Cutting a Centered Slot

[D_Harris]

You say "the cut even when starting out accurately will start to move from center. If I pull out and start the cut again a inch along it will be at the center again. This suggests to me something is flexing."  

I agree it sounds as if something is deflecting, but the router bit is not moving in the collet.  The problem with a 1/16" cut is that the cutter is of necessity quite thin.  I suppose if the plane of the cutter were not precisely parallel to the motion of the router, there might be a problem.  Does the cut move away or toward the router base?  If it moves away, it would tighten up and might need to be restarted to move again.  If it's moving toward the router base, it could be the whole router is riding up.  In either case, the problem could be rotation of the bit around an axis that is not perfectly perpendicular to the router baseplate, combined with a very thin slot cutter that can't easily correct the problem by cutting sideways.  If you can make the cut in a series of shallow passes, that might help.  How deep is the needed cut, and how deep are the carbide cutters on the router bit?  

If you make a mark on your router baseplate, you should keep that mark facing toward the edge as you slide it along, and making sure to hold the baseplate down tightly to the work.  (That last point is what the offset base helps with.)  If your problem is a slightly off axis rotation, you can fix it by trying a series of passes on the edge of scrap plywood.  Between each pass, rotate the base of the router 45 degrees, and try to keep the same orientation for the entire pass.  If the axis is the problem, once you find a good orientation, the router should continue to behave itself if you keep that orientation.  That's because a very slight tilt won't matter in the perpendicular angle.  It is usual however, that router axes are very perpendicular to their bases.

Another possibility is what Charles Neil calls "bump cutting".  If your problem is that the router starts at the right position and then drifts off as the router moves along, you can simply start the cut in very many places along the edge, "bumping" the router against the edge as you go along.  Then go back to the start and make a pass to connect all the bump cuts.  The router should not be able to drift far off before falling into a correctly positioned cut.

These are big cabinets, so a router table is out of the question.

Also I don't think it is plausible to make "shallow passes" using slot cutters.

Nevertheless, I had been thinking of trying what you call "bump cutting".

Thanks a lot.

Darren Harris
Staten Island, New York.

[Alan S]

You can make shallow passes with a slot cutter. While it's simplest with a router table because of the fence, it is possible with a hand-held router as well. You just need a fence, which is usually called an "edge guide" when used with a router. They can be elaborate to facilitate fine adjustment, or as simple as a straight piece of wood clamped to the router base.

[ez-duzit]

Slot cutters usually have bearing followers.

[D_Harris]

You can make shallow passes with a slot cutter.  While it's simplest with a router table because of the fence, it is possible with a hand-held router as well.  You just need a fence, which is usually called an "edge guide" when used with a router.  They can be elaborate to facilitate fine adjustment, or as simple as a straight piece of wood clamped to the router base.

These large cabinets tend to have curves. (They are video game cabinets as well as standalone control panels with curves).

Darren Harris
Staten Island, New York.

[D_Harris]

Slot cutters usually have bearing followers.

Yes.

Darren Harris
Staten Island, New York.

[Richard D.]

You think you are not tilting the router but you probably are. Trim routers are for trimming and not for running larger bits like slot cutters, the cutter is probably larger than the opening in the base which should give you an indication it is too large for the tool.

[Alan S]

Bearings are available in various sizes, which allow different cut depths.

[kurt18947]

One other thought. Is the clamp on your Bosch Colt pretty snug? Some people use them a little loose so they can use the fine depth adjustment wheel. The motor could move from vibration, just a thought.

[D_Harris]

One other thought. Is the clamp on your Bosch Colt pretty snug? Some people use them a little loose so they can use the fine depth adjustment wheel. The motor could move from vibration, just a thought.

I'l try "bump cutting and shallow passes. (One of those has to work).

The fine adjustment on this router is garbage. A lot of trail and error is need to set the correct depth.

Thanks.

Darren Harris
Staten Island, New York.

[CanoeBoy]

I'l try "bump cutting and shallow passes. (One of those has to work).

The fine adjustment on this router is garbage. A lot of trail and error is need to set the correct depth.

Thanks.

Darren Harris
Staten Island, New York.

I must have missed the "bump cutting", what does that mean?  Trim routers are exactly that, for trimming laminate.  If you have a full-size router available use it and make your cuts full depth with a slot cutter.  It is possible that your slot cutter is upside down.  I would think that would be part of the drifting problem.  1/16" seems a little small of "T molding", but it has been a very long time since I've used it.

Mike