A Question About V-Bits and Corner Cuts

[jemelby]

Given the nature of a rotating router/spindle bit, a straight bit would have to be infinitly narrow to achive a sharp inside corner. From what I know of woodworking, and what I have read in these forums, sign makers achive this "infinitly narrow" point with a "V Bit."

This is all well and good as theory, but how does it translate to the shopbot, and which of the many software programs are used for this?

Consider the star graphic. In this example, the blue area is raised about 1/2 inch from the field of red. As near as I can tell, there is no way to achieve a 90° side in a corner with out a slight radius as in "C" (equivilent to the radius of the bit). Corner "A" is a 45° side (or what ever the pitch of the v-bit you're using).

Does the available software compute all these ramp-ups, and z-axis changes to achieve corners like "A"?
Of course, "B", an outside corner, could be achieved with just about any bit.

Thanks for considering this question.


6511

[paco]

Well, there may be some many that can; Insignia is one well known that will do it in ANY fonts and 2D designs... for this you need a (GOOD) "V-carving strategie". Yes, they will compute all the toolpath to achieve this kind of machining. You can do the "B" corner just with a profiling strategie using a V bit... and it will look like a one done with a V-carving strategie. In some VERY simple designs, you can program thoses "sharp corners" manually... just need to know how!... some of us have done it but find it time consuming though we learn some things from this kind of testing/trying...

[harold_weber]

Hey James,

Presumably, the white area in your figure is the sloped or chamfered surface that you want at the edges of the star.

I believe that ARTCAM will do what you want, but its not that hard to program the required moves yourself. You can make "Corner A" be a sharp line by programming your machine move to raise the tip of the Vee bit so it follows (in 3D) the little black line you have drawn across the white space in "Corner A".
As you move from the red to the blue end of this line, the tip of the bit must raise 1/2 inch in Z.
This is not difficult to program since you probably have the X,Y coordinates at both ends of this little black line in your CAD program.

If you look at the sample "raised panel" doors at the web site called doorbot.net, you will see that Wes Mason is selling a piece of software that makes sharp corners at the corners of the "raised panel" formed with a Vee bit.

[daniel_carr]

If the sides of the star are to be sloped (chamfered) at an angle that is equal to (or shallower than) the angle of the "V" on the bit, then it is possible to get a perfect inside corner. I did some playing around in VS3D and constructed a simple star that is raised about 0.2" above the background in a 2" x 2" area:
http://www.designscomputed.com/images/star.jpg

Then I ran a Contour XY path with a 0.25" diameter 60-degree V-bit (and a 0.02" step-over) to clear the surrounding areas. This one path alone did the sharp inside corners:
http://www.designscomputed.com/images/star_cut.jpg

It would be nice to be able to carve out a star with perfectly vertical sides. But the best that can be achieved is a star with sloping sides (at the angle of the "V" bit). Note that the outer corners are sharp at the top surface of the star, but curved at the base of the star. This situation can be changed by sculpting the star with chamfered edges before running tool paths.

[rookie432]

Dan,

Maybe I'm not understanding the solution,however,
If you can get a sharp inside corner the you have the ability to do proper vee carve with your software. To get both inside and outside corners sharp then make an offset line for your star (or an outline) Then run a vee carve between the offset(outline) and the profile line of your star.
This creates a gutter around your pattern. Just vee carve the gutter.
If you are looking to bring the star to a point in the center, i.e. allsides chamfered with no flat top, i seem to remember seeing pics of someone accomplishing this at last years Texas shopbot camp. You might look through the shopbot camps section of the website. I'm pretty sure that photo an info is posted there.

Hope that helps,
BIll

[ron brown]

6512

[paco]

Nice parts Ron!!


Did you make the "texturing" around the star with a 3D strategie or a 2D profiling?

[ron brown]

BTW - I did that several years ago and have updated the cutting files. It cuts fast - that takes about 5 minutes at 1ips and using a PC7518 router.

7.2" star; Her-Saf 120 degree V-bit

Ron

[jemelby]

This is great stuff...

I'm really getting an appreciation for what can be done with a shopbot, and how it's done.

I am still abit overwelmed by the sheer number of different software programs, and their various capabilities. I have narrowed down some of my requirements, but I still don't entirely know what classes of software I'll need:

(early Favorites in BOLD)

2D Design: Illustrator Corel
3D Design: Rhino 3D Studio Max

2D Layout: AutoCAD The Other CAD
3D Layout: Big Fat "I don't Know" version 2.0

3D Design to Cut file plug-in: Seen a couple good ones listed here.

The hazy area is "what is required to generate cut files." I understand that the SB comes with a conversion program of some sort that will convert .DFX files. I also gather that there are third party programs that will generate cut files. I'll still hide and watch for a while, and maybe I'll fill in some of the wholes...

Keep the good stuff coming!

[rookie432]

AHA,

Should have known it was Ron that had mastered the star cut.

Curious though Ron why you dont have the point of the star pointing vertically on your design?
Like I said just curious.

Bill

[ron brown]

Bill,

Those are shelves - and they are downside up.

Paco,

The star was done in RHINO. I just "thought" where I wanted the bit to travel to get the desired shape and imported the DXF file into Vector.

It started with Bill Young's V-cut star back when these things were cable driven and one spent as much time adjusting as cutting. I then thought I could plot the pionts using a spread sheet or calculator and did just that and built a crude raised star. After that, the project set for a while. When I made the final star, as seen, it was done simply to finish what was started and playing in RHINO. The texturing is true 3D as it the toolpaths were projected on a conical surface. But, no "3D" tool path making program was used.

I'm a fan of Vector... I really don't think one needs another CAM program. But to do MillGizzard type work with Vector you need more brains and time than with the other programs. I run low on both at times.

I'll be looking for a real 3D program soon. I'll probably smend 40-60 hours deciding which one I like best.

Ron

[joe]

Ron,

I have often wanted to do stars like yours using our cheap little ArtCam, Insignia program but don't think it can be done.

We've made several attempts on stars that are incorporated in a larger Chip Carve pattern with no success.

So I must ask, can you do this type star, short of a 3D program.

J
www.normansignco.com (http://www.normansignco.com)

[paco]

I'm not Ron but... Surely Joe!!! Insignia is just fine for this... What whent wrong with your previous stars?

[ron brown]

Joe,

I'll be happy to discuss the star at any time. I have made the files available in the past and have "improved" them by optimizing cut loads and such.

There are 2 files available - I need to do some editing and testing before I let them out again. But there is file for a 120 degree bit and one for a 45 degree bit. Right now, I don't have the free time or inclination to test them. So, it will be a while before I turn them loose again.

I will try and take some time this week, put some instructions in the file and see if the kind folks at ShopBot Central will post them again.

Ron

[joe]

Thank You, Paco & Ron.

I have made several attempts to make a star with Insignia but don't seem to get it right.

Here's what I have tried: Clear away the area around the star area. Then change to a Vee bit, Z to top of material and cut. It doesn't do the inside vertical corners without rounding off the star ends.

I must assume Ron is not doing his stars in 3D mode.

J

[paco]

Hummm... as Ron wrote previously, I believe he has done thoses inside sharp corner manually; using inside corner's coordinates and center point of the star to create himself the 3D moves that will machine thoses lines. You need to do this yourself by entreing the code within the cutting file of star create with "bevel carving" strategie in Insignia... or create a star a like by "profiling" it first with the V-bit...be careful since you will be creating a toolpath manually; plan wisely the jogs too!... what I suggest should work; I did it with other shapes than with a star... but maybe Ron have a different approach?!...

[ron brown]

Short course, In Rhino, I drew the planes a bit would cut. I used the lower intersection as the bit path and went from there.

I have also done decorative spiral volutes, animal heads, "barbed wire" and other decorative patterns using the bit shape as part of the cutting and design stratigy. I've never seen a program that does things like I think.

Ron