Fixed 0,0 point:

[twiles@excite.com]

I have read in quite a few posts lately people mentioning the location of the 0,0 (home X,Y) location. On many larger machines this is a fixed point that you usually can't just set by picking a location and hitting a few keys on the keyboard. For some of the items that I am interested in cutting with a ShopBot It will be extremely handy to be able to quickly place the home position wherever I would like. For others, I need it to be at the extreme lower (front) left corner of the table. When I run the programs from the front corner, I need the 0,0 to be exactly the same each time. What methods are there for re-setting the home position of the router to an exact location???

Example: I have a customer that is interested in carving out inserts for jewelry boxes that he makes. I will want to set up a jig on my table that can hold the "blanks" in place while they are cut, and since the quantities are going to be 1000+, I'll need to be able to cut some today, some tomorrow, some next month and use the same jig. I have a design for a jig that will hold 10 of them at a time. This will require a precise 0,0 re-location of the router in relation to the jig so that the pieces come out the same whether I cut them today or six months from now.

[bill.young]

Proximity (sp?) switches are probably the best way to establish a consistent 0,0 position, but there are other way of triggering one of the input switches. I have a low-tech y-zeroing setup on my ShopBot that uses a carriage bolt that runs through a block of wood that's mounted on one of my Y rails. There is some more information and pictures on my web site at http://www.seasidesmallcraft.com/yswitch.htm. The big disadvantage of this style of stop switch is that if there's a bad connection or a break in the wire, the stop ends up getting clobbered!

If you design your holding jig so that it's always mounted in exactly the same place, however ( with pins maybe? ), you won't really need to change your 0,0 position. One way to do this is to create the file as if the corner of the jig was at 0,0 , and then find the absolute coordinates of that corner of the jig. Then have your file move to that corner of the jig when it begins and cut the file in Offset mode.

You could also just create the cutting file so that the coordinates in the file are in reference to the true 0,0 point. The 0,0 point would stay in it's usual spot, and the coordinates in the file would be the absolute coordinates of the points.

Hope this last part makes sense; if not let me know and I'll try to do a better job of explaining.

Bill

[twiles]

Thanks Bill. In the past, I have always programmed machines as you describe in the second portion of your post....with all moves in relation to 0,0 for several parts, also known as nesting. The more I think about it, I will probably base all of my parts off of the normal 0,0 unless I have some special circumstance.

My only question then, is if I change bits, say from a 1/2" to 1/4" I will need to re-set the 0,0 location because of the lack of an internal cutter comp......am I correct?

[srwtlc]

I make some boxes that are made from two 5" x 8" x 3/4" blanks of walnut. Sometimes I make a few, and sometimes I make hundreds. I have a jig that holds twenty blanks at a time. The jig consist of two layers of 3/4" material that has the twenty 5" x 8" x 3/8" deep pockets with the corners opened out a bit to allow the square corner of the blank to fit, then a slightly smaller rectangle inside of those that goes all the way through the first layer, then the second layer has four 2" wide channels cut in it that connect four rows of five pockets to one main channel that I connect a shopvac to to hold the blanks down in the pockets. These two layers are sealed and screwed together, I have the four corners doweled through to my table so when I put the jig back on and screw it down its in the same spot each time. My master file, which by the way Bill helped me get a start on before I got my machine and got acquainted with making part files (thanks Bill), is based on 0,0 at the lower left corner and makes its first move to the first blank at 3,3 and from there the secondary files take over in 2D offset making recesses in these twenty blanks.
I don't have proximity switches to reset my zero back to that corner if I change it to somewhere else, but what I use is a corner block with aluminum angle screwed to the edge of it that I clamp to the corner of the table and jig, or anywhere I want to zero the tool and hook up a ground wire from it to a ground terminal that I have coming out of the side of my emergency switch box mounted on the X carriage. I then put a old 1/4" straight bit in the collet upside down and position the bit near the corner block, then Z2 and then run a modified zzero.sbp file that I've renamed to xzero.spb and yzero.sbp. This may sound complicated, but once you get used to it you can quickly and accurately zero the x and y anywhere you can clamp the zeroing block.
I hope this helps some instead of confusing the issue. If you're interested in how I modified the zzero.sbp files let me know.

Bill, if you remember, we e-mailed about cutting those recesses with a 1-1/4" bowl bit that has a 1/4" radius and leaving a ridge between pocket passes? Well, thanks to Dave at ShopBot, he mentioned that there's a parameter under VC for pocketing overlap percentage. Takes care of the ridge just like that.

Scott

[srwtlc]

Terry,

It took me to long to type all that last one before you posted again, but with the x and yzero.sbp files once its set you can put in any bit and the zero point is always at the center of the bit.

Scott

[bill.young]

Scott and Terry,

Scott...Your zeroing system sounds pretty slick; do you have any pictures?


Terry.. Scott's right; as long as you zero your x and y axis with the center of the bit at the 0,0 point, and write your files the same way, you won't have any problems changing bits.

Where you WILL have trouble is if you write a file for a 1/4" bit, and then try to cut it with a 1/2" bit. If your file just uses circle and rectangle commands you may be able to change the cutter size setting with the VC command and then use the built-in compensation that these commands have, but your start points will be off. The CP command would probably work OK, but I think you would get some un-expected results from the others.

Hope this helps,
Bill

[srwtlc]

Bill and Terry,

I'll have to take some pics. I've had good luck with getting into the habit of putting as one of my setup lines at the beginning of my file a VC command with just the cutter size used for that file.