Re: Router to plasma cutter

Well said Tom.

I think you should write a simple paper on plasma. you certainly have covered a lot here in very easily understood form.

Dave

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Tom" <thom@...> 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
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, Ron Thompson <ron@> wrote:
> >
> > Hey everyone,
> > I have a small (12"x12") scratch built cnc router. I purposely designed
> > it with an open center (when the deck is removed) for future use as a
> > plasma cutter.
> > I have been using it for a few years, now, and it has worked well. Now
> > it's time for the plasma cutter.
> >
> > The machine uses a HobbyCNC Pro 4 axis board in a wooden box. ( X has 2
> > motors slaved together, so it uses all 4 axis drivers).
> > It is over powered with KellingCNC 425 oz in steppers, derated for
> > unipolar to around 380, and has unshielded wire to the motors.
> > I am running a 28VDC brick power supply, and Mach3.
> >
> > The plasma cutter is an older L-tec (Esab) 40 amp HF start machine. I
> > bought a straight head from ebay to replace the L-handle cutter head.
> >
> > What kind of issues can I expect from interference and what, if any,
> > additional parts do I need to interface the two machines?
> >
> > I see torch height controls around the web, but also seem to recall
> > machines without them.
> >
> > I anticipate needing a metal driver enclosure (or maybe foil around the
> > wooden box?), shielded wire to the motors, and a ground wire to the
> > cutter head so it doesn't have to touch the material to start (right?).
> > I have minimal experience with plasma cutting.
> >
> > I have a Reprap style 3d printer, Taig cnc mill, larger manual mill, and
> > various size lathes. Also the usual welder, grinders, 4x6 bandsaw, wood
> > cutting bandsaw, table saw, etc.
> >
> > I am in the process of building a Joe's 4x8 cnc Router with a G540 Gecko
> > driver and rack and pinion drive.
> > Parts are on order and I need some small brackets that could be plasma
> > cut on the smaller router.
> >
> > Thanks!
> >
> > --
> >
> >
> > Ron Thompson
> > On the Beautiful Florida Space Coast, right beside the Kennedy Space Center, USA
> >
> > Think, Draw, Print. 3D printers ROCK!
> >
> > http://www.plansandprojects.com/My%20Machines/PrusaMendel2012-1/
> >
> > http://www.plansandprojects.com My hobby pages are here:
> > http://www.plansandprojects.com/My%20Machines/
> >
> > Visit the castinghobby FAQ:
> > http://castinghobbyfaq.bareboogerhost.com/
> >
>