I had engraved many old CD’s with words and pictures with my cnc machines. Initially, I used to clamp the cd’s onto the waste board with the help of wooden clamps. I had to arrange the setup so as not to clamp the cd’s at places where the tool would travel. This would sometimes pose a problem. This was because some designs would have cuts at certain places. If this happened to be the places where the clamps contact the cd’s, this would naturally need a relocation of the clamps. Because the bolts for the clamps would be in the same position, (I don’t have T-slots) sometimes it would take some creativity to clamp the cd’s such that they would be held in place, while at the same time have sufficient empty spaces left for the engraving.
Then, I found out how to use double sided tape to stick the cd’s in place. This method also worked. In this method, I did not have to use clamps. Therefore, the problem of arranging the clamp position relative to the engraving spaces did not arise. However, the disadvantage was that the double sided tape was a consumable and tend to be expensive. It may be quite negligible when I do very few engravings on cd’s. But when I did a lot, the costs added up. In addition, sometimes I would encounter some difficulty when removing the tape from the waste board. The tape would break and I would have to spend some time scraping off the remaining pieces of tape.
Later, I found another method – using masking tape and super glue. By using masking tape, I did not face the problem of tape pieces breaking off. This was because the glue of the masking tape was designed so that it could be easily peeled off. Since the masking tape had only one side with glue, I would have to use 2 masking tapes, one for the cd and one for the waste board of the cnc machine. I would then use superglue to glue the two layers of masking tape together.
This method also worked very well. Masking tapes were comparatively cheaper than double sided tape, and the superglue could last for a few jobs before they dry off. But I found that the setup took up quite a considerable amount of time. Although it was cheaper, I was actually looking for free! I still like clamping the work piece in place because it was free.
After much thought, I decided to make a clamping jig specially for the cd’s. This was fabricated from a 4mm phenolic board. A round hole with diameter slightly smaller than the cd was machined out of the phenolic board using my movable bed cnc machine. A pocket was then cut all around the round hole with a diameter slightly larger than the cd and to a depth slightly shallower than the thickness of a cd. This would essentially become a rim around the cd.
When in use, the cd would first be placed on the waste board of the cnc machine with the surface to be machined facing up. Next, the clamping jig would be placed over the cd. This would easily slide into place because it was machined slightly larger than the diameter of the cd. With the pocket depth slightly less than the thickness of the cd, the contact surfaces would be all around it. Using my regular clamping bars to clamp the phenolic board against the waste board, the cd would be effectively clamped in between.
I have tested this arrangement many times and found it quite satisfactory. Most importantly, there were no more consumables like tapes or glue to buy.