How do I copy this?

[flyguy]

I am making a replacement part for a Pinball machine and I have done many before but have always used a straight 2d cut and now have a feature that I still may be able to do 2d but I am unsure what's the best way to do it. I'll attach a picture but essentially I have a 1.2" hole all the way through the wood and I need a bevel from about .2" down into the hole back up to the surface, The top of the bevel where it again meets the surface extends about .75" from the edge of the trough hole. It's essentially a large saucer that would cause a pinball to go to the center and drop onto a switch.

I have 1/4" round overs and several 60 and 90 Sign making bits and even 1 or 2 120 degree .75" bits. What's the best combo to use?

Thanks
Mike

[Brady Watson]

You can do it 2D, using the shape of the cutting tool to provide the negative relief, or 3D in a program like Aspire.

From the looks of the shape, a 120 may cut too deeply at its shallowest depth - you might have to go 130-150 deg to get the shape you need.

-B

[curtiss]

Seems like you would cut the 1.2 inch hole first and then do a profile on the same line .2 inches deep with probably a 90 degree bit.

Does it have to be exactly the same taper or does "just close" work ?

[garyc]

Mike...
If you are feeling ambitious, you can do this with a ballnose and some hand coding to set the depth and diameter of a repeating "CP" command. Save as a C# file and use a "drill" postP to locate and run.

[flyguy]

Brady; I think you're right about the 120 being too high of an angle but I was hoping that by cutting 2-3 paths with a gradual depth increase I could approximate the angle I need. I looked and just can't find a more shallow bit. So I am stuck making something close enough I guess

Curtis; Yes, the 1.2 hole gets cut first with my upcut spiral and then I figured a bit change would be required. The 120 degree bit is a little too high but I was thinking 2 or maybe three passes spaced properly might give me something close I could sand out.

Hey Gary; Those two air drill setups you sent me are still working hard. They have run many hundreds of hours since I got them. Is there a way to figure out my step out and step up from the edge, other than to sit down and write each line, I suppose it wouldn't be that hard but I'd have to write a line for each larger circle stepover, correct?

[garyc]

Mike...
If you send me the geometry of the dish in cross section, showing depth and diameter, I can be more specific

gary.campbell(at)shopbottools(dot)com
GC

[rcnewcomb]

If you have Vcarve/PartWorks you can use a fluting toolpath. See the attached example:

[Brady Watson]

Interesting approach, Randy!

Now thinking about it, I'm pretty sure you can do this in SB3 using the Extruder tool with Arc option.

-B

[flyguy]

I think I figured it out. It's not pretty. Gary gave me an idea. I just planned on using a 1" Core Box bit. Then I measured the distance I had to cover, decided 8 passes would produce a smooth slant. I divided the distance into 8, then offset inwards from the outer circle that 1/8 distance, in 8 steps. Next I just divided the Z axis distance by 8 and manually did a cut along the vector for each offset line, gradually stepping down by 1/8th of the Z axis distance each time.

Works perfectly!

Thanks for the inspiration and ideas!

Mike