X & Y shift while cutting plywood

[rickbw]

Recently I've been attempting to cut a couple models out of 1/4 inch plywood 9and also 6mm). I've been using a 1/8" two fluted straight bit @ 14000RPM and 3 ips feed rate.

The bit cuts fine when cutting straight lines. However when it attempts to cut a circle (approximately 1" diameter) the machine shakes and appears to "jump". from then on the pattern gets cut incorrectly (in wrong areas) and after checking the X & Y has shifted by about an inch each.

Any ideas what is going wrong?

Thx!

[bleeth]

Well,you are definately losing steps. Is this a PRS Standard? If so it should handle this. You could be out of square mechanically and/or loose bolts somewhere. This could also be a grounding issue. The other part could be communications related. Have you run a speed test?
How deep are you cutting and exactly what kind of bit is it? Are you using a dust control system? (grounding question). A circle that size would probably be running slower than 3ips due to ramping.
On creating the circle did you create the circle as arcs and save the toolpath as SB inch/arcs? What software are you using to create your shapes?

[jerry_stanek]

check to see if all your steppers are plugged in and working. I had one of my x come unplugged and was doing the same thing.

[rickbw]

How do you check the steppers? Thanks!

[rickbw]

Dave,

It is a new Desktop (picked up 1 month ago in Durham.

I am using a Festool vacuum in the Desktop for dust evacuation.

I am cutting 6mm or 1/4 plywood.

I am using Aspire and the circles are from a model from Woodmarvels (Jon has cut it on a Desktop with no issues in the past).

The bit is a carbide 1/8" staright endmill with two flutes.

[robtown]

Do an air cut with the file. (Set the Z a little high and run the file with no wood loaded)

If it doesn't do it when you do that, try running the cut file half as fast at 1.5 inches/sec

[rickbw]

Rob,

Sounds good, I'm off to try it now!

[rickbw]

OK, I went to the machine and zero'd X, Y & Z so that I could run an "air cut".

After I loaded the file the spindle moved and I quickly rec'd an error message which stated;

"Missing Comm Return. Hit OK to attempt to continue" after hitting OK, I get a quit message from the Shopbot software and after hitting enter, the shopbot software exits. The actual Shobbot desktop continued to run / spin and I shut down with the red stop switch.

I actually rec'd this same message once before and I rebooted the PC - could this be part of the problem?

Thanks.

[bleeth]

Yep. What do you get as comm percentage when you run the speed test?
Under utilities go to diagnostics. Click on the speed test logo, click on it, shut down SB3, and then run it.

[rickbw]

Thanks for the help and the patience with a Newbie - I click on Utilities and then Diagnostic Tools. A window pops up with windows explorer - I then click on the SpeedTest file and it asks me to find a Shopbot (Comm Port Number) - it then does not find anything (states "No Port Connected to aan active Shopbot was Fond!) and then basically I'm stuck.

Am I doing something wrong?

[rickbw]

I rebooted the m/c and then reran the "air test". The spindle shook when it got to the circle in the toolpath. I then redid the toolpath with 1.5 ips and ran the air test again. The spindle shook again (only this time at a slower speed).

I'm really stuck and unfortunately have my two sons with me for Christmas - I was really looking forward to showing off the Shopbot. I guess things don't always work out as planned...........

[jimmya]

what program did you use to make the Circle? It could be loaded with nodes.
Just a thought.
Jimmy

[bleeth]

I have a feeling you are having an issue with the USB port from your computer to the control box. There is quite a bit of info on the forum about this. That being said the fact that you are using the desktop model could have some special issues that I am not aware of as all of my experience is with the other models which use a whole different controller and motors. Regardless I believe it should still be finding your tool. Maybe one of the SB desktop experts will notice this and be able to help out prior to their opening on Tuesday.

Note to Admin: Perhaps we need a whole new forum section dedicated to desktops.

[rickbw]

The file actually came from WoodMarvels & Jon has run it several times without any issue.

[rickbw]

Earlier someone mentioned to check the steppers were plugged in and working properly - any idea on how to do that on a Desktop?

[paul_z]

Rick,
Two things come to mind (what's left of mine):

Disconnect the wires to the steppers and move the spindle/router by hand over the entire travel of the bed. (I'd always do this if I moved a machine.) There should be no binding anywhere. If there is, it needs to be addressed before working further down the list of possibilities.

A second possibility is that your acceleration values may be way off. Try cutting an L shape with each leg 5" long and parallel to the x and y axis. Use a pencil to mark each axis where the machine starts and stops. Do this as an air cut at 1.5"/sec as Rob suggested. The machine should rapidly but smoothly slow to a stop at the intersection of the legs. Without hesitation, it should accelerate back up to speed and cut the next leg. The distance traveled on each axis should be 5". (If the acceleration values are way off, the distance traveled may be off due to missed steps.)

Paul Z

[rickbw]

Here is an update - I sent an email to Ryan at Shopbot and he responded with his cell phone (great customer service on Christmas Day!).

I ran the file with a new Samsung laptop and still had the problem. I tried with and without a USB hub. I have sent the file to Ryan and he is going to run it tomorrow for me.

Also, I found out that in order to run the speed test in diagnostics you need to be in preview mode. When I attempted earlier I was in cut mode. Anyway, my speed was only 47 on the laptop and 53 on the desktop. (the desktop is a dedicated machine just purchased to only use on the Shopbot. Scores were pretty low ...........

[WoodMarvels.com]

I cut this model twice (few refinements were needed after the first cut) and had no issues described by Richard at all - you can see the video that it goes rather smooth and I'm using the cheapest plywood I can find.

http://www.woodmarvels.com/1911-ford-model-t-torpedo-runabout-cnc.html

We are both using a ShopBot Desktop acquired around the same time using the same bit. If it works for me, it should work for him.

Anxious to hear what Ryan comes-up with.

Jon

[bleeth]

Your comm speed number is way too low. If this is the kind of number you are getting (I assume you figured out which port you are hooked up to) then you are down to a couple of things. You definately need the hub and it needs to be installed properly. As I recall you need to load software for it. Are you sure you have a high speed USB hub and not just a switch? You also may have too many other services running on the computer. There is information on "stripping" a dedicated computer of extra goodies elsewhere. Several bottors have had good results with "black viper" suggestions.
If all this is good it is possible there is a problem in the controller card. SB can diagnose that.
Note previously the instruction to run the comm test with SB3 SHUT DOWN.
I don't think problems in the file are the issue.

[dana_swift]

"Wrong", may not be the correct term. But if you have not prepared your PC to be a control computer you will have troubles almost guaranteed.

Turn off all unnecessary system services. Go to BlackViper.com to get a list of what services can be safely disabled. Disable all non-critical services.

Disconnecting from networks reduces background activity, especially if you don't have a firewall between this machine and the internet.

And disable screen savers.

Use USB 2.0 (or 3.0) with a hub. That seems to improve the comm speed. (I have no idea why this would not work the other way around..)

Those three things will do wonders for the COMM reliability. The speed test gives a good clue about how reliable the USB connection is for time sensitive data with the computer you are using.

I have never used a desktop, but I presume the standard bot interface CPU is in use. If so, all the above applies.

When you ran SB3 the first time, the system had to find the USB comm port. If you cant find it in the speed test program setup, you must have one or nothing would run at all. Run the SB3 program and look under utilities diagnostic info. The port number the bot is using is listed in the second block of numbers below "Control Box Firmware", then below the line "IniVersion".

Something is not what it should be, if this does not get it running smooth, give tech support a call. I dont know if SB is open today or not, but give them a call and leave a message. Someone will get back to you.

And rest assured that it can be straightened out. When you have a new machine and its not behaving the feeling of "maybe I made a mistake" is hard to overcome until it is running properly. Then you will find the machine behaves very predictably, and you will most likely be delighted with the purchase!

Most of us have had a problem or two to deal with like that- but they go away. The forum is a fantastic resource!

Hope that helps!

D

[WoodMarvels.com]

We found once source of issues... seems that PartWorks is replacing my splines with nodes... billions of them. I didn't have any cutting issues regardless of nodes but does anybody know of a way to either

"replace nodes with splines"

or

"don't replace splines with nodes"

from within PartWorks? That would at least remove one possible source of problems Richard is having. I've attached the imported DXF outputs from within Illustrator CS3 and PartWorks 3.0 so you can see the difference in how the mesh is imported... both are imported from the same DXF file generated by 3DS Max 2012 to be AutoCAD 2000 compatible.

[rickbw]

Thanks for all the help so far. last night I spoke with Ryan and we fixed the speed issue. I just needed to add a D Link powered hub. The speed is now 72.7 - Still after running the files I get the "shakes". It appears that the circles are loaded with nodes and the Shopbot shakes thru attempting to get to every node. We are working on attempting to clean up the files. thanks again for all the help.

And BTW - I am using a brand new (cheap) e machines desktop that I was sure not to add any screensavers or 3rd party programs. It is dedicated to the Shopbot.

[WoodMarvels.com]

Think we found the solution.

What was happening is that when I imported my DXF file from 3DS Max
into PW... PW adds nodes everywhere. When I import my DXF into Adobe
Illustrator THEN import the AI file into PW... the splines seem to be
saved and not replaced with nodes. Importing DXF into PW creates
nodes, importing AI into PW keeps splines... crazy!

Still doing testing but hopefully all goes will with Richard now, seems to have been a deadly mix of machine and file issues.

Jon

[srwtlc]

Dxf's will do that to ya. Eps exports from CorelDraw will also retain original nodes. If you happen to do an offset in PW, your offset will be made up of many nodes. One way to lessen them is to use "Fit curved to selected vectors" and choose bezier curves.

[WoodMarvels.com]

If it wasn't for Richard, I never would have known about this issue Scott... so all this was a good thing regarding my design process for ShopBot CNCs. I use PartWorks just to do tool pathing, not design. He's since sent me an e-mail that everything works fine now, machine and file wise :)

Jon

[bleeth]

Good you have it solved. The worst is when you have several problems with one project but getting the com speed where it needs to be is critical to everything you do. Anyone following this thread should take note that not any USB hub will work. It does need to be powered and high speed. Even then one may work better on your computer than another or even better in a different port.

[rickbw]

Agreed on the hub issue. I tried several different hubs and the only way I got the speed above 70 was to use a powered one.

[adrianm]

Whenever possible I always import and export using EPS. It's a much cleaner format than DXF in my experience.

[WoodMarvels.com]

I'd really like EPS as well - it's the same format that works with most laser machine Adrian though it doesn't save me any time. I've manually converted (redesigned) 20 laser ---> CNC designs so far with 100 to go!

I expect to do some fresh designs that are basically identical whether they are laser cut or CNC'ed in a few month by integrating the lessons learned from both technologies as right now, conversion/testing take as long as making the original design!

I just provide the PartWorks file along with DXF - they can make their own if needed. I've found DXF works with most CNC/laser machines around the world but I've never had any body asked me to provide EPS for CNC though I see the option in PartWorks.

I'm happy Richard found this issue with my files NOW instead of when I got to the 100th one... backtracking is a pain!

Jon

[bleeth]

Jon:
It sounds like the nodes are coming in the 3ds max export to dxf. I go from Acad 2008 quite a bit and don't have that issue with too many nodes in curves. If 3ds max can convert lines/arcs to polylines that may help.