View Full Version : Aligning top & bottom when flipping over

04-01-2003, 12:56 PM
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).


04-01-2003, 01:57 PM
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.

04-01-2003, 02:03 PM
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.

04-01-2003, 05:48 PM

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).

04-25-2003, 10:53 AM
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.



Jay Wiese
04-25-2003, 03:38 PM
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.

04-26-2003, 07:03 AM
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!

04-26-2003, 08:26 AM
Would you haveany photos of your clamping system?


04-26-2003, 10:39 AM
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
04-30-2003, 10:29 AM

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

Jay Wiese

04-30-2003, 02:53 PM
I think that Bill P. hit the nail on the head when mentioning mirroring in the software. If you are not at the same X,Y position in the software, then all of the mechanical checking and dowels in the world aren't going to help.

I think that you can verify this in PWizard if you go to the transform vectors wizard and check the X,Y point at the bottom left for each file. It's more accurate than just hovering your mouse over the vectors.


05-07-2003, 06:23 PM
I've made up a turnover jig, and on the first try everything seems to be working okay. Pics & stories at http://www.philsfoils.com/jig/


05-08-2003, 02:22 PM
What milling software do you use? Do you draw with the same?

mike windsor
05-08-2003, 06:05 PM
I leave a bit of extra length in the stock and use the shopbot to drill a hole in each end of the rotational axis through to the spoil board to use with alignment pins. The biggest problem I find is getting the correct height of the Z point of the rotational axis . I plane down the stock to twice the thickness of the rotational Z height and make sure that it is not warped and sits flat on the table when it is flipped.

05-09-2003, 02:25 PM
Scott - I design with RhinoCad and then bring it into VisualMill for cutting.

Mike - I was originally dowing the same and dowelling to the table, but can only get 1/4" router bits with 1/2" shanks at a maximum shaft length of 1", and that won't go right through most blanks I'm using. Completing the last inch or two of the drilling with a hand drill seems to throw my accuracy off too much. And not having a 16" planer, I had to plane with the shopbot... very time consuming.

05-09-2003, 08:16 PM
Gerber has long 1/4" bits.


05-09-2003, 11:54 PM
Phil, surely you can get long 1/2" bits (from the metal milling industry) or even 1/2" drills if you are only making 1/2" dowel holes with them?

05-10-2003, 03:22 PM
Has anyone tried chucking a drill bit in a router? Even the lowest speed setting seems 3X too fast.

05-10-2003, 04:58 PM
Yes, we have used 1/4" drill bits in our 1/4" collet and it drills fine - even at 27000 rpm. There is no big technical difference between the cutting/sharpening angles of a drill bit and a router bit. But we only used the tip for vertical z plunges - we wouldn't think of using the sides for routing....yet.

05-10-2003, 07:23 PM
Man Gerald you are batting 1,000 I have done the same, and even done some side cutting with the 1/8" zip bits you know the ones for rotery zip tools I.E. the drywall cutter. they work great for small stock. David in Wyoming

05-11-2003, 03:51 AM
But I must add that extending the length out the collet at very high speed can be very dangerous. If the drill shaft is slightly bent, you could get vibrations and forces that snap off the bit and turn it into a high velocity projectile. THIS IS NOT A RECOMMENDED PRACTICE!!

05-11-2003, 10:44 AM
For those that are tempted to do some deep drilling, these are the safety precautions that I took: Cut the first section of the hole as deep as possible with a standard router bit, then dropped the drill bit down the hole BEFORE turning on the router. i.e. I never had the long drill bit spinning free above the surface of the material being cut. Under these conditions, a broken bit will be held captive by the material.

To drill very deep holes in thick material in one case, I had to move the gantry out of the way, drop the drill bit down the starter hole, move the router above the bit, lift the bit into the collet, clamp and then drill a bit more. Reverse the whole sequence to get the bit out of the hole.