Round tapered and bendy

[rhfurniture]

I am making chair parts that are round in cross section, taper and bend.
Some I do a 3d carving job with Mill wizard and a ballnose bit, but for others that predominantly are shaped only in 2d, I am trying to use roundover bits. Previously I have used slotted collars on a spindle, but this involves a lot of hand work to blend from 1 cutter radius to the next.
If I use, say a 16mm rad roundover router bit to cut a back leg that runs from 32mm dia to 27mm dia, and build a tool path in cad that passes twice and touches the model at 22.5 deg and 67.5 deg from the centre of the profile section, I end up with a shape that is within 0.25mm.
Is there any CAM software out there that can automate this process as it is doing my head in? (All I've seen so far deals with ball nose/end mill/veecarving bits). I use Autocad.
I would also welcome input from anyone who has tried and/or succeeded with this.

TIA,

Ralph.

[Brady Watson]

Ralph,
Post a picture of what you are trying to automate...It's difficult to visualize.

-Brady

[rhfurniture]

Ok,
Here is what I have so far.
Blue=toolpath
Yellow=solid model of eventual leg
White=geometry
The rectangles with quadrants out at either end represent the cutters - 19mm & 16mm roundovers.
As I am using a benchtop, I am machining in 2 hits indexed along a fence, and each quarter is machined in 3 runs, at 45 deg 2mm offstand for roughing, 22.5 deg and 67.5 deg to finish. At top right the profile is 35mm dia with 1 quadrant square, bottom left it is 27.5mm dia round. The middle change is at 32mm dia.
As I say there are some compromises in the geometry, but provided I keep the path within 2 deg of horizontal, I stay within my tolerance of 0.25mm.
I am nearly there but it has been a real slog - but maybe with practice...

Regards,

Ralph

4072
4073

[rhfurniture]

Just to clarify what I am asking, does anyone currently use or know of software to do this sort of thing, either midrange cam or autocad addonns/shareware, plus tips and suggestions.

Thanks to all.

Ralph

[Brady Watson]

Ralph,
To do it with a round-over bit...I don't know of any CAM packages that will account for that cutter geometry and/or give you an accurate simulation.

If I were doing this, I would definately use a ballnose bit. It shouldn't take that much longer to cut than with the method you are presently using...considering all of the setups that you have to do.

In your pic above, it looks like the left end of the leg curves down in Z, right? Why not rotate it + or - X 90 degrees and do 2-sided milling?

-Brady

[rhfurniture]

Brady,
It is laid flat like you suggested.
I could use a bullnose - as a woodworker though it just seems such a crude approach, and I am after the best possible finish.
I won't give up on it quite yet.

Thanks,

Ralph.

[Brady Watson]

Ralph...A BALLnose...not a BULLnose. Big difference!

You are going to be hard pressed to get something right off of the machine that doesn't need sanding. If you used MillWizard and a small stepover to do each 1/2 then you would simply have to knock down the high marks of the tool with a piece of sandpaper. I did 200' of custom molding like that and 3 minutes/8' length with an orbital sander made them smooth enough (pine...) to finish clear/natural.

-Brady

[rhfurniture]

Brady,
I do use Mill Wizard for some parts. It does a good job, but needs some serious scraping and sanding after. I did do some fluting with a Bull (or ball) nose cutter that was curved in 3 dimensions for gilding that was seriously impressive by developing the paths in Autocad. I guess I am just trying to build on that.
The Millwizard approach does seem a bit like trying to do cad in a bitmap editor (but 3d)

Thanks for your input anyway.

Ralph.