In article <jl8ark$93k$
1...@dont-email.me>,
a...@123.com says...
If the cutting height is varying, that's not wear in the bit unless the
shaft is buggered up enough that the bit is moving in the collet.
Either the bit is moving in the collet, the fence is moving on the
table, or the work is being tipped into the bit.
Some things to look at:
First, make sure that the shaft is smooth with no burrs (don't be afraid
to file or sand or grind out a burr if you find one). Also make sure
that both the shaft and the collet are _clean_. It's amazing how much
crud can build up in a router collet and if it's got any at all the
bit's going to move. I clean mine with a bronze .50 caliber rifle brush
and lacquer thinner then use paper towels with more lacquer thinner
until there's no trace of crud either visible in the collet or coming
off on the towel. Do the same for the shaft of the bit.
That's got the bit under control. Now you need to work on the fence.
Don't just use the fence that comes on the router table unless somebody
has made one up special for this operation and it's known to work--from
what you're describing that's not the case here. You need to make one
up.
You want your fence to be tall enough that you have more of the work
piece bearing on the fence than on the bit, so that holding it against
the fence keeps it properly positioned. You want to be sure that the
fence is absolutely square as well. I'd make it up out of some 3/4 MDF
or plywood, with a couple of braces in the back and enough of a foot to
allow it to be solidly clamped to the table, and maybe use some
Confirmat screws in the braces and the foot in addition to glue.
You want the fence stiff and strong and firmly attached--if it comes
apart on you that big bit can throw it all over the place. If it's got
any perceptible give to it at all reinforce it some more. Use a couple
of big C-clamps to hold it to the table, or if there are any dog holes
or the like then through-bolt it. If there's a t-track use that as well
but don't trust it--add clamps.
Be sure to make a big enough clearance cutout in the base on your fence
to be out of the way of the bit. If you can do so safely, make the
cutout in the fence itself using the panel-raising bit so it's an exact
fit, otherwise saw it as close as you can manage. If there's dust
collection available you might want to put a box around the back of the
area where the bit goes through with a fitting for the dust hose on it.
Something that will help is putting a spacer on the outfeed side to keep
you from accidentally tipping the workpiece into the bit at the end of
the cut--saw a radius on the spacer so that it doesn't stop the cut when
the workpiece hits it.
Rig some featherboards--put one on the infeed side and one on the
outfeed, but not one over the bit--that way the cut is controlled
between the fence and the featherboard on the infeed and between your
spacer and the featherboard on the outfeed but the featherboard isn't
deflecting the work right where the bit is located. Use featheboards in
two layers, one at table level and the other above the bit (stack some
2x4s or whatever and clamp the featherboard on top of them) so that the
work is held against tipping. If you put that last one right above the
bit it will also serve as a guard to keep your hands out of the bit.
Now you're got the workpiece controlled against movement in any
direction that it's likely to try to move.
Keep pressure on the top of the workpiece and keep it tight against the
fence and as long as the fence doesn't move you should get consistent
cuts.
Do after every cut blow or vacuum off the table--a chip against the
fence can push the piece away from the fence which screws up your
accuracy. If you've got the dust port I described rigged then this
should be less of a problem but it can still happen.
The idea here is to let the jigs maintain control. Try to anticipate
how the piece can move and put something there to control it, but don't
make things so rigid that you can't feed the piece through the tool. If
you're going to be working with power tools, learning how to make jigs
that control the work is a big part of the job.