Rotary backplate

[chronolith]

Can anyone offer some advice on putting the backplate back on a rotary valve as straight as possible on the first try?

When I put the plate back on it is very easy for the valve to start seizing because the backplate is not exactly straight and then it becomes a guessing game to discover which part of the plate needs to be tapped in to align it better. With a very snug fit and very narrow tolerances this can be fairly frustrating.

My hands are not strong enough to do this by just thumbing down the plates, and the access to the backs of the valves can be challenging depending on the layout of the horn.

[cjk]

lightly tap the rotor shaft on the other side of the rotor (assuming the stop arm and screw are not connected). The force from that should align the backplate pretty well.

[Jay Bertolet]

I use a nylon cup mouthpiece that I got in high school and never use anymore. I put the cup part on the back plate and use a rawhide mallet on the end of the shank to tap the plate down snug. Good luck.

[chronolith]

I bought a cap from a pvc pipe at Home Depot and tried to do something very similar to Jay Bertolet (similar to this one). The cap is obviously hollow in the middle as to not touch the exposed spindle of the valve but slightly smaller than the backplate. I use a wooden dowel to contact the back of the cap and lightly tap with a small plastic mallet. I thought the rounded top of the cap might help even out the impact no matter what angle the tap took place (just a few degrees variance, nothing too silly).

cjk - That sounds like great advice. I will certainly try that.

[bort]

I've heard of people using an old clarinet barrel for this purpose. Right size, nothing in the middle, and one more clarinet off the streets.

[jsmn4vu]

You may not get the back piece perfectly straight during insertion, but alignment occurs when you tap the top shaft. Final adjustment of clearance may require tapping from one side or the other. I see that it's been well described below.

[thevillagetuba]

I've heard of people using an old clarinet barrel for this purpose. Right size, nothing in the middle, and one more clarinet off the streets.

+1

[PaulMaybery]

The wooden dowel and rawhide mallet work for me. After I initially insert the back plate into place with the fingers. I do gently tap around the perimeter of the back plate using the end of the dowel struck by the mallet (much like tuning a drum head) going gradually one side to the other until it is in place and the spindle rotates freely. If it winds up being too tight a tap with the same equipment on the front spindle will loosen things a bit and then just keep trying. As was mentioned, rarely does it work perfectly the first time.

It is important that the plate goes in sufficiently so as to keep the rotor from having any in and out movement. You can test for that by grabbing the spindle and seeing if it moves in and out. If the tolerances are not optimal, you may hear some rattle coming from the rotor as you play. The rotors should move quietly without any clang if the spindle is properly lubricated.

I found that extreme care is important when cleaning the rotor. A tiny scratch on the spindle or the bearing can cause binding. Avoid inserting anything metal into either holes when cleaning. I usually use a Q-tip or a small bit of cloth on a wooden skewer or toothpick. Even certain corrosion cleaning chemicals such as CLR if not immediately flushed and neutralized can pit the surface of the shaft and back bearing and cause a raised surface which can also cause binding. This can be remedied with a little gentle polishing.

Regarding rotor noise, lubrication of course is obvious at all the moving joints.
But the bumpers can also be responsible for some noise if the corks or rubber bumpers are not secure and in all the way. I had one neoprene bumper that for some reason kept working loose and would cause a noticeable sound. For that matter loose screw on the bumper plate will also contribute.

The stop arm also must be secure on the spindle and the screw snug so as to not vibrate. These might seem like small little issues, but the tuba is a gigantic amplifier and magnifies those sounds.

I love it when I can get my rotors to be what I refer to as 'disturbingly quiet.' And at the moment they are. Life is good.

[Dan Schultz]

Getting the back bearing plate in straight is A LOT easier than one might think. I do what I can to eyeball the back bearing plate but the final 'staightness' is performed after the cap is snugged down. (NOT TIGHTENED... just snug). Rap the back cap with a small rawhide or wood mallet. The play in the threads will be taken up and the cap can be screwed on for another 1/4 to 1/2 turn or so. Repeat this until the back cap will not longer turn and the back cap will be perfectly flush with the back of the rotor housing. If your horn is not set up with the proper clearances and the rotor is a bit tight... loosen the back cap 1/4 turn and 'rap' the top of the stop arm to create a little clearance.

[MackBrass]

I do the same as Bloke on this. When seating the back plate take a euph mpc and tap it with a mallet. The euph mpc is about as close as you can get to the actual size of the back plate and centers it very well. For me a tpt mpc is iust a little too small and takes a little more work.