3/4” Bowl Bit Issue

(Jacob Hogue) #1

Hello,

I’m making some catch all trays and I’m noticing a small issue in some of the corners where the toolpath completes but leaves a little uneven ridge. I thought my speeds and feeds were pretty conservative but I can’t think of what else would cause this. Any ideas?

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(William Adams) #2

Usually this sort of thing is caused by deflection when plunging — best fix seems to be to leave a roughing clearance larger than the deviation, then take it off with a finishing pass (which usually requires adding inset geometry in Carbide Create, see: Adding geometry to cut as a pocket with a finishing pass )

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(Jacob Hogue) #3

Okay, thanks for the suggestion, I’ll try that!

For reference, my plunge rate is set to 3ipm. Do you think lowering that would be beneficial?

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(Mad Hatter) #4

What I do when using large bits is I will tell the computer I am cutting the pocket with a bit that is ~0.050" wider than it really is. It cuts the pocket at however many passes you do, like 0.100" passes. . . This leaves 0.025" all the way around the pocket to clean up and remove the layer marks in the wood and the chunky corners. (like /u/WillAdams wrote)

Then I go back and tell the computer I am using the actual size of the bit, do an inside profile at full depth pass and have it do the last bit of cleanup at a single cut (provided the cutting depth of the bit is greater than the pocket depth) and it should clean it up nicely.

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(William Adams) #5

Maybe, but IME, by the time you get the plunge rate down low enough for the machine to not deflect, it’s faster to make the finishing pass.

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(Jacob Hogue) #6

This is a good idea. And no issue running full depth (in my case .375”) in a single pass for the finishing pass?

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(Jacob Hogue) #7

Yeah, makes sense - thanks Will!

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(Jacob Hogue) #8

Hi Will,

To follow up to my question, I tried your suggestion but it didn’t seem to help any. The strange thing is, that I just noticed actually, is that the little uneven ridges are occurring only on the top left and bottom right corners of the pocket. Any idea why this would be?

Thanks!

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(William Adams) #9

Directional problems like that usually come down to climb vs. conventional milling:

https://wiki.shapeoko.com/index.php/Climb_vs._Conventional_Milling

It may be that you’ll need to run the finishing pass in the opposite direction, or possibly even both directions.

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(Jacob Hogue) #10

I didn’t realize you could control the direction of the toolpath in Carbide Create?

[edit] is there a way to run a pocket/inside-left offset path counter clockwise?

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(William Adams) #11

To control direction you’ll need to add geometry and fake the program out with an outside path which is actually an inside one.

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(Jacob Hogue) #12

Yeah I figured that would be the case.

But I’m stumped as to fix the below issue now.
The first picture shows my pocket toolpath, running clockwise.
The second picture shows my outside-right toolpath which is inset .75”, the same diameter as my bowl bit.
But as you can see, there is a small amount of material in the corners that won’t be reached by the second toolpath.
Any ideas?

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(William Adams) #13

The direction of the path shouldn’t change how much material is left uncut.

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(Jacob Hogue) #14

Then maybe my geometry is wrong? I’m not quite sure how else to trick the machine into reversing the direction of the toolpath.

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(Jacob Hogue) #16

Can you tell what I mean from the two images. You can see the second one doesn’t cut the same amount of material as the first one. First is pocket, second is outside right

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(William Adams) #17

The second path is rounded — either redraw it or add some geometry and use a Boolean to make things match up.

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(Jacob Hogue) #18

When would an outside-right path not be rounded though?

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(Jacob Hogue) #19

I feel like this is super simple but I’m just missing something. I just need a finishing pass to run counter clockwise that matches the outside oath of my pocket.

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(William Adams) #20

Try drawing a rectangle of the correct size / position — that should work.

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(Jacob Hogue) #21

I think there might be some confusion here.

First picture is a pocket of the larger rectangle. This is the area I want my pocket to be.

Second picture is an outside right offset of the smaller rectangle in the center, thus creating the finishing pass going counter clockwise. The issue is that this path does not cover the same area as the first path.

I cannot make the smaller rectangle any larger as it will cause the outside right path to exceed the area of the pocket rectangle.

Would it be easier to send my .c2d file?

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