Thread: Dovetail woes

the type of jig you have is designed to be used with a particular sizes of DT bit -- in your case 1/2" not 12mm or 13mm both of which might be sold as 1/2", so please check

I'm not sure what you mean by "had to make a new guide"
the type of jig you have is designed for use with a particular size guide bush, or one that is smaller

if, as you say you have made a new guide (set of Fingers ?) you will have to tune the router / guide / cutter combo (including the material stops) till you find the appropriate depth for the cutter
potentially a very time consuming and frustrating process

is there anyway you can fit a smaller guide bush to your router so that you can use the original fingers?

Ooops sorry for the terminology confusion, the "guide" is the part attached to the router and the one that came with the jig wouldn't fit onto my router. So I had another made with the same dia "guide" which was 12.2mm. The fingers on the template are 12.7mm (1/2") wide and the slot is 12.3mm. From what I've seen on the net that bush (guide) dia is 7/16" ie 11.1mm. So there is a bit more movement in the template slots to clear more material, It is such a standard jig template I was wondering if someone can confirm the correct dia of the guide. I definitely have a 1/2" cutter

I've used the sort of DT guide you have
the guide bush should be a sloppy fit within the fingers -- you need to consciously run the router on the right and left side of each slot to get the right width of cut

the instructions you linked to uses a 7/16" guide bush because -- I think -- 7/16" is the smallest finger template available for the jig, and using a 7/16" (= 11.1125mm) guide bush means once set up the router doesn't need adjusting -- many people leave a router permanently set up for use in that sort of jig

as noted, the depth of cut needs to be exactly set to the recommended value -- often an imperial rule is invaluable as these jigs are often made for the US market.
BTW, in US catalogues you will often come across router bits measured in 64ths of an inch -- the yanks do this to avoid quoting the exact dimension in mm

I can think of several "causes" of your problem,
but initially I'm thinking that the jig is not holding your test pieces squarely

can you post pictures of
1) your set up
2) your problem

Thanks Ian, I will take some pics, have to go to work....I'm pretty sure the guide bush is the prob, I've hand filed the dia down a bit and gave it a quick run and I can see there's more of a match between the grooves and the pins (tails) All settings are as spec for a 1/2" pitch template with a 1/2" bit

Ok finally made progress, I filed away at the bush until it was 11.1mm - 7/16" and low and behold the pieces are going together