scjohnson243

Troubleshooting: Nice Clean Punching

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So today I spent a few hours working on punching and drifting.

I seem to have a problem after I get the hole punch, and try to drift something through it (Using a pointed 1" peice of round stock) It seems like the metal starts to get "pulled" down while I'm drifiting. On the videos it shows you get a nice "punch" in the metal - then drive the drift through the pritchel hole. It goes from my stock getting "Stuck" in the hole, or all the metal tears on the way through... Watching videos it doesn't seem very difficult, I am assuming I dont have my metal hot enough, but its "yellow" when I start, and it cools off very quickly as im driving.

can anyone offer some tips?

Thanks

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How large is the punched hole in the material? If the hole is to small it can be can be hard to drift up to 1 inch in a single so. When I start with a small hole, say 1/4 inch I will first drift to 1/2 inch, Then take a second heat and move up to 1 inch. Also while I am drifting I start the drift in one side and work about half way though, then knock out the drift and turn the iron over and finish drifting from the opposite side. Then I will forge the drag through material flat and run the drift though one last time.

 

Mackenzie

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The "pulling down" is termed "punch suck-in." It mostly occurs when punching a hole with a flat bottomed punch, not a slit chisel. Are you using a slit chisel initially? If so, you'll remove no material or at least, very little. This gives you more metal to drift. If drifting a slit, the drift shape should go from thin to a gradually growing elliptical cross-section; then to a round. The round will be the size of the finished hole for, say, 6" to 8" long. Then there will be a tapered end (the struck end) so the drift can fall through.Take the time to make a  1/4" thick or thicker bolster plate, the hole in the plate slightly larger than the desired hole in the hot material. The bolster can usually be put over the hardie hole. If you desire a square hole, make it round first. In working with heavy stock, some smiths take a localized heat on the slit and upset it. Then drift.

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If you're so inclined, there's math-e-matics to help you plan your finish drifted hole. I use flat bottom slot punches, and as Mr. Turley said, there is some draft when punching . I can minimize that by careful layout, and punching in from both sides. I look at the final hole diameter, say 5/8 inch, or, .625 inch. The circumference of that hole is pi x d , or roughly 3 x .625.   That equals 1.875, or 1-7/8 circumference. A 1/8 thick slot punch works good for this size hole. If I round the edges off the punch, I have a flat bottom slot punch with rounded edges.  (===) Each edge is half a circle.  Pi x d for a 1/8 (.125) circle is 3/8 (.375). So take your 1-7/8 original circumference and subtract 3/8. You come up with 1-1/2 left over. since the punch has 2 long edges, divide 1-1/2 by two, and end up with a 3/4 inch slot punch with radiused ends. when you put the drift thru, the slot will collapse and expand to the size of the 5/8 finished hole. 

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Mr Johnson, I think I agree with Mike? If you are drifting a hole that is larger than the width of the parent stock you have to slit the material longer than you first think. I am sure that the math above will work but after a while you will know when its right.
You should be able to punch a clean hole the size of pritchel hole in flat stock without the drift unless you just have to save the metal for strength.
You saw Brains pritchel plate? It sits in the pritchel hole on the anvil and the different size holes swing over the hardy hole. That would help like Mr Turley said as would the upsetting he mentioned. Keep practicing.

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TAKE YOUR TIME! it sounds to me like you are trying to put the drift through in one heat... next time, try putting the drift in, hit it only 3 times, nock it out then let the heat wick back into the hole until it is all one color again (hold the steel off the anvil) then hit the drift through the other side 3 times... reheat and repeat until the drift goes through, then as the steel cools keep putting the drift through both sides until it just drops through.

 

I'm gonna steal Brian Brazeal's line, Don't believe everything I say, go try it for yourself.

 

Josh 

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So today I spent a few hours working on punching and drifting.

I seem to have a problem after I get the hole punch, and try to drift something through it (Using a pointed 1" peice of round stock) It seems like the metal starts to get "pulled" down while I'm drifiting. On the videos it shows you get a nice "punch" in the metal - then drive the drift through the pritchel hole. It goes from my stock getting "Stuck" in the hole, or all the metal tears on the way through... Watching videos it doesn't seem very difficult, I am assuming I dont have my metal hot enough, but its "yellow" when I start, and it cools off very quickly as im driving.

can anyone offer some tips?

Thanks

 

Check out the "slitter geometry" thread that Wesley Chambers posted.

 

What size slitter are you using, and what size drift? Are you using an opener before drifting?

Ideally you want a clearance hole as close to the same size as your drift as you can stand. I.E. It will not work so well if you try to drift a 1/4-inch hole over a 1/2-inch prichel hole. It does not offer enough support.

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Thanks All - I have to admit - I was starting with a round "punch" and then after making my hole trying to drive a drift through it.  Obviously this never worked - I need to use the chisel to get a better opening for my drift.  I also think I was trying to force it when it was cooled off to much. I was watching youtube of Mark Asberry(sp) and he was doing drifting and I thought I would give it a try - Of course it starts with him drifting, not punching the hole - I assumed since he was drifting a round hole he was using a round punch to start with.

 

Kind of silly now that I look back at it, and the amount of time I spent trying to make a "clean" drift.

 

/sigh... Thank you all again for the information Its appreciated!

 

 

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