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Too tight metal slide on bow.


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Just had the unpleasant task of rehairing and replacing the thumb leather on a modern German commercial viola bow ($2300 list!) which had never been rehaired since new. Glued plugs, seriously stuck slide and thumb leather glued with some kind of horrible goop which could be softened enough to scrape off but left a residue which could not be liquified or dissolved by anything I tried. Any way my question is what would people do about the metal wrapped pearl slide which was WAAY too tight. Obviously on a regular slide a quick stroke of a file fixes the problem but with the metal wrap?? I ended up putting it back in using more force than I felt comfortable with due to no time to screw around with it. Shaving the side of the (parallel) channel could be done but would be a bit of a pain due to not being able to run the chisel past the end of the channel. Any other thoughts? I didn’t even dare lubricate the channel for fear the wax might gum up and make it even more difficult to remove next time. My thought is that ebony will always shrink slightly so the channel gets narrower but I know there are a lot of older bows with wrapped slides which seem to be OK. Any thoughts or suggestions on this welcome.

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I run into this sometimes.  Here are some things that I have done, or considered doing: cutting the slide channel a little wider, sanding the metal slide sheaths a little thinner and lubricating the slide.  But mostly what I have done is replace the slide with a standard one without the metal sheath.  This was on anonymous workshop bows that I owned.  And since I save the sheathed slides that I take out, perhaps I could find one of these that would be a better fit in a frog whose slide was too tight.

I often find Citra-Solv useful for softening and removing goop.

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I’d give the slide a few light file strokes or passes of the slide over 600-800 grit sandpaper glued to a flat board. Also, equal number of passes for both sides of the slide. Lubricate with graphite from a sharp pencil. I often use nail files from beauty supply stores which have a dense foam backing and 4 pieces of micromesh in various grits going down to extremely fine. Good for the final passes.

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In working with metal, sometimes the friction caused by the non- precise insertion of the slide can distort some metal, especially when at a fraction of a mm. It ends up binding and creating a wave of sorts. Because the metal is actually thinning ( stretching, ) it mostly will not come apart at the corners.  

So there might be distortion on the metal facets of the slide. The distortions can be corrected, but sometimes, the soldered corners might have already been damaged, if the installation was rough.

I am with Maestro Dorsey on replacing an irregular fit/ oversized metal slide, when that is the better solution. Let the customer know of the options and see if they are willing to *upgrade* the slide. I do not know of any hardwoods that expand over time. Are there any that attract water?

Without actually seeing the metal slide though, if the fit is supposed to parallel, all facets and angles should be checked, as you have done. I also agree with Maestro Griffiths. The paper on the flat surface is safer. Strokes biasing a wedge. Possibly work the point off of the corner of the slide, that this is a production bow. Materials get clogged in the corners and slide is no longer truly parallel. I also have a non- textured narrow flat burnisher that is used like a chisel to clean out the channels. Paper on stone, with the slide on a block to get the correct or slightly lesser angle.

Files will work on the frog. Might run a pick ( or a brush ) in the channel to dislodge possible build up along the channel. 

Get that pencil from Kindergarten class with the 6- 8mm lead and run it on the surfaces. If the slide goes in and out with double stick tape, that's a start.

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Thanks for your responses. I was feeling a bit dense that afternoon. I will have to look carefully at the next older bows which come in with that type of slide as I am guessing there will be some differences between the final finish of the slide and the modern one on this bow. In particular I am guessing I could improve things by deburring and putting a tiny rounded chamfer in the back corners and that there is enough metal to allow a polishing stroke of a fine file or stone on the sides. Also the use of graphite to lubricate the sides of the slide is something I should definitely have thought of before. Thanks again.

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Another thing that I forgot to mention is that I have a triangular file that I use only for filing the insides of slide channels.  Widening them by filing can be easier and more controlled than by chiseling.

Also, a tight slide is often too tight only in one area rather than equally tight along its entire length.  So if you can figure out where it is too tight, you only need to make it narrower (or make the channel wider) in that area.  It can be tricky to determine exactly where a slide is too tight.  Careful visual inspection while trying to wiggle the slide when it is inserted partway into the channel can help.  And a trick that Arnold Bone taught was to insert the slide in the channel with gentle force and listen while you tap the pearl with a small metal tool, such as the blunt end of the pick you remove the plugs with.  There is often a difference in the clicking sound where the slide is tight and where it is loose.

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