adjusting '80s Miraphone rotor linkages

[jtm]

a Miraphone rotor with little off-white plastic linkage attachment

miraball - 1.jpeg (61.56 KiB) Viewed 732 times

Looks like I got too close for the phone camera, but it should be good enough to id the part. I normally just start unscrewing things to see what happens, but it's mostly working great, so I'm asking here first before I mess it up.

Are these rotor link connectors adjustable for backlash? All the rotors are smooth and fast, but some of them are a little clicky, like there's play in the connector. Is the screw in the end an adjustment? Or does it cover an adjustment? Should I be ready to glue it lightly in place after I finish adjusting?

[bloke]

It’s pretty simple:

The nylon screw in the end of each link should be adjusted so as the valve moves fast and clicking is eliminated - or is nearly inaudible.

Helpful - for determining which end (if not both ends) is clicking - is to hold the stop arm in place and gently depress the lever. When you do this, you will see the white link moving slightly over the steel ball, and will know that there is some play that you can remove.

Don’t confuse rotor noise with linkage noise, by the way. Rotors that rattle up and down usually create much more noise than do loose links.

If you find that it’s difficult to remove all of the play from some of the DVS links without them jamming, there might (??) be some nylon burrs inside one or more of them that need to be cleaned out.

This is a low tech system, and it’s very easy to adjust. To remove a link from a ball (if this seems to be necessary…??), just loosen the screw adjustment screw in the end and pop one off. Being old, there’s a chance that they will break, but they probably will not break. To decrease the chance of breaking, you can pull up by putting a dinner fork with wide prongs – wider apart than the width of the steel ball – under the link, and pull up on the fork.

Is that a gold brass 188?
If “Yes“, have you had it, or did you just buy it from Rob?
Is this none of my business?

[jtm]

Thanks!

Yes, it’s new to me (via Rob), and probably not. It’s a really nice tuba; better than I deserve, but at least now I can’t blame the tuba for any problems with my playing.

[bort2.0]

Thanks!

Yes, it’s new to me (via Rob), and probably not. It’s a really nice tuba; better than I deserve, but at least now I can’t blame the tuba for any problems with my playing.

That's one hell of a nice tuba. Identical to the one I had. If I were you, I'd order a handful of those nylon joints to have on hand. They break after a while. And are simple to replace

[bloke]

That's one hell of a nice tuba.

sorry...(WARNING: YET ANOTHER BLOKE NON SEQUITUR)
Before moving away from crime and heavy taxation, we had a nice two-story house on a small lot with a backyard gate that led over immediately to a very large city park (football/soccer field, baseball diamond, playground equipment, shade trees, etc.), an elementary school, and a middle school (extremely convenient).

We would OFTEN fly kites (cheap ones) in HIGH winds - over there...and use string from a VERY old and VERY large ball of kite twine (just a bit brittle, due to age).
Due to the age of the string and the velocity of many of those winds, most days would end up with the strings breaking, and the kites flying away.

We would end nearly every one of those outings saying, "That was one helluva nice kite", and laughing - as we were always expecting it, and making jokes about the children in China - who would receive and enjoy that kite, in a few days.

[jtm]

You were right. The links were adjusted right — tightening made it harder to work the rotor, and there was no visible play. The clicking is from axial rotor play. If I push down lightly on the top screw, there’s no noise.

Oh, well. If it had been that easy, Rob’s guy would have already taken care of it.

[bloke]

That's actually easy to - at least - b.s.-fix: (ie. make them as good as they can be, without altering any metal)
> Round up a worthless piece of sh!t trombone mouthpiece (garbage/scratched up/bent-shank/etc.)
> Round up a hard plastic mallet. (Rawhide is OK...but this will be hard on a rawhide mallet.)
> Unscrew the valve caps and set them aside (in order, if wish, particularly if they are indexed on their interiors), place the tuba upside-down in your lap, place the face of the mouthpiece on each of the rotor bearing plates, and whack on the (facing upwards towards you) shank of the mouthpiece. AVOID hitting the tuba elsewhere by LOCKING YOUR SWINGING ARM'S ELBOW IN PLACE (perhaps, against your own rib cage). This should drive all of the bearing plates "home". If any of them no longer turn, flip the tuba back over and moderately tap on the center screw JUST until a particular valve turns freely again.
> Reinstall the caps, grab a sharp-bladed screwdriver with a c. 1/8" wide blade (Mrs. bloke would label a "saxophone screwdriver"), and screw the valve caps' center screws in JUST until each valve locks up, and then BARELY back off each screw until they - once again - BARELY turn freely. (Often those cap screws' threads are TIGHT, so use ENOUGH downward pressure on your screwdriver to AVOID fubar-ing the screws' slots. If your fingers and wrists are not particularly strong, you might - depending on whether any of those screws are lacquered-in or corroded in - be semi-outah-luck.)

This is the best you can do, without (if needed - on any of them) barely skimming the inside surface of individual bearing plates (.001" - .003" or so, depending on how much vertical bearing wear) with a lathe.

Hey...If any of this is not clear, Wade can explain it in even more words - along with his disagreements.

You were right. The links were adjusted right — tightening made it harder to work the rotor, and there was no visible play. The clicking is from axial rotor play. If I push down lightly on the top screw, there’s no noise.

Oh, well. If it had been that easy, Rob’s guy would have already taken care of it.

[kingrob76]

It could be tweaked for sure, but that fell into the end of diminishing returns for me. My experience was the sound was intermittent, and I used it as a reminder to apply oil (which for some reason I never remember to do on rotors like I do on pistons). The adjustment is low-tech but for a non-tech it was always tedious for me to get "just right".

[bloke]

Miraphone ships their rotor bearings “just right“. I think it might be an interesting idea for them to consider grinding the bearings down just a little bit too tight, to allow for a decade-or-five of wear. I think this might be more beneficial than the cute little screws in the valve caps.

[jtm]

What’s the purpose of the cute little screws in the caps? I’m assuming it’s NOT for applying oil.

[bloke]

What’s the purpose of the cute little screws in the caps? I’m assuming it’s NOT for applying oil.

...so you didn't read one of my posts, above...

They are a stop-gap, as a substitute for removing and skimming worn rotor bearings on a lathe.

[jtm]

What’s the purpose of the cute little screws in the caps? I’m assuming it’s NOT for applying oil.

...so you didn't read one of my posts, above...

They are a stop-gap, as a substitute for removing and skimming worn rotor bearings on a lathe.

I read it. There's a procedure for what to do with the screw, but not why. When tightened enough, does it introduce a new point bearing surface? If it's a temporary "stop-gap", what did Miraphone envision as the normal use case? My mid-60s 186 doesn't have this feature on its rotors.

[bloke]

What’s the purpose of the cute little screws in the caps? I’m assuming it’s NOT for applying oil.

...so you didn't read one of my posts, above...

They are a stop-gap, as a substitute for removing and skimming worn rotor bearings on a lathe.

I read it. There's a procedure for what to do with the screw, but not why. When tightened enough, does it introduce a new point bearing surface? If it's a temporary "stop-gap", what did Miraphone envision as the normal use case? My mid-60s 186 doesn't have this feature on its rotors.

The "why" is bearing wear, which causes clicking - due to the vertical movement of the rotor body.
Oiling the bearings nearly eliminates bearing wear, but almost no one oils rotor bearings, and Miraphone knows that almost no one does it.
When bearings are worn, they can be driven all the way home (during installation or adjustment), but there is still a vertical gap - thus a clicking noise.
Rotors ride up - when rotated quickly, and smack against the upper bearing. When they fit perfectly, there's no "riding up" possible.
Since the 1970's, there has been an emphasis on rotary valve noise reduction (nylon bushings in S-arms...DVS ball-socket linkage...Minibal links, etc., etc... thus the appearance of the screws in the centers of the valve caps.
If the fact that the bearings are worn (assuming each of them is driven home) bothers you, take them to a machinist and have him skin them (only the worn ones, which click) a little bit. I'm wiling to talk to a machinist on the phone...but you'll surely need to be the one to remove and reinstall the rotors. The machinist will know how to run his lathe, mill, grinders, cutters, etc., but not necessarily (without being shown) how to remove and reinstall rotors on a tuba.

There's actually a way to determine how many thousands of vertical play there are with calipers (to measure) and a screwdriver underneath the stop arm (as a gentle lever) - carefully lifting it, measuring, letting it fall back into place, and measuring again.