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Working on a carved top mandolin. Oval sound hole. I have not yet committed to doing a rosette (most likely a simple inlay of some herring bone etc)

I am looking for ideas that would lead to a clean channel with no rounded edges. Top is contoured.

Mike

Mike, Could you explain what you mean by "no rounded edges"?

If it is an oval sound hole how can it not have round edges? LOL... That is me being funny...


I assume you mean the edges of the route? Couldn't you make a caul that would fit the contour of the top that will give your router a flat surface to ride on?

Maybe I am not understanding what you are asking?

Cheers,
Bob

In its most basic form, a rosette is an inlay. We tend to look at it differently because it’s usually round, and can be jigged to execute the process.

If you’re not planning to make a template and cut against it (because of the arch), I think you called it in the title, “inlay” it, for lack of a better term. If you’re doing a one off.

If you’re going to make more than one, I’d make a thin template to run a Foredom against. How is the hole going to be cut?

The hole was cut buy roughing it with a dremel saw, then using a dremel sander to sneak up to the template I spray glued to top. I think I am going to skip the channel/rosette. I have way to much invested in this first article to make a mistake. And, I do not see a way to do it other than free hand. Yes I meant not rounding the edges of the channel so that the inlay fits tight at surface. If top was not contoured, I could come up with something.

Mike,

The first guitar I built was a partial kit. I ordered the top joined with the rosette already installed. I decided to change things up and copy a late 1800s German parlor guitar I found some pics of. It had a completely different rosette so I had to figure out a way to re-route the channel (since the sound hole was already cut like yours).

So what I did was made an insert the fit tightly to the sound hole I used CA glue to just tack the insert in place. Once it was secure I drilled the center hole and then cut my new channel. It worked out great so it is possible to cut the channel with the sound hole already cut out.

I understand you situation of not wanting to mess something up trying but that is how I did it and I didn't have to cut it by hand. Of course you have the added issue of an arched top so there's that...

Cheers,
Bob

Cutting purfling channels in violin tops and backs presents a similar challenge with the variety of curves and arching. I made a somewhat crude but simple and effective "mini router base" for a Foredom handpiece. The base was just hammered and filed and polished from a hardware store angle brace . I epoxied in a piece of bolt for the guide. You could do something similar with a Dremmel or some of the other small rotary tools.

I "practiced" for a while just going through the motions without cutting to gain some task oriented muscle memory. It worked very well. Similar thing for me was that the last thing I wanted to do was mess up violin plates that were nearly finished.

Anyway here's a pic, not the best picture but I think you can get the idea. You can adjust depth by sliding the base up and down and get some lateral adjustment with shims. For about a buck in parts and an hour or two time it was worth the effort to add it to the tool box.

I know you decided against it but thought a good spot to share an option.

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Brian R, Wood Mechanic
N8ZED

Since the hole is already there, it would be easy to mark out the channel with a purfling marker, or even a compass. The marker would give a smoother edge though.

I have the opposite problem of you; routeritis. I'm far more comfortable using hand tools. A Dremel could easily be used to take away most, or all of the stock in the rosette area after marking. I have done freehand Dremel work. I did a 5 string viola that was basically a half sized Maginni cello. It had a fancy back. I started with knives, and that was way too much like work. Switched to the Dremel just following the line; with the magnifying lighted glasses on; and it was easy.

I have used the SM purfling tool for Dremel, but it won't work for what you are doing. That can even get away from you. Then it looks like wood worms were attacking your instrument!

Something like Brian has would work. I don't think I've ever seen one with a depth stop. I did my back just holding it like a pencil with no base.

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Why be normal?

Mike said it's an oval and that changes things greatly when freehand is not your bag.

Mike I don't see a method other than freehand either and I hear ya too on not wanting to mess it up. Mando tops are a big investment in time and effort and as you experienced carving.

Shooting in the dark here but strapping it into a CNC, investing 40 hours in programming and figuring it out, dry runs and such and Bob's your uncle. Of course Bob may die of old age as long as this will take...

Non-CNC jigs like a pin router would require a fixture too and tooling up as well.

Congrats on making the leap to mandos, is this your first?

never seen anyone capable to freehand a rosette.

simple jigs can be arranged.

I use one for oval sound holes.

what makes this tricky is how to locate the tool. I use a pilot bearing and then feed in the direction that the cutter pulls the took against the jig. If you locate off the sound hole and that is possible but take you time and do it in a few cuts. You again need to pay attention to the cutter direction and use that to help locate.

I would work from the middle out to the edges and. You can work full depth but take small bites. I also would apply a seal coat.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Freehand is one thing, but using what Brian showed is not freehand. Marking the edges with a marker, using the existing soundhole, like I suggested is not freehand. You just have to cut away the material inside the line. You don't even have to go to the line, you can get that with a chisel, or even a file, or knife.

It wasn't that long ago when ALL rosettes were done that way. Some makers still do so today, using markers, hand routers, and chisels. It is a skill. It still uses tools; just different ones.

Even the 5 string I did wasn't exactly freehand. I just cut on the line. But it is easier to mess up than marking with a knife, or using the guide Brian showed.

I wouldn't try to cut a perfect rosette, circular or oval, without marking, or using a tool like Brian showed. But using either method should work. It would not be free hand.

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Why be normal?

The little home brew "router base" with guide pin I posted a picture of was what I used to cut the purfling channels in this fiddle. It's not totally free hand with the pin and much like cutting binding channels. The fiddle was the first instrument I made ~1990. The C-bout in the pic is like 3/4 of a sound hole and the same technique would be used for both. Just another breath holding operation like so many others in luthiery.

The points of the purf joints were cut with an x-acto #11 blade.

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Brian R, Wood Mechanic
N8ZED

I agree that the picture showed a method for location. The rosettes were not done freehand In the past they had an ingenious tool much like a compass to do the score lines. That they free handed out with very sharp chisels the point that needs to be taken is the angle of attack of the cutter to reduce the tear out and chipping risk.
I love Violin purfling I think the tool is also scrapers were used to a degree here is an interesting video
https://www.youtube.com/watch?v=BnxTxHdAYiU

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I would take a low tech approach - make a cardboard template and stick it in place on the top. Scribe around it with a sharp exacto knife and remove the wood from the channel thus delineated with a sharp chisel.
Creative Memories has a matt cutting system which allows you to cut ovals using plastic templates and a "bug" that rides in a track, which might work if you could make it conform to the curve of the top:
https://creativememories.zendesk.com/hc ... ng-System-

I like Clay's approach but I prefer a hard template for the knife to follow so that it doesn't cut and wander into the template. So I would either make a full template from plexiglass or use various metal pieces held in place. The metal pieces could be made up of washers, jar lids, etc., that match the curve you need.

Wow. Lots of thoughts here. Still absorbing

This is how I do it, by hand. Have been doing it this way for nearly 30 years. If there is a better way, I am all ears.

http://petercoombe.com/Construction/soundhole-trim.htm

I've done some oval hole arch top mandos with that type of rosette. I use a modified drill press cutter as a scribe, and chisel out the rest. With a nice sharp tool and some patience, there is really not much to it. This rosette was some local pear wood, IIRC

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Rian Gitar og Mandolin

Awesome description. Thanks!

I took this approach after viewing Peter's page. Its quite simple and effective. It does depend on a good soundhole shape. The double razor took a bit of trial and error, but what I came up with was based on 2 large popsicle sticks, glued and sanded to thickness. I used two standard flat razors, they have three nice attachment points. #4-40 bolts. (yes, I removed that metal strip at the top of each razor).

A swig of liquid courage, and off I went!

Thanks Peter!