Which flush cut router bit to "cross-cut" walnut?

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kooshball

David
Corporate Member
I will be cutting the top for my dresser to size soon and but it is too large to safely cross-cut on my table saw. My circular saw is terrible and doesn't have enough support to make a square cut so my plan is to cut close to the final size on the band saw or with a jig saw and then clamp a rail to the top and finish off the cut with a flush cut router bit.

There are quite a few flush cut bits to choose from and I assume that some are better suited to cross cutting than others.

The top is 3/4" walnut; what is my best flush cut bit option to minimize tear out and yield a smooth cut?

Thanks
 

mark2

Mark
Corporate Member
Me thinks the best option is a wide crosscut sled and a helper to support the top while you cut it on the table saw............ and if you can clamp the work to the sled, even better.........
 
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merrill77

Master Scrap Maker
Chris
I agree with the first post about getting a helper.

My second choice would be to use your circular saw with a good blade and a cutting guide. I made a zero-clearance base from 1/4" masonite for mine to get good quality cuts.

But, you can do it with the router - be sure to clamp a backer to the right side or you'll get a lot of tearout when you exit the cut.
 

thrytis

New User
Eric
Get a spiral cross cut bit for the best cut. If you want to spend less you can get a shear cut bit, but it won't cut as smoothly as a spiral bit, but still better than a straight bit. Make sure to back up the cut with a piece of scrap in any case to prevent tear out on the end.
 

bob vaughan

Bob Vaughan
Senior User
I've done that many times in the past and the type of flush trim bit didn't make a whole lot of difference. Follow a straight edge with the base unless you've got a steel or aluminum straightedge for the router bit bearing to follow. That small diameter bearing sometimes can dig into wood.

What did make a big difference was clamping a scrap piece on the back edge so when the router bit comes off the corner, it continues cutting the end of the scrap piece. This virtually eliminates blowout.
 

ehpoole

Administrator
Ethan
For this operation an upcut spiral bit will prove your best friend. I've done what you want to do with 1/4" carbide spirals for thin sheets but a 1/2" carbide spiral will further reduce the risk of tearout in stubborn woods and the 1/2" or larger is a better all-around choice if the top is more than about 3/8" thick. You could get by with a 1/2" HSS bit rather than carbide, but you will likely find that the spiral bit becomes a go-to bit in your collection and the greater life and extended sharpness of the carbide will more than pay for the difference over the life of the bit.

Spiral bits greatly reduce the risk of tearout since they cut in a continuous shear cut. While a downcut spiral could be used for this task this is the only scenerio in which a downcut bit can be used whereas an UPCUT SPIRAL BIT IS A GOOD GENERAL PURPOSE BIT for everyday use -- an upcut bit will also help you maintain better control since it will continually pull the wood against the router's base ensuring the router can't ride up (lift) if you hit a knot or other difficult section. The only downside to the upcut is that it will draw most of the waste material to the topside (but this is great if your router has dust collection or is mounted in a router table) whereas a downcut will push the waste to the underside (floor).

HTH
 

Gofor

Mark
Corporate Member
I agree with Ethan but would add a caveat: An upcut spiral bit will tend to tear out upwards. Either put the show face down when cutting (making sure the router stays flat and does not undercut) or put a sacrificial piece of 1/4 ply or other scrap over the edge on top to prevent tear out when using it.

JMTCW

Go
 

ZachEakes

New User
Zach
I use a stick of 1/4 inch aluminum flat bar, 6 inches wide as guide to make long cuts. If it is shorter than 8 feet, you can use a factory edge from a piece of plywood, just make sure you leave it wider than 8 inches when you rip it.

If you use a skill saw to make a first pass cut a 1/2 or 1/4 the radius of the router you want to use to finish the cut you should have no problems. If you use the router to "rip" the piece you'll put a lot of wear and tear on the bit, particularly if you run a full depth cut. If the table is that long you'll end up smoking the bit and burning the wood, unless you take a lot of shallower passes... and lots of time.

If your router base is not concentric to the cutter, you can make a plywood base for it and push it through the table saw, marking which side is the fence side and only using that side. I make these home made bases rectangular and use the long side against the fence. You can use a non-concentric base, so long as you hold the router base oriented to your fence in the same position.

You can find out if the base is concentric with a try-square set to the highest spot and looking for a gap... Or cutting something on a fence and rotating the router and laying the finished piece against a good known straight edge.

Cheers,

Zach
 
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