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miters on a router table

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Forum topic by harum posted 03-18-2014 11:05 PM 807 views 0 times favorited 12 replies Add to Favorites Watch
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harum

130 posts in 389 days


03-18-2014 11:05 PM

Topic tags/keywords: question pine router joining miter chamfer

Hello, I am trying to cut 45° miter joints with a large Freud 45° chamfer bit, which is, as the label says, “ideal for joinery with 45° bevels”. After cutting a few miters with this bit I cannot get the 45° joint angle, as in the image:

Even though the miters are clean and flat, all pairs of miters are quite a bit off the right angle, always about 1/4” for every 12”. I have cut miters at different sides of the router table (in case the router is tilted with respect to the plate/table), cleaned the table and router before re-assembly—it’s consistently the same, a bit over 45°, angle. The table and router plate are flat, the lumber is square, nothing is loose. What else can be wrong here? Could the bit angle be off? Would greatly appreciate any hint or comment. Thanks, h.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."


12 replies so far

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harum

130 posts in 389 days


#1 posted 03-19-2014 02:22 AM

Wanted to add that the miters joints are tight and with barely visible glue lines. Except that they consistently don’t make a square joint. Each miter is about 1degree more than 45°. Will try to re-seat the bit in the router.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View ~Julie~'s profile

~Julie~

578 posts in 1780 days


#2 posted 03-19-2014 02:31 AM

Do you have anything to accurately measure the angle of the bit itself?

-- ~Julie~ followyourheartwoodworking.blogspot.ca

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TopamaxSurvivor

15065 posts in 2421 days


#3 posted 03-19-2014 03:47 AM

square could be off. Does a box made with 4 sides have tight joints?

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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harum

130 posts in 389 days


#4 posted 03-19-2014 06:16 AM

Thanks for the responses. No, the four box miters don’t close at the same time, as expected because each closes at 91° individually. The bit is about 2” in size, pretty small, so can’t see how its angle can be measured down to 1° accuracy. Will try re-seating tomorrow after cleaning the collet etc.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

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TopamaxSurvivor

15065 posts in 2421 days


#5 posted 03-19-2014 06:33 AM

If the bit is true, the router would have to be absolutely true in the table.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View Gerald Thompson's profile

Gerald Thompson

437 posts in 980 days


#6 posted 03-19-2014 06:17 PM

The two sides have to be the same length and the two top pieces also have to be the same length for all of it to square up.

-- Jerry

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thetinman

259 posts in 284 days


#7 posted 03-19-2014 08:12 PM

Check your square by laying it on a straight edge, like the edge of your workbench. Draw a line. Flip the square over 180-degrees and draw over this line. If they don’t overlay your square is out.

Check your router to table square with a straight length of metal rod (like a cut off flat head screwdriver blade) installed like a bit. It is long enough to check if everything is square.

Push on this rod to see if there is any play in the router showing bearing wear, etc. under load.

Check to be sure there is no play in the clamps when pushing it through the router.

Lastly, take nibbles instead of bites.

That’s all I can think of given your description.

Good luck.

-- Life is what happens to you while you are planning better things -Mark Twain

View Todd's profile

Todd

269 posts in 422 days


#8 posted 03-19-2014 08:27 PM

Cut something with a straight bit on your router table and see if that angle is 90 degrees to eliminate the squareness of your router to the table. I use the chamfer bits but have never actually used them for this purpose. I’m about to try a lock miter bit to makes some boxes though.

-- Todd, Huntsville, AL

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harum

130 posts in 389 days


#9 posted 03-20-2014 01:03 AM

Thanks! I put a makeshift shim at one side between the router and the plate to compensate for the angle error by tilting the bit and router together. This did the job—the miter joints are square now.

Will investigate the issue later starting with a straight bit and drill bit as suggested by Todd and The Tinman. The good news is that this angle error is not due to loose collet or misalignment of the bit relative to the router, otherwise the miters wouldn’t have straightened up.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View runswithscissors's profile

runswithscissors

1230 posts in 771 days


#10 posted 03-20-2014 07:03 AM

I assumed somebody would have asked this already: why do you want to cut miters with a router bit? There are easier and more accurate ways to do it. Am I missing something, maybe?

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

View BinghamtonEd's profile

BinghamtonEd

1593 posts in 1115 days


#11 posted 03-20-2014 12:20 PM

I see your shim fix…does your router mounting plate have leveling set-screws? Mine does. If your mounting plate is not in the same plane (check by laying a straightedge across the table/plate, should be perfectly flush) with the table, (and therefor your miter slot, or sled if you’re using one), you’ll get the results you’ve described. The shim works, but you’ve essentially squared the router to the table, but the mounting plate is still off. This fixes your current issue, but maybe not future issues where more of the workpiece is in contact with the plate.

If, however, your plate is in the same plane (read : all sides level with table top) as the table, then it would appear your bit and/or collet is not square to the router’s base.

Assuming your collet/bit is square to the router’s base, make sure that it is then square to the plate, then insert the plate and make sure the plate is square to the table.

I’ve never cut miters on a miter table, but I did stay at a Holiday Inn last night. So take it for what it’s worth.

P.S. I stayed at home last night.

-- - The mightiest oak in the forest is just a little nut that held its ground.

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harum

130 posts in 389 days


#12 posted 03-20-2014 04:29 PM

BinghamtonEd, looks like either the router base is not perpendicular to the bit/motor axis, or the bottom of the mounting plate ( to which the base is screwed) is not parallel to the top of the plate. Most probably, it’s a combination of both. The shim introduces a small angle between the router base and the plate. The plate is flush with table; the lumber I cut miters on is under a foot long, so it sits on the plate entirely. The bit is meant for “joinery with 45° bevels”, so I guess I should trust the label.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

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