SHIFT ISSUE

Anything and everything CNC-Shark-related

Moderators: ddw, al wolford, sbk, Bob, Kayvon

Post Reply
stephenb79
Posts: 22
Joined: Wed Aug 04, 2010 4:23 pm

SHIFT ISSUE

Post by stephenb79 »

The last few projects I have ran came up with miscuts and by miscuts I mean in comparison to the drawing or tool path a hole or feature is off a pretty reasonable amount. With this last project I was cutting a five inch circle and I litterally watched the shark pro shift in the negative Y axis (mid cut) about the width of the 1/4" cutter. Please view the attatched file and see if this has happened to anyone else...
IMG_0313.JPG
see the step it created?
Last edited by stephenb79 on Mon Jul 23, 2012 10:02 pm, edited 1 time in total.

stephenb79
Posts: 22
Joined: Wed Aug 04, 2010 4:23 pm

Re: SHIFT ISSUE

Post by stephenb79 »

The story goes on with after realizing there was a problem with the end result I would replace the scrap piece :x with a fresh blank, reload the exact same file, run the path again, and the piece would come out perfect. I just ran that same circle pattern after blowing out the controller and driver real well. I set my zeros considerably higher than the work piece so I could watch the cutter path. I noticed no "shift" in the path this time. Should I keep running it until my comfort zone is re-established or risk more scrap?

Ausworkshop
Posts: 75
Joined: Sun May 08, 2011 4:13 am
Location: Australia

Re: SHIFT ISSUE

Post by Ausworkshop »

Maybe the feed rate was too high and the stepper lost track while trying to push the router. What feed/plunge rate/pass depth did you run for the 1/4inch cutter?
I would try running it again at a slower pace and see if it still happens. I've had a similar thing happen just because I was trying to take of too much material and the stepper motor looses position without knowing it. If you think the feed rate is a reasonable speed then try reducing the pass depth and see if it improves.
I think as a general rule you should never try to take off more than the diameter of the bit in one pass depth. For example if i am using a 6mm cutter i would not try to cut more than 6mm depth in one pass. Two passes at 3mm would be even better. Depending on how hard the material is and the profile it is cutting. I find most people try to run the cnc machines too fast. If you have experience using a router by hand you can feel how much pressure is required to cut at certain depths and if you try to take too much off you will not get a very good result and you can feel/hear the stress on the router when pushing through the cut.
A slower feed rate may take a little longer but there is less to have to clean up after cutting and there is a lot less stress on your router bearings, stepper motors etc.
“It’s not that I’m so smart,
it’s just that I stay with problems longer.“
Albert Einstein

stephenb79
Posts: 22
Joined: Wed Aug 04, 2010 4:23 pm

Re: SHIFT ISSUE

Post by stephenb79 »

cutter 1/4"
pass depth.110
step over .100
mat'l thickness 3/4
total passes 7
speed 45%
Along with feel is noise. When hogging material you can here it. With the shark I always start at 25% and work my way up paying close attention to the pitch of the cutter. I wasn't hogging mat'l in this case. I was kind of watching in boredom and observed the shift occur. In almost two years of owning this I have never seen this occur. The only other issue I came accross was a poor connection on the x motor harness. When cutting diagonals and circles the machine slows down by itself anyways or so it looks. As mentioned speed was 45%. Could dust and heat be a factor? These stepper's don't have an encoder which is a let down on peformance but a boost in our wallet so it is what it is. Hopefully blowing it out helped. I will check my connections again and put it into super turtle mode while i run it. Will update with the outcomes. Thanks for the response,

Don't Servo motors have built in feedback(encoders)?

stephenb79
Posts: 22
Joined: Wed Aug 04, 2010 4:23 pm

Re: SHIFT ISSUE

Post by stephenb79 »

Issue isn't resolved. I slowed the machine down to 35%. I was able to make it through two pieces on my panel and on the third piece the machine made it to a half ellipse and I noticed it glitch a little in the tool path. When it made it back to the the start point it was off the width of the cutter again. Help!

Eagle55
Posts: 788
Joined: Sun Nov 20, 2011 8:44 pm

Re: SHIFT ISSUE

Post by Eagle55 »

I think I would first double check the connection to the stepping motors at the couplings ( not highly suspected but very possible). But what I would suspect the most is possble binding or dragging in the bearings or what ever arrangement where the carriage is attached to the lead screws. I have seen on the forum where material has built up in there and cause a lot of friction causing similar problems. I think at that point the poster had to disassemble and clean it out before proceeding. You may be able to get by with lubricating all of you moving surfaces including the leadscrews (y axis being the hardest to reach of course) Maybe someone else with more first hand experience will speak up, but thats where I would be seriously looking at.

Roger

PS all of your cutting spec look ok to me, although 45% is kind of a meaningless statement without knowing 45% of what. I am assuming that you probably design using the default feed for that tool which is most likely 100 ipm, in which case 45% of that would be 45 ipm which would be in the range that I would use and recommend.
CNC Shark HD ~ Control Panel 2.0 ~ Windows 7 & XP
Located in West Tennessee near the Tennessee River
http://www.eaglecarver4.com

stephenb79
Posts: 22
Joined: Wed Aug 04, 2010 4:23 pm

Re: SHIFT ISSUE

Post by stephenb79 »

I was on the phone with next wave support and he had me check the coupler for loose set screws. All were fine. When the controller is off I can move the x axis freely accross the gantry. I will check the bearings. I noticed today the problem is getting worse. When I jog the -x it freezes up as if it were out of movement even though it is in the middle. The forty five percent comes from the slider position. I do use the default settings for the cutter. How do we know when the motor is bad?

stephenb79
Posts: 22
Joined: Wed Aug 04, 2010 4:23 pm

Re: SHIFT ISSUE

Post by stephenb79 »

Swapped the x and y harnesses. Now the y freezes up in the negative. Pretty sure its the controller now. I'm sending it in to be looked at. Thanks for all the posts guys.

stephenb79
Posts: 22
Joined: Wed Aug 04, 2010 4:23 pm

Re: SHIFT ISSUE

Post by stephenb79 »

I reseated the wires on the punchdown blocks inside the controller. Back in buisness. Talked to a different tech rep. He saved me 180 bucks plus shipping. Thank you!

Eagle55
Posts: 788
Joined: Sun Nov 20, 2011 8:44 pm

Re: SHIFT ISSUE

Post by Eagle55 »

Punchdown block??? Which machine do you have. I never opened my controller box (yet) but that almost sounds scary. Is it the telephone lines coming into the box? LOL Just kidding.

Roger
CNC Shark HD ~ Control Panel 2.0 ~ Windows 7 & XP
Located in West Tennessee near the Tennessee River
http://www.eaglecarver4.com

Post Reply