Metal Casting Zone

I am trying to make these custom cast guitar knobs for my bass but am having trouble. What i did is put machine screws through the foam hoping that it would make a threading around them. what actually happened is they were either compleatly stuck and would not screw or they would fall right out. I think a tap and die set might be the way to go but have never used one. Do you think this could work? I work in zinc primarily and I know lots of screws are zinc plated so I wonder if it is pretty much impossible to cast the threading.


my custom cast guitar knob experiment

Using a die to cut the thread is probably going to be the quickest and easiest way to go.

I'd be interested to hear if anyone has been successful in casting small threads.

to do that would I need a drill press for metal or can that be done with a normal drill. I have no expereince with dies

Sorry, I got a little confused, a tap is what you'll need.

A drill press would be nice but not 100% necessary, I have tapped holes that I have drilled with a hand drill. I can't imagine that zinc would be that hard so drilling shouldn't be a problem. Tapping should be also straight forward in that case.

How deep is the hole, and what is the thread of the screw you're using?

Threads can be cast, however they probably won't be great threads, and I wouldn't count on em being accurate or terribly rugged. To use a piece of metal for a core you first have to run it through a candle flame to get a good coat of carbon deposited on it. You can also use graphite but a candle works just as well. You can then set it in the core print and the metal shouldn't stick to it. After the piece is cast, put some penetrating oil on the threads, let it soak, and work it back and forth until it is free. If you don't put the candle black on the screw the metal will braze to the screw and you will not be able to remove it without stripping the threads as well (or get it out at all...)
Now, these threads that you cast aren't going to be great, that screw acts as a chill and the metal may have a hard time completely surrounding it before it freezes. You may be able to somewhat counteract this by heating the screw in good shape before you put it in the mold, close up and pour quickly while the screw is still fairly hot. This of course won't work with lost foam.
Your best bet is going to be to drill and tap the holes, you will wind up with a better thread. Threads are relatively cheap, under $10 for the smaller ones, and a set of vice grips will work for a tap wrench.

I've cut a lot of threads in steel over the years with no problem. I grabbed WD-40 or oil, whatever was handy. Then last year I was trying to cut treads in Aluminum, Totally different animal. I learned one thing, use the proper cutting fluid for the job. Getting a broken tap out is a real pain.

thread casting is mainly used on large coarse threads. you will find the zinc hard to drill!!! an electric drill and a high speed drill bit is needed . you see cast threads on small items ...draw knobs...handles. but these have been die cast!! wd 40 is the best lube on aluminium ...i tried kerosene today... which is recommended for aluminium... its not as good as wd40!

Sounds like I don't have great options in this situation. Maybe I could cast a good bolt into the piece and let it provide the threading. Thanks for all the thoughts.

mctc wrote:
Sounds like I don't have great options in this situation. Maybe I could cast a good bolt into the piece and let it provide the threading. Thanks for all the thoughts.excellent idea!! dave gingery recommends this approach quite often in his books about making workshop equipment.