What's my problem with the Z height

[magic]

The simulation looks good,

Is it the router, the Bot ... how do I check?
Both are 4 years old. The coin is 2 inches in Diameter.
The rise and fall of the Z is approximately .002
The tool had a step over of .003. I used a 1/16 ball nose.
Took 3 hours to cut .1 deep.

OR... Should I be using a different strategy then the entire coin with a 1/16 ball nose? but that still wouldn't explain the differences in cut depth.


.
8004

[Brady Watson]

You most likely have some backlash in the Z pinion to rack. Careful adjustment should correct this, unless the pinion is also worn.

-B

[magic]

Hello again

So The first thing I should try is moving the Z all the way up so I can put an allen wrench in there then re-seat the pinion.

How do you know if the pinion is worn?
How much pressure should I exert against the motor upon tighting the set screw?

[Brady Watson]

No. You can adjust the Z-axis backlash via the v-roller bearings with eccentric bushings so that the T-rail (on a PRT) moves closer to the rack gear. It takes some patience, good observation skills, and careful adjustment of ALL 4 (or 8) bearings to get it right. You do not need to mess with the motor mount itself, as you will not be able to finely adjust backlash this way. You will need to slightly loosen the concentric bushings EXACTLY the same number of turns (really partial turn) and tighten the eccentric bushings to both take up the T-rail to bearing slop as well as move the T-rail/rack gear closer to the pinion. The 1st time it takes a while to figure it all out. TAKE YOUR TIME & OBSERVE before doing ANYTHING...Then just do it. Do not overtighten the eccentric bushing adjusters - they will spread the 2X2 steel towers on the Z axis and louse everything up...Also verify that the Z axis to spoilboard is perfectly perpendicular, as it is easy to make the Z axis ride up & down like a trapezoid.

Before you do anything, grab the router/Z-axis, with the power ON, and try wiggling the Z axis up & down. Do you hear or feel 'ticking' or any slop? If so, you have to take up that slop in the Z. If not, you are giving it up somewhere else & you will have to track it down.

Is the pinion dry or lubed? Can you see stepped wear marks on it? If it is dry, it's shot. Order up a new one.

-B

[magic]

No wear, no slop... I'm beginning to think it's in the Porter cable router... but trying to push something in and out ,002 and measure or test it seems too finite.

[stevem]

The gearboxes on the stepper motors have between .006" and .012" backlash. The PC router has .002" axial play and .005" radial play when new. You're not going to eliminate backlash by adjusting the pinion to rack engagement. You can measure the backlash by placing a dial indicator against the various parts and moving them towards and away from the indicator.

Did you do a roughing pass to hog out most of the metal first? Use a .125" bit for that.
The ball nose bit should be used only for the finish pass, to remove the last .005" of material.

[magic]

I'll try it.