Hinge Rod Replacement

Who wants to see me make a replacement hinge rod? No one? Too bad, because that's what I am going to show in this post.

So on my school clarinet I found the G#/C# key had a lot of lat play. Because of the way it is made swedging is impossible. The only option is to replace the hinge rod with a larger one. So that's what I did.

Here is the problem key. I can't really show the play but trust me, it's there.

So the first step is finding the right size drill rod to replace the current rod with. I started by measuring the old rod and then trying over sized rods till I found one that fit.

Notice there is hardly any difference between the two. However, a few thousandths of an inch makes a big difference in instrument repair.

Once i found the right size drill rod I found that the key was bent. This was determined by the fact that the new rod would go in about 3/4 of the way and get snug. This happened from both sides of the key.

So how do you fix the bent key? You hit it.

I braced the key on either side and hit it with a light mallet  to bend it back into straight.

After some percussive motivation the key was straight and moved freely on the over sized rod.

So now it was time to cut the new hinge rod out of the drill rod stock.
I began by chucking the new rod in the bench motor and measured the major diameter and pitch of the old threads. I then filed the new rod down to that diameter.

More and more filing went on. I put a sharp face on the end of the taper to give the screw a solid stopping point when it hit the post. I cut a deeper grove in the end as well to prevent the threads from tapering. This probably doesn't make a whole lot of sense so here are more pictures.

Oh no. It's time for math. There is a formula to figure out standard threads via the pitch and diameter. Unfortunatly, while Vito does use standard pitches, they do not use standard diameters. The standard system  goes from 0-12 in whole numbers. This thread came out to something like .57. So what now? I can't cut it to a 0-56 or it will be loose in the post. I can't cut it to a 1-56 because it won't even fit in the post. The solution is a split die. They allow for expation and contraction of the cutting teeth. I slimply put the old screw into a 1-56 die and tightened it until it fit snugly. There is my .57-56 thread.

Now to cut the threads!

The key here is to, one, keep the teeth lubricated and clean, and two, to get the die started square.

Time for more filing. This time I just want to put a strong edge back on the inner end of the threads.

Pretty, huh? Now to cut it to length. First I put it into the instrument and marked the length I needed with a file. I then cut it off, faced it and put a slot in it for the screw driver.

Well, there it is. New hinge rod. In my next entry I will have to repeat the process. However, the hinge rod isn't the issue. It's something more. Stay tuned.