Aligning top & bottom when flipping over

[phil@philsfoils.com]

I'm carving in 3d (rudders and centerboards mostly) at at this time am doweling the workpiece to the table along its centerline. But there's still a problem in getting exact alignment when the work is flipped over to do the other side. I can be out by as much as 1/8 inch, even though I'm using Shopbot to punch the alignment holes into both the table and the blank.

Any great ideas out there for a quasi 4 axis holddown jig?

(all my work is custom - haven't repeated the same design twice yet).

Thanks
Phil
www.philsfoils.com

[billp]

Phil, I've had pretty good luck indexing files like this by making a "corner frame jig", where I use small pieces of wood to"pin" my four corners in place on the first side of the cut. I'll then do the first side, and then when I flip the piece over I use the same corners to line it up again. Then as long as I've laid my second file out properly ( usually a mirror of the first image), I get the same "0,0" point to start from on the second side of my cut. I'll e-mail you a picture of a 3D file I did that way... Bill P.

[ron]

You should also check that the y-gantry is properly square to the x-axis. A flip over doubles the out of square and makes it very visible.

[rgbrown@itexas.net]

Phil,

Ron (without an e-mail address posted) could be right on y-axis square to "X". Also, if one were to do the carving profile along the "X" axis, the offset of the "profile" on a "Hershey bar type" foil would be minimal (please don't make me do the math although I THINK it is a tanget/co-tangent function).

[phil@philsfoils.com]

Yes, I always use the X-axis as the long axis of a workpiece. I mill the blank to the final thickness of the thickest part of the rudder (or whatever) and then tell the milling software that its rotation axis is half of that thickness off the table. I always zero the Z to the table top prior to starting, and I zero X & Y based on where I drill centerline holes on the table.

I've double checked, my Y is square to my X. I think I'm just getting errors from slop in the dowel pins, and lack of accuracy when I have a thick blank and have to complete the centering dowel holes with a hand drill (I start the hole with the ShopBot, and drill the matching centerline dowel holes into the table with the shopbot)

Question: If I were to build a jig that could clamp my blank in such a way that (0,0,0) is always known and reproducible, is anyone using devices such as proximity switches or other mechanical means of positively aligning their shopbot to a jig?

I've got one job coming up that requires me to machine the blank, then laminate a heavy fiberglass reinforcing layer on top of it, then remachine to final thickness. Aligning it for the second machining operation will not be fun.

Cheers
Phil

www.philsfoils.com

[Jay Wiese]

I teach high school tech ed, so our machine is used by tons of students. For this reason, I had to make sure that I used a system that was nearly foolproof. First, I built a low profile wooden vise with lexan clamping surfaces so that if students accidentally hit the vise with the router bit no harm would come to anything but the replacable jaws. The left lexan piece is fixed and the right lexan piece serves as the movable jaw of the vise. Next, I drilled a hole and placed a pin near the lower left corner of the vise to serve as a Y axis stop for the stock. Our machine has the limit switches installed. I adjusted the coordinates on the homing program (included with the ShopBot software) so that when students home the PRT, home position is always located directly over the near left corner of a piece of stock that is against the left jaw of the vise and against the indexing pin. Works like a charm. The only time that it does not work porperly is when students do not follow the written directions.

[tlempicke]

Last Jamboree I learned this - might be too simple to help but it sure works good for me.
We made a couple of pointers and attached one to the X axis and one to the Y. Went out and bought two machinists rules and epoxied small magnets to the backs of them. Once we find the X and Y we want we stick them down to the side rails under the pointers.
Low tech I know, but it sure saves a bunch of time!

[kerrazy]

Jay,
Would you haveany photos of your clamping system?

Dale

[papadaveinwy]

Dale, Go to the main shopbot website then to downloads then to other downloads then to videos and high school Wiese, his vice will work great for your clients. Dave in Wyoming P.S. your pack is on the way "again"

[Jay Wiese]

Dale,

Yeah, what he said! I could shoot a quick picture and send it along. The vise is really quite simple.

Jay Wiese