Finally made a new soundhole/rossette cutter

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Bryan Bear
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Finally made a new soundhole/rossette cutter

Post by Bryan Bear »

I have had this in the back of my head for years and finally got around to it. I pretty much designed it on the fly and would make some changes if I were to do it again.

I wanted a lead screw type of adjustment to allow for fine adjustment. That was the one thing I didn’t like about the crappy one I made a decade ago. I got an 8-32 threaded rod. At the time, I planned to have a knob on the end to turn the screw. I figured 32 threads per inch would be good enough for fine adjustment. Later, I decided to use an old tuning machine to turn the lead screw. The additional 14:1 ratio makes it overkill. Making all but the smallest of adjustments needs the string wonder <g>.

I made the cutter from a HSS jigsaw blade with a double bevel. Eventually, I plan to make a cutter that is 1.5 mm to match BWB purfling. The plan is to be able to make a cut, turn the bevel to the other side and make the cut again. Then on the other end of the blade have a scraper grind. A cut at the same setting with the other end of the blade should clear out the waste and allow the purfling to slide right in. I tried this with the thicker cutter I have in there now. It worked, kind of. . . I have to figure out what shapes to grind on the other end to efficiently, and cleanly, remove the waste.
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PMoMC

Take care of your feet and your feet will take care of you.

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Dick Hutchings
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Re: Finally made a new soundhole/rossette cutter

Post by Dick Hutchings »

It's a beautiful piece of work Bryan. I'm not sure I understand the mechanics of though. I'm guessing you brazed the threaded rod to the tuner? Where's the center pin? I made this and I can't imagine a better tool for the job.
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Bryan Bear
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Re: Finally made a new soundhole/rossette cutter

Post by Bryan Bear »

Ues, o drilled and tapped the timer post to accept the threaded rod, then fluxed and soldered them together. The center pin is in the slider, the wooden piece between the cutter assembly and the tail with the tuner. The threaded rod passes through the slider which has internal threads. The slider has grooves that ride on the brass rails. As the screw turns, the slider moved forward or aft.

I too use a circle cutter with a small router sometimes. I found i still used my manual cutter to define the edges with a nice clean cut. I’ll likely continue to use both at times.
PMoMC

Take care of your feet and your feet will take care of you.

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Bryan Bear
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Re: Finally made a new soundhole/rossette cutter

Post by Bryan Bear »

Yes, I drilled and tapped the tuner post to accept the threaded rod, then fluxed and soldered them together. The center pin is in the slider, the wooden piece between the cutter assembly and the tail with the tuner. The threaded rod passes through the slider which has internal threads. The slider has grooves that ride on the brass rails. As the screw turns, the slider moved forward or aft.

I too use a circle cutter with a small router sometimes. I found I still used my manual cutter to define the edges with a nice clean cut. I’ll likely continue to use both at times.
PMoMC

Take care of your feet and your feet will take care of you.

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Bryan Bear
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Re: Finally made a new soundhole/rossette cutter

Post by Bryan Bear »

Sorry, not sure why my post went up twice. Once before I fixed all the autocorrects and once after.
PMoMC

Take care of your feet and your feet will take care of you.

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Dick Hutchings
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Re: Finally made a new soundhole/rossette cutter

Post by Dick Hutchings »

The first one was more fun to read :-)
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Clay Schaeffer
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Re: Finally made a new soundhole/rossette cutter

Post by Clay Schaeffer »

That is a nice looking bit of kit!
I have been thinking about making something to score the edges of rosettes and that looks like a good design. When the small router bits we use get a little dull they can make fuzzy edges.
Can you post a few more views of that tool?

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Bryan Bear
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Re: Finally made a new soundhole/rossette cutter

Post by Bryan Bear »

I’m having difficulty getting my photos re-sized to post. I’ll try again later. For now, I’ll try a better description.

The front of the tool has what is basically a little wooden and brass plane but the cutter is at 90 degrees. There is a small 90 degree piece of rosewood that backs the cutter and a brass lever that notches into an internal pin. When the brass wheel at the front is tightened the screw pushes the top of the blade all the way back and the brass levers against the pin pushing the bottom end of the blade against the back holding it upright and tight.

The cutter is just a piece of HSS made from a metal cutting jigsaw blade. It has a flat side and two bevels forming a point on the other. I did a couple test cuts with it and it isn’t cutting as nice as I’d like. I think I am just struggling to get a good edge on such a thin cutter.

The body of the tool is made from a block. The two outer pieces were ripped off on the table saw. I then cut a table saw kerf in each side piece and both sides of the center piece. These kerfs hold some brass bar stock. From the center piece I cut a front, back and slider section. I sanded a tiny bit of width from the center section so it could slide when everything was glued back together. A hole runs the length of all three of these pieces. The front piece is the same diameter as the threaded rod. It is katalox so I don’t think I really need to bush it with anything. The center piece (the slider) has a threaded insert embedded in it. As the threaded rod spins, this section is drawn towards or pushed away from the tail/tuning machine riding on the brass rails in the kerfs. The tail piece has a hole the same diameter as the tuner post. I bored a hole in the tuner post and tapped it to accept the threaded rod. I then soldered it all together. Once it was all glued up, I could push the slider and threaded rod back so that enough of the tuner post protruded to allow me to reassemble the tuner and attach it to the back.

The underside of the slider has 3 holes that will accept the pivot pin. You only need 1 but this gives me some adjustability without having to turn the knob hundreds of extra times. As I said, I went overboard on the gear reduction; time will tell if that ends up being too annoying.

You need to have enough material behind the plane/cutter assembly to back up the blade and you need some meat to run the front of the threaded rod through so that can limit how small of a radius you can cut. There is a pin hole close to the front of the slider for that reason. There is one in the middle and one towards the back so that I can make bigger changes to the diameter without having to turn the key a whole bunch of times.
PMoMC

Take care of your feet and your feet will take care of you.

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Bryan Bear
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Re: Finally made a new soundhole/rossette cutter

Post by Bryan Bear »

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PMoMC

Take care of your feet and your feet will take care of you.

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Dick Hutchings
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Re: Finally made a new soundhole/rossette cutter

Post by Dick Hutchings »

I love that we as luthiers have this kind of material at our disposal for use as tools as well as instruments. It's a beautiful tool and I want it even if I don't use it!
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Clay Schaeffer
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Re: Finally made a new soundhole/rossette cutter

Post by Clay Schaeffer »

Hi Bryan,
Thanks for posting the additional photos. That looks like a well thought out design.

Darrel Friesen
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Re: Finally made a new soundhole/rossette cutter

Post by Darrel Friesen »

Very useful and good looking too!

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