Have I got this right?

[Robin Hewitt]

I've been browsing and your end results look fantastic.

So I just buy a SIP plasma cutter, disassemble the torch, throw away the bits I don't need, mount it on a fast XY, slow Z table, plug in the shop air line at low bar and with a bit of practice I can then chop fancy shapes out of 2-3mm steel plate?

This sounds too good to be true, why haven't I got one already?

Why am I paying for laser cutting when I don't need laser accuracy?

OTOH, what kind of accuracy would I get?

[massajamesb]

Here is a comparison for you of laser versus plasma. Bear in mind that I only have a rinky dink 40 amp Thermal Dynamics

Here is some 3/16 plasma cut steel

cut on my homemade plasma table

and this is 3/16 laser cut steel

cut on a 1.2 milliion dollar laser

The two together, with a oxyfuel cut 1/4" piece, couldn't get them to resize right in Photobucket. The laser cut piece is on the bottom




These edges are not ground down, only wire wheeled for clarity.

If you are needing the ultimate in accuracy, then a laser is probably your best bet,i.e you want someone to cut your name in some washers. Plasma is not the most accurate process available, but it is worth looking into, depending on what your needs are.

What kind of accuracy do you need? what do you need cut? These will determine if plasma is right for you.

EDIT: your halfway right about how it all works though there is a bit more to it I don't know that I would throw parts to my plasma torch away

[Robin Hewitt]

Originally Posted by massajamesb What kind of accuracy do you need? what do you need cut? These will determine if plasma is right for you.

I can't see a difference between laser and plasma in your pictures. I did see a difference when someone sold me some 40mm aluminum offcuts he'd taken with a plasma torch, a total mess, guess it kinda put me off.

Would that I had a crystal ball, but like most I can't see much farther than the next job so I have no ideas about accuracy or material for cutting

Largest laser cut I ever did was an entire prototype A0 injet printer in mild steel, most precise was an SG meter for the antifreeze mixing tank at a car plant, last cut was a bunch of scuba backplates in marine grade stainless.

Next job is some decorative pierced iron work and this plasma looks right. Job after that? A complete mystery

[massajamesb]

Originally Posted by Robin Hewitt I can't see a difference between laser and plasma in your pictures. I did see a difference when someone sold me some 40mm aluminum offcuts he'd taken with a plasma torch, a total mess, guess it kinda put me off.

That was the point of the pictures on most thinner (less than 3/8 thick) steel, plasma is great for most of us. Thicker than that and you start having edge bevel issues.
Aluminum is not an easy material to cut cleanly, IMO. takes a bit more work than steel.

Originally Posted by Robin Hewitt Would that I had a crystal ball, but like most I can't see much farther than the next job so I have no ideas about accuracy or material for cutting Largest laser cut I ever did was an entire prototype A0 injet printer in mild steel, most precise was an SG meter for the antifreeze mixing tank at a car plant, last cut was a bunch of scuba backplates in marine grade stainless. Next job is some decorative pierced iron work and this plasma looks right. Job after that? A complete mystery

Decorative metal work is one thing, but to quote another source, "you are never going to cut watch parts with plasma". I cut chassis and suspension parts, on top of a number of other things, and plasma works just fine for me. But, my parts are acceptable if one is 1/16" smaller or larger than the next one, though they are usually well under that.
Can you accept a tolerance of .05-.1" ? if so, then plasma might just work for you too

[millman52]

I agree with James. Plasma is the way to go on most budgets here on this board. The bevel James mentioned seems to get worse as steel & I assume other materials get thicker. OX/Fuel, although the kerf lines across the cut face are a bit more pronounced, & only good in steel, plate thickness from 1/4" through 6" is doable & with a good square edge.

Most of my experience is with OX/Fuel, steel plate, & thicknesses of 3/8" through 1". From others posts there seems to be a point on material thickness where Ox/Fuel becomes cleaner/straighter across the cut edge as well as equal or better in speed. I'm sure that depends some on the abilities of the plasma rig itself.

[Robin Hewitt]

I don't have a spare $1.2m for the laser

So am I fairly safe to assume that using a cheap Chinese 40w plasma cutter, lightweight trapezoidal screws, bronze nuts and ball bushings fixed to an extruded aluminium frame... I can build a meter square cnc table and get a clean cut through a 3 or 4mm steel plate?

If so, I'm thinking maybe I should go away and build it, then come back here so you can complete my education.

Or does past experience make that sound like a terrrible idea?

[massajamesb]

I am not fond of most of those little high frequency or touch start Chinese plasmas, but you may fare better than I in respect to them.

Screws are really not best suited for plasma cutting, the dust created by the burning process is actually abrasive to a point. Screws will not last long. Look into chains, belts, or perhaps spur gear and gear rack. The latter of those probably being the best choice.

If you want to use 8020 extruded aluminum, feel free, just make sure you keep the table square, and check it often. A table thrown out-of-square is all but useless.

Check the forums here, there are a multitude of others building cnc burning tables, and another multitude who have already built them and shared the ins and outs of it
Look at what others have done, and see how well it has worked for them. Make your decisions based upon that.

[xjdubber]

depending on what plasma unit you have you can get really nice cuts equal to laser. The pictures where shown here are extremely misleading. If you need to do any small holes and tight arcs & such you would want to use a laser. If you need very good quality cuts i would sugggest going with and Hypertherm HPR, or HD unit. If you go with an HPR unit it wouldnt suggest building a machine yourself because there is to much involved. However using an Powermax 1000 ~1650 and fine cut consumbables (thinner materials) you will get awesome quality, and very good angularity.

[massajamesb]

Originally Posted by xjdubber depending on what plasma unit you have you can get really nice cuts equal to laser. The pictures where shown here are extremely misleading. .

Really? I didn't think so. I never once said that plasma produced better quality cuts than laser all the time. In fact, I can say for sure that a laser is the nicest cut edge available,especially on thicker materials, if you have the money The point was, the author of the thread stated "why pay for laser when I don't need the accuracy". They wanted to know about plasma capabilities. My cut edge pictures are a edge-to-edge comparison of exactly that. Laser is capable of things that plasma could never do.

Originally Posted by xjdubber If you need to do any small holes and tight arcs & such you would want to use a laser. If you need very good quality cuts i would sugggest going with and Hypertherm HPR, or HD unit. If you go with an HPR unit it wouldnt suggest building a machine yourself because there is to much involved.

I do agree with you about small holes and tight arcs. Hence my question of accuracy.

If you can afford a HPR unit, then you aren't worried about saving money by building your own table. A Hydefinition plasma is a nice alternative to a laser, but it is not within the budget of most hobbiests and home-jobbers.
A mid-tier cnc table costs as much as the smallest Hypertherm Hydef plasma available.

Originally Posted by xjdubber However using an Powermax 1000 ~1650 and fine cut consumbables (thinner materials) you will get awesome quality, and very good angularity.

Agreed. Hypertherm is the best, hands down. I wish I had bought another one when I bought my TD live and learn.

[xjdubber]

Originally Posted by massajamesb Really? I didn't think so. I never once said that plasma produced better quality cuts than laser all the time. In fact, I can say for sure that a laser is the nicest cut edge available,especially on thicker materials, if you have the money The point was, the author of the thread stated "why pay for laser when I don't need the accuracy". They wanted to know about plasma capabilities. My cut edge pictures are a edge-to-edge comparison of exactly that. Laser is capable of things that plasma could never do.

Well yes and no I have a customer with a 6KW Mitsubishi laser. On 1/4 the plasma that i installed (with HPR-130) does just as nice as the laser.....if the cuts dont get too intriquete (spelling?....... but then the plasma runs twice as fast as the laser. At 6KW 1/2" is getting pretty thick. The HPR130 will still cut trough 1.5" (edge start....and slooooow!). But yes I always have to tell that operator that he doesnt have to beat the laser!

[massajamesb]

I have seen some companies have their company logo cut in 1/2" bore stainless washers with their phone number, and use them as business cards. There is no way plasma could do that.

But if you are cutting simple parts, and are on a budget, there is no reason to outsource to laser shops if plasma meets the requirements.
Hydef is a nice option, but I didn't meet the main requirement for using one :
fat wallet

[xjdubber]

Originally Posted by massajamesb but I didn't meet the main requirement for using one : fat wallet

Oh come on, an hpr 260 is only around $50 G's