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dshinn
10-13-2005, 12:09 AM
Greetings group. I'm new here, and far from an accomplished machinist. Just an old retired guy that likes to make things.

I recently became fascinated with metal spinning and have learned to form a blank onto a mandrel with less than 30% failure rate, way down from the original 75-80%. So, now that I'm becoming so down right proficient I find I need a way to cut circles quickly and efficiently for use as spinning blanks.

At one time a tool called a 'circle shear' was readily available from more than one mfr of spinning equipment, but these things are few and far between and when you do see one on eBay, they go for lots of money. There are also lots of designs, suggestions, plans and advice on making one around the web, many of which I've studied, thus I've come to the conclusion that since time is on my side, I can make one of these things. The rub is ....

The cutters need to be fairly hard steel. High carbon steel would probably be OK for moderate use on non ferrous materials like light ga copper and softer alloys of aluminum, but eventually I'll probably decide to risk spinning some ferrous sheet metal as well. So I suspect the cutters need to be pretty hard.

Picture a can opener on steroids is the best way to describe the cutter action on these things. I suspect a diameter or 1 - 1 1/2" with the outter perimeter turned to a slight slope on one or both(?) of the cutter wheels.

It was suggested to me in another forum that dumpster diving in a junk store for an old hydraulic cylinder would yield a solid shaft of some pretty hard material. Annealed to workable hardness in my lathe for machining, then heat & quench to restore the hardness. I've also read about case hardening which I understand involves applying some sort of powder material to the heated material. And/or flame hardening with soot from my torch.

Sorry for the lengthy post , - thanks for any advise and guidance

bobbybeef
10-13-2005, 12:51 AM
I use bimetal circle cutters. They do a good job and provide good circles. If you have a small milling machine you can set them up and delete the centre drill bit and get a complete circle without a hole in the centre. Bimetal will work on all metals. But I dont know about spinning other than brass. You can get a range of sizes. The ones I have are made in USA.BLU-MOL bi metal hole saws.Made by Greenfield Industrial Saw blades. Evans,GA 30809.The box they came in had enough data for use on speed and feed.Like a 3and5/8th"hole saw in tool SS should spin at 45rpm. In Brass 120rpm. My biggest is 31/2"but the box suggests that they go up to 6"dia. Maybe I got that interpretation wrong. a phone call ought to sort it anyway.
hope this is some help.
bobby.

david_r
10-13-2005, 01:59 AM
dshinn,
Hydraulic rod is 1045 steel. You may not need to anneal it unless you happen upon an induction hardened piece -- you'll know it if you do. It'll harden just fine.

I don't think case hardening is the way to go for cutters. You'll need to stone them after heat treat and you may wear through the case while doing that or resharpening them.

dshinn
10-13-2005, 02:21 AM
<font face="Verdana, Arial" size="2">Originally posted by bobbybeef:
I use bimetal circle cutters. </font>

Bobby-

My circles need to be in excess of 10" for the spinning I'm doing. I wonder how safe (unsafe) a home made fly cutter would be for something like this?? The only way I've been getting 'circles' up to the present is to cut them out with snips, mount them on the lathe then spin a bit onto the mandrel then trim true. This works but is a lot slower and sloppier than it really has to be.

dshinn
10-13-2005, 02:23 AM
<font face="Verdana, Arial" size="2">Originally posted by david_r:
dshinn,
Hydraulic rod is 1045 steel....</font>

That, then, would be sufficiently hard for the type of cutting I'm anticipating? I don't know a great deal (obviously) about steel and its alloys.

uute
10-13-2005, 02:38 AM
Could you make a set up to carry a tool bit or piece of High Speed Steel rod, w/ cutter ground on end?

phil burman
10-13-2005, 02:39 AM
I'm not sure a case hardened cutter is the way to go. It might be OK for wear but it of course will not support the same load without deformation and blunting of the cutting edge. I've never hear of case hardening cutters before.

A piece of silver steel from your local metal supplier would probably be the best way to go. Most would class this as the "standard" method.

Regards
Phil

Norman Warfield
10-13-2005, 08:08 AM
I have made sheet metal "blank" cutters by using a home made hole saw.I have done 11" blanks with this method.

Using an aluminum or mild steel 1/2" thick base. Cutting a groove in the base that will hold bandsaw blade stock to the thickness or the blade and diameter of the blank you need.

Drilling and tapping a series of perpendicular holes around the perimeter to hold the "blade" in the groove leaving it protrude to what ever I chose by cutting the depth of the slot to my preference.

in this you may cut a number of "blank" sizes in the one disk as long as you can leave enough stock between sizes to drill and tap the holding screws in from the side.

It is handy however; to have someone a band saw blade welder accessible for welding the blades in a circle.

I hope perhaps this can help.




------------------
Norm'
If it's not broken, why do I keep trying to fix it....

JCHannum
10-13-2005, 08:11 AM
I would second using what we in the US call drill rod. It is hardenable roundstock that is used to make drills & other tooling. It is readily available from most tool suppliers in a wide range of sizes.

The downside is it is usually only available in 36" lengths. But then you would have plenty to experiment with.

Your Old Dog
10-13-2005, 08:40 AM
If I needed some perfect circles I'd use a flycutter in a drill press. I'd start with square sheet metal piece, clamp it in the corners and cut out the center using a flycutter mounted in the drill press. I'd have something like masonite or hardboard under so as not to damage the drill press table.

Don't think I'd want to make mass quantities this way but by facing the cutter right, you can cut 2 or 3 at a time

(most flycutters for drill presses let you remove the centering drill bit with an allen screw)

My way of doing it is only good for 6 inch or smaller but is infinitely adjustable. Norman Warfields idea should work pretty neat for much larger sizes.

[This message has been edited by Your Old Dog (edited 10-13-2005).]

Swarf&Sparks
10-13-2005, 08:47 AM
How about a cheapo 'hobby' bandsaw with centreless circle cutting jig. Just 2 thrust bearings, top and bottom with a disc of friction material on each and some sort of clamping arrangement. Highfield lever or eccentric is quick and easy. Set up the jig on a sliding table and cut any radius you want. I've done this with acrylic, ply, fibreglass PCB blanks etc.
Rgds, Lin

jwaggs
10-13-2005, 09:47 AM
I recently cut some 3" circles on my 10 " lathe. I bolted a piece of wood to the backplate and screwed the sheetmetal blank to the wood. Adjusting the cross slide allows circles of up to say 9" to be cut from the blanks without a center hole. You do have to be careful when finishing the cut so the circle doesn't get away from you.

Charles Lessig
10-13-2005, 10:30 AM
There was an adjustable hole cutter for sheet
metal ducts that used two pipe cutter type
wheels and a heavy backing disk. It needed
a center hole through the sheet metal for the
bolt that forced the cutters against the disk.
That would work if your sheet is thin enough
and you can stand the center hole in your blank. Charlie, also new here

agrip
10-13-2005, 12:11 PM
The sheet metal trade uses various ways to cut a circle.
The lowest cost is a set of aviation snips.
One cuts curves easily to the left and the other cuts easily to the right. How you use them is to learn how to get the feel of the appropriate lean the operator applies to the tool. You layout your circle and snip around.

There are "power snips" for a couple hundred dollars that have short strokes and nibble/ shear their way around.

Already described is the through hole type, rolling wheel, circle "cutter"

Using a deep throat "clamp" rig the rolling wheel can work without the center hole.
There are sheet metal folks that manufacture that rig to make "drum heads" from sheet stock there are "jaws" that cut and "jaws" that form.

If you enjoy rigging stuff you can get some structural channel and some plate, and then make up a parallel rail frame with a plate on the base pair and a bushing between and on the end of the arm pair to accept your rolling wheel Parting arm.
The back end of the "clamp/arm" rig needs to be stout. Possibly doubling the height of your channel and/or putting cap plates between the channels.

A drill press will make a light duty rig similar to what is suggested above. I say light duty because the usual DP column will deflect too far and too easily with the loads involved.

Pipe and tubing cutter wheels are available from almost any industrial supply outfit.

HTH Ag

[This message has been edited by agrip (edited 10-13-2005).]

[This message has been edited by agrip (edited 10-13-2005).]

david_r
10-13-2005, 11:00 PM
dshinn,
1045 will harden to about 50 or so RC. Say as hard as the blade on a good knife. I think that would be hard enough to do what you need. They aren't going to be as good as tool steel but the price is right.

If you just wanted some blades, you might try calling harbor freight and seeing if they stock the blades for this.
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=34104
If they have them in stock, they'll be inexpensive and fast. If they have to come from China, who knows how long that would take. I don't know if they'd be suitable for your application but thought I would throw it out there.

J Tiers
10-14-2005, 12:06 AM
Yeah, I got a Horrible Fright flyer, and tehy had some sort of universal sheet metal tool that looked like it had the circle cutting ability.

As far as that is concerned, the cutters I am familiar with I don't believe were like a can opener. Those have pointy-edged wheels.

The shears I recall had two discs which were ground flat on sides, and sheared the metal as they turned when the piece was rotated. Like round-edged scissors.

dshinn
10-14-2005, 12:08 AM
Wow .... I'm really thankful for all the response to my question. In particular the potential of using cutting wheels designed for tubing and/or pipe cutters. That would be a ready made deal.

One 'feature' of a circle shear of this type is that both top and bottom cutting wheels (picture a canopener mechanism), both wheels need to turn under power, hand power that is. That's to keep the circle blank rotating correctly and centered. Thus I'll be needing to design a geared setup between the hand crank and the two cutting wheels.

But you've all given me lots of good direction. I think I'll be able to tame this beast yet!

Thanks, all.

bobbybeef
10-14-2005, 12:51 AM
dshinn,
Yes, I think your flycutter idea would work. May I suggest that instead of one cutter you mount two. One each end of a stout bar. If you are on a lathe you could mount them on your face plate.Your revs would need to be way down for the diameter you propose and use drill steel(silver steel) for your cutters. Harden and stone them in the accepted way.
Keep them sharp. I dont think they will dull very quickly on brass. I would think if you shape the cutter like a parting tool you should get a good result. I am however happy to defer to better advice on this point in particular.Clearance on the outside of the circle will need a bit less than that on the inside.If you give it ,say 10degrees clearance on either side that might work.
Are you cutting on a lathe or a mill?
Best of luck and keep us posted. We are all interested in what you are doing.
Bobby.
PS.
Just a thought.If you are using a lathe and cannot get your speed down low you might think about ungearing the spindle and turning it by hand with a handle on the end of the spindle.
Bobby.

[This message has been edited by bobbybeef (edited 10-14-2005).]

Samuel
10-14-2005, 01:12 AM
my vote is for using a band saw as the cutter and having the rest of the set up more or less look like a ring shear. ring shear blades are still sold. if that is all you are looking for.


Samuel

L Webb
10-14-2005, 12:41 PM
What you need is a roto-blanking machine. It can cut circles from 12" up to 36" diameter with no center hole at a rate of over 120pcs per hour. The only problem is that there is only one in existence, and it has been retired. We haven't used it in over two years.

We made the cutters out of various grades of tool steel such as A2, S7 depending on the type of material being cut into draw or spin blanks.

You don't want the cutters too sharp. A very sharp edge will cause problems and not last. I'll try and take some pictures of the cutters we used on another machine which did the circles under 12" and post them. They are similar to what you are describing.

Les

madman
10-14-2005, 12:51 PM
I spun fishing reel parts long time ago in the home shop. I made a steel fixture threaded hole in centre with a bi g washer thick to clamp and hold the 6 inch square aluminumn squares. I had these squares sheared up at a shop. The guy did it for free and laughed when i told him what i wanted to do with it. Once you have this pile of squares hole in centre and mount on fixture in lathe and plunge into spinning plate with a trappanning type part off tool. Ensure plenty of tool shank clearance. Then feed through until part is plunged remove and do it again and again till youre done the lot. I find having a few beers gets me in the mood for mindless jobs. Be carefull and good luck.

Evan
10-14-2005, 12:56 PM
Using a flycutter to try and cut sheet metal is a good way to have a bad day. Don't even think of it. The fly cutter will snag when it breaks through, guaranteed. I know, I have tried it a long time ago. If you need a bunch of blanks then stack them up, clamp them, and cut them on a vertical band saw.

If you can stand having a hole in the center it is even easier.

http://vts.bc.ca/pics/fp2.jpg

[This message has been edited by Evan (edited 10-14-2005).]

Samuel
10-14-2005, 01:57 PM
Evan, what kind of band saw is that? it looks like a little ryobi bench top saw with better guides?

Samuel

darryl
10-16-2005, 12:20 AM
Evan's pic pretty much sums up the way I would do it for circles larger than just a few inches diameter. Flycutting large circles is dangerous and results aren't good, in my experience.

There's going to be a minimum circle diameter that can be cut like that on the bandsaw. Any tighter and the blade will be damaged. You might want to experiment first to see what diameter you can do like that. The only limit to a larger diameter is how wide your shop is, and how unwieldly the sheet is.

By the way, you don't really need the through-hole to define the center of rotation for a blank. A bit of jig making will give you a thin sheet disc with a pin welded/brazed/silver soldered to it, and that pin fits a hole drilled in the table at the wanted radius. You could use a piece of mdf attached to the existing table to drill the pivot holes into, if that is more palatable to you. Tape the disc to the bottom of the blank, insert pin into pivot hole, and saw away. The tape will endure a surprising amount of force for a time, more than enough in my experience to get the blank cut out round. I'm assuming that you'll be doing some kind of finishing operation to the rim of your spun article later, so the absolute roundness of the blank probably isn't important at the outset, though this method will get it pretty close.

How elaborate are you willing to go- you could arrange a vacuum disc which comes down onto the top of the blank as it sits on the bandsaw table. That disc spins on a bearing, and the bearing is attached to an adjustable arm that clamps to the left side of the table, or even to the column of the bandsaw. I guess it's basically a vacuum chuck, only it doesn't turn the blank, it just keeps it centered while you turn the blank for cutting.

Anyway, all these ideas just to get away from the center hole. Hmm. Depends on how many pieces you would be making, and how versatile you would like the setup to be.

The 'vacuum chuck' could be as simple as a sturdy suction cup mounted to a bearing, which is mounted to an overarm--

dshinn
10-16-2005, 12:45 AM
<font face="Verdana, Arial" size="2">...I'm assuming that you'll be doing some kind of finishing operation to the rim of your spun article later, so the absolute roundness of the blank probably isn't important at the outset, though this method will get it pretty close.

How elaborate are you willing to go- ...[/B]</font>

Yes, Daryl, there is always the need to trim the blank while spinning since uneven strecthing, especially by wannabes like me, will cause the blank to run out of true after a few spinning strokes. So in reality, the blank(s) don't need to be totally true to begin with since they get trimmed at least once or twice on the lathe anyway.

The main reason for building something to cut circles with is to avoid having to take the time to cut them out with tin snips. I'm beginning to think it would be about as easy to rough cut several pieces, place them all together on the lathe and true them up between a couple pieces of MDF at the appropriate diameter.

But then, that's not nearly as much fun as figuring out how to make a circle shear - and that's what it's all about, right (hehehe)

Evan
10-16-2005, 02:18 AM
Samuel,

That is a cheap 9" Canadian Tire special. Cost about $80 US. It is a pretty good saw for the money although it is really fiddly to set up the tracking. Once set it holds just fine though. I hate changing blades on it but for the price it is hard to complain much.

Swarf&Sparks
10-17-2005, 12:01 PM
Errr, I did mention it Evan. I don't think holes in a spinning blank are a good idea http://bbs.homeshopmachinist.net//frown.gif
same sorta thing but with the thrust bearings.....

Evan
10-17-2005, 12:10 PM
A hole in the center may not matter depending on what the product is. For no hole you don't need to get fancy SnS, just hand held cutting should work well enough.