Lip on the bottom 1.5-3mm of parts

Assembly questions and answers for the Shapeoko 3 CNC Mill
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Chembro
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Joined: Sat May 09, 2015 3:09 pm

Lip on the bottom 1.5-3mm of parts

Post by Chembro » Wed Dec 02, 2015 12:13 am

I have a lip that's coming up on the button of my parts.

I'm not sure if it's belt stretch/slip on the X axis that's causing it but I've made flats on my motor shafts and my set screws are as tight as I could get them without stripping something.

I'm thinking that maybe my bit isn't sharp enough and is causing extra force on the X axis since it's running one belt instead of two like the y axis.

The A Run has the largest lip measuring approx. ~1mm, and is unfit for sale.

Run B had a very small lip approx. ~.25mm and measures close enough to the CAD drawing to mail them to the consumer which is why they're missing.

I highlighted the lip with orange/silver and put an axis for reference.

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WillAdams
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Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Lip on the bottom 1.5-3mm of parts

Post by WillAdams » Wed Dec 02, 2015 1:35 am

Check the Z-axis V-wheels, consider climb vs. Conventional milling / path direction?
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

Chembro
Posts: 21
Joined: Sat May 09, 2015 3:09 pm

Re: Lip on the bottom 1.5-3mm of parts

Post by Chembro » Wed Dec 02, 2015 1:58 am

I'll double check the v-wheels next. I've included a picture of my tool settings for cutting phenolic.
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Fablicator
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Re: Lip on the bottom 1.5-3mm of parts

Post by Fablicator » Wed Dec 02, 2015 2:30 am

Check your endmill!

I had parts turn out like this and it turned out I chipped the tips off my end mill. I only saw the ridge on the deepest pass since the higher up section of the endmill was still OK.

Chembro
Posts: 21
Joined: Sat May 09, 2015 3:09 pm

Re: Lip on the bottom 1.5-3mm of parts

Post by Chembro » Wed Dec 02, 2015 2:18 pm

If it were the cutter tip you would see this lip all the way around the part.

This issues is more of a shadow on one side. Something is skipping steps.

My z-axis v-wheels are solid, unless another one cracked and when it gets close to the wasteboard it falls into a rut on the wheel. There is flex in the z axis plate though, which shouldn't be a problem if the endmill is cutting and not pushing.

WillAdams
Posts: 8489
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Lip on the bottom 1.5-3mm of parts

Post by WillAdams » Wed Dec 02, 2015 2:31 pm

Yeah Garolite is tough stuff. I wonder if reinforcing the Z-axis spindle carriage plate isn't going to be the biggest bang for the buck upgrade for the SO3. Still debating what I want to do for mine.

Another consideration --- are the top / bottom layers tougher than the inner? Maybe rejigger the paths to take that into account?
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

Chembro
Posts: 21
Joined: Sat May 09, 2015 3:09 pm

Re: Lip on the bottom 1.5-3mm of parts

Post by Chembro » Wed Dec 02, 2015 3:30 pm

I'll just slow down the machine to 40IPM on the next run and see if that helps at all. If so I know where my issue is. This is actually CE Phenolic which is a cotton weave epoxy sheet and is much softer than Garolite. Garolite is usually a glass weave and is a pain to machine and will eat through carbide like butter.

Ask me how I know :lol:

If I can tinker and find a solution I'll post it here as a reference if anyone else is having the issue.

Will, I'm not sure how the z axis can be supported, I was thinking of adding an extra set of v-wheels but it wont work once the machine plunges and they will derail. Maybe Edwards Z axis mod that covers the springs added a little rigidity to the set up?

I'm not too familiar with g-code to actually code by hand or modify it. I'm using MeshCam and adding toolpaths together is about my limit. :?

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Fablicator
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Joined: Thu Jul 02, 2015 7:59 pm

Re: Lip on the bottom 1.5-3mm of parts

Post by Fablicator » Wed Dec 02, 2015 4:26 pm

Chembro wrote:If it were the cutter tip you would see this lip all the way around the part.

This issues is more of a shadow on one side. Something is skipping steps.

My z-axis v-wheels are solid, unless another one cracked and when it gets close to the wasteboard it falls into a rut on the wheel. There is flex in the z axis plate though, which shouldn't be a problem if the endmill is cutting and not pushing.

Couldn't tell it wasn't all around.

Are you 100% sure of your work holding?

Chembro
Posts: 21
Joined: Sat May 09, 2015 3:09 pm

Re: Lip on the bottom 1.5-3mm of parts

Post by Chembro » Wed Dec 02, 2015 6:29 pm

I'm bolting things to the the wasteboard with 1/4in -20 hardware with 6 prong t-nuts.
Doesn't mean it can't shift though.
"Shrugs"

I'll figure it out. Eventually.

Chembro
Posts: 21
Joined: Sat May 09, 2015 3:09 pm

Re: Lip on the bottom 1.5-3mm of parts

Post by Chembro » Wed Jan 20, 2016 9:45 pm

So after running the machine again for the first time since I made this run. I did a "test" by not changing anything from the last run and I didn't get the lip this time.

My conclusion is that I was pushing the machine too hard. Instead of it cutting all the material in front it was putting strain on the x axis belt and in return jumped a tooth at some point in the toolpath. I cut down the feedrate from 60ipm to 40ipm and the quality of the cut increased TREMENDOUSLY.

It's pretty conservative but for CE grade phenolics I recommend:
3 flute coated carbide endmill
40-50IPM (1016-1270mmPM)
.008" depth per pass (.203mm)
#2 on Dewalt DW611

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