Been a while since logged in, although been reading up periodically.
Anyway, I've been having a problem with sign foam and chatter using a Shopbot. Design files generated in Corel are exported as AI and brought into Artcam. 3D reliefs, prismatic letters, etc. exhibit more chatter in the finished pieces vs. when I was sub-ing this work out. Gantry stiffness is fine, etc. Know that the foam is being screwed down, no vacuum. Speed are nominal on prismatics, say 2"/min. In other words, mechanics-wise everything seems to be fine. Other CNCers have suggested that Corel's the culprit, but I have my reservations about tiking it might be the AI export mechanism/filter. Still, I look at the number of nodes of text, for instance, after it's been converted to curves and they are acceptibly fine. Methinks it's that fact that the foam is only screwed down and substrate movement is occurring.
Any thought or suggestions as to the source and fix for the problem?
Thanks and kind regards,
Fran
P.S. How's our moderator "Steve" doing these days? Please advise
Posted by Fran Maholland (Member # 3609) on :
Whoops I meant 2"/second, sorry.
Posted by TJ Duvall (Member # 3133) on :
Where do you have the screws? Corners only? And where is the chatter occurring. If you are only holding down the corners you may be getting some "bouncing" of the piece in the middle.
Posted by Mike Pipes (Member # 1573) on :
Have you tried slowing down the feedrate or adjusting the spindle RPM?
My CNC experience is with 4 and 5 axis mills cutting steel and aluminum, but it sounds like you might be trying to "hog out" too much material too quickly, forcing the cutting bit to catch on the material and kick itself back.
Sign Foam is soft (comparatively) but you can still experience the kickback if you're pushing speed to the limit, especially if the router isn't quite as solid or steady. It only gets worse as you cut with larger cutting bits.
Posted by Fran Maholland (Member # 3609) on :
Screws are usually at the extremes. Just did a V-groove and there was a lot of chatter inside the letters. I'm told this is normal, but doubt so. People, without vacuum hold downs, used to double side tape their pieces down in addition to screws. Spindle is a variable speed. Tried all sorts of stuff, speed-wise, and chatter is still there. I can believe it's files orginating from Corel as, for instance, jaggs would show up similarly when cutting vinyl if it's in the linework.
Posted by Kevin Gaffney (Member # 4240) on :
I do a lot of prismatic work in foam, no probs. Can you explain term "chatter" I might be able to help.
Posted by Darren Grefe (Member # 3441) on :
Fran, What spindle speed are you using? Try speeding up the spindle RPM, try reducing the (chip load)IPM or amount of cut. Try replacing the cutter it may be dull. You may need to drop your "Z" and recut everything. Do not be afraid to try things, you should be able to adjust something to achieve the finish you want.
Posted by Joe Crumley (Member # 2307) on :
Fran,
I too am running Artcam on a SB. This unit is about four years old and has been very dependable, however it has a few flaws. I've also experienced the chatter with HDU and other substrates such as PVC and Trupan. Here's my take on it:
Slowing down the feed rate will help, but not solve the problem. I think is caused either by the step-motor feed, which is fixed, or the processor output which also set from the factory. It seems to me, servo CNC units cut much smoother and twice as fast.
Your correct about Corel, it sometimes does generate tons of nodes, however I get chatter on very clean DXF files generated from Flexi 7.5.
Like you I've used the process of elemination to get to the bottom of the problem. Some of my attempts in cludes re-grounding, cleaning and lub, and carrage allignment, and tightening.
I had this problem on my Practical CNC with a homemade vacuum table. It was caused by Z-axis bouncing of the table and substrate that was being excited by too much XY acceleration. Once I slowed down the acceleration and installed some tensioning cables across the frame to increase the resonance frequency all my problems disappeared.
ernie
Posted by Fran Maholland (Member # 3609) on :
Hey, thanks for all the responses especially yours "Joe" since you are on the same (or similar) SB system platform. I'm going over some things with my local SB CNC guru (Doc P). Upon examination and an extreme zoom in Artcam of an EPS file he says he sees potential chatter from the virgin Corel generated file (to EPS), so I'm trying to come up with a file/export formula that minimizes that observation (which may be screen res related). I'm preparing several different versions of same file to see which produces the most desired effect with minimal chatter. I wonder if export over my network and/or transfer via the internet of files can add to the dillema?
I've always designed in Corel for many applications and never observed a problem cutting or large format printing-wise, but CNC is a whole different animal. It is now being suggested to me to design in another proggie more suitble for CNC work, but Corel, understand, allows me to to the full-color conceptuals for presentation purposes... and then I'd have to re-draw the approved design in another proggie like Signlab, for instance, just to get reliable CNC files???? Seems like a duplication of effort. Joe, I'll ponder yours and everyone elses notes here. Still, other recommendations and followups are most appreciated.
Thanks.
Fran (or...errr Robin Hood to Steve Shortreed...hehehe... hey Steve, how the heck are ye? I haven't laughed (and cried) so hard since yonder post of dream of Sherwood... methinks ye'll reprimand me for the postscripted note here, nay?... anyway, best regards to ye and lady Barb if you're reading this)
Posted by Joe Crumley (Member # 2307) on :
Fran,
Here's a suggestion. Try setting your type in Artcam, or doing a basic design there to eleminate Corel from the equasion.
My thinking's there's stepping action going on. If this is true, a slower or faster feed rater, or increasing the spindle speed won't have much affect. The reason being: the impulse which drives the motors is segmented. The motors are called stepping motors for a reason.
I have refined my search from software, to viberation, and finally to the harmonic ballance in the motors.
I've seen this chatter affect at it's worse when cutting 1/2" PVC. The unit has plenty of power and speed so this just shouldn't happen. A second pass seems to clean off some but it's still there.
Happy routing.
J
Posted by Fran Maholland (Member # 3609) on :
Yeah, Joe, that occurred to me, "eliminating the middle man" so to speak. But still, right now, it isn't practical for me to start designing in another program with th faculty I have to design in Corel. I'm not completely opposed to designing in Corel and template re-drawing designs in a more suitable proggiefor CNC. It just seems a waste and I do agree with you that the dilemma probably is machine-related. A nominal and minimal amount of chatter is anticipated depending on the level of machine one uses; that is, High end Multicam vs. SB. What do you know about the new SB with it's alpha motors that might help facilitate the problem; that is, are they a step(pun intended)towards the better cutting servo motors? What machines offer servo motors. I understand the new SB alpha motos are a vast improvement in speed, performance with a contiguous "loop" now available. Please advise of what you know... and thanks again. I'll provide a summary of findings here once the I get a handle on the chatter culprit. Anyone consider "Gremlins"? I hear that since airline security has been enhanced, they've moved into the CNC market... low end, of course. hehehe
Posted by Randy Campbell (Member # 2675) on :
Well it seems Mike P has the right ans.You must be trying to take to much out at one time.I was a tool and die man for six years and did this many times. Posted by William DeBekker (Member # 3848) on :
Fran, I was having Similar Problems at one time also. It ended up my timing was off so when my bit went to change directions the steppers weren't ramping down so I would get a hard stop causing vibration and causing a run out look on my finished piece. Try typing "UP" and see if your computer will re time itself to the controller. (I still use the DOS version as I will never trust windows to run CNC properly.. Some habits will never change)
Was just setting up a cut file and thought of this when I clicked the button.. Far reaching but.. when you cut your file in Artcam are you using Conventional or Climb Milling on I always use Conventional cutting that way the bit actually cuts the material whereas Climb Milling the bit runs backwards (Cant think of the actually Terminology..
[ February 24, 2005, 12:45 PM: Message edited by: William DeBekker ]
Posted by Joe Crumley (Member # 2307) on :
Fran,
Please look at the SB Forum on a post today under Techniques for Drilling, Machining by Lonni Prince.
The gist of this post is much like yours and it doesn't matter if your using the Alpha unit.
I wasn't suggesting you swith design programs, only to do a test.
J.
Posted by Rene Giroux (Member # 4980) on :
I always had problems with files (curves) gnerated by Corel, it would make a polygon out of a circle. I usually output jobs using my Graphics Advantage wich works just fine. But sometimes I have a file that's from Corel, lets say a script, and if I send directly to the AXYZ machine, the edges are going to be jagged. What I found out is that I'll send the file to GA, and add lets says a 0.005" outline and then delete the original lines. The fact that my letters have now been generated by GA and not Corel makes all edges very smooth...
I hate when I forget to do that step sometimes...
Posted by Amy Brown (Member # 1963) on :
We used to have a problem with too many nodes from Corel. You can just reduce the nodes in Corel and get good results as well. Bob Stephens taught me.
Posted by Fran Maholland (Member # 3609) on :
Well, thanks for all the replies (and chatter). Not sure where this is going, but I do appreciate the input. I'll just have to test things out.
Posted by Dale Kerr (Member # 4661) on :
Fran, I run A SB here and when I do prismatic letters I reduce my feed rate to .70/sec I find any faster and I get the chatter. Also I you the same feed rates for Incised letters, that way the machine doesn't get carried away as it pulls out of the letters.
I only use 1.5 - 2 in/sec on my profile cut in Sign foam.
I know sign foam is very soft, but I find the Tool is not stiff enough for any great feed rates so it causes the spindle to bounce a bit. Call me if you want any more help. 613.880.8292 Dale
Posted by Joe Crumley (Member # 2307) on :
Ditto to Dale's technical information.
I was very encouraged SB's new Windows update. The variation in ramping speed will really catch your eye. It's slows down on the exacting small curves, and run back up to normal speed on the strait aways. My first cutting tests looked pretty much the same as the precious DOS version. Not much improvement on smoothness however.
I do love the ability to change the cutting speed, while cutting. Dang it's nice. Sometimes when you have larger profile letters along with smaller deliclate ones, on the same panel, it would be beneficial to change the speed, especially if you can do it on the fly. And you can. Hold down the control along with the < > button to speed up and down.
So far the new Windows version appears to be a big improvement.
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