JKN-K or retraction settings?

[Edward Wingate]

I've got a Thing-O-Matic running Sailfish with a MK6 stepstruder.  I'm having an issue with accelerated printing where the edges of the print have too much plastic.  It seems to affect opposite sides of the print with each line, so I figure it's just on acceleration or deceleration, but not both.  Adjusting my JKN K value doesn't seem to do much, and now I'm wondering if it's got to do with the retraction settings.  I have deprime set to 0.

Any insights before I head off into blindly tweaking values land?

[Dan Newman]

On 24/03/2015 11:13 PM, Edward Wingate wrote:
> I've got a Thing-O-Matic running Sailfish with a MK6 stepstruder. I'm
> having an issue with accelerated printing where the edges of the print have
> too much plastic. It seems to affect opposite sides of the print with each
> line, so I figure it's just on acceleration or deceleration, but not both.
> Adjusting my JKN K value doesn't seem to do much,

Have you adjusted K2? It may also be that your max acceleration is too high
and the bot cannot really slow down as fast as you've told it that it can.
This can be particularly troublesome along the Y axis with a ToM or Cupcake
as they develop play/backlash on the Y axis.

Dan

[James McCracken]

I have a similar issue on my cupcake, and the only real solution is to slow it down so the motion stage is more accurate.  When I print gears, if I want them to mesh, I have to print at 35 mm/sec or slower... Its a backlash issue, as Dan alluded to.

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[Edward Wingate]

I had a feeling it wasn't tunable, it's unfortunate, I really like the extra speed of 80mm/s.

[James McCracken]

oh yes at 80mm/s you'll see definite issues!

I can go around 65 before bad artifacts start showing up and I've seen thingomatics that can print gears at 45... 

One thing that helped me was I put a tensioner on each belt.  It's just a paperclip folded up right... http://www.thingiverse.com/thing:4535 basically like that.  If you have a working printer (mine was so out of tension it wasn't working right at the time) there are better printable designs on thingiverse, but that's what worked for me.  Instead of a simple S shape, I put a circular, horizontally oriented, loop at each 90 degree turn, which helps to lock the tensioner in place on the belt.

On Wed, Mar 25, 2015 at 2:30 PM, Edward Wingate <tedwi...@gmail.com> wrote:

I had a feeling it wasn't tunable, it's unfortunate, I really like the extra speed of 80mm/s.

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[Dan Newman]

On 25/03/2015 11:39 AM, James McCracken wrote:
> oh yes at 80mm/s you'll see definite issues!
>
> I can go around 65 before bad artifacts start showing up and I've seen
> thingomatics that can print gears at 45...
>
> One thing that helped me was I put a tensioner on each belt. It's just a
> paperclip folded up right... http://www.thingiverse.com/thing:4535
> basically like that. If you have a working printer (mine was so out of
> tension it wasn't working right at the time) there are better printable
> designs on thingiverse, but that's what worked for me. Instead of a simple
> S shape, I put a circular, horizontally oriented, loop at each 90 degree
> turn, which helps to lock the tensioner in place on the belt.

Another item which may or may not help is to print two of these,

http://www.thingiverse.com/thing:15770

and use them to do this,

http://www.thingiverse.com/make:9316

That will help if you've developed play in the Y axis on the righthand
side of the X carriage from the press fit bearings getting loose in
the wood.

And, I definitely recall someone -- perhaps Joseph Chiu -- doing
a nicer version that had a larger flange which perhaps even
was held down by one of the bolts on the X carriage. However,
I cannot seem to find it on Thingiverse.

Dan

[Edward Wingate]

I've considered a linear bearing mod on the bushing side of the Y-Stage.  I've got a bearing mod on one side of the X-Stage to deal with it being over-constrained.  I also installed belt tensioners for both belts (U-shaped things that pull on the motors), and have the Y-Idler reinforced.  I'm waiting for bearings to arrive in order to modify the idlers, currently I'm using PTFE grease to keep them quiet.  At this point I'm dealing with diminishing returns for the effort I'm putting in, but I dig it, and it's become something of a habit.