ShopBot not cutting accurately!

[MitchTalmadge]

Hi guys! Back again with another problem with our school ShopBot :) Here is what is happening; nearly every file I cut now is a bit inaccurate. What I mean by this is that lines aren't cut where they should be, they always seem to be offset just a little bit. Sometimes it seems like it cuts too far, sometimes not far enough. It's difficult to explain in words, so I will let the pictures do the talking.

Here is a test file I made in ArtCAM. The idea was to draw a bunch of shapes and then connect them with lines. Here is what it looks like on the computer:
25123

And here is what it looks like when cut:
25124

Notice that the line connecting the bottom of the star to the bottom left box is completely offset, also if you zoom in, some of the lines don't attach to the corners of the shapes.

As another example, here is the Arrow of Light on the computer:
25125

And after cutting:
25126

You can see in the tail of the arrow how it messed up a lot, also in the rays of light, etc. Lots of messed up lines on that one.

Some useful info:

I am running the motor at 16,000 RPM
Move speed is 50 in/min
Plunge rate is 28.5 in/min
The cut depth in those pictures is about 0.03 inches.
I am using the original, white control box that says "ShopBot" on the front in blue.
I believe we are using a 4' x 4' PRT
Software version is 3.1.7.
Ramp settings are default.
Tool being used is a 5/8 inch 90 degree V-Bit.

I thought this may have been caused by the machine having a hard time cutting through the wood, so I tried it with a 0.015 inch Step Down, and that didn't really change anything. Even when cutting just barely into the wood, it still messes up.

What is going wrong? Thanks for any help!! I can supply any more info needed.

[bleeth]

Check your pinions. One or more may not be tight on the motor shafts.

[steve_g]

Mitch…
Tell me more about your cutting strategies… are you telling the software to cut inside, outside or on the line? It appears as though you have vectors that aren’t closed and the software is cutting left or right of the line. This can be exaggerated when using a V bit as the offset is greater with more depth.
Try cutting the vectors “on” the line and see what you get…
SG

[Kyle Stapleton]

Can you preview you toolpaths? If you can you should, the preview will give you what will be cut and if your preview looks like your cut, your bot is ok.

[MitchTalmadge]

@bleeth
Thanks, I will check this! :)

@steve_g
I generate the toolpaths in ArtCAM to cut along the line, not inside or outside of it. Thanks for the suggestion!

@Kyle Stapleton
Good suggestion! I'll try that! Thanks!

[knight_toolworks]

on the line can be a issue too depending on what direction it cuts. have two liens side by side cut one one direction one the other and you will see.

[MitchTalmadge]

on the line can be a issue too depending on what direction it cuts. have two liens side by side cut one one direction one the other and you will see.

Didn't know that! I'll try that out! :)

So, I checked the pinions today and the x-axis pinions were perfectly fine, but the y-axis pinion was completely loose! I could spin it around on the shaft of the motor, and I could even push the entire gantry a little bit while the pinion was in the rack! It's odd, because I remember having to re-tighten the y-axis pinion not too long ago. Maybe the pinion is wearing out. Either way, the problem seems to have gone away after re-tightening all of the pinions :) Thanks for the help everyone!

Where can I buy a new pinion in case the y-axis pinion is wearing out?

[MogulTx]

After ensuring you have closed vectors- another question I might ask is" Are you telling it to use the VCARVE function? VCARVE is great, but you need to have the geometry input correctly into the tool data base. Otherwise, it might think you are using an infinitesimally small cutter. Or a really large one! And it makes cutting choices based on the geometry of the bit. If you select the standard "Profile Toolpath" it will cut on, inside or outside - as you select those options.

From looking at it, I would first be checking for vectors that are not closed. Then I would examine for extra lines or line fragments or specs (depending on how you brought the "artwork" in for tool pathing.) When you say you generated it in ArtCAM, what do you mean? HOW did you generate it? For example, you may have told it to trace a bitmap or something and it could have gotten some erroneous data from that- which would need to be eliminated. You might have imported a DXF that lumped in some erroneous data that was on another layer that you didn't see... look for simple little errors like that by clicking on the vectors and examining the type and density of line that gets highlighted.). I would then start looking at mechanical issues.... loose pinions or bolts, poorly performing motor. Bad VU setting's... or some other issue...

Good luck. You will have this one little issue fixed in no time and will be off to the races!

Keep learning!

Monty

[srwtlc]

Mitch,

Here's a recent thread post that will answer your pinion purchase (http://www.talkshopbot.com/forum/showthread.php?21547-Variation-in-Calibration-%28X-amp-Y%29&p=180447#post180447) question. Also, use a little blue loctite on those pinion grub screws.

[MitchTalmadge]

After ensuring you have closed vectors- another question I might ask is" Are you telling it to use the VCARVE function? VCARVE is great, but you need to have the geometry input correctly into the tool data base. Otherwise, it might think you are using an infinitesimally small cutter. Or a really large one! And it makes cutting choices based on the geometry of the bit. If you select the standard "Profile Toolpath" it will cut on, inside or outside - as you select those options.

From looking at it, I would first be checking for vectors that are not closed. Then I would examine for extra lines or line fragments or specs (depending on how you brought the "artwork" in for tool pathing.) When you say you generated it in ArtCAM, what do you mean? HOW did you generate it? For example, you may have told it to trace a bitmap or something and it could have gotten some erroneous data from that- which would need to be eliminated. You might have imported a DXF that lumped in some erroneous data that was on another layer that you didn't see... look for simple little errors like that by clicking on the vectors and examining the type and density of line that gets highlighted.). I would then start looking at mechanical issues.... loose pinions or bolts, poorly performing motor. Bad VU setting's... or some other issue...

Good luck. You will have this one little issue fixed in no time and will be off to the races!

Keep learning!

Monty

Thanks for all the tips Monty! I used a Profile Toolpath, not a V-Bit Carving. The first test was made using the tools in ArtCAM, simply drawing circles and boxes and such. The Arrow of Light was a bitmap image. I'll check to make sure that all the paths are closed :) I believe a loose pinion was causing my problems, but I haven't had time to fully test it yet. I did let it run for a minute and it seemed to run much better than before though! I'll be testing it all in the morning, so we'll see how it works out! :)

[MitchTalmadge]

Mitch,

Here's a recent thread post that will answer your pinion purchase (http://www.talkshopbot.com/forum/showthread.php?21547-Variation-in-Calibration-%28X-amp-Y%29&p=180447#post180447) question. Also, use a little blue loctite on those pinion grub screws.

Thanks for that post! Super helpful :) Good idea on the loctite.

[MogulTx]

Mitch,

I got to looking at the cuts on my computer- (I was on my phone this afternoon)... now that I see the deviations... I would have to strongly suspect loose or worn
pinions, also. Don't want t sound like a broken record, but check those out first!

[MitchTalmadge]

Mitch,

I got to looking at the cuts on my computer- (I was on my phone this afternoon)... now that I see the deviations... I would have to strongly suspect loose or worn
pinions, also. Don't want t sound like a broken record, but check those out first!

Alright, thanks!! :)

[MitchTalmadge]

Everything works now, thanks for everyone's help!!

Here's a picture of the most recent Arrow of Light carving:
25171

It's perfect! All I had to do was re-tighten the y-axis pinion. The accuracy on this machine is incredible.

Thank you everyone! Fixing this was very important, and I'm glad it worked. :)

[bleeth]

Glad we could help. I would suggest pulling all pinion grubs and getting a bit of Loctite in there if you haven't already.
Pinions do wear and you should have a spare set on hand. (SB sells them and ensures you get the right ones) Comparing the existing to a new one is a good way to see if you have wear. For you guys it would likely be an annual replacement.
There is a general maintenance schedule in the shop-bot docs that if you haven't already printed out would be a good idea.
Considering that it is a school you may want to convert it to a calendar chart with checkboxes, date done and name/initials.
You would be leaving a "legacy" for future students while you go on to your further education.
Keeping up on that schedule can prevent a lot of costly problems coming up in the future.