This is how I make steel doming punches to shape soft metals (gold, silver, copper, brass,) for jewellery making.
Doming ( or dapping punches as they are often referred to by jewellery makers) punches are expensive for what they are- basically highly polished pieces of curved steel. I have a few comercially made punches and a brass dapping block but I needed larger ones for a project. I couldn't justify the expense knowing they would only see occasional use, so I made my own.
they are cheap, easy and quick to make with only a few tools, yet they still delivers excellent results.
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Step 1: Tools and Materials
The tools are straight forward,
1) Sanding sticks of various grits I've used 120, 240, 320, 400, 600, 800,1200.
2) A few loose pieces of sand paper of various grits
3) Buffing stick (an old leather belt glued to a piece of hard wood) or a polishing motor with stitched cotton buff.
4) Buffing compound (I've used blade honing compound as it 'cuts' steel quickly, you could use jewellers Tripoli or brasso with good results)
6) A file.
Step 2: Selecting the Steel for the Punch.
For this project I've used an old carriage bolt (domed bolt). As I don't have a lathe to remove large amounts of material a piece of preshaped steel was important to reduce the need for labourious hand work ( this project is about saving money not losing time)
DON"T CONFUSE STEEL BOLTS WITH LEAD HEADED ROOFING NAILS!!!
lead is super soft and will conform to the shape of whatever it is hit against, meaning flat lead not domed metal.
when considering the steel you need to take into account the curve of the face. This bolt head is approx 28mm wide and 7mm deep. which is appropriate for the curve i want, you may need to look for a few different sizes before you get what you need. If you are going to use your finished tool in a commercially made dapping block CHECK that the dome will fit! also some carriage bolt aren't 100% round, if the aren't made round they can mar the side of the dapping block.
For a small punch a large nail or small bolt could be ground or filed to shape as less material needs to be removed.
It is also necessary to consider the condition of the face, you want it to be as smooth as possible, again to reduce the amount of work required to produce a quality tool.
Give the bolt a quick rub with 400 grit paper to help show any bumps or dings
- As you can see in the photos there are several marks in this bolt, there is the raise type along the top and a dent just to the left of the centre.
Step 3: Cut to Length
It is important that the tool is comfortable to use. This particular tool was to long.
Mark and cut with a hack saw.
The length of the shanks of the commercial doming punches I own vary between 8 an 12cm I've cut this one to be just over 9cm long.
Step 4: Round the End
Gently round the end of the stump. this is an important step. by rounding the end, even by only a few degrees you create a small crown this helps to direct the force from the hammer blow straight down the punch even if the hammer does not strike the punch perfectly flat.
Step 5: Starting to Shape the Dome
In the initial stages of shaping you want remove the bumps and dents identified in step 2, and if necessary modify the shape to suit your requirements.
Use a medium cut file to remove bumps and dents from dome, you want to use long sweeping strokes of the file. Starting from close to or on the outside edge, angling towards the centre you want to cover as much of the face with each smooth stroke as possible.
IT is important NOT TO FILE FLAT SPOTS ON THE DOME! this will result in an uneven finished product.
Step 6: Sand the Dome
In this step we continue to shape the punch with sand paper and remove the tool marks from the previous step.
Depending on how coarse the file or grinding stone was in the previous step, start with either 80 or 120 grit paper.
With the sanding stick use the same long strokes that you used with the file. The idea is to remove all the tool marks left by the stone or wheel.
Inspect the dome once you have sanded its entire surface. Then take a loose piece of the same grit paper holding the piece of paper in the palm of your hand rotate the dome against the paper. This help to even any out the sanding marks and leaves the dome with a uniform surface for the next grade of paper.
For a scratch free finish it is essential to remove all marks from the previous paper before starting on the next grit. So using the 240grit paper make sure you can't see any deeper scratches left by the 120 paper before progressing on to 320 or 400- It will be impossible to remove these later with having to start the sanding again.
Repeat this step, working your way through the different grits of paper coarsest to finest right up to 1200.
Step 7: Polishing the Dome
Once the dome was been sanded up to 1200 grit it should have a uniform face. To achieve a mirror finish it is necessary to polish the dome. This can be done either using a polishing motor or if you don't have access to a polishing motor with the use of a buffing stick.
To polish with a buffing stick load the leather with compound by rubbing the stick over the polishing compound. Then vigorously rub the stick back and forth over the surface of the dome. This is can be quite a labour intensive excercise and while a true mirrior finish is hard to achieve good results should still be possible.
NB: DANGER in the photos posted I don't have a guard on the motor. Not only is this bad practice it is extremely dangerous- polishing motor run at SEVERAL THOUSAND R.P.M. if what you are polishing goes flying there is a high probabilty you could be seriously hurt.
To polish using a polishing motor load the wheel by lightly touch the polishing compound to the spinning wheel. Hold the dome between 4 and 5 oc'lock on the wheel ( the position not the time) don't 'dig' the dome into the wheel but rather use a firm even pressure you'll get a feel for the correct pressure quickly. Move the dome so the face receives an even polishing (with softer metals it is possible to polish a groove into the surface- we don't won't this) Inspect your progress often.
Then rotate the dome 45' around its centre and start again- this is to polish out all the little scratches let by the 1200 grit paper as polishing perpendicular to a scratch is more effective at removing it. - repeat this rotation and polishing several times until the dome has been polish from all angles.
THINGS TO REMEMBER WHEN USING A POLISHING MOTOR:
NEVER OPERATE A POLISHING MOTOR OR GRINDER WITHOUT A GUARD ON IT
ALWAYS WEAR SAFETY GOOGLES
hold the item you are polishing firmly to prevent it from being pull from your hand
Take your time you'll get better results.
watch out that the piece doesn't get to hot, you can actually burn yourself.
Step 8: Using and Testing Out Your New Tool!
If you have a commercially made dapping block that your dome fits in you can use it. however if you don't have one you can also use a block of lead, urethane or a sand bag.
(If you using a lead block with silver or gold make sure that no lead is transfer to the metal by using a thin layer of latex or plastic wrap. Failure to do this can result in pitting of the silver or gold when heated.)
1) Cut a small circlular metal disk,
2) Place the disk on lead or dapping block of appropiate size
3) Centre the punch on top of it
4) deliver a few blows with an appropriate sized hammer
5) inspect your results and enjoy the wonderful feeling that comes when you make something yourself