Routing double rounded edge on MDF

[diditmissen]

I'm just about to embark on my first proper project since acquiring a router. I want to rout curved edges on a long length of 18mm MDF (to give a D shaped edge).

I assume that a "standard" rounding-over cutter can be used, but I'm not sure about something:

Once the first edge has been completed and the workpiece flipped over, the bearing will have to follow the now-curved edge rather than the flat edge of the initial cut. Will it follow this accurately enough or do I have to go to the expense of a double round-over cutter (which seem more widely available in the USA than over here)?

Any advice appreciated. Thanks.

 

[imamartian]

i'm a diyer, not a pro.. but i have used my router on mdf... and it's not the best as mdf is so very fibrous... that said, if you're careful, and use a decent bit you should be ok.

I would say, that depending on the radius of your curve, make sure the corner of the router cutter (if you're just doing round over) doesn't come into play, it will make a mess of mdf.

As for your second pass... it depends on your depth (sound a bit frankie howard) your edge will be straight, but the bearing needs to follow it...
maybe think about clamping/screwing/hot glueing a straight edge to it while you cut?

 

[diditmissen]

I've had a bit of a practice on a scrap piece of MDF to get the initial cut right and have done OK so far but I've since buggered it up doing something else so couldn't try the second cut.

I've seen several US sites selling "profiled" bearings which are designed to run against a non-flat edge, but are these really necessary?

Unfortunately the piece I will have to work on is curved so no straightedge possible and it would need a hell of a template (approx. 8' long) to do it that way. When I get some more scrap I'll try again - if I can't make it work I may settle for a very small chamfer along the second side so the bearing can run along the flat in the centre of the edge.

Would still welcome more suggestions in the meantime though as I am still a rookie when it comes to routing.

 

[imamartian]

i made an archway between rooms out of mdf... and the rounding over bit was fine... i'd say go for it, and if you fusch up, get some more mdf - it's cheap enough !

 

[big-all]

go for 1/8 radius [3.17mm] or even 4mm then you will have a 2mm flat for the bearing to run on
you wont notice its not a continuouse curve
do not complicate things just go for a 20 plus cutter bit set and work round it
you cannot accurately use a profiled cutter without a table or clamped strait edge
so 100 times quicker to just go for 3-4mm and 2 quick passes

 

[diditmissen]

Cheers guys. Much appreciated. Will look for a small radius cutter and have a go with that. I would prefer the look of an edge with a slight flat in the centre anyhow.

 

[Jasonb]

If you want a full bull nose then use a 3/8" (9.5mm) bearing guided roundover cutter, do the first pass as normal, flip the work over, put a few winds of masking tape cut into a thin strip onto the bearing and then run the other side. The tape will compensate for the slight step you get if the bearing is run on the curved face.

Alternative is to route one side using the bearing then use the routers fence rather than the bearing on teh other side but only works on straight edges.

Use MR MDF if you can it gives a much better edge.

BA check your maths, two 4mm radius cuts equals 8mm so you will be left with a 10mm flat, hes working on 18mm board not your usual 12mm

Jason

 

[big-all]

BA check your maths, two 4mm radius cuts equals 8mm so you will be left with a 10mm flat, hes working on 18mm board not your usual 12mm

Jason

lol yes your right as always jase
well it was `a "merry" bank holiday

and nice tip about the masking tape to save the step