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Inconsistent Z ribbing/banding

Posted by eviltoy 
Re: Inconsistent Z ribbing/banding
September 06, 2016 12:57AM
Super solid no flex no play in the rods
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:07AM
belts and bearings are smooth with no play? bed firmly mounted?

Edited 1 time(s). Last edit at 09/06/2016 01:08AM by deaconfrost.
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:08AM
Yup all smooth. I switched leadscrews as well as I thought they were the problem.
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:11AM
is it happening all 4 sides ?
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:11AM
Correct bands go all around but its not the same as the pitch of the leadscrew its finer
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:14AM
only thing left I can think of to try is lower the micro stepping to 1/4 instead of 1/16, the less micro stepping the more repeatable position, you will need to change the step per mm in firmware

Edited 1 time(s). Last edit at 09/06/2016 01:14AM by deaconfrost.
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:14AM
Will give that a shot thanks
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:31AM
I am wondering if it might be the drivers themselves. I have TMC2100 drivers that I wanted to use on X&Y and DRV8825 that I wanted to use on the Z and Extruder. Would this be a worthwihle exercise?
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:36AM
the higher the microstepping the less torque you going to have, I never used tmc2100 so I couldn't comment on it, I also hear a lot about drv8825 not as good with the current,

heres a review of the tmc2100 I watched

Re: Inconsistent Z ribbing/banding
September 06, 2016 01:38AM
I know my old a4988 are good to go so to minimize any unkonwn possible issue on a new build I designed myself, I use all electronics that I know been working well before trying nything else
Re: Inconsistent Z ribbing/banding
September 06, 2016 01:39AM
hmmm ok will hold off for now then. This is really a strange issue its as if i have a consistent irregular extrusion happening. I realigned the Z motors and rods to be dead centre so theres like 0 wobble in them. I tried printing with the bearings ontop of the leadscrews and without with the same results. Used fixed couplers same issue then flex couplers the same issue. Belts are tight axis runs smooth and Z doesnt skip steps
Re: Inconsistent Z ribbing/banding
September 06, 2016 02:02AM
if everything else are perfect, then only thing I can think of are motors or drivers

Edited 1 time(s). Last edit at 09/06/2016 02:02AM by deaconfrost.
Re: Inconsistent Z ribbing/banding
September 06, 2016 02:11AM
Will try that
Re: Inconsistent Z ribbing/banding
September 06, 2016 12:02PM
Well i switched out drivers changed microstepping checked the axis again annnnnndddddd still the same sad smiley
Re: Inconsistent Z ribbing/banding
September 07, 2016 11:39AM
do you hear a hiss when extruding? if its humid where you are your abs could have absorbed water and it boiling out when in the hotend can wreak havoc on consistency of both temperature and the extrusion itself
Re: Inconsistent Z ribbing/banding
September 07, 2016 11:41AM
Nah no hissing or popping i pop it in the oven before printing.
Re: Inconsistent Z ribbing/banding
September 07, 2016 02:14PM
Does the machine shake at all while it prints? Is your bed stationary or cantilever? I've seen a similar issue on one of my CoreXY when it does short infill too fast it begins to vibrate the entire machine and I get something similar to the z banding in your pictures.

Edited 1 time(s). Last edit at 09/07/2016 02:14PM by PDBeal.
Re: Inconsistent Z ribbing/banding
September 07, 2016 05:23PM
No shakes at all the bed is not cantilevered
Re: Inconsistent Z ribbing/banding
September 07, 2016 05:25PM
Wait the bed does move though its like a prusa i3
Re: Inconsistent Z ribbing/banding
September 08, 2016 01:59AM
I am wondering if it is not the stepper motor creating this grief. Ill swap out the stepper driver and switch motors afterwards to confirm
Re: Inconsistent Z ribbing/banding
September 08, 2016 09:19PM
I am wondering if it might be the drivers themselves. I have TMC2100 drivers that I wanted to use on X&Y and DRV8825 that I wanted to use on the Z and Extruder. Would this be a worthwihle exercise?

How hot is your stepper driver running? I'm not familiar with your ones, but the a4988's can take a break or reduce current if they get too hot... Its a common safety feature in many IC's.
Re: Inconsistent Z ribbing/banding
September 08, 2016 09:38PM
I am running a4988 on all axis at the moment. They dont get too hot.
Re: Inconsistent Z ribbing/banding
September 09, 2016 08:26AM
Only other thing i can think of is an out-of-round hobbed bolt, if your extruder is a Wades design. I make my own hobbed bolts and had a slightly elliptical, inconsistent diameter hob job that could be seen in the print surface.
Re: Inconsistent Z ribbing/banding
September 09, 2016 09:39PM
These suggestions may seem obvious and you have likely checked them, but... Check them again using different methods.....

Extruder temp. How stable is it via IR or K-probe? Is the plastic actually coming out at that temp? ie it comes out colder if feed rates go up.... Do you have access to a good thermal camera? Have you removed all sources of drafts etc? Is the solvent percentage in the filiment exact all the way through? Because evaporation is great at stealing heat. How precise are you trying to print??

I like this idea the best because there is clear colour changes with your ribbing (I just had another zoomed in look at the pics). Darker sections where its under extruded and lighter sections where its over extruded. Which indicates to me a variation in temperature. Can you thermally insulate your heatblock? ie wrap it with a blanket? then print really slow to minimise thermal fluctuation? Or just print 5-10c hotter and re-calibrate flow rate to suit?

If you want perfect temp readings you need a k-probe(not hooked up via I2c as its too slow), lab quality amplifier (not cheap) with cold junction offset. Inside the nozzle measuring actual plastic temp at the point of extrusion. Even then there will still be some small error. I have made and repaired a lot of electronic test kit over the years DMM's temp sensors, gas sensors etc etc). There is always an error percentage, its often disturbingly big. I have checked my hotend all over and inside. there is over 30c of variation at different points. More if I run a fan! Its a cheap Chinese one so that's about what I would expect. But I have yet to see a design that will (in theory) give stable temps with less than 5c variation at 250c. Even at PLA temps tiny variation in air temp and humidity will make significant changes to the thermal transfer rate to the surrounding air. Combine that with variations in filiment additive ratios (its not going to be the same composition all the way through look into home brew filament makers and you will see a ton of issues getting plasticisers etc evenly mixed in) and its an uphill battle. There are at least 3 significant variables that you can't control without a climate controlled enclosure and without relying on filament manufacturers to maintain a ridiculous (not practically possible) level of quality.

I put a blanket over my printer in crappy weather.... Helps a lot!

Other stuff to check using new/alternate methods:

Roll spooling or inconsistent filament thickness. ie is the filament feed in extremely consistent? How much variation in filament thickness do you have?
I just checked 2 rolls of abs 3mm. one averages 2.85-2.98 thick after checking 25 spots over a few meters I got 10-15 different readings in this range. The other roll is 2.9-3.05... Its also not perfectly round. in the same spot one axis is 0.02 bigger... Pretty hard to get exact flow rate when the input has variation.

I also had problems a while back where the filament would pull the roll hard enough to make it roll out a bit extra. If you have overhead feed maybe its pushing a bit hard when it does this? Mine was lifting the extruder a tiny bit as the tension was building up enough to turn the spool then dropping it again after the spool out.. Try cutting a length long enough for a print and remove the spool from the equation. I'm thinking of making a pre-feeder with a heater to keep a constant pressure/drag for the extruder, and dry out the filament at the same time. As I am in a sub-tropical climate and you cant stop a long print every hour or two to put the filament in the oven... (Well you could, but I'm not going to)

Missed z steps or extra E steps. Probably only by tiny amounts. Could be hard to detect. Does increasing current make a change?

Is your layer height divisible by step distance? Maybe its rounding down a step every so often? Probably not as its not a regular pattern, but if its a tiny amount you could have a weird harmonic pattern that only becomes obvious over longer distances. Have you printed something to full height and looked for patterns?

You seem pretty confident with your calibration, but maybe check it again a different way to how you have been? I found my M6 screws are actually 1.0656mm per rev rather than the 1mm advertised.. Which is pretty accurate for rod that costs less than an arm or leg... Ever measured drill bits? I had to with 5mm bits a while back. I had 7x5mm bits. No two where the same diameter.. The smallest was 4.65 and the fattest was 4.92. Most drill bits are 0.15-0.25 smaller than advertised for a good reason, but even 2 bits the same brand are rarely exactly the same.

My point is no machine tolerance is exact. Maybe looking for something like that will help? Another point here would be thread play. There will be some. How big is it? Have you tried a longer nut and thicker grease to dampen play, or 2 nuts with a spring between?

How free are your bed springs and how much pre-load are they running? I've seen mine bind randomly (probably not random, I just haven’t found the cause) as well as with thermal change. I wish I had of considered thermal expansion before I drilled my holes in the sub bed, because the hole spacing in the heated build plate is 0.75mm greater with the bed hot, because some genius made it with Aluminium in it.... Plays havoc with getting a free movement up and down with minimal side play. Trying more and less pre-load on bed springs helped identify the problem. I'm still at a loss as to a fix. Aside from changing sub beds for different temps or having adjustable pin spacing... Imagine the look on my face when I spent 2 hours getting the bed movement perfect, at room temp, only to have it bind hard at print temps.

Its pretty hard to accurately measure down to this level with callipers etc. Are you using a good quality micrometer? I have zero delusions of getting better print quality than your pics using digital callipers and thermistors for calibration.... Not to mention cheap bearings, rods etc etc. ie I bet the mm per turn rate changes a bit over a few meters of threaded rod. Maybe only by hundreds of nano's, but more likely by 10's-100's of microns. That stuffs made really cheaply. The error margins can be a lot bigger than you would expect. Can you get a datasheet for your rods etc? or call the manufacturer and ask? Don’t even get me started on thermistors and thermal runaway etc.
Re: Inconsistent Z ribbing/banding
September 09, 2016 10:17PM
Going to skip the first few points as I dont have the ir probe etc. What I can say is that everything is pid tuned and the temp graph is very stable not ever a variance of 1 full degree.

The filament is quite consistent over the length of the spool variance of maybe .01 its esun green.

Layer height is .2 which is good according the prusa calculator

I am using TR8 Leadscrews so the thread play in those brass nuts are a fair bit however I have tried different leadscrews and nuts with the same effect.

The bed is fixed unfortunately. I considered bed flex I need to get a tool to measure if it was the case but I doubt the flex would happen at such regular intervals but still worth a shot.

I played with different voltages on the Extruder and Z axis and its the same.

Doubt that the supplier has data sheets for their leadscrews unfortunately sad smiley
Re: Inconsistent Z ribbing/banding
September 13, 2016 12:00AM
confused smiley I got nothing.

Maybe the problem will become obvious if you get another printer and no longer need that one lol.
Like the time I couldn't drive for a week due to lost keys (spare set too). Ended up hot-wiring it and found my keys 10 min later. I have many stories like this...

Seriously though. I think the colour changes matching the banding is related.

In my limited experience, and only printing in ABS, I have noticed white discolouration seems to happen for two reasons.

A, under extrusion due to combined low temp and high speeds or poor e-step calibration. Its a similar effect as when you bend the plastic till it goes white.
I think this is cause by friction causing excessive localised heating and messing with the plasticiser. Because the printer is trying to deform it when its too stiff.

B, too hot. It goes white because heat has cooked out the plasticiser.

A is obvious due to under extruded layers and poor layer bondage.

B is identifiable by over extrusion, sagging and other signs of too much heat.

Seems you've used process of elimination on every other suspected part...

Have you tried other hotends or temp sensing methods? I know one of my cheap nasty hotends has a terrible physical design. The nozzle is on one side, heater in the middle and temp sensor on the opposite side of the heater.... Checking it with a K-probe on a DMM reveals the nozzle temp can be very different to sensor temp. So even if its a good sensor, its not really taking readings where it needs to. Aluminium is a great conductor of heat, but its a double edges sword as it can cool more in some places than others...

Suggested things to confirm/deny.

Use a second temp probe. Preferably not thermistor, but even that would be better than nothing. Any reasonably accurate temp sensor that can handle the heat. A DMM with K-probe would be a pretty decent investment if you like to build stuff that has electronics or hot/cold bits. I have a few and use them all the time. Great for checking stepper drivers, transistors etc too.

Try and make the nozzle temp more stable with insulation. Suggestions include wool, fibreglass cloth, Ceramic fibre cloth, maybe even cotton for PLA temps.
Failing any of those items I'd even try stuff like newspaper or cardboard or half a mile of Kapton tape. Anything you can think of to improve temp stability/consistency over the whole heating block... Obviously you'd want to re-PID tune if you did this. As it will cool a lot slower if it overshoots.

I love to collect stuff like that from broken appliances etc. Old stoves/ovens are a great source of good fiberglass insulation. Handle with care though. The small fibres can present some heath and safety concerns. If I was going to buy something for this job I'd get some ceramic fibre insulation. Or see what they have in stock at the local appliance repair place. Fire blankets are another source of fibreglass cloth. Of just get a bit at the local hardware. They have it with the resins...

Edited 1 time(s). Last edit at 09/13/2016 12:16AM by Mongrel_Shark.
Re: Inconsistent Z ribbing/banding
September 13, 2016 12:27AM
Hmmm you know you might have a point. I noted that the power supply was dying. So I replaced it. Also I noted that the leadscrews I have doesnt have the reported diameter or pitch so I updated accordingly. Another thing I discovered was that I had the recalled drivegear on my titan extruder so that will be replaced. I think you might be onto something with the temps and extrusion because the more I decrease the multiplier the better the prints look however part strength suffers. I have now replaced the leadscrews and will look into swapping out the hotends. Ill be getting some e3d socks as well for the hotend
Re: Inconsistent Z ribbing/banding
September 15, 2016 01:05PM
Chicken dinner new heaterblock thermistor and drivegear and perfect prints
Re: Inconsistent Z ribbing/banding
September 24, 2016 09:40PM
Double check your stepper voltages. Go at least .6.
Re: Inconsistent Z ribbing/banding
September 25, 2016 12:24AM
Yup they are running voltages above .6 already. my issue came back and I am not sure why. I have logged a support ticket with e3d as I suspect its the titan extruder I have.
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