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Thread: Rule of thumb for plasma cutting?

  1. #1
    Member kb3gun's Avatar
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    Rule of thumb for plasma cutting?

    Is there a suggested Amp/Thickness chart or rule of thumb for plasma cutting? I have the LP-40D and often jump between many different material thicknesses. Most of the time I've been leaving it set pretty high. Unfortunately, I don't have a lot of time (or scrap for that matter) to try many different settings. With the higher settings (to high), I end up with a lot of clean-up afterwords.
    Is there a basic chart kind of like the charts in most mig welders giving basic settings for different materials and thicknesses?
    Thanks!
    Smitty -- Western PA, USA
    Hobart HH-187
    Longevity LP-40D Plasma
    My '66 FJ-40 Build Thread: http://forum.ih8mud.com/pa-appalachian- ... -fj40.html
    Appalachian Land Cruiser Assoc (ALCA)

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    Junior Member eldermc's Avatar
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    Quote Originally Posted by kb3gun View Post
    Is there a suggested Amp/Thickness chart or rule of thumb for plasma cutting? I have the LP-40D and often jump between many different material thicknesses. Most of the time I've been leaving it set pretty high. Unfortunately, I don't have a lot of time (or scrap for that matter) to try many different settings. With the higher settings (to high), I end up with a lot of clean-up afterwords.
    Is there a basic chart kind of like the charts in most mig welders giving basic settings for different materials and thicknesses?
    Thanks!
    I don't know of one yet, but I too would like this information. I can tell you however that on my LS-200 (50A plasma built in) 25A works quite well on 3/16" steel.

    Over the next few weeks I will be experimenting with different settings. I'll try and post the results on the board somewhere.

    Matt
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    Matt Elder
    Orangeburg, SC

    Favorite Project - http://kr1.infinigral.com

    Equipment:
    -LS-200P
    -CNC plasma table <under construction>
    -O/A setup
    -135A MIG
    -Some other odds 'n' ends

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    Moderator KHK's Avatar
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    I think that this is a great idea!
    We could probably make one chart for all the machines. I have a 160P and may have some time tomorrow to attempt a start.
    keith
    The older the Boys, the more expensive the TOYS
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  4. #4
    HerbD
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    Ipm

    In an earlier post I was looking for help on how fast to move the plasma torch when cutting 20 ga stainless steel sheet. After some searching on the web I found a chart. Unfortunately it doesn't go "thin" enough for my needs and I'll be doing some experimenting also.

    So far the problem has been excessive slag on the backside of the cut. Too slow? Too hot? Too close, too far on tip to metal distance? Air pressure? Several variables to track. I've even read where you need gas on the back side to get really clean, no discoloring, in the cuts.

    I was hoping that someone (Gadget?) that has a CNC cutting setup might share some Inches Per Minute (IPM) experience, and pictures, on this. I'm designing a low tech (I hope) linear cutter (Plasma Torch based) so that I can make straight cuts in fairly large sheets using some sort of mechanical weight and pulley device that can pull the torch at a constant speed along a light track. Looking at mechanical governors etc to control speed.

    HerbD
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    Last edited by HerbD; 05-03-2009 at 10:26 PM. Reason: Change Picture type

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    Moderator Gadget's Avatar
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    Herb,
    I have not run any speed tests on different thicknesses of metal. I imagine it would help but cutting metal for simply testing can get expensive. When I get some scrap, I will do some testing but that might be awhile.
    Dan
    Units owned Longevity PROmts 200
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    Force Cut LP80 plasma cutter
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    Home made CNC router/plasma/hot wire foam cutting, 3D printing table powered by Longevity Force Cut LP80
    Home built aluminum foundry, HF 4x6 bandsaw, O/A torch

  6. #6
    HerbD
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    Thanks

    Thanks Dan,

    I was hoping that you had already gotten some benchmarks while calibrating your CNC table. I've been practicing to familiarize myself with Mach 3 in anticipation of getting my milling machine conversion finished.

    Don't laugh, but I've been doing some dry runs trying to correlate my arm motion/speed over a measured distance to see what XX inches per minute (from the suggested chart) would feel like with the plasma torch in my hand. Let's see . . . 160 IPM should take me ??? seconds across a 12" piece of stainless?

    I've got the straight line and circle parts figured out, now I just need to get the height, amps, air pressure and torch speed.

    I'll share what I find out.

    HerbD

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    Moderator Gadget's Avatar
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    I have learned that too much heat will cause excessive slag. Also the faster you can cut the better the cut but as I said, no chart for different speeds/thicknesses yet. To be honest, I am still figuring everything out and am still experimenting.
    Dan
    Units owned Longevity PROmts 200
    Longevity WeldPro LS200PI (IGBT)
    Force Cut LP80 plasma cutter
    Longevity auto dark welding helmet

    Atlas 10x36" lathe
    Craftsman 5HP 30 Gal compressor
    Home made CNC router/plasma/hot wire foam cutting, 3D printing table powered by Longevity Force Cut LP80
    Home built aluminum foundry, HF 4x6 bandsaw, O/A torch

  8. #8
    HerbD
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    Heat

    Thanks again Dan,

    Hopefully Thursday I can sit down and make a bunch of test slices through some stainless cut offs I've accumulated. You are probably right about the heat. I tend to just crank up the amps when I cut through thicker materials and don't think much about tuning it down for thin sheets.

    HerbD

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    Member kb3gun's Avatar
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    I scrounged a small sheet of 3/16" today. Used a 1/2" high standoff. Found that 35A did the best cut from my machine (40D). Speed was a little over 12" a minute. Some slag but it busted right off with a tap from the hammer.
    Smitty -- Western PA, USA
    Hobart HH-187
    Longevity LP-40D Plasma
    My '66 FJ-40 Build Thread: http://forum.ih8mud.com/pa-appalachian- ... -fj40.html
    Appalachian Land Cruiser Assoc (ALCA)

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    Member woofer456's Avatar
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    Myth about plasma settings

    Hi Guys:
    During my time in the shipyard (40+ years) about 10 years were running a 300 amp CNC plasma cutter on a 10’ X 40’ water table, I have cut thousands of tons of steel, stainless and aluminum from 1/8” to 3/4" thick, I don’t think there is much need for setting the amps on these small torches, just turrn them on full and go, just changes the speed of your cut to accommodate different thicknesses, if you have different consumables you might test the differences between the large and the small tips… While I was running the 300 amp machine (other than making sure your tip is clean and not burnt out), the tip size, gas (air) pressure (we used nitrogen), speed of travel, and the height of the torch were the only things that were considered.
    I hope this clears up some of the controversy covering machine settings.
    Bob
    Last edited by woofer456; 05-11-2009 at 01:27 PM.
    Longevity WeldAll LS-200P
    250 amp Airco-matic Migit CAV II
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