Many people who are looking at this project may notice some similarity between it an the reference design Jason from the openpnp.org project posted. His design (and great software project) gave me the confidence to know that building a cartesian design could work.

The designs Jason and I have posted are very similar. Let me explain the main difference and why I went the way I did. The main difference is his design uses wheels that ride in a slot on the extrusion, and mine use steel rail and slides. The reasons I chose rail/slide as opposed to openbuilds:

1. I had experience with other x/y platforms like the shapeoko and quickly grew tired of tinkering with the eccentric nuts dialing in the tension. Too tight and it wouldnt move (or skip steps), too loose and there was slop. And even worse (perhaps because it was CNC) it changed every time you used it so you had to go over the machine regularly tinkering to keep things operational. I have heard from several people that this wasnt their experience, but as I evaluated my options, and give my experience, I knew that if I designed around wheels on extrusion, and it didnt give me the accuracy or precision I needed for small pitch PNP parts, then I would have effectively painted myself into a corner.

2. The rail/slide option gave me a variety of options in quality/cost which would be easily swapped if an option was not able to deliver the speed/accuracy/precision I was after. Had the cheap chinese rails works (they didn't) they would have been a more cost effective solution than the openbuilds option.

3. Slide/Rail were already proven to deliver great speed/accuracy/precision over a long lifespan with minimal maintenance, I wasnt sure the openbuilds solution could deliver that.

4. I wanted to have a passive rail and avoid the complication/expense of having a second stepper to drive the Y axis. Only rail/slide could deliver the kind of butter smooth motion that I would need to do that.

5. I love clearpath closed loop servos, and wanted to leave the door open to jump from cheap steppers over to the more capable servos which come in a nema23, the openbuilds brackets dont come in a nema23, so building my own gave me that flexibility.

It obvious that either route will give you the ability to pick and place parts. I would bet that the openbuilds route may come in a little cheaper, but I think long term we will be able to eek out more performance, with lower maintenance, from a rail/slide based solution.