This is my first blacksmithing project. I made a pair of tongs
yesterday and learned a lot doing it.
Hot punching the rivet holes gave me a bit of trouble, though. I
managed to remove the hardness from the tip of my Craftsman
center-punch and also managed to bend a drift punch. What are the
proper tools and techniques for hot punching holes?
There are a couple of things to remember when hot punching. First, you
want to roll the end of the punch in some of your coal fines (powder)
so that it will not tend to stick in the hole that you are punching. Do
it each time that the punch will be contacting hot steel. It will cause
a little fire to flare but will allow your punch to slip out of the
hole easier. After punching make sure to cool the punch in the slack
tub. Also, watch the end of the punch as this may start to "mushroom"
from getting hot and being hit against steel. You may have to dress the
tip now and again. Next, when you are punching drive the punch down
into the steel until you start to feel the punch "refuse", that is, the
punch will be getting close to the other side of the material. When the
punch doesn't want to "go anymore", stop, cool the punch, recoat with
coal, reheat the material if necessary, and look at the backside of the
place where you were just punching. When you are getting to the right
depth, the area where the punch was trying to come through will show up
as a circle on that backside. It will make it easy for you to place the
punch over this circle and drive the plug out. Just make sure to line
up the punch correctly on the circle, and place the material and punch
over the Pritchel hole so the punch can be driven through the material
and the plug can fall out of the bottom of the hole. Be careful with
the plug, IT'S HOT.
Hope this helps,
Good question. The first operation, that is starting the punch hole on
the first side needs to be done over the solid area of the anvil. If
you think about the operation, you will see that the punch is actually
compressing the steel so that some of it along the sides of the hole
will ooze sideways out of the hole area and into the material around
the hole. It becomes clearer when you look at the cooled plug after it
has been punched out. The plug is actually thinner that the plate it
came out of. So, start the punching over the solid part of the anvil
and then knock out the plug over the Pritchel hole. If you begin the
first punching over a hole, it will tend to cup you piece. Then you
will have to flatten and then repunch, so it's better and easier to
start the punching on something solid.
Also, take care not to drive the punch all the way through the first
side and end up hitting the anvil face. It may mark your anvil and will
"do a number" on your punch.
Side Note: If you can find some old auto coil springs, the high-carbon
steel in them makes good punches and chisels. Frequently, you can get
them free from local repair garages. If you can find a local truck (big
trucks) garage you may be able to get some large gauge coils to make
big punches out of. It's handy stuff.
Hope this helps,
I make hot-punches from old ball-peen hammers found at the flea market
for a few cents.
Remove the handle, and heat the ball to cherry red. Draw it out to a
TAPER (you DON'T want it a cylinder!). make sure the end is square.
Quench and draw to blue.
Requench after each use; when it starts to get soft, re-harden and
The handle should be a press fit, so it can easily be removed for
re-hardening - remember that you're not striking WITH the punch, you
striking IT, and you don't need to worry that the head will fly off.
You need two tools - a punch and a drift.
The punch is huge, even though it has a narrow tip. This makes it
easier to handle and gives better heatsinking. Sometimes its easiest
if fitted with a handle (and a 3-armed smith)
The drift is the overall shape and diameter of the finished hole. The
leading end is smaller than the punch, and has a long taper. The
trailing end has a short taper, so that it will fall clear through the
piece without needing to be hammered near the surface.
A punch is a much heaver tool than a drift. As drifting is merely
re-arranging unconstrained steel it's quite easy work. Punching is
having to shift metal by squeezing it sideways under hydrostatic
pressure, which is always tough work.
Tools should be made from weird air-hardening steels that don't lose
their temper in use. Look for tool steels with chrome in - they're
common enough in scrap these days. OK, so you have to work them by
grinding rather than forging, but it's worth the trouble. Try that car
coilspring you tried to forge but couldn't.
I wonder how well titanium punches would work ?
Place the hot workpiece on the face of the anvil and punch it. _Not_
over the pritchel hole. Punch almost-through, until you start to see a
dark chilled spot on the back of the piece.
Turn it over (probably after reheating) and place it over the pritchel
hole. Now punch again, to make a through hole.
Swap tools (maybe reheat) and use the drift.
If you have trouble, work hotter, reheat more often, and hit it
harder. When you do it right (ie hot) this is an easy process. If it's
a slog, you're doing it wrong.
reminds me of when I made my first attempt at punching a hole.
I tried to punch through on the first attempt with a sears craftsman
drift punch. It stuck, it turned red from the heat of the railroad
spike I was trying to hot punch, and it broke, melted? off leaving an
inch of it's end imbeded in the railroad drift punch. Oh well, live and
learn, that was more than 35 years ago. From the other reply, it sounds
like Paul has some good advice.
... OK, so you have to work them by grinding rather than forging, but
it's worth the trouble. Try that car
coilspring you tried to forge but couldn't. ...
Thanks Andy, great information. Could you elaborate on difficulties
forging air-hardening steels? I am new to this and wasn't aware of
this issue. My only experience is with mild steel. Thanks. John
Sounds cool. :)
It was mentioned here that a guy can find odd left-over pieces of
H11 and H13 tool steel on ebay. They are "hot work die steels"
for industrial uses, formulated for exactly what you are doing. :)
A horse-shoe maker/modifier here uses that type steel, and he
mentioned S7 too, but he's in some sort of production mode?
I remember getting excited that maybe I'd find some O7 or F2 tool
steel for knife blades on ebay too :) ...no luck there tho.
Alvin in AZ
There are modern steels (not all strictly air-hardening) that are
"impossible" to forge by normal hand processes. You might be able to
forge them, but they have to be worked extremely hot. In general
they're more trouble than they're worth and are best avoided, but they
can be useful for tools like this that you don't want to soften at
Car suspension coilsprings are one source.
Trailer axles. There's nothing like forging three times to convince a
chunk of yellow-hot steel to change shape. It didn't budge at orange, so
it's definitely a candidate for red. Look for a trailer fab company and
prowl their scrap bin, or hunt the junkyard.
First, I wouldn't use a center punch hot. I'm not sure why you are
using one at this stage of the process at all. I'd use the center punch
on cold metal to mark the location of the hole, then heat up the part to
do the drifting.
Secondly: You only have about ten seconds or less of having the drift in
the hole of the hot part before it will soften if you are using drifts
made for cold work. Which that drift probably is.
You were lucky in that you apparently didn't get the drift stuck
inxtricably in you part. This often happens with cold-work tooling
when the end mushrooms into the hole!
The old rule is:
hit- hit- hit and quickly quench (the drift). Also, you are not
trying to punch all the way through. You want to drift about 3/4ths of
the way through, then turn the part over (as the other poster said) and
drive the slug back through the hole.
We often make drifts from old truck springs. Even though that
material (often 5160) isn't exactly a hot-work steel, it is tough enough
even when annealed to stand up pretty well if you hit-hit-hit-quench.
Cold-work steels, like your drift punch, may be made of good quality
carbon steel that was hardened and tempered for its intended use. But,
as soon as it gets above, let's say, 500 or 600 degrees it will loose
most of its hardness.
Hot work steels like S1, S7 and Atlantic 33 stay hard up the the
point where they glow and don't need to be cooled in between uses.
I suggest that you practice this punching process on a 1/4" thick or
3/8" thick plate or bar until you get comfortable with the punching
rythym and the art of locating the center of the hole from the backside
by (as the other poster said) centering your drift on the "shadow". You
don't need to have the back side particularly hot to dirft out the slug.
The part needs to be glowing red or so, but the shadow can be down to
almost no color at all. What you are doing is shearing the slug off.
In my experience, most of the automotive axle/spring type steels
(5160-types I think) are only sligly more difficult to forge then mild
steel, but you have to be careful about the temperature on both ends -
don't forge it when it is red because it might crack, and don't get it
yellow-white hot because it will turn to mush. The same is true of S7.
There are many books and web resources that will have temperature
ranges/colors, common steel types for various junk, and forging
techniques. Check The New Edge of the Anvil.
Un-hardened auto steel will also be more durable then mild steel in
Yeah, what Don said. :)
To add, compare grade 2, 5 and 8 bolts.
As as rule of thumb, think of them like this...
Grade 2- work toughened/hardened mild steel. (1010 to 1020?)
(like a commom nail or the hard steel wires in field fencing)
Grade 5- work toughened/hardened medium carbon, low alloy steel.
(like 4140 or automotive suspension springs, sway bars and axles)
Grade 8- a heat-treated grade 5 bolt.
Alvin in AZ