X/Y Dimensions off. How can I fix it?

[Harblar]

So... I haven't used my printer in quite awhile, but I had some projects I've been wanting to do. I also switched to a .8mm nozzle and have been playing around with that a little. (actually getting decent prints and a lot faster) I went through a quick recalibration in order to level the bed and think I've got it pretty close.

That being said something is definitely off. By my figuring it appears as though my X/Y dimensions are approximately 95% of what they should be. One part I printed was designed as being 71.875 mm wide. The final print was only 68.1mm wide. I printed out a 20mm calibration cube as well and it was smaller than it should be as well. Only 19.5mm on each side (97% of what it should be). So it seems as though the bigger the X/Y footprint the more the outer dimensions are shrunk.

In the past, all of my prints have been very close to accurate. Could this error be related to switching to the .8mm nozzle?

The only mods I'm running over stock are an E3D v6 hotend and the .8mm nozzle. I'm printing ABS with the first layer at .55mm and then .35mm thereafter. 235C on the filament and 90 on the bed.

Any suggestions or good calibration guides I could look at that would point me in the right direction?

[Xenocrates]

http://forum.seemecnc.com/viewtopic.php?f=37&t=10276

That will fix your issue.

[nebbian]

It's not always diagonal rod length that can cause this issue. If you've carefully measured your rods and are still having scaling issues, it could be:
* Steps per mm being wrong due to GT2 belt not being exactly 2mm between teeth (I've had this error on both my printers)
* Twist in your frame

Blindly adjusting diagonal rod length without measuring it can lead to issues with Z height in certain parts of the bed.

[Xenocrates]

It's not always diagonal rod length that can cause this issue. If you've carefully measured your rods and are still having scaling issues, it could be:
* Steps per mm being wrong due to GT2 belt not being exactly 2mm between teeth (I've had this error on both my printers)
* Twist in your frame

Blindly adjusting diagonal rod length without measuring it can lead to issues with Z height in certain parts of the bed.

Steps per MM would result in a Z inaccuracy as well, as it affects everything. Twist in the frame is a much more complicated thing to work out, and if it turns out not to be the problem, the person may well have spent a large amount of time working on re-adjusting the frame when a minor EEPROM value change may have fixed it first. I do understand that there are other causes, but this gives them a quick answer to try, and if it doesn't work, it's just as easy to find and fix issues as it would be if that hadn't been applied, and works in 75%+ of cases. Note to mention that most people lack the equipment to measure the rod length well enough to to check against things, and that it's not just measuring the length of the arms, which many assume, due to the use of virtual towers that are related to the physical ones, but not identical in the kinematic calculations. (Such as the carriages having an effect of rod length, when in theory they should only affect the carriage offset)

It could also be that the extrusion width that's automatically selected is off in addition, as if it's over the width the printer thinks it is, that can cause the smaller prints to be a off by less than the larger ones (Such as is seen here), due to the extrusion overage being fixed and arm length being a percentage offset. Slicers often don't work well with finding automatic values for large apertures.

[geneb]

Despite views to the contrary, steps per millimeter are a constant and should only be changed if you want to introduce scaling errors.

g.

[Nylocke]

Yeah, the pulleys are machined in large batches and have to be in tolerance (probably less error than everything else on the printer) and the belts are similar. Any slight differences are negligible. If they arent, then you have bigger problems.

[Windshadow]

and lets not forget that the law of averages means that in volume production you can get additive (ors subtractive) tolerance build up... the best example of this was with the first 747 jetliners where if all the assembly tolerances were on the tight side you had a plane the was XXX feet long but later in production they were stacking up on the fat end of the allowed range for the parts... result were some planes that were as much as 30 inches longer in the Cabin than the early ones of the same 747-100 model... and everything was in spec and perfectly safe but its a great illustration of the problem. the fact that you will get a mix of som parts on the fat end of the spec and some that are on the skinny end means that almost all the time everything averages out but things did happen when perhaps assembly jugs were used right until they were in danger of making out of spec parts... I doubt it is any thing like that today but it was in the early 1970s at Boeing I am told by retired engineers that worked there.

[nebbian]

Despite views to the contrary, steps per millimeter are a constant and should only be changed if you want to introduce scaling errors.

g.

If you use a set of digital calipers, and measure very carefully (average of at least 10 different operations) the distance that a carriage moves when you command it to move a certain amount... and you discover that the carriage consistently moves 0.4% less distance than it should... and your parts are consistently measuring about 0.4% too small...

... then what are you gonna do?

[geneb]

....figure out what the mechanical problem is and fix it.

g.

[Xenocrates]

I think the mechanical problem in this case is out of tolerance pulleys. It's very possible wherever he sourced them from (Whether they came with his Kossel's or not) went for cheap ones, even though properly toleranced systems aren't that expensive. If the diameter is off, or the steps on the pulley are, it's very possible that he can have issues. Not everyone here is using SeeMe supplied hardware.

[Mac The Knife]

I think the mechanical problem in this case is out of tolerance pulleys. It's very possible wherever he sourced them from (Whether they came with his Kossel's or not) went for cheap ones, even though properly toleranced systems aren't that expensive. If the diameter is off, or the steps on the pulley are, it's very possible that he can have issues. Not everyone here is using SeeMe supplied hardware.

According to his post, He is using a SeeMeCNC machine, with the exception of the hotend.

[Xenocrates]

I think the mechanical problem in this case is out of tolerance pulleys. It's very possible wherever he sourced them from (Whether they came with his Kossel's or not) went for cheap ones, even though properly toleranced systems aren't that expensive. If the diameter is off, or the steps on the pulley are, it's very possible that he can have issues. Not everyone here is using SeeMe supplied hardware.

According to his post, He is using a SeeMeCNC machine, with the exception of the hotend.

I was referring to Nebbian's printers, as Geneb was replying to him. He has a pair of Kossels, and from what he last said, no Seeme printers. we got a little off topic.