Undercuting and channels

[birdsofplay]

I'd like to do "Clean" under cut channels.
ie and 1/8 to 1/4" lip and a wider channel underneath; in this case only 3/8"

I've tried the following in solid maple plywood, Oak and cheapo Shelf grade particle board.

I cut the channel with a 1/4" spiral bit then went back in and did the undercutting with a 3/8" ball ended bit on a 1/4" shaft.

In both the maple ply and solid oak, 95% is ok but randomly and not always in the same places I'll get a bustout/flakeoff/split.
BTW the maple ply was scrap for a steel rule die place so it was "from" $300/sheet solid maple on all plies ... quality stuff.

The shelf particle board had a cheapo laminate and it did not bust out but it did show a lot of edge chipout. The other cases had corner problems only.

I tried low speed .25" and higher router speeds too.

I'm thinking that this may only work reliable if I have a "tightly" laminated venier on MDF or similar.

I cant do much to affect cut order of direction.

Any other ideas ?

[rfpaul@hotmail.com]

Help!!Today I was trying to cut some fret work, I turned my speed down to 0.10, I use the 'SS' command to change it. But when it was cutting the speed is changing back & forth from 0.10 to 0.50, my speed setting on the screen doesn't change at all! I checked all connections, rebooted the computer & nothing works, I also tried other files and different settings below 0.50 and the same thing happpen's. Any ideals would be helpful, thank's Rick

[seaside@esva.net]

Rick,

This is just a guess, but when you lowered your speed did you also lower the ramping value? I think the default is .4 for a 1.0"/sec cutting speed. The ramp value is the number in parentheses after the speed display.

My understanding is that the ramp value is the speed at which your ShopBot starts and stops a move, making these transitions smoother. You might try using VR to set the ramp speed to a little less than 1/2 the move speed (0.04 for your 0.10 move speed) and see if it solves the problem.

Good luck,

Bill
seaside@esva.net (mailto:seaside@esva.net)

[rfpaul@hotmail.com]

Bill, I never changed the ramp speed before and I lowered the speed several times already in the past with no problems, but I'll give it a try tonight, thanks for the reply & I'll keep you posted of what happens, this is a wierd problem! Rick

[seaside@esva.net]

Rick,

I figured it was a long shot. I tried to duplicate your problem today using the newest beta software and couldn't.

Anything changed with your ShopBot between the times that it worked in the past and this time?

Bill
seaside@esva.net (mailto:seaside@esva.net)

[Saintjohnbosco@yahoo.com]

Bob,

Have you tryed using a keyhole or T slot cutter, or maybe a dovetail bit?

[birdsofplay]

Yup ! :-) I tried that first but the one I have
only is about 1/8 thick on the "in"side so it took
about 3 passes to get it deep enough and left lots of fuzzys down in the channel.

Next I tried a 1/4" spiral upcut for the 1st pass then followed by a 3/8" ball end cutter on a 1/4"
shank.

It worked but it's still two passes.
I figure I'll need to have a special bit made for one pass performance. Or forget the undercutting idea.

[SaintJohnBosco@yahoo.com]

I was looking at some freud bits they have a convex edge bit with a point for plunging. The convex has a 1/2 radius. I'm imaginining the bit plunging in and stoping at the center of the convex. That would leave a smaller channel on top with a larger below with the v on the bottom. It would also give a sort of taper going into the hole from the top. But its probably too large for what your doing. Your pictures are great by the way.