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Any ideas on how to make a 3D router jig to rough out a scroll?

I've attached a picture of what I'm trying to do - this scroll is for a bandura. The one in the pic was from basswood and was really easy to carve. My current build adds one revolution to the scroll, is soft maple and it's a pain to carve. It's not that it's too hard, it's that it splits at the drop of a hat and I'm ending up CA-ing tons of little pieces back on.

The jig wouldn't have to make it perfect, just get the rough shape and slopes correct, I can finish by hand. I just think that after todays session I've taught the kids enough cussing for the time being

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

A small duplicator?

Looks like you are basically cutting a thread shape/helical shape. Maybe you could setup the router such that the axis of the bit is at 90 degress to the axis of the helix on the part....have the part setup on a leadscrew with the right pitch and screw it into the bit?

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http://www.PeakeGuitars.com

Brilliant! I'm thinking a 3D binding cutter type thing with three sets of drawer slides. Shouldn't even be that hard to do!

On the other hand, I just re-watched a video of "the woodwright's shop" where a guy cut a volute (which is similar to a scroll) by hand in about 10 seconds. The key was to have enough and the right sized gouges...which I don't. Even with a duplicator, I still have to hand carve #1.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Yes there is always a good set of chosen carving chisels for sure. Probably your best bet unless you want to build a CNC router. You might want to make a router template for the outside shape and even the scroll outline and just take your sweeped carving chisel/ chisels to it. Sure seems like with sharp chisels it should take about 5 minutes to do after you do a few and get your system down. I'd say check out some relief carving books and buy good quality chisels.

Something like this:



This is from Franks tour of Ted Megas's shop. It's set up for roughing archtop plates but the design could
be adapted to reproduce almost any 3d shape from a master template.

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- Louis Freilicher

Oh No! Not another learning experience!

I think a dupilcator that moved on a true vertical axis would be of more use such as routing inlay channels etc. I think there is a plan for a simular above style available in MIMF's library if you are interested in building one. You can also add tables that rotate much like the Doolin neck shaping jig that would allow one to shape a neck heel along with the neck. You can always Google duplicators and get ideas on designing one of your own.

I agree, that's why I'm thinking something like the binding fixture with two added axiseses (plural of axis anyone?). I'd use a straight cut bit. That would make the vertical sides of the scroll really nicely I would think.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

I once was thinking of a system like you say that would work by stacking template under the work piece. Sort of like if you made a small rolling cart if you know what I mean. The template would be on the bottom shelf and the work piece on the top shelf. The limitations would depend on your Y axis depth mainly. If I were to design a stacked duplicator I would put the router below and the stylus above and have the router carrage move on all three axis. That way you could enclose the routing section for dust and safty control. But if you are going to use the binding machine I think a counter weight might be concidered for the Z axis.

I was actually thinking side by side, just concept wise using drawer slides, three sets, like a binding machine has. Definitely a counter weight would be in order.

I'll probably skip it for this build but when I get to a point of doing 4 or 5 per year it might be worth building one.

Interestingly, after checking some violin sites, it seems that most violin guys use a hand saw and bench chisels to rough the scroll and only switch to gouges once the rough shape is there. Carving volutes with gouges is a bit different because there's no 3D - type thing going on with the spiral....I won't let that stop me from picking up a few extras though

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

This will work.With good drawer slides on the face of the box, it will straight up and down.

more like this guy:



Frank Ford's bridge carving machine.

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- Louis Freilicher

Oh No! Not another learning experience!

I was thinking of a more simply way. Here is a mock setup picture to give you some idea of what I'm talking about. There would be an arm linking the router carrage to the stylus sort of like a C shape. You would register the template on the bottom and the work piece on top. The table could be just slid around as needed. And you would build the router carage as needed for your Y axis and the length of the sled would be built as to your X axis need. Pretty simple idea with no X/Y axis bearings needed as the malamine slides easy enough. Like I said it's just a thought I had that I think would work and be easy enought to make if you have this type of binding machine.

Andy,

I believe you will get better results if you learn to carve the thing by hand. It will look more appropriate with some tool marks. You don't really need too many gauges but finding the right ones is the trick. I have two rolls of gouges and would probably use 3 or 4 tools at the most in carving that scroll, but I would likely try about 10 in finding the correct scoop and size. Sharpness is critical and the correct bevel really helps.

I would start with a saw to chunk off the majority. Then move to the near correct scoop gouge for cutting in and then you can use a file to round the scroll sides. A protected file makes it easy. This is where the right angle side of file is ground down to smooth so it can ride without cutting as the adjacent side rounds the scroll. At this point it looks flat so you must undercut the scroll or scoop it a bit. Try to go across the grain if possible on most cuts with the shallowest gouge that will put a little scoop on the turn, going slightly deeper as you go up to the eye.

Finish with a single chip removal at the nick of the eye. Don't get too fussy and it will look hand made. A scraper will smooth it out but probably too much, I would leave the tool marks.

It looks like about a 1 hour operation at most after you know what you are doing.

If you give me a full size drawing I can tell you what gouges you might need.

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Ken

Thanks Ken. I don't have any full size drawings but included some pics of the scroll I'm working on right now with a dime in it for reference. I decided to skip the extra revolution for this one because there are some wrong proportions - i.e. the lead up to the scroll needs to be changed to get it to look right to my eye and I'd need to add wood to do that. I also kind of like the simple-ness of this design. (BTW the hole is so I have somewhere to hold the instrument when I'm spraying the finish. After I'm done I'll cover it with an abalone dot).

This only took me about 30 min or so, I think you're right, with practice I'll be able to knock them out pretty fast. Obviously it's still pretty rough but you get the point.

This is the back side of the scroll that I'm using for practice, the front side will be more exaggerated as there's more material.

I've also included pics of what I do have for carving. The two older gouges seem too thick for what I'm doing. It seems like I'd like to have two sizes between the 3 and the 7. A 5 is the obvious choice - what do you think. I've also got a couple rifflers in there which I've protected one side of.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Looks fine Andy.

A couple things, your eye is perfect round and your next turn is more oval. The eye wants to see one or the other but not together. But that is a small thing, really.

You might find it easier to draw the outline of the turns using your gouges themselves rather than a pencil. Or trace the gouge to make the template if you are using it again.

Twirl, or spin the gouge to make the cut of the eye as far as you think and then you will need a smaller sweep tool. And a straight tool can actually take over by using just the edge or a knife even. This will make the "cut in".

Your curved gouge will probably make a good eye, try twirling it on a piece of scrap.

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Ken

Here is some doodling I did, I like to doodle.

I was trying for sweet lines, imagining the paper roll, unrolling.

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Ken

That is a really nifty idea Chris. It would take almost no work to do that and would add yet another use for a current one trick pony.

I picked up a #5 sweep gouge today and now I have enough to do what I need by hand. I just spent an hour doing the front and it's coming out pretty well. The design itself still looks primitive because of there being only one revolution but part of me thinks that looks a lot less stuffy than the typical violin style scroll.

One of my dreams (perhaps even someday a goal) is to make a low(er) cost bandura that would sell for around $1000 - duplicated scrolls would certainly help that.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com