Questions on using a moving gantry style mini-mill...

[Davek0974]

Hmm, back to school, two issues tonight.

Offsets, seems i have not grasped it yet or I am in the wrong work sequence...

Yesterday I saved the work offsets for my production job - G55, I also added G55 to the start of the code. I then loaded up the material, changed the tool & set my top-of-material Z zero. Pressed cycle-start and got Soft-Limits warning on Z, looking at the numbers on the DRO's I could see something was wrong.

I deleted the the G55 from the code, switched to G54 Offset, reset my tool zero just in case, set work X&Y zero as normal, and ran the job as before.

So, not sure what i am doing wrong but clearly offsets do not work totally how I envisaged them to work. Do you have to be in the correct offset BEFORE setting the tool and Z zero?? If yes then that was likely mistake No1 as I was in default G54 when I set the tool. What I expected was for the offset to only affect X & Y not Z (i think)

Z Zero, again.

yesterday the job cut perfectly, onion skin just about held it together and a nice part came out. Tonight, same file, onion skin failed as the tool chewed the bed by about 0.1mm or a bit less - this meant the part got 90% of the way and failed on the finish pass, luckily the cutter survived but the part was toast and now resides in the scrap bin.

So, I have two issues here, top-of-material setting and work-holding.

Here is the part before it went flying to the bin in a red-mist


Now, after cooling down, I miked the metal up and it seems the thickness is not very reliable, the 7 bits i have left ranging from 5.05mm to 5.25mm depending where you measure it - I think this accounts for the failed onion-skinning and subsequent junk output.

My first resolution to this is to mark a spot with a sharpie, measure it, note it, CAM the part specifically for that thickness, set the tool zero exactly on the sharpie mark and try again - I do not think this is a machine error, more a material error.

Work-holding, these parts must be 100% flat and clean, if I tried adding some carpet tape etc under it, would I be able to get the part off the bed when cut?