Circular cut has me stumped

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John E
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Joined: Tue Jul 14, 2009 5:26 pm

Circular cut has me stumped

Post by John E »

I'm using a CNC Shark SD120 router table with a Dewalt 611 router. I've cut perhaps a dozen pieces (not of the design shown here) and never had a problem with the beginning of a circular cut not meeting up with the end of the cut. This one is driving me nuts. My machines are only a few months old and I've double-checked that all the router fittings and dust shoe are secure before making the cut. The fact that my machine will duplicate this error time and time again tells me that this is likely not a hardware problem.

As you can see from the attached picture, the beginning of the Circular Recess .25 EM cut does not line up with the end of the cut. Here are the things I've tried to fix the problem:

- I began using a .25" dia. end mill. I made a profile cut around the 5.324" dia. circle. After several miscuts, I deleted the circle, replaced it with a new one, and then calculated the new toolpath. Same result.

- I changed from a profile cut to a pocket cut. The inside of the pocket is the 5.324" circle, and the outside of the pocket is the 5.824" dia. circle. Same result.

- I left the pocket cut in place and changed to a .125" dia. end mill, then recalculated the toolpath. The result was even worse.

As you can easily see in the .crv file, the 3D toolpath shows a perfect circle. I've made multiple attempts at cutting the circle only on a piece of scrap board. Every !@#$ cut turns out the same! What the heck am I missing here? Thanks a bunch for your assistance.
Attachments
Adam-Jami anniversary.crv
(1.12 MiB) Downloaded 58 times
Circular Recess cut mismatch.jpg

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TReischl
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Re: Circular cut has me stumped

Post by TReischl »

Do not be so sure that you are not having a machine issue.

It is easy to see if it is the software. Just look at the cnc gcode and see if the end point of the circle matches the start point.

It is surprising how repeatable some machine issues can be.

So, take a look at the gcode, if you are not able to read it then post it here and one of us will take a quick look for you.
"If you see a good fight, get in it." Dr. Vernon Johns

John E
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Re: Circular cut has me stumped

Post by John E »

Well, I tried to upload the .tap file for the Circular Recess and I get an error message that says I cannot upload a .tap file. Is there another way to upload a gcode file? And BTW, I checked that I am running v10.512, the latest software build.

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Rcnewcomb
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Re: Circular cut has me stumped

Post by Rcnewcomb »

The preview does not show the issue.

It looks like machine flex. Slow down the feedrate on the circular recess from 120IPM to 60IPM.
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John E
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Re: Circular cut has me stumped

Post by John E »

OK, RC. I will try reducing the feed rate tomorrow. Machine flex would certainly be repeatable. Thanks!

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Rcnewcomb
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Re: Circular cut has me stumped

Post by Rcnewcomb »

You can also try changing the cut direction from Conventional to Climb and see how that changes the behavior.

I'd also recommend enlarging the outer circle outward by 0.02". Currently the space between the two circles is exactly 0.25" and you are pocketing with a 0.25" end mill. If you make the pocket a bit wider that would be better.

Alternately, you could use just a single circle vector and profile ON the line at 0.15" deep
Last edited by Rcnewcomb on Tue Jan 26, 2021 2:01 am, edited 1 time in total.
- Randall Newcomb
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John E
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Re: Circular cut has me stumped

Post by John E »

OK, will do. Will see how this works. Thanks.

John E
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Re: Circular cut has me stumped

Post by John E »

I could not post a .tap file so converted it to a .txt file. Thought I had posted this but will try again. :(
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Circular recess .25 EM.txt
(1.25 KiB) Downloaded 46 times

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TReischl
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Re: Circular cut has me stumped

Post by TReischl »

G code looks correct. Start and stop points are spot on.
Capture.PNG
Looks like machine issue.
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sharkcutup
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Re: Circular cut has me stumped

Post by sharkcutup »

Slow down the Plunge rate! The Z-axis is flexing/forcing the router bit outward toward the text and away from the number six. The return/stop location is correct (looks Good).

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4DThinker
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Re: Circular cut has me stumped

Post by 4DThinker »

Sharks are notorious for having flex in the router mount/Z axis. I own one, and have essentially stopped using it for that reason. Some day, perhaps after I retire, I'll likely rebuild the carriage to hopefully eliminate all the plastic parts which should never have been used in the first place.

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sharkcutup
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Re: Circular cut has me stumped

Post by sharkcutup »

Yeah, if you feel like spending approximately $899. for an all Aluminum Z-Axis Mount. There is a fellow in Washington State making them using a modified Beefed up HD2 Shark. His handle is Rando on the CNC Shark Forum.
20210117_113341.jpg
Here is what it looks like

Nextwave Automation now has a minor aluminum Z-axis mount that can be swapped out or fix for about $100. too!

Just Saying!!!

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John E
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Re: Circular cut has me stumped

Post by John E »

Thanks, everyone! Don't know what I would do without the Vectric wizards here. :)

John E
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Re: Circular cut has me stumped

Post by John E »

Reducing the feed rate for the Circular Recess to 60 IPM made a huge improvement. I'm attaching a picture that shows, well, lots of my test cuts for this recess. :wink: I've highlighted the one issue that remains: The cutter barely makes a mark on the ID of the recess as it is starting its cut. You have to look closely to see this, but it will show up in the finished project. Any ideas from my forum friends as to what is causing this mark and how to possibly eliminate it? Per a previous post, I changed the machine vectors to Climb. Thanks again.
Attachments
Adam-Jami anniversary.crv
(1.35 MiB) Downloaded 48 times
Circ recess 0126.jpg

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Rcnewcomb
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Re: Circular cut has me stumped

Post by Rcnewcomb »

The cutter barely makes a mark on the ID of the recess as it is starting its cut. You have to look closely to see this, but it will show up in the finished project. Any ideas from my forum friends as to what is causing this mark and how to possibly eliminate it?
Click the checkbox in Ramp Plunge Moves and give it a 0.5" ramp distance.
Screen Shot 2021-01-26 at 4.32.37 PM.png
- Randall Newcomb
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