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Screws
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nacoran
6720 posts
Apr 22, 2013
11:00 AM
Not all harps are screwed together equally. I've got harps with one cover screw on each end and three reed plate screws, and I've got harps with 2 screws on each end and lots of reed plate screws. That got me thinking-

Assuming you've got a flat comb, what is 'optimal' and why? What screw configuration do you consider best? Where is it most important to fasten your plates down?

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Nate
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arzajac
1033 posts
Apr 22, 2013
11:32 AM
One of the harps I use daily is a customized Hohner Blues Harp MS - its reedplates are held to the comb with only two screws. The comb and reedplates are flat and the harp is airtight enough to allow for sustainable and bendable overblows and overdraws.

But two is no magic number. I have restored older Marine Bands and as a general rule, I use the nail holes on the draw reed plate as pilot holes for screws. Some Marine Bands only have two such holes. Although those harps can be made highly airtight, they require more than two screws, or rather, using only two screws in the nail hole positions isn't enough. For those kinds of harps, I use two of the nail holes on the blow plate and create a third.

The other thing I have learned recently is that the presence of the rivet "dimples" in the comb can affect airtightness a lot more that I once thought. I came to this realization while prototyping custom combs. I will not be making any combs with dimples. Customers will have to flat-sand the reedplates to use my combs. There is a lot of benefit in flat-sanding the draw reedplate, though, and it doesn't only involve the rivet heads...

But this relates to the original topic because the presence of "dimples" can affect the design of the position of screws. You may need fewer screws if the comb and reedplates are flat and the back of the comb is far away enough from the back of the lowest reed channel.

I would say the most important thing about screws is to not overtighten them.

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Last Edited by arzajac on Apr 23, 2013 11:38 AM
MP
2716 posts
Apr 22, 2013
1:39 PM
two, three, six, eleven..i don't think it matters much. one of the finest harps i ever played was a Rupert Oysler Blues Harp (two reed plate screws).

i think flat sanding the bottom reed plate is a good idea, even on a stock plastic comb job. ditto on not over tightening them


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MP
affordable reed replacement and repairs.

"making the world a better place, one harmonica at a time"

click user name [MP] for info-
repair videos on YouTube.
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nacoran
6722 posts
Apr 22, 2013
2:15 PM
What's the name of those little screws that hold the cover plates on on Blues Harps (Seydel uses them on a couple harps too) that look like screws on both ends but one end is actually a nut? Has anyone ever seen something like that, but instead of a screw a pin?

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Nate
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MP
2719 posts
Apr 22, 2013
3:48 PM
they may be called male/female post screws...dunno. you need any? i have tons of 'em

Edit. i do know that they are Pozi-drive and not Phillips though a Phillips will work if you a very careful.
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MP
affordable reed replacement and repairs.

"making the world a better place, one harmonica at a time"

click user name [MP] for info-
repair videos on YouTube.
you can reach me via Facebook. Mark Prados

Last Edited by MP on Apr 22, 2013 3:50 PM
Sherwin
64 posts
Apr 22, 2013
3:50 PM
@nacoran, I've heard them called sex bolts or Chicago bolts, the former being a proper and widespread term. The Germans must have some other name for them, twenty-six letters long would be my guess.
nacoran
6724 posts
Apr 22, 2013
5:06 PM
Thanks guys, found them. I'm trying to simplify having different brand harps with different screw drivers and everything.

MP, yeah, I know to be careful. Of course, I would have expected the screw to strip, not my screwdriver! (That was awhile back. I guess I should buy better quality tools.)

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Nate
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Last Edited by nacoran on Apr 22, 2013 5:08 PM
Roverharp
37 posts
Apr 23, 2013
11:15 AM
@arzajac Interesting tip about the dimples. (I call them divots). I've taken to valving the lowest three holes on my own harps. That and the rivet heads have required me to actually route the divots deeper.

When complete I don't see any light passing through so I've assumed airtightness. Apparently not. I'll have to give your process a try. Do you just sand the comb thinner until the dimples are gone?
arzajac
1036 posts
Apr 23, 2013
11:37 AM
Roverharp: No. It's just that in making prototypes for a comb, I found that I'm better off to not put them in. My goal is to make the most airtight comb I can, so the dimples/divots don't help that at all.

In working with a stock comb, you would have to sand down the comb a whole lot to get rid of them and your comb would end up being way too thin. Don't worry about them. I just mentioned it because I think that's one reason why only using two screws to hold MB reedplates to the comb isn't enough. I think you can get great results using three screws positioned where the nails were in the draw plate.


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MP
2722 posts
Apr 23, 2013
12:05 PM
From Andrew-

"I think you can get great results using three screws positioned where the nails were in the draw plate."

that's how many i use. i use the old nail holes to start my drilling on MB 1896s.
----------
MP
affordable reed replacement and repairs.

"making the world a better place, one harmonica at a time"

click user name [MP] for info-
repair videos on YouTube.
you can reach me via Facebook. Mark Prados
Baker
294 posts
Apr 24, 2013
4:57 AM
From what I have read and through personal experience it's the flatness of the comb and the reed plate which really effect the seal. I think Chris M said that if both surfaces are really really flat they will create a kind of vacuum seal on their own. The screws are just to hold them all in place.

I use three along the back where the nail holes are on a Marine Band - The same way a MB Deluxe etc is screwed together. Personally I feel three is better than two as you get less lateral movement when the cover plates are off – This can happen when the screw holes through the comb aren't that snug a fit. I guess it doesn't make too much difference when they are on.

So, IMHO, flat sanding and (again) not over tightening the screws is what makes the biggest difference to the seal.


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