Official Luthiers Forum!

Solely owned and operated by Lance Kragenbrink
It is currently Thu Nov 23, 2017 7:07 pm


All times are UTC - 5 hours





Post new topic Reply to topic  [ 6 posts ] 
Author Message
PostPosted: Sat Mar 24, 2012 12:26 am 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Thu Aug 04, 2005 7:50 am
Posts: 3143
Location: Canada
Hello people! I am cutting some tricone tops for a customer. I have drawn the files in Rhino and post processed in MADcam. I am having some issues with smooth lines, mostly on the shorter runs. I am using a 1/16" upcut spiral at 80 ipm and .050 doc. I thought the issue may have been speed related but in the 8 polygons inside the tricone I have the wavy cut pattern in each piece that is cut out at the same spot, so this is not a random event as one would expect with bit chatter, etc. I think I don't have some custom tolerance parameter set properly somewhere in Rhino. Anyway here are a few pictures that hopefully will help in advising on the issue.

Attachment:
Tricone.jpg


Here it is in a plywood test run

Attachment:
Bumps2.jpg


You can see the unevenness of the cuts

Attachment:
Bumps1.jpg


And again

Attachment:
Plan.png


And here is the Rhino screen shot.

Thanks

Shane


You do not have the required permissions to view the files attached to this post.

_________________
Canada


Top
 Profile  
 
PostPosted: Sat Mar 24, 2012 6:28 am 
Offline
Cocobolo
Cocobolo
User avatar

Joined: Fri Jun 22, 2007 11:14 am
Posts: 355
Location: United States
A couple of thoughts here--first, you should be able to look at the G code where it is cutting those polygons to see whether or not madCAM told the machine to cut one line or many. If it is programmed at one line when it's cutting the scallops, it's probably a machine issue of some kind. If you run through a simulation in Mach 3 and single step through the G code when it gets to the polygons, it should be easy to spot. It looks like you might be using a radius lead in rather than a ramp on your profile cuts--that can give you all kinds of weird little unwanted, but consistent, scallops.

Good luck!

Dave


Last edited by ballbanjos on Sat Mar 24, 2012 12:18 pm, edited 1 time in total.

Top
 Profile  
 
PostPosted: Sat Mar 24, 2012 10:27 am 
Offline
Contributing Member
Contributing Member

Joined: Thu Mar 19, 2009 10:16 pm
Posts: 188
Location: Bell Buckle, TN.
First name: kevin
Last Name: waldron
City: Bell Buckle
State: TN
Zip/Postal Code: 37020
Country: USA
Focus: Build
Status: Professional
Several things come to mine....

Engage/Retract (Entry/exit ....lead-in/out) of the tool
Precision of following the line with-in the cam program (Intol/Outol in Rhinocam)
Machine post processor is set to broad of a tolerance in following a line/curve....

One of the 3 is probably the culprit.

God Bless

Kevin


Top
 Profile  
 
PostPosted: Sat Mar 24, 2012 12:36 pm 
Offline
Cocobolo
Cocobolo
User avatar

Joined: Fri Jun 22, 2007 11:14 am
Posts: 355
Location: United States
In madCAM, there aren't a whole lot of settings to deal with--you probably know this but if you hit the question mark on the madCAM toolbar and bring up the help page, you can go to the settings chapter and it covers everything.

madCAM has a setting for absolute tolerance--if it is set any finer than Rhino's absolute tolerance, it will default back to Rhino's in use if I understand it correctly. I leave both set at .001" and it seems to be a good setting. Too much finer than that and it takes forever to generate a toolpath and the toolpath it generates doesn't do any better job on the final work. There's also a setting for maximum distance from surface.

There's a good write up on tweeking madCAM at:/http://betterlivingthroughcnc.com/2011/10/14/maximizing-toolpath-quality-with-madcam/.

Other than that, there are the settings that you set at toolpath generation time--ramp lead in vs. radius lead in etc., including distance for these to go.

Dave


Top
 Profile  
 
PostPosted: Sun Mar 25, 2012 11:51 am 
Offline
Brazilian Rosewood
Brazilian Rosewood
User avatar

Joined: Thu Aug 04, 2005 7:50 am
Posts: 3143
Location: Canada
Thanks Guys. And thanks for that article Bill. I am thinking exactly along the same lines that this is an issue solved in Rhino. Here is a picture of four of the Parallelograms that were machined out of the tricone:

Attachment:
polygons.jpg


You can see that the 'bumps' all line up. So that has to be a toolpath issue rather than a random issue with machine rigidity or tool stability (my machine is Precix 49" x 49" table with timing belts and servos with Perske 3.3 kw spindle and is very rigid (about $25K to replace). So the issue is not the equipment but the operator! I have adjusted the mesh controls, surface to edge which I do as routine anways, and will try a couple of the tolerances expressed in the article.

Thanks again guys!

Shane


You do not have the required permissions to view the files attached to this post.

_________________
Canada


Top
 Profile  
 
PostPosted: Sun Apr 01, 2012 12:27 pm 
Offline
Koa
Koa
User avatar

Joined: Tue Nov 28, 2006 1:44 pm
Posts: 1105
Location: Crownsville, MD
First name: Trevor
Last Name: Lewis
City: Crownsville
State: MD
Zip/Postal Code: 21032
Country: USA
Focus: Build
Status: Semi-pro
Hi Shane, have you tried cutting this at a slower feed rate? I have seen some machines that lose precision as the speed increases.

Just something to check out...Good Luck!

Trev

_________________
http://www.PeakeGuitars.com


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 1 guest


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