I want to take a cylinder and engrave a zig-zag groove around the circumfrence in the center of the cylinder as opposed to the face. It will require a 4 axis i.e. angular, using a stepper driven rotary table. How is this done in BC? I suspect it would be easy to do on a face using boolean function and NC x,y,z moves but around the center circumfrence is puzzling me.

You can do it by using your 4th axis rotary table as a substitue for the X or Y axis. You would need to know the circumference of the cylinder (Pi * D) then draw the zig-zag out in 2D. Convert to G-Code and cut. Doesn't matter what program you use with this method.

Marv

I have a picture of it here. If I can figure it out, I'll post a picture here of some candles I was playing with, similar to what you want.

http://cnczone.com/gallery/showphoto.php/photo/453/sort/1/cat/500/page/1
http://cnczone.com/gallery/data/500/223PICT0168-med.jpg




Marv

Candles are here: http://cnczone.com/gallery/showphoto.php/photo/454

Marv

Thanks Marv, that's exactly what I need to accomplish. All I need to do is (Pi * D) for my distance on the substituted X axis for example, then calibrate the Angular axis so that it makes one complete revolution for that (pi*D) distance. Correct? What brand 4" rotary table are you using? Happy with it?

Not that it's important, I'm curious whether I can illustrate this with BC in 3D. I know it can wrap text around a hemisphere, just wondering if it will do a groove around a cylinder.


Many thanks Marv!

BTW I like the low budget CNC machine in your pics that uses the drawer slides! Probably not all that accurate but did/does it work well for say wood signs?

Actually I haven't figured out how to use the angular stuff yet. What I am doing is to find the circumference then convert the "Incremental" setting in TurboCNC to coincide with 1" = 1 surface inch of circumference (Hope I said that right) then just draw a regular 2D drawing of what I want and the "Y" coordinates are fed to the rotary axis as if it were the regular "Y". Works out pretty good especially if you have a consistent diameter or circumfrence. Candles vary a little. I have also (Using the same procedure) done carving/engraving in a spiral around candles and ball point pens. I also use this procedure with Meshcam also to do photo engraving on cylindrical stuff.
My rotary table is from Little Machine Shop and I really like it. I am sur there are better ones, but this one does what I need to do with plenty of accuracy. I used it to make a vernier for my lathe lead screw and it is very accurate.
Thanks for the compliment on my drawer slide machine. It's actually pretty accurate for what it is. Almost as good as my other machine. I haven't tried it with the trim router, just the dremel. I have used it to make cutouts for some DB25 and DB9 connectors in aluminum. It also does a pretty fair job on photo engraving in wood if I use the right bits.

Marv

I think if you hunt around in the program, Bobcad can do the 4th axis scaling for you. You use the method that Marv outlined to draw the part in 2d, then you look in the nc setup for a conversion to 4th axis. You can substitute A for Y in conversions, and then make sure the scaling factor for Y output is set at 57.295778. This will convert your Y dimensions to radians, which will then become the actual A axis degree rotation (when factored by the Z height). This was the way it worked in Bobcad 17, but in Bobcad 18, you had to fiddle with the settings somewhat to make it work out. I don't know what they have done in ver 19.

When laying out the 2d sketch, draw a horizontal line (parallel to the Y axis) at a distance of Pi*diameter of the part. This will help you keep perspective of where the part will begin (at Y0) and end (at Y=Pi*D).

To the best of my recollection, version 18 would not simulate rotary axis.