Official Luthiers Forum!

Owned and operated by Lance Kragenbrink
It is currently Thu Mar 28, 2024 4:03 pm


All times are UTC - 5 hours





Post new topic Reply to topic  [ 9 posts ] 
Author Message
 Post subject: Surface "ripples"
PostPosted: Sun Aug 31, 2014 12:40 pm 
Offline
Walnut
Walnut

Joined: Fri Dec 03, 2010 11:26 am
Posts: 39
First name: Jeff
Last Name: Kosmoski
City: Beaverton
State: OR
Country: USA
Focus: Build
Status: Semi-pro
I've noticed this interesting artifact in a number of different pieces I've made on my CNC, and I'd like to get rid of it.


Image

Image

These are actually pretty subtle. I had to position the camera and the lighting to get them to show up in the photo. They sand-out, eventually.

Because the cutter is actually traversing back-and-forth at 15 degrees from the X-axis, I'm thinking it's some kind of strange artifact in the X-axis of my machine (ShopSabre 3636) - either the bearing ways, or the lead-screw. Or ??

Any and all theories, conjectures and thoughts on the issue greatly appreciated.

Thanks in advance,

Jeff


Top
 Profile  
 
 Post subject: Re: Surface "ripples"
PostPosted: Sun Aug 31, 2014 11:10 pm 
Offline
Contributing Member
Contributing Member
User avatar

Joined: Thu May 12, 2005 5:46 am
Posts: 2931
Location: United States
What packages are using to surface your model with and cut it?
It may be that the software doesn't do a true spline CAD or CAM, but uses a series of short line segments that approximate a spline within some predefined tolerance of deviation.
Sort of like you were cutting a circle with short line segments using G01 instead of interpolating it a G02.
Just a guess.

_________________
Jim Watts
http://jameswattsguitars.com


Top
 Profile  
 
 Post subject: Re: Surface "ripples"
PostPosted: Sun Aug 31, 2014 11:52 pm 
Offline
Contributing Member
Contributing Member

Joined: Sat Feb 09, 2008 2:39 am
Posts: 519
I agree with Jim on this one. I have seen the same thing using Rhino and Madcam and discovered I did not have my mesh tolerances set tight enough in Rhino. The same thing can happen in you machine from true stl triangle meshes if the mesh density is not heavy enough, only it will show up as triangles instead of what you show in your photos.

Check your cad mesh/model tolerances.

Mike


Top
 Profile  
 
 Post subject: Re: Surface "ripples"
PostPosted: Mon Sep 01, 2014 1:23 am 
Offline
Koa
Koa

Joined: Fri Jan 25, 2008 9:55 am
Posts: 982
Location: Traverse City Michigan
saw dust on the rails...

_________________
Ken


Top
 Profile  
 
 Post subject: Re: Surface "ripples"
PostPosted: Tue Sep 02, 2014 9:28 am 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Fri Jan 15, 2010 3:34 pm
Posts: 2047
First name: Stuart
Last Name: Gort
Country: USA
Focus: Build
Status: Semi-pro
There may be a function in your software to:

1. Create arcs in lieu of line segments.
2. Reduce the minimum length of these line segments. You'll still get lines but they will sand out easier
3. Create arbitrary line segment lengths, which will eliminate all the points falling in a row.

If you have a toolpath editor you can go through and observe each line and endpoint to make sure this is happening in your toolpath. If you can read your g-code well then you can see it there too. This COULD be happening out at the controller.

I think in any case you're going to find that these lines sand out easier than the tool marks.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic


Top
 Profile  
 
 Post subject: Re: Surface "ripples"
PostPosted: Wed Sep 03, 2014 9:18 am 
Offline
Contributing Member
Contributing Member

Joined: Mon Jan 28, 2013 8:29 pm
Posts: 113
First name: Rand
Last Name: Kennedy
State: CO
Focus: Build
Status: Semi-pro
That area looks like it has the smallest radius of that top surface ? I'm guessing it is a relatively small amount of material, a few thou at most that is being left uncut. It could be chordal tolerance in the cam settings causing it to square off instead of follow the radius. Does your cam simulator show the faceting ? I'd like to think it should. The cam I use shows all the tooling marks and has a function to display excess material not removed by the toolpath that still needs to be removed with a smaller or different tool or strategy. I have had a surface in Solidworks which looked good there and passed checks, which my cam software did not like the quality of. Going back into the model clearing the selections in the dialog boxes for boundary/loft etc and putting the same geometry back in made it recreate the surface better and everything was OK. If the meshing/curvature combs show something complex going on in that area, the geometry might be a little too busy. Like Stuart says, I'd look at the g-code for what it is trying to do in that area, maybe just do a test toolpath with North-South direction so it is easy to look at. Should just be short G01 moves that follow the surface radius. What CAM are you using ?


Top
 Profile  
 
PostPosted: Fri Sep 05, 2014 10:40 am 
Offline
Walnut
Walnut

Joined: Fri Dec 03, 2010 11:26 am
Posts: 39
First name: Jeff
Last Name: Kosmoski
City: Beaverton
State: OR
Country: USA
Focus: Build
Status: Semi-pro
Thanks for all of your input on this. I appreciate it.
I’ve since had a chance to investigate this with the tech support folks at MecSoft, and it looks as if the problem had to do with my program settings - particularly with regards to "Part faceting tolerances".

Additionally, and maybe just as importantly, if I had set my display settings to "Flat shading", and not "Smooth shading", I might have caught the issue beforehand. Oh well, we live and learn (on good days!).

Here's a screen shot from VisualCADCAM with the faceting tolerances set at .002"
Image


And here's a screen shot with the faceting set at .0001"

Image

I haven't actually machined the new version of this part yet, but I suspect this change should clear things up.
Thanks again for your input.


Better living thru better surfaces!

Jeff


Top
 Profile  
 
 Post subject: Re: Surface "ripples"
PostPosted: Fri Sep 05, 2014 10:45 am 
Offline
Walnut
Walnut

Joined: Fri Dec 03, 2010 11:26 am
Posts: 39
First name: Jeff
Last Name: Kosmoski
City: Beaverton
State: OR
Country: USA
Focus: Build
Status: Semi-pro
Ken McKay wrote:
saw dust on the rails...


Man, I have to admit I had no idea what you were referring to when I first read this. For some reason, the Bob Dylan song "Blood on the Tracks" was the first thing that popped into my head, and I thought you were obliquely referring to some C&W song I'd never heard of.

However, the coffee kicked in, and I get you now.

My ShopSabre has sealed linear bearings, and I tend to be kind of anal about keeping 'em relatively clean... so I wouldn't tend to suspect this.

Thanks anyways!


Top
 Profile  
 
 Post subject: Surface "ripples"
PostPosted: Fri Sep 05, 2014 12:15 pm 
Offline
Koa
Koa

Joined: Fri Jan 25, 2008 9:55 am
Posts: 982
Location: Traverse City Michigan
Ok good. Mine are not sealed so it can get bumpy if i am not careful


Image


Sent from my iPhone using Tapatalk
Ken

_________________
Ken


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 9 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 10 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
phpBB customization services by 2by2host.com