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Making keystone style rosette pieces

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Making keystone style rosette pieces

Postby Craig Bumgarner » Fri Dec 16, 2016 12:27 pm

I have a commission with a request for a rosette made up of 24 pieces of shell and ebony. The pieces will all be identical in size & shape and will look like a keystone with rounded top and bottom to match the curve of the sound hole. I could do them by hand I suppose, but would probably be more accurate and certainly faster if I have some way of jigging the cuts. Any ideas? Is it time to buy a laser cutter?

Like this:

JPEG of rosette piece.jpg
JPEG of rosette piece.jpg (2.43 KiB) Viewed 1759 times


I guess could make a little miter box with slots for both sides to saw the angles. The a spindle sander to sand out the curves.
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Re: Making keystone style rosette pieces

Postby Alan Carruth » Fri Dec 16, 2016 1:47 pm

A miter box will certainly get you close. I use diamond files to dress off shell when I want it to fit well, or you could use a diamond stone to adjust the angles.
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Re: Making keystone style rosette pieces

Postby Ryan Mazzocco » Fri Dec 16, 2016 8:08 pm

I would go spindle sander and vertical belt sander.
If you don't want to invest in a spindle sander yet you could get a set of drums that go in your drill press from harbor freight.
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Re: Making keystone style rosette pieces

Postby David King » Sat Dec 17, 2016 4:55 pm

I just picked up a 2" x 6" diamond encrusted steel plate with "600" (actually more like 220) grit on ebay for under $10 and free shipping. Aside from the fact that it rusts if I leave it wet it's great for quickly trimming pearl. I won't use it for sharpening as I'm pretty sure all the diamonds would scrape off of it in no time. I used to use files and sandpaper for this job but the files dulled quickly and the sandpaper never gave me a straight edge.
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Re: Making keystone style rosette pieces

Postby David King » Sat Dec 17, 2016 5:34 pm

I just looked at my diamond plate again and it's 3" x 6".
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Re: Making keystone style rosette pieces

Postby Barry Daniels » Sat Dec 17, 2016 5:37 pm

I use the large disk sander on my Shopsmith to shape the straight cuts. Once the pie is glued together, the inside and outside perimeters are cut with a guided router.
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Re: Making keystone style rosette pieces

Postby Randy Roberts » Sun Dec 18, 2016 11:00 am

For this sort of rosette, take the 360 degrees of the circle and divide by the number of tile pieces, and then divide this by 1/2 ( half of the angle for each side of the tile.) for your miter angle between tiles.

In your case:
360 / 24 = 15 degrees

15 / 2 = cut each side of the tile at a 7.5 degree angle.

I would glue paper to your pearl to mark the 7.5 degree angle and then sand to the line with a diamond plate, or sandpaper on a plate of glass.

The ebony I would cut with a miter box.

I would leave the inner and outer radiused faces proud (with plenty of overhang)

1. Glue the tiles together in a circle. (Glue circle to thin veneer or plywood centered on a hole for your circle cutter.)
2. Cut inner circle of the rosette's border strip into your top, and without changing the circle cutter's settings, also cut this circle into your glued up circle of tiles. Make your border strips to be the same thickness as this bits radius.
3. Do the same for the outer circle border strip on both your top and your circle of tiles. [ 2&3 will result in a perfect fit for your rosette into your top.]
4. In the top, hog out the space between your inner and outer border cuts for the trough for your inlay tiles.

6. If you were to add cutting these same circles into a piece of HDPE (white cutting board) while you are cutting them in the top and tile circle, and hog out a trough in the HDPE when you do that step in the top, it would give you a place to glue up the rosette tiles , border strips etc. all as one piece without risking beating up your top, and then be able to inlay the whole rosette into the top as one piece that will fit perfectly.

If you cut a thin wedge out of the HDPE first, it will let you get to the glued up rosette to pop it out. The glue won't stick to the HDPE. You can then also put the rosette back into the HDPE upside down to sand the veneer or plywood on the back or the rosette off and have it all be a uniform thickness for inserting it into the top.
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Re: Making keystone style rosette pieces

Postby Alan Carruth » Mon Dec 19, 2016 12:40 pm

A good way to mark shell for precise cutting is to black the surface with a felt tip pen and then scribe the lines. It does obscure the figure in the pearl, but not as much as you might think.
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Re: Making keystone style rosette pieces

Postby Craig Bumgarner » Mon Dec 19, 2016 3:13 pm

Randy, thanks for the step by step. I don't usually make round sound holes, so just to confirm, what kind of circle cutter would you use in steps 2 & 3? Dremel router tool in a rosette jig ala Stewmac's? And a spiral router bit? A 3/64" bit would give me about the right width for inner and outer borders.

What kind of glue would you use for gluing the tiles together?
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Re: Making keystone style rosette pieces

Postby Randy Roberts » Mon Dec 19, 2016 7:40 pm

I use a laminate trimmer rather than the dremel because the dremel's tend to have some much slap in them anymore. But Dremel will work.


A down-cutting spiral bit gives a good clean edge to the cuts. And it's far easier to thickness the border bands to fit the with of the bit than to try to cut the circle to fit a particular thickness of border strips.

I use thin CA after assembling the pieces of whatever rosette in the HDPE trough cut when everything else is cut. Small amounts at a time.

I usually also use thin CA to glue the rosette into the top, so there isn't any swelling to screw up the fit, but if you do, remember to thoroughly paint the edges of the trough in the top with shellec a couple times or it will wick into your spruce and stain it.

If this isn't a round rosette then I don't know what to tell you.
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Re: Making keystone style rosette pieces

Postby Craig Bumgarner » Tue Dec 20, 2016 10:10 am

Randy, thanks again! Yes, this sound hole is round. My comment was to plead ignorance of round sound holes, heretofore, all of mine are oval or shield shaped.

Thanks to everyone for all the suggestions! I'll post a pic when I'm done.
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Re: Making keystone style rosette pieces

Postby Keith Howell » Thu Dec 22, 2016 4:18 am

2. Cut inner circle of the rosette's border strip into your top, and without changing the circle cutter's settings, also cut this circle into your glued up circle of tiles. Make your border strips to be the same thickness as this bits radius.


Shouldn't that be the bits diameter?
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Re: Making keystone style rosette pieces

Postby Barry Daniels » Thu Dec 22, 2016 10:53 am

Good catch.
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Re: Making keystone style rosette pieces

Postby Craig Bumgarner » Fri Feb 03, 2017 2:28 pm

Well, it worked out well, thanks for all your help!

  • Drew the rosette in CAD, printed a couple copies full scale
  • Cut out paper tiles, glued them to bits of shell and ebony.
  • Cut the angles, left them long as Randy suggested
  • Glued the tiles to the paper pattern, glued with CA.
  • Glued paper with rosette to a poplar veneer to support
  • Made a compass plate for the router out of plex
  • Cut the inside and outside of both the rosette and the trough with a 1/32" inlay bit. This made for a really clean accurate cut.
  • Removed the rest of the wood from the trough
  • Set rosette and inner/outer bands of veneer in fish glue
  • Leveled, done.

The design is a duplicate of a one of a kind Selmer played by Roger Chaput in the Quintet of the Hot Club of France. Chaput was on of the first rhythm guitarist and the only gadjo (non-gypsy) to play rhythm guitar with Django. The guitar is said to have been his and had this unique rosette and round sound hole. I made it on request of the new owner:

IMG_9014-2.jpg


I love the look, really brightens up the guitar, the large tiles of MOP are like LED head lights when the light plays on them. The standard Selmer style rosette is just strips of b/w veneer around an elliptical soundhole hole with an ebony keystone at the top. I'd like to try some shell around the elliptical hole. I can fit them by hand I suppose, but like the crisp lean look of the router cut above. Any ideas on how to cut the rosette like the router compass, only for an elliptical hole?
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Re: Making keystone style rosette pieces

Postby Todd Stock » Sat Feb 04, 2017 7:16 am

Here's how I do radial rosettes - the only real difference is the tolerance you'll have on the join line between tiles.

- Lay out the rosette full size on a piece of 8" x 8" x 1/64" plywood (Michaels or any hobby shop that carries Midwest products balsa/ply/spruce assortments).

- Use double-stick carpet tape (Duck Brand...$9 per roll from Amazon or big box stores) to mount the plywood to a 1/2" or 3/4" MDF carrier board.

- Cut the tiles to the correct width, but oversized with regard to inner and outer radius.

- Glue the tiles to the ply with thin CA...I like to add a black surfing line between each tile if the darker tiles are not jet black (your eye sees the edge between the light and dark as more distinct). Once the tiles are assembled. re-flow the joints to ensure good adhesion.

- Run the carrier board through a thickness sander to level (the 1/64" ply plus .060" shell can be taken to .065" total thickness and still retain .040" of shell or more).

- The center pivot point should be marked during the full sized layout - drill and install the pivot pin and use a precision radius cutting jig like the Wells-Karol Router Jig to mill the inner and outer radius (Chris Paulick has a YouTube video that describes the process of making the jig). Set the depth to mill to the carrier board.

- Carefully released the rosette from the carrier using naphtha.

- Mill the rosette channel in the soundboard a few thousandths oversized, and (after cleaning off any of the tape adhesive on the back of the ply with naphtha), glue the ring in place.

The inner and outer purflings can be installed by milling the channels in place with the Wells-Karol jig or similar, but for really thin purfling lines, the channel can be milled to correct oversize and undersize dimension, and a very thin line fitted...but it's much easier to do it after the ring goes in if the purfling lines are going to be .020" or more. Fractional and decimal end mills, as well as 1/8" and 1/4" shaft router bits all work well for milling.
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