Official Luthiers Forum!

Hi all,

Looking for a judgment and advice here on my first self-made (not store bought) rosette install. As you can see in the picture attached, there are some gaps along the inner purfling ring from the 5-7 o clock positions, and the outer purfling rings from 7-9.

I think my wooden rosette was the problem, as when I was cutting the rosette with a hand tool circle cutter (old LMII), I was cutting from opposite sides of the blank, and believe I may have cut the rosette slightly out of parallel.

I used a dewalt trim router with Downcut bit in a circle cutting jig for the soundboard channel, and as you can see, got it to fit seamlessly in many areas, so I don’t think that part of my process introduced the error (but I’m happy to hear if you think otherwise)

Given the size of the gaps here, I’m looking for a judgment on what you would do for this guitar to fix it. Note that this is for me, I’m still a newer guitar builder, but I also am happy to learn fixing methods for the inevitable errors that come along the way.

If it were you, what would be your preferred method that balances success (great looking rosette) with effort:
A) rout out the purfling lines only, and re inlay thicker purfs to take up the gaps?
B) rout out the entire thing, inlay a slightly larger rosette/purfs
C) seal with shellac, try black CA
D) fill with black shellac stick
E) something else?

Thanks in advance, and looking forward to the responses and suggestions!

It’s hard to tell from the picture just how big they are. Maybe it looks worse in person? Well, the last thing I would do is route anything out and start over. I’ve learned that it can make things worse. I would try a little surgical sanding on the brown wood and see if the brown dust would fill the gaps and what it would look like filled with brown.

If it was mine, I’d cut the purflings back out, cutting enough material from the guitar top and the rosette to provide a truly parallel channel for a new purfling scheme. It also looks like the purfling aren’t one continuous length. Diameter x 3.14 will give you a rough length for the inner and outer purflings.

Next time cut the rosette infill a few thou smaller than the rosette pocket, glue in, then cut your purfling channels. I usually allow an additional 3-4 thou over the purfling thickness.

It’ll look like it grew that way -

Cheers, M

Like Michael, I'd rout out the purfs and replace with something a bit wider. Pretty easy operation.

Problem with being a builder and taking pride in your work is once you see a flaw you will always be looking for it. Best to just fix it, give yourself less to worry about, and move on.

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Brian R, Wood Mechanic
N8ZED

Definitely A.

On the rare occasions I do a rosette like that, I will first install the brown part into a snug but not necessarily perfect pocket. Then with a bit with a smaller diameter than the purflings I want to install, I will cut a clean edge on the brown part just licking the edge of it in a clockwise climb cut til the edge is perfect, and then I will widen the channel til it fits the purflings perfectly by cutting the spruce in a counterclockwise climb cut. That’s for the outer ring. For the inner ring, I cut the brown with a counterclockwise climb cut and a clockwise climb cut into the spruce…

I usually revert to my dremel with a 1/16” downshear for that task…

This is a good place to use a hand cutter for the grove. Get a thin piece of soft wood veneer about 1/2" wide. Drill a 1/4" hole in it near one end and use a pivot in the hole in the top. Stick the point of an X-Acto blade or equivalent through the stick, perpendicular to it, at the correct point to hit just outside of the outer ring. The blade should lean forward, so that it's cutting down into the top. With the cutter tip protruding just a bit less than the height of the purfling line you'll use [u]lightly score[u/] all around the outside. Then deepen the cut carefully, Do the same with all the other cuts, and then ground out the channel. If the cutter is really sharp you can go against the grain safely with a light cut. It can be tricky to reverse the cutter so that you're always cutting down hill at the same radius, but it's better, so try it on some scrap.

I'm filling gaps almost exclusively with epoxy + West Systems 406 silica . I mix the silica with epoxy or with finish. The silica is bulking agent, fills gaps in one, sometimes two drop fills. Its invisible- give it a try off the guitar on scrap. Literature says it dries an off-white, but its invisible in small quantities in gaps. You can add sanding dust if you like....

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Measure Twice,

Karl Borum

Here’s what’s helped me. it may save a lot of headaches and be worth a try.
A fairly simple way to avoid mistakes, gaps, etc., and reduce the risks to the top while making the rosette, is build the rosette elsewhere.
The pictures happen to be from a coffee table using BRW and ancient Kauri segments (the pics happened to be handy), but are the same method as for the guitar rosettes.

As you cut the rosette's channel in the top, - before changing any router settings (depth, radius, etc.) repeat each cut in a piece of medium or high-density polyethylene (HDPE - think cutting board material). It’s best to slow your router speed in the plastic to prevent melting the HDPE instead of cutting it. Start with the central part of your rosette and work outward and inward from there.

Then use the cutting board's channel as a mold to assemble your rosette. CA won't bond to the HDPE, and the entire rosette will easily lift out of the channel by sliding a thin screwdriver or other wedge under it. (A radian wedge cut out of the mold facilitates both assembly of the rosette, and popping it out of the mold.)
Once satisfied with the central portion, figure out your inner and outer borders based on what size bits you have available (I prefer downcutting bits). The total thickness of the strips making up your border needs to match the width of one of your bits. A light wipe or two with 600 grit along the length of thin strips can thin them a thousandth or so if the total is a touch too thick.

Cut the border’s radius in the HDPE first, such that it just slightly includes the edge of your completed inner section (the HDPE holds it quite well for this cut), then before changing anything with the router settings, make the same cut in the top.

Glue and scrape down the inlaid material while it is in the HDPE at each step, so the router is not lifted by the previous inlay when you make the next cut. Again, the CA won’t adhere to the HDPE and so the whole rosette can be popped out fairly easily to check things during the process.

Repeat for your other border.

Glue in your border strips and then, doing a small area at a time, gradually flood the entire rosette with thin CA so it is one solid piece (any gaps or pockets are easily fixed with a drop or two of CA at this time). This will prevent pigment bleeding from the rosette into the top, prevent swelling of the rosette if using Titebond etc. to glue it into the top, and lessen dust getting ground down into the lighter colored woods if you sand.

The entire rosette is then popped out and, with light touch up of the edges with fine sandpaper, set into the top with a perfect fit, as both the top channel and the mold channels were cut identically.

If you choose to use CA to glue the rosette into the top, you will still need to hit the rosette’s groove with shellac to prevent CA wicking down the fibers of the topwood. It also is helpful to lightly break the edges of the deep face of the rosette to a slight bevel, to ease pressing it into the top.

The biggest advantage to this method is the only time I’m threatening the top is cutting the channels and the final gluing of the complete rosette. All the screwing around is done while in the HDPE, and you can get everything absolutely perfect before gluing it into the top.

Other benefits are: Thin strips slide pretty easily into the slippery plastic. You can take all the time you want, play around with arrangement, alter design, replace broken pieces, pore fill, pop it out to see how it looks on the top and pop it right back in, etc., all with the top safely out of the way. You can completely build a complex rosette “dry” before making it permanent with CA, prior to installing it into the top. It also leaves very little sanding/ scraping to bring the rosette flush once in the top.

The method also turns multiple thin fragile strips into one solid stable piece that fits perfectly

Great idea RNRoberts!

Never thought about building the rosette in an HDPE 'mold' but I like the idea a lot.

I've been building mine on a flat board and using pins to hold the purfs in place then flood with CA.

I like a complete rosette to inlay in the top.

Thanks for the tip!!

ps -- Nice looking inlay work on you part too.

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Brian R, Wood Mechanic
N8ZED

I use the same technique as RN. Very nice explanation there!

A couple of small things I'd like to add.

It can be hard to lift the finished rosette out of the plastic channel. I drill two or three 1/4" holes in the bottom of the channel before so I can push it out from underneath using a dowel. I also wax the inside of the channel with liquid paste wax. The rosette can stick to the plastic _slightly_ and it doesn't hurt to facilitate the release with wax.

I can't emphasize enough how important it is to hit the edge of the spruce rosette channel with shellac before applying CA! Especially on the end grain, one application may not be enough. DAMHIKT. I brush on 3 or 4 light coats of shellac. I've never had any trouble with discoloration of the spruce doing this. The rosette adheres well to the shellaced channel.

_________________
Tim Allen
"Never hurry, never rest."

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_________________
Tim Allen
"Never hurry, never rest."

Thank you all for the ideas and suggestions!

I love the idea of pre making the rosette outside of the soundboard and then inlaying—I will definitely be pursuing that method for future builds. For this build I wanted to practice repairs in situ, so I went ahead and routed out the old purfling and inlayed new—all successful. Routing the channel, shellacking, placing the lines, and then CA glue worked well.

As you can see, the outside black line on the outside ring from 7-9 got planed/sanded away, but I’m happy enough to move on at this stage.

I used wood veneers as my purfling lines and I had a tough time fitting the 6 lines (B W B B W B) into the channel in. Clearly I didn’t fit the outside black into the channel enough in that missing spot. I plan on pre making the rosette as suggested above in the future, but any suggestions for the fit here if this situation arose in the future?

Either route the channel a little bigger or sand one of the lines a little thinner. The ability to take it back out and fiddle with it until it fits perfectly is the main advantage of CA. The middle black looks slightly wider in that area, so your channel was probably good in this case. Also prioritize fitting of the line against the spruce since nobody would notice a thin spot in the black line next to the dark walnut.

Something I've noticed worth keeping in mind in making complete rosettes separate from the top, especially if tiled and/or solid wood is incorporated, is they can change shape as humidity fluctuates.

I often make several at a time and let the customer choose what they like best. But weeks or months later the unused rosettes may not fit like they did after assembly. My shop will never be humidity controlled perfectly. Keeping them in a couple zip lock bags helps and I may try some desiccant packets to see how that works for storage. Some I've had to rout off the outer purfs to a perfect circle again and redo the purfs. Not a big deal but it happens.

One thing really nice about building them separately is they can be a perfect complete circle. We spend so much time building a 'perfect' guitar I've never been able to get past gaps in the rosette even if hidden by the fingerboard. OCB, I know!

_________________
Brian R, Wood Mechanic
N8ZED

I set my router bit depth to .070. This depth allows several passes through the thickness sander on the rosette side without fear of going through the rosette. I typically sand just until the rosette is cleaned up, then do the rest of the thicknessing from the back side.

I typically inlay all the pieces of the rosette at the same time, and usually all the purfling lines are the same height. After the pieces are in, I take the rounded edge of my fret nippers and go around the rosette with a rocking motion pushing everything down to the bottom of the channel.

Occasionally there will be height differences between the purflings. In that case, I go around with the fret nippers as usual, then go around again on the lower height purflings with the round edge of my 6” rulers, and roll the end of the ruler along the purfling line to push it down. Very often you can feel it seat properly in the channel as you go. I usually give it a few go’s for good measure.

I choose .070 depth as it will never go all the way through the top, and then when it’s time to cut the sound hole, I do the first cut from the top, then take the top off the jig and do the second cut from the back. This means you never have to fiddle with the bit height once it’s set, and that you don’t get tear out on the back edge because you’re coming in from the ‘top’ on both cuts.

Unless for some reason you didn’t cut the channel depth correctly, the little ruler trick would have saved your purfling line…

Good catch Tim – the inlay may want to stick, especially the first time you pop it out, and a few small holes in the “floor“ of the mold makes it easy to push the rosette up and out of the mold. I’ve never tried waxing the mold. Have you had any problem with the wax interfering with subsequent adhesion of the rosette in the top once it’s been glued in?

As Ed points out, it’s important to make sure all the pieces and strips of your rosette are seated down to the bottom of the mold before applying the CA. If they are not all the way down when glued, they can end up so proud of the final top surface after scraping / planning/ sanding that you have scraped all the way through and end up with a gap in your final rosette where this has happened.

Brian, a ziplock freezer bag and a small desiccant packet should work well for you. Back when working out of the garage (great humidity control there …sigh), with sometimes months passing between build times, I found zip-lock bags for storing clothes that were just like a big ziplock freezer bag. Keeping all the semi – assembled “parts”, bracewood, tops and backs, etc. in those, along with a handful of desiccant packets, even with the wild fluctuations in humidity here in the Midwest, seemed to work well. If you hit the final rosette thoroughly ( but slowly) with the thin CA, it also should stabilize the rosettes and lessen the fluctuations.

A couple other things that may help:
When the rosette includes shell, metal , or other hard material, if you seat the shell or metal a little below the surface of the rest of the rosette, then gradually build up a dome of thin CA above it and scrape this flush to the rosette surface it will prevent subsequent sanding down through the “show” layer of the shell (especially frustrating with the laminated shell). It will also prevent getting a raised hump during final surface sanding due to the harder shell or metal not abrading away as much as the softer wood around it. The CA sands away much the same as the wood around it. With metals, it can lessen the likelyhood of the metal oxidizing, tarnishing, or corroding with time by sealing it off from the air.

It also can render somewhat of a 3-D effect. (Granted this one is somewhat extreme)

As mentioned, a notch cut out of a section of the mold gives access to the rosette from the side as you build. As the rosette progresses, you can rotate it so different portions are exposed in the gap, and can be accessed from the edge. Especially if you need the rosette to be a complete circle it can make joining the ends of thin strips by a scarf joint easier. You can just walk up to a perfect scarf a little at a time using sandpaper on a credit card or other thin stiff backing.

Ed’s method for cutting out the sound hole also works well if you want to bind the sound-hole. Make one cut a little over half the thickness of the top and inlay it with your binding. Then flip it over and do the same on the other side. Make the subsequent soundhole cuts so they just touch the edge of the binding, and Bob’s your uncle.