Hardware calibration - things you might overlook

Quite often there postings about printing problems where it becomes obvious that the machine was never really calibrated.
How to calibrate your extruder and axis through the E-steps is well documented in more than enough places, so let's focus on those things not mentioned too often.

Everything that moves needs support for this, usually bearings of some sort.
But the rails, roller system or whatever is in use also needs calibrating, especially after transport or the first build.
Take a look at a standard bed mount and you see two smoth rods with linear bearing or slider on them.
It does not matter too much if those rods are a few mm out of the supposed position but it does matter that they are fully parallel and exactly at the same distance as the bearing mounts on the bed!
Imagine one rod would be slightly lower:
No matter how good you adjust your bed once you move it one corner will go down with the rail.
Imagine they are not fully parallel either:
The bed will move smooth up to a certain point where more force is required. This not only wears out the bearings but also messes with your prints.
This point becomes even more important for the axis with the hotend moving around.
This axis or both rods must be parallel to each other AND to the print bed!
So you imagine that setting up the bed "correctly" can mean you actuall set in an angle that corresponds to the axis with the hotend!
Some say it does not really matter as long as it is parallel, which is partly true, but I say it does.
Let me explain why:
See your moving axis as moving plates covering your build area.
Your print bed is located between them.
If now either the lower or the upper "plate" is at a different angle to the print bed you can adjust the bed to match.
But if the misalignment of the two "plates" is in more than just one direction it becomes next to impossible to compensate.
IMHO the only real way is to remove the build platform completely and to align all smooth rods directly to each other, first the bottom ones, then the top ones.
After that the bed levelling only has to take care about the bed itself or whatever is on the bed to be printed on.
The reward is very smooth movements allowing for higher speeds

Framing....
When it comes to things holding it all together we have come a long way from simple triangles made with long screws to acrylic, wooden and metal frames.
But there are even more design variation than materials, so what makes a printer good in terms of the frame?
Small, low budget printers are usually quite small and have little moving mass to fight with.
Heated beds, glass plates, dual extruders and more will change things quickly.
What the motors and electronics are capable, the frame must stand up to it without moving.
But do some really fast infill that goes parallel to your axis and you might notice some shaking.
This shaking can cause problem like prints with perimters poking out a bit, wavy lines or in sever cases prints popping off the bed mid print.
Modern printers should not have much problems in this department, at least at normal speeds.
But if you do notice movement in your framing there are things you can do to improve.
For example trying to redunce the moving mass - instead of a 5mm glass plate try a 3mm one, instead of two direct extruders try a bowden system...
But the frame itself can be made more strudy by adding angle brackets, either metal or printed in the areas that move, sometime even a simple wire under high tension will give support for "shoebox movements" - like the back panel on a free standing wardrobe.
One of the best improvements can be vibration feet like used for high end speaker systems - a sharp cone on the speaker rests on a disk, due to the tiny surface are the generated forces will cancel out most vibrations.

Dual motor systems...
There is a real benefit to using two motor over just one but it comes at a price.
Especially at high speeds or in case of some accident there is little to no way you can see if both motors and what they drive are still really parallel.
And of they suffer from lost steps like any other single motor system, only the here just one motor could miss a step causing a misalignment.
So it really pays off to check this every now and then, especially when suddenly the bed levelling seems to be out of whack for no reason

Belts and pulleys....
When it comes to belts and pulleys you have a near endless choice of combinations available.
But for us that does not matter here, what matters is how they work together and move things.
Belts with insufficient tension cause the axis to perform unwanted moves.
If you know Z-Wobble than you know what I mean as a similar thing happens with loose belts.
Too much tension is no good either, so it is best to use a tensioner if it is just made from a spring loaded clothes peg...
In many cases the pulley are on ball bearings and use big washers on their side to make sure the belt stays in place.
If your pulleys or motor mounts are not properly aligned the belt will always wander off, some just to one side, some to both depending on the direction of the movement.
Up to a point this movement is normal and poses no real problem but if you notice blank, shiny areas on your washers it is a good indication that the belt is rubbing.
This rubbing causes vibrations that can be transfered onto the print.
After the obvious alignment check you can still cheat a bit if you still have problems.
By using silicone grease in very small amounts on the sides of the belt you reduce the friction to a level that is no longer a concern.
Best way is to replace such pulley with types as used on the motors, you the kind where the belt actually sits in a proper groove?

What's left?
I guess not too much apart from the normal calibration procedures for your steps....

I have to disagree about the dual Z motors being an advantage. Until I converted to one I had nothing but problems keeping my X carriage even from left to right. Out of level by as much as .060 inches. Sending Z home and then checking parallel to the bed produced a different measurement every time. A single Z motor and a belt and pulley system has eliminated this issue.

Thanks Downunder for taking the time to compile this!

Sooner or later, we all run into printing issues and that is when this kind of comprehensive writeup is extremely helpful.

Thanks,
/Chris

I see a lot of pointing out some obvious potential problems but almost nothing about how to fix/prevent any of it.

Sure, guide rails that aren't parallel can cause problems. How do you go about making them parallel?

The frame needs to be rigid and free of wobble. How do you make a frame that doesn't wobble? Spiked feet is the best improvement? Gimme a break!

Dual motors? Ugh.

Lubricating a belt to "fix" an alignment problem? Hmmmm...

What's left? Just most of the normally overlooked mechanical problems:

How about making sure the axes/guide rail are orthogonal to each other so that circles print as circles (it really helps if you're trying to print gears!) and squares print as squares.
How to align bearings/bushings for smooth, play-free movement on the guide rails.
How to recognize when the guide rails flex too much and what to do about it.
How about calibrating the extruder before the axes so that the the axis calibration will produce accurately sized parts?
How about explaining what happens when dual motors get out of sync. How about explaining how to keep dual motors in sync (hint: you can't).
How about explaining why it's so difficult to get your print bed leveled, why it won't stay level, and what to do about it?
etc...

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Well your points are valid but how do you go on about explaining it all with thausands of different printer models out there ?
I tried to point out the (fo us maybe) obvious things a noob might not even think about when he trusts the manual he used.
And lubricating a belt as you call it is not fix an alignment problem but I see it is always far easier to make fun out of the work someone else did than to actuall do it better in any way
Every single complaint of yours can be covered with the right explanation on the fix - if you know the real problem.
Guess you want me to write 20 more pages going into all details and then complain noone reads it because it's too long LOL - No offence!

What you wrote is a very incomplete list of potential problems, with almost nothing about how to fix them, and the few "fixes" offered are not solutions to the problems but band-aids. It doesn't help anyone to say that it's important to have parallel guide rails without saying why or how. You don't have to get specific about printer models.

It does take a LOT to first explain the problem and then its solution. For example, most people have never checked the orthogonality of their printer's axes. Most probably don't know what "orthogonality" means, much less how to test it. But orthogonality is essential in all Cartesian type printers because the firmware assumes orthogonal alignment of the axes. Without orthogonal alignment every print comes out distorted. So you have to start with a geometry lesson. That turns off about 95% of your potential audience right there. Most printer designs do not incorporate any means to adjust the orthogonality of the axes (or parallelism of guide rails for that matter) so even if you check it and find it off, how do you make the necessary corrections? How do you explain it to others? Most of the kit and printer makers simply assume that their cuts and measurements of the parts that go into the machine will result in an orthogonal relationship. If you've ever tried to print gears that wouldn't mesh properly or threaded, screw-together parts that wouldn't, you've probably encountered an orthogonality problem.

If you're going to make a guide for others to follow, do it right or don't do it at all, and know in advance that when you're done, your explanations will mostly fall on deaf ears. Very few people care as long as their machine keeps spitting out Yoda heads.

Edited 1 time(s). Last edit at 05/08/2016 11:53AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Then how about we all get together here and make a proper guide that covers all the problems, how to notice and fix them plus the required steps in the right order?
Don't know about you but to me it sounds more productive than complaining about what is not there...
Can't be too hard to agree on some webservie that allows document sharing for little workgroups.
Just a thought though as I still guess we are here to help