pocket cuts

[john_hartman]

A short while back I posted some issues I was having in the tenon/dado cutting. I have most of this cutting much better by cutting a bit slower and doing multiple passes.


The one issue I can't seem to lick is the pocket cut which creates the tenon height. I am cutting these at 3ips in conventional. The attached photos will show this; but the right side tenon is nice and straight, while the left is mostly straight but recessed about 1/32" from the corner where the outside profile meets the blind part of the tenon. Bit deflection is the first thing to come to mind, but both sides don't have the same issue. What am I not thinking of here? Any and all ideas welcome..


I'm using a centurion .25 mortise compression @ 10K.


Photos 1/2 are of the right side, 3/4 of the left problem side

[rww]

Is there any chance you are getting some movement on your parts on the through cut?

The only time I have had this problem is when I didn't have the settings matching the bit I was using but I think this happened on both ends of the parts.

[john_hartman]

Jason- I do not believe I am getting any movement. The right side tenon comes out fine and the perimeter cutout is square and smooth.

[Gary Campbell]

John...
2 things can cause this.

First is bit deflection caused by a dull small diameter bit (excessive feeds) AND selecting conventional for dados, and climb for outline. This will show angled edges on the parts in cases as extreme as yours.

REMEMBER. That if a bit that is exposed an inch or so below a collet is deflecting, the edge of the part shows the same angle that the bit bent. YOU CANNOT BEND A BIT (DEFLECTION) AND HAVE SQUARE EDGED PARTS.

Second, and 10 times more likely, is that the machines motion adjustments need some love. First suspects are:

X pinion to rack (usually shows on both ends of parts)

Lower Y rollers (my favorite for the one ended glitch)

Z rollers (also has yielded one ended miscuts)

Call me

[dhunt]

I do not believe I am getting any movement.

We all believe we're not getting any movement
-until we inspect the machine thoroughly (and pull at the Z car, discovering significant movement).

We tightened up several roller wheels holding the Y- and Z-cars is place
and Hey Presto...that annoying groove automagically went away!


__________________________________
Remember this? (below) -now History!
We too didn't think we had any movement...

[john_hartman]

I've been told and have checked for anything being loose. Everything is tight. The biggest issue I have with the loose screw suggestion is that all of my parts would have numerous issues. Except for this all of my parts are square and fit quite well together. This seems to be an isolated issue for a specific operation. Bit deflection is the most likely issue, but again its only on one side..

Gary I'll give you a ring in a short while.