Adrian Lopez

Tools needed for cutting a bridge

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I'm trying to assemble a set of tools for cutting new bridges. I figure I'll need:

  • A knife for carving the bridge's profile.
  • A knife for shaping the feet.
  • A knife for cutting the various incisions.
  • Something to grind the knives into a suitable shape.
  • Sharpening tools.
  • Other tools such as a chisel for thicknessing and sandpaper for finishing.

For one of the knives I've ordered a 12mm Pfeil for carving the profile and cutting the feet, but I'm going to need a smaller knife for shaping the heart, kidneys, ears, and other such parts of the bridge. Would a smaller Pfeil knife be good for this? What size?

Once I have the right knives the next step is to give them the desired shape. For the shapes of the knives, Johnson & Courtnall recommends giving the blade a knee for cutting the bridge profile and feet, but for the other cuts it says only to use a fine blade. What would be the best shape for this blade?

Also, what's a good tool for altering the shape of the knife as opposed to just sharpening?

Edited by Adrian Lopez

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I can only share what I use, but I also know not everyone does the same. It's a combined result of how I was taught + the tools I happen to own because I like them & could acquire them on my budget at the time.

  • Block plane for initial thickness (I could probably use the chisel instead if I was trying to go really minimalist/budget)
  • Wide-ish curved knife for the feet — http://jpschmidtviolins.com/mknife.html
  • A flat file to clean up the top curve (but I suppose sandpaper would work too)
  • Narrow chisel for tapering the inside of the kidney wings and heart dangle-y bit (but, honestly, the knife will do this just fine)
  • Narrow knife for the cutouts, bevels, etc. — https://www.etsy.com/shop/TBsmithy [just tell him you need a bridge knife]
  • Wide chisel for the belly profile 
  • Scraper (but many use sandpaper here)
  • Joint round edge precision files for the notches (but if you only want to buy one, a rat-tail file will do)
  • And then I have my sharpening stones, which happen to be a set of Shaptons but whatever works for you. I have the Grizzly Tormek knock-off and it works just fine but it's hardly necessary.
  • Don't forget bridge templates (I made my own but they are pretty cheap) and possibly a jig or planing stop, depending on how you like to work, to hold the thing.

You may also find https://trianglestrings.com/carving-a-violin-bridge/ informative.

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The triangle strings website has excellent information. You don’t need a lot of tools to do it, but it’s worth investing in good ones if you  intend to cut a lot of bridges.

There are all kinds of opinions about what kind of grinder/honing  setup you ought to have, but it will ultimately come down to what works most consistently and efficiently for you. Get a good block plane and a couple knives that have good quality steel that will hold an edge. I use a bench chisel for initial fitting and thicknessing, but that’s my personal preference, not a necessity (I think it saves me a little time and keeps my plane blade sharp longer). These are the basics, below I’ll list some other tools to consider.

-Dividers

-Fine low-tack tape for layout

-Template for curvature 

-Round needle file 

-Carbon paper, graphite, chalk, or grease pencil for fitting the feet

-Ruler

-Calipers for thicknessing

 

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Thank you both for the information. Very useful.

Any advice on shaping a knife blank? Would I need a grinder or can this be done with just files and stones? I know nothing at all about modifying knives.

I think I'll contact TBSmithy for the bridge knife, as I don't have a blank for that yet.

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Here is my 12mm Pfeil knife after grinding it down on a 6-inch grinder, and again after thinning it down and refining it using a coarse water stone. You can see I managed to burn the tip in the first image -- hopefully this won't cause too much trouble. The next step is to sharpen it as well as I can manage and see if it'll do for shaping the feet.

a.jpg

b.jpg

Edited by Adrian Lopez

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Got my bridge knife from Mats Thureson (TBSmity) a couple of days ago. Looks good. It's the one at the top of the picture below.

In the middle is the 12mm knife I want to use for the feet and the profile. I had to regrind it a second time after it lost most of its curvature during sharpening (I'm still learning to sharpen using water stones). I have no idea if this particular shape will do, but I'll give it a try. I've noticed others use knives closer to 18mm in width, so I may end up getting a blank for a knife that size instead.

At the bottom is the 1-inch chisel I intend to use for thicknessing.

c.jpg

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That tip with the burned temper is unfortunate and all too easy to do with a dry wheel grinder. The knife won't hold an edge there until you hone down beyond the burn. I now use diamond honing plates for a lot of the things I used to do with a grinder. The coarse grit ones cut so fast that you can efficiently reshape tools like knives, small chisels and plane blades with no danger of burning. A set of them represents a large investment, but for me they're well worth it.

You might also consider getting a diamond wheel for your grinder. They cut far easier, safer and cooler than aluminum oxide wheels. And because they cut so efficiently, you might start with a 180 grit, instead of the typical 80 grit that people get with aluminum oxide.

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Glad to see you’re getting some tools together! You have some good sizes now, just a little more setup to get it all working well. 

I think your 12mm blade might benefit from more adjustment to its curve. I’d recommend making the cutting edge longer so you have a tighter curve close to the tip and a flatter one at the other end. Also, the bevel looks like its inner and outer edges aren’t parallel. Grind until the bevel is uniform—it’ll make honing a lot easier if you have a good hollow that allows the blade to register well on the stone. It takes a lot of practice and patience to get it right, but you won’t regret it later on. 

To avoid burning, use a light touch and check the blade for heat buildup often. Dip it in water regularly to help keep it cool, especially if your grinder has a high rpm.

 

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The bevel in the first set of pictures is a kind of Frankenstein: part factory bevel, part failed attempt at developing a bevel along the curve I added with the grinder. The second set of pictures shows a knife with no bevel. I've thought about beveling the knife using the grinder but I don't want to risk burning the tip again, as even by working more lightly and dipping the knife in water more often I still managed to burn a bit of the tip (though not as much as the first time). I'm thinking of using a coarse water stone to develop the bevel.

I like the idea of making the cutting edge longer. I'd like to use this knife to cut soundposts as well as bridges, and it seems to me a flatter edge away from the tip would help with that.

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