Today we started testing the jig for drilling the angle on Shopbot. Designed and cut by Mike Gittelsohn, the jig is basically a 2'x4' double-layered MDF bed with 9x2 symmetrical channels where 4' lengths of angle are placed and clamped by the third sheet of MDF that goes on top. Several dowels align the sheets relative to each other and to the Shopbot table.
Opened up the jig after drilling one 4' length:
Small error in X (about 0.03", we didn't zero the head properly):
The angle looks pretty good and might require no countersinking which would be a huge time saver:
The holes were not exactly drilled, but cut with 1/4" spiral O-flute carbide router bit for aluminum: http://www.amanatool.com/cncroutingdetails/aluminum-cnc-spiral-bit-51402.html. We started out at about 10 IPM for Z down feedrate and quickly dropped it to 5 IPM, then to one pecking cycle and then to about 1 IPM.
We still have the following problems to solve:
- Even though the channels seem to be tight, the angle moves lengthwise in the channels. This should be easily fixed by adding some restraints at one end of the channels.
- There is noticeable vibration in the gantry and Z stage when it's over the middle part of the jig. This might be more difficult to solve.
