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Flush trim bit on table router

4017 Views 9 Replies 6 Participants Last post by  Cherryville Chuck
Hello, I am fairly new to woodworking and VERY new to using a router. I need some help figuring how to trim a piece of wood without getting myself hurt. Yesterday I tried to trim a 3/4" piece of pine to a 1/4" masonite template, using a brand new 1/2" flush trim bit. I'm doing this as practice before approaching the same project with hardwood. The template is about 3/4 of a 7" circle with a flat bottom.On the first piece things went smoothly about halfway around, and then the bit tore about an inch and a half chunk from the pine. I figured I was trying to trim too much, so I made another and sanded the pine to about 1/8" of the template and tried again. This time, it took much smaller chunks, but took them nonetheless. In all cases, the sudden explosion of wood was similar to my experience of feeding the wood from the wrong direction. (I presume that scares everybody when it happens!) For clarification, I am using a table router, feeding from the right to the left, touching the wood to the bit on the operator side of the bit (I presume that makes a difference?). The process SEEMED like it should be similar to using a round-over bit. I've not had too many problems with that yet. Is the cutting of the arc problematic since the wood grain changes direction at some point? Is the problem that pine is a soft wood? Is there some kind of trick? Any help anyone can offer would be welcome! I really hate that sudden sound of shattering wood and the feeling of the project being torn from my hand in a micro-second! Thanks
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Welcome N/A...

what you experienced is tear out...
we just did a thread on this...
see this link here...

Also, as a new router user you need to go to this link and do some serious reading...


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The end grain is the problem.
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The end grain is the problem.
and the grain in pine can be very unpredictable...
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Would a spiral up cut bit help this situation?
Would a spiral up cut bit help this situation?
a helix spiral would work better...

Freud Tools - Search Results for helix
I have a Freud Helix flush trim bit, works great. Pine is very tear out prone, this bit should help.
When routing on the outside of a template always proceed from left to right (Counter Clockwise). The rotation of the bit dictates which direction you route. As you found out trim your piece close to the template. The less you are cutting off the better. If the overhang of your material is wider than your bit you can get in trouble.

When routing on the inside you cut clockwise. You mentioned that you had a circle on the inside. Drill a hole bigger than your router bit and route clockwise inside the circle.

As some have mentioned a spiral bit works a little better than a straight flush trim bit. A straight bit cuts just fine if that is what you have but if you are going to buy a new one get the ones that are canted. Shearing is better than straight trimming. It is like a hand plane, shearing gets a better result than straight planing.

Infinity has 3 bits that the bearings are top, bottom and both ends. They are spiral and cut very well.


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Thanks for all the responses!
I've read all the provided threads and PDF files.
They've given me a fair amount of insight, especially the "Tear out - How to avoid.." PDF.
That one shows photos looking very much like my project, and gave great details.
I did try a 3rd piece of pine, sanded down to about 1/32" from the template. I trimmed the rest off fairly cleanly.
From my reading, 1) take smaller bites - make more passes; 2) Pine seems to be prone to such failures if caution is not taken; 3) People that know what they're doing have experienced this...I'm not the first. So, I'll keep trying, with a little help from my friends.
The Infinity bits look very interesting. If I get comfortable enough to plan on some production run, I'll probably drop some coin down on better bits. For now, I'm just trying to figure out what bits do what, and which ones I might need, and my Diablo and Rockler bits will have to do.
Thank you all for all your help. It is greatly appreciated.
By the way, I expected an email letting me know my post had received replies. I didn't know there were any until I logged in this morning.
Is there a setting I may have missed?
Thanks again.
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Craig it's been a long time since I looked at the screen where you do that but you need to go back into your profile and edit your info and preferences. Somewhere in there is a Notifications setting that you have to turn on. I turned mine back off years ago as I'm on the forum enough that I don't want or need the email notifications too. While there you can change N/a to a name so that it's a bit more personal and it is often necessary that we have some idea of your experience and the tools you have to work with so that we can give advice that will work for you.
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