Pocket Depths

[Tim Owens]

Generally if you are loosing steps because you are plunging too fast or going too deep with the chips not getting out. What you get is that each following pass will not be going as deep as before. So when you finish the piece and move to 0,0,0 you will be above the wood. What can also happen is when the Z axis lead screw is not cleaned (silicon spray) now and again you can get contamination in there that will resist having it move all the way up on rapid moves. So as a result at then end of the program and if you move to 0,0,0 the Z would be lower then the top of the wood. Spraying the Z usually fixes this problem. The other questions I would have is are we seeing this on the Pro plus units or on the White units. I would need to see files and speeds people are running to confirm. The two start points might be the issue. I will have to consult with vectric about initial sink points that require alot of material removal in the initial plunge. But I would suggest slowing down the initial plunge.

Thanks

Tim

[jeb2cav]

Thanks Tim for chiming in. From our email discussion around 7 Jan 10 - in my case it is a clean and well lubricated Pro Plus.

[hdtheater]

Generally if you are loosing steps because you are plunging too fast or going too deep with the chips not getting out. What you get is that each following pass will not be going as deep as before. So when you finish the piece and move to 0,0,0 you will be above the wood. What can also happen is when the Z axis lead screw is not cleaned (silicon spray) now and again you can get contamination in there that will resist having it move all the way up on rapid moves. So as a result at then end of the program and if you move to 0,0,0 the Z would be lower then the top of the wood. Spraying the Z usually fixes this problem. The other questions I would have is are we seeing this on the Pro plus units or on the White units. I would need to see files and speeds people are running to confirm. The two start points might be the issue. I will have to consult with vectric about initial sink points that require alot of material removal in the initial plunge. But I would suggest slowing down the initial plunge.

Thanks

Tim

Hi Tim,

I am running into this issue again. I have slowed down my plunge rate to 5 and it still has not improved. I am letting the tool path finish up and then checking its Z value and it all checks out just fine. What I have done for a work around is run the same job twice. The first pass is .125 for depth and the second pass is at .175. Doing this is getting the final product as expected, but having done all the things you have suggested has not improved my situation. Are there any other things I can try?

Thanks,
-Eric

[jeb2cav]

Hi Eric,

While you're waiting for Tim's response - can you post the VCarve project file to look at?

[hdtheater]

I'll post it when I get home. Thanks.

[hdtheater]

Here is the crv file. I hope you see something I haven't.

-Eric

[jeb2cav]

Hi Eric,

Thanks for sharing the crv file. You have a pretty complex cut going on there.

Pocket Depth Piece

There are 22 or 23 distinct move to, plunge, cut and then raise the cutter before moving to the next plunge point steps. What I mean by that is that the Shark is plunging and raising 22 to 23 times during the execution of your pocket cutting job. You can see this when in the Preview mode of the Toolpaths section - instead of hitting Preview Toolpath, click on the Run to Retract button.

Preview Step Through Run to Retract Button

When you do that with this piece, you'll see that the first plunge to retract cut results in

First Cut (Plunge to Retract)

Ok - I've reached the 3 attachment limit, so will continue in next post.

[jeb2cav]

Continuing from last post...

The second plunge to raise cuts brings you to this point

Second plunge to raise cut result

And so on.

I suspect that if you look at these individuals sections (if you will) of the cut process, that you will find that the height differences in your pocket match. What would be interesting to me if that they are all slightly rising with cuts, or if they actually vary - some are higher than others and some are lower.

Can you measure some of these to an accuracy in the 1/100ths and comment on this?

As I said in an earlier post, I ran into a similar situation - more than one plunge to raise - and was able to juggle the shape and make other choices in the toolpath setup that resulted in a single plunge to raise from start to finish. So, I "got rid" of the uneven edge between plunge/raise sections as I only had one section. I've fooled with yours a little, and am quite confident that forcing it to use only one plunge/raise is not possible given your design.

So, I think this goes back to Next Wave for them to clarify on the accuracy of the Shark so that users can know what to expect. Again, it would help if you could measure these cuts to know what your outcome was with regard to accuracy. I've read somewhere that the expectation for the shark is 0.001". I don't know if that is the manufacturer's view or not. If you hear from Next Wave or Rockler on this, please update us all.

Lastly - a possible work around. Your depth of cut is 0.125. Consider running the pocket toolpath twice. Run the first one at 0.123. For the second one, set your start depth on the Pocket toolpath to 0.120. Set the cut depth to 0.125.

Sorry I couldn't do better.

[hdtheater]

Joe,

We are on the same wavelength! The variance in the cuts do not get slightly higher as I had expected, it is more like each plunge gets shallower as it cuts and then when it goes to the next plunge it is back to the correct depth. After the toolpath is complete, I checked it for correct Z setting and it did not shift as it had before.

This is a result from my last attempt at this. Since then, I have slowed my plunge rate to 5. I left feed rate at 150 and RPM at 12000.

What I have done as a current workaround is run it through at .125 and then again at .175. My desired cut is .125. However, I don't want a lot of scrap and I am going with .175 as a second pass to correct the errors in the first.

I would need to rerun the job on another piece of wood to get the variances between the plunges. I do know that there are some pretty steep edges between them, so I know it is more than .001. Hopefully, I can get a response from Tim with a different suggestions to try. I have the work around, but it is taking twice as long to get right.

Thanks for your help on this. We will find out the issue.

-Eric

[hdtheater]

While I have not received any feedback yet, I am running the same job again and changed it up a bit. This time I cut only 1/16" deep pocket and the issue I have been seeing has not gone away. After I completed it, I reset my z height down another 1/16" and it cleans up the variances that I have been seeing.

It is the exact same tool path file and is removing the same amount of material. The only difference is the the Z height setting for the beginning of the job.

Very strange.

-Eric