Page 1 of 1

Valve surface finish

PostPosted: Sat Jul 20, 2019 8:17 pm
by WillDellinger
Ever since I saw that a typical Hetman lapping compound is just 1200 grit, I've wondered how smooth a piston is supposed to be.

I got MAW valves for my horn and after being lapped in by a local shop, I can see that patches of the valve are very shiny (fingernail moves very smoothly over it) and other patches are grey/dull/slightly pocked when you look really close.

But I know oil - bearing surfaces shouldn't always be very smooth. Like hand - scraped mill/lathe ways that need to slide vs super smooth jo blocks.

I will say...the valves work okay but not great.

Re: Valve surface finish

PostPosted: Sat Jul 20, 2019 9:55 pm
by the elephant
Lapping is an overused way to try and solve valve or slide problems without a ton of work (passed on to the customer as a higher price that might cause them to not return in the future). There are *many* issues that can affect rotary and piston valve movement and lapping indeed does cure a lot of them, but in many cases it is just a simple bandage over a more serious wound.

Also, lapping compound comes in many different grits. Hetman offers several, but you have to be a shop to get a hold of anything other than the 1200. The smooth parts were there before. The dull-looking patches were lapped. It is a type of liquid sandpaper, and it can make a sticky valve much worse if it is overdone or done improperly. If your tech *only* suggests to you that lapping is the answer without volunteering better methods it is probably because he does not know those methods or own the tools needed to perform them (more likely, IMHO). I would always seek out a second opinion when it involves valve acton work and sanding off material from the valves and casings. Just because a tech offers a few different ideas at varying price points does not mean you have to pay the highest one, but it does let you know you are dealing with someone who knows valves pretty well. I lap stuff a lot. But most of what I deal with is stuff that will be improved by removing some material. I also own valve dies and casing slugs, a set of reamers that have had the blades polished down, etc. I use whatever it is I need. I get whatever tools I need if the job merits the work. I also know very well my limitations and standards and that I don't know half of what a lot of guys know on this topic. Sometimes I call a friend who knows the particular problem and get a brief tutorial on the phone. I am always afraid of taking off too much. I suppose I would have made a slow and timid barber, huh? HAHAHA!!!

There are always alternative methods and tools. Try to steer clear of a tech who only offers to take metal off your bearing surfaces to restore lost action.

Best of luck.

Re: Valve surface finish

PostPosted: Sun Jul 21, 2019 9:27 am
by bloke
I haven't put those Meinlschmidt valves in any tubas for several years, now, but - in the past - I tried them out in at least five tubas, and kept them in two of those tubas.

I put them in the casings, oiled them, there was some minor sticking for about 30 minutes, and then they worked great - no "lapping".

I tend to wonder if people mis-diagnose/overlook/do not adequately fit (new) valve guide issues, as it requires quite a bit of attention to detail and powers of observation (of things tiny) to property trim valve guides.

my secret...?? I simply (carefully, gingerly) moved the already-fitting guides over from the o.e.m. pistons. :|

When I do have to fit valves to casings, I leave the commercial lapping compounds that I own on the shelf, and use automotive paint polishing compound... #7 (no longer Dupont, but the same stuff, and still in a white and light green tub)...and mix it with thin oil...slightly thicker than valve the lubrication is not merely water-based, and thus won't evaporate from the heat caused by friction.

If valve will not already go into casing and can be made to manually go up-and-down, they are too ill-fitting - at that point - to "lap", and more actual repair or sizing is required. Likely (if worse-fitting than that) at best, someone would probably break off the valve stem and - at worst - the piston will hang, and badly score the piston and the casing.

bloke "time to go back out to the shop, and be a Sunday Sousaphone Slave"

Re: Valve surface finish

PostPosted: Sun Jul 21, 2019 2:37 pm
by WillDellinger
I looked at everything I could figure on the horn before taking it to the shop. I did measure the guides to be a bit "taller?" (Further from the center of the piston) than the OEM valves. But filing them down to match the others did not make the difference. And their other dimensions matched. When first purchased, the valves would go in the cylinders, work alright for about 15-30 strokes, and then get quite stiff/stuck. Both the cylinders and the pistons were clean

In as many places as I could get the micrometer, the old and new valves were the same size.

I'll end up putting in a purchase request to have the valves fitted better by a different shop since it's a gov horn, but I was curious to get some input on what the optimal piston surface is.

Re: Valve surface finish

PostPosted: Sun Jul 21, 2019 5:05 pm
by bloke
...the valves would go in the cylinders, work alright for about 15-30 strokes, and then get quite stiff/stuck.

not to be argumentative, but - having repaired way too may brass instruments - I never have found another cause for inconsistent fine-then-bad valve action other than dirt or lime.
Lime - fwiw - is invisible, unless casings are "bone dry", and then it shows up - if well-lit - as a white or whitish-green coating.
With lime, casings are - basically - coated with limestone, and - compared to brass or other malleable metals - limestone isn't the greatest surface for reliable surface-against-surface movement.

Re: Valve surface finish

PostPosted: Sun Jul 21, 2019 7:03 pm
by WillDellinger
I considered the lime. But I cleaned well, let it all dry, and saw no white.

15-30 may have been generous. I think it was something else. Especially considering that all 5 sets of old valves (3 OEM, 1 Maw) from among the three horns that use that valve set worked interchangeably, but the new maw set wouldn't work in any of the three horns.

...actually the horn they are currently in was the horn in which they were closest to working in the first place.

I suppose this has turned into two separate questions...
But does anybody know about the surface finish thing?

Re: Valve surface finish

PostPosted: Sun Jul 21, 2019 7:54 pm
by bloke
I attempted to answer it without a number, but hinting that 1200 is probably more coarse than top industry standards.
Again, what I use is designed to take the final tiniest scratches out of car PAINT - YET, without going through the paint...and even it, then, is diluted with oil. Coarser that the "polishing" compound that I use is "rubbing" compound, which is designed to remove worse scratches from car paint, and also to remove oxidation from car paint - yet - still - without going through the paint.

I have noticed that recently-manufactured USA tuba/sousaphone pistons' surfaces are quite coarse (and loose-fitting as well) certainly compared to 1960's standards, the time during which - arguably - some of the highest-level USA manufacturing occurred.

The stuff I use - OK...since it's not labeled "lapping compound" - some might look askance at it...but - a few years ago - Peter Hirsbrunner, Jr. sold me a set of pistons which FIT an instrument (perfectly) that I was trying to get up-and-running (a what-in-the-heck-happened-to-the-pistons-?!?! 4/4 tuba) which all worked quite nicely, but were all nicked up (small dents). They were the only ones he had, and he charged me accordingly (a bargain price). Dave Secrist, prior to his retirement, rebuilt them for me (to the same dimensions), and I refit them into the casings. (Typically, automotive "rubbing" compounds (if you can find the specs on them) are around 1200 grit, but - again - this is "polishing" compound...the next step BEYOND "rubbing".) That was the very first time that I tried what I use, and the surfaces ended up WORKING and LOOKING just as I desired (resembling o.e.m.) Oh yeah...and it's only three bucks.

those aftermarket Meinlschmidt pistons needing to be lapped/fitted:
Yeah, I've heard about it, and even have had someone tell me that they are "authorized" by their designer/retailer to do it...but I've never had to fit those pistons to any B&S-made (B&S or M-W) tubas in which I've tried them.


Re: Valve surface finish

PostPosted: Sun Aug 04, 2019 6:58 am
by hup_d_dup
WillDellinger wrote:But does anybody know about the surface finish thing?

It looks like you will have to ask the question in a different form.

Or maybe start all over in a different thread.


Re: Valve surface finish

PostPosted: Sun Aug 04, 2019 8:36 am
by the elephant
hup_d_dup wrote:
WillDellinger wrote:But does anybody know about the surface finish thing?

It looks like you will have to ask the question in a different form.

the elephant wrote:… The smooth parts were there before. The dull-looking patches were lapped.

He never actually asked a question beyond what I answered, so far as I can see. What he asked was akin to "Does anyone know about cars?" It needs to be tightened up so that something specific has been asked. Please point out the actual question that was not already answered by me.

BTW, if Hetman sells mostly 1200 grit lapping compound then it is probably pretty effective. I personally use it when it cannot be avoided. I also use more coarse and more fine compounds. Good stuff.


[EDITED for idiotic typos and poorly constructed sentences that did not really say anything, sort of how my mind works...]

Re: Valve surface finish

PostPosted: Sun Aug 04, 2019 5:01 pm
by roweenie
I haven't lapped any valves (not only have I been "lucky" to not need it in any of my projects, but if they did, I would only trust that to a seasoned pro), but for lapping valve slides, I've used the Dupont #7 that bloke recommended, with good results. Used with a light oil, it works well.

There is another lapping compound I've used on slide tubes called "Timesaver", that I've also used for lapping the babbitt in crankshaft and connecting rod bearings, where tolerances need to be just as precise as piston valves. I usually use their number 100 yellow, made for soft metals:

The thing I like about it is that it is so fine that it is designed to degrade quickly and won't embed into the work.

FWIW, Meinlschmidt is the "Cadillac" (or should I say "Mercedes-Benz") of valve manufacturing, and I've personally never had an issue with anything they've made.

Re: Valve surface finish

PostPosted: Sun Aug 04, 2019 6:02 pm
by iiipopes
Pre-cyborg King would leave the valves "rough" and marketed that as micro-grooves that would better hold onto valve oil, or something like that. Now, whether that was actually what they did on purpose, or just gave a marketing spin job (pun intended) for lack of valve polish to get more instruments done and out the door quicker, is probably not discoverable. The valves on my early '70's Super 20 trumpet are smooth, and look to have been replated and lapped in properly. I have no issue with oiling.