Pin Indexing for Two-Sided Drilling

Here are some ideas for quick, accurate positioning of panels when you need to drill holes from both sides. October 26, 2012

Iíve found that drilling two-sided pieces is a hassle. The way I do it now is using blocks to position the part, I don't have pop-up pins. Does anyone have ideas on how to position the part without using the block method?

Forum Responses
(CNC Forum)
From contributor D:
I'm guessing you need the holes to line up, and drilling all the way through tears out the bottom? Have you tried instead of the drill bank, a compression bit smaller than the hole and cutting circles?

From the original questioner:
They are typically 5mm holes. You did make me think why not drill the holes all the way through. In my mind I thought of this as being cheesy so I never thought of doing it. Another case of stuck thinking I believe.

From contributor S:
When we have to drill or machine up both sides of a piece we sometimes drill some pin holes or dowel holes in the spoil board. Add a couple of extra holes on the face up side, mirror, and use the holes to index your next operation. Many times a couple of small pin holes are not seen or can be hidden on the first side.

From contributor M:
Using a 5mm v point bit can really work well for drilling all the way through, especially if you choose a solid carbide bit. Contributor S is onto it. If you choose to index, I use 5mm dowels for an awful lot of things, including drawer construction/ the 1 inch or 1-1/4 length works well. I have made stack laminated panels, door jambs, moldings and other items from 3/4 MDF aligned with 5mm dowels. You can also drill a few 5mm holes in the spoilboard to act very effectively as occasional pop up pins. In other words, store one program for the holes, and a matching template program for your work.

From contributor H:
When precise alignment is required for double side processing I will also use the pin method. I'll try and locate two 3/8" or 1/2" dowel pins at a symmetrical point in the design. Doing it symmetrical eliminates the possibility of being off by 180 degrees. Itís not always possible depending upon design but worth trying to do. Also the larger the pins, the more precise the alignment.

From contributor I:
There are no pop up pins on my machine. The design doesn't allow it so we drilled holes on the outside edges of x0 and y0 in the phenolic table. We use 1/2" fiberglass dowels with knobs epoxied to the ends and they fit snug into the holes and give you a pin to align against when needed. The holes have to be very snug to be accurate. Without the knob on the end you would need a tool to tap them in and pliers to pull them out.

From contributor Y:
I use 3" x 24" wooden boards with dowels to index into the spoilboard. I can use the indexed boards to lock in very small parts I must machine. For example, put a 4"x 4" part against the indexed boards, put a larger piece of something against the small piece to keep it locked in place, then machine away. No screws and it works great to index flipped parts.