Bosch FSN OFA Hack!
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Hello all. Happy New Year!
Been doing some tinkering and tool servicing between Christmas and now. Thought I'd share a solution to a problem with the OFA someone else brought up on the forum recently - that when you're routing an edge and use a rail+OFA, not having anything to rest on, the OFA can wobble.
I took a couple of old guides - I think they part of the fixed base attachment for the old POF 500 - butchered them and the OFA base a little and made a drop down support leg with a wheel to lend support. I haven't actually used it yet as my rail set is still onsite but the photos below should give you an idea and you can see it supporting the weight of the OFA and router no problem. It's really very fucntional.
The little piece of tapped aluminium you can see embedded in the OFA is held there with epoxy (Aruldite) and is in there for good I'd say. When the support leg isn't needed, there is no difference in the use of the OFA at all.
The only tools I used really was an angle grinder, mini hacksaw and a screw driver.
Pic 1 shows the bits used
Pic 2 shows them post op, making the support leg (I got rid of the butterfly screw to secure the wheel in favour of a countersunk machine screw for clearance)
Pic 3 shows the threaded aluminium piece being inserted into the OFA base.
Pic 4 is the support leg attached to the OFA
Pic 5 and 6 show the leg doing it's job!
Having looked around to see if anyone else had done this I see Festool do a router with a drop down support foot for use with rails (I have the router but not the support foot. Must be an extra?). Perhaps I'm biased but I think my hack is better due it's all metal construction and it has a wheel rather than just a foot - so there Festool!
If anyone would like any more info or pics just let me know.

 
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I do believe this was my problem, quite an ingenious bit of a solution. Well done! Although it still requires setting up a steady surface, that matches the level of your cutting piece, a bit lower. Which is rather faffy outside a workshop environment. If only someone at bosch could come up with an ofa that doesn't rock on the rail? Hmm.. Maybe an extension off the back to balance the weight of the router. Reckon that is a viable alternative fix?
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The idea of the drop down support leg rather assumes you're cutting on a surface - a bench or table, even a makeshift one on site, which is where mine will be put into action next week. I need to knock up some bespoke trim where to and fro from the workshop (and router table) is not possible.
Don't know about a counterweight on the back end. Would make the whole affair quite a lump.
In your worktop scenario, you'd be just as well using one of the masons mitre worktop jigs - a large 900mm wide one - and supporting the other side of it with another piece of worktop/offcut.
For posterity, below is a picture of the Festool drop down support leg
 

This post was edited by bailey on 02.01.2018, 16:48 o’clock
Reason: forgot picture

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On Bosch coming up with an OFA that doesn't rock on the rail, I quite agree. In their defense, the OFA doesn't rock when used as intended - that being the cut being made inside a workpiece as opposed to on the edge. That's why the off-rail part steps down to compensate the height of the rail.
I don't suppose they envisaged it being used for edge routing. I didn't either until I was discussing an upcoming problem onsite for next week.
My gripe with the OFA is that it's such a pain in the ass to connect your router in the first place! It really is a faff.
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Here's a little demonstration of the OFA support leg I made in action.