"I have recently constructed a simple attachment to ensure accurate and repeatable lengths when cutting on the 'Rat. I am making a rake of railway coaches and I needed to cut repeat window holes in the corridor division. For the sake of looks I needed a fair degree of accuracy. I could have drawn up the corridor and cut as per the previous set-up, but I am never to be trusted with direction of travel, so the odd cut in the wrong direction would be inevitable. With this simple attachment turning the feed handle in the wrong direction does not matter - the cable slips. But a repeatable pattern is established. I enclose two photos, the first shows the outcome, the second the attachment.

In use the router cutter is centred on the centre line of the (in this case three) cut-outs. The attachment is positioned by sliding it along the "T" channel so that the stop pin is central to the attachment and the attachment is then locked. The first cut can then be made, its length governed by the length of the slot in the attachment. For the other cut-outs, the pin is removed and the carriage moved until the pin can be placed in the next slot - the attachment itself must not move until all cut-outs in the group have been completed. The prototype was constructed of steel, but forces acting upon the attachment are quite small and I am confident that a hardwood/ply or acrylic set-up would work just as well. A hole needs to be drilled and tapped in the carriage. A pin the diameter of the cutter (for ease of calculation) screws into the hole."

Why not put the template in the left cam-lock to engage with a detent from above I hear you ask? I suppose you could  do it that way but I like how Bob has used the oft forgotten T-slot under the channel which makes zeroing in the template's start position so very easy.

It did occur to me that instead of drilling the carriage that perhaps a strip of plastic or metal of the required width i.e. 6, 8 or 10mm could be locked into the left cam-lock to engage with the slots in the template.

Bob you have devised a novel template here. Finger joints next?

Thanks for sharing your idea. Pleas send in any comments.

Well Bob has posted back a comment and here it is:-

"Because of the length of the work (about 650mm) both cam locks were in use, so I had to use the lower "T" slot.
Having read your comments, and being very aware that many owners would not wish to drill into their Rat, I wonder if a lockable block could be introduced into the ratchet track directly above the stop pin in my design? A small door bolt/catch might then serve as a stop pin, or a vertical pin. I have included a rough sketch to illustrate this idea. I must emphasize that close tolerances would be required with this mod due to the increased likelihood of sideways movement in the pin, also it has not been tried out!
I opted for a drilled and tapped hole for simplicity and lack of slop_.

I use a computer print-out for finger joints, often adjusting the spacing to suit the cutter, usually stacking them as per the Rat book but with packers clamped either side to reduce splintering. Even works well on ply! Several of my G clamps have routed grooves in them as a result!!"