trockmop start outside shape

[Chip Owner]

Is there anyway to start a trockpocket outside of a shape?

Had to cut some small offset block out of barstock today,  effectively an island in the middle of the stock.  I thought it was a great opportunity to use a track mop, however couldn't make it work at the time.  I thought it would be a great way to sneak up on the part in the middle centre of the stock.
 
I've just had a play now in CB to try and find out where I went wrong and the only way I could get a toolpath was starting inside the outline.

[Bob La Londe]

Create secondary geometry.

[Bob La Londe]

Alternatively you could use a Trocho Profile with a cut width adequate to waste away the stock. 

[Bob La Londe]

Creating "helper" geometry can help in hundreds of different ways.  Its a good idea to at least think about how it might help you in any difficult operation to constrain. 

[Chip Owner]

Create secondary geometry.

That's kind of what I'd created, I thought rather than plunge into the stock, I might be able to attack it from the side, strting at the outside edge.

Edit - On reflection I should add I made the secondary geometry the same width as the stock, no idea why I constrained it that way, it would have worked had I expanded it the width of the tool outside of the stock, the width of the tool, outside the stock.    doh!

[Chip Owner]

Alternatively you could use a Trocho Profile with a cut width adequate to waste away the stock.

You know those things that wake you in the middle of the night...

Didn't hit on the cut width, however profile in conjunction with pocket.   I've just added a cut width and while not clearing it all, did help.

I've got this part done now, but I can have a play with some fictional parts to create starting styles to kick it off. 

[Bob La Londe]

Trocho MOPS are not intended to create a clean operation in my opinion.  They are intended to rough away material. 

https://rumble.com/v2acd5a-mesquite-wood-machining-pauls-wood-1.html

[lloydsp]

Sorry, but I just must ask -- why not simply use a regular profile cut?

Lloyd

[Bob La Londe]

Trochoidal operations if done properly never overload the cutter.  A regular profile or pocket operation routinely:
FORCES THE CUTTER INTO 100% ENGAGEMENT EITHER BREAKING CUTERS OR FORCING YOU TO RUN SLOW ENOUGH TO TOLERATE IT.

The OP was wasting away material to cut a part on the end of a piece of bar stock as mentioned in their first post. 

I would love to be able to machine 3D cavities with Trochoidal milling.  As with many things CamBam related there is a work around, but its slow and tedious. 

[lloydsp]

But Bob, regardless of which method you use to remove less material per pass of the tool, the end result is the same -- it takes the same amount of time!

You can use a trochoidal MOp, and reduce 'engagement' by that means, or you can use ordinary profile MOps, and reduce the engagement deliberately through 'feeds-n-speeds' and depth-of-cut management.  The only benefit of a trochoidal MOp is that you can use 'full depth' of the tool, but at the expense of a wider cut, meaning more material has to be removed for a given profile.

Maybe I should have put that in bold, supercaps!  Sheesh!

Lloyd

[Bob La Londe]

... and trochoidal never buries your tool 100% in a corner direction change.  Before you disagree consider a simple square pocket. 

[lloydsp]

I don't disagree, but I've never had problems with adjusting things so that wasn't a problem.  I've used the trochoidal MOp occasionally.  I just don't see it as an end-all-save-all solution to what is simple tool management.

L

[Bob La Londe]

I didn't say its was the be all and end all of all problems.  Just that it does not have one of the problems inherent in other methods of material removal.  Going slower works, but I don't want to go slower.  Using yet another work around also works.  LOL. 

The closest to ideal roughing material removal pattern would be a spiral finish that automatically switches to trochoidal as it gets into the corners.  No direction changes until its necessary, and no excessive load in the corners and direction changes.  Trochoidal actually does this, but better more efficient tool paths could be generated. 

Of course the material you are cutting matters.  I can get away with all kinds of fast "less ideal" tool paths in poplar that will eat endmills like potato sticks in steel or even aluminum.