question about hybird rack & pinion and leadscrew drive

[ikeike]

Hi, this is my first post and I'm looking for some basic advice. I'm just starting out with my design and I plan to build a 4'X8' router. I am using the shopbot prs as my inspiration and will be using a two motor drive for the X axis on a rack and pinion setup. The Y will be a one motor setup also implementing an R&P drive system. As of now I would like to use a premade Z axis from K2 routers www.k2cnc.com which incorporates the leadscrew drive off a NEMA 23 mount. First off, can you incorporate these two different drive systems together and adjust the difference in lineal ratios with the controller software? I realize that I will need a geared reduction on both my R&P axis and I plan on using some sort of planetary gear box that mates directly with the steppers. Any ideas on reduction ratios? I'm not looking for an ultra speedy machine and would rather error on the side of accuracy. My rough estimate on gantry weight is around 100-150 lbs depending on materials. Could I get away with NEMA 23's on the X and Y or will I need something with a bit more muscle? Also, any ideas on rack and pinion parts. I've seen Boston gear sited here occasionally. I think I will be using a PBC al extrusion profile (www.pbclinear.com) that has built in guide ways for both x and y axis. Any advice would be great. Thanks!

[ger21]

1) Yes, you can mix and match screws and rack and pinion.

2) Everyone building their first machine says speed isn't important, but it is. Really. Especially on a 4x8 machine. Nema 23's are on the small side for a large machine. You want something that will allow you to accelerate very quickly, which needs more power.

3) I think you should seriously consider the Mechmate. www.mechmate.com

[freecncplans]

I agree, if you can build it, the Mechmate is the best option for the money. It will be the main machine(s) of my shop when I get to that point.

I have used a screw on the Y and Z and Rack and Pinion on the X and A with no issues. They may not have been perfect, but it worked will I was waiting for larger springs for the Y pinion setup.

Sean