Chamfer of extruded polygon. How do I do it?

Jim Canale

Hi!   I was hoping someone here can describe for me, in detail, how to go about creating a chamfer of the type shown in the attached drawing.    This chamfer is the type you would get when a hexagonal bar is chucked in a lathe, and a 45 degree cutter applied to the end.  The "Quad" tool can't do this.   I'm sure that this involves slicing the part, but I'm even having problems drawing the center axis through the part.

Roy Klein Gebbinck

1. Create a hexagonal polygon and extrude this (red in the image)
2. Create a cylinder with a radius that matches the polygon (yellow in the image).
3. Create a cone matching the cylinder, with the correct angle for the chamfer. Height = radius. (green in the image).
4. Switch to view front (the hexagonal extrusion should appear as its narrowest) and draw a temporary line from the top of the cone at an angle of 45 degrees (white in the image). Use something like @-20,-20 for the second point.
   
5. Switch to a 3D view and draw a temporary line from the midpoint of the correct vertical face of the hexagonal extrusion (white in the image). Use ortho mode.
   
6. Subtract the cone from the cylinder.
7. Move the resulting shape using the intersection of of the two lines as the base point, and the midpoint of the top edge of the vertical face from step 5 as the target point.
8. Subtract the new shape from the hexagonal extrusion.

There are no doubts other ways to achieve this. And actually the cylinder can be any other shape with a flat bottom surface since it is only temporary.

Hex_chamfer.png

Roy Klein Gebbinck

Mmm...the numbers of the numbered list in my previous post have somehow disappeared...

Jim Canale

I'm afraid I lost you after you switched to 3D mode.   I've created a cylinder with a radius = distance from the center of the polygon to any side.  I subtracted a 45 deg. cone of the same radius from one end of the cylinder.   Now you want me to subtract that object from the hex bar?  How is that going to chamfer the hexagonal bar?

Roy Klein Gebbinck

If you subtract a cone from a cylinder you end up with a shape that looks somewhat like a pencil sharpener. If you use a pencil sharpener on the blunt end of a pencil and make only a couple of turns, you get the type of chamfer that you are after. Subtracting the hollow cone shape from the top of the hex shape accomplishes the same thing. Actually you describe a similar process in your first post. In both cases it is a 'circular' tool that subtracts material at a 45 degree angle. Maybe a side view of the 'pencil sharpener' shape in the correct position before the last subtraction clarifies things.

Hex_chamfer_sideview.png

Jason Bourhill

Jim,

here is a animation to illustrate creation of a chamfer using pretty much the same method described by Roy. Alternative to drawing a _CONE directly is to create a _CIRCLE (use _2POINT option & select opposing vertices), then use _EXTRUDE with your preferred taper angle. When giving a height you can put in any large number.

note if this is something you do a lot, then you could create a block of this (at unit scale), allowing you to bring in and use as required.

Regards,

Jason Bourhill

CAD Concepts  

HexChamfer.gif

Jim Canale

Jason,

Thank you.   I am new to 3D, having spent the past 10 years in a 2D only drafting world.  So I am slow to catch on.   I'll keep trying.  As I told Roy, What I need the most, is help manuvering around in 3D space.  

Jim

@Jason Bourhill:

Jim,

here is a animation to illustrate creation of a chamfer using pretty much the same method described by Roy. Alternative to drawing a _CONE directly is to create a _CIRCLE (use _2POINT option & select opposing vertices), then use _EXTRUDE with your preferred taper angle. When giving a height you can put in any large number.

note if this is something you do a lot, then you could create a block of this (at unit scale), allowing you to bring in and use as required.

Regards,

Jason Bourhill

CAD Concepts  

Roy Klein Gebbinck

An alternative method:

1. Create a hex extrusion (red in the image), a cylinder (yellow) and a box (green) with the same center and the same height.
2. Use the _DMCHAMFER command to chamfer the top edge of the cylinder.
3. Subtract the hex extrusion from the box.
4. Subtract the box with the hex shaped hole from the chamfered cylinder.

With this method I had problems creating a chamfer with the correct dimension.
To get the chamfered edge to line up with the white circle I had to use some Lisp:
(distance (getpoint "\nCorner of hex shape: ") (getpoint "\nPerp point on inscribed circle: "))
... There must be an easier way...

Using this method the end result looks a little different.

Hex_chamfer_alternative.png

Roy Klein Gebbinck

@ Jason: Thanks for the nice animation.

Roy Klein Gebbinck

@ Jim: Finding your way in 3D space will require practice. The 'Look From' toolbar can be very helpful. It is also a good idea to position your model in some 'known' location in 3D space (e.g. center of bottom of hex is WCS origin). This makes drawing something like a center axis a lot easier.