Hand-held routing a radius edge with a template (beginner)

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geojay

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I’d like to accurately radius the corner of a piece of MDF. I have a Bosch POF 1200 AE plunge router and various edging / trimming cutters. I’ve only used it once before to do some flush trimming which was very successful.

I assume I need a template and that I should fix this template to the underside of the corner to keep the top surface unobstructed? I’ll use the cutter bit with the blade in between the shank and the bearing if this is correct.

Assuming I have the correct idea, can anyone recommend a template? I can’t see this being something I use that often…

Thanks in anticipation!
 
look up trammel bars
or a teardrop bit off ply slightly longer than the radius screwed to the router base but first jigsaw the excess to within 5mm off the cut line to make it easier
 
OP, the comments about trammel bars is correct, because you aren't going to be able to buy ready made templates - but I think in your case that you shouldn't use the trammel directly on the workpiece, because it can be difficult to start and stop a cutvexactlybwherevyou need to. Instead you should use the trammel to make up a template jig for use with the router and use that on the workpiece

Diver Fred said:
And the thickness of the MDF.
Your router is a little underpowered to cut, shape material over 12mm especially if you are taking 5mm or more material off.
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There is, however, some possible mitigations here: by setting out the curve with a pencil (using a template), then jig sawing or band sawing to within a milimetre or two of the line (removing most of the waste) before affixing the router template and routing to the finished shape it is possible to get a lower powered router to make an acceptable cut.

A larger diameter cutter (e.g. 19mm 16mm or at least 12mm) is preferable to a smaller diameter cutter and will heat up less resulting in a reduced risk less of scorching whilst making the cut (attaching a vacuum to remove waste also helps in this respect)

With a 1/4in shank cutter the OP will need to cut slowly, because feeding to quickly and making heavy cuts can overload the cutter which can result in the shank of the cutter bending or even breaking in some cases. The thicker the cutter shank, the less likely this is to happen, so an 8mm shank is better than a 1/4in (6.35mm) one, whilst a 1/2in (12.7mm) would be better still. I believe the POF1200 only runs 8mm collets as a max

Also, by swapping to a spiral router cutter instead of a straight cutter the power required to make such a cut will be reduced by something like 20 to 30%.

1200 watts may not be a lot of power, but it was all that was available in even professional/industrial plunge routers in the 1970s until the "massive" 1600 watt models came along...

20230730_110915.jpg

Above: Elu MOF31 industrial plunge router from about 1969. 1200 watts at 18,000rpm fixed speed. Probably not too different in size to the OPs tool
 
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robinbanks said:
Maybe if you told us the shape you want to rout.. "A radius" could be anything
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Apologies, it would be to round off the corners of an otherwise rectangular piece of 12mm MDF. I suspect a radius of 20 - 40mm will be suitable.
 
geojay said:
Apologies, it would be to round off the corners of an otherwise rectangular piece of 12mm MDF. I suspect a radius of 20 - 40mm will be suitable.
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If you want rounded corner radius on sheet material, I use a jigsaw, after drawing the radius around a can or sealant tube (example).

Sand paper any inaccuracies with some sand paper double sided to a block of wood.
 
https://amzn.eu/d/jlvTEdq is the kind of thing that looks close to what I want. They look best suited to a table router where you can hold the template in place by hard on top of the piece. I’d need it to be secured somehow on the underside to use a flush trim cutter…
 
geojay said:
https://amzn.eu/d/jlvTEdq is the kind of thing that looks close to what I want. They look best suited to a table router where you can hold the template in place by hard on top of the piece.
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You can make something similar yourself to any radius using a router, a straight cutter and a trammel but TBH a router table isn't the only way to go. I have a similar set, somewhere. They have never been near a router table

In terms of safety template jigs aren't just "held" to the work piece they need to be physically attached so they cannot move, that way you don't risk a face full of template being ejected at over 100mph should you suffer a cutter strike on the template. The three best ways I know (and use) are pins (not feasible in the case of a metal or hard plastic jig), screws (which require holes to be drilled in the template jig) or a few blobs of hot melt glue. A bit basic, but I have been known to hot melt glue a Carnation can to the underside of some MDF so I could radius the edge (trimmed the excess off with a jigsaw first, though no pointnin overworking the router or cutter). The hot melt glue comes off with a chisel

Remember, a trammel can be as simple as a rip of 1/2in plywood with the router screwed to one end, and a screw or nail through the other end at an appropriate distance. It ain't rocket science
 
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