You hammer is likely too light, or you are not holding the wedge tight enough to restrict its motion. What type of hammer?

You need two things a 3lb hammer and a really solid piece of metal (anvil) to put the wedge on.
It may not seem like it but you a moving quite a bit of metal to make a deep imprint.

Do I need a golf clamp?

How can I keep the wedge from moving?

Beyond what the others are saying of needing an anvil and a 3# or larger mallet hammer. I also use double sided tape to stop the wedge from shifting on the anvil and it takes a lot of force. Once you get an imprint I always hit it multiple times from all angles to make an even impression.

It takes a lot of practice but looks really good when you have personalized SM6s

Is there a cheaper substitute for an anvil? Thanks

Try seeking a machine shop that might do it for you. Downside is, it is a small job and they might not do it....on the other hand they might do it for free since it is a small job and won't take much time. Good Luck?

Hi guys, chiming in regarding...
Golf clubs are made out of Carbon Steel..
Carbon hardens the steel, during the air cooling process.
I say, hardness raises to 58/60 on the Rockwell C scale.

Your not stamping that with a hammer.. Take it into a machine (CNC) shop as suggested above. FYI, CNC shop will use a ball nose "Carbide Tip", High Speed Cutter, end-mill.. Hope it helps..

Umm no - a casting like this might be high-30's to low 40's on the "C" scale. With the proper tools hand stamping shouldn't be too difficult.

I do my own stamping/painting quite often, just tinkering. It also depends on the stamps you have, I'm on set #3. And we're not talking the $20 sets on Amazon or your local cheap tool shop. You need a VERY stable work station, or vise. I use a steel plate table in our shop with the wedge head directly over a table leg. I also use a safety eyeglass set with a cheater lens in it, for precision. If you don't get the imprint you desire, you MUST re-align the stamp perfectly before re-striking, and re-check between strikes....You need good stamps, and ALOT more energy on your strike than most would believe.....