New router build

folks, there is a deal at the moment with my welder, long story short i have someone to build a good frame for my cnc. i am hoping to cut hardwood, epoxy and aluminium.
my plan is to build first with what i have on hand, then evolve. eventually i want toolchange and 4 axis.
i have an ethernet smoothstepper, some gecko drives G203V, a 120va thoroidal converter with all the bells and whistles i need to push 80VDC, 3 HGH20ca 1500mm long. a 2.2kw water cooled spindle with a 3/4hp chiller, 2X 1500mm ballscrews that have a bit of runout
a bunch of aluminium extrusions roughly 5 feet long, 35mmX35mm, and 35mmX70mm, which i am planning on using to make and reinforce the bed as well as holding the 4th axis and it's tailstock.


for now, the plan is to build the frame to maximise those 1500mm rails and ballscrews on one axis, i would like to use that 3rd hgh20 rail, cut in half should give me plenty of Z.
the other axis, i would like to target 3 feets of useable space.

that would give me 1200mm or so X 900mm or so of working area.

The gantry will run on the 1500 side, i will eventually use 6in or so at one end for the tool rack. also, shorter beam will make it stiffer.

the frame is set to be made out of 4X4X1/4
the gantry will end up being fabricated with 1/4 steel(likely a laser cut box all welded and foam filled)

Nema 34 steppers for motors,
i am undecided wether i should use ballscrews or helical rack and pinion
i am unsure what kind of accuracy i can get out of those helical rack and pinion.

i want the speed of the rack and pinion, i also want the capacity to get into precision carvings with those tiny mini carving bits.



any inputs on those rack and pinions would be apreciated.

Hi Ben - You need to get busy in CAD There's lots to sort out. Your lengths are not too long for ballscrews just depends on what speed you want to run them at... You need to define what plenty of Z is as this will determine a lot of things. The Z axis size and gantry size (100x00x6 is too small to cut aluminium over 1500mm efficiently) will determine lots of things.. CAD sorts that out and the Shark Tank here will sort the rest. Peter

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Originally Posted by peteeng

Hi Ben - You need to get busy in CAD There's lots to sort out. Your lengths are not too long for ballscrews just depends on what speed you want to run them at... You need to define what plenty of Z is as this will determine a lot of things. The Z axis size and gantry size (100x00x6 is too small to cut aluminium over 1500mm efficiently) will determine lots of things.. CAD sorts that out and the Shark Tank here will sort the rest. Peter

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actually you need to look at it the other way. the gantry will be parallel to the 900mm.
this is really a reclycling project. i even found some 1'' aluminium plate that look like it will be perfect for the Zaxis.
originally i wanted to buy a toolchange spindle. i was planning on using 6in out of that 1500mm and have a rack of tools and the 4th axis installed permanently. after seeing the price of those spindles, i decided to buy the cheap 2.2kw. whenever its burnt i'll buy the toolchange spindle.
750mm is plenty of z, because it's what i have on hand. i really just want 12" of Z, i have more than 24" of rail to do it.

i'm kind of cheating over here, i have a co2 laser to make cheap 1/4 mdf mock up of everything before i send it to whoever will laser cut it.
it will definitly change after the first mock-up but i will know then what to change.


my big thing, before i make the move, is to decide wether i am going with ballscrews or helical rack and pinion.
either way is the same price.

i can't find accurate data about backlash of those rack and pinion