ZRN Coated bits

[Craig Thompson]

Hello all! I have a question pertaining to ZRN coated bits. I was cutting a Shield of Arms with a ball nose bit. I used a 1/4 inch ball nose to which was carbide. It cut the pine wood like butter. When it was time to do the finish cut I used a 1/8 ball nose ZRN coated bit. While this bit was cutting it squealed and seemed like it was also vibrating. The cut was clean but extremely noisy compared to the non ZRN clear away bit. Both were used at 18000 speed and 120 feeds. Has anyone had the same problem, or know how to stop the vibrating and squealing. I appreciate any any advise.

Thanks
Craig

[Mobius]

This thread interests me because I've noticed the same thing. I have several different sized and fluted ZRN coated endmills that just scream. I thought I was just getting the speeds wrong, but maybe not?

I haven't noticed the same thing with my coated ball mills, but they generally don't remove much material in a given cut.

[Craig Thompson]

I don't have any problems with any other bits, its only the zrn coated bits. I have broken two zrn coated end mills due to over vibration. I then replaced the zrn coated bits with non coated bits and had no problem at all. Both zrn coated bits were replaced free from the dealer, but it seems as though the coating has something to do with it. The second broken zrn bit went only about 8 inches at 1/8 in depth then broke. I was carving Cherry at that time. Not sure what happened, but it was vibrating and screaming then broke.

[Rcnewcomb]

Coated bits provide no benefit in wood. Metal is another story...

[Adrian]

Not sure if it applies in this case but when a spiral bit is squealing it usually indicates that the rpm's are too high or the feed rate is too slow. Decrease the rpm or increase the feed rate until the noise stops on the majority of the cut.

[ger21]

Coated bits provide no benefit in wood. Metal is another story...

Coated bits are also not as sharp as uncoated bit, because the coating is covering the cutting edge.

Having said that, I'd be interested in trying this bit:

https://www.amanatool.com/46282-k-cnc-2 ... r-bit.html


There is one application where coated bits work well. Cutting cabinet parts and other sheet goods. I've used both the Amana Spektra, and Onsrud coated bits before, and they do last twice as long. The downside to coated bits is that if you get them sharpened, the coating is ground away. We get our bits sharpened 3-4 times, and a coated bit loses the benefits of the coating after the first sharpening. Because of that, we prefer bits made from harder grades of carbide. These give the same tool life as coated bits, and don't lose any performance after sharpening.

[Craig Thompson]

Thanks for all the info. I will try to drop the rpm's and see if that helps. This is an awesome place to get answers to your questions.

Again Thank you all

Craig