Wavy vertical walls

Hi:

I am having some problems with my Mendel, and I am wondering if others do also.

I have designed some parts that are about 12mm tall. They have vertical sides. However the print quality on the sides is rather poor, leaving wavy and or tilted walls that should be straight. Through holes are also winding up at an angle, due to this drift. Please see the pictures for the results. The direction of increasing x and y is labeled.

I am wondering about the cause of this behavior. I do not think it could be backlash, since the perimeter is always executed in the same direction. There might also be temperature effects where the higher the print layer the cooler it is (farther from the heated bed). I think the frame is square.

Any thoughts would be appreciated. I wonder how anyone can a good print for a Prusa, with 50mm+ high walls?

Is it possible to home between layers with skeinforge, and would it help?

My equipment is: laser cut mendel, gen3 elect, pololu stepper extruder (wade), skeinforge 40, java host, heated bed (alum plate at 110C), 35mm/sec feed rate

many thanks

john

Edited 1 time(s). Last edit at 06/01/2011 03:25PM by j_andberg.

First disable the backlash feature in Skeinforge. I found that turning it on does more harm than good, at least for me that was the case.

Second, your Y-axis seems pretty good compared to X. Have a look at the pulley gear and make sure that there is no sliping on the belt. Sometimes the belt and pulley are slightly mismatched, and you can see it when the motor reverses direction.

How hot is your X-axis motor? If it's too hot to touch, the current setting of the driver might be causing skips.

Last suggestion is to make sure there is no binding on the axis. disconnect the belt, unplug the motor, and move the cariage by hand. It should be absolutely free to move, with little friction.

Are you resetting home between layers? If so then check your opto flags are straight and well fixed

if not then maybe your motors are missing steps slow down the print speed by 25% and try again

---

[richrap.blogspot.com]

How big is the part in the X-Y direction? You can get this if you're feed rate is too fast and you're printing over a layer that is still too soft. Try turning the cool option in Skeinforge on and select slow down. With ABS, 20 sec minimum time per layer might be enough but you might want to try 40 s to start with. If that doesn't fix it, then as jcabrer suggested, check your X axis.

I don't think he's missing steps since with 1/2 stepping, the misregistration of the upper layers would be very noticable.

There's a homing option in Skeinforge. But I don't think you want to home between layers. It's not necessary and it slows down the print. In addition, some plastic will probably ooze during the time it takes to home and go back to your part.

How well is the pulley attached to the shaft? Usually when my walls get wavy it is because the pulley is slowly wiggling loose.

Other things to question/try,

Are your z axis threaded rods straight? if the rods are slightly bent it can cause a wavy pattern by skewing the entire x asis on it's way up.

Is your belt tight?

Can you wiggle the carriage at all by hand when the steppers are holding? If your bearings/bushings are not tight enough you will get small random positioning errors.

Does your hot end wobble at all?

If nothing here helps, try printing at 10mm/sec and see if it still occurs.

I have similar problems, and have tried many different things.

After a suggestion on IRC, I made sure the smooth rods was perfectly parallel and repositioned the y belt to make sure it was completely straight.

The belts was very tight, so I loosened them a bit, and turned the potmeter on the stepper controllers down until they started slipping, and then turned them up slowly until I got better prints. As a bonus the machine is much quieter now.

I slowed down from 60mm/s to 50mm/s as well. And it seems to work pretty well. I do miss a few steps on the y axis still, so working on that (1mm on 10mm height).

---

--
-Nudel
Blog with RepRap Comic

Hi All:

Thanks for the input, sorry to have not posted sooner. Last weekend I tried lowering my feed and flow to 15mm/s. VERY slow printing, but it eliminated the problem. Then I pulled the machine apart to put in 10 tooth machined pulleys on x and y, to see if it helps. Still not quite together and adjusted yet.

It might be helpful to know what feed/flow settings are typically achievable for a mendel with acceleration off (per skeinforge) and host firmware.

many thanks,

john

I've been keeping it around 25 mm/s at a 0.35 mm layer and getting some nice prints. I've tried printing in the low 30s for objects with less detail and have had some okay stuff come out. 25 moves pretty quick though.

I also have one wobbly z-axis rod that I should get around to swapping out.

Edited 1 time(s). Last edit at 06/11/2011 10:54AM by chase82.

I'm now printing at 30mm/s with a travel feed rate of 45mm/s and a layer thickness of .32mm. My Mendel is not normal though and is a bit experimental. Mine prints really nice at those speeds but 20 to 25mm/s might be better for a normal one.

I also have a 5mm aluminium heated bed I attach 3mm aluminium plates too with the tape on so I can change them quickly. So that's 8mm of aluminium in total and I get no skipping even when infilling really small parts where it shakes back and forth really quickly!

The firmware settings can be really important in avoiding missed steps as I have found out recently. If its set wrong it will skip even with the motor power turned right up.

---

Make your Mendel twice as accurate.
[www.thingiverse.com]

Madkite Wrote:
-------------------------------------------------------
> The firmware settings can be really important in
> avoiding missed steps as I have found out
> recently. If its set wrong it will skip even with
> the motor power turned right up.

Can you give any tips as to what settings in the firmware can help with motor skipping ?

---

[richrap.blogspot.com]

Hi All:

Last weekend I tried 25mm/sec (0.4mm layer), with the new 10 tooth machined pulleys. As bad as ever (on the x axis), with no backlash due to a good fit on the pulleys. Next I will try 20mm/sec. I will also loosen the x axis belt and turn up the drive current. I may have to live with 15mm/sec until I change my drive belt design to a Prusa-like x belt arrangement.

Will keep everyone posted.

john

Not sure what to advise really as the settings I changes were not in the old firmware.

I had to alter a very specific setting but it said in the instructions to do so if you kept missing steps. And that worked a charm.

I fiddles with the acceleration settings but I would be lying if I said I knew what they all did. That wasn't the problem for me anyway.

I was using sprinter firmware BTW. There's a thread about blobbing in the Mendel section where I explain what I changed.

---

Make your Mendel twice as accurate.
[www.thingiverse.com]

Thanks Madkite

I found the references STEP_DELAY_RATIO & STEP_DELAY_MICROS. so when I switch over to Sprinter on my RAMPS setup I will play around with the stepper ramping. I'm using NEMA 23's on my setup so ramp tweaking is going to improve things when I speed things up again.

If anyone else knows where the stepper ramp software is handled in the 5D firmware can you point me in the right direction please?
And I'm not talking about axis acceleration but the first stepper ramp table code to get the motor's up to their initial running speed.

Thanks.

Rich.

---

[richrap.blogspot.com]

Hi All:

Back to 20mm/sec and is pretty good. Been rebuilding a flaky extruder drive bolt. Be aware that the latest instructions on the wiki about coarse bolt hob are the best. The M3 kept filling up with plastic, leading to a lack of feed. Most of last weekend were dealing with that. Printing much better now, but still do not think I can print over 20mm/sec (skeinforge, no firmware accel). Is this reasonable?

thanks,

john

Sounds a bit slow. I have settled for 55mm/s as my gen6 tends to get errors sometimes where it moves at the maximum speed without aceliratnon and if I go faster it can skip.

Is the problem the extruder will not work any faster or it keeps missing steps on the X/Y?

Why no firmware acceleration? I have found this to be extremely useful. It was hard to make short lines infill properly on small parts higher speeds. They would start to hollow out. This was partly an extruder problem but I also set up acceleration to be really soft so when doing short lines it is much slower traveling but is fast over a long line. This really makes the infill much more consistent on my machine while keeping build time down.

I may experiment with harsher settings again later but I'm happy for now. I only made it softer for the extruder issue but it may be better now I have fixed that. It never missed steps because of fast acceleration only the movement errors.

Solving those will be another story I'm sure.

---

Make your Mendel twice as accurate.
[www.thingiverse.com]