I’m terrified I’ve bitten off more than I can chew.

I’m terrified I’ve bitten off more than I can chew. I’m going to need help on this build design for those that can offer. Some of you have already been a great source of encouragement and information, and now some of the parts have begun to arrive. I’m trying to build an accurate and reliable CNC with as large a table area and z-axis travel as I can without causing the gantry to flex or distort. I’d already had the spindle, VFD, 4 ft lead screw & ballscrew purchased. I recently received 2, 74” 1030 rails (80/20) and one 58” 3030 rail should be in soon. I just received a Nema 34, (for the Z) and a NEMA 23 with a gearbox for the X. I think I will end up using 2 Nema 23s for the Y. I think I’m going to use linear guide ways for the X and supported rails (purchased already) for the Y & Z. If I had more experience with rack and pinion system I’d use that for the Y, but I’m afraid that would be disastrous. I’m still uncertain about the design. Any input would be appreciated. Please be kind.

Starting from scratch is a lot of work. Even the mods I am attempting on the R7 are a lot more involved than I had hoped. What controller are you using?

I haven’t made that decision yet. It will depend on final design and capacity. I definitely hear you and realize I will have to later adapt to a more realistic design. One thing that is less important to me in the design is z-travel, though I’d prefer between 6-8 inches, if possible

I don’t know how much you like math but this is the important thing to remember in Z flexibility. missing/deleted image from Google+

missing/deleted image from Google+

If you double the length you have 4 times the deflection.

Thanks, that helps. I’ll have to take an in-depth look at this.

Where did you get that info?

I just saw some formulas derived from that in 80/20’s catalog. The cantilever formula is out of the picture.missing/deleted image from Google+

I think I’m going to design it generally to cut wood. I’ve gotten comments that the SBR rails can be sloppy and the 1030 beams (as I gathered) won’t withstand those forces over a period of time.

I’m going to go with the linear guide ways (at least for the gantry)

A college level Strength of Materials class text would be helpful but this is pretty good for free information.

http://ruina.mae.cornell.edu/Courses/ME4735-2012/Rand4770Vibrations/BeamFormulas.pdf