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Spectrum 375

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  • Spectrum 375

    Hi all,

    Am about to buy the Spectrum 375 but was hoping to find a few things out first...

    Can I get away with using a 1 hp compressor rated at 4.5 cfm @90 psi with cut-in/cut-out pressures of 70 psi & 100 psi? I printed something from Miller's site that spec'd out air requirements for the compressor (5 cfm @ 90)and another for the torch (4.5 cfm @ 60). If I'm running at 60 psi, I figured I'd be ok, but I'm not sure why Miller had that additional compressor requirement.

    Can I use the auto darkening helmet that I use for arc welding for plasma cutting?

    Also, does plasma cutting produce alot more sparks than what you might expect during arc welding? I'm concerned about my neighbor's car which is parked only about 15 feet away. I do all of my metal working in my driveway.

    The plasma cutter would see little use. It would be only for hobby use. I'm just tired of wasting time cutting with the Sawzall and angle grinders. My cuts would primarily be of 1/4" thick steel plates.


  • #2
    Sounds like you're on a budget!

    Scrimping on an air compressor is usually a bad idea. Plasma requires lots of air and the more you try to cheat it, the warmer and more moist the air you feed it will be, which will also lead to shorter consumable life and reduced overall performance.

    I had a DeWalt/Emglo 2 "HP" 4-gal. unit on a Spectrum 375. The compressor ran at 100% duty while using the plasma. It CAN work.

    You can use your auto hood. You may find the the dark state is too dark. Some models stay in the clear (#3 or #4 or #5 usually) state while off and may be a good way to go. Since most of the arc is directed through to the bottom of the work, sometimes the hoods don't react to it anyway.

    The Spectrum 375 will cut 1/4", but not at its best quality level. But it will probably be sufficient. It was for me.


    • #3
      I ran my PowerMax 380 (same machine as the Spectrum) on a Porter Cable pancake compressor for a short time before I upgraded to a 60 gal. upright. It will work in a limited fashion. The compressor will run all the time. You may have problems maintaining the arc. And as MAC said the air quality will be poor.


      • #4

        I have the DeWalt D55155?? compressor and another 10 gal compressor. Even if I have to stop intermittently to let the 10 gal compressor recharge, then I think I'd be ok. This is for hobby use.

        Was curious though why MAC said the 375 would cut 1/4" ok but not the best. Any thoughts on upgrading to the next better plasma cutter? Miller's advertised cut for the 375 is 3/8", isn't it?

        I think the thickest material I ever had to cut was 3/8" thick angle, but mostly it's 1/4" steel. That's mostly what I find on the side of the road.


        • #5
          Originally posted by HiHo
          Was curious though why MAC said the 375 would cut 1/4" ok but not the best. Any thoughts on upgrading to the next better plasma cutter? Miller's advertised cut for the 375 is 3/8", isn't it?
          Oops, good catch. I haven't had that machine for so long I actually forgot. I was reading and typing "1/4" and thinking "1/2". That machine does very well with 1/4". You really only need to even think about upgrading if you know you need a bigger duty cycle.


          • #6
            Originally posted by MAC702
            Oops, good catch. I haven't had that machine for so long I actually forgot. I was reading and typing "1/4" and thinking "1/2". That machine does very well with 1/4". You really only need to even think about upgrading if you know you need a bigger duty cycle.

            Mac, you had me worried there for a moment, because my Hypertherm 380 has no problem with 1/4", and actually does quite well on 3/8" MS too.


            • #7

              cool, I just ordered the cutter today


              • #8
                yo yo ma

                I want to make an adapter to use my stock Spectrum 375 110V run off of 220V without cutting the stock cord. It's easy enough. All's I have to do it get: a 20A, 125V plug , about 1 foot of #12 stranded wire, and a 220V plug all with the right NEMA configuration. If I wire the adapter right, I think I'd be in good shape. This way, I can use it on both 110V and 220V circuits. I would just have to plug in the adapter when I want to use 220V

                Aside from the obvious fact that I have to make sure the switch behind the welder is on the right voltage setting, is there any other reason why I shouldn't to this?

                I just want to maintain portability. I have 220 in my garage, but everywere else I use this thing is 110V.

                Oh and by the way, I have no skill in plasma cutting. My cuts are so jagged that I spend alot of time at the grinder smooting things out. Freehanding these cuts is tough. How'd you guys do it? Jigs? Fences? Straight cuts seem to be the toughest.

                Last edited by HiHo; 07-07-2006, 07:41 PM.


                • #9
                  The trick to smoother freehand cuts is a steady hand and a fast travel speed. To get the fast travel speed you need a plasma cutter that is bigger than you need to cut the actual thickness.

                  For example, the Spectrum 375 is capable of a rated cut of 3/8" but you have to be good to do it smoothly freehand. If you had a Spectrum 625, you could do it much more quickly and more easily do it smoothly.

                  Of course, practice plays a part as well, but you see what helps.

                  Your adapter idea is fine. Just to clarify the terminology, the female end is a receptacle, not a plug, so you want a 20A 125V receptacle (NEMA 5-20R) on the cord and the appropriate 250V plug on the other end. Since you're going through all the trouble to make the adapter, feel free to make it longer and have an extension cord at the same time. I have tons of these adaptors for virtually any receptacle configuration I find. Some are short, the common ones are usually as long as whatever handy piece of scrap cord I had handy.


                  • #10
                    I went the other way with my 375, I replaced the coordset with 20' of #10 SOO and a 240V plug. Now when I get around to it I need to make a adapter from the old coordset to go back to 120V, so far I havn't needed to use 120V so the coord so the adapter still a future project.

                    I am using a Sanborn Blackmax that is 3hp with a 25 gal tank and puts out 8.5 at 60. While it works ok the problem is that after a few long cuts on 8 X 10 or 12 sheet the motor does a thermal shutdown and then it's 10-15 minutes before it will run again. Oh well, I wanted a bigger compressor anyway ... but for now it will have to wait as there are other priorities in the way.
                    Last edited by Sundown; 07-08-2006, 06:55 AM.
                    Regards, George

                    Hobart Handler 210 w/DP3035 - Great 240V small Mig
                    Hobart Handler 140 - Great 120V Mig
                    Hobart Handler EZ125 - IMO the best 120V Flux Core only machine

                    Miller Dynasty 200DX with cooler of my design, works for me
                    Miller Spectrum 375 - Nice Cutter


                    • #11
                      Spectrum 375

                      Hi Ho,

                      I think the machine you chose will work just fine for what you are using it for. This unit cuts 3/8" very well and can actually cut up to 5/8" if absolutely needed.
                      Regarding the air compressor, If you already own the small 1 hp compressor, it should work OK. A large tank would actually help out when using this small of a compressor. If you are shopping for a compressor, you would probably want to choose a larger one.
                      Air quality is actually more important than the size of the compressor. I recommend a good quality air dryer. When using a good air dryer the cutting performance is much better and your consumables will last much longer. Miller offers two such dryers that can be purchased at your local distributor.
                      Have a great day!

                      John Leisner
                      Product Manager
                      Miller Electric Mfg. Co.

                      Owner and user of:
                      Trailblazer 302 and Legend 301
                      Smith Dual Guard oxy-fuel system
                      Various borrowed Millermatics and Spectrums.


                      • #12

                        I glad you said that because my cuts have been terrible. I can't seem to keep a steady hand, there's alot of jagged metal probably from me not keeping the torch tip close enough to the metal, and I can't see what I'm doing with a #9 shade. I think the manual says I can go down to #3 or #4 or so for cutting provided i keep my head above the workpiece. Doesn't look like it came with a drag tip either. Have only cut 1/8" or so metal so far.


                        • #13
                          I have used a good wrap-around pair of sunglasses with UV protection and they work fine. About like a #5 lens.
                          Now I use a full face shield with #5 tinted lens and UV protection. A little pricey but works great. It gives the added protection needed when piercing a starter hole.
                          Of course, you can wear the glasses under a regular face shield too. Just one more item to put on though.


                          • #14

                            anybody out there use miller plasma cutters and live in Philadelphia, Pa?

                            Went to my local welding supplier and couldn't get any drag tips for my spectrum 375. In fact, they didn't really have any consummables for miller plasma cutters. Salesman told me that, although you'll find plenty of Miller welders, you won't find many places in this area that deal with Miller plasma cutters. He said Hypertherm is the most popular in this area. He even called a few of his buddy competitors as a courtesy and even those guys didn't have anything. This place is a pretty big operation so I kind of believe what he said.

                            Guess I'll have to settle for mail order. Funny - I see Miller welders all the time. Who'd a thought the plasma cutters are an exception in this area.


                            • #15
                              I don't think they make a drag tip for the 375. I've never seen one.
                              Just do some practice on some scrap and it will get better. Concentrate on uniformity in cutting speed and keeping the torch flame perpendicular to the workpiece. For straight edges on plate I usually cheat by clamping down a straight edge to ride against. I even used a old bearing race as a hole guide on a job and it worked great.
                              Just practice and it will get easier.