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Discussion Starter · #1 · (Edited)
I have not noticed this before but in this project it was my first attempt at milling Aluminum. The plate is 1/8" thick (0.125) and 18"x18" I set everything up to use Virtual Zero. I'm running V-Carve Pro 9.5

I set it to a maximum cut depth of 0.030 and the end mill set to maximum pass depth of 0.010 for a total of 3 passes. See pics

The problem is the first pass was 0.035! The next 2 passes were correct at 0.010 each. I ended up with 0.055 total depth. The total depth I was OK with because I had enough material thickness to work with but the initial pass of 0.035 caused the end mill to "Dig" in or be pulled down into the material which caused a few imperfections in the sign. I checked a few tutorials and they all have the Start Depth at 0.0. And I did set it up to use the material surface for starting point.

Any ideas why my first pass is going way beyond the set point? What am I missing?
 

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Discussion Starter · #2 ·
The picture of the R is a test piece I tried after I made the sign and it did it again. (The R is actually from the sign. I just set it up separately on another piece of material)
 

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Sorry I'm no help but at least you're not alone. My first aluminum cut did the exact same thing. I never did figure it out. Broke 2 bits, rebooted, recalculated everything and then it worked fine.
 

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Make sure you're using a coolant cutting Alum.
Some do get by on plain air others do WD40.

I hate the WD40 smell and the mess it leaves.

Actually surprised at the cost of the FogBuster

Pretty soon I'll be cutting alum but not looking forward to
giant mess that'll be left all around the machine.

When doing the Alum cut setup, wouldnt be just the same as you
normally would? just a less than thru cut?

Can that program do side-to-side cuts? They look better
than the spiral if paint filling.
 

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Discussion Starter · #5 ·
Make sure you're using a coolant cutting Alum.
Some do get by on plain air others do WD40.

I hate the WD40 smell and the mess it leaves.

Actually surprised at the cost of the FogBuster

Pretty soon I'll be cutting alum but not looking forward to
giant mess that'll be left all around the machine.

When doing the Alum cut setup, wouldnt be just the same as you
normally would? just a less than thru cut?

Can that program do side-to-side cuts? They look better
than the spiral if paint filling.
I did the WD40 and it worked real well. I actually prepped the entire area pretty well to keep the mess as contained as possible. I can do the side to side cuts and have done that several times in wood. My only issue with this was the initial cut of 0.035 depth instead of the programmed 0.010 depth.
 

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Check your Safe Z and Home position settings.

Does the preview show the deep cut?
 

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Discussion Starter · #7 ·
Check your Safe Z and Home position settings.

Does the preview show the deep cut?
My Safe Z is set at 0.800
I didn't look to see if the preview shows it. I can check when I get home this afternoon.
 

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My Safe Z is set at 0.800
I didn't look to see if the preview shows it. I can check when I get home this afternoon.
Your pic shows Safe Z at .2 - not .8
 

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Is it possible that you forgot to recalculate your toolpath after setting your passes = 3? I have forgotten to do that on occasion after making a toolpath change. You could look at the gcode and see what it is being told to do on the first pass.

I would also recommend ramping instead of plunging to cut depth.
 

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A couple of possibilities. How was the stock held down? If clamped around edge, possibly not flat everywhere or lifting do to upcut. This may be a good application for the blue tape and superglue method.

How did you zero off the top of material? If you use touch off puck, make sure that the thickness is set correctly. Mine seems to have not read some types of bits as consistently, have mine back off to 1", and double check with a 1-2-3 block.

Several sharks that I have seen tend to have a little flex in the gantry do to the unsupported rails, possible that "grabbing" of the aluminum is pulling the entire Z carriage down a slight bit. If you push up or down on the collet, is there any movement?

Do you know the alloy of the aluminum? I have had better luck with harder alloys (6061) than with softer (3003) alloys. The soft ones are gummy and grab more.

When cutting aluminum, I like to lubricate the bit with this spray. Use it all the time, but it seems to make a more noticeable difference with aluminum. May not be as necessary if you were using wd40, I have been cutting dry most of the time (or just air blast).
 

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Discussion Starter · #12 ·
Is it possible that you forgot to recalculate your toolpath after setting your passes = 3? I have forgotten to do that on occasion after making a toolpath change. You could look at the gcode and see what it is being told to do on the first pass.

I would also recommend ramping instead of plunging to cut depth.
I'm sure it's possible but I even did the test piece and it was set to 3 passes of 0.010 and it also started at 0.035. I would normally ramp instead of straight plunge but since it was supposed to only go 0.010 I didn't think the ramp was as necessary.

How do I bring up the G code? Can I just open the .tap file in another program?
 

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Discussion Starter · #13 ·
A couple of possibilities. How was the stock held down? If clamped around edge, possibly not flat everywhere or lifting do to upcut. This may be a good application for the blue tape and superglue method. Clamped around edge but had no noticeable lifting

How did you zero off the top of material? If you use touch off puck, make sure that the thickness is set correctly. Mine seems to have not read some types of bits as consistently, have mine back off to 1", and double check with a 1-2-3 block. I did use the touch plate. I checked calibration a few weeks ago but will check again

Several sharks that I have seen tend to have a little flex in the gantry do to the unsupported rails, possible that "grabbing" of the aluminum is pulling the entire Z carriage down a slight bit. If you push up or down on the collet, is there any movement? No movement in collet. I thought about flex but everywhere I measured it was 0.035 deep so being this consistent I ruled out flex.

Do you know the alloy of the aluminum? I have had better luck with harder alloys (6061) than with softer (3003) alloys. The soft ones are gummy and grab more. It is the 3003. The last 2 passes of 0.010 it runs very smooth and no grabbing at all.

When cutting aluminum, I like to lubricate the bit with this spray. Use it all the time, but it seems to make a more noticeable difference with aluminum. May not be as necessary if you were using wd40, I have been cutting dry most of the time (or just air blast).
I can try that spray. I have used WD40 in the past and a friend of mine who is a tool maker with the big CNC stuff also recommended it. But I'm always open to try stuff

Please see the Red responses above.
 

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I'm sure it's possible but I even did the test piece and it was set to 3 passes of 0.010 and it also started at 0.035. I would normally ramp instead of straight plunge but since it was supposed to only go 0.010 I didn't think the ramp was as necessary.

How do I bring up the G code? Can I just open the .tap file in another program?
Try opening your g code file in 'notepad'. My post processor uses the extension *.tap and it displays in notepad just fine.
 

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Discussion Starter · #15 ·
Try opening your g code file in 'notepad'. My post processor uses the extension *.tap and it displays in notepad just fine.
Doug
Thanks I will try that when I get home today from work. I should have brought the laptop here! lol
 
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Discussion Starter · #18 ·
Here is my G-Code. I don't see any reason for the first pass to be 0.035 deep. I looked at the entire code and it shows what I should be seeing of first pass depth of 0.010. I guess I need to check other places. Hopefully it's the touch plate calibration.
 

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Discussion Starter · #20 ·
Your Z zero is set incorrectly.
Gerry
I was hoping you would chime in!
Where do you see that it's set incorrectly? What am I missing or what did I set wrong?

The same issue happened on my test piece. But on the original sign the first thing I did was some engraving of 2 words and had no depth issues with the engraving bit and I set the Z zero the same with the touch plate.

I plan to do some more testing after work today on some wood and also check the calibration of the touch plate.
 
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