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View Full Version : I hate idiots with plasma cutters



spope14
10-24-2002, 05:08 PM
My shop war story of the year thus far. A teacher in the locl High school sends a plate up to me to mill square and with steps and a profile - all 90 degree angles. he gives the stuent a piece of metal - whatever it is, and decides to help me by Plasma cutting this plate to within .500 of the lines. So far so good.

Problem is this. The plate is D-2 Tool steel we got by a bulk from a tool steel company - the kid absconded it from me while I was gone one day, thus irritating me right off at the first - the teacher came in with him, seeing me not there, took the liberty to take a plate that is probably 10 x 10 and slicing it to 6 x 4 - 1/2 thick. We have a liberal agreement, but we usually check first - he deals with 1018 normally.....

Second problem - they cut this material, and dipped it in water right off "for safety" 0- which hardened the living hell out of the cut line......

Third problem - NOTHING I HAVE CAN CUT IT - regular carbides, some Tin coat carbides run slow - nothing gets through the cut slag, and my perserving studen in my class trying to help has burned out six end mills thus far to remove about .030 on one edge. I finally sent it back, and said "figure a way to anneal it, this is tool steel you took, and you can figure this one out...." -= but the educational world does not persecute kids for the follies of adults.....

How would I cut this is my question? I know my feeds and speeds, know this one is coming back, and can see this being a problem tossed back to me for the immediate future.

This one tops the kid who tossed little 3/8 diameter x 1/4 length cut off ends in a 740 RPM moving chuck to see how far they would go. The third one - the first I saw - went ten feet, or right beside me. That student is now enrolled in study hall.....

Dr. Rob
10-24-2002, 05:24 PM
I have a feeling my head will roll for saying it, but an angle grinder, patience and a guilty party to do the work, will accomplish a good deal.

Sorry for asking, but what happens if you reheat it and let it cool slowly? (Clamp it down of course, so it doesn't warp & twist)

Forrest Addy
10-24-2002, 06:08 PM
Anneal it. It's small enough to go in a ceramic kiln. Pick a day when yu'll be hanging around doing other things. Heat it up to 1400 under a pile of charcoal briquettes (to retard scaling) and lower the temp about 100 degrees per hour till it gets about 600 and then shut off the kiln.

Treven Baker
10-24-2002, 09:14 PM
OK here is my story about the plasma cutter. I wanted some big washers so I took a piece of 3/16 plate and free hand cut a couple of discs. I then chucked them up and drilled a 1/2" hole through the middle. I then put them on a half inch bolt with a nut to snug them on and chucked them up so I could round up the outside diameter. Well the slag was so hard nothing would cut it. I put in one of my surpluss carbide cutters and turned the lathe speed up fast and started cutting deep so as to cut under the slag. The chips cam off bright yellow and as I poured on the water saturated cutting oil I use (came out of the old forklift when I changed the hydrolic oil) it flashed into flames immediatly. It worked and I had nice big round washers when I was done. It was like a pyrotecnics show! I wish I knew a little more about slag. It seems to be really hard stuff even when I use OXY ACC. I even have a hard time grinding it off sometimes.
I have two lathes; one is an old timer that is a little worn for the above rough work and a nice tight one for accurate work. In my area of California the practically give older lathes away at the machine shop auctions and if you have room they are nice for rougher projects.

Stepside
10-25-2002, 11:43 AM
spope

You are a man of great patience--- I would have thrown the piece of steel in the trash--had a great yelling fit and then sent him to the store for the correct material. Why should you tear up your gear for his stupidity and cheapness? Is he going to replace your cutters?
Actually I would have sent him for the right material and turned it into a learning situation with the student and my students--Sometimes I feel like doing the other. I seems there are a lot of "I can't do poop, but you can do it for me for free on your time, within my timelines" teachers out there. Sorry about the rant and rave but I feel better and I hope you know that a lot of us appreciate what you are doing.

Pete

halfnut
10-25-2002, 03:23 PM
Might just hang it on wall as a reminder for other idiots of what not to do.

But if you need the steel you need to anneal it.

My book say to heat to 1550/1600 deg in nuetral packing or controlled atmospere furnace and cool at rate of not more than 20deg per hour down to black.

600 deg at 20 per hour, thats 30 hours.

I'd probably wrap with heavy brown paper, then tool wrap. Bring up to 1600 deg. turn off oven and let cool in oven. Hope for the best.

Be a good piece to play with the EDM with if you had an EDM.

GEE WIZZ

Thrud
10-26-2002, 10:04 PM
SPope
Can you cut the kerf off with a bandsaw say 1/2" off to one side? Problem with using an angle grinder is the ground surface will be as hard as the slag.

If this does not work you could try a diamond saw with LOTS of water to keep the D-2 cool. Diamond burrs of a blade could avoid this, but it be best to keep the plate cooled in water. A diamond masonary saw (about $20/blade) may be able to cut it but I doubt it as the concentration of diamond is nominal on this saws. You can take a bronze disc and imbed diamond grit in the circumference with a hardened roller (I use a bearing on a handle) it can then be nickel plated or used as is. Diamond grit is not expensive, although the larger grit like 60 cost around $25/100carat wt. Diamond cut-off wheels are available for cold cut saws (great for Aluminum). I use 1-1/2" Diamond wheels to hack off chucnks from surplus T-15 2" endmills (scrap) with my 1/4 hp Foredom flexshaft.

CBN or Cermet inserts (if you have a machine ridgid enough) could machine this off, but the cost is more than the steel.

Alternately let the shop class replace it with a new piece of D-2 and make sure der komendant chews his butt out.

spope14
10-27-2002, 02:30 PM
Figured this one out. Got a piece of 1018 and did the job right. Seems this student was making a part for a trailer hitch for the instructor. I sent him out and he got the metal - the instructor that is.

I don't mind machining things for others, but hate being sandbagged.

Took the old metal, did an annealing job on the edges with a torch - heat blue, and such many times over. Got the slag off patiently with a hand grinder first - I think the slag was a big part of the issue.

I then cut it off with a real good carbide insert end mill until workable again.

I use quite a bit of tool steels for my jig and fixture design aspects of my course - something not normally taught in HS, thus my beiong a bit more than peeved by this all. Each year I come up with some new first year projects, and the second year students and independent study students make the fixturing and jigging for the projects, as well as re-engineer and set the processes for the first year troops.

The tool steel company sent me a new piece of this steel - donation. I called for a price, it is on the way as a donation.

Thrud
10-27-2002, 11:14 PM
spope14:
A beautiful ending to an ugly story - I'm all weepy eyed - sniff, sniff! http://bbs.homeshopmachinist.net//biggrin.gif

spope14
10-29-2002, 09:31 PM
Wish I were weepy eyed about it. Twas a good ending, but the whole circumstance reminded me of a show called "MONK", or at very least CSI.

Cut the plate today, used much of the advice from this page. Cut somewhat nice, bit of a grunt overall, but worked.

I hate it when a problem stumps "the great metal genius of the High School", but love it when I win one.....

But then again, I is not a genius, I just know whom and where to ask for advice, the HSM board!!!!!!!!

Thrud
10-30-2002, 03:11 AM
spope14:
I have never met a person that was not a genius at doing something. It is a sad thing that most never recognize this in themselves or others. Children with Down's syndrome amaze me - if kids with an IQ of 58 can handle life so well and with a smile on their faces, there is hope even for the rest of us. Unless of course, you really want to appear on Jerry Springer... http://bbs.homeshopmachinist.net//biggrin.gif (I would worry then)

[This message has been edited by Thrud (edited 10-30-2002).]

Dr. Rob
10-30-2002, 10:21 AM
Spope, I was reminded of high school days. Ever heard this one?:

So, my bud and I are in Metal shop class, messing around and not doing our assignment, which was a bent & rolled flatbar coat hanger. Instead, we were making bike parts or ninja throwing stars or somethin'.
Time is running out...We're supposed to be finished in ten minutes...And my friend has an idea to save us! He walks on over to the display case, pilfers the displayed coathanger made perfectly by the shop teacher himself, and dirties it a little. Writes my name on it, and dares me to go hand it in for grading! I do it, and score a B. Right on...So we erase my name, add his, and do it again...and he scores a C!!

What the hell!!! Now he took the C, since he wasn't so dumb as to complain. The teacher, on the other hand, wasn't too clever. This is a true story!! I'm Rob, my bud was Craig, and the teacher was J. True!!

Really, we had a lot of stories about that guy, but this is enough for now.

spope14
10-30-2002, 04:13 PM
Had a kid make a BONG (smoking of illegal materials item for those who are going wha....). Did one heck of a job on it. Bored a 2 inch hole right on the money for nine inches, leaving a .100 wall around. Figured the angles, fits, base materials, the whole nine yards. Problem is, the project had to be turned in to the authorities, or properly disposed of. The assembly was dismantled afterwards, the bowls were melted down, the base removed. It made a great clean up "GONG" for three years until I finally dosposed of it. Brazed the holes.......

The kid thought he was sneaky, but late on, the project started to take the wrong shape. It was supposed to be a bearing for a tractor or something, but the added holes kind of clued me in and the added parts also did the trick. I kind of had an inkling anyway from the start....no tractor part gathers so much "class interest"

gave the kid an "A" for the job of the boring, fits, and such, but also a letter in his file for referral in case of future incidents. This was in 1993. The "kid" lasted three years with me, 2 1/2 years after this. Removed the letter fronm his record of mine, we burned it in the heat treat furnace as he was also honored as the student of the year for the second time in three years, this burning in his final year. The "kid" is now the head of apprentices at a local shop, and a part of my "advisory committee".

Just a chance. Bottom line, I do not support drugs, do not allow this in my class, but have a way to deal with this in each case (like the time I cut a small bong just started into 1/16" wafers). Had a cannon once that a student wanted to make a firing unit, I "accidently" broke off a carbide drill (1/8") about 2" long in the barrell (already burned out drill). Used to make these as paper weights (3 inch length limit)until school issues and laws changed (1995 I changed this project). The teachers loved it, as did the parents, very detailed. Used to limit holes to 1/4 inch deep, and the rule was that one night I would take the item and make it un machinable in the bore. Had 300 1/16" dull carbide dills from a company I used to break off in the bore.

Thrud
10-31-2002, 01:17 AM
spope14:
So, I suppose paintball guns and toilet paper bazookas are not encouraged even with parental permission? I do not see why that would be a problem if the parents sign a waiver. I have seen some beautiful paintball guns made - they should be cronographed to make sure they do not exceed State, Provincial, or Federal regulations though. Water cannons would be cool too, never built one of those.

This would be more fun than the file, file, file, - Mr. Jenn! - Whack! - better file that divot out, eh. But I liked that in a sick, demented kind of way(now...). I have a great deal of respect for files at least... http://bbs.homeshopmachinist.net//smile.gif

So to all you shop teachers out there - thanks for putting up with boneheads like me! http://bbs.homeshopmachinist.net//biggrin.gif

Dr. Rob
10-31-2002, 03:35 PM
Yeah, and like me...
School daze...Next year, Metal Shop class again. Hum dee dum what to do today? No, not the boring ol' class assignment...(Psst! Hey, Scott! meet me by the drill press when Teach ain't lookin'! We'll sneak out and smoke a big ol' spliff in the john!) And sure enough, out we went.
We had a new teacher that year; a sharp-eyed rascal. He didn't miss that play. We were just about to spark up that Cohiba with the handy oxygen lance when, KA-BAM the door flew open. And guess who...Teach. Standing there like John Wayne entering a saloon. "You two- Get back to class." was all he said. And took the club from Scott. I guess we knew a good thing when we saw it, cuz man, back to class we went. And chips, elbow grease and sawdust flew.
We never did hear about it again, and he didn't seem to hold it against us. Maybe he knew, boys'll be boys. Or he knew the power of silence.
Funny though, he seemed really tired and droopy-eyed the next morning.

Ah, well...School daze indeed. Time goes by. Teach is probably retired, Scott died a couple of years later, and I'm still in Metal Shop. Maybe years from now I'll become a teacher or a Teach, and learn something new.

trap
11-02-2002, 12:01 AM
My how things have changed since I went to school. We just made knives and zip guns, but maybe i went to a different school than most.

docsteve66
11-02-2002, 12:51 AM
Naw trap, I went to lots of schools, changed several times a year. not a year in oneschool in one state. Every school a while back made zip guns with .22 's. And they think of gun control! Some zip guns were nice, some were mainly tape, pipe and a spring. the tape jobs were made by the types who would problay use them.
Steve

Thrud
11-03-2002, 01:21 AM
Steve
Reminds of of "Donald & Ronald". Two idots if there ever was. The optional science class I was in required us to come up with our own projects. These two knobs decided it would be fun to make black powder. They made up about ten pounds of real black powder. They even cast concrete blocks with milk carton cavities to hold the powder, NiCr wire "fuse", placed it in a snow bank outside the window of the class room and were getting the power supply from the supply room when I told the Assistant principle (the class teacher, BTW) that they were about to detonate their "bomb". They later blew something up in the only vacuum bell jar the school had destroying it.

As an encore, the last day of school Ronald rammed Donald's head into the gym door. It broke instantly - the door that is (2" solid hardwood). These guys gave a bad name to "morons".

Stepside
11-03-2002, 12:04 PM
After 37 years of teaching you would think I had seen it all. Never had one make black powder. For awhile they were trying to make "throwing stars" only they said they were "Christmas ornaments". The other one has always been "scale model baseball bats" which end up under the car seat as a weapon.
Friday was one of the days that keep me working-- every student on task, every student enjoying learning something new ect. I went home just totally pumped up. Wow getting paid to play what a deal.

Since I have your attention--- One of our locals burned up two trucks, his house and some of himself--- He was "siphoning" gasoline with a shop-vac. I worked okay for the first canister full, but when he turned it on for the second load things went a bit sidways. Probably will sue Sears because the brushes arced in the motor. From what was left, I doubt they will honor the service contract on the vacuum.

spope14
11-03-2002, 03:16 PM
Hey Thrud, I do allow paintball gun barrells, and the parents DO sign a waiver. The kids think this will be an "easy slide" of a project, but by the time I get done with the little buggers, they think otherwise.

The toilet paper bazookas, never heard of those, maybe like a pototo gun. The plummin teacher and i made one of those, super powered it beyond reason and common sense, and we could blow a tater about 500 yards uphill on the mtn beside the school. Seems many of them disintegrated at about the 200 yard mark (mashed taters) as after about 20 pounds of these it looked a bit like snow up there.....

We found a few of the rotten ones up the mtn a few days later when we lead a football team run up the mtn. which is hiow we got the 500 yard didstance coordinates......

One has to realize that a shop teacher MUST experiment now and then (or as one kid said to us shop teachers, do you do this to keep from growing up?????)

Dr. Rob
11-03-2002, 05:10 PM
I'm diggin' this, man. What a great thread.

Sprocket
11-03-2002, 09:52 PM
Spope14 - that's a line I've used on my kids, "Just because I get older, it doesn't mean I have to grow up!" I can't remember who said "We don't stop playing when we get old, we get old when we stop playing." but I believe it.

Thrud
11-03-2002, 11:10 PM
spope14:

Toilet paper bazooka just fires a roll of TP a few hundred ya..I mean feet. You first have to get the roll started so it unravels in midair. They have a light (hollow) large piston that stops on an o-ring bumper in the bore. Carbon Dioxide fire extinguishers are often the gas source feeding a large expansion chamber. A 2" butterfly valve between the chamber and piston is the "trigger". The rolls usually will unwrap in trajectory leaving a TP streamer in its wake. The design is just a smaller version of the "pumpkin chuckers". Carnuba wax in the bore adds a nice little extra Oompf to the trip! http://bbs.homeshopmachinist.net//biggrin.gif

I understand "Junk Yard Wars" is going to have a full auto Golf ball launcher mounted on cars next episode. I guess they pelt targets - seems to me you could raise more havoc on the back 9 with one... http://bbs.homeshopmachinist.net//biggrin.gif

mnadeja
11-04-2002, 02:40 PM
spope14,
What school do you teach at? It sounds exactly like the one in Western Pennsylvania that I went to! I guess they are all the same. The ones that want to will learn, but some will end up just as stupid as when they started.