Kossel Mini circular objects/ corners small bumps...

Hi everyone

I'm still fairly new to printing & for the most part have been really impressed by my Kossel Mini kit assembled outcome, but something I've noticed now that my eye is getting more critical, is that my prints are being produced with small bumps which appear randomly (all objects but never at the same point on the same objects) I started watching the print more closely when in progress & notice very momentary stops occurring particularly in circular objects. As the print head circles the object it stops for a fraction of a second perhaps at around every 170 degrees on a 2cm diameter object. On a straight run it doesn't happen until it hits a corner, but not every corner, just the occasional random corner. The reason I've noticed it on circular objects is because circles are essentially a series of straights with corners in high concentrations. I think this is just long enough to allow a slightly increased build up of filament that ends up as a small bump on the surface. I don't believe this is intentional but rather an interruption to the movement as the processor gets busy with other tasks such as recalculating or loading the next set of co-ordinates. Is this normal? Is there a way to avoid it i.e. extrusion speed, temperature etc?

My current slic3r settings for 1.75mm PLA are 190DegC .4mm hot end nozzle, Perimeter 30mm/s, infill 60mms/s, travel 130mm/s no brim. These are pretty much the defaults recommended. Any ideas?

Here's what I'm talking about...

You didn't say what electronics you are running and whether or not you are printing from an SD card or via USB connection, but it sounds like either a USB data transfer delay or else you're running a 16Mhz RAMPS/Arduino board possibly with a graphical LCD and red-lining the CPU doing Delta calculations in the round parts.....

I think you have hit the nail on the head. Although I don't know the arduino processor speed, I am running via USB with an LCD so your redlining theory requires further investigation. I'll see whether printing from SD improves things as well. How do I find out what the processor speed is?

If you have the popular RAMPS/Mega2560 (or single board clones like the Megatronics), it is 16Mhz. There's a reason why serious Delta developers are adopting the next generation of 32-bit controllers like the Arduino Due with RADDS or RAMPS-FD add-on boards, Smoothieboard, Azteeg X5, BeagleBone, etc.

I was playing with my Delta/Megatronics running Repetier firmware last night, cranking the speed multiplier on the graphical LCD up until the printer started stalling regularly, and then turning it back slower until everything ran smooth again. If your firmware or host program have the option, don't be afraid to use it to show things down until they run smoothly.....

Yes, it's a ramps 1.4 sitting on an Arduino Mega board. So as you have indicated, it must be 16mHz. This is a real eye opener & perhaps a trap for new players such as myself starting off with a kit. I will now give some serious consideration to upgrading my controller boards. What would you recommend as a reasonably compatible solution for running Marlin with ramps type stepper drivers & I/O?

I'm also looking into my next build & thinking that it might be best to get familiar with more capable electronics that I can move forward with. As you say I might be able to wind down the print speed to achieve better results on my Kossel Mini but for anything new I should try to future proof myself as much as possible. Thank for this valuable insight!

Marlin is a dead-end when it comes to 32-bit processors. Here's a long discussion thread where you can see why:

https://github.com/ErikZalm/Marlin/issues/626

Repetier-firmware *does* support the Arduino DUE processor, and either RADDS or RAMPS-FD cards for stepper controls and stuff. Both take removable stepper drivers. RADDS is based out of Europe with no North American distributor at the moment, and the developer of RAMPS-FD has told people to buy RADDS instead.

All of the other options require new firmware. The Azteeg X5 Mini and Smoothieboard both run Smoothieware, which has Delta support. If you're in North America, Panucatt.com sells the Azteeg X5 for a fair price. I bought one last month, but still haven't installed it in my printer yet. Configuring it took only a few minutes editing one file, copying it to Micro-SD, and putting power to the board. The only down side is that the stepper driver chips (8825) are soldered to the board, but it does 1/32 stepping out of the box. A few of the key players on the Google Deltabot group have Azteeg X5's, and all are happy. I personally think that Smoothieware is the future, if for no other reason than it presents the on-board micro-SD card as a thumb drive over the printer's USB cable (in addition to the traditional serial terminal interface).

I don't know much about the BeagleBone options, but the Google Deltabot group is starting to order BeBoPr boards as a group.

RepRapPro has a DUE-based board available, but their firmware does not support Delta printers the last time that I looked.

Regarding your current RAMPS/Mega2560 setup, if you find that slowing down the speed multiplier stops your random pauses then you can try removing the LCD drivers from your firmware to buy some more CPU cycles back. If it is a full graphics LCD, there is whole development thread here describing how Repetier had to leave out animations and other stuff in their GLCD package to save clock cycles, along with criticism for how Marlin handled the same things in a less than optimal way. You already have the RAMPS board, and it is a stable platform albeit slightly under-powered for a Delta at full speed.....

Thanks for taking the time to explain all this to me. I added the LCD before really getting familiar with what I had & I didn't understand the "hit" that adding a graphics based LCD was going to have. This is the logical first thing to remove to improve my prints but hopefully it will be compatible with a likely Azteeg x5 on my next build with smoothie firmware, so that it will get some use, or perhaps I can sell it on to a non-delta user.

The same exact thing has happened to me, all the same specs and outcomes, I have a mini delta running marlin firmware with the big graphics LCD and for some reason all my curved prints are starting to get pimples. The only thing that I cannot understand is why it was working perfectly at the beginning and then over time it gradually getting worse. Could the board be slowing down with age?

Anyways did you manage to fix the issues by removing the graphics LCD?

Edited 2 time(s). Last edit at 06/05/2014 11:00AM by vcazan.

I just got home and reuploaded marlin firmware without the LCD and the printer is making the curves perfectly and is moving without pausing.

So that confirms that the arduino is not able to update fast enough.

But it does not explain why it was working perfectly for 3+ months with the screen attached and then it started to slow down and loose the speed.

You might want to try Repetier firmware. That's what I'm using with the GLCD, and it seems to be a little bit better optimized. Not a huge difference in performance, maybe 100% down to 98% of redline.....

https://groups.google.com/forum/#!msg/deltabot/jwwNE356D04/NSypwPQ-i0MJ

Per Jeff Short's post in the Google Deltabot group, lowering the Delta_segment setting in his firmware down to 50 helped his printer to fix little bumps on the walls of his prints. Giving up accuracy to keep the CPU/memory load down?????

Quote
vreihen
https://groups.google.com/forum/#!msg/deltabot/jwwNE356D04/NSypwPQ-i0MJ

Per Jeff Short's post in the Google Deltabot group, lowering the Delta_segment setting in his firmware down to 50 helped his printer to fix little bumps on the walls of his prints. Giving up accuracy to keep the CPU/memory load down?????

Thanks for the help I did try lowering the sgments but it still had the issues. I did not go as low as 50 tho. I think its time for 32bit MCU.

Hey, wow that is a lot of info. Anyway, a good way to get rid of the bumps is by disconnecting the bigger smart graphics lcd from the printer and use the computer??? I like using the LCD is there a way to keep it and have smooth prints. My mini kossel set up is as follows: ramps 1.4+ arduino mega, EXTRA LARGE FULL GRAPHICS SMART CONTROLLER , 15amp power supply, using cura as the slicer. However, I have to have my printer hooked up to my pc or else my lcd screen will not power on even though its power by the 15amp power supply. You know what I just need some help. That would be greatly appreciated. The only issue I have is the bumps on my prints and I have to keep the printer plug into my pc for the lcd to power on,

I tried a Poke'Ball and you can see my problem.

In my experience your LCD is not powering up because you are missing the D1 diode, or the D1 diode is soldered the wrong way. Secondly, my first guess for the small bumps and stuff would be your retraction and or retraction speed is too small. Seeing as you are printing a cube, I don't think retraction comes into play too much. Might be the segmentation, but to tell you the truth, I just finished building my own delta style printer and have no experience regarding a delta style printer. I am in the process of printing my first calibration cube.