Router bits

[davidwpack]

Eyloww! I just got a circle cutting jig for my router. With it came a couple 1/4 bits. One reads "spiral up cut"; the other reads "spiral down cut". I just want to cut out a couple of circles and not sure which one to use. I didn't even know there was a need to differentiate. Anyone have an idea? Or a completely different bit?

[pompeiisneaks]

Here's a good explanation:

https://www.rockler.com/router-bits-up-cut-down-cut-and-now-quadra-cut

I'd never heard of this either, so I lernt somthing too! :)

~Phil

[davidwpack]

Thanks for the info! That clears a lot up. I guess I could use either one for circles I'm thinking

[Fresh_Start]

Thanks for the info! That clears a lot up. I guess I could use either one for circles I'm thinking

I could be wrong but I think straight or upcut bits are safer in that they won’t try to push the bit away from the workpiece. For your circle, put the side you need clean down. Upcut bit will pull trash out of the groove you are cutting.  Good if you need to cut more than 1 pass for your circle.

[jjasilli]

Note that it's not possible to get a truly clean circular through-cut with a circle cutting jig.  Though you can get a circular hole hole that may be good enough.  The reason is that the circular jig may shift a bit when cutting a hole in deep material; and at the end of the cut-through, the waste circle of wood that the jig is centered on is no longer anchored and is free to shift.


For a truly clean circular hole, you can use a 1/2" straight bit with a circle-cutting jig to cut a circular "dado" about 1/4" deep in the baffle board.  Use a jigsaw to rough cut away the center waste material, cutting near the outer line made by the straight bit.  Then use the router with a patterning bit to finish the circle.  The roller on the patterning bit will follow the "dado" cut made previously. 


You can refine this technique to recess the speaker rim; or use a use a rabbeting bit as a final step.

[Fresh_Start]

This just came in on email:
https://www.finewoodworking.com/2016/07/27/straight-talk-on-straight-bits?source=W1724ENL&tp=i-H43-BC-FaM-kirqo-1o-Uv4R-1c-kivxe-1icxRR&sourcekey=W1724ENL&utm_campaign=fine-woodworking-eletter&utm_source=eletter&utm_medium=eletter&utm_content=fw_eletter&cid=59914&mid=690404894

Hope you can see that.

Chip

[Willabe]

For speaker cut out's, I always use a 1/4" up-cut spiral carbide bit, best cut I've ever seen. 

...... and at the end of the cut-through, the waste circle of wood that the jig is centered on is no longer anchored and is free to shift.

I use 3 or 4 shims, the same thickness of the bit, ~1/4" wide, to keep the cut out from moving.

I cut 2/3's or so around then stop and insert the shims. Now the cut out for the most part can't move.

Watch out, it will still want to 'kick' the cut out when the last of the wood is cut, right at the last ~1/4".

Turn off the router immediately when you finish, don't let it move, while keeping a firm grip on the router, with downward pressure, the router compass/base will help hold the cut out in place.     

Use a sacrificial piece of plywood, 1/2" to 3/4", under the piece your cutting, it gives a stable work table and keeps the baffle from splintering around the cut out edge. Only cut into the piece underneath a 1/16" or so. With the sacrificial base in place, you can also use double sided tape or a couple small brad nails to hold it in place or a combination of those, shims/tape/brads.

Works real good. 

[sluckey]

and at the end of the cut-through, the waste circle of wood that the jig is centered on is no longer anchored and is free to shift.

Surely you have solved this problem. 

[jjasilli]

Yes, much like willabe, I have used a long 1/4" center pin in a home made circle jig.  The pin runs through the workpiece and into a sacrificial support board below.  This is an improvement, but still not "perfect".  I guess you could countersink screws to hold the center circle steady, and use clamps on the outside to prevent movement of the main baffle board. (or double sided tape a willabe suggests)


The method I described above is most useful for a thick baffle board. 

[sluckey]

Double sided tape will solve all circle cutting tasks. Then you can go back to a 1/8" pivot pin and only drill a 1/4" deep hole. Then you have a nice frisbie to throw at the neighbors cat.   

I've been using double sided tape in my shop since the early '80s. That's before most woodworkers ever discovered how useful it is. It was called carpet tape back then and I learned about it when we moved to Mobile and had the carpet replaced in the house. The installers left a roll and I immediately put it to task in the shop. Haven't been without ever since.

[jeff_free69]

I use a spiral upcut bit and  3 pieces of 1x2.
One piece is long enough  to span the hole by an inch or 2 on each side.
Attach it to the back side using 2 screws close to the center pin  and one on each side of the cut.

the other pieces of wood are just prop to it up and balance. ( i even  keep them handy in the router kit)

Fool proof - just make sure the screws are well away from where the cut will be