[max_imum2000]

hello
i can see that all THC controllers will exceed the cost of the building a diy cheap plasma cutter table.
is there any way around using THC ?
or maybe a cheap THC solution outthere , DIY maybe ?

i was thinking i can leave the z-axis floating , and attach some kind of probe to lift the z-axis with it or lower it , according to the sheet beeing cut.

any ideas ?
thanks

[Torchhead]

Huh? The THC300 from Campbell Designs is less than 400.00 bucks. I guess if you are going to build your table from old bicycle parts and drawer slides then a floating drag head would do fine.

[xjdubber]

use a roller ball head

[massajamesb]

I had considered the use of a roller ball head, with the roller bearings only 2.50 each at www.surpluscenter.com, the only problems I could see would be
1. plasma spatter sticking to the ball/s, and making them drag across the sheet, either moving the sheet, or losing steps.
2. cutting a certain size or shape piece, one or more of the rollers might get caught on the edge of an adjacent part, thereby either missing steps, or dragging your sheet around.

I have seen a number of builders attempt it, but no one has said how well it does/does not work.
If someone has built a roller ball THC, and has had good/bad results with it, I am sure myself as well as other members would love to hear about it.

My thoughts are to ensure that your table is as equidistant from your torch tip through the whole travel of the table.
I always clamp my sheet down, and I take scrap 1/2" plate, box tube, etc. and lay it next to the area I am cutting, to help weigh the sheet down. I am also in the design stages of a water table, so that should prevent warping for the most part.

I think the combination of water table, clamps, weights, and little or no variation from the torch to the table, should preclude the neccesity of a THC, though I could be wrong. That does happen. The only problem is with diamond plate steel, corrugated sheetmetal, etc. where the torch HAS to go up and down. Even there, a roller ball THC wouldn't work.

[Torchhead]

The problem is that the average cut gap while cutting at 100+ IPM is .063 above the material. It doesn't take a lot of variation before the cut quality is degraded or worse the tip crashes. Cutting anything thinner than about 10Ga causes a lot or warping unless the cuts are big and far apart. Just the stress relief of cutting out pieces in the center of the material will often cause the material to buckle up. A drag tip or roller ball tip will snag those popped up edges and move your material. Even with it clamped down something has to give. Once the material moves. the chances of getting the machine stopped and everything put back into registration are slim. It ususally results in a large piece of decorative scrap!

I think the roller ball/drag tip approach is usable on a table that is only used for occasional cuts of larger objects. For detailed cuts or lots of small parts it will result in a lot of blown consummables and lost time and material. It requires the constant involvement of an operator; you don't dare walk away from a machine while it's cutting. The pierce cycle is an important part of the process that often gets overlooked. You should piece higher than you cut (to prevent blow-back from clogging/ruining tips and electrodes. That means the unit needs some way to pick the tip higher off the metal for the pierce then drop it quickly to cut height. Only problem is that if the control software doesn't know where the tip is in relation to the top of the material it can't make those moves.

Just programming in a set pierce delay is not in my opinion a good approach to automated cutting. That varies even on the same piece of metal based on the state of the purge air. The better controls will provide some intelligent way to control that time interval. At the very least an interface to a signal from the plasma (higher end units made for automated control have the "Arc Xfr/Arc Good/Ok to Move" type signals).

I think there is a level of ignorance about the complexities of plasma cutting. It's actually more complex than other types of metal removing. It's a lot more than slamming the tip down on the metal and pulling the trigger.

Kinda like blowing the lock off your door with a shotgun rather than using a key, crude methods will work but the quality of the result is different.

[max_imum2000]

ok now i have understand some information about plasma
and it really dont seem that simple anymore.
i have still 2 ideas.

1. place a probe that go through the tool path (or at least selected parts) before the actual plasma cutter goes, and record exactly where the sheet is locted,
then the cutter height is adjusted according to the previous reading of the probe, however this approch require some software ideas.


2. place some kind of device the dont actually touch the sheet to know the plasma heigh (ie: ultrasonic distance measurment, infrared, or what ever can fits) but solution has to be found for the radiation from the plasma cutter itself if there is any. or maybe solution 1 and 2 can be combined togther, so that the probe is a measuring device.

lets read your thoughts once more

[blackhollowmfg]

Sounds like reinventing the wheel to me. As Torchhead pointed out, there are inexpensive yet very reliable alternatives that already exist.

The problem I see with #1 is that no matter what the "probe" might read before the cut, it will be meaningless during/after the cut since some warpage is bound to occure and change the heigth of the material in relation to the torch.

#2 just seems way out there. It is by far easier to read and maintain arc voltage, which again, systems already exist that are inexpensive and proven.

[max_imum2000]

have anyone read the installation pdf for the THC pointed out at 350$ from torchead ?
well i did
and its not really easy to do it (for me at least)
we use here mainly china made plasma cutters , which are very compact units, its cuts fine though.
they require me to open the unit and search for contact points and install from there.
even if i can do that, it will void my warranty.
beside this forum is all about reinventing the wheel again and again and again

[xjdubber]

ok now i have understand some information about plasma
and it really dont seem that simple anymore.
i have still 2 ideas.

1. place a probe that go through the tool path (or at least selected parts) before the actual plasma cutter goes, and record exactly where the sheet is locted,
then the cutter height is adjusted according to the previous reading of the probe, however this approch require some software ideas.


2. place some kind of device the dont actually touch the sheet to know the plasma heigh (ie: ultrasonic distance measurment, infrared, or what ever can fits) but solution has to be found for the radiation from the plasma cutter itself if there is any. or maybe solution 1 and 2 can be combined togther, so that the probe is a measuring device.

lets read your thoughts once more

The first idea wont work as the metal will warp as youre cutting. The seccond most likely wont work because of what you mentioned. Overall your ideas wont work and the best idea is already with voltage sensing.

[xjdubber]

I think the combination of water table, clamps, weights, and little or no variation from the torch to the table, should preclude the neccesity of a THC, though I could be wrong. That does happen. The only problem is with diamond plate steel, corrugated sheetmetal, etc. where the torch HAS to go up and down. Even there, a roller ball THC wouldn't work.

I work for a multicam distributor and we have sold some machines with a roller ball head, if your into cutting light gage material they actually work quite well. ill see if i can find you a video of one in action. They use about five balls about .75 in diameter. Yes the balls do clogg up they do need to be cleaned regurarly. Ive been told by operators that diesel works well. The only reason i dont like water tables is because they can make a mess

[massajamesb]

I work for a multicam distributor and we have sold some machines with a roller ball head, if your into cutting light gage material they actually work quite well. ill see if i can find you a video of one in action. They use about five balls about .75 in diameter. Yes the balls do clogg up they do need to be cleaned regurarly. Ive been told by operators that diesel works well. The only reason i dont like water tables is because they can make a mess

Which model has the roller ball head? I am familiar with the 1000 and 3000 series, and those that I have seen all had the Hypertherm THC on them.
Post up a video or a link to one, I as well as others, would love to see one working.

[massajamesb]

beside this forum is all about reinventing the wheel again and again and again[/QUOTE]

I will agree partly with this, a lot of threads on this site are people building their own machines their own way. A lot of us know that THK or IKO rails are the nice and easy way to go, but a lot of us choose to do it differently.
There are a number of us that build our own driver boards, but it seems to me that even those are still far less complicated than a voltage arc sensing THC.

I don't see (even with the wiring involved) the CampbellDesigns THC being overly expensive, or a bad deal, for 350 USd.
If you are worried about warranty, how are you going to hook up your torch without modifying any wiring?

[Torchhead]

The "installation" consists of:

Finding a place to monitor the Tip voltage;
The wires to the torch switch to turn on the torch;
A place to put the Current sense transformer for units that don't have an arc good signal;

Three pairs of wires. There is of course the problem of setting up MACH and adding in a 2nd parallel port. And the cables.....I think you are right. FAR too complex. Better stick with the roller ball concept.

(off to re-invent another wheel)

[xjdubber]

Which model has the roller ball head? I am familiar with the 1000 and 3000 series, and those that I have seen all had the Hypertherm THC on them.
Post up a video or a link to one, I as well as others, would love to see one working.

Hmm, as far as i know there is no 1000 series with THC but one. And that one is currently being a pain to me! Both the 1000 and 3000 series can come with Roller ball heads. Multicam doesnt use the Hypertherm THC system they have made their own (which if you ask hypertherm is better then the one they build). The only hypertherm part they use is the voltage devider board. This board divides cutting voltage by 50 (so 100v becomes 2 volts). When starting a cut the torch comes down with ohmic sensing finds the plate backs off to pierce height. After piercing comes down to cut height THC then does nothing for usually a 1000 msec ( User setting). During that time it samples voltage and takes the average and cuts at that height. so if the average is say 140 volts it will mantain the 140 volts. Then there is a user setting called voltage gap this will freeze thc when the the voltage drops lower or rises higher then sampled voltage. so if again the sampled voltage is 140v if the voltage gap is set to 5 it will not let it drop below 135 or above 145.

Im sure one of you guys is smart enough to brew something like that together!

PS: im working on putting the video on google video its kinda big

edit:

The vid is acutally on youtube http://www.youtube.com/watch?v=_OLh7KG3yOE

[massajamesb]

Here ya go.

Now I remember the setup on the 1000 series I saw, though it was a 4x4 cutting area. I didn't know it was a roller ball design, though. It ran real smooth, although it was not cutting anything at the time, just dry runs.

Thanks Xj.

[max_imum2000]

i sure didnt look its running dry to me

[BobWarfield]

If you are worried about warranty, how are you going to hook up your torch without modifying any wiring?

No problem:



Z motion tightens the chain and pulls the trigger. Wing nut lets you adjust the threshold.

Best,

BW

[massajamesb]

Ah, yes. Almost forgot about that.
Thanks for posting that up, Bob.

[SCOTTY76SA]

Hi guys, you look like people that can help me. I downloaded mach3 from the net but can't import any drawings. On the file menu there are no import command. Pleasew help!

[Torchhead]

Hi guys, you look like people that can help me. I downloaded mach3 from the net but can't import any drawings. On the file menu there are no import command. Pleasew help!

You are missing a step.

1. "Drawings" need to be in a Vector (line) format. DXF, PLT
2. There is not native import of drawings. Earlier versions included LazyCAM. I read somewhere that they have now split that out and it's a separate program. Use www.MachSupport.com to see if it's there for download.
3. MACH3 actually runs g-code (like most other CNC controllers). G-code varies so you have to use a version compatable with your controller (MACH3)

So to summerize. You need a CAM program to import the artwork/drawing using a vector format. It should then allow you the define HOW you want the machine to cut it (feedrates, kerf offsets, lead-ins, etc).

Look at the SheetCAM (www.SheetCAM.com) for a program that will import DXF, HPGL (PLT), Excellon and WMF formats. It has a "Post" made specifically for MACH for routing and another for plamsa.

A lot of this depends on what you are using for generating your drawings. It would be nice if you could just scan a picture and cut it bui its not quite (especially for plasma) that easy.

TOM CAUDLE
www.CandCNC.com