# Couple Router Bit Questions.



## wm460 (Feb 12, 2012)

I am thinking of some router bits but am confused by there Specifications 

880 Corian® Roundover Bits with Ball Bearing Guide : CARBA-TEC

Shank 1/2"
Cut Dia 25.4mm
Cut Len. 12.7mm
Cut Radius 6.35mm

What do they mean by Cut Radius?

Are Roundover Bits better with a bearing or with out?

How do you work out what size Bull Nose Bit you need for say 19mm board?



854 Bull Nose Bits : CARBA-TEC

BTW this store is about 2200KM from me so a bit hard to pop in and have a chat. :sad:


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## rrj (Jan 16, 2012)

Mark,
IMO a bearing mounted round over bit is best, have both, the one with out is a cheap one I bought 25 years ago and never us it since buying the bearing mounted ones.

The cut radius is the measurement from the bearing to the outside of the cutter, if that makes since. See picture, the cut radius is "R", click on the picture to enlarge it. Don't know the answer to your other question.


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## Mike (Nov 22, 2004)

Mark, bearing guided bits have several uses that make them unique. The bearing guides along a work surface or template. By changing bearing sizes it is easy to use partial profiles. By removing the bearing you can get a nice accent line with your round over. Set up is quick and easy with a bearing guided bit; adjust your router fence close and use a brass set up bar across the opening so the bearing is isolated.(stops turning as you move the bar across it.) Plunge round over bits are also useful but harder to find.


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## Gene Howe (Jul 10, 2007)

Plunge round overs are often called groove forming bits used to make beaded panels. 
Plunge Round Over


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## jschaben (Jun 21, 2009)

Hi Mark - On roundover bits, I prefer a bearing guided one. That said however, there is one little detail. If you want to do a bullnose with one, the first pass will remove the surface the bearing will need to guide on for the second pass so you need to provide a guide to compensate for that. There are specialty bearings available but an edge guide will/should suffice, or if doing them on a router table the table fence will do that also. 
As far as bullnose bits go, you want to look at the bead diameter which should equal your stock thickness or the radius which should equal one half the stock thickness. For your example and link, the proper bullnose bit would be part #854-507-11.
Hope this helps


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## malb (Sep 15, 2008)

Hi Mark, I am also in Oz, and travel past the Melbourne Carbatech each day on way to from work.

Are you aware that the round over bits you linked to are for working Corian, a thick sheet plastic for benchtops etc, rather than for woodwork as such. CT also have a range of CMT and other bits for woodwork if that is what you need. I know that the Corian bits have a plastic outer on the bearings instead of metal to avoid marking the edge of the Corian sheet. I do not know for sure but suspect that the cutters may be mounted into the bit at different angles to give a more efficient cut with Corian, with the possibility of being less efficient for wood. I suggest that you get bits for the material you intend working, be it Corian or wood.

Others have covered the radius question for roundover bits.

For a bullnose bit, a bit with radius exactly half the thickness of the material being used should give a smoothly integrated half round on the edge of the material if properly centred on the edge. A larger radius bit will 'flatter' edge with a definite transition either side. A smaller radius can also be used and will develop a shoulder either side of the curve. Both of these are viable options, depending on the design requirements and what you wish to achieve.


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## wm460 (Feb 12, 2012)

Thanks for your replies, They are very helpful and stopped me purchasing the wrong bits. It is starting to make sense now.
I am going to be using wood not corian. 
I have a catalogue on the way from MLCS.
Carbatec is having a 3 day sale 23-5th.


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## darsev (Feb 3, 2012)

Mark,

I am not sure if Carbatec have bull nose bits in their own brand, but do have some in the CMT range. Carbatec have dropped their prices and I think they are now cheaper than importing when you consider freight. More important, they are very contactable on the phone. I live about 10 minutes away from their head office in Brisbane, and they are always on the phone giving answering questions such as yours when I have been. there. If you do call them, they do shut on Sat afternoons, so with your time zone it does narrow down the window you can use on a Saturday.

Also, I don't think that router bits are on special in the current sale, so don't panic over timing.

Darryl

UPDATE: Just checked the catalogue - only a rail and style matching set, and 2 three wing panel raising bits are on sale. All the others are normal price.


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