Tabs in SolidWorks HSM not cutting properly

[Anonymous]

Hey All,

I've been programming quite a few files lately that all have tabs built into them. The parts are all being cut from 12mm (.47") Baltic Birch. The tabs vary in size but are generally about .15" thick and about 3/4" in length. The goal is to flush cut the tabs off the CNC table after the CNC is done running. 

The problem is that we are getting a protrusion or offset all the way up the piece, at each tab location, making it impossible to flush cut. To further describe the problem: the tab cuts correctly, it is .15" by .75" long, but above the tab (the remaining ~.32" has a protrusion of roughly 1/8" outwards. 

Our process for programming part contours is as follows. I'll detail #1 more as this is where the problem lies: 

1: We create a contour selecting the base contour of the part, ensuring the contour runs consistently with the part and through the tabs, not around the tabs. We then select the bottom height to be the top of the tab and the top height to be the top of the part. This, in theory, should create a smooth, consistent contour, around the whole part cutting all the way down to the top of the tab. 

2: We select the base contour again, excluding the tabs. Bottom height is the bottom of the part and the top height is the top of the tab. The problem likely occurs here too, you just can't see it because the tabbed area doesn't get cut. I've attached 2 pictures to better show the problem. Once shows the tab still on the part and the protrusion all the way up. The other shows the protrusion with the tab removed. I've also attached a file if anyone has the interest and time in looking into why the first contour pass is producing a smooth result.

If you have any clarification questions, or issues with the attached file, please let me know and I will respond as soon as I can. 

Thank you all for your help. It is greatly appreciated!

- Ben 

 

[Laurens-3DTechDraw · Accepted solution]

I can't see anything wrong in the program.

Are there any feeds and speeds difference between the first time and the second?

Do you see the same thing on both sides of the part?

[Anonymous]

The feeds and speeds are the exact same for both contour passes. And yes, we see the same thing on both sides of the part.

[Anonymous]

We have been doing some testing with these tabs and have further information as to what is causing the problem. 

The first contour pass cuts a perfect part, no indents or extrusions, where the tabs should be. However, each part is measuring larger than it should be. 

The second pass, which creates the tabs, takes away more material, getting each piece down to the correct size. Since the tool doesn't cut where the tab lies, the material above the tab isn't reduced, leaving the extrusion. Its almost like the first contour is a roughing pass and the second contour is a finishing pass. 

When I look at my toolpath as well as run a simulation, the toolpaths line up perfectly and I do not see anything of concern. The same tool is being used for both contour passes. 

Any ideas? 

Cheers!

Ben

[Laurens-3DTechDraw]

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@Anonymous wrote:

We have been doing some testing with these tabs and have further information as to what is causing the problem. 

The first contour pass cuts a perfect part, no indents or extrusions, where the tabs should be. However, each part is measuring larger than it should be. 

The second pass, which creates the tabs, takes away more material, getting each piece down to the correct size. Since the tool doesn't cut where the tab lies, the material above the tab isn't reduced, leaving the extrusion. Its almost like the first contour is a roughing pass and the second contour is a finishing pass. 

When I look at my toolpath as well as run a simulation, the toolpaths line up perfectly and I do not see anything of concern. The same tool is being used for both contour passes. 

Any ideas? 

Cheers!

Ben

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Sorry I didn't respond earlier.

I think you see the machine and tool deflect during the first cut. The second cut is less heavy so the deflection is less and it will cut the correct diameter.

Are you using a long tool?