Hand lapping

[TubaSailor]

Hi - since nobody with real authority on the subject has chimed in - I'll put in my 2c worth - Lapping (valves or slides - same basic process) is done by coating the opposed surfaces of two closely fitted pieces with a fine abrasive paste, usually with a grease base, and working them against each other. This removes metal only where the two pieces touch (or come closer than the grit size) It can be overdone, hence "hand" lapping to limit the cutting and give a feel for when the pieces slide well, but still fit tightly. If overdone, the pieces need to be plated to fit tightly and re-lapped. Lots of time, skill, and patience involved to do it right.

Hope I helped.

[TubaSailor]

Hi Elephant - I hope I'm not encouraging him to try this himself - hence the caveat about " it can be overdone", "Lots of Time, Skill and Patience" " If overdone, it needs to be plated to fit" Your advice is 100% on the money - but nobody had yet offered such advice. I also took the question to be a request for information rather than a "DIY" how-to destroy a horn question. If I was wrong flame away! I got the impression that the question was based on the Yamaha advertisements, and he just wanted to know what they were touting.

[Dean E]

Hi - since nobody with real authority on the subject has chimed in - I'll put in my 2c worth - Lapping (valves or slides - same basic process) is done by coating the opposed surfaces of two closely fitted pieces with a fine abrasive paste, usually with a grease base, and working them against each other. This removes metal only where the two pieces touch (or come closer than the grit size) It can be overdone, hence "hand" lapping to limit the cutting and give a feel for when the pieces slide well, but still fit tightly. If overdone, the pieces need to be plated to fit tightly and re-lapped. Lots of time, skill, and patience involved to do it right.

Hope I helped.

Here's another method. DO NOT TRY THIS AT HOME. For professional use only.

Rather than lap the surface of a valve against its metal cylinder, another method is to lap a valve surface by rotating the valve in a split fixture made of wood or other soft material.

The valve is lightly sandwiched between the two halves of the split fixture, and contained in a cylindrically conforming aperture. A fixture can be made by drilling a hole in a piece of oak, and then sawing the oak piece in half, through the center of the drilled hole.

The split halves of the fixture are adjustable (by clamps, screws, or bolts) to reduce the distance between the valve surface and the aperture, and to increase pressure lightly on the spinning valve and lapping compound.

[windshieldbug]

How'd you find such a fetching picture of Camilla? She doesn't look THAT good all the time, you know...

[andrew the tuba player]

I wasnt gonna try to do it. I'm smart enough to know not to. I was just wandering. Thats been a question that ive had a long time And yeah, i was referring to the yammaha advertisement.

ya hear that Elephant? I'm not stupid. I know when i can and cant do things. As far as my project goes, Yeah, it is the schools, but i have permission to do what i want with it. They were gonna throw it away (they did throw away the old body). And, if i let the band director do something with it, then nothing will got done bc we dont have the money. I dunno if your used to being in a school with a very small buget, but we have to do alot of repairs our selves and everytime we need something fixed they come to me...ands the lost piston...Just get off it ok? Yeah i screwed up but, hey we all do sometimes. I know that this is a proceedure that takes many years of practise and perfection. I'm not gonna try to do it at home...And if i screw this horn up what have i lost? I've lost nothing. I've lost a horn that isnt able to function. And, yeah thats how my band director sees it. And just so you know, its not the 20J. Its a very old fiberglass souaphone that was falling apart that im putting a valve section on. So lay off man. All i wanted is some info. I would hope that noone would keep that away from someone who wants to learn.

[ken k]

new words to the old classic...

Mary had a little lamb, little lamb, little lamb.

Mary had a little lamb, with mashed potatoes and gravy......

ken k

[Tubaguy56]

hmmm, even though the horn is in "throw away condition" you may still want to get an estimate on the horn. if the valve is really the only issue, take it to a repairman and get an estimate, if he can fix it and your band director doesn't want that horn, hey, free tuba. (not to say this is a good thing to do morally, but I also highly disagree with throwing away a horn thats only "lost" one valve). I took some "throw away" condition trombones from my high school that my band director didn't want (to my credit i asked him how much he wanted for them and he said 5 dollars each). I had them all repaired for 50 dollars, 3 trombones with a net cost of 165 dollars, and they all play fairly decently. I've seen horns like these 3 sell for more than the price i paid for the repairs, so, something to keep in mind.

[andrew the tuba player]

i don't wanna throw it away. Thats actually one of the things i like doing. takeing horns noone thinks could be good and makeing them beautiful. I'm still searching for the valve. Im pretty sure that It's probably laying right in front of my face. I really need it to work cause the other fiberglass souzy wont play in tune at all...so, yeah, im not gonna throw it away...They threw away the body that the valve section came off of. The body was scrap...so, it had to be done to conserve space...

[tokuno]

new words to the old classic...

Mary had a little lamb, little lamb, little lamb.

Mary had a little lamb, with mashed potatoes and gravy......

ken k

Mary had a little lamb, a little beef, a little ham.
Then she passed her plate again and had a little more.

[andrew the tuba player]

good one.