Kossel mini not printing straight lines.

Hello Folks

Last week i completed building my first delta...a kossel mini! It was certainly a lot of fun, i printed all the parts and sourced everything else myself including making my own carbon pushrods in a jig to ensure they are exact to each other as possible within reason.

I am running Marlin firmware, i bought my electronics from Sintron so i also got a hold of the firmware they use so i'm using that, of course of made dimension adjustments for offsets and whatnot to suit my own build.

I have checked the frame verticals with a large carpenters square and it's good and within a 1mm from top to bottom and is also square to the bed. The nozzle lays down a decent first layer, not perfect but good enough till it comes time to fine tune later on.

*The Issue* The issue i am having is if i print a 100mm x 100mm or anything else with flat sides three of the sides will not be straight, they curve in a little for some reason. I have tried another file that is not a square but has a lot of flat surfaces and the same thing. I have checked everything mechanical, belts pulley's you name it. I spoke to James from Sintron and he believes one of my stepper is losing steps and he thinks that's what is causing the slight curve in what should be straight lines...i tested the electronics before putting them in the printer and the steppers all looked to rotate and sound the same, but who knows.

I thought i would post here for some idea's as i have spent about a week googling and messaging back and forth with the Sintron guys without coming to a solution, i have three new steppers on the way to try but i dunno, gut feeling says it's not that but i am willing to try it anyway.

Apart from this issue everything else is working fine and i printed a nice vase in the process to make me feel better and hide my dodgy straight lines

I'd appreciate your help

Did you check the vref values of the stepper drivers or the set screws on the timing pulleys?
If one of your steppers are skipping steps, the z-layers would probably not align together properly but since you said you managed to print a nice vase, the problem may lie somewhere else?

Hi yes i have checked and set all Vref values on stepper drivers with a multimeter and i have checked grub screws on motor pulleys...all fine. Gotta say though i'm pretty stumped as otherwise the delta prints beautifully, it doesn't make sense to me at all at this stage as to why it's happening and not affecting anything else print result wise.

I have been spending some more time going over the delta checking everything once again. My corners are printed and i think my "X vertice" is twisted off axis by a couple of mm. I noticed this because the clearance of where my belt runs through the carriage is not the same as the other two carriages, if i twist the x vertice with my hand gently then the clearance opens up to match the other two carriages.

I have aluminium corners ordered from Leap3d in the states which should be here any day now, i will rebuild and resquare everything up with those and see what the result is, can't believe i didn't spot it earlier.

I am pretty sure this could be the exact course of the issue i am having with my straight line?

*EDIT* I have fixed up the twist, no change! now this thing is doing my head in haha, nobody seems to know what is wrong with it and i have no idea...very disheartening after all i've put into it so far to be stuck like this.

Edited 1 time(s). Last edit at 09/11/2016 12:20AM by silverbullet.

SilverBullet,

Welcome to deltas. They are frustrating, and often difficult to get to print straight.

It's unlikely to be missing steps. More likely is one or more of the following:

* Towers not parallel
* Towers twisted
* Bed not at 90 degrees to the towers
* Diagonal rod value in firmware not matching physical measurement
* Delta radius in firmware not matching physical measurement
* Rod end distance different between carriage and effector (causing effector tilt at different areas of the bed)

Those are the usual suspects on a delta, good luck finding the issue.

Quote
nebbian
SilverBullet,

Welcome to deltas. They are frustrating, and often difficult to get to print straight.

It's unlikely to be missing steps. More likely is one or more of the following:

* Towers not parallel
* Towers twisted
* Bed not at 90 degrees to the towers
* Diagonal rod value in firmware not matching physical measurement
* Delta radius in firmware not matching physical measurement
* Rod end distance different between carriage and effector (causing effector tilt at different areas of the bed)

Those are the usual suspects on a delta, good luck finding the issue.

I've checked and rechecked all those things, that's why it is doing my head in. There is physically nothing i can find wrong, corner to corner measurements are spot on and towers are square to the bed which i used a brand new Lufkin builders square to check with.

Your not wrong about them being difficult, as much as i want to throw the towel in on the delta part of me wants to keep going for the prize and somehow work things out

You may want to consider taking apart and putting your printer together again if you have no other choice. I also had a self sourced delta, which I had to rebuilt twice before I was able to get it print properly.

Alternatively you may first want to check for effector tilt, using a spirit level.

I was using a E3D-V6 clone and i noticed the thread for the heaterblock was on a bit of a slant (so when the block is threaded onto the heatbreak the block sits on slight angle and of course the nozzle too i assume, not much but noticable enough to throw the nozzle off probably a mm or two...would this be causing my issue? Either way i have ordered a genuine V6 and it should be here by the end of the week

I have aluminium corners also on the way so i'll be rebuilding the printer later on...but for now i have my eye on the extruder funkiness maybe being the cause?

Edited 1 time(s). Last edit at 09/12/2016 01:21AM by silverbullet.

You can try to calibrate the printer better. Measure your diagonal rods precisely with calipers. Optimize tower positions and endstops with dc42's web page (*) or this maxima notebook: [github.com]

(*) Search this forum for dc42's calibration web page url.

Quote
silverbullet

Quote
nebbian
SilverBullet,

Welcome to deltas. They are frustrating, and often difficult to get to print straight.

It's unlikely to be missing steps. More likely is one or more of the following:

* Towers not parallel
* Towers twisted
* Bed not at 90 degrees to the towers
* Diagonal rod value in firmware not matching physical measurement
* Delta radius in firmware not matching physical measurement
* Rod end distance different between carriage and effector (causing effector tilt at different areas of the bed)

Those are the usual suspects on a delta, good luck finding the issue.

I've checked and rechecked all those things, that's why it is doing my head in. There is physically nothing i can find wrong, corner to corner measurements are spot on and towers are square to the bed which i used a brand new Lufkin builders square to check with.

Your not wrong about them being difficult, as much as i want to throw the towel in on the delta part of me wants to keep going for the prize and somehow work things out

To add to that list:

- rods not exactly the same length
- carriages rotated about their faces, so that the two bearings on them are not at the same height (or effector bearings not all in the same plane, which has the same effect)
- carriages rotated about the Z axis. If you are using wheeled carriages, this can occur if you have different numbers of washers between some wheels and the printed part than others, or if the printed part is warped

All of these cause the effector to tilt by varying amounts s it translates in the XY plane. I have a small bulls eye spirit level mounted on the effector to help me deect tilt.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks for giving me some more ideas to look at

I have checked pushrod lengths, i made them on a jig they are .5 of a millimeter within each other, pretty much close as humanly possible lol.

I spent some more time on it after work today and i did notice the carriage on the x axis was a little closer to the vertice, i don't have any washer on any of them but i flipped the bearings and the carriage is now the same distance floating off the vertice as the other two on y and z, i think the x carriage was a tiny bit rotated as well but is now good. I have not done another test yet as i have taken the hotend out as i am expecting a genuine E3DV6 to arrive any day to replace the clone which was working fine but i always wanted the real deal, support the company who designed it and all that

I also don't think i am losing steps as i believe i would have some kind of layer shift in the print which i don't so i am going to forget about messing with those.

In regards to the carriages, i think i have them spot on now...measurements say i do but you never know with this touchy thing. If they give me any more trouble i think i will order some linear slides off ebay, i've heard the knockoffs are fine once they are lubed and in place...hopefully it doesn't come to that though as my carriages are nice and quiet.

I need to put a screw a in the top of each carriage as well for fine tuning my endstops, i don't like doing it in firmware so what i do is i get out my big carpenters square set it on the bed and measure all three endstops off of that which gets me real close, then i work out my z then i use pronter to swing the nozzle to each tower and eyeball the clearance to see if i am concave or convex, it usually takes me about two tries to get that sorted in firmware to sort flatness and then fine tune everything with the carriage endstop screws...i'm not sure if it's the right way to do things but it works for me and i understand it better doing it that way...i'm very mechanical minded (not fricken Delta minded though haha), know enough about firmware to save my life but that's it

This delta is still doing my head in because i am still not 100% on the cause but i know somehow i will get there and this bitch will print how it is supposed to and when it does i'll have a bigger grin than i already do

Thanks for your help so far guys, really appreciate it!

Edited 1 time(s). Last edit at 09/13/2016 07:21AM by silverbullet.

You'll get there. It sounds like you're on the right track. You need to check everything, twice, and then again once just to be sure.

Note that you can enable the eeprom in Marlin which allows you to adjust endstops using a computer and pronterface. I must admit though that I spent a couple of months adjusting screws as I found it easier to visualise than typing numbers.

Once you get your printer printing nicely then consider printing one of these: [www.thingiverse.com] it works really well on both my deltas. I haven't touched endstops for months, it just probes the bed before printing, meaning perfect first layers every time.

You don't need screws on top of the end stops. If you use any kind of auto calibration procedure, or my web calculator, you will end up adjusting them in firmware anyway. It's quite easy to get them at the same height to within 0.5mm just by sliding them on the towers.

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I agree that screws on endstops are rather useless. At the end, if you want to calibrate it well then you need to adjust endstops to the values which are returned by a numerical calibration procedure. I.e. you want to adjust endstops with precision of about ±1 microstep. This is not easy to do with screws.

Also, I think, the error of 0.5 mm on diagonal rod length is quite big. When you do them in a jig then it should not be problem to make them with precision of about 0.1 (my biggest error for diagonal rods is 0.05 mm). They do not need to have a particular length. They just need to have the same length.

I never had problems with tilting carriages or platform. I guess this problem does not appear in a traditional rostock (which is the only delta printer I have experience with). Anyway if you have tilting problems then it should influence XY precision more than Z precision. That is what you have got. Bottom layer sticks but walls are not straight. But I guess other reasons can lead to curved wall too.

If you calibrate numerically and your printer is a solid built then you should be able to level the bed with precision of about 0.05 mm (i.e. base ±0.025 mm). If you have bed leveled that precisely and you did not optimize diagonal rod (i.e. you used precisely measured them) then also your XY error will be about the same as the bed Z-height error.

Bit of an update!

I decided to throw some more voltage at my stepper drivers just to experiment some more, they didn't look like they were missing or skipping steps and they sounded fine too BUT after setting my steppers to .35 it seems my lines have straightened right out, not absolutely perfect but definitely good enough for now and to allow the printer to be usable. I decided to set my extruder stepper to .45 and i was able to wind in the tensioner a bit more and there is no more skipping on that either now.

I installed my E3d-V6 hotend and it went well for a bit then i started getting jams with pla which seems fairly common, i seasoned it with a tiny bit of olive on the end of the filament and it's been fine ever since, i will print up an "oiler" over the weekend and install that to keep things in check and also to clean the filament off before it enters the bowden tube and into the hotend.

I have no idea why the extra voltage on the steppers helped other than maybe they were not holding there position well against the moving opposite carriage etc as i still don't think i was losing steps as my actual layers always looked perfect.