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Forging a Cone Mandrel


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I managed to light my forge for the first time in months this week, and made a leaf-handled bottle opener. For the opener part, I punched and drifted before shaping into an ovoid loop. Since my stock of drifts is very limited (read: nonexistent), I used the horn of my anvil for the drifting. That was a bit awkward, and I couldn't help thinking that a cone mandrel would be quite useful.

I have a piece of 3.5"x10" round mild steel that I was going to use for a horn on a fabricated anvil. However, since I have my Hill, I don't need it for that purpose. I was thinking of forging it into a hardy cone. To do this, I'm looking at teaching a friend to strike, since I have a sledge, but no power hammer.

Anyway. I'm looking for some detail on hand-forging large-diameter pieces. I know I'm going to have to make sure to heat it all the way, evenly through. I'll have to watch out for fish-mouthing the end, particularly when I am shouldering it down to fit my hardy hole.

Anyone have any specific techniques I might apply for this?

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That is beast of material to work by hand, 3 1/2 inches! You are going to take turns, and pay attention to hydration, and exhaustion. Best of luck.

To eliminate fish mouths you can start by forming a very blunt taper on the work piece, figure 1/2 your starting diameter, or so, in length. You are pushing the end in at a 60-45 degree angle here or 1/4 to 1/2 the diameter of the bar in length. This will start to define your square. Then draw the taper out square. Any time you think you are just beginning to form a fish mouth drive the end back in to form a new blunt taper. You have to keep ahead of the fish mouth, or be prepared to cut it off at the end.

You can draw out in stages. When you get the square taper fully formed, then take it round. If you do some simple volume calculations using cylinder, pyramid, and cone you can accurately estimate how much material you need to start with to get the desired results.

You probably want to form the square shaft for the hardy hole first, upset it into the hardy or your bolster plate, then draw out the point on the other end. Alternatively, weld a long square shaft on at the beginning (arc weld), this way you can avoid use of tongs and simplify your life.

The length of a cone to the cylinder is 1/3, so the cone is 3x as long as the cylinder. The ratio of the square taper to the round taper is 22.3% so the taper will be 77.7% the finished length when the square taper is complete.

Hope this helps.

Phil


http://www.iforgeiro...ng-a-point-r191

some math and discussion
http://www.iforgeiro...mmer-eye-drift/
the source
http://www.iforgeiro...e-but-no-cigar/

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I use a striker quite often, and I have learned how to rate my hammer just like you would with a hand hammer or power hammer. Know how much material you can put under your hammer so you can accomplish whatever you should in each given heat. I can do 1 inch square and under with my hand hammer. It does not matter if it is a one heat taper, flat horse, or whatever. Or it could be a 3D horse, for example, I take 5 heats to complete the horse head and with my hand hammer I do anything from 1/4 inch to 1 inch. If I use a striker, I can do the same up to 2 inch square. If I go larger I would have to get a bigger hammer or take more heats than it should take. For example, it took 1 1/2 hours to forge a horsehead out of 2 7/8 inch round tool steel where it only takes 20 minutes to do the others in the heats it should take. I do not reccomend using an inadequate hammer for anything, but I have occassionally and probably will do it again. So if you must, I would suggest forging a hexagonal taper over the far side of the anvil held at the appropriate angle with half hammer faced blows with the rounded face of a sledge hammer to rough the taper out then flat side of the sledge with half hammer faced blows held the same rotating and feeding the material onto the anvil rounding and planishing as the "unicorn horn" forms on the bottom side and you take it away on the top side. If you have never done this before, you may want to practice with something like 1 or 2 inch stock, and start with 1 inch over the edge if you are using 1 inch, 2 inches over the edge for 2 inch, or 3 1/2 inch if you really want to start with 3 1/2 inch. I'm pretty sure it will take you more than one heat.

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(Note that I wrote this before seeing Brian's post. I'll have to process his advice a bit more before commenting further.)

Wow. That means, omitting the hardy post from consideration, I'd be looking at a 30" cone. Methinks that's way more than I need.

3.5" is a pretty big cone, and a big one to forge by hand, you're right. But it will go a long way towards satisfying my (limited) need for a cone mandrel, so there's real value.

The question would then be whether or not I put the material on my band saw and cut it down before forging. Or mabye I forge the cone, and then cut it down after I'm done, once I see how much cone I want/end up with.

And by the way, Phil, I really appreciate your coment "...pay attention to hydration, and exhaustion. Best of luck." It's good for me to keep in mind the amout of effort required to do this.

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hmmm at 10" could you throw it on a lathe and turn it into a cone then weld a post on? the cost of the lathe work could be shocking but you would be getting a perfect cone!
just a thought
Josh

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Thanks for all those links. I think it was a very subtle way of trying to convince me not to try to do 3.5" round by hand. Very clever, and effective!

I may go back to my previous plan of waiting until we get the 200-lb Bradley fixed up at the Vista Forge. This may really be more than is reasonable for hand tools.

Since I have no real need for the tool on a schedule, I'm more interested in having the tool be a product of forging, which contributes to my skills and experience, than machined, which deducts from my checking account. The lathe is a good idea, and I was going to go that route when I was looking at using the metal as an anvil horn.

Drifting away from the specific topic a bit, I note that a lot of your threads you posted were about drifts. When I look at it, that's really what I need to do: make a drift. I have some bar stock that I think will work. That may be my next step.

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When I had a couple of feet of 2.5" I wanted to forge shafts for stake anvils from; I carefully put it aside until I could borrow another smith's powerhammers (100lb LG and 200# Chambersburg) even so it was a a job and 1/2. We welded some 1" sq to it for a handle and worked it at welding temp---this was known as another person sharing the gas forge accidentally welded their piece to mine by sliding it hot against my piece---had to be sledged off!

OTOH if you have access to a 1000 pound hammer, a big forge and chainfall or jib crane system this would probably be a trivial task.

With strikers I would want 3 who could strike in rhythm for a long time and a very large anvil---say 500+ pounds

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I was thinking that 3.5"x10" is a pretty good size for a cone to mount on an anvil or in a vice. So, were it I, I would take an angle grinder and cut off disks and take off large chunks until I had something cone-ish in shape. Then I would try to forge it round and relatively smooth. Then I would take it to the belt grinder and use some flap wheels to clean it all up.

What I ended up with would, I hope, be relatively conical. Knowing my skill, though, it wouldn't be truly conical or even pretty. So I would opt to have a machinist turn it to shape and then weld a stem onto it. Or just buy a small cone from one of the supply houses.

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I managed to light my forge for the first time in months this week, and made a leaf-handled bottle opener. For the opener part, I punched and drifted before shaping into an ovoid loop. Since my stock of drifts is very limited (read: nonexistent), I used the horn of my anvil for the drifting. That was a bit awkward, and I couldn't help thinking that a cone mandrel would be quite useful.

. To do this, I'm looking at teaching a friend to strike, since I have a sledge, but no power hammer.




Anything's possible.....I've seen a 25lb LG forge 2'' sq on youtube, but a human drawing 3'' round? He must be a burly fellow........ :D

http://coolnewsninja...-scaled1000.jpg
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I made the mistake of taking on a job about 5 years ago making 25 eye bolts out of 2.5"x4" 4140. I spent 2 days forging one with a 100 lb power hammer at a welding heat.

I still have a stack of 14" long pieces of 2.5" x4".

Your steel being mild steel will help but I would think you need a minimum of 100lb to forge 3.5"

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If you're lucky, ... as you get older, you start to differentiate between what you CAN do, ... and what you SHOULD do.

You probably CAN forge that chunk into something that maybe you can use.

But in my opinion, ... you SHOULD stick it in a lathe, face and tap the bottom on center, ... then turn it around and taper the other end.

Then you'll have something you can use forever.


( I recommend tapping the bottom at 1/2" or larger, rather than turning a shoulder and pin on it, because it gives you so much more versatility in how you mount the mandrel. )

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Several months ago I was at an auction where I saw a post hole digger/bar with an eight inch long and a 4-5 inch diameter base on the end of a 6ft long heavy bar. I have been kicking myself ever since that I didnt buy that think. I could have cut off all but 3 inches of the bar and made a hardy mandrel out of it. Just a thought for you if you got to auctions and such rather than going whole hog on that piece you got....

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Any logging outfits in your area or commercial truck dealers? Might want to look for a bunk pin or carrot. Keeps the bunks on a log truck from turning when empty. Will look in the shop on monday, think we have one upstairs. Will try to post a pic. All it needs is the ring for the chain cut off and a shank put on. Might be a little small at somewhere around 2" dia by 8' long. But it is something to thimk about.

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  • 7 years later...

3 1/2 inch is pretty big to sledge out by hand. I guess it's possible (?) But that sounds like an awful lot of work. If you could locate someone with a press it would be well worth buming some time in someone else's shop. For stock that size my 250 pound could do it, but I dont like working that big under the 100. It is really kind of big for even the 250. A press works big stuff more effectively. The easiest approach might be to lathe down your taper and weld on a hardy shank

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