Thread: Interesting design... not seen this before..

Yes, have seen one, although rather than setup for oxy plasma it was set as a pneumatic scribe in a shop about an hour from my place. They used it to put part labels on sheet metalbefore it was cut by a laser. Spoke with the guy after he emailed me with some questions. Turned out it wasn't very good. Apparently flexes alot, makes sense as it is supported at only two points and if it is fully extended acts like a fulcrum.

In saying that, its not a super heavy load and remember, oxy fuel cutting as well as most plasma machines, are not super accurate due to the variations in the plasma arcing or the flame so any slight flex would not be noticable as most of the cut parts would be linished to clean the edges.

Just my two cents.
Daniel

I have seen two of these. One is a monster that is hardly used at a TAFE College, and the other is a smaller plasma in a local boilermakers which is almost identical to the one in the link (although he apparently paid about ten times more than that). It has apparently been plagued with issues from day dot, and from the time I watched it, the tiniest bit of grit in the track or rollers is multiplied enormously by the extended arm which then draws squiggly lines.
The other major drawback I see is they have twice the footprint of the actual cutting area.
My 5 cents.

On the other hand, the reason a normal CNC machine needs to be so rigid is because of the pressure exerted on and at the cutter bit. No such force is applied to a plasma cutter, which is basically just suspended in the air above the item being cut.
So, as long as the arm was rigid enough to support the cutter without undue flexing, then I see no need for any greater support.

Bob Willson

As an exercise to prove why i wouldn't, get a broom handle and tape a pen to the end and try to write on a piece of paper whilst holding the end and various places up the broom handle. Then inspect your "handy" work and see how well you did. Unless your superman or i am really bad, It will be rough, until you get close to the pen end. The metal will vibrate and flex too and as alluded to above will be amplified by the cutter.

Daniel

That isn't really an accurate comparison Daniel.
The movements required by a pen aren't the same as those for a plasma torch. When cutting with a router you will use speeds that are much higher than those needed for a torch. So, given the much slower acceleration, speed and X Y axis movements and the apparent rigidity of the torch arm, I think it would be quite doable.
On the other hand, I have absolutely no experience in this and so I am only going by my slightly educated guesswork.

Bob

Bob,

I was not intending to be technically correct with regards to motions and speeds, and i didn't mean doing it with a router, just manually by hand. Just trying to exaggerate the problems with the design in relation to the singular beam at a fixed point some distance from the base point, much like a fulcrum design.

After seeing photos of work off one of these machines when trouble shooting for a metal work company i can certify that what i saw is a close representation to doing the above(will try and find photo in archived emails). It may not be as bad as the result doing my little experiment but for the money invested it may as well be. Just from memory i remember variations from design to part in the 2mm range both using a plasma and scribe.

In saying that, your correct, it is do-able, but your speeds would be frustratingly slow.

Daniel
P.S An average plasma runs at near enough to the same speeds as an average router. I believe it is a small mis-conception. Decent plasma cutters have a cutting speed almost equivalent to a 4-8HP spindle when installed on a cnc. Its just limited to thickness of material in singular pass. Only big difference is the load rating, routers have huge forces and the palsmas have very little in comparison.

Interestingly, I have problems reaching the recommended cut speeds required for much of the plasma work I do on <3mm sheet on my gantry machine but can easily reach the maximum speeds I can route at.
Does this mean my spindle is underpowered or my plasma is overpowered.
Good acceleration is key for nice plasma cuts, the router doesn't mind if speed ramps more on direction changes, but the plasma prefers constant velocity.
Keep in mind on lighter gauge sheet recommended cut speeds for the plasma are up to 10m/min.
I agree with the above analogy.
The only real redeeming feature I can see on these machines is portability.
That'll make it my 10cents

Firstly you bring another good point, this machine is portable and there are not too many machines you could use and carry away.

Secondly, almost everyones spindle is underpowered. In the hobbyist market we are governed by price and availability and by what size a machine we built and its type. Matter of fact is a standard spindle for routers of commercial quality is much higher and a decent router to match a machine would be around the 10HP mark for woodworking. Anything less commercially would be a waste of time to manufacturers due to longer cutting times. So idealistically we are all running underpowered spindles compared to what our machines possibly could handle. lol.

Daniel