Self centering fixture

[ger21]

I don't know how you're generating your g-code, but it shouldn't take more than a minute or 2 to do each different size. I'd use 0,0 and program for each size part.

[anoel]

I'm with the guys suggesting that you offset from one corner with a set of stops. A simple method would be to zero in on the corner of say a Y-12" x X-24" door. Then reset the coordinates of the Y and X to -6 and -12 respectively and that'll put you axis dead on the center of the piece. and you know that the corner that you offset from is -6 and -12 to get zero for your next part. I've done this for a couple of engravings that I've needed to repeat that required the engraving datum to be in the center rather than part-left+bottom.

[buscht]

The self-centering jig is a good idea, but I too would use the software version of this.

Let's say that you always want the engraving to be in the center of the part.

Write the engraving program as a subroutine or subprogram.

Write a parametric main program that asks for the X and Y dimension of the part.
Simply have the main program call up the subprogram at X/2 and Y/2.

Keep the part gaging fixed at 0,0.

Overall, this method is just as fast as the self-centering jig, and much more flexible.

The only downside would be its not 100% mistake proof, because the operator has 2 dimensions to enter.
Trent

[mvaughn]

Originally Posted by jderou Here is a drawing of a simple gear rack system. The pinion would be stationary (pinned at center).

That's a great idea... a common use for the dual rack and pinion are paper alignment trays in printers.

[NEATman]

Instead of rack and pinion, you could use a belt or cable. As long as the pulleys are on thier side (the axis of rotation is vertical) you could attach a stop block to each side of the belt, so that they move in opposite directions. You would need one of these set-ups in each direction.

If your parts are always rectangular, you could clamp across the corners. I realize that everything will not be the same aspect ratio, but to take care of that, make the self-centering jig pivot about it's center. For instance, in the rack and pinion arrangement, you could use the pinion shaft as a pivot for the entire clamp. Then all you would have to do is make the part paralell to the one axis of travel.

If you followed that one, I have another idea that would center it in both directions with one adjustment. Arrange the rack and pinion or belt system on an angle, preferably the average of the aspect ratio of the parts you are making. Each moving end of the clamp would have a pivot pin. Atop these pivot pins would be a bar, and at each end of the bar would be a pin that would contact the part to be engraved. When you tighten the single angled clamp, each of the pins at the ends of the equal length bars would touch a different side of the square or rectangular part. The angled clamp would center it along it's axis, and the equal length pivoting bars would center it perpindicular to the clamping direction.

Let me know if this is not described well enough, and I could probably model it.

Keith

[Hack]

The self-centering jig is a good idea, but I too would use the software version of this.

Let's say that you always want the engraving to be in the center of the part.

Write the engraving program as a subroutine or subprogram.

Write a parametric main program that asks for the X and Y dimension of the part.
Simply have the main program call up the subprogram at X/2 and Y/2.

Keep the part gaging fixed at 0,0.

Overall, this method is just as fast as the self-centering jig, and much more flexible.

The only downside would be its not 100% mistake proof, because the operator has 2 dimensions to enter.


Actually the software idea would work well. Maybe even better than the centering jig. I use my router for other things and with the jig, I am afraid of installing, uninstalling, installing...well you get the point. Also, it would allow unlimited part size as long as it fit on the table. I think I like it. If the operator can't enter 2 dimensions and be trusted......especially since that would be me. Yes mistakes will happen, but I got to beleive they would be rare.

I could easily set up the corner fo my table for 0,0 both for the router and for the part. But how do I do the code to ask for the inputs. I didn't know it was possible. Still really new to g-code.

[Kmed]

Well what cnc control are you using. That will determine what subroutine / programs and macros or variables you can run.