1800x1200 Gantry Vibrations

Tehvine
Posts: 1
Joined: Mon Dec 26, 2016 7:12 pm

1800x1200 Gantry Vibrations

Postby Tehvine » Sun May 28, 2017 7:13 pm

Hoping maybe someone has run into this issue. I have the big 1800x1200 XY and I have issues with squiggly lines during raster engraving anywhere in the middle 2/3's of the X axis. Maybe this is just a characteristic of such a large machine, but I am wondering if anyone has any ideas on how to eliminate it. Immensely slowing the machine down and/or using unilateralism will mostly cure it, but, the speed is needed.

I've tried removing my e-chain from the gantry, adjusting belts, adjusting rollers, but none of it gets rid of the issue. The X axis beam is just not rigid enough to avoid flexing due to its size. It's almost like it needs a truss on the back side of it to make it more rigid. If I cut something small right at either extreme end, it's fine. That's just not usable for production as just about everything is bigger than that little area.

In real use it's not extremely obvious as most things we do have decently large engraved areas or such a small scan gap that the gantry doesn't accelerate enough to cause a problem. If I do a test run with a scan gap of 0.75, my return swing on x-swing raster will be so wavy that it almost touches the raster line above and below at the edges of the engraving where the gantry is stopping and reverberating. It'll get more exaggerated as it progresses and shakes more.

I realize at this point that such a large machine is probably best suited to large cutting jobs only and we may need something smaller for precise small cuts. 100W tube in this machine coupled with this issue means I couldn't dream of cutting card stock or paper since it'll just annihilate it if i go slow enough to eliminate the wavy lines. Sort of like using a sledgehammer to drive a brad nail. Just wish I had known before building it, but, you live and learn.

If i'm missing something, let me know! I'm open to suggestions. I've played around with all sorts of accel and jerk values. I do have to play with X backlash a bit to clear up x-swing engravings. Just a lot of mass and belt length to deal with.

Techgraphix
Posts: 475
Joined: Fri Jan 20, 2012 1:39 pm
Location: Appelscha, the Netherlands
Contact:

Re: 1800x1200 Gantry Vibrations

Postby Techgraphix » Mon May 29, 2017 5:52 am

You may try to find a better setting for the microstepping. this might solve some or all fibrations as motors can run smoother.
Can you have one or more worn bearings in your rollers?
If there is room for it, you can always enforce (truss) the gantry with a piece of U-profile glued (temporary) to the gantry and see if that works.
Too much tension on the belts or an excentric drivewheel can also introduce som oscillations.

Kees

Tech_Marco
Posts: 4372
Joined: Mon Jun 15, 2009 3:00 pm

Re: 1800x1200 Gantry Vibrations

Postby Tech_Marco » Mon May 29, 2017 11:37 am

Post your parameters here and I may help
Also, what micro stepping are you using on the stepping motor drivers?

Marco

SWMS
Posts: 158
Joined: Mon Jan 06, 2014 4:28 am

Re: 1800x1200 Gantry Vibrations

Postby SWMS » Fri Aug 25, 2017 9:22 pm

What kind of steppers are you using? I recently upgraded to closed loop steppers after a fire and the lower resonance of the closed loop steppers is amazing!

Edit -

Just woke up and all my best ideas are when I wake up.

You are basically experiencing what machinists call chatter. If the simple steps don't work you can try counter intuitively turning the speed up and the power up till you pass the resonance of the gantry. You can do your own little graph too.

cnc cookbook has a nice section on resonance. Admittedly a lot of it isn't relevant as we don't have a router and bits.

http://www.cnccookbook.com/CCCNCMillFee ... hatter.htm


So the main issue as you know is machine resonance. If you can't strengthen the gantry can you isolate what's causing the problem and move it somewhere else? You may have to redesign part of your machine for this. Move the x axis motor somewhere? For example, I've seen cnc machines with the x axis motor actually on the carriage, moving with the cnc cutter. Maybe the extra weight on the head will stop the resonance.

Your other option is - I know Wikipedia isn't fantastic but it's a starting point.... - passive isolation

Pads or sheets of flexible materials such as elastomers, rubber, cork, dense foam and laminate materials.
Elastomer pads, dense closed cell foams and laminate materials are often used under heavy machinery, under common household items, in vehicles and even under higher performing audio systems.[citation needed]

I hope you sort your problem out. I have a homebrew 600x1200 so I have a gantry as big as yours and I've had plenty of wobble issues.

Pm me with pics of you like. It would be good to see the design variation and maybe we could bounce ideas off each other.

Ryan.


Return to “CO2 Laser Discussion”

Who is online

Users browsing this forum: No registered users and 1 guest