Build Platform Levelling

"Levelling" your platform is one of the most important things you can do to help get good prints. The process of levelling the platform may vary a little from printer to printer, but the concepts pretty much remain the same. In this article we cover the factors related to levelling a 3D Printer platform and offer one technique that works for us.

Levelling versus Tramming
When we level a 3D Printer's platform, we are not really trying to make it level. We are trying to make it a uniform distance from the nozzle across the entire platform. We may achieve this and not have a level platform at all. This process is better known as Tramming. However, most people intuitively understand the phrase Levelling better and so the two are often interchanged. Regardless of what you call it, the end goal is still the same - the distance between the nozzle and the platform should be the same, regardless where the nozzle is relative to the platform.

Distance matters
While we can achieve a perfectly levelled (or Trammed) platform, it still may be too far away from the nozzle. What we are after is to ensure the platform is the correct distance from the nozzle before the first layer of plastic comes out. The "correct" value here changes depending on your environment, the particular printer, and/or the plastic being used. If you don't get this right, you'll see issues such as peeling, warping, cracking, or simple no-stick.

Common Techniques
There are some common methods out there for levelling your platform. Some require a little background information before they work well though. Normally each of these techiques is applied in the four outer corners of the platform (as far out as the nozzle can reasonably go), with the understanding that those 4 points define a plane. If the distance between the platform and nozzle is the same at the 4 points, the nature of the plane suggests the rest of the platform will also be at that height. Unfortunately, platforms may be slightly warped in some way. So some fiddling may be needed to get things "right" for your platform. There are likely other techniques out there, but we have found that by combining the test print idea with the Dial Gauge technique, we can quickly level the bed with the right distance in a precise manner.
 * Paper - some people use a piece of paper of a known thickness.  They'll pass this paper under the nozzle and if it is too encumbered they'll move the platform away from the nozzle a little in that area.  If it slides under the nozzle without resistance, they raise the platform towards the nozzle.  The trick here is knowing the "right" amount of resistance.  This is generally a gut-feeling type of technique and often only get's you into the right ball park.
 * Feeler Gauges - some people use feeler gauges.  They determine which gauge is the correct value (the distance between the bed and nozzle), and then use it to adjust the platform height. This is very similar to the paper technique.
 * Dial Gauge - some people will use a dial gauge to quickly adjust the platform to match an "anchor" corner.  Basically, they select a corner - presumably the one that has the correct distance, position the dial gauge there, and then zero's the gauge.  Next they move the gauge to the other corners and adjust until those corners until the gauge returns to zero.  This is a quick way to make sure the platform is levelled/trammed, but does not account for the distance.
 * Test Prints - some people will simply print a test object and adjust the platform on the fly until the print works right.  This may be suitable for quick prints, but may not offer the precision needed for others.
 * Eyeballing - some people carefully observe the first layer of plastic to make sure it is properly "smushed".  The plastic should not be perfectly round, but it should not be perfectly flat either.  Usually the first layer should have the bottom quarter to half of the line flattened by the platform.  This requires good eyesight and some trial and error to determine the correct "smushiness".

Replicator 1 - Proven Technique
When we say "proven" here, we only mean that it has worked reliably for us. Your mileage may vary. Feel free to tweak the technique if you can get better results for your environment.
 * Start by levelling your platform with paper.  This is only to quickly get us into the right ballpark.  Make sure all 4 corners of your platform are close enough to offer resistance when passing the paper between the nozzle and platform.  The four corners should have about the same amount of resistance.
 * Print out a one layer thick object.  This could be a hollow rectangle, a simple line, or whatever other shape you'd like.  This object should be modelled to have a very specific height - say 0.25mm.  Now when you print the object, set your layer height to match the object's height - again 0.25mm.  Then when you print you will get only one layer.Note: For cantilever platforms with a heated bed:  The process of heating up the bed for printing may introduce drooping to the unsupported side of the platform.  To minimize this heat the platform for 5 to 20 minutes before levelling.  This ensures we are levelling the platform to match the heated state it is most likely going to be in for the duration of the printing.  Additionally, because of the potential droop factor, we really want to make sure the back, or supported, part of the platform is at the right height.  So we may only print our object at the back of the platform.
 * When the print is done, remove it from the platform.  Take care to make sure you know how it was oriented on the platform.  Now, with a pair of calipers, measure the print height in the corners.  If it is less than our layer height (i.e. we expect 0.25mm and measure 0.15mm), then the platform is too close to the nozzle - adjust that corner to move the platform away from the nozzle a little.  If the corner measures more than we expected (i.e. we expect 0.25mm and measure 0.35mm), then the platform is too far from the nozzle - adjust that corner to move towards the nozzle.  Chances are that you will not get extremely precise corners.  We are aiming to be within 0.02mm of our expected value.
 * Print another test object.  Repeat step 3.  Repeat these steps until you are confident you have one or more corners that measures the right layer height.  For printers with a cantilevered heated bed, aim for the right layer height at the supported corners.  When you get a corner with the right distance, we'll use that corner as our anchor point.
 * Now use a Dial Gauge.  Position it in the corner we have just proven is the correct distance from the nozzle.  Zero the gauge.  Now move the gauge to the other corners.  Adjust those corners until there is zero (or very close to zero) difference from the anchor corner.

Replicator 2 - Proven Technique

 * During leveling, avoid touching the build plate except when necessary to turn knobs, this avoids inaccurate level readings
 * Rather than using the makerbot card to level the build platform, use the classic machinist technique of cutting a 1" x 8" strip of printer paper, this will get the nozzle closer to the build plate and provide better results. Adjust the thumbscrews until you can push the paper under the nozzle without it bending upwards in the center, there should be slight friction.
 * Use a .001 feeler gauge to properly level the platform rather than paper.
 * Use whpthomas' interactive leveling file. Thing 39430  While printing, adjust the thumbscrews and let print periodically. Build plate is properly leveled when all areas are smooth and glassy (highly reflective) with no ridges. After the print is removed, the center areas should not have threads, but be a single film of plastic.
 * Instructional Video Levelling the Build Plate (5 of 8)

Congratulations
You should now have a properly levelled platform. The next few prints you do should work much better. If you want to prove it, print your test object again - the 4 corners should all measure the same amount.