router design

[diycnc]

attached is a work in progress

it is going to be a 4x8 machine using china rails and screws.

[Shinosky]

If I were you I would switch the gantry to the narrowest direction. You don't want that long unsupported gantry. Make the long direction supported. Just my 2 cents...

[diycnc]

i did this so i could have some cost savings. the long ball screw is 2x the money of the short one. ,also the heavier rails for the gantry are more money.

also i can make the gantry fairly heavy as i have 2 motors driving it.

i feel confidant that i can make the gantry quite rigid over 8ft.

also if screw whip becomes a issue on the longer screw this way i can make a moving center support out of uhmw. if i flip the gantry around and i have screw whipping problems there is nothing i can do.

[BobF]

I would switch it anyway and look into rack and pinion for the drive. 8 ft screws are hard to find, and hard to ship. 2 more cents :-)

[diycnc]

rack an pinion will increase the price greatly. check out the mech mate fourms they all run geared steppers at 350$ a piece. plus you need 4 of them. for just the price of the motors i can get all the motors controls breakout board power supply from kelling.

if i am buying 8 ft rails from the same seller what is the problem with shipping the screw? wouldn't they tape them all together and box them.

what is the concern with the longer rail? if i make it plenty stiff enough what problems will it cause?

[diycnc]

also rack inst cheap either. grainier wants 120$ a length of rack and i figure i would need 5 of them.

so that's 600$ for just the rack

then the gears are 25$ ea for a total for 100$

plus every axis need to have a spring loaded pivoting mechanism that i would have to pay to get machined for me.

using screws i can make almost all the parts using tools available at my home or work. and they are under 500$ for the screws machining, supports, couplers, nuts. also i have to buy rails anyways as i don't feel like going thru the bs of grinding bevels on stock to use v wheels.

[BobF]

Sorry for the shipping comment. I was think UPS length limit was 7 feet, its 9.
http://www.mcmaster.com/#gear-racks/=1j7iop