I have been using the IDC Woodcraft BEAST roughing bit, cutting a 1/2" deep pocket in some curly maple. I have struggled to settle on feeds and speeds to get the bit to cut the way it does in IDC’s videos. I am getting a lot of chatter and high pitched ‘screeching’, especially on the first pass after the plunge, where the bit is fully embedded on all sides. I’m sure some of this has to do with the nature of curly maple. I ended up settling on just using their recommended settings of 100ipm at 22K rpm with an 80 percent stepover. Even at those settings, the bit seemed to be ‘surging’, leaving severe undulations along the sidewall of each pass. I switched to climb cutting and that helped alot.
During all of this, in between tool changes I noticed the base of the cone on my ER20 tool holder has a sort of slightly ‘gouged’ ring around it. It’s not very deep, but just enough so you can feel it with your fingernail.
Could this mean the tool holder is ‘spinning’ in the spindle chuck? (I have the PWN ATC system) I don’t see this happening on any of my other ER20’s, just the one holding the BEAST. I attached pic, although I couldn’t get it to focus great.
While i can’t hook one with a finger nail. I believe your assessment of it spinning in the cone might have something to it but i don’t even know how that could be possible. The nut on the top is the only thing grabbing on, but if that’s finger tight… then idk how it could move.
Thanks for the feedback, Chris. I really think I was just trying to take too much too fast, and the chatter / harmonics were so severe they were literally vibrating the holder in the chuck. The bit and spindle are capable of it, but I don’t think the 1F is. I’ve said for some time now that I have been disappointed in the lack of rigidity in the machine. A very capable machine yes, but not to the level advertised… at least in terms of rigidity. I can grab the top and bottom of the spindle, push / pull lightly in opposing directions and literally see the whole z-carriage move. I think it also explains why I have such an issue with tool marks.
That’s not right. I would check screws that are part of the pivot. My whole machine moves because its on locking casters, that i cant seem to lock, and even if i did, they would be on floor mats as seen in the video. My whole shop is layered with them.
I’d be cautious about assuming the holder is definitely spinning in the spindle taper, but the fact that you can catch the mark with a fingernail is worth paying attention to.
A few thoughts:
ISO20 holders are wear items to some extent. They are precision-ground tooling surfaces, but they do get handled, loaded/unloaded, exposed to dust, and pulled into the spindle repeatedly. Light witness marks or polishing on the taper/contact area are not automatically alarming. That said, a gouged ring, raised burr, or damage that only appears on one holder should be inspected more closely because anything that affects the taper fit can affect runout, tool life, surface finish, and vibration.
I would do a few things before using that holder for aggressive roughing again:
Clean the spindle taper and the ISO20 holder taper extremely well.
A tiny chip, dust, resin, or pitch buildup between the holder and spindle taper can keep the holder from seating fully and can create fretting marks.
Inspect for a raised burr.
If the mark is raised at all, I would pull that holder from service until it can be dressed very carefully or replaced. You do not want a burr on the holder transferring damage into the spindle taper.
Check the pull stud / retention knob.
Make sure the pull stud is tight, undamaged, and matches the rest of your holders. The ATC drawbar/pull stud is what pulls the taper into the spindle. If that connection is loose or slightly off, the holder may not be seating with full retention force.
Compare it against another holder.
Put the BEAST bit in a different ISO20 ER20 holder and see if the behavior follows the bit/cut or stays with that specific holder.
Back off the cut and test.
A 1/2" deep pocket with a large roughing bit fully buried on the first pass is a pretty demanding cut, especially in curly maple and especially on a machine with limited Z rigidity. If the first pass is fully engaged on all sides, chip evacuation and tool pressure are both at their worst.
Check machine rigidity before chasing spindle/tooling issues.
Being able to visibly move the Z carriage by pushing/pulling on the spindle is not something I would ignore. That can absolutely create chatter, screeching, poor sidewalls, and the “surging” pattern you described. I would check the Z-axis wheels/rails/linear bearings, mounting screws, spindle mount, tram plate, ball screw/lead screw mounts, and any bolts that allow the Z assembly to pivot or flex.
I would also be careful with the 80% stepover at that depth. Even if the bit and spindle can handle it, the machine frame and Z assembly still have to resist the cutting forces. Climb cutting helping is a clue that the machine/tool engagement was not happy in the original direction.
Bottom line: light wear marks on ISO20 holders can happen, and holders should be considered consumable over time. But a holder should not be visibly fretting, gouging, or moving in the taper under normal conditions. I’d clean/inspect everything, temporarily retire that marked holder, try another holder with the same bit, and reduce the roughing load until the Z rigidity issue is sorted out.
