# dont know size of flush cut bit



## sealik84 (Apr 24, 2012)

Hey guys I was wondering, i have some 5/8" stock stair treads that i have to cut down to a specific profile. I need to know before i buy the router bit which size bearing assembly i should buy either the 1/2", or the 3/8 " bearing. i don't even know if it matters but any help would be appreciated.


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## TomE (Dec 17, 2010)

Bearings should be interchangeable, get extra bearing set.
I quite often swap out bearings to vary profiles depending on needs.

PS... I see you're talking about a flush cut bit. Normally I go with a bigger diameter for heavy stuff.


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## mgmine (Jan 16, 2012)

Are you trying to round off the edges or some how change the edges? If so the bearing size doesn't matter as much as the radius size of the cutting edge. For example a 1/2" rounding over bit will give you a different look than a 3/4" bit. Also the height that the bit is set at will also affect the look.


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## sealik84 (Apr 24, 2012)

No i am just trying to cut off of a tamplate. and did not relize there were so many choices. i don't know if 1/2" or 3/8" matter when cutting srom the template.


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## TomE (Dec 17, 2010)

If you can, rough cut the tread with a jig saw or similar leaving 1/8" or so to trim off with the router. Makes for an easier go of it.


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## malb (Sep 15, 2008)

For a flush trim bit, the bearing diameter and bit diameter are the same, so for a straight line cut following the pattern, 3/8 or 1/2 in should both work without any variation in the pattern. However if what you are making has an internal corner, any bit will leave a radius in the corner equal to the radius (half diameter) of the bit. If this might be an issue, the smaller the diameter, the smaller the corner radius that will be left.

Otherwise bigger is better, I normally use 5/8 or 3/4 skewed bits for external pattern following.


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## CharleyL (Feb 28, 2009)

When doing this, the larger diameter bit will allow you to remove more material in one pass than smaller diameter bit. You should never try to cut away more than 1/2 of the diameter of the bit in one pass or you will experience serious chipping and splintering. Keeping the removal at 1/3 or less of the bit diameter produces the best results.

Charley


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## Quillman (Aug 16, 2010)

"but any help would be appreciated"
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I'd use a big fat bit, somewhere between 3/4 and 1" in diameter with a flute length that closely matches the thickness of the work.
And, of course, a collar and a plunger.
Maybe 2 or 3 passes/thickness. Why?
Very little tearout, the cutter can stand it, and there will be less chatter, as the collar transmits it vectors to the casting not the armature.
Straight bits are cheaper too & the collar guide bush is a safer way of routing.


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