Basically I first cut out the main hole then used the hole as a guide for routing the recess. To do this you are forced to work from the outside inwards. The dimensions of the Penn handles that I have are:
Length 6 3/8’ (161.9256mm)
Width 4 ¼’ (107.9504mm)
Corner Radius 13/16’ (20.6376mm)
Step 1 is to calculate the size of the cut-out with the following formulae:
Overall Length – Bearing Diameter + (Corner Radius * 2) = Cut-out length
6 3/8’ – ½’ + (13/16’ * 2) = 5 ¼’
Overall Width – Bearing Diameter + (Corner Radius * 2) = Cut-out Width
4 1/4’ – ½’ + (13/16’ * 2) = 3 1/8
Cut-out = 5 ¼’ X 3 1/8’
I used a common method for routing the cut-out buy first drawing the required cut-out on a template then measuring the offset of the edge of the router guide.

And attaching some guides to the template with double sided tape (I actually put some pins in the guides as well because the tape came loose the first time I tried to route



Using a 1/2' cutter I routed out the hole. It is worth noting that it is not critical if you make a mistake and gouge the edge of the cut-out as we leave the guide blocks attached to the template and actually use them for the real cut. This of course is not true if you are using a following bearing to do the actual cut.

The template can now be used to route the cut-out in the boxes. Note that on my boxes I had already routed out the cut-outs so I just used the template to enlarge the cut-outs to the exact size. Thankfully my original cut-out was undersized. You would normally route the cut-outs before fitting the sides to the boxes.

Once you have a nice neat cut-out you can use that as the guide for the recess route. I put together the cutter from the shaft of a buiscut cutter, the cutting blade from a rail and stile cutter and a bearing. I used the big router for this part as the cutting blade is too big for the little hand router



This is then used to route out the recess

Clean up the hole

And fit the handle. These actually came out perfectly with a press fit


Hope this is of some use to someone. Cheeers S