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Router Bits, so how do you decide?

July 30, 2010 by  
Filed under Router Tips

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The most popular router bit on the market is a “1/4″ Round over bit”. (Note: From a survey of a long list of Router users.) When buying router bits the only way to tell a good or bad bit is by looking at the characteristics of the router bit.  And as always not all router bits are created equally so when looking for your next 1/4″ round over bit look for the following:

1) The Carbide,

The bit should be carbide with the size of the carbide chip large enough to yield 3 to 5 sharpening. The grades of carbide range from C1 rough, C2 general purpose, C3 finishing and/or C4 precision. Having said that not all grades are created equal. There are thousands of manufactures with thousands of different grades. The US uses the “C”, which is used to grade upon kind of uses. In general the C2 and C3 are tougher and less brittle than the C4 but need to be sharpen more often. C4 is more brittle but holds an edge and doesn’t need to be sharpen as often.

2) Grinding,

Is the face polished or dull and full of grinding grooves? A polished face usually indicates it has been ground with a fine diamond stone and the use of grinding coolant. The price is one indicator of the quality of the carbide router bit. It is determined by the amount of work that is needed to manufacture the router bit. It is easier to face polish a C2 or C3 carbide router bit than it is the face polish a C4 carbide.

Please Note: We have found that in most cases the additional cost doesn’t yield that much more benefit to the DIY woodworker. Why? Well because each DIY woodworker doesn’t need their round over router bit to cut a thousand lineal feet of molding where as the professional might use their tools more often and longer. Next, there are many benefits to using the tougher C2 or C3 carbide over the more brittle C4 grade. These lower grade of router bits can usually stand more abuse than the more brittle C4.

3) Clearance,

Does the carbide extend beyond the router bit body? If not you may experience Burning. See the Clearance Samples in Photo One. The cutting edge must have clearance from the bit body. Next, what is the Rake Angle? All router bits will cut much better if the bit has a positive rake angle. See the rake angle comparisons in photo one.

The last characteristics is the Shear Angle, so is the carbide mounted straight up and down to the body or does it lean at a small degree ahead giving it a positive shear angle. To see the shear angle you need to look at the side of the router bit to see that it has a positive shear angle. See Photo two

Note: Think how the bit must cut. The least amount of resistance the better. When using a hand plane if you push it square to the work piece it is hard to push and does not leave a good surface. Angle it either way and it cuts better and is easier to push. It is the same with a router bit.

4) Chip load,

When the bit is running it is at a high speed and has to get rid of the chip load. Therefore, you need clearance to get rid of the chips. This is accomplished by having slim body with both the shear and the positive rake angle.

5) Shank,

Check the bit shank. Does it fit snugly into the collet and always select the larger diameter shank (1/2″ as opposed to 1/4″). I found one customer that made a go/no-go gauge that he used when purchasing router bits. It was a steel plate with precisely drilled holes in it (1/4″, 3/8″ and 1/2″). He tried every bit shank in his plate before he would purchase the bit. A shank that is not true will not run true.

That’s it for this post, thanks Bob and Rick


11 Responses to “Router Bits, so how do you decide?”

  1. john stark on July 30th, 2010 1:52 pm

    B&R Speaking of bits and hand tools I need some storage box ideas. Any tools left out corrode because of the warm moist climate. The same goes for my measurement and scribing tools which I constantly need. Anything in your videos that might inspire me?

  2. john stark on July 30th, 2010 1:55 pm

    B&R I assume that if I buy router bits from you they will meet your criteria. How about recommendations from Fine Woodworking or other DIY magazines?
    john s

  3. Sharkey on July 30th, 2010 3:25 pm

    This is one of the best articles I have read in the bit selection category.

  4. Bruce on July 30th, 2010 4:20 pm

    Thanks B and R that was very informative. That’s the first time I’ve heard anything more than a good bit has carbide. Keep them coming!

  5. Ralph Wilson on July 30th, 2010 8:16 pm

    I also SCUBA Dive and there are some water tight boxes (check out http://www.pelican-case.com/) that you might be able to use. They come in all shapes and size and, with a bit of foam, could hold the router bits and keep them dry (or, at least, as dry as the air that you let in when you shut the box ;-) .

  6. S S Han on July 30th, 2010 10:37 pm

    To John Stark, Hi, I read an article about “Camphor Blocks”, available at drugs
    stores or on-line on e-bay. the article suggested drilling small holes in either a
    small prescription or any small plastic holder. Place pieces of the camphor
    inside and that is suppose to prevent rusting. Does it work ?, time will tell. just
    passing on someone else remedy to the problem. Good luck.

  7. Michael Burke on August 1st, 2010 11:32 pm

    Very informative article.

  8. john stark on August 2nd, 2010 1:32 pm

    thanks for the feedback guys
    john s

  9. Keith Ames on March 7th, 2011 7:03 pm

    I have worked with router bits for years but have never seen that complete of detail along with pictures to compare. Keep on coming with the informative and good information.

  10. David Snow on December 18th, 2011 12:03 am

    great tips.I know I am going to like it here. I found this site from joining router forum.This is a great forum to learn from,talk about routers,pass information around and just talk to folks with the same interests.so long and have a nice week. DAVID

  11. Bill McQueen on January 31st, 2012 11:31 pm

    I too learned some things I didn’t know the side by side pictures helped a lot.