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Author Topic: Milling marks????????  (Read 3979 times)

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Milling marks????????
« on: September 02, 2010, 07:57:05 PM »

Cut some corian today and experienced something I've experienced before, but I'm afraid this customer is expecting a smoother product.

PRT96, geckos, mach3, 15K rpm, 100ipm, 1/8" ball nose w/.009 stepover.
File is their solidworks file right into Mastercam. The raster is very nice, hardly feel it with thumbnail. Straight fillets aligned parallel with raster are smooth, but all other fillets have little gouges in the edges of the letter.

So, it's gotta be in the machine or Mach settings...any ideas?

The photo is of an approx. 1" patch. The little bit of foil is just to help my camera focus.

http://www.cncworks.biz/images/omega.jpg

Offline Sam

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Re: Milling marks????????
« Reply #1 on: September 02, 2010, 09:20:46 PM »
It could be any multitude of things. If you have cut other projects with the same parameters, (feedrate, stepover, etc..) and achieved good results, then that should rule out the machine. If you have a scrap of material, you could slow the machine way down and cut a few lines to see if it still digs in. It could be the way they went about making the file in solidworks. My first impression of the picture, was that something is either not set correctly in mastercam, or the surfaces are not of a high enough resolution. Have you tried different settings for the filters, gap settings, etc. in mastercam? How about additional toolpaths for cleanup such as restmill, pencil, or finish leftover? You might be able to zoom way in on the toolpath, inside mastercam while stepping through a backplot, to see if the gouges are actually in the toolpath. If I were you, I would post your problem at CNC Zone. I think Mike Mattera is one of the Mastercam fellows there that knows a thing or two. Sorry I can't be of any more help! Maybe someone else will chime in with some advise. Let us know what you find out, I'm rather curious myself. Good luck!
« Last Edit: September 02, 2010, 09:22:36 PM by Sam »
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."
Re: Milling marks????????
« Reply #2 on: September 03, 2010, 02:11:20 AM »
If I had to guess I would say the backlash in the z is not repeatable.

Offline Tweakie.CNC

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Re: Milling marks????????
« Reply #3 on: September 03, 2010, 05:34:59 AM »
Just a thought, well a wild guess really, I had a problem which looked similar to this which was caused by tiny particles welding to the cutter tip and making unwanted gouge marks. This was with polycarbonate - the same problem did not occur with Plexiglass / acrylic.
Could you perhaps try a different material, with a higher melting point, and then see if the same problem occurs.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Milling marks????????
« Reply #4 on: September 04, 2010, 07:43:57 PM »
I engrave a lot of Corian, and get the same effect; even with a step-over of .005.  My suspicion is that it is caused by the original raster image (BMP - JPG - etc.).  To check, enlarge a simple raster drawing until the individual pixels can be seen in the pronounced height changes (light to dark colors).  It would help to see the original picture to confirm if this is the cause.  The effect is probably not noticeable in wood, but Corian engraves much more fine details than wood and other materials.

Regards All,
John Champlain
Re: Milling marks????????
« Reply #5 on: September 06, 2010, 01:03:37 PM »
Thanks so much for all the input.

The original file is not raster, but drawn in Solidworks.  And, fortunately corian has little tendency to melt at any feed/speed.

Macoma, that comes closest to a possibility, but again, it is so similar between the two machines.

The progress I've made is primarily only as to what it is not. First of all, it is not machine specific. I ran the same tool path on my smaller, more precision CNC and got the same results. So at this point the only thing there is in common is Mach3...with one slightly possible exception. Both machines have spindles and I know the weight on the smaller CNC's z is probably close to the limit and on my Shopbot the springs just barely keep it neutral when the power goes off, but it would be pretty amazing for the cut pattern between the two machines to be so similar with so many variables unless it was generated by the same thing.

I checked the Solidworks file and could see nothing obvious, though I am far from a SW expert. I closely examined the toolpath lines generated by Mastercam and saw nothing to account for the gouges, fiddled with the gap settings and still no change. So, what setting in Mach3 might influence this z transition?

Man, it is always that last little bit of performance that is the hardest to track down, eh?

Donn
Re: Milling marks????????
« Reply #6 on: September 06, 2010, 04:59:30 PM »
It occurs to me that if you have any slight amount of play where your router can "shake" a micro amount (and most all cnc routers do as far as I know) when it comes to an abrupt stop or change of direction, then this might explain the gouges.  Try running the program at a slower velocity to see if it reduces the problem.

Regards,
John Champlain
Re: Milling marks????????
« Reply #7 on: September 06, 2010, 05:13:47 PM »
Thanks for thinking for me John, I need all the help I can get.

However, my small CNC is so rigid I cannot imagine much wiggle.  My Shopbot could possibly.

Donn
Re: Milling marks????????
« Reply #8 on: September 06, 2010, 07:30:43 PM »
Donn,
Have you tried with CV turned off?  I don't know if CV affects the Z axis moves, but I know it can affect the X to Y moves.  Anyone else know?
John Champlain

Offline Sam

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Re: Milling marks????????
« Reply #9 on: September 06, 2010, 10:30:04 PM »
Can you attach the code, or mastercam file?
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."