Tom May

Creating a cup-shaped depression in sheet / flat bar

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I'm hoping someone with more experience can give me some ideas on how to work around my limitation in tooling.

I want to create a cup-shaped depression in a 3x3" square of 3/8" flat bar.  I have a big piece of steel plate as an anvil, a 4" bench vise, some tongs, a few hammers, and an assortment of punches / drifts.  Maybe most useful of all, I have a 1 1/2" diam steel billet, which could be used to hammer down into the sheet to provide exactly the depression I need.

But, I don't have any way to support the sheet in a way that I could use the cylinder to force down the sheet into a cup.

I'm sorry if this is totally obvious - it would be easy if I had a deep ring to put in the vise, but I don't 

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We need more dimensions other than a 3 x 3 inch square of 3/8 plate. What size (diameter) is the depression and how deep?

DO NOT build a box and then try to think outside the box. If you do not build a box, anything is then a possibility and an opportunity.

Lots of possibilities, all you need is a positive and a negative die, heat the plate, and apply pressure to push one die into the other. Pressure can e hydraulic, manual, or a hammer.  If you want, just use the hammer and the negative die on the bottom.   The dies can be what ever is available to you in your area, such as bearing races, pipe, pintle hook towing rings, large chain link, etc.  A blacksmith (you) could form a ring from scrap metal in short order.

The positive top die can be what ever is available to you in your area, such as bearing races, pipe, trailer hitch balls, large ball bearings, and the list goes on and on.

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the negative die could be as simple as a tree stump, the positive a ball peen hammer

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The depression will be about 1.5" deep, straight-sided.

I can use my steel cylinder as the positive die.  It's the right diameter, and I can hammer it into the sheet with the appropriate support.

The idea of using a tree stump as the negative die is interesting.  Would I need to hollow out a depression beforehand, or could the heat from the piece of work burn out a hole?

 

I do have some scavenged railroad clip fasteners that are pretty thick.  I could form one of those into a circle without a whole lot of drama.  Maybe I could make a "tail" for it to place in  my vise to hold it.

A pintle hook ring would be ideal, if I can find one.

Thank you both for the insight and inspiration.

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You can chisel out the depression in the stump, flap wheel on a side grinder or use other tools you have available. 

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I have used a 4-1/2 inch grinding disk for making the depression. Does not take much of a depression to go a long way.  Wood is good as you can play with the bottom die of different depths and different shapes to find what you want.

This is where modeling clay works well. Try the top and bottom dies shapes to get what you like. Make changes a little bit at a time until you get it right.

 

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Greetings Tom. 

         Making a 11/2 deep depression in 3/8 is difficult. You will find the sides will raise and hard to return to flat without the proper tooling. You could grind the area to be depressed to 3/16 or so on the underside. This would be much easier to press down . You could purchase a 2 in shaft collar to support the bottom for the depression . Just don’t hit hammers with hammers . A large ball pein and a brass hammer will work .  Just this ol boys 2c .

Forge on and make beautiful things 

Jim

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Out of curiosity, what are you attempting to make?  If this had been thinner sheet, I would have said use a wooden stump, but not at 3/8".

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Have you thought of using a short section of steel pipe welded to a piece of plate as the negative die?

Pnut

 

 

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Good Morning, Tom

Roll a piece of flat bar to the diameter you need. Weld the ends together. Make a round ring of 1/2" round bar, weld the ends together. Forge a piece of your sheet into a dome, using the round ring. Weld your dome piece to your rolled flat bar. Think simple, K.I.S.S.

There is no law against using using a welder. It makes your problem simple!!

Neil

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Here's my solution to your question. I have made a set of these from 1" to 4" diameter. I make them from seamless pipe. This one is unfinished. I cut the pipe off a couple of inches from the top and weld on a piece of 3/4" square bar across the bottom. This gets clamped in my post vice. The top tool can be whatever you want depending on the diameter. This one is about 1-1/2" or so. A small ball peen works well to sink your work. And you should have no problem sinking 3/8" plate. 

If you make a punch to set this down, don't forget to take into account the thickness of your material × two. Plus a bit more for "windage". 

And yes, always keep the KISS principal in mind. This is the blacksmith'd version.  ;)

To give credit where credit is do, this came to me via Tom Joyce, a while back.

 

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