Ramp Damage

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jrw5574
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Joined: Sun May 10, 2015 1:29 am
Model of CNC Machine: Laguna SmartShop 2

Ramp Damage

Post by jrw5574 »

Hi All.

I use Vcarve for nest based manufactiuring and mostly cut with compression bits. When I ramp in the corners are always a little bit damaged where the ramping occurs. I've just been sanding this little deformation out since I need to sand the plywood fuzz off anyway but I'm pretty sure this should be avoidable. I've tried zig zag, smooth and different lengths and angles.

We are running a Laguna Smartshop II with 5' x 10' table.

Any ideas?

Thanks,

Jason

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Adrian
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Re: Ramp Damage

Post by Adrian »

You can improve things a lot by adjusting the start node and using the last pass feature but there is going to be some sort of mark as the load on the tool increases and with a compression bit it's worse as you're passing through two different cutting areas on the tool. The only way to avoid it totally is to use leads and do the ramping/plunging on those so that when the cutting proper starts the tool is at the correct depth.

ger21
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Re: Ramp Damage

Post by ger21 »

+1
Gerry - http://www.thecncwoodworker.com

jrw5574
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Re: Ramp Damage

Post by jrw5574 »

Thank you sir. I've thought about playing with leads, I'll experiment to see how much extra space I need between parts.

When you say adjust the start node are you referring to where the cut starts on the part?

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Adrian
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Re: Ramp Damage

Post by Adrian »

Yes, with the correct toolpath settings (Use vector start points, don't optimize) moving the start node can make a difference if the marks are caused by loading but with a compression bit you're passing through an up cut/down cut transition which is nearly always going to leave a mark without a lead.

agahn
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Re: Ramp Damage

Post by agahn »

If there's room in the workpiece, you can extend a vector to ramp in the compression bit before it gets to the cut of the finished product.

Another option I've used is to run a downcut bit first, halfway through through, then run an upcut bit to the final depth. Disadvantage is that it will take twice as long to cut a part. An advantage is in dust collection. The final upcut lifts all the dust out of the cut.

Kayvon
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Re: Ramp Damage

Post by Kayvon »

Adrian wrote:the last pass feature
I tried using last pass once with an upcut bit. Only 0.001" last pass, but I found my bit was being pulled down out of the router, resulting in increasingly deep cuts as I cut through more pieces. It took me longer than it should have to determine that the problem was the new setting, not the router, CNC, or 2 bits I tossed.

It sounds like you've had better luck with this. Can you tell us about it?

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Adrian
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Re: Ramp Damage

Post by Adrian »

There's no way the software would cause that. That's a physical problem with the collet and/or bit. With the forces on an upcut bit it will try to pull itself out of the collet so if the collet is worn, dirty or not torqued properly you may well have that issue.

Kayvon
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Re: Ramp Damage

Post by Kayvon »

Well, it's not the collet. It was nearly brand new from Elaire Corp, which makes high-quality precision collets. I tried two different bits, but the blame is still possibly on them. They were both discount HSS bits from China. It's possible I didn't tighten enough, I suppose, but I gave the second bit a little extra tightening and I'm hesitant to go any tighter and risk harming the collet.

Mostly, I've learned to avoid the feature. I've not experienced the problem before or since. It only occurred when trying to take the 0.001" off the edge of the entire thickness of the piece in a single pass.

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adze_cnc
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Re: Ramp Damage

Post by adze_cnc »

Kayvon wrote:Mostly, I've learned to avoid the feature. I've not experienced the problem before or since. It only occurred when trying to take the 0.001" off the edge of the entire thickness of the piece in a single pass.
The next question has to be is: does the thickness of the material exceed the cutting edge length (CEL) of the bit you are using to shave off that last 0.001" ? If so I can see that causing such problems.

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