Flexible routing jig

[Enrico Schiaffella]

Hello,
I was wondering if any of you has ever used this kind of tool:
https://www.cmtorangetools.com/na-en/sy ... ed-routing
I guess it is useful when making the plantilla or outsid mold. But I am not sure. I am afraid that it doesn't completely fit to the curve. Especially the tight curve at the waist. I think I will give it a try sooner or later. Unless any of you says that it doesn't work properly.
Thanks Enrico

[Bob Gramann]

I would expect that it would help to smooth out the curve when making a mold. I don’t see it as necessary. I make my molds in three layers. I cut the first half of the first layer just shy of the line and take it to the line with an oscillating spindle sander. Screwed to the second half, it is the guide for the pattern bit to transfer the outline to that half. As I stack the layers, I use the pattern bit on the router to match each layer to the one before. If you can draw the initial pencil line, the rest is easy.

[Dick Hutchings]

It looks nice but would be at the bottom of the list for expenses for me.

[Bryan Bear]

I don't see how I would use this in guitar making. I don't think it would be a good option (for me) in making body molds or templates. I start with a drawing and cut, sand, file and/or rasp thin sheet goods into my master template. I use that template as my initial router template for making molds and forms. Part of the process of shaping the template is fairing in all the curves. For me, that is a feel thing that I don't see being able to do properly with this flexible tool. Others might be able to do it well with this but I don't think it is for me. In this application, it feels like a solution to a problem that doesn't exist.

[Enrico Schiaffella]

Ok Thanks. So far I have always built plantillas and molds freehand. Some of them are pretty decent, others are not as good as I would like. Curves are a bit bumpy. I don't know how noticeable they are. Sometimes it's just a matter of how close your look and what kind of magnification you use. There is universal rules. It's all relative. Anyway that is the reason I was thinking to buy this tool. It's not in my priority list either, anyway.

[Alan Carruth]

I have seen articles going back decades about using bent sticks (the original 'splines') to draw guitar and violin shapes. I learned a bit about using them in a wooden boat repair class in the Navy, a long time back, but even then they'd stopped using wood boats, and I never got to use the technique for real. I've used bent sticks a lot for plotting out arches, and worked out a computer program to generate that sort of curve for drawing guitar shapes. This looks like another version of the bent stick, and should work so long as the thing doesn't develop 'kinks' from use.

I usually draw out the curve I want, however it's defined, on paper. I clamp a piece of 1/4" plexi over the paper, and scratch a line on it above the one on the paper. This is visible enough to cut out on the band saw, staying close to the line, and then gets refined using files and rasps, or a drum sander, until it's 'close enough' to the plotted line. The plexi piece then becomes the pattern for making the mold pieces with the bandsaw and router.

[Enrico Schiaffella]

Hi Alan, this is what I have been doing for my whole "lutherie" life. Like I said, results were pretty good. I was just wondering if this jig might give me an even better result. I am not at all convinced. I will probably leave it alone. I just found a great guy close to my house with a laser machine who can make great jobs!

[Clay Schaeffer]

Hi Enrico,
Thanks for showing the routing jig. I think it could be useful to smooth out the curve as Bob mentioned. Rather than sanding to the line, you could rout to the line. This might allow you to make minor adjustments and smooth the transitions of the bending and assembly forms.
It might also be helpful in the design process for drawing out potential body shapes.
I like the idea, the cost seems a - little - high, so I will probably use a strip of kerfkore and attach it with hot melt glue to do something similar. If I didn't already have the scraps of kerfkore and needed to make a number of templates I would consider buying it.

[Enrico Schiaffella]

That's interesting. Never heard of kerfkore. It looks like a nice material. Thanks

[Thomas Beltran]

Hi Enrico,
Thanks for showing the routing jig. I think it could be useful to smooth out the curve as Bob mentioned. Rather than sanding to the line, you could rout to the line. This might allow you to make minor adjustments and smooth the transitions of the bending and assembly forms.
It might also be helpful in the design process for drawing out potential body shapes.

This sounded like a great idea to me, since I have been in the process of rebuilding my laminating molds and templates. I was thinking along the lines of routing templates per an article in AL #120, by Jayson Bowerman, about making matching inside and outside templates. He takes an existing plantilla, and makes an outside mold that fits exactly. He uses an intermediate throwaway piece, which he makes larger then the existing plantilla, using a router bit with a bearing to follow the original template. Then, using that routed intermediate piece and a different follower bearing, he brings the third piece back to the same size of the original template. He calls it "expanding or shrinking a curve by a fixed offset." I read his well-written article, which took a bit for me to get a clear picture what he was doing. Then I saw this thread, it sounded more direct and easier.

The main thing I wanted to know, was the smallest radius that the CMT jig could handle. I googled and could not find the answer. CMT is actually an Italian company, with offices in the US. I called, back east, and spoke to someone who said they did not have the spec. There is a magazine, Sustain, Number 8, Spring 2015, that had an article about a similar product, ProTus Kurvenlinfix, written by Marting Koch. He does not give the tightest radius that can be used either, but there are pictures of him doing exactly what I want to do. It turns out that Tools for Working Wood carries the exact same stuff as Mr. Koch used, and has a very long free return period. I think it is also less expensive than the the CMT product. I called Tools for Working Wood, and left a message, and got an email from them saying basically, that it should do what I want.

I bought both the Picco Kurvenlinfix which has a 5/16" cross-section and is 1000mm long, and the Mini Kurvenlinfix which has a thicker 1/2" cross-section and is 1200mm long. The picture was taken after unboxing them. My wallet is there for scale. The bags hold the screws. I have been at home lately recuperating from a relatively minor surgery, but I was able to use cans and jars from my kitchen, which will do for now, but this was not too exact. I want to mount it on a panel, using my laminating mold and see how that works. But, I fairly easily bent the Mini around a 5" can, so the radius is 2.5", which should work for my classical plantillas, I'll check for sure when I get back in the shop. The Pico could bend to a 1.5" radius. The round holes around the edge become ovals so I want to play around with it some more and make sure the curve is still fair. Hopefully, I can return one of them, and still be able to do what I want. Another question is just how much pressure from the router bearing can be put on the template without the template moving out of place. I probably won't get to it for another week or so, but this may be helpful to someone think, like me, that this could be useful in the shop.