Adjustable Router Bit - advice needed

[Matthew Houston]

I have an adjustable double roundover bit which I use on a router table to make frame mouldings. The guide says the max. cutting width is 31,75mm and minimum cutting width is 11,1mm. The smaller widths are achieved without use of the bearing. I would like to use it at 8mm width and the many varied shim washers would allow this. However I'm reluctant to go against the instructions as I'm not an experienced router user and know they are potentially dangerous tools. I can't see any obvious reason why this double roundover bit should not be used at narrower cutting widths than 11.1mm - any advice from experienced users would be much appreciated.

[Stephen C Cunningham]

While i don't know what cutter you're using, I suspect it has a 5.5mm radius. If you stagger the bits you can get them to the 8mm you want, but you likely wont have a uniform rounded edge to your board. I was using this for reference https://www.infinitytools.com/double-roundover-beading-router-bits

[Matthew Houston]

I am using 3mm radius on this bit https://www.manomano.co.uk/bits-for-routers-laminate-trimmers-and-spindle-moulders/adjustable-double-roundover-bit-hw-r2-r3-s127-d34x3175-80062211-1471962?model_id=1471962#product-description
It could be shimmed down to 8mm or less with the washers but for some reason the instructions say 11.1mm minimum. Is there any safety reason for that?

[glenn bradley]

I use these bits. They are always used in the router table. Using the fence in place of the bearing to control the depth of cut should present no problem.

[Matthew Houston]

Yes thats just how I use it - always in the table and with the fence set to control depth of cut. What I don't understand is why the min. width is said to be 11.1mm With a couple of the thinnest washers it could be around 7mm. Does anybody know any reason to avoid that?

[Jim Morgan]

Does the carbide project a bit above/below the body of the bit? The 11mm minimum might be to allow enough clearance so that if one half or the other slips on the shaft, the carbide inserts won't contact each other.

[Jim Becker]

If by minimum width you mean the space between the two cutters, it may be to help insure that the material you are edging doesn't shatter from being too thin between the edges. If your desired dimension is smaller than the suggested minimum, but only marginally, perhaps you'll be fine...run some test pieces. Carefully. If it deviates substantially from the suggested minimum, I wouldn't do it since the manufacturer has likely already tested things as part of the design process. Find another way to accomplish the task.

[Matthew Houston]

James - good point but on this cutter the carbide doesn't project above/below the body of the bit

Jim - makes very good sense what you say about the design and testing. And yes I do mean minimum width between the two cutters. I'm using hardwoods so there is a chance they might take a narrower bead. I'm only looking to go a little below manufacturers minimum so I'll test it very carefully and post the result. Many thanks.

[Jim Becker]

The limit may also be related to the distance you can tighten the nut... ;)

[Matthew Houston]

Sure....I see what you're saying....but it came with loads of extra washers of all thicknesses so no problem there!

[Matthew Houston]

Well I set the cutter at 8mm and it works perfectly. I guess I was being over cautious.....but better that than doing something daft. Thanks for all comments and help on this.