Cracking of tops when running a sink

[countertopperscnc]

Hello All,
I have been running a Park Destiny for about 9 months now and just recently started experiencing a problem of my tops cracking on the wall side running from the sink. It only seems to happen on tops where the sink is in a corner at a 45 degree angle and happens on the mill bit. It has happened on 3 different jobs for a total of 5 tops. I am running a Silver mill bit from Gran Quartz at 4500 rpm at 12.8 ft per sec. All three jobs have been LG Viatera but different colors. Any ideas?
Thanks,
Guy

[VThartzog]

It might be where you are starting the sink cutout. My cutouts have a dummy cup off center so the cutout falls to side where the fingerbit starts/stops. I had this problem when I would start and stop at the sink rail than on the sides where there is more meat. You could also place a sink saver on the piece while its running. Others may have suggestions.

[clhilde]

I havent run enough es to give any input.
Not form lack of trying.

[Curtis R. Marburger]

Warped slabs ?

[tim farr]

never had an issue. internal stress maybe?

[Dan R.]

X 2, internal stress. LG should replace those slabs.

[Rick George]

I'm not an expert in this area by any means, but have not had this issue with quartz and cutting out sinks. With this happening to multiple pieces and different colors and such, I would more likely look at other causes such as the finger bit and where you are starting and stopping the cutout. I am not familiar with this finger bit your using, but is it possible that it is getting glazed over causing extra stress while cutting? Do you have pods under cutout so it doesn't break off and fall near the end of the cut? Start and stop your sink cutout where there is the most "meat" left.

Just a couple other things to look at before you just blame it on internal stress and keep having issues. Good luck!

[countertopperscnc]

thanks for the responses. I have tried changing where I start my cuts. I have slowed my bit down on a run. One time it cracked right over the top of a pod I had placed for extra support. I am leaning towards the mill bit since I changed from a uhs bit a couple months ago. The slabs being warped isn't something I had considered but mayb added extra pods has increased the pressure instead of relieving it. I am open to more suggestions if anyone has them.

[countertopperscnc]

A little follow up. I ordered a uhs orange bit from GranQuartz and I contacted LG. LG wanted me to send pictures and the color names to forward for warranty. The rep stated that they have this problem occasionally for internal tension.

[countertopperscnc]

I am not familiar with this finger bit your using, but is it possible that it is getting glazed over causing extra stress while cutting? Do you have pods under cutout so it doesn't break off and fall near the end of the cut? Start and stop your sink cutout where there is the most "meat" left.

Just a couple other things to look at before you just blame it on internal stress and keep having issues. Good luck!

It happened with a new and an old bit. changed the location and the break happened about 1/3 of the way through the sink run. I am leaning toward slab stress but haven't ruled out the mill bit. oh and I support the piece with a block underneath.

[DavidL]

Guy - Check you cup heights and your support height. If you have a high point (dummy cup) and have vacuujm pressure pulling the slab down over the high to the other cups that could be your issue. Is one of your cups damaged from a tool hitting it? Maybe has a little lip in the metal?

[countertopperscnc]

Guy - Check you cup heights and your support height. If you have a high point (dummy cup) and have vacuujm pressure pulling the slab down over the high to the other cups that could be your issue. Is one of your cups damaged from a tool hitting it? Maybe has a little lip in the metal?

Yes I have a cup or two like that. I thought about checking my whole table height/level. I will take a look at all my cups. Thanks.

[apex]

Are the slabs jumbo size or 120x55? I would guess Jumbo?

[Mid Missouri Surfaces]

We cut probably 10-15 slabs a week of quartz. Have never had this happen. As often as this is happening to you it can only be a few things. I doubt that every slab has internal stress. It has to be either the pods being different height or the way you are cutting your sinks out. I'd also call your GQ guy and make sure you are running that bit at the rights speed and load.

[countertopperscnc]

Just a follow up on this problem. We fixed it months ago but I failed to update the situation. The gear on my X - axis drive was slipping under load and causing stress in the material as well as other problems(i.e. machine never homing to the same place twice.) replaced the gear assembly and no related problems ever since.

[Joshua Hopkins]

Glad you got the it taken care of.

[DavidL]

Thanks for posting the follow up resolution. Definitely helps all of us when trouble shooting.