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curriergroh
03-23-2012, 03:19 PM
I'm trying to replicate what was done in this post. I'm not having any luck.
Below the link I have tried to detail my steps. I am using a circle .75" thick and a profile curve. Can anyone shed some light on the rhino commands used for splitting/trimming/subdeleting the grouped tool paths to create a tab. I need tabs for sheet material that will be profile cut.

http://www.cnczone.com/forums/madcam/64196-2_5d_first_parts_hints.html

FIRST TEST- CAN A TOOL PATH GROUP BE UNGROUPED THEN REGROUPED AND STILL WORK? (YES, BUT IT MUST BE REPAIRED)
Generate a tool path by profiling.
Test in simulator - working.
Ungroup tool path.
Test in simulator - not working.
Regroup tool path.
Test in simulator - not working.
Repair group.
Test in simulator - working.

SECOND TEST- CAN A TOOL PATH BE MODIFIED BY SELECTIVE DELETION TO CREATE TABS?
Using trim and split the tool path stops at the first break in the line then starts the next pass.
Using deletesubcrv the tool path stops at the first break in the line then starts the next pass.

THIRD TEST - CAN A TOOL PATH ONCE PARTIALLY DELETED BE RECONNECTED WITH A MODIFIED PATH?
Delete a section of the tool path then draw a vertical line to safe clearance height, draw a horizontal line to the end of the deleted section, then draw a vertical line down to the end of the deleted section.
Regroup.
Repair.
My result, the second pass (2 of 3) was skipped so that the order was 1, 3, 2. But it did create the tab. Found out that this was caused by a hidden line in the second pass. When that line was revealed, regrouped, repaired the result was 1, 2, 3 but no tab. Trying to replicate the results is not working. It seems to be stuck in the pattern 1, 3, 2 now.

svenakela
03-23-2012, 07:52 PM
Why don't use skin cut instead? The function is there already...

i use tabs in 3D-models, in 2D I always use skin cut.

skin:
MADCAMCNC: Making an extender with 2D contouring (http://madcamcnc.blogspot.se/2011/01/making-extender-with-2d-contouring.html)

tabs (a couple of minutes into the clip you'll find a bunch):
MADCAMCNC: Foam core - double sided milling (http://madcamcnc.blogspot.se/2012/01/foam-core-double-sided-milling.html)

curriergroh
03-24-2012, 08:55 AM
If I could get the tabs to work then there would be zero chance of the part moving that is why.

I will try the skin cut again. I have used it before but the part still moved on the final pass, caused binding, and I lost steps.

Can you suggest a way to program using the skin cut and break through for this scenario.

cutting 3/4" plywood, which is actually 23/32"
a 1/4" dia flat end mill

If the material is .7" deep and I set the step down to .25 and the skin to .05 will the program leave .2" of material for the skin or .05"? I ask this because the 3d roughing program only completes step downs that will accommodate the full step down parameter.

curriergroh
03-24-2012, 10:22 AM
If the material is .7" deep and I set the step down to .25 and the skin to .05 will the program leave .2" of material for the skin or .05"? I ask this because the 3d roughing program only completes step downs that will accommodate the full step down parameter.

I can answer this myself. Just did another test. This is the behavior I got.

Settings:
Material Top 0
Material Bottom -.7
Step Down .25
Skin .05
Breakthrough .05

What it did was:
first pass depth .215
second pass depth .215
second pass depth .22 (This put it at -.65)
left .05 thickness for skin
final pass was .1 because of the .05 breakthrough.

So it seems to me that the 2d profiling handles the step down differently than the 3d roughing and I am so glad that it does.

Can anyone offer advise or experience on an appropriate skin thickness and break through depth and feed rate so that the parts don't move? Because that is the reason for doing it right?
I get good cuts at F400 S18000 but better edges with F200 S16500. At F200 the parts move on the breakthrough cut.

I do not have vacuum. Does that make this technique inappropriate?

Does the size/weight of the piece determine if this approach will work?
I am cutting 10-20 parts out of 4x8 sheets.

OCNC
03-26-2012, 12:01 AM
I don't know if you are familiar with Grasshopper within Rhino but the tabs can be easily generated with a rather simple and simple to use GH definition. If you're interested I'll post a screencast on how to use the definition but I won't have any time for that until tomorrow. Basically what the definition does is takes your profile curve and offsets it the radius of the cutter and then breaks that offset curve into suitable subcurves to allow tabbing to be created in madCam using the 'Skin Cut' and 'Break Through' options. I don't know how complex your parts are so can't say for sure how much it will help but it might be a starting point to a solution.

Chris

curriergroh
03-26-2012, 07:23 AM
That looks very helpful. Can you post the definition file?
I'm pretty good at reading GH components but if you could elaborate on the description it would be helpful.

Is the GH path being used for just the last pass or all of the passes?
Is MADCAM still using the 2d profiling strategy or is it using the along curve strategy?

Thanks.

OCNC
03-26-2012, 08:12 AM
Is the GH path being used for just the last pass or all of the passes?
All the passes.


Is MADCAM still using the 2d profiling strategy or is it using the along curve strategy?

The original curve is offset by the cutter radius and then the centerline option is used.


That looks very helpful. Can you post the definition file?
I'm pretty good at reading GH components but if you could elaborate on the description it would be helpful.

I meant to attach the file last night...anyways here it is. It was written using GH 0.8.0066. I think it will be backward compatible to any version 0.8.00xx but I'm not positive about that. Here's a quick screencast (http://www.screencast.com/t/OQHwbyEK) that should be enough to get you experimenting. I'm off to work right now so it will be some hours before I'm back at the computer. Let me know if you have more questions or if you find you have certain profiles that don't work correctly.

curriergroh
03-26-2012, 11:47 AM
I've received a lot of help on this forum on many topics and this was spot on.
Thank you for the file. It is working on the first set of profiles I tried. The webcast also explained what you meant by using the skin cut to make tabs.

If I wanted to share this file who would I attribute it to?
Most GH files this useful usually have a Creative Commons text box in them.
If I modify it in any useful way I will update this post.

Thank you.

OCNC
03-26-2012, 01:54 PM
If I wanted to share this file who would I attribute it to?
Most GH files this useful usually have a Creative Commons text box in them.
If I modify it in any useful way I will update this post.

Thank you.

You're welcome. I spent all of about five minutes on that. The credit has to go to all those people who have shared their knowledge and experience on both the cnczone and the grasshopper and rhino forums. It's just the continuation and enhancement of that activity. I've already got a couple of ideas on how it might be improved. In any case I'm glad to hear that it's useful to you.

Chris

curriergroh
03-26-2012, 01:59 PM
Can you share any experience on the differences between Rhino's offset behavior as compared to what madCAM would produce.

I'm noticing some differences in the generated curve in spaces that are at or near to the cutter diameter size, where madCAM goes in further and the Rhino offset takes a more averaged path, for example a dog leg type slot in material.

williamsmotower
03-26-2012, 02:49 PM
Is grasshopper something you purchase?

curriergroh
03-26-2012, 02:54 PM
No, it is free for users of Rhino. It is a plugin.
One of the many reasons to use Rhino is the ability to use plugins to extend its capabilities.
Grasshopper gives designers the ability to produce complex parametric designs or to create rule based operations for other purposes like tabbing.
It is graphic based and easy enough to pickup by following online tutorials.

Grasshopper - generative modeling for Rhino (http://www.grasshopper3d.com)

Some people are even skipping CAM software and writing GH definitions that will produce gcode.

Grasshopper is a major reason for the growing interest in building CNC routers, laser cutters, and additive machines.

OCNC
03-26-2012, 07:57 PM
Can you share any experience on the differences between Rhino's offset behavior as compared to what madCAM would produce.

I'm noticing some differences in the generated curve in spaces that are at or near to the cutter diameter size, where madCAM goes in further and the Rhino offset takes a more averaged path, for example a dog leg type slot in material.

Can you post a graphic to illustrate? I can imagine that there could be an issue when the radius of the curve is less than or within the drawing tolerance of the cutter radius. If you were makeing a dog-leg type slot in material why would tabbing be necessary?

OCNC
03-26-2012, 11:15 PM
Here's a screencast (http://www.screencast.com/t/S2dHszD4L)for another GH definition that doesn't use an offset curve. It may improve the accuracy of the cut. The file is attached below.

OCNC
03-28-2012, 12:22 AM
Here's one more go at the tab problem. Attached is a Rhinoscript that does the same thing as the previous GH definition. It uses the profile curve to generate the interrupted profile curve. There are three successive command line requests. The first is to select the profile curve, the second is to indicate the number of tabs to be placed and the third is to specify the tab length. The result is nearly instantaneous and may ultimately be easier to implement than the GH method. If you want the options to be 'sticky' and carry over from the previous use I can add that. The easiest way to test the file is to just drop it onto an open Rhino window. This will immediately put the script on the command line. If it proves useful you may want to embed it in a toolbar button. Look at the Rhino Help file for info on how to use Load Script and Run Script commands if you're not already familiar with them. Let me know if you need any further help with the script.

Chris

svenakela
03-28-2012, 07:29 AM
Here's one more go at the tab problem. Attached is a Rhinoscript that does the same thing as the previous GH definition. It uses the profile curve to generate the interrupted profile curve. There are three successive command line requests. The first is to select the profile curve, the second is to indicate the number of tabs to be placed and the third is to specify the tab length. The result is nearly instantaneous and may ultimately be easier to implement than the GH method. If you want the options to be 'sticky' and carry over from the previous use I can add that. The easiest way to test the file is to just drop it onto an open Rhino window. This will immediately put the script on the command line. If it proves useful you may want to embed it in a toolbar button. Look at the Rhino Help file for info on how to use Load Script and Run Script commands if you're not already familiar with them. Let me know if you need any further help with the script.

Chris

That's what I have, a custom button in my own toolbar that makes tabs with a Rhino script. But I rarely use it, as I wrote before I use skin cuts instead.