plasma cutter for aluminium

[smashweld]

Hi...wondering what size/power rating of plasma cutter you would need to clean cut 7mm aluminium tube
or if it is even possible with a plasma?

 

[WorkshopChris]

Is that 7mm diameter or a tube with 7mm wall thickness?
If 7mm diameter tube i would imagine you will struggle to get a clean finish as it will be thin wall and vaporise instantly before you could spin it round quick enough.

 

[WorkshopChris]

Think you would struggle to get a decent finish as the underside would be 7mm away from the tip. If its is 7mm then its going to be a hacksaw job.

 

[Hood]

No expert as I am new to plasma but from what I can see is, if the specs say it will cut X in, for example Steel, then it will do the same in any other material. Probably best going for one that will cut a bit thicker than you are looking for though and also be aware that there are often several different values given such as clean cut and severance cut.

 

[smashweld]

Yupp 7mm wall (6.4 to be precise)

Am I right in thinking you need more power for aluminium as it needs to slice through the metal and move quicker than with steel
Like...the heat will spread further (easier) with alloy so will melt the edges rather than clean cut whereas with steel itll just melt the line you're trying to cut.....if that makes sense!

 

[carbon]

I have a cebora prof 90 and use it to cut aluminium sheet, I usually cut 6mm but wouldn't say it was a clean cut. Can't remember the specs on it but seem think it's rated lower for aluminium than steel

 

[123hotchef]

I would be cutting the ali bar with a saw

 

[Gareth0123]

For Aluminium and most Alloys a rule of thumb I use for Plasma cutting is to reduce the thickness by 30% over Mild steel for the same amps and air feed pressure.

So for 6.4mm (7mm) thick Aluminium I would be looking for the equivalent to clean cutting 10mm MS. ..... so you are in the realms in of a 40 Amp machine.

I have an R-Tech 30 amp plasma cutter that will clean cut 8mm M/S, 6mm S/S and 6mm Aluminium. I don't doubt it will severance cut 7 or 8 mm ally but you really need the additional amperage of a larger 40amp or more machine to ensure a nice clean cut.

Example. R-Tech P30C Plasma cutter and this is the spec for it:
Amperage Range 15 - 30A
Input voltage/amps 240v 13A
Clean cut mild steel 8mm
Severance cut mild steel 12mm
Clean cut aluminum 6mm
Clean cut stainless steel 6mm
Air consumption 100Ltr/Min (3.5CFM) @ 3.45 Bar (50PSI)
Net weight 14KG
Dimensions 390 x 190 x 290 mm
Post flow air Yes - Cools torch when cutting stopped
HF Start Yes - Enables easy arc starting
Cooling fan Yes - Cooling fan with thermostatic protection

 

[Hood]

The most I have cut is 20mm Alu on mine but it did it with ease but it is a 65amp TecArc OptiCut. Finish is decent enough, not super smooth like steel, kind of hairy finish but still pretty good and a quick brush with a file or grinder makes it smooth. Just this minute cut some 1m x 50mm strips out a sheet of 5mm 5083 alu was cut at 4.5m/min. Pic below.

 

[Hood]

Just found a bit of scrap 20mm 5083 and cut it, went too slow i would say going by the amount of slag on the bottom, only 500mm/min, probably should have been 600 or 700mm/min.
Anyway here it is showing the cut, part of it I ran over a single pass with the grinder you see in the pic (40 grit flap disc) and as you can see it cleans up fairly easily.

 

[Robotstar5]

Can't help with size requirements, but can say it's certainly possible. A plasma will cut 'anything' conductive.

Is it 7mm wall? I'd guess that it would take less power than same size steel, but that really is a guess.

When we looked at hiring a cutter to do some 30mm Ally plate the guy recommended something like 200Amps as Ally sinks the heat away quicker than steel.

 

[smashweld]

Thanks all for the responses
I see 500mm/min mentioned, is there something on the machine that measures that? I'm assuming that's how fast the torch is moving? (this may sound ridiculous!)

 

[Hood]

No, I built a CNC table for my plasma hence the feedrate mentioned.

 

[WorkshopChris]

As you are cutting tube its worth practising how you will move along the cut line a few time with the torch off just to get comfortable in a position you can see you line and keep the torch at the correct angle.

 

[smashweld]

ahh I see. Had to google CNC table...looks interesting - do you mind saying how much it cost roughly?
not that I need that just now but just read something in this link http://www.instructables.com/id/CNC-Plasma-Table/ saying things to consider when looking for a plasma cutter (if using it with a table)

 

[Hood]

Not really sure how much as I had most of the bits such as servo motors, servo drives etc, I have a few retrofitted CNC machines so I pick up motors and drives off eBay when I see them at reasonable prices.
Also had the controller and computer from the wee lathe I had previously retrofitted, was just using it as a test bed for a new controller at the time and never used it, so stripped and gave the bare lathe to a friends son.
Also got the profile rails and rack/pinion from a scrapped machine along with the cabinet etc.
Frame was made from heavy box I got for free as it was left over from a job, was a bit rusty, I had intended to clean and paint it but that didn't happen and likely never will

Here is a vid of it working, cutting too slow for the material but had just been troubleshooting some issues I had.

 

[smashweld]

smart....fortunate to have things like that lying around!

 

[Hood]

If I see things that are cheap that I think may come in handy one day I buy them, probably why I never have any money
Had an afternoon with the plasma, first thing I did was machine a slightly bigger pulley for the compressors motor, it wasn't quite keeping up the last day when I was doing a fair bit of cutting. Once fitted it sounded like the compressor used to and it kept up fine.
Did a couple of bits for Christmas presents, a Salmon and an Elephant. Salmon was 2mm stainless and about 450mm long, Elephant was 4mm Alu and approx 1m x 840mm.
Just designs I picked up from the net, will have to learn how to convert photos to be suitable to plasma cut as quite a few of the fishing boats owners are wanting their boats immortalised in metal

 

[the snooper]

As you are cutting tube its worth practising how you will move along the cut line a few time with the torch off just to get comfortable in a position you can see you line and keep the torch at the correct angle.

Might be worth making a couple of rollers and mount the torch above then just spin the tube on the rollers, it would be more accurate

 

[Hood]

You want them converted to outlines?
I'll ask the wife about it, she's into that kinda stuff (Graphic Design student)

Thanks although it is not just outlines, I think knowing which internal parts to cut and which to leave makes the part stand out.
I think most use programmes like InkScape to trace and then convert to DXF.