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Nakamura-TOME Chip breaking


Nov 17, 2021
Hello there,
I am having quite the hard time breaking chips and maintaining tolerances with a part im trying to make. I am using a half inch boring bar with a CCGT 060204 AS IC20 Iscar insert that has a .016 radius. I am trying to bore the inside of a hole from .750 to 1.419, at a z depth of about 2.203, but since i can't get enough space to finish the hole on the side closest me, Im turning upside down. I am currently running from 700-1200 SFM, my spindle speed shouldn't go above 3200. The aluminum 6061 T6 is cutting like long spiral spears, and also getting nested on the part, each one has to be manually removed before finished the sequence. I've tried everything from increasing the spindle, to decreasing it, to increasing the feed rate to about .012" IPM to decreasing it to .005" IPM. I have a lot of luck when the insert is running at 3200, with .0105 IPM and depth of cut is about .050" each time, but im still not breaking chips each and every time AND im getting that really nerve racking "CRUNCHING" nose, and i have to change my insert every 50th peice. (see my part space and Z depth for an idea of how big the part is). Does anyone have any suggestions?
Last edited:


Hot Rolled
Dec 16, 2011
I agree with bigjon61. I find it much easier to break chips in 6061 with an insert designed for steel than one designed for aluminum. If you still get crunching, it's because there is not enough room for the chips to get out of the hole. Consider breaking your boring passes up so that you're not going to the finished depth right away. Try making all your rough boring passes to only 0.750" depth. Then start over at the smallest X diameter and make all your boring passes to 1.5" deep. Then finally do it all over again to your finished depth. This way, you're opening up the hole as you're going along and giving the chips a chance at getting out.


Aug 27, 2002
West Unity, Ohio
I am with Wimpy as far as take the Z in stages for sure!

But what on Earth has you boring that all out?
Shirley there's got to be a more better means of blowing out 90% of that material?
And then you can finish with a real bar yet to boot.


I trust that you are green?
Can you show us what you are trying to doo so that we can help you much better than a 1/2 hour bore cycle on a screaming 1/2" bar?


Think Snow Eh!


Jun 29, 2023
What's Nakamura Tome model? Try Oscillation cutting to breaking chip. With Nakamura Tome they use G8.5 for this funtion.


Oct 22, 2021
Depending how you're programming it, you can try a few things:
1. Rough in segments to near-full-diameter rather than immediately to full Z depth like wmpy said
2. Feed much harder; peck to break chips if required
3. Cut radially rather than axially. Depending on the lead angle of your boring bar, you can probably rough at SUPER high feed rates from full X roughing diameter back down to the 0.75 ID, with a low depth of cut (ie lower than the intrusion depth of the insert in Z), and the insert geometry will act like a high-feed mill. Because you're not throwing the bar in there deep before it has cleared out most material, you'll evacuate chips much better too, and they'll get broken up each time you reach the 0.75 ID.
4. Drill an eccentric hole with a live tool between your 0.750 and 1.4xx diameters (seems like you can probably fit a 0.250 drill in there) to create an interrupted cut. In some materials where DOC is not a big concern (like delrin), drilling the initial hole way off center like that can help too because each chip becomes like a crescent instead of a continuous ring
5. Feed inside to out (ie back to front)
6. Get some 6262 rather than 6061. It's mechanically almost identical but breaks chips much better.