spliting and drifting - help

[2Tim215]

Having trouble spliting and drifting 16mm square bar. I drill a 6mm hole, heat and start with a tapered round drift then open up with a 16mm square drift made from the same stock. My walls end up too thin and keep on tearing when I work the piece.

 

I thought that maybe I should use a thin hot cut chisel to split and then only open up instead of doing the above. If the chisel is slightly wider than the stock say by one third then I should get the same thickness in the walls that would be half of the stock used - ie: 16mm stock would end up 8mm wall.

 

What I am trying to do is thread the 16mm bar through a square eye.

 

Thanks

 

Tim

[yves]

Tim,

 

It might help to go and see Uri Hofi's slitting and drifting blueprint.

 

By drilling the hole for one thing, you loose all that metal. 

[2Tim215]

thanks yves - that's what I thought - mind you that's also what I used to do until someone said try the drill method. Couldn't figure out why it wasn't working like it used to LOL. Just me being stupid and lazy.

[PaulKrzysz]

Please View the attached video.

[2Tim215]

Thanks Paul - Excellent vid and best explantion I have so far seen.

[Dan C]

I was having this problem as well until I used a larger slit punch, problem solved.

[Charles R. Stevens]

Note, Dan's use of the term "slit punch" a slit punch will give you a cleaner slit than a "slitting chisel"

[Rich Hale]

In the tool section Brian Brazeal wrote a great piece about this,,you may have to search back through a lot of pages,,but it is worth it!

[K. Bryan Morgan]

[2Tim215]

Thanks all. Appreciate the help. Being self taught in a country with very few balcksmiths it helps to have you guys around. I learnt more in the last few hours watching Brian's vids on some of the more technical aspects than I have in 5 yrs of figuring it out on my own. Should have asked earlier.  Thanks to Brian Brazeal especially for taking the time to share his knowledge so simply for guys like me in the slow lane.

 

Concerning the slit punch and the slit chisel - I assume that the slit punch is flat compared the chisel that has an angled point?

[yahoo2]

Did you have a look at Brian's video titled "how to make tongs" on youtube? He has a very detailed demo on how to punch a hole starting at the 15 minute mark using a center punch style tip.

How to forge tongs it is worth watching this bit a few times

 

Gary Huston shows a flattened chisel demo for slotting

slit/slot & drift

 

Mark Aspery

Forging inch square holes

 

Ring Project punching and drifting square bar

 

I cant remember if they make the point in the videos but the idea is that moving the metal in a shearing plane will detach a biscuit of metal away from the parent stock. I guess this is a punching or slotting action and for thicker material Hammer heads and the like, the greater mass of the hot steel holds up better to deformation of a cutting action so a slitting chisel is used.

[Charles R. Stevens]

Depending on the profile of the hole you're after, and the thickness of the stock your punching. For a long thin hole in thick stock, the thin profile of the punch looks like a very blunt chisel (more than 45) and similar on the long profile (kind of rocked) the punch pushes a lot of mental out of the way, untile it reaches the anvil and then it cools and compacts, you flip the stock over and punch from the other side removing a thin puck of steel.
For thin stock your punch is flat bottomed and has the edges rounded . This dose two things, as your working in thin stock you don't "cut" or tear the stock out and it minimizes the tendancy for your punch to mushroom (ruins your day to have pritchel lock into a shoe your punching)
A chisel has a tendancy to be ever so slightly of center from the initial cu on the other side, leading to a cold shunt inside the hole.

[Frank Turley]

Being in the U.S. without an apprenticeship or proper schooling in ironwork, I struggled in the "olden days" trying to figure out things like slit/drifting. This was before ABANA and way before internet. My first clue was when I visited Volunteer Park to see the Seattle Asian Museum. The foyer leading to the galleries had a large Samuel Yellin gate. I could see remnants of the edge splits on the bottom rail where vertical bars were inserted. Soon after, I acquired Schwarzkopf's book, and I encountered his line drawing of a slit chisel. I think it is important to note that his pictured chisel was squarish as viewed from the side. It was sharpened on three edges, meaning on the bottom and running up the two side edges as well. The two corners were radiused to help prevent them from overheating and rolling over or upsetting in the hot material. If you go the route of using the slit chisel, the sharpened sides will slice into the hot metal leaving a clean, thin cut, whereas it you simply sharpen the bottom, the ends of the slit will be blunt and out of shape. Much later, I visited Tom Joyce's studio and noticed that he sharpened the bottom cutting edge to an obtuse, centered point. By working carefully, the point would center the chisel on the previously made center punch mark. It is advisable to center punch, cold, both sides of the piece and to go in from the forepunch side a little more than half way. Then, turn over and backpunch. The slit chisel is designed not to remove material from the hole, but if the backpunch is eccentric, a thread-like burr may appear and be removed. By fore and backpunching as described, you get more uniformity to the slit and later, the drifted hole. Some people upset the slit with a localized heat before drifting, and some don't.

 

At about the same time that I was experimenting with slit/drifting, I acquired the two books out of London, England, "The Blacksmith's Craft" and "Wrought Ironwork." This was the first time I encountered a "slot punch." The slot punch is designed to remove a slender slug when backpunching. On thick stock, it is helpful to forepunch a little more than halfway and then to backpunch. There is a tendency for neophytes to forepunch into the hot material until the punch bucks on the anvil face and then backpunch the thin slug. The trouble with that is you get a tapered hole which is difficult to drift and to obtain a uniform thickness on the side walls.

 

The slit chisel and slot punch can be tall tools, perhaps 11" to 14" and hand held on their shanks. They can also be hafted, either with wood or with a wrapped 5/16"D or 3/8"D rod (British style). The haft can be put on at an angle to the work length in order to keep the holding hand away from the heat. Well fitting link tongs can be used to hold a short tool.

 

Reference: "Plain and Ornamental Forging" by Ernst Schwarzkopf

 

Sayings and Cornpone

"The use of the hammer manifests itself."

     Charlie Conger

[Charles R. Stevens]

Neophyte? Coming from you Frank, I'm more than willing to exept that.

[2Tim215]

Thanks again to all of you and thanks Frank for that detailed explanation. Will be bookmarking this for further reference.

[brianbrazealblacksmith]

Please View the attached video.

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