Tools for routing templates

template
curve
rhino5

#1

Hello!
I’m a Luthier and I use Rhino for modeling my guitars and making templates.
This is a common issue for me:
On the right there’s the template I designed for cutting out the piece on the right. I use a 1/2’’ router bit for the cut, with a ball bearing to copy the template. The black circles are the areas were, due to the size of the router bit, the cut is more rounded than expected.
http://imgur.com/a/F3Pjq

How could I modify my curves so that they look exactly as they will turn out on reality, based on the size of the router bit?
thanks!


(Pascal Golay) #2

Hi Mat - it looks like you need a 1/2" Fillet there - does that do it?

-Pascal


#3

Actually a 1/4" (radius of the router bit) Fillet would do it :wink:


(Pascal Golay) #4

Yes, radius of the bit.

-Pascal


#5

And you can use filletCorners to get them all at once.


(David Cockey) #7

Simple filleting does not always work for predicting the shape from routing with a bit guided by a bearing. It works for sharp interior corners, but sharp exterior corners remain sharp. Similarly if the curve is convex towards the side the cutter is on the template shape will be reproduced exactly. If the curve is concave towards the side the cutter and the radius of curvature of the template is equal to or greater than the radius of the cutter the template shape will be reproduced exactly. However if the curve is concave towards the side the cutter and the radius of curvature of the template is less than the radius of the cutter the template shape will be bridged by a curve of the radius of the cutter.

To get the shape which will be cut start with the shape of the template curve. Offset with Corner=Round a curve the radius of the cutter on the side the the cutter will be on. This curve will be the path of the center of the cutter. Then Offset with Corner=Round a curve the radius of the cutter on the side to be cut. This will be the curve left by the cutter.


#8

Thanks Pascal! I knew there was a simple command for that


#9

Thanks David for the comprehensive post! I’ll try that for my next template to see how it works out.


(David Cockey) #11

Are you referring to the post I made and then deleted? I made the post and then decided to rewrite it.


#12

Sorry, I thought that message was refering to my original post!


(David Cockey) #13

Here is an example of various situations when template routing if the template has sharp interior corners or too tight concave curves. The template bearing and cutter have 10 mm radii.
Template Routing DC1.3dm (51.7 KB)