Flush trim routing without exploding wood?

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Forum topic by Scott C. posted 03-12-2013 12:49 AM 2683 views 0 times favorited 13 replies Add to Favorites Watch
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Scott C.

147 posts in 1474 days

03-12-2013 12:49 AM

I regularly have the problem of wood grenading on me when I try and rout it with a flush trim bit. It seems no matter how careful I am 1 out 3 or 4 pieces catches and tears out something fierce. I’m currently making a dresser with some repeated arched pieces and want to make one really good one and use it as the template for the other pieces. I’m doing this on a basic router table with walnut and maple wood. I’ve thought of getting a speed control unit to slow the bit down, would that help?

-- measure twice, cut once, swear and start over.

13 replies so far

View Loren's profile (online now)


8172 posts in 3071 days

#1 posted 03-12-2013 01:05 AM

Use a pin router setup instead, or template collar rings.

These methods allow you to make the shaping cut
in small increments and stress on the wood is thus
much reduced.

View Tony_S's profile


598 posts in 2506 days

#2 posted 03-12-2013 01:21 AM

I’m betting that most or all of the tear out is in the second half of the arch. If it is, it’s because of the grain direction in relation to the cutting direction. The first half of the cut, the bit pushes the cut INTO the grain, the second half of the cut, the bit pulls AWAY from the grain.

If this is the case, you can run the first half of the cut till just past the center of the arch and stop. remove the template and put it on the other side of the arch and finish the cut.
That way your always pushing the grain into it’s self.

-- It is the mark of an educated mind to be able to entertain a thought without accepting it. Aristotle

View vipond33's profile


1405 posts in 1921 days

#3 posted 03-12-2013 01:47 AM

Two things. Using an insert trim bit will minimize or eliminate most of these explosions because of its chip-breaker design. Most trim bits are flying wedges that break out wood when running into shallow grain. Tony’s advice is very good if you don’t have one. Second, you may try climb cutting if the amount to be removed is not great. With this procedure (details available everywhere) you are never digging up under the grain – your last point of contact is the finished surface. Oh yes, as well, sharpness really does make a difference. Stick with the highest speed you can.

-- gene@toronto.ontario.canada : dovetail free since '53, critiques always welcome.

View handi's profile


128 posts in 3863 days

#4 posted 03-12-2013 01:54 AM

There is a video on my website showing how to flush trim with no blowout.

In essence, you work with the grain. Use a top bearing router bit with the template on top for all the parts where the grain runs away from the cutter rotation. Then you flip the part and template over and trim the rest using a bottom bearing bit. I even include a link for Rockler’s Dual bearing bit. It has both so you do not need to change bits, just adjust the height.

Scroll down the page to “Flush Trimming for Best Results



View MNgary's profile


294 posts in 1840 days

#5 posted 03-12-2013 02:02 AM

+1 for Tony_S.

-- I dream of the world where a duck can cross the road and no one asks why.

View kdc68's profile


2526 posts in 1700 days

#6 posted 03-12-2013 02:15 AM

+1 vipond33 and Tony_S....My added $0.02 is just be careful when climb cutting if you are not experienced with using a router…the work piece may get pulled in the direction of the rotation..(climb cutting is moving the work piece in the same direction as the rotation of the router bit)...good luck

-- Measure "at least" twice and cut once

View oldnovice's profile


5656 posts in 2791 days

#7 posted 03-12-2013 03:58 AM

I look at the grain and identify potential trouble spots … fairly successful so far, and then I do small sections of climb cutting and revert to conventional over the “climbed” section which, so far, has resolved my problems. But, as stated above, be careful as there is “negative” cutting resistance.

-- "I never met a board I didn't like!"

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404 - Not Found

2544 posts in 2392 days

#8 posted 03-12-2013 11:38 PM

Guide bushes allow you to lower the cutter into the piece a small bit at a time, only thing is you have to work out the offset on the template, or freehand small increments with the trimmer bit until you are just a whisker away from the template for a final cleanup pass. Your small passes will tell you if the wood is about to splinter. It’s often a combination of small passes and small climb cuts that work best.
If you are flipping the template, keep the template and piece long, bore a hole for a dowel top and bottom in the waste area and use the dowels to register the template topside and flipside.
Some timbers want to ruin your day anyway. Ash and walnut to name but two.

View Nicky's profile


695 posts in 3515 days

#9 posted 03-13-2013 01:08 AM

I agree with a lot of the posts here. It is important to read the grain direction to minimize the blow-outs.

I’ve been using shear cut flush bits for template routing with great results. I would also think that an up-cut spiral bit would be a good alternative in a router table. Any thoughts?

-- Nicky

View lumberjoe's profile


2893 posts in 1671 days

#10 posted 03-13-2013 01:46 AM

+1 for everyone above. They actually make bits specifically for trimming curves
With some careful set up you won’t even need to move your template. cut, flip, cut


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404 - Not Found

2544 posts in 2392 days

#11 posted 03-13-2013 01:49 AM

Don’t forget to use a spelch block at the end of the cut if it’s tearing out there.

View Scott C.'s profile

Scott C.

147 posts in 1474 days

#12 posted 03-14-2013 01:59 AM

Lumberjocks come through once again! thanks guys!

I think I knew most of this but hadn’t put it all together and was looking for the easy way, which of course is all to often not the right way. The shear bit seems like a great idea, I’m wondering why they even make straight trim bits? However I need to take a brake from new tools purchases so I’m going to work with what I have for now.

-- measure twice, cut once, swear and start over.

View Loren's profile (online now)


8172 posts in 3071 days

#13 posted 03-14-2013 02:02 AM

“spelch block” is my new favorite woodworking term.

We tend to say “blowout” on my side of the pond.

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