Re: [CAD_CAM_EDM_DRO] Re: Build CNC Plasma cutting Table

indy123456 wrote:

>I used heavy steel floor grating (24"x24" sections) in the cutting
>area (bought one to check it out, found it was very flat, so I got
>more) and got them all leveled to the carriage axii, and was able to
>bolt risers in fixed locations where the cut path wouldn't hit them,
>since I would always be cutting the same parts.
>

Same here. I picked mine up from a "Raising company" who tears down old
buildings. Far cheaper than new stuff. The only thing I did maybe
different is put that on a completely seperate table, that rolls between
the frame of the plasma cutter. This way I can load stuff away from the
machine and roll it into place. I too have adjusters to level if necessary.

If I had time to do it again though, I would use the typical zigzag cut
points to set stuff on. This way things "fall thru" after cutting and
you have a lesser chance of the torch tip getting caught when you are
not looking.

>The problem I ran into was gap control... no problem making the torch
>travel in a flat plane of course, and no problem establishing a flat
>table plane. The steel being cut is the problem. Even assuming it
>is flat to start with (I got a lot that wasn't, and was useless), it
>doesn't stay that way long when you start cutting... edges of cut
>sections pop up, catching on the torch tip, moving the part or
>stopping progress.
>

This is true.... But it does depend on the thickness of material, and
how fast and even you can transverse the steel.

> I know some costly systems use sensors that
>manipulate torch height with a servo... I tried to come up with a
>mechanical version that rode the surface. I know people have plasma
>tables that work, so I'm not discouraging you from your project...
>just warning that, with HEAT involved, things don't always go the way
>you envision.
>

I see Torch Height Control discussions in the MACH1 newsgroup now and
then. It could be that there are fellows who have this working under
Mach1, but I am not sure. I do know it requires a Plasma cutter that can
deliver a signal that indicates current amperage draw as that changes
continuously as the tip gets closer or farther from the material. Not
everyone needs torch height control though.......

> To avoid headaches and heartbreak, investigate the
>marketed systems thouroughly and ask lots of questions first and talk
>to people who use them; see how they handle the heat warp problems.
>The feed control that CNC allows vs. my manual path tracing (hard to
>maintain a steady path following a pattern, fighting carriage
>inertia, etc.) may go a ways toward reducing the heat induced into
>the sheet.
>

The ability to control feeds under CNC control is the key to keeping
heat minimzed. You must have a controller capable of very smooth motion
thru mixed geometry to avoid excessive heat and also to avoid any
jittery cuts. Good adjustable Acceleration is also important because you
need as little ramp up and down time in the corners as well.

> (snip)I thought plasma cutting was a neat, "little-guy-enabling"
>technology until my experience with it... now I'm not a fan.
>

There is no doubt that it depends on your needs. If you are really in
need of a "production" machine in the immediate sense, you likely do not
have the time to fiddle with building a CNC Plasma cutter. However, if
you cut things occasionally, or if you would like to be able to cut any
"one off" item now and then without the hassles of getting another
company to do a "onesey twosey" for you, you will very much appreciate
the time and energy you spent getting your own machine.

The one I built could *never* run as a production machine. It was built
so I could create "prototypes" rapidly to make sure they work. In my
case, I made 50 or so prototype designs for one application before
concluding how it really should be. I would have went crazy and lost
lots of time waiting for someone else to "fit in" those 50 samples on
the way to the final item. I do send all the final work to someone else
and like mentioned, I don;t think I could do it for what they charge.
But I'm not giving up the ability to make what I want when I want
anytime soon. Even though it could never be a production machine, It
takes little time to slam out a few hundred things now and then.

I do not have Torch Height control either. I do have a "machine torch"
style head with holder, which allows me to simply rotate a knob to raise
or lower the torch. On any challenging cut, I can just stand there and
move it up and down if necessary, but with what I cut, it is seldom a
problem.

I could envision a half dozen cheap alternatives for my Torch height
control needs..... A cable operated hand held device to "Squeeze and
Release"- Raise Lower.... while standing at a distance, A motor Driven Z
axis using my Kids servos and Radio from his Rc Car...... Or even a
"full pull" electric selenoid lift just for emergencies.

I guess really, If all it takes is a motor driven Z axis, an easy to
build circuit, and a control software with some THC functions built in
like Mach1 (you'd have to research how that is coming along), you may as
well "design for the future" and at least make sure you could ADD the Z
axis if necessary. You can start with just a to axis.

So, My advise would be to consider your needs. Then determine just how
"in depth" the machine to fit your needs must be. If you plan on turning
out thousands of parts with no-one standing there, you should consider a
proven OEM machine. However, if you need to computer generate a hundred
parts now and then, it is amazing how little of machine you really need
to accomplish that goal.

Chris L