CNC Core bit question

[Alex V.]

I have a Park Destiny CNC with Alpha wet core bit and the bit keeps glazing over and not cutting well. It is running at 2500 rpm and inch and a half on the Z axis. Should I be running faster or slower on the rpm or increase the rate of travel on the Z axis? The Alpha bit is a standard wet alpha bit for a grinder 1 3/8ths diameter. The CNC has broken a couple of pieces because of pressure. Any tips would be appreciated.

[Nick]

I would change bits, go to 3500 rpm and I am not sure about our feedrate, I think it is 4"?

[tim farr]

The Alpha bit is a standard wet alpha bit for a grinder 1 3/8ths diameter. .

If this is not a cnc thin wall bit that May be your problem. I've been using the off brand orange bits from granquartz with good luck.

[Mark Smith]

Bump up the rpm to 3,500 and dress the bit. It's probably glazed from running it too slow. The rpm you are running is correct for alphas "cnc" core bit but not the "manual bit". Furthermore next time buy a "cnc" core bit not a "manual" core bit. If you like alpha they make a cnc version >> http://www.alpha-tools.com/Product.aspx?PageCode=1230

[Alex V.]

I was running the thin wall from Granquartz for some time but only getting ten to twenty five holes before the bit was done. I would change to the alpha CNC bit but I went with what I knew that worked. The manual bit has always worked for me. Our Granquartz rep said the bits should last but I have not seen that result. I am dressing the bits daily and gauging the finger bit as well everything is working fine but core bit.

[GuyboR]

Are you getting enough water thru the spindle?

[Nick]

Something is wrong, I have used both CNC thin wall and manual bits, and neither have problems and get hundreds of holes.

[Alex V.]

I haven't had any problems with the water with any of the other bits. The only bit I have trouble with is the core bit. I am going to try increasing the rpm to 3500. Thanks for the advice.

[Steve A]

Yes definitely something wrong going on. In my experience any core-bit on a CNC should give you a 1000 holes.

The only problems I've had with core-bits was related to water flow. Our Intermac has a sticky valve block controlling internal water that acts up now and then, mostly when the machine hasn't been used much. The halo water does nothing for a core-bit. With little or no internal water a core-bit will burn out very fast. Take a bucket and a timer and check your internal water feed rate.

[GuyboR]

I haven't had any problems with the water with any of the other bits.

Other bits are working from the outside "grinding"....so the halo water will do a ton to keep them cool. Core bits are cutting into the stone so halo water doesn't do as much to help, you need the spindle water also.

[mikedean]

My last 3 GQ - ADI thin wall core bits have toasted after 25 holes. I say bad batch.

They are getting replaced.

usually we get 200-300 holes with these.

[ash20ash]

At least 500 holes per bit for me. Could be 750 I guess.

Your got something major wrong with only getting 25 holes

Hell. I have never dressed my core bits. Terminator

[Alex V.]

Okay I will check the flow rate through the spindle. Thanks for the input.

[flav]

Recently we burned through 5 core bits in 5 days. Then we checked the water running through the spindle (not to be confused with the 'halo' water) and it was very low (about 1 gpm) instead of the required 5 gpm. We changed the water filter, checked flow, and bits are lasting again.

[Camzl1]

First thing, is use the proper RPM for the bit. Most Cnc core bits thinwall do run at 2200 rpm and 2"/min. 3500 rpm is not recommended on Terminator thin wall bits (normal cutting speed). But we offer a high speed core drill that does run at 3500 rpm 6-10"/min. So go by the manufactures specs and check the water as the most common problem. If that doesn't work then yes switch bits and find one that does work for you.