Plasma Cutting Small Holes?

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I just got my first plasma cutter last week.  Like everyone else, I cut up a bunch of scrap metal to get a feel for it.  Over the weekend, I started working on an actual project with it, and everything went fine ( well, eventually, I learned about drag-cutting and electrode condition along the way ).   So far, so good.  Now, I need to cut a bunch of relatively small holes in 1/4" steel plate.  The holes are just under a half-inch in diameter.  If I had a drill press, I would use it for this... also my bits that are the right size are worn out, and won't cut butter.  I may just buy a drill press, but since I do have a plasma, I wouldn't mind using it.  The retaining cap on my SL60 torch is an inch wide, so the offset from the edge to the arc is 1/2".  The only way I can think to make a precise hole would be to take a piece of pipe with an ID of 1/2" + desired hole radius, and circle the torch inside it.  I think that'd work a) if I can find the right pipe size and b) figure out a way to secure it that won't interfere with the torch movement.   Is there an easy way to do this, or do I just need another tool?  Yeah, I know, any excuse to buy a tool is a good one, right?  I searched, but didn't find anything.   Thanks.__David Hillman
Reply:A; what are the holes for?B; could you tack the pipe to the surface? C; wouldn't it be better to get a pipe that was 1.25" ID so that the whole plasma torch head can fit inside, that way you're riding on the outside of the torch, and not next to your consumable?D; why can't you just sharpen your bits and use a hand drill?Option #1 use a hole saw in a piece of hardwood, soak in water over night. clamp board to surface and use the hole that was cut as the guide. this allows you to clamp away from the work area.There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:I too have a new plasma cutter and am studying how I can do some of this type of thing...1. You do not have to have metal for the jig to control where your torch goes... on Youtube several people use things like Masonite, plywood.... etc... for the puzzles I am going to make I am going to make Mesquite plywood...    The trick is that under the jig you relieve the form some with a router or something... to lessen the burning of the jig...You mention precise hole.... which to me really means drilling it.... extreme precision means drilling slightly undersized and reaming to final fit... I also suggest ... with no drill press and needing that size holes.... looking up an old fashioned item called a ' chain drill'.... which is sort of a portable blacksmith post drill... in that it self feeds ...and it can be clamped to lots of things out in the wild with the chain.... Why don't you learn to sharpen your drill bits ?I do not think you will want to cut with plasma and then drill the same hole... like to get the edge smooth... drill bits need to be in constant contact with relatively consistent material to cut nice clean round holes....If you were going to do that then the more proper machining process would be boring... which it does not sound like you have access to...Last edited by GBM; 09-26-2011 at 05:05 PM.Weldandpower Lincoln 225 AC,DC with Briggs 16hp gas engine.WW2 era Miller TIG.
Reply:Originally Posted by ThorsHammerA; what are the holes for?B; could you tack the pipe to the surface? C; wouldn't it be better to get a pipe that was 1.25" ID so that the whole plasma torch head can fit inside, that way you're riding on the outside of the torch, and not next to your consumable?D; why can't you just sharpen your bits and use a hand drill?Option #1 use a hole saw in a piece of hardwood, soak in water over night. clamp board to surface and use the hole that was cut as the guide. this allows you to clamp away from the work area.
Reply:Even a cheap arse DP would be a better way to go about this, heck a hand drill would be better.I can't believe you don't have a DPEd Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:Originally Posted by Broccoli1Even a cheap arse DP would be a better way to go about this, heck a hand drill would be better.I can't believe you don't have a DP
Reply:I have tried to plasma cut small holes.  For stuff that doesn't have to be all that accurate, it's not bad.  I have done it on 1/8" plates to mount casters to, since there was going to be bolts through them anyway.  But, like you, I need a drill press.  If you really want nicely finished holes, you really need to drill them.
Reply:You can plasma some really nice holes with a CNC table, even small ones. I've never had great luck with templates on smaller holes. They work, but the holes aren't any where near as nice as those drilled. Depending on where the holes need to be, a drill press often won't cut it with bigger projects however. You have to use the plasma, hand drill or if you are lucky enough to have access to one, a mag drill.The big advantage of using a template is that if you need to make repetitive parts, you usually get parts that are very close in size, even if they are not perfect. I can easily make a dozen brackets say with slightly  oversized holes ( saves having to go back and drill or ream them) that are all very close in size very quickly. I'd don't have to do a lot of time consuming layout on each as long as I account for the time to build the template and compensate for the offset.  6 weeks later I can crank out another batch that's again almost exactly like the originals if I make the template out of something that will last and save it. It's not machine tool tolerance like you can almost get with some CNC systems, but for "field" grade stuff it's a nice thing to have in your arsenal of tricks..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Be aware the plasma will leave a layer of hardened metal at the cut edge.  So once you cut the holes , you'll probably ruin a drill or reamer if you try to clean them up.Dynasty200DX w/coolmate1MM210MM VintageESAB miniarc161ltsLincoln AC225Victor O/A, Smith AW1ACutmaster 81IR 2475N7.5FPRage3Jancy USA1019" SBAEAD-200LE
Reply:you say a bunch of small holes...... if you have the measurements of where u want them. your best bet is to just lay them out. buy new drill bits. and drill by hand. it will be a pain. but alot better then u wishing you did if after u messed it up with the plasma cutter. and what "AndyA" says is right youll be kicking your self when u realize ur messing up more dill bits and reamers trying to clean it up then if you would have just tried drilling it in the first place.....for a welder/fabricator  a drill press is almost a "must have". even if u invest in a cheep one from home depot or sears and work your way up to a good American made one..
Reply:Best way is to grab some scrap and get after it. Everyone has their own favorite way anyhow. Plus that's the only way you're going to be able to say "been there, done that". No jig or template needed for practice shots, just freehand them. Draw some half inch circles and see how easy or hard it is. See if that's the way you really want to go. You're going to have to do it all sooner or later anyway, just as well dive in. "The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:There are some torch designs (all of the Hypertherm hand torches) that are made for drag and template cutting that work very well with guides, straight-edges and hole templates. I make them out of gauge steel.....or cardboard or plywood.....whatever is available.Air plasma cut edges will have a nitride hardening (based on the 80% nitrogen content in air and the heat input from the plasma). If you wish to drill out an air plasma cut hole...use a solid cobalt 42 drill. They are expensive compared to Home Depot drills.....but worth their cost with their long term performance...as well as the ability to be resharpened many times. Coated drills will lose their advantage if resharpened.Here is a picture of cnc air plasma cut holes on 1/4" plate, the smallest is 3/16" and the largest is 1-1/2". Also pictured is a bracket I made that needed a bunch of holes that were tapped 1/4"-20....these holes were all cut on my cnc plasma (Hypertherm Powermax45) to .187", then drilled to .201" with a cobalt drill, then tapped. The hardness (approx .005" thick) is removed by the drill so that normal tapping can occur.Jim Colt Attached Images
Reply:Very pretty Jim.... I have not determined if I need to hold my L-Tec 31 torch head off the surface of what I am cutting... so I am planning on making a ring around the head like the clamp on circle cutters to determine the standoff from the surface based on  my mesquite plywood templates....I really want to make some of those 3D puzzles like that T-Rex.Weldandpower Lincoln 225 AC,DC with Briggs 16hp gas engine.WW2 era Miller TIG.
Reply:Hey Dave Hillman,Geeeeezzzzzzus......if you have a number of 1/2" holes to drill, go get an inexpensive HF d/p & get them done. You can get a heavy duty bench or floor unit that can do 1/2" easily & HF is very good with refund or replacement if it quits. You are NOT going to get a clean 1/2" hole with a plasma unit unless, like Jim Colt, you invest $12K+ for a cnc plasma system. You can also pick up a good grinder & a Drill Doctor at HF & learn how to sharpen you drills. It's not hard to learn angle/rake grinding by hand also. I hand-sharpen all my drills & can alter the cutting parameters as to material if necessary. Don't be so rigid that you HAVE to have an older USA d/p to get the job done. Keep an eye on C/L & one will turn up eventually. There are many used d/p's here in my area of SW PA on C/L all the time. Get the job done first......Dennyhttp://www.harborfreight.com/garage-...ess-43378.htmlComplete Welding/Machine/Fab. ShopMobile UnitFinally retired*Moderator*"A man's word is his honor...without honor there is nothing.""Words are like bullets.... Once they leave your muzzle, you cannot get them back."
Reply:I agree....it will take a long time with a plasma torch if you include cleanup of the holes...unless you have a cnc. Drill presses are much cheaper.Jim Colt
Reply:I got a perfectly acceptable portable drill press... five speed...on CL the other day for $20 plus $7 for gasoline to go pick it up.   My nicer one at the front house near the metal lathe is so heavy I have to take it apart to move it.. so I do not move it... this one can be placed near my project and run off extension cord...   It is possible to shoot yourself and projects in the foot being too particular while saving for that ' nice' tool....Weldandpower Lincoln 225 AC,DC with Briggs 16hp gas engine.WW2 era Miller TIG.
Reply:Thanks guys.  Luckily, I'm not in a real rush to complete this project.  I realize I can buy a cheap Chinese drill press, but that just keeps them in business with my money, which is what I don't like doing, unless I have no choice.  In this case, I have a choice, and prefer not to give my money to people who do business the way China does.   That said, I have found something that should fit the bill, and then some.  Hope to pick it up tonight. Originally Posted by Sandy  Best way is to grab some scrap and get after it. Everyone has their own   favorite way anyhow. Plus that's the only way you're going to be able   to say "been there, done that". No jig or template needed for practice   shots, just freehand them. Draw some half inch circles and see how easy   or hard it is. See if that's the way you really want to go.   You're going to have to do it all sooner or later anyway, just as well   dive in.
Reply:Must be the "new generation" of welders."Got to have a plasma" before I get the other basic tools needed for metalworking.Don't get me wrong.  I love my plasma cutters (have two of them), but I was fabbing metal for 40 years before I got my first plasma.A drill press (even a cheap one), is a much better option for 1/2" holes than any hand held plasma cutter.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by SundownIIIMust be the "new generation" of welders."Got to have a plasma" before I get the other basic tools needed for metalworking.Don't get me wrong.  I love my plasma cutters (have two of them), but I was fabbing metal for 40 years before I got my first plasma.A drill press (even a cheap one), is a much better option for 1/2" holes than any hand held plasma cutter.
Reply:One problem with a hand drill is that if it is powerful and the drill bit catches on the metal... it spins the drill.... if line powered wrapping up the electrical cord around it... if battery powered may not be strong enough to do enough of these holes without stopping several times to recharge.. Even  a really cheap drill press does not have these problems....Weldandpower Lincoln 225 AC,DC with Briggs 16hp gas engine.WW2 era Miller TIG.
Reply:Good thing I'm not in a hurry... I now need to curl up with a good book.  The manual for my Shopsmith Mark V 510    I've always wanted one, and I have at least as many wood projects as metal projects on my list, and this one just popped up on Craigslist today.  I don't think I could've bought a 1 hp, 16" drill press for less... and that's ignoring all the other things it can do.  This one is older, but barely-used, and came with a ton of extras, to boot.   Thanks for the all help, now to crack the book and figure out how to use it all.  First I have to put it back together... had to disassemble most of it to make it light enough to unload by myself.__David Hillman
Reply:WOW David... you had a great day !!!   Those are super machines.  How much did you give for it ?Weldandpower Lincoln 225 AC,DC with Briggs 16hp gas engine.WW2 era Miller TIG.
Reply:I traded an ethernet cable, and $400 for it.  Boy it takes up a lot of room in vertical mode, though... less than a drill press, lathe, table saw, jointer, and borer would need, but it's not as small as I thought with the table hanging off one end.   I got it into drill press mode, and made about eight or ten of the holes for my next project this evening.  Works fine, although the table flexes some when drilling steel.  I might have to make a brace of some sort.  Could've done more, but I stopped to weld a couple pieces.   Now I have to re-plan my on-going garage/shop remodel, because I didn't have anything close to a spot for this piece.__David Hillman