How I do accurate plasma cutting (demo'd using Longevity logo contest entry)

[Tensaiteki]

I realize that many here have strong opinions on Longevity and the other import people, but please, this thread is not intended to promote any particular brand of anything so please try not to turn it into another bash-the-China-machines-thread.

The purpose of this thread is so I can share the methods I use to accurately cut shapes out of sheet metal without a CNC machine or making stencils and the like, just by using simple tools and methods that are easily available.

Anyway, the project I will be using to demonstrate these methods is the Longevity logo I made for the Longevity logo contest.

(Click all pictures for larger versions)

I started with a piece of 16 ga. steel measuring approx. 13" X 32":
http://www.tensaiteki.com/images/stories/LGContest/LGContest_blank_sheet_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_blank_sheet_large.jpg)

I then traced an image of the Longevity logo in a CAD program and offset lines for the kerf as well as the width of the tip of my plasma cutter and printed it off. I printed this one off on a inkjet plotter but any sort of printer will work (inkjet, Laser, etc.). The pattern does not have to fit all on the same sheet of paper, multiple sheets can be used and simply taped or glued together.

To glue down the paper, I first position it on the steel and weight down one half of the paper. Then I lift up the unweighted half and spray with 3M Super 77 spray adhesive (available at Wal-Mart).

http://www.tensaiteki.com/images/stories/LGContest/LGContest_template_half_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_template_half_large.jpg)

After the first half is glued down, I remove the weights, lift the other half and apply more glue. Using this method you can accurately position the template without having to try and get a lose piece of paper aligned on a sticky surface.

http://www.tensaiteki.com/images/stories/LGContest/LGContest_template_glued_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_template_glued_large.jpg)

Here is a close up of the paper template. The solid lines show where the kerf (material burned away by the plasma cutter) will be. The broken lines mark the width of the tip of the cutter.

http://www.tensaiteki.com/images/stories/LGContest/LGContest_template_macro_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_template_macro_large.jpg)

For all the straight cuts I use a regular steel framing square as a guide. I just line the edge of the straightedge directly on the broken lines (the square is actually directly above the broken lines, the camera angle and the warp of my heavily used square make it look like it isn't.):

http://www.tensaiteki.com/images/stories/LGContest/LGContest_square_macro_small.jpg
(http://www.tensaiteki.com/images/stories/LGContest/LGContest_square_macro_large.jpg)

My plasma cutter does not have a pilot arc, only a high-frequency start. The high frequency usually cannot start an arc through the paper so I just take a pocket knife and cut a small hole in the paper to expose bare metal. This is only necessary when starting a new cut, If I am starting from an existing cut this is not needed. If your plasma cutter has a pilot-arc this is not necessary at all.

http://www.tensaiteki.com/images/stories/LGContest/LGContest_start_spot_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_start_spot_large.jpg)

I always position myself so I can drag the torch toward me. I simply drag the torch like a box cutter on the surface of the work piece. Even without a special drag-cup on the torch, dragging at sheet-metal amperage should not damage the cutter.


http://www.tensaiteki.com/images/stories/LGContest/LGContest_E_cut1_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_E_cut1_large.jpg)

Then I re-position the square for the next cut:

http://www.tensaiteki.com/images/stories/LGContest/LGContest_E_cut2_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_E_cut2_large.jpg)

By positioning both "legs" of the square on the offset marks and cutting into (towards) the corner of the square you can ensure that you stop the cut exactly were you want to.

http://www.tensaiteki.com/images/stories/LGContest/LGContest_cut_stop_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_cut_stop_large.jpg)

(Continued in next post)

[Tensaiteki]

(Continued...)

Simply continue to reposition, cut, repeat until everything is cut.

http://www.tensaiteki.com/images/stories/LGContest/LGContest_E_almost_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_E_almost_large.jpg)

Well, almost everything..:

http://www.tensaiteki.com/images/stories/LGContest/LGContest_straight_done_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_straight_done_large.jpg)

The framing square works great for straight cuts, but what about curves like the 'O' and 'G'?

You could make a stencil-type thing out of thin plywood or some such material, but that's a lot of extra work (and expense) and in the end, you have a bunch of useless stencils that you either have to throw away or store until the day that you might need them again.

However, I found another way. While wandering the aisles of the local Hobby Lobby (hobby supply chain) I found a drawing tool called a flexible artist's curve. It's a rubberized doohicky that you can bend into any shape and it will hold with very little spring-back (I think it's just a bar of lead on the inside). All you have to do is bend it to the shape of the curve you want to cut and use it just like the steel straightedge.

http://www.tensaiteki.com/images/stories/LGContest/LGContest_artist_curve_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_artist_curve_large.jpg)

Even though it's coated in a sort of rubberized-plastic material, I don't have any problems with it burning or melting because I only use short sections at a time and use different parts of the curve so no one spot gets too hot.

http://www.tensaiteki.com/images/stories/LGContest/LGContest_curve_cut_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_curve_cut_large.jpg)

After everything is cut out, the workpiece is usually warm enough that what remains of the paper will simply peel off:

http://www.tensaiteki.com/images/stories/LGContest/LGContest_parts_cut_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_parts_cut_large.jpg)

The glue will leave a residue on the metal which will interfere with welding so after removing the slag I wash them off in a solution of water and a citrus-based cleaner called "Goo-Gone." After rinsing with water and drying they are ready to weld. I found that cleaning with this method makes using acetone unnecessary. The Goo-Gone solution is nowhere near as smelly, flammable, or toxic as acetone:


http://www.tensaiteki.com/images/stories/LGContest/LGContest_parts_clean_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_parts_clean_large.jpg)

I then cut a bunch of 7/8" wide strips of the same 16 ga. material and bent and welded (picture only shows tacks) it around the edges of the letters:

http://www.tensaiteki.com/images/stories/LGContest/LGContest_parts_welded_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_parts_welded_large.jpg)

Then I welded all the letters back onto the original piece:

http://www.tensaiteki.com/images/stories/LGContest/LGContest_no_paint_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_no_paint_large.jpg)

Finally I painted it (the white was sprayed, the red and black were hand-painted):

http://www.tensaiteki.com/images/stories/LGContest/LGContest_painted_small.jpg (http://www.tensaiteki.com/images/stories/LGContest/LGContest_painted_large.jpg)

And that, ladies and gentlemen, is how I do things.

[Throttlehead250]

very nice!

[Jasondt2001]

This post makes me want a plasma cutter that much more... thanks! LOL
Very nice! I like the square tip - I'm so shaky most of the time it looks like I'm cutting out halloween graphics for the kids...

[longevity-inc.com]

Wow! Very nice work! I will be sending you and the two other people who have emailed me contest entries a DHL return label so we can analyze the work here in the office.

I have all contact information. Thanks for joining the contest. We will pick a winner here shortly once all the contestants turned in their Longevity Logos!

Thanks,

Simon

[Joe H]

Nice tutorial! Great work.


I started to build an entry myself. I felt like it was cheating, for a professional custom sign builder with access to a shop full of great tools to enter. So I didn't, but I did go as far as tracing the logo in CAD like you did.

I was going to do pretty much the same thing you did, actually. Only a little bigger, using 1/4" plate and 1/8" thick 3"wide returns. Returns are what we call the 7/8" strips you used.

[Jolly Roger]

Nice work.

[Me!]

I like the guide lines.
I make templates much the same way, I make the "part" I want and then over or under size it by 3/16 (my plasmas drag cup offset) then I print it masonite. Take it to the shop and cut it out on the jig saw, sand it depending on the quality needed, and then I have a reusable template.

That loge looks neat, like the box idea.

[chopper5]

cool right up and nice work

[joebiplane]

Thanks for the "How to' Article. It is very tempting to try for practice. did you Mig the parts together or tig /

I guess after a winter of practice, practice, practice i can use my shiney new LS 160 P to atempt thye project or something like it, myself

Now if simon would only get those hats and shirts available.......:blob3:.....
Thanks for sharing
joe