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Learning how to build Lotus Seven replicas...together!
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PostPosted: Mon Jul 05, 2010 11:40 pm 
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ok i'm ready for a plasma cutter. after trying to cut some 3/8 plate for brackets on the 7 with the chop saw, then the band saw, then the chop saw, then an angle grinder with cut off wheels, then the band saw again. i'm ready for some power and quickness.

only problem is i dont want to electrocute myself. i can wire a car stereo and done a few outlets for the garage. re wired the 220v from 4 to 3 prong and not worried about being able to do the 7's wiring but i dont know about the PC. i dont want to get all :ack:
so any suggestions? should i just get some adult supervision or just study up on my electrical engineering and go for it??

and i was wondering how does it cut compared to just oxy/acyt torches? faster or slower, as much slag and sparks, how much material does it burn off? i really like the band saw for cutting compared to chop saws as they dont sacrifice as much material but sometimes is akward to make the right cut with.

thanks for the help and thanks for taking the time to post and share all the super cool info

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PostPosted: Tue Jul 06, 2010 1:58 am 
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lusiphur134 wrote:
ok i'm ready for a plasma cutter. after trying to cut some 3/8 plate for brackets on the 7 with the chop saw, then the band saw, then the chop saw, then an angle grinder with cut off wheels, then the band saw again. i'm ready for some power and quickness.

only problem is i dont want to electrocute myself. i can wire a car stereo and done a few outlets for the garage. re wired the 220v from 4 to 3 prong and not worried about being able to do the 7's wiring but i dont know about the PC. i dont want to get all :ack:
so any suggestions? should i just get some adult supervision or just study up on my electrical engineering and go for it??

and i was wondering how does it cut compared to just oxy/acyt torches? faster or slower, as much slag and sparks, how much material does it burn off? i really like the band saw for cutting compared to chop saws as they dont sacrifice as much material but sometimes is akward to make the right cut with.

thanks for the help and thanks for taking the time to post and share all the super cool info
OK.. lets go for the easy stuff first and work our way back!

1) How does it cut compared to a OA rig? Accuracy... No comparison. Plasma wins. Speed.. Close. OA will cut thicker materials faster, but use more gas doing it. 3/8 is the pushing the limit of this set-up. It will cut it, but I found I had to cheat a bit to get it to cut accurately and predictably. Simply drilling small pilot holes and changing the direction of some cuts was all it took.

2) Slag and Sparks? Both about the same, BUT... PC throws off molten metal in a fine spray. Less heat from a PC into the surrounding material. If set right (not over amped), you can handle the material seconds after the cut.

3) Adult Supervision? BY ALL MEANS!!! KB58 was not simply being too cautious. This is very easily a killer if not built or used right. In it's completed form (with Iso Transformer!!), it's fairly tame, but make no mistake.. touching the wrong part in the box while using it or while building it could wind up giving you a new nickname.. Stumpy.. or worse!

Lets get ready to rumble!!!!!!

This is a fairly typical OA cut. They can be cleaner, but it's not always easy. You can see the ragged edge before he starts from a previous cut. Look at the flame.. time.. excess heat... all that stuff that goes with it!


OK.. now here is a typical PC cut on what looks like a similar thickness... this is my machine. You see me using a metal guide. I've since began using a piece of wood simply because I can hold it and it won't short out the spark from the HV Arc. It only generates enough heat to burn it if your going VERY slow on 3/8 stuff. 1/8 or 1/4 it's fine!


And for the final kill shot... Look below.. I took this a few minutes ago for you. Try doing this with a OA... it can be done.. but it's not easy (and you'll never get to keep BOTH pieces!!). That is .125 and was cut in less than 30 seconds... and it's sitting on a piece of paper less than 30 seconds after it was cut. It was warm, but not so hot it burned the paper. Notice there is no color change to the metal?? Didn't even get hot enough to turn blue. That shows you your waste and ability to impress detail into your parts you cut.

PC is almost always the hands down winner. Things like power and air supply issues (remote location and need a compressor) and consumable requirements (OA tips last forever!) sway people back and forth.

Hope this helps you decide. BE SAFE ABOUT IT NO MATTER WHAT YOU DECIDE!!

If you need more info or would like to see it do something to help you decide... Let me know!

Thanks for the comments!!

KS


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PostPosted: Tue Jul 06, 2010 12:31 pm 
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botbasher wrote:
1)OA will cut thicker materials faster, but use more gas doing it.

3) Adult Supervision? BY ALL MEANS!!! KB58 was not simply being too cautious. This is very easily a killer if not built or used right. In it's completed form (with Iso Transformer!!), it's fairly tame, but make no mistake.. touching the wrong part in the box while using it or while building it could wind up giving you a new nickname.. Stumpy.. or worse!
KS


about the gas i see just compressed air works but what of other options. if a person uses either MIG or TIG gases this can be used as a TIG welder technically? albeit maybe closer to welding with OA torches but doable.
or does using other gas(than air) cut different or faster?

and i will procure some help in building then. i understand the ability of capacitors and how much one little car stereo style one holds for a charge, i cant imagine a whole bank of them with 220v going to it.

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90 talon as old dd turned into donor for the locost
06 suzuki sv1ks for the kneedragging fix

mitsu 4g63 powered 442e - viewtopic.php?f=35&t=7317&start=0


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PostPosted: Wed Jul 07, 2010 9:56 am 
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lusiphur134 wrote:
about the gas i see just compressed air works but what of other options. if a person uses either MIG or TIG gases this can be used as a TIG welder technically? albeit maybe closer to welding with OA torches but doable.
or does using other gas(than air) cut different or faster?
To cut thicker materials, you need more O/A CFM for 3/4 than you would for 3/8. PC, you simply turn up (or down) the air pressure. OA is more expensive to run in that respect. Other than the initial purchases to make the unit, I have spent a grand total of $13 for consumables and still have lots left, compared to the $53 to refill my pony-pack OA 14" bottles for my steel bending and used 1/3 of it!!! Quite a dramatic difference.

No, TIG and Plasma Cutters work on completely different levels. TIG uses low voltage high frequency AC or DC, where PCs use High Voltage DC only. I did a lot of searching and never ran across any MIG/TIG to PC conversions. Doesn't mean it doesn't exist though!

The only cross-over use I found was pointed out to me here. Using an ARC or gas less MIG as an Carbon Arc Welding/Gouging. You can check it out here. You still need a compressor and a capable supply, so it was not a cheaper alternative in my mind!

More food for thought.. Hope it helps!

KS

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PostPosted: Mon Oct 24, 2011 7:15 pm 
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Just postet this one http://www.youtube.com/user/cheaphardwarez in another plasma thread

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PostPosted: Mon Oct 24, 2011 8:44 pm 
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AceOfMace wrote:
Just postet this one http://www.youtube.com/user/cheaphardwarez in another plasma thread
DON"T BELIEVE THE HYPE!!!!

Yeah.. except that the diagram and instructions he supplies are bupkis! I got them and had it together only to find it wouldn't strike an arc. Tried hard, but just wouldn't cut! I inquired and was told that because I didn't use exactly the same parts he wouldn't help me (I've been playing with electronics since I was 8, with 4 years as a Rework Tech for TRW, so I knew this was BS!!). I figured he lifted the design from someone else and is passing it off as his own. There is no way that someone could "design" this and not know that a full wave rectifier can be built from separate components (not a single component) and is electrically the same as 4 diodes properly wired. Yes, he tried to tell me that!

I re-did the layout with everything the same as his design and guess what?? Yep.. No workie again!! So my EE friend and I went through it only to find some flaws with his "thinking" about how it should be done. When asked about these, he fumbled through and then eventually refused to answer any further emails. We corrected the issues with it and guess what? It works great!!

So, if you want his plans.. save your money and drop me a PM and I'll send them to you. They don't work as-is, so.... I'll even include the revised drawing that actually works at no extra charge!!

Cheers!

KS

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PostPosted: Mon Oct 24, 2011 8:55 pm 
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Location: Niagara Falls, ON.
Awesome!

How much air do these require? How much pressure and flow for how long? I've got a complicated electrical sitch and could either run the PSU or the compressor, so I'm wondering if any reasonably sized tank would give me say 5mins of cutting before I turn the compressor on again.

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PostPosted: Mon Oct 24, 2011 9:10 pm 
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RoadWarrior222 wrote:
Awesome!
How much air do these require? How much pressure and flow for how long? I've got a complicated electrical sitch and could either run the PSU or the compressor, so I'm wondering if any reasonably sized tank would give me say 5mins of cutting before I turn the compressor on again.
I typically ran my cuts at about 30-35 psi. I never took the time time to calculate flow rate, but the ESAB spec sheet (the tip I used) says they use 80 psi at 250 CFH (about 4 CFM).

But like I said.. I rarely used over 40psi. I did have to go up to around 55psi for cutting the 3/8", but I learned a trick to that too and was able to turn the air down to 38psi. 5 minutes is a lot of cutting... most cuts are a minute or two, except for the thicker ones!

Descent size tank.. sure, you could cut.. fill, cut fill... I had to do something similar! Just a lot longer between fills!

Cheers!

KS

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PostPosted: Mon Oct 24, 2011 9:41 pm 
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Thanks, yes, that sounds plenty doable, my 5 gallon portable tank lasts a reasonable while for "dusting" with the gun, regulated to 40 PSI, but you only get maybe 2 shots at 90... and the compressor has an 8 gallon on it.

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PostPosted: Tue Oct 25, 2011 10:20 am 
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RoadWarrior222 wrote:
Thanks, yes, that sounds plenty doable, my 5 gallon portable tank lasts a reasonable while for "dusting" with the gun, regulated to 40 PSI, but you only get maybe 2 shots at 90... and the compressor has an 8 gallon on it.
Heck.. Tie em both together and make 13gal from it! Did this one time to make a High Pressure bank (had 6 different sizes of bottles) and although ugly, it gave me the volume to do what I needed to!

You know what... thinking about it, you could make an interlock to run both of them without changing plugs.. if the Plasma Cutter is on, it cuts out the compressor.. and vise versa. That way, every time you stop cutting, the compressor will have the option to kick on if needed. The switch on the PC head that engages the contactor could be made to do that easily. Put a plug for your compressor ON the box that you build the PC into.. Plug the PC into the wall and the compressor into the box. That way, you'd never have to worry about blowing the breakers!

Good Luck!

KS

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PostPosted: Tue Oct 25, 2011 12:40 pm 
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Seems like a lot of work for something you can buy for around $250.00.

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PostPosted: Tue Oct 25, 2011 1:14 pm 
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Trochu wrote:
Seems like a lot of work for something you can buy for around $250.00.
Got a link? I found used Starfire units going for $3-400, but they needed work and parts likely to cost nearly that.

If you know where, let us know... I'd happily buy it with a warranty and a good supply of parts!

Cheers,

KS

P.s. Sometimes its not about the cost, but the knowledge. Building a Locost is a royal PITA, but we still do it, some for fun, some for knowledge even though kits are available, right?

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PostPosted: Tue Oct 25, 2011 1:56 pm 
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botbasher wrote:
Trochu wrote:
Seems like a lot of work for something you can buy for around $250.00.
Got a link? I found used Starfire units going for $3-400, but they needed work and parts likely to cost nearly that.

If you know where, let us know... I'd happily buy it with a warranty and a good supply of parts!

Cheers,

KS

P.s. Sometimes its not about the cost, but the knowledge. Building a Locost is a royal PITA, but we still do it, some for fun, some for knowledge even though kits are available, right?


There are about 150 units on e-bay for less than $300.00. Can't speak for the quality, but it would likely be better than one I built myself. Definitely true, if I just wanted a car, buying a used Neon would be cheaper than building one. I'm just stating, if your doing this to save money, there are likely better option. If you building a cutter for the experiance, knock yourself out.

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PostPosted: Tue Oct 25, 2011 2:07 pm 
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Trochu wrote:
Seems like a lot of work for something you can buy for around $250.00.


Well, I am truly a "Locoster", but I'm with Trochu on this one. He's right - plasma cutters can be bought for very low prices now. Granted, they are Chinese in origin, but one California retailer (for example) offers a 3-year parts & labor full warranty on their Lotos machines, full stock of parts and Consumables, US-made air/gas regulators, German-made (Siemens) electronics, and they claim to individually unpack, fully test, and re-pack every machine they get from China before shipping, to ensure it works. And if it doesn't, they claim to pay all shipping & handling charges to return it to them, and they'll replace it.

As one who has a healthy respect for electrickery (and an almost limitless lack of knowledge about electronics), and an almost complete lack of available funds, this seems like a pretty good bet... :cheers:

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PostPosted: Tue Oct 25, 2011 4:23 pm 
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This is all pretty fascinating stuff, and as an EE myself, the whole thing seems pretty doable.
But it does look potentially rather lethal the way it is, without any mains isolation........

So that has now got me thinking about the whole problem of a simple "Locost style" plasma power supply design.

Four requirements, FULL MAINS ISOLATION, constant dc output current, around 180 to 220 volts dc open circuit output voltage, adjustable output current, and a high voltage pilot arc supply.
All to be done on a "poverty" sized budget with old scrounged stuff.

What I will try soon, when I get some free time, is rewinding the secondary of an old buzz box stick welder I have here, and no longer use.
This should be ideal.
Fully mains isolated, an adjustable fairly constant output current, but the output voltage is far too low at only around an expected 50-75v.

So the trick would be to strip the secondary winding off the constant current (shunt magnetic gap) transformer, and rewind it with maybe about three times as many turns, with wire roughly one third the thickness.
Should be able to reach target voltage range easily enough.
The big vertical current setting rod that slides up and down on top, to set the output current, has markings on it indicating 20 Amps to 180 Amps. If I can get 6 Amps to 60 Amps for plasma cutting out of it after rewinding at just over 200v , that would be rather nice...

Of course it still needs an output bridge rectifier and a high voltage arc starting circuit, but it should do the job, be a lot safer, be FAR more power efficient, and cost very little as these ancient old stick welders go for scrap value these days.

Just sharing a few mental ramblings here, for some future experiments.
Before I rip into this old welder, I will measure some open circuit voltages, and load currents with various load resistors fitted, to characterize the transformer.
That should give me a very good basis for deciding how best to modify the secondary winding.

Thoughts anyone ?


Last edited by Warpspeed on Tue Oct 25, 2011 4:36 pm, edited 1 time in total.

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