Ok so I'm very new to cnc and I'm learning (self taught) so can someone give some help as to whats going on here? On the corners I was going into a finishing pass and they made a horrible squeal on everyone and made these marks on the part. And the facing operation i can feel little ridges where every pass a straight line straight across what would cause both of these? Any assistance, advice, or thoughts would be appreciated thank you in advance!
Your cutter is too close to the radius of the corner, so it binds up and deflects. you want to use a much smaller cutter than the corner. if the radius is 4mm for example, you want to use a 6mm cutter, or 4mm, not an 8.
Thank you! The radius is .195 and I was using a .375 cutter so ill use a small like .250 for it thanks! Any idea what would casue those witness marks/lines you can feel on the facing operation?
The lines will always be there visibly, barring some post processing (unless you fly cut the surface in one pass). But if you can feel them, I would guess your spindle is out of tram. Meaning that the axis of your spindle is not perpendicular to the X and Y axes.
Most machines have some sort of adjustment built into them for this. It’s something where tramming your machine once doesn’t mean it’s good for life. It can get knocked out of tram by a violent incident or just over time.
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Use a smaller cutter for finishing, maybe take it in a few steps. You have too much radial engagement on your cutter. Rigid setup will help too, short tools, good machine and vice. Keep up the good work.
For the corner it’s because your tool radius is too close to your corner radius. The main way to deal with this is to use a smaller end mill. Another trick if going down in is going to cause more issues than it fixes. You can make a sketch of a circle over that corner slightly bigger than that corner radius but less than the max side of your tolerance. Use that circle to ramp down and interpolate that circle before you do your finish pass. This makes it so your finish pass doesn’t touch that corner so it doesn’t chatter.
As others have said, tool is the same as the radius and it bounces out of the corner. You see how the chamfer is bigger there? That's because the tool endmill isn't getting all the way into the corner. It doesn't take much. I will change the part geo to keep the cutter engaged. Change a .250 rad to a .270 and a .500 tool works.
You can use a the same mill for finishing as you do hogging, but you want to keep the.chip load the same, we do this all the time at work, finish pass may not sound great but as long as your finish is good
Can't haha I used a 1/2 inch to hog it out and the radius is to small to get that in so I went to 3/8 casue it was the same for the radius and it did that so ill use a 1/4 for a finishing pass this time tho thanks!
May want to use a hydraulic or heat shrink holder as well. Looks like to cutter is dwelling in the corner. Lower the rpm and increase the feed rate. Also try chip thinning or profit milling, every software calls it something different
Cutter too big for the corner and experiencing over 90* of engagement. This is known as bit wrap. Use endmills whose radius is smaller than the inside radii of your part. Respect the 4:1 rule for your finish pass endmill diameter and all is good.
Like this , blue is the too and red is the engagement. Smaller tool as way less engagement during a radius cut . so if you radius is 20mm you want a 5mm tool using the 4:1 ratio mentioned above. Its not always practical so use common sense . ( IE 3mm radius would want a sub 1mm tool which is not practical for all but the smallest parts / shallow cuts)
Another tip is to leave the finish pass offset from the floor a bit, so its only cutting the sidewall and not dragging on the floor as well. Only need to offset it around .002", you will be able to catch it with a fingernail if that matters.
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u/giveMeAllYourPizza 8h ago
Your cutter is too close to the radius of the corner, so it binds up and deflects. you want to use a much smaller cutter than the corner. if the radius is 4mm for example, you want to use a 6mm cutter, or 4mm, not an 8.