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I make a flat top mandolin with a small oval sound hole. aprox 2"x3". So far, I've only bound the sound hole and I have not tried to put a rosette on it. The main reason is that I can't think of a way to reliably cut the rosette and perfling channels.

To cut the sound hole itself, I use the scroll saw and then the spindle sander to sand down to the line that I scribed with an oval template. The rosette channels have to be very concentric with the sound hole or it doesn't look right. Some test cuts I made with a series of templates showed me that being even a little off is too noticeable.

There are oval cutting jigs for scribing and routing but they are all way too big for my purposes. Other than using a CNC machine, how do other do this? I've seen some beautiful sound hole on other mandolins so I know that it can be done.

The fine motor control of my hands is not up to doing this completely by hand. Imagine that you have two left hands to get a feel for what I mean.

Mike,

If you were going to do a lot and the rosette on each one was the same, and you knew someone with a CNC machine (like Tracy at Luthier Supplies or John Watkins) - lots of if's I know - you could design a plexiglass jig to use with a laminate trimmer with template cutting part attached (my Makita has one). I'm thinking of a plexiglass sheet big enough to clamp on the top with the oval cut out to the outer edge of the rosette (plus the appropriate template follower extra depth). The jig would have an inner plexiglass piece that fits in the oval perfectly with a pivot hole in the middle that you would use to locate and centralise the jig. Then clamp it down, remove the centre section and carefully route using the template guide and router bit of the rosette channel depth.

No idea of the cost to make one or how well it would work but its fun to think these things up on an idle afternoon.

I'm sure that others will have much simpler ways.

_________________
Dave White
De Faoite Stringed Instruments
". . . the one thing a machine just can't do is give you character and personalities and sometimes that comes with flaws, but it always comes with humanity" Monty Don talking about hand weaving, "Mastercrafts", Weaving, BBC March 2010

Hi Mike,
I made a router jig that fallows the inside edge as the cutter cuts a channel around the oval.
It gets a little tricky if you want the channel to increace distance with the wider part of the oval but it is still possable.

Wade

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Wade
Nashua, NH
http://www.wadefx.com

I do know someone with a CNC and I might use him to make any templates I devise. However, my build rate is so low that it might be easier to just have him route the rosette channel and sound hole. But, I was hoping to be able to do it myself somehow.

I thought of a series of concentric templates that fit inside of each other and then using a collar on the router to follow the template. Having them CNC'ed is an interesting option.

I can't seem to shake the feeling the there is another way, however. Lots of oval sound hole were made before there were CNCs and they must have done it somehow.

Wade,
How do you keep the distance from the pin that follows the inside edge to the bit the same? Wouldn't any small deviation from perpendicular move the bit too close to the sound hole?

If the guide the rides in the hole is not a pin but has some width to it, it would be easier to keep the router aligned, However, my sound holes are quite small and the width of the guide would cause the bit to creep in toward the sound hole when I routed near the pointy ends of the oval. I haven't built one of these so the problem may only be in my mind though.

Mike,
Actually you want a small pin. If it were a large diam. it would be more proned to deviate. As long as you are clear as to where you are along the edge as you rout and keep the router pointing in the right direction, you should be fine. Slow and steddy.

If I were doing this again, I would make a thinner channel and closer to the edge.

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Wade
Nashua, NH
http://www.wadefx.com

Mike,
Actually, I was thinking of making and selling a jig that is based off of one I saw at Edward Dick's shop. I didn't have my camera with me that day, but it was one of the coolest jigs I've ever seen for cutting oval soundholes, and cutting rosette channels. This jig is designed to make any sized oval from 2" to 10" and change the shape of the oval. It even does perfectly round holes too! I think I'll be at his shop later in the week, or early next week. I'll take a pic of it. The only problem is that it is a complicated jig to make and it would take some time. I'll post a pic of it and you can try to make it if you like.
Tracy

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Tracy
http://www.luthiersuppliers.com

Somthing like this should do the trick

Ya, the great thing about that tool is the unobstructed view.

Nice one Michael!

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Wade
Nashua, NH
http://www.wadefx.com

Michael,
I considered that tool but my ovals are really small. I said about 2"x 3" earlier but they are more like 1-1/2x2-1/2. The Stewmac jig wont fit. If there was one with about a 1" base on it, it might work but it might be too tippy.

Tracy, I'm looking forward to anything you might have.

make your own that will fit from rock maple

[QUOTE=MichaelP] make your own that will fit from rock maple [/QUOTE]
Worth considering. What are the thread specs on a dremel? I recall that they are somewhat unusual.

I have done it with a gramil and chisel, but a custom dremel rig sounds good too. Good luck and keep us posted.

Louis

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- Louis Freilicher

Oh No! Not another learning experience!

A pin router setup might be the way to go...that's what I do on my oval soundholes.

Find the smallest elliptical shaped object you can, tape it to a piece of hardboard and using a small pattern bit, cut out an oval in the hardboard. Then use your router guides/bushings and pattern bit inside the oval cutout. You should be able to go pretty small that way.

If its not small enough, use the first oval hole and a bushing to cut out a smaller oval to make another outside guide. You could keep making smaller and smaller patterns and when you're through, you'll have a size for any need.

Does that make sense?

Ron

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OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

I suppose I should explain a little about what I meant by having two left hands. I have to use jigs that only have one degree of freedom. The reason is that I don't have good fine motor control in my hands. Going slow and careful is not a practical option. Imagine that your hands are driven by an automatic transmission that is low on fluid. When you try to move slowly, nothing happens until, suddenly, your hand jerks and goes to far and not necessarily in the direction you thought you were pushing.

Im thinking you could do something like the spirograph I had when I was a kid. Start with a template out of MDF, hardboard or plexiglass. Just a big piece of something flat with an oval the same shape as the soundhole, just bigger.
Then make some circular plates that are smaller out of the same material with a hole in the middle.You can make them perfectly round if you use a screw or bolt through the middle and attach it to a surface adjacent to a sanding drum. Rotate the disc around the screw that makes the central axis, sanding the periphery against the drum until it is perfectly cirular. Thus, you'll have a disc that is nice and round with a hole exactly in the center.
Mount one of these circular plates on your dremel base. You can then use this dremel base inside your larger template with the large oval.If you make sure that the round dremel base is in contact with the oval template, you can just go around and rout out a perfect oval. If you have different size circles to mount to your dremel base, you can make channels of different thicknesses, and even rout out the soundhole, all corresponding to one another. you could do this for anything, whether it is a circle or an oval. As long as there are no corners.
Just think like a spirograph.
You would need to make sure your dremel bit was centered exactly on your circular base.
You cannot make the dremel accidentally go outside of your intended rosette border, because the large template wouldn't permit it. The only way it could goof up is if you didn't keep the cirular dremel base up against the side of your oval template opening. That should be easy to prevent if you are careful.
Cheap, easy, and low tech. What do you think?

Mike,
I have access to milling machine and lathe.
If you need parts for this jig made, let me know.
I'm in Nashua btw.

Wade

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Wade
Nashua, NH
http://www.wadefx.com

I know patternmaking is rapidly becoming a lost art, but going to someone with a CNC machine just to get an oval template strikes me as an over the top high tech solution to a low tech problem. There are lots of oval templates available from art supply stores. There is that orange polyethylene set of ovals available from a lot of woodworker suppliers. You can make a pattern smaller or larger with a compass (or using the carpenters trick of a pencil inside a round washer) to draw an expanded or contracted version on paper. Then you paste your paper pattern to a piece of plastic and cut it out. Finish with files and/or sandpaper. When it looks perfect to your eye, it is done. This isn't a part for a rocket ship.

Use a set of router template guides and different bit diameters to fine tune the size when you have a template shape you like. You can buy or make a jig for centering the router base to the collet (a disc that fits the hole in the base, and has an inside hole the diameter of any bit you choose and put in the collet. For a mandolin size rosette, you are best off with an outside pattern, so that the router base will rest across the oval hole in the pattern and not be able to tip as it could with an inside pattern. As for locating the pattern--well, if you can build a guitar, you can figure that out. Cut the soundhole from the same pattern and locator pins (using the router template guide set and different bit diameters again) and you won't get any deviation in the distance of the inner rosette ring from the hole.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

I've used a marking gauge and chisel for this sort of thing in the past, and it works well enough. Of course, I only have one left hand, even though I keep it on my right.....

I've often thought that if I wanted to do more of this sort of thing I'd make an ellipse tramel. This has a base plate with a perpendicular pair of dovetail slots. Two riders run in the slots, and these have pivot pins sticking up from the top. They are hooked together by an arm with two holes in it. The arm has a cutter on the end. The distance from the cutter to the nearest pivot is half the minor axis, and the distance to the further pivot is half the major axis. The two sliders run along in their tracks, and the cutter follows the ellipse. If you move the cutter in from the end, without changing the pivots, you get ellipses that are equidistant from each other, which is what we need. Again, I'd set this up as a marking gauge, and then use whatever means to clear the channels freehand.

This sort of thing goes 'way back: take a trip into the Old Schwamb Mill in Arlington (Mass.) some time and have a look at the big elliptical faceplate lathes that they have, which date back to the 1820s, iirc.

Al,
I know about the ellipse tramel (but not by that name so maybe I'll be able to do a google search and find out more). I even worked on building one but my mandolin sound holes are pretty small and making one that will to a 2"x3" oval would make for some tiny parts.

I'll look at it again, though, perhaps I can draw one up and see if it makes sense.

I made one once and it worked very well for anything larger than a Selmer
petite bouche. I made the base from plexiglass and routed tracks into it as
Alan wrote. I kept going smaller and smaller until I was routing into the bass
and it became oval itself. Then the pins were so close together that they
were bumping into each other...so I made them shorter...finally the blocks
that ride in the tracks would not go straight past the intersection.

Look here in the
MIMF archives

Scroll down to near the end to see my drawing.

I am sure someone smarter than me could make it work with reliable ease.