More on the Tabbing Function

[groover@americanwoodsign.com]

Hi Everybody,

Just wondering if anyone has a procedure that will allow me to cut out circles using the Tabbing function and placing the tabs at specific points on the circle. Actually, I would like to place a tab at the beginning and end of the circle as well as one at the 120 degree and one at the 240 degree point. I would also like to be able to do this on various size circles.

If not, maybe this could be something for the future wish list?

Hugh

[groover@americanwoodsign.com]

Hi,

Since I first posted my dilema, I have solved (at least for now) my problem and I thought I might share it with you for whatever it might be worth.
What I did was create a subroutine to cut out a circle in segments with 4 degree segments spaced at 90 degree increments that are raised .02" from the rest, to give me the tabs. The top segment is , in fact two 2 degree segments with the cutter starting at zero and dropping after two degrees of travel. When the top of the circle is reached after having cut the rest, I over travel the last segment to eliminate any cutter mark at zero. Works quite well. I call the subroutine on the last pass and use variables for the depth and diameter dimensions.
If anyone else has a better idea, I am all ears...

Regards,

Hugh

[bill.young]

Hi Hugh,

I like your solution, especially the overlap at the start and end point. I'd like to see how you wrote the subroutine... would you mind pasting it into a forum posting?

You could do a similar thing by changing the tabbing parameters with the VB command to fit the circumference of the circle, and then turning tabbing on in the CC command. The advantage is that the bit will ramp up and down at each end of the tab so that it keeps moving and might give you a little smoother edge. I'm not sure that you could place the tabs as accurately this way as you can with your method, though, and it would require some figuring to get the overlap at the starting/ending point.

Bill

[matticai]

I wrote a program in response to Hugh's original question. The program will cut any diameter circle with as many tabs as you want. The tabs will be equally spaced around the circle starting at 12 o'clock. There is a .25" entrance and exit segment that is tangential to the start/end points of the circle. The 12 o'clock tab will be cut into a little by the entrance segment. I've uploaded the file (named circletab.zip) to Shopbot's ftp site if anyone is interested.

If someone needed to cut a bunch of circles of the same diameter, the S_array.sbp file could be modified to do this using the FP command.

Matt

[groover@americanwoodsign.com]

And let me tell you, Matt's program works wonders. I used it tonight and just got done cutiing 36 9.5" disks from a 4x8 sheet of 1/2 MDO and every one popped right out after the sheet was cut and not one broke loose early, yet I could control the position of the tabs precisely.
Thanks all.
P.S. If you still want the part file I did I will upload it to the ftp site. But Matt's is better.
Hugh

[srwtlc]

Where is this ShopBot fpt site? I can't find it on the ShopBot web site.

Thanks

[groover@americanwoodsign.com]

Scott:
ftp.shopbottools.com
Hugh

[tlempicke]

This is probably obvious to everyone but me, but then it worked so well that I just have to post it here.
We are cutting out nose pieces to be used in the ribs of an experimental airplane. they look kind of like a 7 inch tall "D" when they are done. The tabbing function works great to keep them from popping out (we cut several at a time out of one piece of plywood.) but we have had to sand them to get the little tabs off. That is until we tried a formica trimmer in a regular router! Cleans them up just as slick as a button and in a couple of seconds.

[rgbrown@itexas.net]

Tom,

I have done a lot of the 'nose ribs' One of the things I do is make sure the tabs are where they will not be "critical". One of the things that a ShopBot can do for an "Experimental" is 'skeletonize' the ribs and save weight. I put tabs on the inside of the rib where the 'skeleton' is and then use a bevel edge bit to trim even more of that nasty ol' unnecessary weight off.

Ron Brown - rgbrown@itexas.net (mailto:rgbrown@itexas.net)

If Stupidity got us into this mess,
then why can't it get us out? - Will Rogers

[flyboy]

Just my 2cents. I've been making airplane parts too and A just don't use tabs at all. I'm using Bobcad though and make sure the inside cuts of ribs are done first and then the outside. I made that mistake once. But for the most part, I use a long stick to help hold the part down and just let it cut it out. The accuracy is fine. That may or may not work for you depending on your software. But I used to use two programs for the inside and outside cuts before I started using bobcad. That was all shopbot software. Vector could do it as well -if I could figure out vector...