help me choose a direction

[mike_belben]

im new to the diy CNC world, please assume i know nothing of controls, coding, etc. i wont take offense. im in the collecting phase at present but will soon begin a simple benchtop engraver run by gecko/mach3 to get my feet wet. the machines are necessary to insource my locally outsourced product line in order for us to move across country.

ive acquired what was formerly a twin pallet changer. id guess about 4x7' base with a 3x4' X axis table riding on surfaced train style rails with a large ballscrew, about 30" of travel. the X table accepts a pair of independant Tslot tables about 20" x 30" that i would put on linear rails/guides + ballscrews. sweet, an X and a pair of Ys. ballpark weight, 2500 give or take.

i will build a nice heavy bridge over the table for the Z axis, likely flanged square tube filled with a damping material and epoxied square at the joints, or even a skeletal structure sandwiched in steel plates and filled with concrete, almost like a safe. easy enough.

heres where i wrestle with myself. what to put on the bridge/fixed gantry thingy? single Zaxis spindle fixed in place, twin fixed spindles, single or twins on a linear axis? the cats meow would be two Z axis spindles on a common linear rail, driven by independant ball screws. taken a step further, one spindle could be on a standard Z axis slide table, the other could be a compounded "5 axis" type.

before i start spending money in either direction, i need to know how challenging its going to be to control all these ballscrews. is there any open source or reasonably priced software that can run 2 tables and 2 spindles on one machine from one PC?

feel free to beat this idea out of my head if its infact a bad one. thanks in advance for your time.

mike

[mike_belben]

i should mention that i dont intend to run both spindles at once. the machine wont have a toolchanger so i was thinking 2 spindles = two tools on hand.

i dont have any pictures of the base yet but its possible to build the bridge in a way that you could have one spindle pulled against its home and the other spindle having full range of the work area on either pallet, then park the first spindle and bring in the second. would give tooling time to cool, and allow one spindle to be built heavier for roughing and heavier cuts, then the other to be lighter and loaded with a finishing tool. two spindles should last twice as long, or atleast provide a backup option should one spindle need repair/etc.

im mostly concerned about the ability to control it without spending a fortune on some fanuc controller.

[awerby]

You want to have two separate tables moving at once? And what good would a fixed spindle do, not to mention two of them? Even if the table moves in Y as well as X, you still need the spindle to travel up and down, no?

Mach3 can control up to six axes at a time, but you might need to add a second parallel port to accomplish that (something I've never had much luck with). It seems like you've got everything you'd need to make a 3-axis bridge-type router out of that thing; why not start with that? It seems unduly complicated to try to control two separate spindles, but it has been done. The simplest way to achieve an automatic tool change, given that you've got two spindles, would be to mount them on a rotating bar, so that you could do the roughing with one of them while the other one points upwards, then pull it up to a safe position, rotate the bar so the other spindle points down, then activate it and do the finish pass.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[mike_belben]

any spindle would have to be mounted on a Z axis that plunges vertically toward and away from the horizontal work surface. the question would be whether to have the Z axis permanently centered on a bridge (think bridgeport column, the head is always sitting still, just quill motion) or to incorporate horizontal travel to the Z axis along a gantry, think plasma table/router. yes, there would be a redundant X axis in that respect.

i make a product line in batchwork and would like to set it up on a tombstone with say 20 blanks at a time. i would only want one spindle working over one pallet at a time, and the other pallet staged for loading the next cycle of parts. its been suggested to me that a toolchanger would be a better investment than a second spindle and i guess i agree.

i work for a major handgun manufacturer with several hundred CNC machines running 3 shifts. nearly all of our newer machines are running multi-pallets and several stages of machining at each center.