Can you reduce built in U-Channel clearance ?

[BeauKim]

Hi,
I have done a lot of custom reed work and some custom slide work so far, but have haven't modified any u-channels besides jeweling the edges.  I've looked at a few older posts here, and I think I get how to do it.  I'm wondering if the instructions were only for models with separate u-channels, like the Hohner 270.  Are you able to reduce the clearance on models with u-channels incorporated into the mouthpiece, such as the Suzuki, Easttop, and Hohner 280 chromatics? 

Thanks,
Boaz

[SlideMeister]

You could probably do it by hand (sorta) but the best way would be with a Bridgport/mill

[The Lone Harper]

Unless I'm mistaken I believe that Wally/Pyrofire modifies the u-channels of Easttop chromatics.

[Keith]

I did it on a cheap chrom, to improve playability a little, but it wasn't easy, the metal was hard to file.

(If I was to try to improve a channel again, I'd see if I could shim it.)

[SlideMeister]

Actually, it shouldn't be too difficult to fashion tool from a fine file, if you're handy with a good bench grinder.

[Jimmy Halfnote]

 Eh , if the channel in the mouthpiece allows too much slide movement that means the channel is already too big ( one way or another) , so how are you going to reduce the channel size with any kind of tool ? If the channel is engineered by state of the art 'machines' ( such as Easttop use) then there should be no need to interfere with the channel, maybe a bit of smoothing , but every channel on every Chromatic should be precise when new, when well used i am not so sure. Anyway as i see it IF the channel is a bit sloppy then the slide has to compensate somehow, because i can't see how the channel can be reduced , but if there is a way i would love to hear it.
                                                      jh.
               

[Keith]

I filed the outside edges of the U channel part of the mouthpiece, which meant that there was a smaller space for the slide.

[SlideMeister]

Yep! If one were to "carefully" cut a file to the picture I have in my head, it would work like gangbusters in about two or three strokes. Heck, I might even be tempter to make one. 

[Jimmy Halfnote]

  Outer edge ?  The outer edge overlaps the comb , the MP rests on the rail , wouldn't you have to work on where the MP mates to the comb ?

                                                                jh.

[SlideMeister]

No, the next edge in, from the outer edge. (looks kinda like a notch) and NOT the actual channel that slide rides in.

[Jimmy Halfnote]

 Are you talking about the rail ( edge, ledge) that mates to the comb ? I will take it that is what you mean, you are going to file this  ? ...... dead level , length and width.....?
                                                         jh.

[The Lone Harper]

Something I've found with Suzuki and Easttop cross-tuned chromatics is that the slides have a longitudinal bow in them (the same thing Doug Tate found with 270 slides) which I believe comes as a result of them being stamped out as opposed to laser cut. As a result, and based on the results of my own experiments, no matter how much you reduce the depth of the slide slot in the mouthpiece (and any reduction will certainly help!) you'll never get optimal reduction of air loss unless you use a perfectly flat slide.

You can shine a light in one mouthpiece hole of an Easttop or Suzuki cross tuned chromatic and in a darkened room see that light between the slide and the mouthpiece when looking into one of the holes either side. When you try this experiment on one of the very airtight cross-tuned slide assemblies made by Will (of Will's Make harmonicas) there is no light visible either side of the hole with the light shone into it.   

[SaxonyFan]

All else equal: Reduced channel size -> Increased channel friction

So why do it?

[SlideMeister]

Are you talking about the rail ( edge, ledge) that mates to the comb ? I will take it that is what you mean, you are going to file this  ? ...... dead level , length and width.....?
                                                         jh.

Yeah. The little file giz-dong (in my head) will take the same amount off the entire length of that little inward notch. It won't make it wider; just a tad deeper. It will work similar to a hand, wood plane (or block plane or whatever you call them on your side of the pond) Every stroke would have to be uniform and non-stop from end to end, but I'm sure it would work. The amount of strokes needed would depend on the coarseness (or lack thereof) of the file you make it out of.

[The Lone Harper]

All else equal: Reduced channel size -> Increased channel friction

So why do it?

It is done to reduce the amount of air leakage between the slide and the slide channel.

Doug Tate had an extremely fine tolerance regarding the space between the slide and slide channel with the Renaissance chromatic. As long as the slide and slide channel were perfectly flat then friction wasn't a problem. Regardless of whether the gap is 1mm or 0.1mm, if there is a gap between the two surfaces then friction won't occur. The downside was that the narrower the gap the quicker the build-up of gunk which affected the movement of the slide and required cleaning on a very regular basis. For me that's a price I'm willing to pay for a more airtight instrument.

[SlideMeister]

Yeah, I got a stainless steel 270 from Vern Smith that's like that. Every time i go to play it, the slide is stuck. I give it a sharp tap on the button end with a suck-harp (and sometimes put a few drops of water in the button end of the slide) and it's the tightest 270 I've ever played. Stainless steel comb with Gardner reed plates; I call it my "poor-man's Rennie"

[SaxonyFan]

All else equal: Reduced channel size -> Increased channel friction

So why do it?

It is done to reduce the amount of air leakage between the slide and the slide channel.

Doug Tate had an extremely fine tolerance regarding the space between the slide and slide channel with the Renaissance chromatic. As long as the slide and slide channel were perfectly flat then friction wasn't a problem. Regardless of whether the gap is 1mm or 0.1mm, if there is a gap between the two surfaces then friction won't occur. The downside was that the narrower the gap the quicker the build-up of gunk which affected the movement of the slide and required cleaning on a very regular basis. For me that's a price I'm willing to pay for a more airtight instrument.

Obviously that’s why some might consider doing it but it’s going to increase friction. “If” is a tricky little fellow.

[Jimmy Halfnote]

 I don't know guys , but to me there is one obvious problem being ignored, the slide runs between TWO surfaces, and in the vast majority of cases these two surfaces are different materials ,one is metal.. one is plastic. So before getting all worked up about the channel in the MP...... how about first checking the comb surface, at least make sure it is as level as you can get it ... that CAN be done....... and check it regularly.
                 Now i have never come across a slide that didn't have rub marks somewhere, very often at the spring end or near the middle, the spring action is one of the problems causing an arc = friction= ? Then there is your breath and chemicals getting in between the surfaces, not to mention other particles of gunk,all of which are being compressed and ground into the the plastic and metal mating surfaces........... think about this , and then consider is it worth chasing over exacting tolerances and absolute perfection in an imperfect set up with an MP  that isn't even straight to begin with and plastic material as a base ?

                                                                     jh.

                                                                 

[SlideMeister]

Yeah, that's the easy part and is the first thing I do with a new Chrome. And yes, slides and related components are ALWAYS nasty looking, like maybe they went out of their way yo make them that way to prevent sticking or something?   Some of those surfaces remind me of tuning marks in brass reeds.  .  I've noticed, however, the more you polish, and the tighter the fit; the more they are prone to stick; which is a small price to pay for an extra air-tight axe, IMO.   

There is however (and always has been) no excuse (IMO) for that "chainsaw cut" mating surface on the 270 mouth piece. (TBF, I haven't seen the underside of a new 270 mouthpiece yet)

Oh well, We're off to the Waffle House! 
Yummy!
Age

[BeauKim]

I understand what some of you explained with reducing the U-Channel clearance.  I think the best way would be to have a file that is almost as wide as the channel and take a few swipes, then reassemble and use a shim to measure.  I have not tried this, yet, but it would definitely improve almost allNow, are some of you doing this free handed or with a different method?  Keith, I didn't understand what you meant by reducing the clearance by just using a shim.  Could you explain? 

Thanks!

[Keith]

Re using a shim - a shim is just a very thin bit of (usually) metal - if it was cut to fit, with the necessary holes cut out, it would leave a miniscule less of space between the comb & the slide - similar to the idea of a gasket filling in air gaps.

(Hope I've managed to explain it OK.)

[Grizzly]

A slide running in a u-channel is usually pretty sloppy, with as much as .005" slop. Find a shim that fits in the channel that is bigger than the slide by the amount of gap you want, say .002", and then file the rails of the u=channel down to the level of the shim, without taking any material off of the shim. E voila.

amirite, techies?

Tom