Leveling the Print Bed
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For leveling a Delta Printer, like a Rostock, have a look at this HowTo: http://minow.blogspot.co.at/index.html#4918805519571907051
There are many variable inputs to your RepRap prints. The key to great results is to go after the low-hanging fruit, and nail down as many of those variables as you can. One of the simplest things you can do, which many of us avoid, is to level your print bed. These instructions are based on my experience leveling a Prusa. I'm sure other machines will use similar, if not identical steps. There are a few prerequisites that we must cover before moving on to leveling, but theses too are low hanging.
Before you start I strongly recommend looking at these two upgrades. The are simple and simply brilliant.
Bed leveling is one of the things you are going to have to do on a periodic (constant?) basis. I would seriously recommend adding the following two upgrades:
Allows you to adjust the height of your z-endstop with a screw driver and one hand. This makes a huge difference. I highly recommend this.
Bed leveling thumbscrews
These replace the nuts under the bed base that you use to adjust the bed level. With the thumbscrews you can adjust each corner of the bed with one finger (or thumb). I highly recommend these.
Why Level your bed
Perhaps the answer to this is obvious, but as a newbie I really didn't understand how important this was.
If you have the following symptoms then you probably need to level your bed.
- The initial layer is not sticking to the bed.
- The initial layer isn't complete; parts of the print just don't get laid down.
- The head scrapes the bed in some spots (you probably worked this one out for yourself).
- Plastic gathers around the head during printing of the first or second layer.
- When printing the second layer the print head is picking up the first layer
These symptoms can also be caused by other problems. But leveling your print bed is the best and easiest spot to start. If you know other symptoms please add them.
Apart from having a level bed you also need to set the distance between the bed and your nozzle.
Essentially the nozzle needs to 'squash' the plastic against the bed. If you watch the first layer being printed each thread should end up wider than it does during the rest of the print. As a guide the nozzle should be a paper thickness above the bed. With a piece of paper between the nozzle and the bed you should feel the paper drag against the nozzle as you try to pull the paper out.
- The print bed material should be absolutely flat.
- The Y-Axis smooth rods should be leveled to each other.
- The Y-Axis base plate should make firm contact against the smooth rods on all four contact points (PLA bushings in the case of Prusa). There should be no rocking when pressing the corners.
- The X-Axis smooth rods should be level across the Y-Axis rods.
- The Z-Axis Opto/Mechanical switch and flag should be located on the motor side of the X-Axis carriage.
- A piece of A4 paper (or Letter if you from one of the more under-developed countries :D ).
I've used ordinary 3mm house hold glass on a prusa mrk I hot bed and it works really well.
If you can meet at least some of these prerequisites, it will be better than nothing. Each will contribute significantly to improving the quality of your prints.
Leveling the Print Bed
The process of leveling is fairly straightforward, and does not require any fancy tools. It involves only seven (7) easy steps:
- Stiffen the print bed support screws.
- Set adequate tension in three (3) springs.
- Adjust the Z-Axis homing flag.
- Set the tolerance.
- Level first diagonals.
- Level second diagonals.
- Secure hardware.
Stiffen the Print Bed
To stiffen the print bed, tighten the nuts under the bed so that the support screws are absolutely perpendicular to the print bed surface. Nylon-backed nuts insure that the screw will remain set, but if those are not available, Krazy glue, LockTite, paint, or nail polish will get the job done. If using these, allow time to set before moving on, as vibrations tend to loosen things up.
Set Spring Tension in Three Springs
The springs most commonly used on Prusa Mendels are the type you find in many ball point pens. While more than adequate for the job, they provide little resistance when fully extended, so they need to be compressed enough so that they provide sufficient support for the weight of the bed, while still allowing for slight compression during the occasional head crash, or low to the surface print (more on this below). We ultimately want to set the tension in all the springs, but for now, we only want to set three (3), leaving the last spring relatively loose. We will leave the front-right spring loose. To set the tension, tighten the nut under the base plate of each support screw, beginning with the two in the back, until the front and back of the print bed are about 2mm above the top of the fender washers. It is not important that they be level at this point, only that they be within this range, as this is where we will establish our Z-Axis home position. It is generally easier to slightly over-tension the springs with the intent of loosing them off during the leveling process. This allows you to set the Z-Axis homing flag (in the next step) to just above the bed and the you will raise the print bed back up to the hotend during the leveling process.
Adjusting the Z-Axis Home Position
As mentioned in the prerequisites, the Z-Axis min limit switch (Z-endstop) should be located on the same side as the X-Axis motor. The reason for this is that this side of the X-Axis weighs more, and is less likely to lag behind during downward movements like homing. Through repetition, bring the Z-Axis nozzle down to the surface of the print bed at the near corner on this side of the print bed. Now reset the homing flag (Z-endstop) so the head stops at this position. In my case, this is the front-left corner. It does not have to be perfect, but should be within +/- 0.5 mm (but Ideally just above the bed), so that we don't have to make huge adjustments to the tensional nuts. I prefer to be a little above the surface, so as not to reduce the clearance to the fender washer further, but either way will work.
In addition to being level the distance between the hotend and the bed is important. If you are using a strongly flat bed, such as glass, you should be able to achieve a gap of 0.2 mm. For less flat surfaces your gap will need to be larger. A common method of setting the tolerance is to place a piece of paper onto the bed, so that you can still move the piece of paper, but there is a slight drag.
As you go around the bed, adjusting the level, you should use a piece of paper to check the tolerance.
Leveling Diagonal 1
The leveling order is Front-Left, Back-Right, Back-Left, Front-Right. We refer to the first pair as Diagonal 1. With the Z-Axis homed, and positioned over the Front-Left corner of the print bed, use the tension nut to adjust the height of the print bed. Using the piece of A4 paper between the bed and the nozzle adjust the height until the nozzle touches the paper but you can still pull the paper out with a little bit of drag. Re-home the Z-Axis and checking that the paper still drags. Adjust the nut as needed until you can achieve drag without movement of the print bed.
Once you have set the front-left corner, repeat the process with the opposite diagonal corner in the back-right. Return to the front-left corner and verify that nothing has changed. On or two repetitions may be required.
Leveling Diagonal 2
The second diagonal is leveled in the same manner as the first, but starting in the back-left corner, and ending with the front-right. It may be that after completing the procedure to this point, you find that Diagonal 1 is no longer set. It will most likely be a small adjustment, and a second repetition of the leveling process will correct this in most cases.
Securing the hardware
One thing I cannot recommend enough, is that you secure the hardware. The RepRap is subject to high and low frequency vibrations, which will loosen any part, given sufficient time. A quick dab of hobby paint at the base of each nut will insure that your leveling effort pays off for the duration. On my machine, I use a second nut to lock each of the tensioning nuts, and then add a drop of red paint. It gets the job done, and is easy enough to remove with a hobby knife, if I need to take something apart.
Avoid adjusting the homing flag during leveling. If you move the homing flag for any reason, you must begin the leveling process from the beginning.