Changed from Z top of material to bottom & bit went DEEEP

[davidtu]

Total newbie...

In order to account for variations in material thickness (we're cutting 2D profile in 3x doug fir for rafter tails) late Friday I changed the model to use the machine bed as Z-axis zero and went back to the machine and redid the Tool Set command with the Z-axis tool on the spoil board. Did not make any other changes to the model but of course did recalc the toolpath. With the original setup the cuts were working, basically. Now, after changing the Z-zero it lowered the bit about halfway into the workpiece and of course was overwhelmed. It is setup to cut through 2.5" material with 7 passes of .371" each. Feed rate is 50 in/min, plunge 30 in/min, cutter is a CMT 1.2" spiral upcut with 2" cut length and 4" length overall, running at 16000 RPM (max).

Did I need to make other changes than in the Job Setup (Z-axis zero to machine bed) and on the machine to Tool Set at the spoilboard?

Just fyi, faced with prospect of handcutting and routing 200 rafter tails we jumped in and picked up an AR8+ Pro with no background in CNC. Unfortunately we're right away in a production situation without the requisite time to learn first so with your indulgence we're trying to learn on the fly with your help.

[savannahdan]

Ouch.. I use top of material for setting my Z. I just went through the process of flycutting or planing a piece of slab which is hard as nails dry oak. At some spots it was 3.5" above the machines bed and at others it was about 3.25". I began my cuts using the highest level for Z 0. On one of the cuts I measured at a lower point that I should have and the bit bogged down. Fortunately I was holding the pendant and stopped the job, turned everything off and then restarted. I have to admit that I'm not using the best planing bit out there. One of the things I liked about a different CNC that I have is the ability to measure the Z at 5 locations on the workpiece. This gave the ability to complete a job without having to level the workpiece. Usually when you setup the workpiece measurements (Job Setup) you'll indicate the thickness (z) and then you'll tell the machine how deep you want the end mill to cut in the 2d Profile Toolpath. I'm presuming you're using VCarvePro? In the case of my slabs I let the CNC make the profile outline cut for me down to about .5" and then I cut waste off with a bandsaw and lastly with a flush trim/pattern bit. All works well until you run into some metal in the slab. I should have recognized what all that grey/black wood was. I'll post some pics when both of them are completed and placed in their proper setting.

[davidtu]

It seems like there is some issue (ie. my understanding of) the gap position in the material setup. I've decided to abandon this track and go back to having z-zero at the top of the material rather than the machine bed as I was trying to do.

I'm still curious how this *should* work or what concepts I am not getting but its not blocking my work any longer.

[pdabk]

When doing cut through profile paths, and zeroing off of the spoil board. You need to make sure that the cut depth on your profile tool path matches the material thickness in the "Job Setup". Also check your depth per pass in tool settings

[Deleted]

If you're having a variation of stock thickness from piece to piece you need to make sure your top cut is reasonable over the range that you expect. That is, for thinner pieces you may get a light first cut or even some air cutting if the variation is large and for thicker pieces, you aren't cutting too much in the first pass. Also, don't forget to add extra for clamping or whatever else may be on top of your workpiece.

[grg]

What software? If you are using Fusion360, the only post file I've found requires that Z0 be at the top of the material (it seems like a bug in the post processor). The move from the index position to the start of a Fusion360 CAM program moves the tool from the index Z0 plus the clearance dimension with no accommodation for material thickness....I rammed tooling into my material multiple times before I finally figured this out. You have to set Z0 to the top of the material if using Fusion (until someone fixes the Post Processor).

If you are using Aspire, VCarve, etc (Vectric Softwares), they are very reliable and chances are you have some setting incorrect in the software.