Saturday, December 15, 2012

Pleased to Meet you, Mr. Project Trumpet!

As I write this, I am actually just about done working on my project trumpet. We've covered a lot of ground at school this semester, and it is tough to keep up with all the activities we get to work on, so I apologize for not writing about this yet. This post is a quick overview of my project trumpet, showing how it was when I received it, and the first few steps to fix it.

When I first looked over the instrument, a Bach student trumpet, the first thing I noticed was many dents alllll over the instrument. Almost too many, hmm... But, really these horns are our chance to practice a lot of standard repairs and dent work that we learned about in class--things that can happen all the time in real life to people's instruments. So essentially, if the selected horn didn't have the problems we were looking to fix, said problems were (ahem) added on a case-by-case basis.

Here it is!  A lovely shot of the bent mouthpipe and lower-main to 3rd casing knuckle dent.

More knuckle dents on the opposite side of the valve block.
One of the problems we all had to fix was alignment of the mouthpipe, bell stem, and bell bow. Some instruments were a lot easier to adjust than others. My mouthpipe and bell seemed to be in the medium-hard range. As with dent work, we needed to treat these alignments "like butter" to start with. You can always add more force, but it's tough to go back when you've done too much.

Looking down the length of the horn, you can see where the mouthpipe, bell stem, and bow are all bent. Plus some nice dish dents along the bow!
 Before straightening or any other work, we had to first check-in, then disassemble and chem-flush our trumpets.

All pre-cleaned and ready for the chem-room! See the anodized aluminum valve stems? Staying right where they are, on my bench, since they'd turn into little bath-fizzies in the phosphoric acid pickle. Part of cleaning is separating out any reactive parts.
With everything cleaned, and all needed work logged on the repair tag, it was time to do some flexing. First: the bow! I started by hand, as below, but couldn't get it to move enough to straighten completely.


I used some clean buffing gloves to get a more cushioned grip on the bow. The vise holding the bench peg is loose (pivots if turned) to ensure proper bracing while flexing. Also check out the lovely sharp dent in the throat, ow!

To get enough force to move the bow where I wanted, I had to loop a woven belt through the bow, put both belt-ends in a vise, and snap the bow downward against the belt. This was a technique created in a shop that worked on many Yamaha trumpets, which have notoriously thick bells, making them tough to move. I'll post the name of the technique as soon as I get back to my notes, to give credit where credit is due.

Hooray! The belt worked great, and it's all straight again. What a cool idea.

More to come soon on dents and my mouthpipe project. Since the mouthpipe on my project trumpet had a tiny spot of red-rot or dezincification, I got to use this instrument for that project too. Stay tuned!

Tuesday, December 4, 2012

Trumpet Inner Slide Mandrel Project, or More Fun with Lathes

Hello again! Another lathe project post. This time our mission was to turn a piece of brass stock down to a specific diameter and thread the end to fit a bolt. The diameter needed to be within 0.001" of the goal so that we could use it as a mandrel to fit a standard inner slide tube on a trumpet. First I faced the end of a piece of stock, like in our earlier projects. Next I touched off with the tool bit near the end of the stock, and re-set the micrometer scale on the cross slide to zero. This allowed me to control the amount of material to be removed with each pass as I turned it down. Because we have so many different lathes in the shop (yay!) I had to be careful reading the scale on the cross slide. Since the stock is spinning in the chuck and material is removed on both (well...all) sides of the stock, for every 0.001" I advanced the cross slide, the tool bit removed 0.002" of material. 

To check how much material I was actually removing with each pass, I did a test pass first, then checked the new diameter with my caliper before turning the full length of the stock I had measured out. 

The first test-pass! The tape in the chuck helped eliminate chatter, since the stock was extended a bit farther than usual.

Finishing the first full pass...


In total we reduced the diameter by about 0.050" and used multiple passes to accomplish the finished dimension. The finishing pass had to be within 0.005"-0.015" so that the stock would have the cleanest finish and accurate dimensions. Although you can safely remove up to 0.050" of material in a single pass, we did 4-5 passes in total to get more practice with the process.
Action shot of turning!
Next we drilled and tapped the end which would fit a bolt to hold the mandrel...

Using the live center to steady the tap for the first few twists.

Voila! Another new tool:


Again, it was very neat to work on the lathe, and I feel lucky that we have so many to work on at school here.