Help Needed with Part

[flyguy]

Hey Guys;

I have been using my shopbot to make old pinball playfields. YOu can see the work at www.classicplayfields.com (http://www.classicplayfields.com)

I use the shopbot to cut all the 2d cuts and use jigs to make the few 3d cuts there are. On my next project I want to make as many of these cuts that I now use jigs for with the Shopbot.

Here is my target. Its the ball groove that the ball sits in before its launched into play.
http://i1.tinypic.com/zssvwz.jpg

I have designed this ball groove in autocad its really a simple slot that begins at the edge of the playfield at a depth of 1/8" and a width of 13\16" and rises to the PF surface about 16' up. I can send anyone my file if they want to try it. Here's my problem, I can make the slot in AutoCAD but I can't get it into a .sbp cutfile, no matter what I do. I can often get something into the cutfile but it never cuts like I want. The closest thing I have ever had was when I first created a project the size and shape of the PF and then using CAD subtracted the ball slot. It worked great but it had to cut the entire surface of the PF to get a small slot. it took hours and of course I can't use it because I may have more than 100 to cut. It should be a relatively fast and easy cut to do this small slot.

I want to simply be able to make a small groove part and be able to add it to any future project I have. I have been at this for days and just can't seem to get it to cut the way I want. I have made the part in AutoCAD and in RHIno but Parts Wizard or ArtCAM doesn't seem to want to output a cutfile that is representive of the part in Rhino or AUTOCAD.

Any ideas?

Thanks
Mike Purcell

Ball Groove AutoCAd File

2662 (7.1 k)

[drodda]

Maybe I am missing something here but isn't this a simple one line command with a say 1-1/2" boxcore bit.

J3,24.0,2.0,.25 'move the bit over lower
' starting point of groove
M3,24.0,2.0,-0.125 'plunge bit to 1/8"deep
M3,24.0,18.0,0.0 'move 3d 16" and raise to
' 0" deep
Jz,5.0 ' raise bit up

This would give you a slot that is 1/8" deep at the bottom and it would taper up to nothing 16" up the board.

I was assuming that your 16' was a typo?

You would actually use the appropriate boxcore bit for the size of the steel balls. And zero at the top of your material.

Please tell me the part that I am missing as this seem to me to be a simple one line cut?

Hope I explained myself correctly?

Dave

[flyguy]

Hey Dave;

Yes, its 16", at 16' that would be one BIG pinball machine :-)

My problem is I am trying to do it with a 1/4 ballnose upcut spiral cause its the same one I cut the rest of the PlayField with. I may be getting a second Z Axis and that may solve my problem, but I should be able to do this with the 1/4 bit.

Thanks
Mike

[drodda]

Bit change takes two minutes tops. 3 seconds to cut tapered slot. 3d cutting with a 1/4" bit takes 15 to 30 minutes depending on many variables.

Just a suggestion.

You can do the exact same thing with a 1/4" bit though. You just have to figure out how far to step over and up on each new move. You start in the center and deepest part and then move 16" and raise to zero. Then you step over 1/32" at the bottom of the cut and probably raise .003" and move to the exact same location as the first move 16" form the start and zero "z" This will give you a taper in the "z" and also give you the taper in the horizontal. I have done this many times before I bought a 3d cutting package to get 3d looking results.

J3,24.0,2.0,.25 'move the bit over lower
' starting point of groove
M3,24.0,2.0,-0.125 'plunge bit to 1/8"deep
M3,24.0,18.0,0.0 'move 3d 16" and raise to
' 0" deep
Jz,0.25 ' raise bit up

J3,23.97,2.0,.25 'move the bit over lower
' starting point of groove
M3,23.97,2.0,-0.122 'plunge bit to 1/8"deep
M3,24.0,18.0,0.0 'move 3d 16" and raise to
' 0" deep
Jz,0.25 ' raise bit up

J3,23.94,2.0,.25 'move the bit over lower
' starting point of groove
M3,23.94,2.0,-0.119 'plunge bit to 1/8"deep
M3,24.0,18.0,0.0 'move 3d 16" and raise to
' 0" deep
Jz,0.25 ' raise bit up

Once again I hope I am explaining myself good enough for you to get the idea.

The numbers in the example are not exact as I did not calculate the actual offsets for your bit. But they would be really close since I have done this with a 1/4" ball nose many times.

Dave

[drodda]

What I do is draw the bottom of the slots arc in autocad and then draw a profile of the 1/4" bit that I am using and copy it many times to figure the offset in the "Y" and how much to raise it in "z" for each new pass.

If you need more info let me know.
This seems pretty primative but it works.

[flyguy]

Dave;

I think I got it, I'll give it a shot. Any idea where I'd get core box bits larger than 1"? I think I'd need 1.25 or even 1.5"

Thanks
Mike

[drodda]

Whiteside has them and so does MLCS

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_core.html

http://www.woodworkersworld.net/round_nose_bits.shtml

Whitesides are better IMHO but also more expensive. I buy mine from Alan at Woodworkersworld

On a side note I just looked at your drawing and you can make lines from offset 1/32" over from the center to the top point of the center line and this and then list these and they will give you the coords that you need to cut this with your bot using the 1/4" ball nose bit. You just have to decide how much sanding you want to do. If you get more aggressive like 1/16" offset there would be a very small ridge say .004" tall to have to sand down but could be very easily done. And this would take half as long to cut.

[bill.young]

Hey Michael,

You could also the Extruder program that's in the latest Bill's Corner article with a 1/4" bit to create the toolpath and then manually edit it to make it 3d.

The Extruder will create a file that will cut a groove of the correct shape but at a constant depth, and you would have to manually add 1/8" to all the Z-axis values at the 16" end. It would be kind of tedious to do the editing but would only have to be done once and would let you use the same bit that you're already using...a semi-automated method of doing what Dave suggests above

Bill