Arc profile cut

[cnc_fabricator11]

Hello,

I'm trying to cut the profile in the attached image below, however it seems as though a typical roundover bit will give me a semi-circle profile as opposed to the custom arched profile that I need. I would hate to have to use a tapered ballnose in a 3d file to cut this as time is an issue. I would really appreciate any suggestions.


Thanks,

Patrick

[srwtlc]

Something like one of these in the right profile dimensions....

http://www.magnate.net/index.cfm?event=showProductGroup&theID=41

[cnc_fabricator11]

Maybe I'm looking at this the wrong way, but those bits will produce a semi circle if machined on both sides right? The profile I am attempting is an arc which does not have a consistent radius all the way around.


Thanks

[adrianm]

As far as I can see your only options are to find (unlikely) a bit with the correct profile, have one made or do it as a 3D job.

[John David]

Couldnt you use a 1/8 bit and cut the profile to depth?

Good Luck
JD

[MogulTx]

The curves you are looking to cut appear to be elliptical in shape. I also am assuming that you are cutting this in a long length for a moulding or something. You could go to a machine shop and have them cut a tool specifically for the curve that you are looking for, but you will need some definition of the curve so they have something to define their work by. ( The information in the drawing would not be sufficient. If it is something other than spherical, and it appears that it is, then they will have to know the curve, or will have to match something by eye, which will mean experimenting with the curve until they are satisfied- and then hope that you are satisfied... not a good method because the customer is always 10X pickier than the machinist.)

What defines the curve you are looking for? What formula was used?

When your tool is finished, you could just plunge and cut the length of your stock, and step over the appropriate amount and do it again.

[MogulTx]

Upon a second close inspection, and knowing what woodworkers would normally do: I am wondering IF the curve is ellipsoidal at all.

Imagine this: A spherical round over-like cutter is much easier to make, but you might want the appearance of the flatter, more difficult elliptical surface. What you can do is use a flatter radius cutter on the narrower spacing. But you would not want it to plunge all the way down in the material.
But if it did not plunge all the way down, in this case, it would make the crown of your material flat, which you do not want. So you would need to grind down the point of your round over bit, so that you can plunge it far enough to make the peak of one pass meet the peak of the next pass in the series.

Which upon further review is a lot more likely a method in wood working.

To follow this method you would probably need to look in Rockler, Woodworkers Supply or one of the other tool catalogues and find something like a veining bit, rather than an edge "round over" bit. Then you will need to blunt the nose on it (grind it down) until it provides you with the gap needed in between your convex structures (OR LESS! The bottoms could overlap to create the profile you want!). If it is rough, it is going to make the bottoms "hairy" which could give you a lot of finish sanding- so watch for that.

That should get you done in straight passes with a minimum of additional work.

Good luck on it.

Monty

[cnc_fabricator11]

Thank you all for the helpful info.



-Patrick