Damaging a bowl model in V-Carve Pro

[robb]

I'm posting this here and on the Vectric Forum for V-Carve Pro.

I was running a couple of sample 3D carvings to show a few customers. The material was English Oak, (at least 200 years old, super-stable and recycled from some ancient furniture), and the model was a simple 30 dome inverted to form a bowl. I configured a .125" end mill to rough out. The 3D finish was to be a .125 ball nose. Unfortunately, I didn't get that far. See the attached image of the second attempt. During the early stage of the second pass the spindle moved out of the set perimeter by about 1/4" and cut very much deeper than the pass-depth of .0625". I hit the E-stop when I smelled the burning - too late to stop the EM breaking. I checked through the Vectric design and couldn't find any problem in the design or the result as shown in V-Carve Pro. All I did was to bring a standard 30 dome into the 7" X 7" square and centered it. I added a Zero Level and checked that the dome was now a bowl in the 2D window. I chose a .125" EM for the roughing and a .125 BN for the finish. Pass depth set in the tool DB was .0625. This might sound a bit shallow but the oak was very old and very hard and I didn't want to cause myself more trouble than necessary by being too brave in the pass depth. Feed rate was 90 and I had a 40% stepover. Anyway, the result is in the attached. The attached image is the second attempt. This had already happened previously and the second attempt was to run a fresh, seperate, job to make sure that I had not caused any confusion in the V-Carve software when I was messing about with the configuration for the job. I'm wondering, because I don't know, whether Masso is at fault? I'm running Masso G3 - 3-Axis v3.43.2 which is the latest update for my system. I checked the hardware after the first failure to make sure that everything was 'tight' and nothing was 'jumping'. I watched carefully during the second job in case it was caused by hardware.

Anyone have any ideas or has anyone experienced this kind of problem? Note: Since this happened I have run other jobs successfully. No 3D domes or bowls though - as I want to find the solution before breaking more tools and wasting expensive hardwood.

 

[masso-support]

@robb can you please send the gcode file.

 

[robb]

As requested.

I did send it as a reply to your email message. Not sure if that got through.

Thanks

Robb

 

[masso-support]

Hi Robb

Have had a look at your file and it all looks good.

I then ran the file on my machine and it ran perfectly. Came out with a nice little bowl shape. Doesn't show up well in the photo because of the material I used but it is as you wanted.

I suspect from your photo that you have either lost steps on the Z axis which then caused the cutter to dig in and caused a loss of steps in the X axis because of the loading.

Another possibility for a cut to suddenly get deeper is the cutter is loose in the collet and if it is an upcut spiral bit you are using they tend to pull themselves deeper into the material given a chance.

Also check your machine acceleration setting if this is the first 3D machining project you have done as 3D machining will show up any weakness in your axis setting.

Hope this helps

Cheers

Peter

 

[robb]

Thanks very much Peter for your time and attention. I've done quite a bit of CNC 3D work, although I would not profess to be an 'expert'. The collet was tight, I always double check that in any case. I have a wide range of collets and match to the tool shank diameter. Tool set up is fine and I do err on the side of caution for feed and acceleration. My thinking is that the problem is concerned with the stepper. Whether it's the motor or the drive belt, I will have to make some really forensic checks. I will contact the hardware vendor and put this problem to the support team. It has done this twice when trying to create a bowl. The fact that my gcode is good is comforting but, actually adds to my diagnosis investigations. I do a lot of complex 3D carving for various customers and the intricacy requires keen design and accurate feed/speed rates (chip load). So far, this is the first time I've hit a repetitive problem.
Thanks again. Much appreciated.
Robb