Maintenance, Mods and Tips'n'Tricks - Prusa i3

[old man emu]

The original MakerFarm Prusa i3 has been around for a while now, and a lot of users have provided Colin with suggested improvements, many of which have been incorporated into the i3v.

The reasoning behind this Thread is that there needs to be a repository of hints and tips relating to the maintenance and modification of the old i3.

If you have a maintenance solution or tip'n'trick for the i3, please post it here after making sure that you give a title to your post so we can find your contribution in the future.

Old Man Emu

[old man emu]

The Y-axis stepper motor on the i3 is attached to a plate and doubler which slot into the rear frame of the printer. When the drive belts for the print bed are tensioned, the plate and doubler flex toward the centreline of the bed. This puts a side load on the pulley and belt assembly, causing strain on all the components, and which may affect the accuracy of movement in the Y direction.

Here is a picture of the underside of my printer, taken after I had done a temporary fix:
Y-axis stepper support.jpg

What I did was to join two cable ties and wrap them around the stepper body and the large threaded rod. I pulled the ties until the plate was square to the back frame plate. The pulley, belt, bed attachment point and bearing are now all in line. (OK I was holding the camera a bit low on the left hand side.)

As a permanent fix, I am going to get some 1/4" (6mm) threaded rod from a hardware store. I'll also need four penny washers -these are washers which have a larger diameter that the small washers usually used with this sized rod - and four standard nuts o suit the rod.

Then I am going to drill a hole in the side frame of the printer, and another one through the plate and doubler. The holes will be towards the bottom the plate and doubler and between the stepper motor and rear plate. The holes through the side frame and plate and doubler will be the same distance from the inside edge of the rear plate so that the rod is parallel to the rear plate.

I'll fit the 1/4" rod the same way as the large threaded rods are fitted, and tighten the two nuts at the stepper end of the rod. I'll back off the nut of the inner side of the frame, then pull the plate/doubler into position by tightening the nut on the outside of the frame.

Here's a rough diagram of this mod:

Y-axis stepper support with labels.jpg

Old Man Emu

[old man emu]

There are three things that affect the tension of the Y-axis belt:

1. Location of the stepper motor in its mount
2. Length of the belt
3. Length of the large threaded rods.

The first step in tensioning the belt is to back off the two inner nuts on the front plate which holds the idler bearing. This will allow the plate to move towards the stepper motor, loosening the belt.

1. Location of the stepper motor in its mount:

The four screws which attach the stepper motor go through slots in the support assembly. These slots permit the stepper to be moved about 1/4" (6mm) towards the rear frame plate for adjustment of the belt tension. When adjusting the tension of the belt. fit the stepper so that the screws pass through the ends of the slots furthest from the rear frame plate. Tighten down the stepper motor.

2. Length of the belt.

Assuming that the belt has been cut to the correct length, locate the screw nearest the stepper motor which goes through the attachment bracket and pass a short tag of belt around it, making sure that the teeth of the belt are on the inside of the loop. Secure the tag to the belt using a thin cable tie.

Feed the long length of belt around the idler bearing from the underside of the printer to the top.

Loop the belt around the toothed pulley attached to the stepper motor shaft.

Pass the end of the long length of belt around the idler bearing from the bottom of the bracket, making sure that the teeth of the belt are on the inside of the loop. Apply some tension to the belt by pulling the tag towards the front plate. The tag should not be more than about 1" (25 mm) long. Secure the tag to the belt using a thin cable tie.

Unscrew the outer nuts on the threaded rods until the end of the thread is just protrude from the nuts. Then wind the inner nuts against the inside edge of the front plate until the desired tension is obtained in the belt. (It is said that the correct tension is reached when the sound made by the plucking of the belt is similar to the bass tone of a cello.) To obtain more length of threaded rod, loosen the outer nuts on the rear frame plate by a few threads, then tighten their corresponding inner nuts against the back plate.

Y-axis belt tensioning.jpg Y-axis threaded rod exernal nuts.jpg


Old Man Emu

[AbuMaia]

If you decide to put vibration- and sound-dampening feet on the i3, you need to use at least 6. Two for the ends of the back plate, one behind each Z stepper, and two for the front Y idler plate. If you only put 4 feet on, the weight of the printer will cause the Y rods to flex and put the bed out of level.

[old man emu]

Access is the biggest hurdle to overcome when you want to tension the X-axis belt. The ends of the belt are hidden behind the plate which holds the bearings in place, and between that plate and the extruder assembly. The first step is to get the extruder assembly out of the road.

This is what the typical view of the parts you are going to work on:
Extruder and X axis bearing plate viewd from rear of printer.jpg

If you assembled the printer by following the video instructions, then you will have the nuts of the three screws (which form a triangular pattern) facing you and the screw heads hidden behind the extruder. Grab a pair of pliers to grip the shafts of the screws and then undo the nuts. Undo the screws which are in a straight line pattern and everything will fall away.

Take the plate which holds the linear bearings and extruder assembly and the three screws and nuts. Put the screws through the plate so the nuts will be between the plate and extruder assembly. Screw the nuts on a few threads so they hold on the screws. Now grab some painter's tape (or any thin tape) and wrap it around the screws under the nuts. Apply a few dabs of epoxy glue to the flat sides of the nuts and pull the screws through the plate so the nuts contact the plate. Set aside until the glue dries.

Printers tape around screws before gluing.jpg

Once the glue has dried, unscrew the screws and discard the tape.

Fit the plate so that the linear bearings are in their slots and temporarily hold the plate, bearings and rods together with a zip tie.
Bearing plate held in place with Zip tie.jpg

Now loosen the screws holding the stepper motor enough to move the stepper to the centreline of the printer. The nut of a screw on the Z-axis frame will prevent the X-axis stepper from moving the end of its slots. Live with it.
Screw preventing further loosening of X-axis stepper.jpg

Check the security of the belt around the right hand screw of the line of screws. Replace the zip tie if necessary. Push the assembly all the way to the right so that it is hard against the right hand Z-axis assembly.

Bearing Plate hard up against Z-axis assembly to permit tensioning of belt.jpg

Making sure that the teeth of the belt are inside the loop, grasp the loose left hand end of the belt and pull like crazy to tighten the belt. If you can grasp the axle of the stepper motor turn it anti-clockwise (that's counter-clockwise) to get a bit more tension. Temporarily secure the tag end of the belt with a clothes peg, or small bulldog clip. Permanently secure the belt around the left hand screw with a zip tie. NOTE: BOTH SCREWS WILL POINT TO THE SIDES OF THE PLATE AS THEY ARE UNDER TENSION. NO PROBLEM, IT WILL COME GOOD LATER.

Once these belts are secured to the screws, place a lever between the left hand Z-axis frame and the X-axis stepper motor. Using the lever, and superhuman strength, move the stepper motor to the left and when it has gone as far as you can move it, tighten the four stepper mounting screws. Pluck the upper section of the belt. It should produce a deep mellow sound like a cello.

Since you've got the extruder assembly detached from the printer, its a good time to clean off some gunk. Soak some acetone into a tissue or paper towel then pack it around the extruder nozzle and surrounding parts. Go have a suitable beverage break, leaving the acetone soaked paper to do its thing. When you come back, you'll find that the acetone should have softened the gunk, making it easier to get off. You might like to remove the hobbed bolt and its gear wheel and clean out any gunk in the teeth in the shaft of the bolt, of in the cavity of the filament feed. Sparingly apply some light machine oil to the bearing in the extruder assembly. You might like to lubricate all the other bearing in the printer at the same time. But don't go splashing the oil about. It will only attract dust and particles of filament.

Pop the three nuts into the nut slots of the extruder plate and refit the extruder assembly to the X-axis bearing plate.

Job done!

Now attach the extruder

[old man emu]

OK. You've tightened the belts on the X and Y axes, and they make angels weep with joy when you pluck them. Now it's time to check the calibration of the stepper motors.

You will need a fine tipped marker pen; your painter's tape and s blank sheet of paper, and a computer interface that allows you to give movement instructions to the printer (Pronterface is the one I use.)

Firstly, using your painters tape, attach the marker pen to the extruder stepper motor so that the tip of the pen will touch the print board when the Z-axis is homed.
Marker pen stuck to extruder stepper.jpg

Here's a better picture showing the marker against a white background.

Marker pen white background.jpg

Notice that the tip of the pen is to the right of the extruder tip along the X-axis. It is also towards the front of the printer board along the Y axis. What the distance is doesn't matter. You just have to take into account these offsets when you move the extruder assembly around.

Stick your sheet of blank paper to the print bed using painters tape to hold the paper down. Make sure the paper is flat and tight.

Now we get to play with Gcodes and M codes.

The Gcode you will use is G1. This code means "go to a point"

Just check that the tip of the pen will just touch the paper when Z=0 by entering the code [G1 z0] Note: I'm putting square brackets [ ] around the code for clarity. the square brackets are NOT ENTERED as part of the Gcode syntax.

If the movement is as slow as a wet week, you can hustle it along by including a Feed Rate code (F) to give you:

[G1 z0 F5000]

Adjust the position of the pen if necessary and re stick it to the stepper. When you are satisfied that the pen tip is in the correct place, get it out of the way by sending [G1 z10 F5000]

Now move the extruder to the centre of the print bed. My bed is 200 x 200, so the (X,Y) coordinates of the middle of the bed are (100, 100), which confuses me because my Home position (0,0) is at the right rear of my bed. All my printing is done in the (-X,-Y) quadrant of the Cartesian System.

Anyway, to get to the centre of the bed enter [G1 X100 Y100 F5000] (or the applicable X & Y values for your bed)

Now you want the extruder over on the left hand side of the bed, so enter [G1 X180 F5000]

When the movement stops, enter the Machine code [M114] . If you are using Pronterface, it will return this {X180 Y100, Z10}

Now home the Z axis using the interface's home button or enter [G1 Z0]

When the Z axis home, the marker will make a dot on the paper. Now raise the pen off the paper with [G1 Z10].

You want another mark 100 mm along the X axis from the first, so enter [G1 X80 F5000]. Again, when the movement stops, home the Z axis to make a mark on the paper and raise the pen out of the way. You will have two marks on the paper like this:

Pen marks on paper.JPG

Measure the distance between the two dots. If it is 100 mm, there is nothing more to do. If it is a milimetre or more off 100, then the Configuration.h file will have to be amended in the same way that the extruder calibration is done.

Now you have to do the Y axis. Use the same numerical inputs as you used for the X axis, but this time, use Y in the instruction, for example after going to centre of the bed, the first pen mark should be reached by entering [G1 Y 80 F5000], then the second point is reached by entering [G1 Y180 F5000].

Once those marks have been made, measure them to see that the are 100 mm apart and adjust the Configuration.h file if necessary.

You can run another check by having the pen inscribe a good ol' 3-4-5 triangle.

Make these moves:
[G1X180 Y0 Z0 F5000] then [G1 X180 Y80 Z0 F5000], then [G1 X120 Y80 Z0 F5000], and finally [G1X180 Y0 Z0 F5000]

Now, if I have done this correctly you should see something like this:

3-4-5 Triangle.jpg


Old Man Emu