Re: Newbi needs advise on torch table.

> * I would like to build a table that can
> handle a 4x8' sheet at a time so I think I would
> probably need to build the system slightly larger then
> this some where around 4 1/3 x 8 1/3'.

Figure one axis or the other for full clearance so you can drop a
sheet onto the table without having to slide it under any components.

Preferrabley, have the gantry move so there is a full 8 feet of
clearance for the parts.

also, once you determine your gantry size, then figure your *real*
table size.

>
> * I plan on powering the system with two
> stepper motors on the y axis one on each side driven
> with two lead screws. From what I have seen most
> people are using motors in the 175-200 oz/in range.
> On the x axis I would like to use a single motor and
> screw of about the same size.

We go over this every couple months.

leadscrews are great when power transmission is required like for
routers or such, but not required when non-contact things are used.

a rack or even a single belt will offer lots of benefits. not the
least of which is that a pair of 10 foot screws and anti-backlash
nuts of 1.5 inches in dia or so will cost the better part of the
whole project. you can only spin a long shaft so fast before it
wobbles, and you need to compensate by larger diameters and then you
compensate by being lots lighter in the wallet.

with a gantry, considder a shaft link with gears on both sides and
one motor. again simple and strong.

> * For the z axis I would like 4-6" of travel,
> so that I could put a small router or die grinder type
> tool for wood routing and engraving, though this is
> not terribly important. I was planing on using a
> smaller motor to drive this probably via a linear
> gear.

Check out the 'instant Z' axis most of your problems of design go
away when you can buy a ready to run part. ( for lots less than you
can make, even if you are a great scavenger)

> * For the z axis I would like to eventually
> hook up a programmable
> micro controller to keep the torch at the correct
> height but for the time being I would like to put just
> a up down switch to manually control
> the torch height. Can I hook up a three way
> controller in this manner and have the computer
> control the x,y and me or a second circuit handle the
> z axis?

Torch height for sheet metal is a function of X and Y with an
independant Z.

you can have a totally seperate Z for independant height control.

makes life simpler, but you do need that seperate axis control.

> * How does the on off on the torch work? I
> understand that I will need a machine torch head for
> either plasma or oxy/acetylene is the switch
> build into the torch?

I think the simplest on/off is a stepper with an eccentric cam
instead of a pulley. rotate 180 degrees and it presses the torch
lever. very simple. could be a gear motor and a couple end
switches, or even a solenoid.

>
> * How much would one expect to spend on a
> system like this?

figure 2-3 times more than you expect.

Dave