PRS Z-Axis Problems

[martmar]

Greetings,

I have been running in to a nagging problem with sharp internal corner cuts since I purchased my bot (4 months ago) and have not been able to complete a single successful cut to date the machine plunges in the corner making an indention when I use sharp internal corner cuts option that I can’t seem to prevent from happening. I have a BT 48 Standard, and I am writing in the general area because I believe the PRS all have the same z-axis. I have been working with Frank form shopbot and I tried every which way to adjust the eccentric bearings and I feel I got them just right, I believe but the problem still precise. I once tried to put pressure on the spindle to see if it would help the problem and it helped, but when I let it go again, it messes up again. I am wondering if there is something else that I am missing or overlooking. I am using a 60 degree v-bit and I have tested the bit angle accuracy and it is still giving me problems. I have attached a picture of my troubles.

Thanks in advance.


7500

[benchmark]

Marty,

Make sure there on no free play in the Z axis pinion.


Paul

[erik_f]

Maybe your bit is wider that the software thinks it is?

[cnc_works]

Marty, if you were using Mach3 I would be suggesting some combination of CV (constant velocity) problems, ramping, I think, in SB terms. It seems too specifically repeatable to be mechanical. There are others on here who could give you more specifics on how to check your settings.

It is an area of magic, mysticism and frustration, so good luck.

Donn

[dubliner]

Marty, that does look very like a problem I had with "slop" in the Z, albeit hardly noticable when hand pressure was applied. Systematic "tuning" of the z car & alignment wheels took it out. Perhaps that is your issue also.

[dubliner]

Marty, sorry I forgot that I had given you this suggestion before. In reference to the post on the Buddy section, When tuning up the Z, I think I went past correct and still had a problem, its difficult to know or explain "just right". It took quite a few tries and a lot of bad cuts.

[martmar]

Hi Neville,

I want to thank you and everyone for replying to my postings I really appreciate the help. I have been taking your advice about the z car and alignment. Your problem is exactly what I am experiencing, because when I put pressure on the spindle is goes away. I just had a few questions about your experience tuning the z car.

1. Did you use any special tools besides the wrench Shopbot gives you to loosen and tighten the bearings and alignment?

2. Where you able to get all the bearings to move like you wanted them to or just 3 of the 4 bearings.

3. After you got the bearings exactly like you wanted to be, do the bearings keep the same "just right" feeling as the z car travels the whole distance?

4. When you feel the bearings for "just right", on a scale of 1 to 10 (1 being free spinning and 10 being cant move) what would you consider just right?

5. When you hold your finger on the bearings and slide the z car up and down; can you stop the bearings from rotating at any point in the z car travel?

6. Did you use a sequence in tightening or loosening the bearing?


These are the questions I have been beating myself up trying to figure out.


Thanks again.

Marty