Noisy Z...

[harryball]

I thought I saw a thread on this but can't find it.

In a previous conversation with shopbot I noted that when jogging from the open table at times my bot sounded very rough and I couldn't identify it... well thanks to the ShopBot lab and S_tunes I found it...

When my bot sings happy birthday it goes daaa da daaa da daaa GRRRRRRRRRR daaa da daaa da daaa GRRRRRRRRR

I tried the keyboard and in Move it sounds normal, in Jog it makes a sound that doesn't sound healthy. It's not the springs vibrating as I used some debris to jamb both of them. It sounds more mechanical like teeth grinding or something.

Pointer to previous thread? Ideas? What should I inspect?

Thanks,
Robert

[Brady Watson]

Robert,
This is and Alpha, right? Power up the Bot and wiggle the X car back and forth. Listen for clicking. Inspect the pinions and look for flat spots worn/raised on the teeth. Chances are you will need to change pinions.

While out in the field I've have seen quite a few Alphas that were ready for pinions. They need to be replaced a lot more frequently than a PRT because the speeds and forces put on the pinions are much greater. I have seen them wear out as quickly as 3 months on production machines running 2 or 3 shifts a day, so depending on your mileage, you may want to replace them at a certain interval. I replace the ones on my machines once a year (both Alpha and PRT)

How are your cuts? Worn pinions can really degrade cut quality...and I believe that some of the complaints about cut quality spoken about recently on Alpha machines is a result of worn pinions; not all, but several...but that's a subject for another thread. Degradation of cut quality may be a good indicator pointing to the pinions.

Now..if the pinions are good and you don't get play or clicking, then it could just be mid-band resonance that you are encountering. All steppers suffer from at least some of this resonance and that could be what you are hearing.

-B

[harryball]

It is an alpha 3 weeks old... very low usage but it was the demo at the IWF... I assume it was a new Z axis. The X & Y movements seem fine and cut quality has not been a problem on side cuts.

Area clears, however, I've been fusing and confusing over. For example, I surfaced my table top clean and then cut a file... the profile cut was a single tool path but I noticed on the spoil board in several places I had cut marks... yet in others none. You can see a recent post where I made some plaques... I'm still having that issue. I cut a plaque that was clean and good... then the next plaque has tooling marks in it where it looks like the Z depth decreased for several passes. I don't think it's the bit anymore. I've been fusing with my holddown and been using a vac for some practice cuts.

I also had an instance where I zero'd Z and ran a cut file that began by cutting all the way... but when it finished there was a skin left. My caliper shows the board to be from .484 to .486... but the skin thickness was .009... still scratching my head on that one.

When you say pinions, do you mean inside the stepper motors or the roller bearings the cars ride on?

I plan on closely going over the Z axis tomorrow so I'm fishing for suggestions of what to look for.

Robert

[richards]

The pinion gear is the toothed spur gear attached to the shaft of the stepper motors with set screws. It's the gear that rides in the toothed rack.

[Brady Watson]

Robert,
1st check that the V-roller bearings on the Z axis are contacting the T-rail properly. Wiggle the router and see if there is excessive play. If there is, this could have happened if you didn't loosten up the Y-car extrusion when you installed it. When you tighten up the 4 big bolts to attach the Z axis it can spread and throw the Z out. You may have to adjust the v-roller cam bolts to get proper contact or loosten up the extrusion on the Y and redo it. You have to watch that you don't mess up the Z-axis pinion preload against the gear rack when you adjust the v-rollers. Too tight and the Z pinion wears out prematurely, too loose and it wears out AND affects cut quality from the pinion 'slipping'.

Your 'Z drop' could be a result of a warped spoilboard. Considering all of the rain that we had last week...I'd put my $ on that unless it has been happening consistently. Since this is a new machine, I am going to go out on a limb and say that it's time to resurface the spoilboard with the CR commmand. After doing this, try cutting again and see if you get the drop.

On a side note, take your digital caliper and measure your Zzero plate. Note the thickness & open up C:\SBParts\Custom\my_variables.sbc In there change the &my_ZzeroThickness = 0.131 to match the thickness that you measured on your plate.

-B

[harryball]

OK, problem identified and solved, she now plays happy birthday!

I spoke with Chris at ShopBot and checked out a few things. I discovered the spindle was rock solid moving side to side but with only a little pressure I was able to wiggle the z axis up and down as much as 1/32" of an inch. Looking closely revealed the pinion was only about 70% meshed to the teeth. It was actually 130% engaged since it was off to the side away from the motor. I removed the Z and found that one of the set screws was loose, the other was tight but not holding it solid.

The pinion shows some excessive wear from riding the teeth edges. Chris is sending me another pinion. In the mean time I filed the largest burr off and checked the pinion over. I corrected the placement and made sure the set screws are tight. It now moves smoothly and sounds correct.

I know this was causing the noise and believe it caused the cutting quality issue for area clears. I even understand why the down spiral bit showed the most variation in cut quality. When the down spiral was used the force was lifting the spindle which was able to lift due to the slacked engagement. The 1/32" (maybe a tad less) seems about right for the variations I was seeing.

Anyway, I'm going to re-square the Z axis and make some sample cuts to see what I obtain this time.

I'm glad I found it. Thanks for all the help and suggestions.

Robert