# Flush Trim Bit?



## cbsjoez1935 (Mar 14, 2007)

Hi guys & gals,

Well here I am with another bit (no pun intended) of confusion. I had ordered a 1/4" flush trim bit with bearing attached. I decided, for some unknown reason, to put my micrometer on the bit. Here is what I found. The shaft measured .250 (14"), so far so good. The shaft that the cutters are on measured .236 (no big deal). The distance across the cutters measured .270 (should that not be .250?). No comes the kicker, the dearing diameter measured .275 (17/64"). Am I being rediculously concerned that with a bearing diameter larger than the cutter diameter I am not going to get a true flush trim following a pattern. I know, I know, wood is wood and not metal.

JoeZ


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## bobj3 (Jan 17, 2006)

Hi Joe

Because it's not a slotting bit that can be true, the bearing on the bit is the key.... 
You may want to check it one more time,, a quick way is chuck up the bit and make a pass or two...and if it does the job your good to go.... .005 is the standard for many router bits/bearings.....the .005 will change as the bit spins so to speak...point A to point B....thing...


Bj


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## Charles M (Apr 10, 2006)

JoeZ,

It is sometimes difficult to get an accurate reading of the cutter diameter but as long as the cutter and bearing are concentric the 0.005" difference (which would only be 0.0025" on each side) shouldn't be a problem. If the bearing was smaller than the cutter you would have an issue. Also, just to note that the bit must actually be 7mm instead of 1/4" (6.35mm). What is the brand?


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## cbsjoez1935 (Mar 14, 2007)

BobJ and Charles,

Thank you guys for getting back with that information. I may just be nit-picking where it is not necessary. Charles, my mic measures thousands, not mm, but coverting the measurement I made, .270 comes out around 6.9mm (close to the 7mm you recommended) so I should be OK. I have no idea of the brand since it was purchased from MLCS and those are usually Asian imports. These are my starter bits and I have had no problem with any of them. I was just curious about the measurements. Thanks again for you responses.

JoeZ


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## bobj3 (Jan 17, 2006)

You'er Welcome JoeZ for my small part


Bj


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## awh (Mar 3, 2006)

cbsjoez1935 said:


> Hi guys & gals,
> The distance across the cutters measured .270 (should that not be .250?). No comes the kicker, the dearing diameter measured .275 (17/64").



The actual diameter of a flush trim bit has no affect on its usage. The difference between the cutter and bearing is only 0.005" - that seems like it would be well within any manufactures tolerances.


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