I have the Waldron punch set and it says to use a soft metal (like brass) or nylon hammer. Personally, I use the back end of #3 Xacto handle. I biggest concern is not damaging the striking end of the punch. As long as the hammer is of softer metal than the punch, you should be fine. Micro-Mark sells a hammer with different faces on it: http://www.ares-server.com/Ares/Ares.asp?MerchantID=RET01229&Action=Catalog&Type=Product&ID=83380
Just stay away from using a hammer with a steel face. I also noticed in the picture of Micro-Mark’s punch set, that it looks like either side of the punch can be used in the die. On Waldron’s set, one side of the punch is flared for striking while the other side fits into the die. As a word of advice, I would mark one side of Micro-Mark’s punch as the striking end and use that end only to strike with your hammer. That way, only one side of the punch will suffer from wear over time. Just my opinion.
Mike…as a caution…brass can pein steel that hasn’t been heat treated properly. Try the soft faces of the hammer first and see if they have enough heft to do the job. I’m not familiar with the punch set…but it would be sad if the punches were not fully hardened…for striking and for maintaining a sharp cutting edge.
I think that might be over-kill. That kind of hammer is used for striking chisels and such. It’s kind of big for modelling. I think you might be suprised out how easy the die will go through thin plastic. Like I said before, I just the back end of #3 Xacto handle. One hit and I’m through. Just a though…
I have a similar puch and die set, but a little larger. I’ve used soft steel hammers on them with no problems. But I’ve also had to have the cutting end of the punch sharpened a couple times. Most all are just case hardened steel. Lyman sells a neat little brass headed hammer that also has a nylon head on it. You can get the hammer at just about any gun shop.