more knowledge sharing (HOLTON 345) - valve-whistling SOLVED

[bloke]

OK...Credit is due to the smart young man who owns this instrument re: pointing me in the right direction to solve this problem.

345 tuba pistons (ALL of them) make a "whee-whoo-whee-whoo-whee-whoo-whee-whoo...etc." noise, when they go down-and-up.

The top vent holes were drilled ADJACENT to the stems, defining that the washer actually COVERS UP the vent. (THAT's STOOPUD!)

Further, the vents (I ascertained - after using a hole-punch on the washers - as the whistling sound DIMINISHED, but did NOT disappear) are TOO SMALL.

...so I drilled NEW LARGER upper vent holes (the piston hat-metal is THICK !!!) away from the washers (aka: "felts") and ALSO beveled the holes.

UNLESS I'm imagining things (I think NOT ), the whistling HAS STOPPED.

...the slightly rough edges on the outside rims of the bevels...??
They PROBABLY make it play out of tune in the upper register.

[the elephant]

I have found that chamfering the ends of these holes on all my pistons has helped with this. (Mine are all large enough. I just softened the edges without having to drill them out, or — heavens to Betsy! — MOVE THEM. WOW! Good job!) Further — when practicable — I will chamfer the Inside edge of the same holes.

The excellent Japanese firm Noga makes a blade for their deburring tool handles designed for this exact purpose. It is great for deburring the inside edge of things like one of those 3 to 5 mm waterkey holes that were drilled with a too-slow RPM, thereby leaving a "shark tooth" on the inside.

It works pretty well on piston vents, too. It depends on whether there is room (depth) for the blade. It is angled like 30º so it might not fit through such a small hole if the material is too thick.

[djwpe]

I have found that chamfering the ends of these holes on all my pistons has helped with this.

I was about to respond similarly. I had a case where a piece of HVAC equipment manufactured by a friend had a distinctive tonal from. Airflow through a nozzle which i identified in testing. We ended up redesigning the air nozzles to reprofile away from the sharp edged exit and that eliminated the tonal.

Don

[bloke]

One thing that I did learn - due to supplying more airflow - was that the entire brazed-in tops of these vintage Holton pistons are very thick slugs.

I’m one who appreciates a combination of minimal mass/weight while maximizing strength - particularly where movement and velocity are involved.

These piston tops needed to be no thicker than 1/16 inch, except in the center - where the threads are located for the valve stems. Knowing the original thread size, a deep center (drilled/threaded) cylinder of brass certainly wouldn’t need to be more than 3/8 of an inch in diameter, and perhaps even only 5/16 might’ve been adequate.

Anyone who’s ever picked up a 1930s 3/4 inch bore York piston - and noticed how featherweight they are (even though they feature an extended length), will appreciate this contrast.