Slide/Piston Lapping?

[Kory101]

So,

What is slide lapping? I did a quick search and didn't really find an answer. What does it do?

[Doug Elliott]

Wade, you're such a killjoy...

[Dan Schultz]

So, What is slide lapping? I did a quick search and didn't really find an answer. What does it do?

Once it has been determined that the inner and outer slides tubes are straight AND in-line.... fine lapping compound (basically grease that contains grit) is applied and the slide is worked until the desired amount of clearance is obtained. I've done this many times especially on #1 slides in order to make the slide more 'pullable'.

[Mike-ICR]

If it takes your tech more than a few minutes to lap two parts together then lapping was not what was needed and has probably damaged the instrument.

This isn't always the case. Many imported horns (not the good ones) come with poorly matched parts and need more than just a few minutes of lapping to get things right. Also, the techs you refer to often replace parts with poorly matched parts and they also need more time to work-out.Inexperienced platers over plate pistons, crummy techs over expand inside slides. Plus you never know what kind of compound the tech is using. Draw rings can only get so close and sometimes parts are unavailable. There are all sorts of problems that can come up to screw with the repair. I agree that lapping should only be done as a last resort or for fine tuning. I don't agree with a time limit.

[Mike-ICR]

Sorry, I should have been more clear. I'm not suggesting that lapping is a way to fix poorly fitting parts. There are methods (expanding/shrinking/aligning/straightening/dent removal/part replacement) to fix the major issues. I don't think spending all day lapping mismatched parts would fix anything or be worth the time. All I'm saying is that when it comes to the lapping portion of the process there are too many factors involved to assign a time limit. The quality of the parts, the types of repairs done to those parts up to that point, the speed of the tech, the grit of the compound and the type of metal being worked are just a few factors. A crummy tech could do a crummy job in 1 minute and a great tech could do a great job in 30.

Do the research, find a tech you trust, and let them do whatever they need to do to get your horn working the way you need it too. They are pros for a reason. Oh, and don't time them. They'll let you know when they're finished.

[hald]

Lapping is sanding using a very fine paste that usually contains pumice....YOU CANNOT UNLAP. ONCE REMOVED, THE METAL IS GONE FOREVER.

With that in mind, have fun!

Over the past few months I've acquired several instruments, new and old, that have stiff slides. I also read the thread about valve and slide oils and lubricants. In a way it's fortunate I encountered a tuba with slides so loose they would fall out, so I understand the dangers of lapping.

If an instrument has stiff slides what should the non-tech do? Is there a break-in procedure on a new instrument?

[iiipopes]

I can't remember where I heard this, but on new instruments, I've heard of cleaning everything off the tuning slides, holding them up over a candle to soot them with lamp black, insert them once and withdraw. Look for the places that the lamp black rubbed off to bright brass, then very gently rub just those places with a little Lava soap suds. Then clean and check again. At the point the entire slide comes out looking even, stop, clean up everything, lube and use.

[Mike-ICR]

sorry, elephant and I were (kinda) screwin' around...and the site owner prefers that we avoid a lot of sarcasm on the "TubeNet" forum...

"Lapping" (when the word pertains to brass instruments) generally refers to this:

Two "action" surfaces are already the correct dimensions, located in precisely the proper places, and already move reasonably freely against each other. "Lapping" is when those two action surfaces have a mild abrasive put between them (600 - 2000 grit...??) and are set in motion to allow the surfaces themselves to "define" each other.

bloke "OK spectators...Is that a sufficient explanation/definition?"

Don't worry about it. Actually, I choose to follow your (Bloke/Elephant/Tinker) post because I like the wit.

In this case I overreacted because I encounter many "nosey know it alls" around here. A few years ago I started inviting customers into the shop while I worked on their horns. Bad idea. I have nothing to hide, I'm actually very proud of my work and I enjoy a very good rep around here. Even though I work relatively quickly and I use generally accepted techniques I still got customers saying "should it take this long?" or "what's that tool you're using?" or "is that the right way to fix that?". It was very frustrating so now I tell most customers to go and get a cup of coffee. By the time they get back it's time to play test!

I LOVE your definition! So much so that I saved it for future reference. I notice you didn't include a time limit.