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Bit of head scratching but doable.

Yes. I think the offset base has a lot of potential, but it is supplied from the manufacturer as a bit of a half trick pony.

You can mount the plastic bit onto the standard base casting and install a handle in the hole for the offset part. It gives you a nice wide base for stability.

I suspect these are end of line stock clearance prices, so they are worth buying to put away for the future.

I have drawn and 3D modelled the plastic base bit, so if it is any use, I can put a copy here. Can you show a picture of the bush you want to fit (Trend style or Porter Cable style?) and I can 'virtually' see what possibilities there are.

If it is only a single size bush you need, a bespoke 3D printed one, that is unique to the base, might do instead of one following existing size/design conventions.
just to update this for anyone having to do this job. the offset base is a wonderfully heath Robinson contraption with several alternate configurations. anyway the collet on mine was poorly machined and wouldn't fit so I had to grind it in situ after 20 mins it was pretty decent fit( I've never had to do this ever!) it works by a small cogged belt driving an offset spindle. the issues of packing the base didn't materialise as my jig was 9mm anyway. I then made stuck a 9mm ply spacer with a stuck on alignment strip so it was straightforward to align with the top bearing 1/2 inch cutter.
it could also be used to sink hinges in rebated door frames with a simple spacer/jig arrangement.
what let's it down a bit is its slightly flimsy construction.


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just to explain how it's used with reference to the last photo. the sapele strip is first screwed on around the door with the edge lining up with the cut required the using a 1/2 inch cutter and a 30mm guide run all around the door. After that the ply spacer is screwed to the first guide in the corners then the offset 1/4 inch shank 1/2 inch top bearing cutter run into the corners. finally the last 15mm is chopped using a chisel.
(then of course heavy fake oak doors etc)
This proved to be a very helpful thread for me; so thank you to:
- @johnnyb for raising the questions that were germane to my problem
- @TRITON for linking to a very good deal on some chisels
- @ChaiLatte for linking to some very good deals on the Katsu router and offset base etc (unbelievably cheap)

Anyway, I have now successfully used this strange offset router setup for routing out some unconventional hinge recesses in some window frames in situ. I will add a couple of photos and a bit of explanation as it has been very useful and I didn’t know such a thing existed before seeing this thread.

The job is to recess some (30) custom-made cranked projection hinges on the front face of some window frames. It was a long story as to how we ended up with this design problem, but in short I designed the hinges for some stormproof arched windows to allow the window to open without the curved head fouling on the arched exterior wall reveal (I never liked the window design, but we were where we were and this was the only practicable solution.) The hinges work well in fact, but they were poorly fitted by the on-site chippy and now after many years I am refitting them (hopefully better!). These required rebates abut the exterior reveals and are high up on the building - chiselling out precisely is never easy with softwood and I didn’t fancy doing that.

Hopefully these pictures show much of how I did the routing:



The offset base gets to within about 8mm of the edge I think - that final bit does need cutting/ chopping out with multi cutter and chisel, but that is very easy from the routed reference.

I used a flush bearing guided bit from Wealden (8mm shank) - by sticking on a 6mm mdf base this was a good starting point for the required depth - I fine tuned the depth by adding some 8mm washer shims (I bought a selection of 1.0mm/0.5mm/0.1mm on eBay). Slipping the required shims onto the shank of the cutter gave very precise adjustment. The only remaining problem was the varying thickness of the nasty old plywood I had made my template from and the Katsu base is not very rigid particularly on the offset part.

I now need to make a replacement base or maybe two in differing thicknesses - does anyone have any suggestion re the best material for this (phenolic or acrylic?)

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Ahh I see what your doing. I reckon it's a fairly handy thing even better if it was a touch better made and rigid. Mine all turned out really well the doors fitted super because I'd levelled up all the rebates using a laser! But the dust. Yours looks a lot less dusty and a nice job. Sinking stuff perfectly even is extremely challenging with a chisel but removing the corners or a little bit is a doddle as you have a jig in the flat routered recess..looking 👍
I did the last door using a bit of lath and a multi cutter using new japanese blades(there was to much electric and other stuff in the way)
It was OK at first then got gradually more difficult. At full depth it was impossible to find the corner. Made a bit of a mess tbh. Not recomended.
Just a little update to this thread that wasn’t mine.

I chipped in on the Katsu offset router attachment and this has proved to be really useful on a few awkward jobs now.

I made a new base out of ½” Perspex that is a big improvement on the rather flimsy plastic base supplied. The thicker base also allows more flexibility on depthingvthe bit.


I have also knocked up a guide rail adapter that allowed me to rout some little channels where my normal router would not reach (due to the weather bar on this window). [One of those jobs that takes about 100 times longer to make the jig and set up than to execute.]


I would not push this setup too hard, but it really is a valuable bit of equipment.


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