# Defining a chamfer

Hi Guys,

Quick question that I just can’t seem to figure out. I want to make a chamfer in a surface that has a length of 15mm, however Rhino only gives me the option of an offset from the intersection. In my example there’s a big difference between the two. The red line displays the Rhino chamfer set to 15,15 and the green line is what I want to achieve.

What am I missing here?

You are not missing anything. What you want to to do is not an option with the chamfer commands in Rhino. But here is a method to do it.
ConstantWidthChamferDC1.3dm (274.4 KB)

Create a mid-surface between the two surfaces to be chamfered using TweenSurfaces

Offset the mid-surface one-half the width of the desired chamfer on either side using OffsetSrf. The Flip option in OffsetSrf is used for one side.

Check the intersection of the offset surfaces with the original surfaces. If they do not intersect the full length of the original surfaces then either extend the offset surfaces or go back and extend the mid-surface and then offset the extended mid–surface.

Trim the original surfaces using the offset surfaces.

Loft the trimmed edges to create the chamfer.

Join as desired.

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The constant width chamfer which Orthodynamics wants is not uniquely defined. The method I provided above sets the chamfered surface perpendicular to the mid-surface. But there are an infinite number of other options including perpendicular or other specified angle to either of the intersecting surfaces.There are also alternative ways to measure the width of the chamfer.

@davidcockey, Thanks for your reply, in the file you provided it works like a charm and it’s exactly what I need. Unfortunately it doesn’t work for me. When I perform the Tween function it gives me this:

Flipping of any sort gives even worse results.
Too bad Rhino doesn’t give the option of setting a chamfer length and angle.

@Orthodynamics For TweenSurfaces to work properly you may need to swap the U and/or V directions on one surface using Dir.

@Orthodynamics How do you want to specify the angle? Angle relative to what?

Either specified from a reference surface or edge (fixed angle), or say the average angle between the two surfaces (similar to what your tween surface method gives as a result (dynamic angle)).

Here’s an example from Solidworks where the chamfer is dimensioned as 0.04in. Solidworks then calculates how much should be taken off from each surface. Should be easy as pie right?

Try VariableChamferSrf with RailType=DistBetweenRails and use the SetAll option so select the chamfer width. No control over angle and the chamfer in the test I tried was at a different orientation than from my method above.

@davidcockey, YES! It works! Thank you.