I’m seeking validation on flush trimming using a router and router table. Right now, unless I do things just exactly, my router sends the piece flying across the shop.
My Set Up: PC 3hp Router in Benchdog Router Table with a half inch shank half inch dia. solid carbide flush trim (bearing on bottom) spiral bit and a starter pin. Note when I say bearing on the bottom, that is reversed for the router table, bearing is on the top because router is inverted in table, got it?
Template: Typically quarter inch, but usually half inch mdf.
Stock: Right now 1.5″ stock, poplar, white oak etc.
Technique: Apply template and layout outline of piece. Remove template and band saw to about an eight outside the line or as close as I dare. Apply template again, and bandsaw again this time to about 16th or 32nd outside the line–absolutely as close as I can. Then trim. Of course, watch the direction of the bit and rout from left to right, moving the piece right to left across the spinning bit.
Problem: With 1.5 inch stock, the bit really wants to chip out and grab the piece and send it laterally. Scares the heck out of me. I can, and have, successfully trimmed many pieces now, but honestly, have to have the excess down below a 16th over the line to avoid chatter, tear out, and a rocketing piece. Of course, with quarter or half inch stock, this problem does not develop–its only with the 1.5 inch stock that I have to get the stock just barely over the line.
Remedies: I’ve tried two flute flush trim bits, spiral bits of both direction, a starter pin (which helps a lot), but really seems to be a function of how much stock I have to remove. I’ve actually used a Robo-Sander to remove the stock down to the template, a hand plane and belt sander. Once I get below a 16th the problem magically disappears.
How to you guys/gals flush trim wide (actually deep) pieces?
Thanks in advance.
Replies
Scooter,
Though you have a couple confusing sentences in there, it sounds like you are doing everything right. If you are standing at the router table with the workpiece between you and the bit, you will start with the work on your right and feed it to the left, against the rotation of the bit. Chipping out has more to do with the wood than the technique. Only so much can be done about this. When you say that the bit wants to "grab the piece and send it laterally", it sounds like a climb cut. That's the only thing that I can think of. If your feed direction is correct, the only possible (albeit remote) scenario that I can think of is that your router was somehow wired backwards so that it rotates the opposite direction.
I have used a flush cut bit on stock as thick as 1-1/2" without any major problems like you mention. The only time where I didn't quite feel in control was when I was turning a sharp corner (~3/4" diameter) and had about 1/8" to remove. Chipping was a bit of a problem in certain areas. Where the router needs to remove more stock, the natural reaction is to slow down the feed rate. However, this often leads to burning. Instead, try letting the template move away from the bearing to take a lighter cut, then take a second cut with the bearing riding the template. The spiral bit should be a big help getting a clean cut.
Good luck & be careful.
Chris @ www.flairwoodwork.spaces.live.com
(soon to be www.flairwoodworks.com)
- Success is not the key to happines. Happiness is the key to success. If you love what you are doing, you will be successful. - Albert Schweitzer
you didn't mention what kind of curves.in a concave shape the first half will be with the grain but the second half is against.this is especially problematic in fir and oak.they are very splintery.if you are routing off less than a 16th it should minimize it.what kind of wood are you using? and what kind of template? mdf is the best.particleboard and ply tend to be a bit wavy, and although it is unlikely, it could be causing extra vibration.not good when you are routing uphill.oops! i reread your post and you use mdf. are you sure you are feeding the right way? you shouldn't have pieces flying if you are going the right way only removing less than an 8th or a 16th.
Edited 1/15/2009 2:21 am ET by gossamershavings
I've found with template routing that an inverted pin router arrangement (Lee Valley sells a nice option, but you could make your own) helps quite a bit with control. Allows the cutter to only cut and not also be the guide for your template.
Template routing requires some firm pressure sometimes and the bit will flex, the pin router setup essentially eliminates most of the flex.
Also the grain orientation is wicked sometimes. If the template requires you to cross the end grain and then rout against the grain unfortunately its going to require care and attention, its just tricky getting those small diameter bits to behave.
1/16" material removal maximum but it sounds like you have that in check.
FWIW spiral downshear (towards the table) have always given the best results for me.
Good luck.
I've had this happen to me too with oak. Everthing goes fine until I go against the grain then it takes a long chunk out of my workpiece. Pisses me off. I've thought about the template bits that have the bearings that ride on the bottom and the top of the cutter. Then I could just flip the piece over and move on.
Cool. I've been at this for years, and am entirely self taught. Glad to see I'm on the right track. Yeah, a 16th is the absolute maximum.
Its funny, because I see these TV woodworking wizards breeze through template routing (David Whats His Name) in seconds, and the process for me is quite painstaking. If I don't have that excess wood South of a 16th, I will get tear out. Also very firm pressure on the bearing helps. If I let it off the bearing and there is a 16th or a tad more, that piece will go flying.
Sometimes I wonder whether simply laying out out the piece, bandsawing and clean up with a plane and scraper is more efficient.Regards, Scooter "I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Scooter1,I've got a new rule of thumb that I've been practicing: when something I'm doing with a machine doesn't go well, I immediately turn to the hand tool method that the power tool replaced. I do this rather than turn to a catalog or visit a wood working store for a solution. Usually, the hand tool solution is the most effective all the way around. In your case I'd try a spokeshave or scraper...
I've found that the key to good flush trimming is the bandsaw. Keeping your bandsaw well tuned with the table and blade lubricated and cutting square allows you to cut closer to the line. I trace my template with a slightly dull pencil then cut right to the line. It's okay to even hit the line as long as you don't cross it. This leaves very little work for the flush trimmer. Of course, some boards will still explode because... well, it's wood.
Some good lubricants are TopCote for the table and DriCote for the blade. They won't mess with your finish. Also, it helps to round the back edge of the blade slightly. Use a piece of sandpaper stuck to a board for this. *Disconnect the dust collector first!
David
Of course, some boards will still explode because... well, it's wood.
No truer words ever spoken except for the 10 Commandments...
Scooter,
How large are the pieces you're trying to rout? I've found that smaller pieces don't have enough weight to keep them from chattering. And sometimes that chattering leads to the bit grabbing too much of the wood and causing problems.
It helps if you can add a "holding fixture" that not only grasps the piece so your fingers are further away from the exposed bit, but also adds weight and mass to it so it's not as prone to vibration and chattering. You could do this with your templates by making them quite a bit larger than the piece you're routing, and screw some handles on it to make it easier to control.
Another alternative, if the pieces you're routing would allow this, is to do the routing before you cut a smaller piece free from a larger chunk. For instance, I do this all the time when edge-routing thin strips of molding. I rout the molding along a larger stick, then cut it free on the tablesaw after all the routing is complete..
Zolton
If you see a possum running around in here, kill it. It's not a pet. - Jackie Moon
I prefer to use a template bit (bearing at table end of cutter) and attach the template to the table side of the workpiece.
I've also found that a 1 1/8" dia. bit has far fewer tearout problems than 1/2" or 3/4" dia.. A bit that size is pretty intimidating at 25,000 rpm so I always use a purpose built guard that overhangs the bit and also captures about 1/2 it's diameter in a V notch. The larger diameter gives a shallower exit angle from the work so the cut is much more tangential and consequently much better backed up by solid wood.
Wondering where you source the 1 1/8" pattern bit?
I buy mine locally from a tool store that is supplied by these folks: http://www.samona.com/site/Alternatively Lee Valley carries them: http://www.leevalley.com/wood/page.aspx?c=1&p=30166cat=1,46168,46171&ap=1After side by side comparison, I suspect Lee Valley buys a lot of their bits through Samona and has their own colour applied.
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