the only real difference between the 2 systems that might make you think twice about Rack & Pinion.



Click to watch


Cost 
when trying to decide between the various drive systems cost can play a big part in your decision. It was probably the biggest factor for me because I had to import either Rack or Leadscrew and postage was the biggest factor. For a machine like mine I would have needed a 6 foot leadscrew or a 4 foot Rack and the shorter the package the cheaper it was to send. Rack has the advantage that if in the future I need a longer rack I can easily join it while with leadscrew I would need to replace what I have with something longer. Another issue with sending long packages through the mail system is then could easily get bent. A bend in a leadscrew no matter how slight can be difficult to remove while straightening a rack is easy. the disadvantage of Rack is i needed to buy the drive plate though it is also possible to make one if you know what you need. They are not that complex.

Resolution
Something I didn't really cover in the video is the resolution of each system. By that I mean how many steps per unit each system is. In my case the leadscrew has 4 times the resolution of the Rack & Pinion drive but when you consider that each step on the R&P is 0.013mm or 0.0005 inch then that should be all the resolution I will ever need. We are not building parts for NASA and the wood we use changes dimension by more then that depending on whether it is a wet or a fine day. 

Measuring tools
For this video I purchased a Digital Dial indicator. Up until now I have borrowed an analogue one but for this I decided a digital display was easier to read. the resolution on the dial far exceeds the machines capabilities. I have put a link below showing the dial indicator I purchased for this video.

Ebay Affiliate Links. By using this link a small proportion of any sale is credited to me at no additional cost to you. There are many such dial indicators on the market and this is just the one I chose.

Dial Indicator
https://ebay.to/2yR4alc


Magnetic Dial Base
https://ebay.to/2q3rQit


Macros For UCCNC and Mach3
Thanks once again to John Revill for his work in making Macros for UCCNC and sharing them with us. Over the last few weeks he has made and shared several Macros that I am excited to be sharing with you soon. It is thanks to his Backlash measuring Macro that I was able to easily measure my Axis backlash and in the next episode we will explore Installing  the macros then using them to eliminate system backlash.

UCCNC Macro
http://bit.ly/2OFAJxd


Mach3 Macro
http://bit.ly/2PSXnP6


Thanks to John's easy to follow Macro writing I was able to create a Mach3 version of the Macro that behaves the same. My first Macro written from the scratch. These are posted here for anyone who wishes to use them to measure their backlash. In the next episode I will be demonstrating how to install and use them so don't worry if you cannot figure them out right now.

Well that's all for now so until next time

Cheers
Peter

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