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jeepers
02-04-2010, 09:52 PM
I am making some 3" discs out of 1/2" plate. They don't have to be 3", just close. I have a sheet of 1/2 plate and I am cutting circles out with an oxy acetylene torch. I have tried to machine after letting it air cool and while it was still fairly warm. ( I have tried on lathe and mill). The steel has some very hard spots in it that will tear up an end mill or a HSS lathe bit in short order. Once I finally make it through those hard spots it machines fine. I know this is not the ideal way to do this, but it's what I have laying around. As you can tell, I am in no way a machinist. The machines I have to work with are an old round ram Bridgeport and a Craftsman(Atlas) 12x36 lathe. Any ideas on a way to make the steel easier to machine?

TGTool
02-04-2010, 09:59 PM
It sounds like you're getting some local hardening with the torch heat and rapid enough cooling. The solution would be to anneal them. If you've got a wood stove or fireplace, put them in the coals of a good hot fire, then let it burn down and out overnight. Basically, the steel should be brought up to transformation temperature (good red hot) and cooled slowly. You might be able to do it with the torch if you lay them on a bed of ashes for insulation, heat them up red, then cover them to cool overnight.

KINGWELD
02-04-2010, 09:59 PM
Grind ALL of the mill scale off. Flame cut steel is hard at the cut as you found out. Once you grind it ,it will cut quite well. Jim:)

gregl
02-04-2010, 10:04 PM
Kingweld is right. Get thee an angle grinder, Harbor Freight has 'em sometimes for $20, and take off the heat affected zone.

I also flame cut and have an Atlas lathe and this works just fine for me.

jeepers
02-04-2010, 10:06 PM
I have an angle grinder. I will try that. Thank to all for the replies.

jeremy13
02-04-2010, 10:31 PM
Carbide inserts work for me. Run at medium fast rpm and deep cut but slow feed. Try to cut under the torch cut part.

hojpoj
02-04-2010, 10:43 PM
Maybe try trepanning (sp?) the circles instead of torching them out.

4 Jaw chuck + Squarish plate + cutter = Round Disc

http://www.homemodelenginemachinist.com/index.php?topic=8167.0

gregl
02-04-2010, 10:44 PM
Jeremy13:

Keep in mind that the OP has an Atlas lathe, which has about as much mass as a 6-foot sub sandwich and ways that are about as rigid as a bamboo scaffold. A cut of even .050 at any speed is asking a lot from this light-duty machine. Turning a 3-inch dia. disk at a speed and feed appropriate for carbide would bog mine to a standstill.

digr
02-04-2010, 10:48 PM
If they don't have to be close just use a hole saw on the mill

lugnut
02-04-2010, 10:59 PM
Hey, gregl, you might want remember where you are "Home Shop Machinists" not a Big Pro machine shop forum. He has a bigger and better lathe than the average home shop has and just needs a litte friendly advice. Not cut down for his equipment. If you was half the machinist you think you are you would have a decent answer for him. If not your on the wrong site.:mad:
Mel

Willy
02-04-2010, 11:22 PM
What the others have said.
I usually drill a hole in the center for a bolt and nut, then stick the bolt into a drill, mount the drill between a couple of pieces of wood in a vise, and run at slow speed. With an angle grinder cutting the heat affected zone while the drill is spinning it hardly requires a visit to the lathe if dimensions are not critical.
If a through hole is not wanted simply tack a nut to the center of the disk, you can knock it off later.

camdigger
02-04-2010, 11:33 PM
What's worked for me (repeatedly) is Step 1. to use a circle cutter with the torch - this cuts down (no pun intended) on the amount of slag, etc you deal with in the next step. Step 2 is to use the angle grinder (or any other rough grinder) to remove all the cutting dross and slag down to clean steel, even if you have to grind a groove to get it all. An interrupted cut is easier on your tooling than the slag or cutting dross will be.

Then mount in the lathe and start the clean up. Your lathe will tell you how heavy a cut to take. The first few passes should be done wth light cuts and under fine power feed. The interrupted cut should "tick" rather than pound or slam. Patience in prep and machining is the key.

If there are hard spots after all the cutting dross is removed, then annealing as posted above is in order. Regardless, you will not regret the time spent with a grinder before taking to the lathe whether you have to anneal or not.

My $.02 cdn.

P.S. I'd post pics, but they're on a different computer, sigh.

Carld
02-05-2010, 12:02 AM
lugnut, your out of line with that statement because he is giving him honest advise. What good is it to lie to him and tell him he can do what his lathe probably can't.

gregl, is right, his lathe may not be able to cut .050" DOC to get under the hard part of the disc. What he needs to do is burn them out slightly oversize and grind the burned area away.

HSS tool bits get eat up by cutting torch surfaces and carbide is the best thing to use but you have to get under most of the surface burn. Using insert tools is not good because he would destroy to many inserts. the best thing is brazed carbide cutters and resharpen after each pass on a small lathe.

You don't have to run carbide fast, just not have interrupted cuts.

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What I want to know is how is he going to hold the 3" disc in a chuck and turn the outside of it? Has none of you seen the problem there? I have a way but it requires welding the disc to a stub shaft.
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Long ago I made an attachment to lay the cutting torch in with a point to set in a center punch in the center of what I want to burn. With that I can burn almost perfect circles when everything goes right. It's called a circle cutting attachment.

knedvecki
02-05-2010, 12:05 AM
Flame cut the circles bigger by .25 inch on the radius. Set your tool bit so that the front, leading, cutting edge is set at a negative rake angle, (tip trailing), and take a deep enough cut so that the tool tip is in the soft, (i.e. not flame hardened)part of the steel, using a slow spindle speed and hand feeding. This keeps the tip from getting buggered up by the hard spots which are better absorbed by the full leading edge. I use those cheap brazed cemented carbide tool bits in a C-5 grade, (Enco 3/8 X 3/8 X 2 1/2 @ about $1.50 each).

Black_Moons
02-05-2010, 12:11 AM
Agreed, Flamecut, Grind (Draw a circle on the part so you only grind whats needed) and then mill to perfection (If even needed! grinding to a line can get supriseingly accurate if a little bit of time is taken)

Just use the tip of the 1/4" grinding wheel like a cutting disk to do the roughing (higher angle = fast stock removal, 90 degrees = fastest), then use it at a less agressive angle to smooth it out once you get near the line.

PS: using a peice of stock as a clamp in the headstock(chuck), and a cover for your tailstock live center, can produce a 'disk clamp' as I like to call it, letting you turn material into a disk without welding to it or cutting into it or drilling it. I used it to make some UHMW cup coasters, One problem however is it has next to no drive torque, so anything more then thin cuts will stall the work (on plastic, it just stalled and would resume as soon as you removed the cutter, never flunge the work out, but that was a LIGHT peice of plastic, steel might get flunge out when you hit too high a cutting force, stay OUT OF LINE with the work, and maybe cover your ways!)
Good news is your passes are incredabley short length, and with the right tool you can turn left and right, so each pass is only seconds if your manualy carriage feeding (Not worth the time to flip the levers!)

Willy
02-05-2010, 12:14 AM
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What I want to know is how is he going to hold the 3" disc in a chuck and turn the outside of it? Has none of you seen the problem there? I have a way but it requires welding the disc to a stub shaft.
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Yes indeed Carl, it was the first thing that crossed my mind.
Although the OP did not state if the disks were to have a hole in the center or not, I assumed they would as he had already turned some on his lathe. And as my previous post mentioned, if no hole is wanted in the disk then it would be a simple procedure to tack on a nut which could easily be removed later.

Actually the procedure I outlined in using a drill, in post #11, was for many years my "lathe" of sorts. With a little practice and desperation, a guy could do some pretty decent fab work with a drill, angle grinder, and a file. LOL

Machinist-Guide
02-05-2010, 12:23 AM
My dad had a 12X36 Atlas when I was a kid. I learned to run a lathe on that machine. I would love to have it today.

Carld
02-05-2010, 12:25 AM
Yes, Willy that would work and a creative mind solves problems. We used to machine some pretty big burnouts by welding them to a piece of tubing or shaft and turning them as required mounted in a 4 jaw chuck.

One would be surprised how much four tack welds will hold against heavy machining. It always amazed me every time I did it.

Willy
02-05-2010, 12:32 AM
Carl, I'm not sure if it is a creative mind or a desperate one. But yes you are right, after desperation comes creativity.:D
How does that saying go...nessesity is the mother of invention.

darryl
02-05-2010, 12:33 AM
Hmm- is it time for a circle cutting attachment for the oa torch- or at least a guide hole jig to run the torch around inside of- like a router guide basically. The discs should come out as round as you can get them, then you need a turntable of some kind, maybe made from a stub axle assembly, or a wheel bearing hub. One speaker magnet to hold the discs on, and something to hold the angle grinder. No lathe work at all, just grind to a finish.

Jigs, jigs, and more jigs-

oldtiffie
02-05-2010, 02:31 AM
I am making some 3" discs out of 1/2" plate. They don't have to be 3", just close. I have a sheet of 1/2 plate and I am cutting circles out with an oxy acetylene torch. I have tried to machine after letting it air cool and while it was still fairly warm. ( I have tried on lathe and mill). The steel has some very hard spots in it that will tear up an end mill or a HSS lathe bit in short order. Once I finally make it through those hard spots it machines fine. I know this is not the ideal way to do this, but it's what I have laying around. As you can tell, I am in no way a machinist. The machines I have to work with are an old round ram Bridgeport and a Craftsman(Atlas) 12x36 lathe. Any ideas on a way to make the steel easier to machine?

Jeepers.

As you have an oxy-acet torch, you can use it for heating and annealing as well as cutting.

I'd suggest grinding off any scale where you are going to cut as "raw" steel cuts better than steel with scale, oil, paint and "gunk" on it.

Cut the disks as before either free-hand or preferably with a circular cutting guide (preferred - better). The guide can be as simple as a steel disk "template" cut so that the flame cuts about 1/4" or so larger than you need the finished job to be. It is very similar to using "guides" with a wood-working router.

The better the cut the less inclusions and "hard spots".

As soon as the part is cut cover it with dry fine sand or dry cement or even flour from the kitchen as it slows the cooling and hardening process.

When you have finished cutting - or preferably before you start cutting - build a small furnace out of dry clay (not cement or concrete) bricks - 1 brick thick is enough - with an open front and a small vent at the top - at the back. Have an extra brick or so as the furnace "door".

Put some fine dry sand over the "furnace" and heat the furnace with your OA torch - an LPG torch will do as well - slowly and when it looks bright red to white keep it there to "soak" for a few minutes, then close the "door".

Heat the previously cut disks individually until they get to red heat and start to "sweat" (looks like scale or scabs) and put them in the furnace as they are individually heated as that will boost the furnace and keep it hot.

As soon as all the disks are in the furnace - disks spread so that hot gases can circulate - re-heat the furnace ("door" included) and soak it for a few minutes and then close the door and cover it as required with more dry sand or cement and leave it "as is" for say 12 hours and then open the furnace and remove the disks.

Dust off the disks and give them a "go" with an angle-grinder - to remove grit and scale and any "snots" on the cut surface.

The disks should be OK to cut with a well-ground well-supported HSS tool bit.

Black_Moons
02-05-2010, 03:13 AM
Hmmm, lazy susan, serious magnet, Angle grinder, If done just right I bet you could get the angle grinder to rotate the work for you! then its just a matter of holding it ever so still as the work rotates around for you :P
Oldtiffie: Sounds great.. If you get your oxygen/actylene free!
Might I recommend trying to preheat the furness with propane insted? Even just a tiger torch or something would likey be good for the initial preheat, maybe with the O/A or just O/P used to bring it up to high temp afterwards.

oldtiffie
02-05-2010, 06:19 AM
Hmmm, lazy susan, serious magnet, Angle grinder, If done just right I bet you could get the angle grinder to rotate the work for you! then its just a matter of holding it ever so still as the work rotates around for you :P
Oldtiffie: Sounds great.. If you get your oxygen/actylene free!
Might I recommend trying to preheat the furness with propane insted? Even just a tiger torch or something would likey be good for the initial preheat, maybe with the O/A or just O/P used to bring it up to high temp afterwards.

I don't give a "rats" as regards O/A or LPG or any other consumable as that's just part of the cost of running a shop - same as electricity is.

I don't use too much more than I have to - but if I have to use it I do as I can't see the sense in grizzling about the cost.

I stuck to the OP's requirements.

If it were me, I'd have probably got it cut out of a selected plate from the rack in a local specialist metal-cutting firm near here - water, laser etc.

Depending on accuracy and finish requirements, a lot of the "off the cutter" finishes are remarkably good in many cases and - depending on the job - may not need any or much post-cutting machining.

Other than that, the 1/2" plate is at the limit of my plasma cutter - but it leaves hard edges as well - but better than oxy-acet - and much better as regards machinability.

Toolguy
02-05-2010, 11:21 AM
I would cut the disks out of plate on the mill with a regular or carbide tipped hole saw. Done that many times in steel,using a hole saw made for wood. Keep the spindle speed low, use lots of cutting oil. On the mill you may use the drill bit in the center or not, as required of the job. To turn the edge on the lathe, use the hole in the middle, or put a center drill in the middle, put the lathe jaws smaller than the OD you want to turn and hold the part tight against the end of the chuck jaws with the live center. Take light cuts till you get where you're going.

oldtiffie
02-05-2010, 03:31 PM
I have a circle cutting accessory for my OA cutting torch. It it very simple, effective and easily made. It uses the centre-punch mark used to mark out the hole. It has a roller/wheel to set and maintain the required torch to work distance as well.

I have a similar one for my plasma cutter.

I will see if I can find the time and remember to take and post a couple of pics later - or if I have them on my computer.

oldtiffie
02-05-2010, 10:55 PM
As promised, here are a couple of pics of my oxy-acet welding and cutting set and my plasma cutter.

My oxy-acet with the straight line roller guide fastened to the the nozzle on the cutting head. The circle cutter is lying on its side and is fitted to the cutter head as well.

http://i200.photobucket.com/albums/aa294/oldtiffie/Welders%20and%20air%20tools/Oxy-acet1.jpg


My portable oxy-acet kit:

http://i200.photobucket.com/albums/aa294/oldtiffie/Welders%20and%20air%20tools/Oxy-acet2.jpg


My plasma cutter with the "scraper" guide and distance-setting collar. The circle cutting guide is shown at the front. The straight line roller guide is mounted and is on the right.

http://i200.photobucket.com/albums/aa294/oldtiffie/Welders%20and%20air%20tools/Plasma-cut1.jpg


The circle and straight line attachment are mounted on the cutter head (remove a wheel as required). The "pick-up" on the radius bar are (from left to right): centre-punch; prick punch with knurled hand grip; and magnet.

http://i200.photobucket.com/albums/aa294/oldtiffie/Welders%20and%20air%20tools/Plasma-cut2.jpg

wierdscience
02-05-2010, 11:50 PM
Try leaning out your torch flame,too much on the rich side makes localized hardening worse.

oldtiffie
02-06-2010, 01:45 AM
I've dealt with the OP's proposal - I think.

The requirement is for 3" diameter x 1/2" thick discs made from hot-rolled steel.

Why has it got to be cut from plate? with all the "follow-on/up" works etc.

It might just as well be made from 3" hot-rolled bar and cut to say 5/8" length and just faced-off to length (thickness)? and "job done" - quicker, easier and cheaper and no hard wear and tear on the lathe and its tools?

I'd have it cut at my steel supplier.

Willy
02-06-2010, 08:31 AM
Jeez Tiffie I dunno, perhaps he has a piece of 1/2" plate laying around doing nothing, and wants to use it?
What would you do? Buy round stock, when you have 1/2' plate, a torch, and lathe at your disposal?
I'm almost positive that if he had a piece of 3" round stock laying around he probably would have used it, don't ya think?

Black_Moons
02-06-2010, 09:04 AM
My local steel supplyer stops around 2 1/2" :( I did however snag an awsome 14" chunk of 3 1/4" HRS for $20 (At least I think its hot rolled.. kinda odd slick black scale on it) for cheap as it was the end of the bar they had and the end was all bashed to hell, perfict for a project where I needed to turn down a major section of it anyway.

Sarbatche
02-06-2010, 10:21 AM
Grind ALL of the mill scale off. Flame cut steel is hard at the cut as you found out. Once you grind it ,it will cut quite well. Jim:)

We get a lot of plasma cut plate on the ship for big jobs. Sometimes it's easiest to try and cut past the hardened edges but usually we hit the edges with a grinder (angle or pedestal).

gregl
02-06-2010, 10:51 AM
Hey, gregl, you might want remember where you are "Home Shop Machinists" not a Big Pro machine shop forum. He has a bigger and better lathe than the average home shop has and just needs a litte friendly advice. Not cut down for his equipment. If you was half the machinist you think you are you would have a decent answer for him. If not your on the wrong site.:mad:
Mel



Hey Lugnut:

There was no intent to offend. I know full well the forum we are on. If you will scroll up you’ll see that I was the third person to respond to his query and I did provide a decent, polite and friendly answer for him about how I solved the exact same problem also using an Atlas lathe.

My second response was to the suggestion by someone else that the OP use a heavy cut with carbide, which will be difficult if not impossible considering the capabilities of the Atlas lathe.

I didn't make it clear in my second post that I also have an Atlas lathe and have used it for some 20 plus years and share the frustrations with it that many other owners have. I have turned parts to an accuracy of .0001 with it, but not easily, and I am fully aware that it's the operator who counts for much more than the machine itself. But, as a long-time Atlas owner, I still consider the machine about as sturdy as a willow in the wind and that a heavy cut with carbide will probably take the machine beyond its capabilities.

Your personal insult regarding my machining skills was uncalled for. Besides, I have already insulted my skills. See my sig line.

darryl
02-07-2010, 05:11 PM
Something I just thought of now, and OT just presented the idea a couple posts above- why not just have a shop cut a number of discs for you from solid bar.

I've struggled with this a couple times, but when my senses returned, I found it cost effective to pay the shop a cutting fee per cut, and it would be cheaper anyway than paying for gasses and spending time coming up with mechanisms for the O/A torch. For larger discs, yes use the torch and a circle cutting jig. For three inch and smaller, a shops bandsaw can make pretty short work of supplying you with discs- and no hardened layer to deal with. Save the plate for another use.

That reminds me, I have a project in the works where I needed some solid discs- I have them in a bag somewhere-

Carld
02-07-2010, 05:21 PM
jeepers last post was #5 on 2/4 and I guess he has gone to bigger and better things.

Your idea works if you don't need a smooth surface on the disc faces and if you do then you would have to machine the faces. The problem with that is keeping the OD square to the face and with both faces saw cut it's near impossible to indicate them in.

It just depends on the finish requirements of the parts. If they do a good job of squaring the saw cut then the saw cut is a good way.

Be sure to tell them they have to be a square cut.

Your Old Dog
02-07-2010, 08:57 PM
Tiff, thanks for taking the time to post the pics of the burning outfit accessories. That would sure make life easier for me if that was in my burning outfits box :D

Weston Bye
02-08-2010, 02:25 PM
Try leaning out your torch flame,too much on the rich side makes localized hardening worse.

Wierd may have nailed it. A rich flame has an excess of carbon and some of this carbon may be migrating into the steel at the margins of the cut, allowing the steel to be hardened due to rapid cooling by the surrounding cold material.

A test, performing comparable cuts in the same material with an O/A, both rich and lean mixture, and a plasma torch would be interesting. Anybody so equipped and game?

madokie
02-10-2010, 06:21 AM
if your cutting a lot of disks,and you dont have plasma cutter,you could get one of thoses GASOLINE POWERED CUTTING TORCH.it seems the chinese are bringing back and old idea from the 1950's, it cutts a lot cleaner with almost no slag,straight thick cutting capability. and cheap to run.plenty of video on u-tube.i worked in a shop we did a lot of flame cut disks, we just put in lathe and cut with carbide, slow time wasting ,but they didnt want added mess from angle grinders in machine shop area,and wouldnt let us do it anywhere else in shop.