Re: [CAD_CAM_EDM_DRO] Re: Router to plasma cutter

On 10/3/2012 11:34 AM, Tom wrote:

> Ron: It's hard to predict what issues you are going to face. Plasma
> cutting is different animal than other types
>
> 1. You have to account for a different pierce height (prevents blow
> back of molten metal) so the "pierce cycle" consists of a set of
> coordinated and properly timer moves. If MACH is your control choice
> you can do that through a POST in your CAM
> 2. The thinner the material the faster you have to cut (see some cut
> charts like for the Hypertherm 45)...they won't work for your ESAB BUT
> they will give you an idea of what speeds you will need.
> 3. While there are little cutting forces in plasma you do have to have
> good acceleration rates at the higher feedrates....translated: You
> need plenty of torque to the final drive mechanics to make sharp turns
> and square corners at higher speeds
> 4. Make sure your expectations for plasma cutting are realistic. It is
> NOT a precision cutting process. It is like carving out a door with
> RPG's comared to milling. You are vaporizing metal and blowing it out
> the back with air. The flame is "floppy" and trails behind the motion.
> The kerf width is dependent on the feedrate, the arc Gap (height above
> the material) the age of the consumables and to an extent, air
> pressure and the current setting. If you can hold + or = .015 on a cut
> you are doing better than average, Typically plasma is a process used
> for large sheets being used in fabrication (weldments) or for
> decorative cutting neither of which requires tolerance fits
> 5. While a 12 x 12 work area is interesting it will end up like a
> hockey game in a closet. Even the little 24 X 24 tables are more a
> novelty than really usable for what plasma is intended
> 6. Torch Height is essential for any thinner material or for larger
> cut areas. You have to skim along the cut hovering up at .063 to .120
> while moving at 65 to 250 IPM and all it takes to ruin a set of
> consumables is to let the gap get too low. to pierce too low or to let
> the material bow up and have the nozzle contact it while cutting. That
> being said a THC on a tiny table may not be practical. the process of
> IHS (initial height sensing) is part of the THC process where the
> top-of-material can move on you and Z zero has to be reset. The "touch
> off" (probe) process can be done using several ways: ohmic ,
> capacitance proximity, and mechanical[floating torch holder]. Each as
> pros and cons. Even if you elect to not use THC than consider the
> inclusion of a Floating Torch Holder to act as the IHS and as a safety
> backup in case the Z tries to drive the torch through the metal.
>
> There is a misunderstanding that plasma cutting is just routing with a
> hot tool....it is actually a lot more complex than that and converting
> a table or building one to do both takes some engineering and an
> understanding of the Physics involved.
>
> Sorry to be so verbose but these are questions I answer several times
> a day and you need a minimum set of details.
>
> Tom Caudle
> www.candcnc.com

Tom,
Thanks for your time! I was aware of most of this. My router is made
from laser cut steel from a place I used to work. I also have a supply
of scrap plate from the same source, mostly 12 ga., that will fit my
machine.
This will be a starting point for making a larger machine. A learner, if
you will.
The brackets I am needing will be fine at those tolerances, but I
expected more like .005" with proper kerf control.
I am looking forward to the adventure.

--


Ron Thompson
On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA

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