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Dynamic undercutting - Slot cutter


Rstewart
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I have box I'm machining that has a .45" wide lip overhanging from the top.  I want to use Dynamic contour to chip out the corners.  Regular contour paths are not very good for this as the tool engagement in the corners is Bad.

There is a starting distance in the parameters, but no Exit distance parameter available (dynamic contour) Enhancement Request Please 😀  My tool must move away from the wall .5" before retracting!

What's my best option for this?  I can post a screenshot if needed, but it's pretty self explanatory. 

Help Please :welcome:

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Use dynamic contour like your thinking, but make the ref points at in and outs at the depth your cutting. Make the clearance moves, restract and everythign in the window you're cutting in. Then make points tool paths to get into the cuts and out of the cuts. I have done this for used using under cut tools. I did a manifold with some 10" Gauge length Sandvik tools for a customer that has HSK-100 on their Mill/Turn. They were impressed how smooth and nice the cuts were in the 17-4 PH SS we were cutting.

Here is a screen shot of the tool:

image.png.8accb5b76581a4f02bd424d16e3d1899.png

This was round undercut, but the shape doesn't matter.

image.png.ebfed713cd4b66f4c4f06e1cce9dee6f.png

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Ok, you have to turn off the clearance move.  I'm assuming that I can use a Point Toolpath to get my tool in and outta there.

Am I going to have to use 9 different point toolpaths for each depth of cut???  This is easy with just the regular contour paths, but since dynamic doesn't have Exit Distance you have to direct it where to go each depth.

I'll don't mind copying down a ton of paths, just thought someone had a trick maybe

 

Thanks for your input Ron 👏

parameters.JPG

Ref_points.JPG

undercut_image.JPG

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No you set the tool path like you're thinking and use the depth of cuts to make the one dynamic toolpath cut from top to bottom. The approach ref point will be at the same depth as the 1st cut and the last ref point will be at the depth of the last cut. I would probably do a center cut and work my way up and then work my way down, but really no real difference. I would think just starting at the top of the undercut and working your way down will be just as good. Take full depth of cuts equal to 95% of the key seat cutter. Same principle applies on this as other endmills with dynamic toolpaths. Spread the wear across the flutes and don't think you have to take it easy on the depths you will be making up for it on the ROC.

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I made it work, but I couldn't get what I wanted with just one path.  I had to copy down eight dynamic paths and point toolpaths.  I'm not so sure it can be done with one TP...

Ron, I'd be interested to see an example of a Dynamic contour path that can do Multiple depths while only retracting to the reference points ( Same Z for each level).

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38 minutes ago, Leon82 said:

You could project the path instead of making a bunch.

You probably have to play with the depth pto get the last one Wait what

You could draw 8 surfaces for each zdepth, then project the toolpath onto each of the surfaces, that sounds more efficient than having 8 toolpaths.

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9 hours ago, Rstewart said:

I made it work, but I couldn't get what I wanted with just one path.  I had to copy down eight dynamic paths and point toolpaths.  I'm not so sure it can be done with one TP...

Ron, I'd be interested to see an example of a Dynamic contour path that can do Multiple depths while only retracting to the reference points ( Same Z for each level).

Point toolpath to rapid to deepest Z

1 dynamic path at deepest Z

Use Transform for required depth cuts

Point toolpath at final Z for safe retract motion

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On the ref point, you only want an XY value.  You can also turn off retract and reference in linking and then use a contour path to get in and a contour path to get out if you want to feed in XY instead of rapid.  I can make an example later today if you want to see it.

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2 hours ago, jlw™ said:

On the ref point, you only want an XY value.  You can also turn off retract and reference in linking and then use a contour path to get in and a contour path to get out if you want to feed in XY instead of rapid.  I can make an example later today if you want to see it.

I want to see it. I occasionally have the need to do this type of cut, I've always just used contour paths, it never occurred to me that dynamic might be an option.

In fact, we have a part at the machine ready to cut as soon as the custom ground cutter hits our dock later today.

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Another way is to use the toolpath editor to adjust the lead out.  I just used it a week ago to dynamic rough a undercut with a keyseat cutter and got exactly what I wanted.  The one downside to the toolpath editor is that it locks the toolpath.  If you need to make any changes you have to unlock it then go thru the process again to reedit the retract point.

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Optirough does not allow undercutting, no. 

BUT- on a shape like this, where we just have to avoid the lip around the boundary, we could just neglect to tell Optirough the lip is there, set our Minimum depth to be the underside of the lip with a stepdown of the thickness of the slotting tool, and add in large entry and exit values in the Linking page, and voila- dynamic rest roughing with a slotting tool that also properly clears the lip on entry and exit.

 

Now, this is just using a Roughing Tool setting in Stock rest material.  If we have a complex stock model, with maybe some variable stock in floor areas, we'd need to somehow remove the 'lip' of stock to allow this method to work correctly and ensure Optirough continues to ignore geometry and stock higher up than the lip. In a case like that, we could use a ghosted facing operation to 'clean' the stock down to the underside of the lip, and then generate a stock model for our Optirough based on this ghosted facing op.

 

Undercuts.thumb.jpg.588591176b42e2f00756bcb07653b902.jpg

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Sorry had things to take care of yesterday to come back to this topic, but you got it sorted out. This is what the forum is all about helping each other solve problems and get better in the process. Have a good day and thank you everyone that added and turned it into a educational lesson.

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I love using Dynamic toolpaths for Wheel or Keyway cutters.  

 

I put together a example file with several strategies based upon the help and suggestions of some of the contributors above.

 

In the past, I  mostly did the toolpath edit thing like Ben Wood describes and find that I have a lot of control with that strategy but it is a PIA to unlock, make a change and the re-edit the operation.

keyway undercutting bc4.zip

 

One of the strategies is for a 3d Optirough.

Another is a 2d Dynamic with point operations 

and the third is a variation of the 2d Dynamic with point operations to do an alternating cut

image.thumb.png.ea9f046ab3dcfcba34a1e1bcb556619f.png

image.thumb.png.697c19cfe08a9529ccc4b6e91798e28e.png

 

There are probably errors in this example and the tool size and shape in relation to the part is not in any way accurate.  I am just trying to share how to generate the motion.

 

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