Nasty resonance / rattling - possible assembly error?

[MitchL]

Our high school has a PRSStandard that's basically ownerless (wood shop classes are no longer taught, the bot was purchased only a couple of years ago and seldom used).

We (school's robotics team) have basically inherited it.

I am starting to wonder if it was assembled correctly (the limit switches weren't correctly installed, for example).

There's a nasty rattling noise that you can hear in the following video:

http://www.youtube.com/watch?v=5IB2NeJ2ktI

The video is an air cut, router off, so all you're hearing are the carriage motors.

It's mostly present on the left-hand (Y+ side) X axis carriage and on the Y carriage.

- The pinions do have a small amount of dirt, but it's not terrible.
- The rattling occurs everywhere on the table, so I don't think it's rack or pinion wear (the machine's basically brand new).
- There is some backlash that's either in the gearboxes or possibly a loose set screw on the pinion.

The rattling seems to be introducing unacceptable vibrations into the cut, particularly when I'm cutting aluminum. I'm cutting at 60IPM / 0.005" per pass, so it should be a light touch from the router's perspective.


So: Should I be taking the motors off, inspecting the pinion set screw, and getting them back on nice and tight?

Any other assembly issues I should look into?

Thanks a bunch! I'm looking forward to giving our ShopBot some much needed TLC before the robotics season heats up.

/Mitch.

[MogulTx]

OHHHHH! That is awful!

Have one of the Techs from shopbot listen to this. A couple years ago, I was running a PRT that was loud and jumpy and the final diagnosis was blown Zeiner ( sp?) diode(s) on the board. This was the old style board- but bad connections (maybe incorrect connections?) to the drivers might do this to you. You might have the wrong pinion gears on the motors ( z is often different from X&Y and one may have been installed on the wrong motor?)
But it sounds awful- and should almost hum as it is running around with the router off...


Get their professional opinions and do some check out. You won't be sorry.

[MitchL]

OHHHHH! That is awful!

Have one of the Techs from shopbot listen to this.
...

But it sounds awful- and should almost hum as it is running around with the router off...

Yeah, it hurts to listen to it. The shop is a huge echo chamber, which enhances the effect :-)

I'm a hobby CNC builder on the weekends - the machine I'm currently building is very ShopBot-like (rack and pinion, gearboxes, nema34 motors). My machine's not done yet, but my experimental carriages move smoothly and quietly with very little backlash - I figured the ShopBot should be at least as smooth!

Get their professional opinions and do some check out. You won't be sorry.

OK, i'll pursue that - I am not certain our ShopBot is still under maintenance anymore. (actually, I'm so new to ShopBot I'm not certain there even _is_ a maintenance program, but I assume so!).

I'll submit a request to support via the website and see what happens.

Thanks a bunch!

/Mitch.

[bleeth]

This sounds like a combination of ingredients.
First: SB support is for the life of the tool and transfers with ownership. So contacting them is definitely in order.

Now:
This puppy sounds completely out of level and square. You need to start by verifying the x rails are parallel, straight and level, and the correct distance from each other. You then need to move on to the y rails, and then verify that the gantry is perpindicular to the x axis. Your final step (although this issue will not make much noise) you need to verify your z is plumb.

There is ample documentation on that in the shop-bot docs (setting up your PRS) and also an article on squaring by Gary Campbell in the columns section.

It will be a very "fiddley" process, but the result is all of your v-wheels will ride smoothly on the rails and with the control box off AND the motors unplugged when pushing it around by hand. (Never push it by hand with the motors plugged in-you WILL blow out drivers). If you disconnect it now and push it around you will find you have wheels not sitting correctly in rails, binding, and generally messed up. When properly tuned the whole thing will run smoothly and quietly. When all of the above is done, then make sure your pinions are properly seated and tight, as well as not overly worn.

Oh yeah: With the motors on try to move each side of the gasntry and see if they are both on. If one side doesn't want to move, and the other does, then you have a loose pinion, or a blown driver. Motors rarely go bad.

[bleeth]

By the way: This sounds exactly like a louder version of the typical resonance that PRT's make. It is so evident in them that Bill Young, of Shopbot, wrote a program to move the tool using a "musical note" program based on a small keyboard and had them playing happy birthday for shopbots tenth anniversary.
As you are new to the forum, my machine started as a PRT standard, and over the years I upgraded it to a PRS Alpha. When it went from Old control board standard to 4g resonance got quieter, and when it went to PRS it got very low. When it went to an Alpha resonance virtually disappeared.

Do make sure all frame and rail bolts, nuts, and screws are tight.

[bleeth]

Doc links:

http://www.shopbottools.com/ShopBotD...%2012%2031.pdf

http://www.shopbotblog.com/index.php...he-prs-gantry/

[MitchL]

By the way: This sounds exactly like a louder version of the typical resonance that PRT's make. It is so evident in them that Bill Young, of Shopbot, wrote a program to move the tool using a "musical note" program based on a small keyboard and had them playing happy birthday for shopbots tenth anniversary.

That's awesome. I've got a script somewhere that converts MIDI files into G-Code that I use to play music on my home (Mach3-based) CNC. It always amuses :-).

As you are new to the forum, my machine started as a PRT standard, and over the years I upgraded it to a PRS Alpha. When it went from Old control board standard to 4g resonance got quieter, and when it went to PRS it got very low. When it went to an Alpha resonance virtually disappeared.

Yes, I'm new to the forum, new to ShopBot, but not new to CNC. I'm here to learn how to take care of our ShopBot from the experts!

The ShopBot is owned by the school, so getting money for upgrades might not be the easiest thing to do. Worth pursuing though, just in case. We do have the newer control box AFAIK. I'm not super familiar with the differences between Standard and Alpha (will do my research) - I believe ours is a standard based on its purchase date.

Do make sure all frame and rail bolts, nuts, and screws are tight.

Will do, and will read the links you posted and do as many measurements as I can to see how level and square it is.

/Mitch.

[bleeth]

You can tell if it is a standard or an Alpha right away from the motor numbers.

Standard: 9412KTG

Alpha: ASM98AAT7.2 (Although you may have 3.6/1 and not 7.2)

[MitchL]

You can tell if it is a standard or an Alpha right away from the motor numbers.

Standard: 9412KTG

Alpha: ASM98AAT7.2 (Although you may have 3.6/1 and not 7.2)

I'm not near the machine but happen to have a close-up of the motor.

It's the standard one, model A7328-9412KTG.

Is the upgrade to the Alpha just new motors and a controller? I suppose I should contact ShopBot for details.

It's tempting to swap out the motors and switch the controller to Geckos/Mach3, but that's the hobbyist in me. Need to keep this one pure ShopBot :-).

/Mitch.

[bleeth]

Yes. I wouldn't call it "just" though. Many thousands of bucks for new Alpha motors and drivers, even if you buy them direct from Oriental and build your own control box to handle them.
You may already have Geckos. Standards are, although there is some "special" shopbot construction of them. SB3 software will run g-code, but since the design software that writes Mach also writes SB code no real reason to. A long way back, before SB started running Geckos (It's a long story) some guys built a gecko box and ran Mach and there are still a few of them out there. Some of them insist there Mach runs better than SB3, and for some of the more touchy releases of SB3.xxx they are probably right. For your machine, check your software and if it 3.6.4x I wouldn't change it. The 3.8xx has nothing in it you need and has caused some people who upgraded issues.
I ran those motors with Gecko 202's for years on SB software with no problems. Yours probably has a SB version of the 203's. The motors are custom built for SB and have Tapered hob gears built in (3.6/1)