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  #1  
Old 09-10-2019, 01:12 PM
cncdood cncdood is offline
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Default Poor cut quality only on a portion of the workpiece

Hi all,

I am having an issue in which the cut quality degrades for only a portion of the workpiece. Attached are 3 images showing good and bad cut quality very near each other on the same boards.

This is 1/2" baltic ply and I'm using a new 1/4" Amana downcut. I've recently tightened all the belts and replaced the x-axis pinion gear and checked the others.

I've also attached the setup sheet showing the exact parameters of the cut.

After the last maintenance effort just a week ago the machine was performing excellently. This issue just cropped up. Specifically, there seems to be some tear on on top and bottom of the sheet as well as in the middle. I think the pictures show it clearly.

Any feedback on what to check next?
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  #2  
Old 09-10-2019, 01:38 PM
barney barney is offline
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I cut a bit of birch multiply and the best way I have found to get a clean cut is do the first pass in a climb cut than follow up with a conventional pass.
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  #3  
Old 09-10-2019, 04:22 PM
Doug S Doug S is offline
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What speed and feeds are you using.
Is that a two flute downcut?
Saw you tool but could not read it.
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Old 09-10-2019, 04:30 PM
cncdood cncdood is offline
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Feedrate is 300 with a 12k spindle speed. This puts the chipload right in the middle of where Amana recommends for a 1/4 bit.

And yep, it's a two flute downcut.
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Last edited by cncdood; 09-10-2019 at 04:33 PM.
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  #5  
Old 09-10-2019, 06:36 PM
Doug S Doug S is offline
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It looks like tooling to me, but I am nowhere an expert.
What is have seen multiple times here is to create an pattern back and forth cutting full depth and while running, increase the bit speed and speed. I run my 1/2 Baltic at 800 ipm and 18,000.
I tend to get better cuts higher speeds.

I know your Cobra can handle it.
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Existing:-2014 Cobra 5x10 ATC w/ 10 hp spindle, Mozaik, 25 hp Becker High Vacuum Pump, 5 HP Oneida DC-Central Texas
New:-2014 Cobra 5x12 ATC w/ 10 hp spindle, pop up pins, phenolic top, lathe, vacuum relief valve, mister system, 25 HP Blower.
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  #6  
Old 09-10-2019, 07:44 PM
cncdood cncdood is offline
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Oh really wow. You’re using a 1/4” bit and cutting how much of the material?
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  #7  
Old 09-10-2019, 08:52 PM
Doug S Doug S is offline
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One pass, 1/2 Baltic birch for drawers. 800 ipm at 18,000 rpm.
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Existing:-2014 Cobra 5x10 ATC w/ 10 hp spindle, Mozaik, 25 hp Becker High Vacuum Pump, 5 HP Oneida DC-Central Texas
New:-2014 Cobra 5x12 ATC w/ 10 hp spindle, pop up pins, phenolic top, lathe, vacuum relief valve, mister system, 25 HP Blower.
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  #8  
Old 09-11-2019, 08:54 AM
Jim Becker Jim Becker is online now
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Have you tried a compression cutter instead of the down-cut?
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  #9  
Old 09-11-2019, 12:23 PM
cncdood cncdood is offline
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Yes, I tried a compression cutter first and found that the downcut produced better results. No idea why that would suddenly stop being the case.

Also, just to ensure that the work holding wasn't an issue, I just ran a sheet with tabs in addition to the vacuum and the dirty edges were still there.
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  #10  
Old 09-11-2019, 12:30 PM
Doug S Doug S is offline
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Sometimes the plywood we get is of lesser quality and I notice strands of wood pulled out from the cut, so much so that I have to sand prior to edge banding.
Some of the Baltic I have now splinters on the top when plunging where it never has prior.
So darn many variables.
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Existing:-2014 Cobra 5x10 ATC w/ 10 hp spindle, Mozaik, 25 hp Becker High Vacuum Pump, 5 HP Oneida DC-Central Texas
New:-2014 Cobra 5x12 ATC w/ 10 hp spindle, pop up pins, phenolic top, lathe, vacuum relief valve, mister system, 25 HP Blower.
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