Bit breaking cutting poplar

[knight_toolworks]

sounds like a bad collet then. I don't think I have broekn a 1/4" bit from resistance befroe.

[jerry_stanek]

run a test with a dial indicator to see if it is the collet of could be a bearing going south

[bleeth]

Chuck up your bit and spin it in the air at a slow speed (3-4K). Take somehing like a steel rule and lay one edge against the un machined part of the bit while you are spinning. If it moves at all you have a problem in collett or bearings. Run the "trammel" test for z alignment. Although 18k is too fast it still shouldn't be popping bits at that speed quickly.

[gene]

what type hold down are you using? if there is vibration in the wood this can cause the bits to snap

[cnc_fabricator11]

We are using a vacuum hold down system with additional screw down. It does seem to be the vibration of the material as we have replaced the collet and collet nut multiple times. Would making more passes in a cut reduce some of the vibration that is occurring? It's really strange because the last time we were involved in this type of project with this type of material we didn't have any issues with material vibration. Also, does anyone have other suggestions for holding down boards/lumber in addition to vacuum and screws?


Thanks,

-Patrick

[bleeth]

What's the size of your boards? Have they been surfaced already?
Have you trammeled your z?

[cnc_fabricator11]

The boards have been surfaced 2 sides (top and bottom in relation to the table). The average width is 6.25". This is the first time I've heard of trammeling the Z, could you explain please?


Thanks,

-P

[bleeth]

Okay. One thing I was thinking is that if the boards are not flat then they may be rocking on the table. With that narrow a size your vacuum may not be helping depending on how you have the zones set up on your table and any area within the zone not covered by the board being handled.
Another thing: If you are, for example, cutting through the board in the length direction as you get through the board you may be experiencing enough of a movement in the board to be grabbing the bit much like a board can pinch a tablesaw blade from tension in the board closing the gap as you cut.
You haven't spoken yet of the effect on reducing spindle speed.
As far as trammeling, this is a way to check that the z is properly perpindicular to the table. See the following link:
http://shopbotwiki.com/index.php?title=Z_Axis
The "bent wire" is a poor mans way of making a trammel and will work fine and the dial indicator is the more technical version.
You can bend a piece of 1/4" rod of some kind (aliuminum from big orange or something and that works.
Need more info about what, how you are cutting to get into holdown comments in addition to screws. Maybe it's time to post a screen shot of your toolpath and strategy.
From your last posts I get the impression that the bit is breaking above the spot where it enters the collett. You aren't by chance putting the bit so far in that the collett is grabbing the cutting area, are you?