Misaligned worktop join using router + template jig

Hi all,

Newish woodworker here. I want to do a simple(!) 90degree join on a laminate worktop using a route + worktop template jig. I've been practising on some scrap wood but every time I'm getting a significant misalignment and can't work out why. See images for two different attempts...

The corner is misaligned by approx 2mm. I can't work out whether it's the female slot that's too shallow or the male end that's too long, and even then wouldn't know what to do to fix it.

I'm using a Makita 3600 router, 30mm Makita guide bush, 12.7mm straight router bit, and a Silverline MDF template jig. I realise the template jig isn't the best quality but expected it to be a lot more accurate than this. I've repeated it a few times on completely different scrap bits of wood and get exactly the same result each time, so I suspect there's something I'm doing fundamentally wrong.

Also shown below is the router instructions I'm following...

Any help greatly appreciated!

is your guide bush and cutter the correct size and tight
also are you using a long worktop cutter

Is the guide bush centred on the cutter? That requires the use of a centring mandrel. If the cutter and guide bush are not concentric you'll get discrepancies. Also the Makita steel guide bush is hardly brilliantly accurate with some being out or round, so is yours actually 30mm, or is it in reality 29.5 or 30.5? (check with dial callipers) Finally is the jig you are using of reasonable quality? Some i=of the cheap MDF ones are terrible

As they're offcuts are you scribing the male section to meet exactly the edge of the female cut?

Or just doing them separately and mating up later?

Blup

Here's the problem:

MT3000 said:

a Silverline MDF template jig.

Click to expand...

Test pieces may be slightly warped, its intended for machine produced perfectly square worktop.

MT3000 said:

Also shown below is the router instructions I'm following...

Click to expand...

The part that's missing from those is that all of the initial cuts are made with the guide bush held against the edge of the template closest to you (the lower edge of the slot as in the diagram), and the final full depth finish pass is made with the guide bush against the other edge of the template (the upper edge of the slot in the diagram).
That way the initial cuts leave a thin amount of material, which is all removed in one pass on the final cut.

Hi all, thanks for the advice. Checked all alignment etc. Worked out the problem, and it was indeed the crappy Silverline jig. Specifically, the issue was that the alignment pins have a lot of play in their locating holes. Managed to work-around the problem by adding a ~2mm shim between the pins and the worktop edge when cutting the male slot - right old faff though.