Strange behaviour - thought it was X axis problem but not sure?

I am talking about the LinuxCNC tool table.
(probably in your config folder, and called "tool.tbl")
Most LinuxCNC GUIs have a menu item "edit tool table". Open that and make sure that the X and Y offsets for every tool are zero. (It is very unlikely that any rotating-tool machine will need X or Y offsets, they exist for plasma, laser, lathe etc.

andypugh wrote: I am talking about the LinuxCNC tool table.
(probably in your config folder, and called "tool.tbl")
Most LinuxCNC GUIs have a menu item "edit tool table". Open that and make sure that the X and Y offsets for every tool are zero. (It is very unlikely that any rotating-tool machine will need X or Y offsets, they exist for plasma, laser, lathe etc.

Thanks for that Andy. I've just set off on my holiday and won't be back home until Thursday but will certainly check then. I've not changed anything like that though and, on a previous carve with only the 2mm Ball Nose, it started correctly and then cut through the letters on the next pass so I'm guessing any offset would be consistent?

However, I will check when I get back just to rule it out.

I've also ordered a 3mm ball nose today as my software has that bit pre-programmed into it so I'll try that when I get it and see if it behaves the same way.

In the meantime, any other ideas are more than welcome for me to try and rule things in or out as the source of the problem.

Cheers

John

The tool offsets are saved in the tool table of Linuxcnc, but that shouldn't have been your problem because the g-code files are using the same tool offsets (unless you changed them between runs. (You didn't do any touch off or tool touch off between runs did you?) If you did a touch off of some kind between runs, a mistake there could have caused it.

The files look to be in the same positions.

You changed tools between runs, Did you have the motors disabled while you were changing tools? If you did, you could have easily moved the machine's position while wrenching on the spindle to change tools.

There is still the possibility of a mechanical issue, a slipping coupling, lost steps, or you forced the spindle to move while changing tools.

As to your fuzzing problem milling the MDF, to some extent it is just the nature of the beast. MDF can be very hard on tooling. Different kinds of MDF from different sources mill nicer than others. (The MDF in your photos looks to be of the less nice variety.) Only use carbide tooling if possible for MDF (steel will dull very quickly), but to minimize fuzzing use very sharp carbide tooling with no more than 2 flutes (cutting edges). We use a lot of PCD (diamond) tipped tools for MDF, but they are expensive and only come in larger tool sizes. Use the largest diameter tool possible for the job. Keep your chip load high (about 40mm/sec for a 3mm tool at 16000rpm is a decent speed.) Don't cut deeper than about twice the diameter of the tool in a single pass, when cutting a slot (finish passes can usually use the full cutting length of the tool).

That's great info Todd. The motors were definitely locked when I changed tools and nothing moved at all. I didn't touch off etc between tool changes.

It must be losing steps somehow. I wondered about electrical noise. When I get back from holiday I might try and set up a simple carving of a series of holes and try and keep repeating them to see what happens.

A massive thanks for the info on tools and speeds. I really need that kind of info and I really appreciate you taking the time to write all that. Brilliant. Cheers

John

For the tearout, try using a downspiral. looks like either the bit is not sharp or you need to use a down spiral bit.


Just my .02.

bevins wrote: For the tearout, try using a downspiral. looks like either the bit is not sharp or you need to use a down spiral bit.


Just my .02.

Thanks for the tip bevins. The bit was just a really cheap eBay one but I've ordered a better bit to try and will give that a go.

Thanks again for your advice