Z registration help

[jwinslow]

Hello All -

Looking for some help dialing in some very fine Z movement.

I am experiencing these depth changes and looking for help in removing them. Running this on a PRS Gantry Alpha 96-48-8 with an ATC. I've taken the plunge and feed rates way down and have experienced some improvement but still get the below results.

STAR BAR
This circle of stars sit on a concave base. One side of the circle is slightly raised, the other side of the is slightly lowered below the surface.
star registration.jpg

LETTERS
Looks like Z height is a struggle on these letters.
letter registration.jpg

[kbraat]

I would check the tightness of the z axis motor pinion gear. I experienced a similar issue on my older PRT and that was the solution. The loose gear was introducing backlash.

Hello All -

Looking for some help dialing in some very fine Z movement.

I am experiencing these depth changes and looking for help in removing them. Running this on a PRS Gantry Alpha 96-48-8 with an ATC. I've taken the plunge and feed rates way down and have experienced some improvement but still get the below results.

STAR BAR
This circle of stars sit on a concave base. One side of the circle is slightly raised, the other side of the is slightly lowered below the surface.
star registration.jpg

LETTERS
Looks like Z height is a struggle on these letters.
letter registration.jpg

[evan]

Brady Watson wrote a great blog on ramping values and how to tune the ShopBot

[Brady Watson]

You gotta power up the machine and shake it down. Starting at the spindle, lift it, push, pull, wiggle and both listen and feel for slop. The following are the major sources of backlash/hysteresis/slop in these machines:

1) Z pinion gear to rack lash. Pinions wear and the mesh loosens up. Loosen up the four 3/16" socket head cap screws holding the Z motor on the back of the YZ car and pull it out of mesh with the rack, then slide it all the way back in to engage into the rack and tighten it up. Check your work. If it's still sloppy, do it again.

2) The YZ car bottom V-rollers that ride on the bottom of the beam are loose. Get the funny looking flat wrench that came with the tool and adjust the eccentrics on the bottom V-rollers until they touch the bottom rails. Then tighten an additional 1/8 turn. Don't make them too tight...When they are loose, the entire YZ car can lift up.

3) Depending on the year and generation of PRS tool you have the adjustment procedure varies...Have a close look at the bearings that guide the Z axis. Move the Z 1" off the spoilboard and try to wiggle the spindle in all directions. Move it up another 1" and repeat this procedure. Keep advancing in 1" increments until you've covered the entire stroke, noting any slop in the Vroller bearings/rails that guide the Z. On later tools, the rails are female and the adjustment is on center wheel of the 3 wheels that ride on the rails. Take care not to cut yourself on the female rail...they get razor sharp.

[jwinslow]

This is super - I'll check it out. Thank you!

[jwinslow]

Brady Watson wrote a great blog on ramping values and how to tune the ShopBot

Super - thank you.

[jwinslow]

I would check the tightness of the z axis motor pinion gear. I experienced a similar issue on my older PRT and that was the solution. The loose gear was introducing backlash.

Looks like I need to take the tools in next time! :-) I'll take a look. Thank you for your time on this.

[jwinslow]

You gotta power up the machine and shake it down. Starting at the spindle, lift it, push, pull, wiggle and both listen and feel for slop. The following are the major sources of backlash/hysteresis/slop in these machines:

1) Z pinion gear to rack lash. Pinions wear and the mesh loosens up. Loosen up the four 3/16" socket head cap screws holding the Z motor on the back of the YZ car and pull it out of mesh with the rack, then slide it all the way back in to engage into the rack and tighten it up. Check your work. If it's still sloppy, do it again.

2) The YZ car bottom V-rollers that ride on the bottom of the beam are loose. Get the funny looking flat wrench that came with the tool and adjust the eccentrics on the bottom V-rollers until they touch the bottom rails. Then tighten an additional 1/8 turn. Don't make them too tight...When they are loose, the entire YZ car can lift up.

3) Depending on the year and generation of PRS tool you have the adjustment procedure varies...Have a close look at the bearings that guide the Z axis. Move the Z 1" off the spoilboard and try to wiggle the spindle in all directions. Move it up another 1" and repeat this procedure. Keep advancing in 1" increments until you've covered the entire stroke, noting any slop in the Vroller bearings/rails that guide the Z. On later tools, the rails are female and the adjustment is on center wheel of the 3 wheels that ride on the rails. Take care not to cut yourself on the female rail...they get razor sharp.

I'll be taking the tools in next week and will give everything a wiggle. This is a brand new maching with about 40 hours in total on it from install so I'll be interested to see what I find. I'll let you know for sure.

[jwinslow]

Hi Evan - went in and adjusted some values based on the blog - very helpful, thanks.

Here is the new settings but am still getting some "drag" along the Z as it attempts to make up the height. It has improved the result but still getting drag/striation.

v2 Original Ramp Speeds.jpg

Here is the result. Improved but still there and still noticeable.

image2 (1).jpg
image0 (2).jpg

[jwinslow]

Thanks Brady - went in with tools and worked the issue but did not find any slop. Tightened an x axis motor on the rail but could not find any more issues.

One thing I have noticed is that the z depth lifts ever so slightly off the surface on one side of the round plaques I am cutting - as though it's lifting as it approaches near "0" on the Y axis.... ???