Frame, part 2

Again, we are using instructions similar to the Prusa Mendel, but with minor modifications:

1. We are using manufactured linear bearings instead of PLA bushings.
2. For the Y axis, we have printed bearing mounts which can be screwed to the base plate, rather than glued.
3. The X-axis motor mount and idler do not have closed ends for the X-axis smooth rods. Instead, use two M3×20mm screws in the X-axis idler to hold the rods in place. This allows the X axis and its smooth rods to be removed without dismantling the Z axis as well.

NB: Whenever the front of the frame is referred to, this is the side with the bearing guide and without the y motor bracket. Right and left are as viewed from the front of the frame.

Pre-assembly checks

Check the following before assembling part 2 of your TVPrusa:

• The LM8UU linear bearings run freely on the smooth rod.

Tools

• 2.5mm hex/allen key
• 13mm spanners x 2
• Digital callipers
• 8mm drill bit

Y Axis

Y LM8UU Holders x 4

• LM8UU linear bearing x 1
• M3 nut x 4
• Y LM8UU holder x 1

Insert the linear bearing into the LM8UU holder printed part. The fit should be tight. If not, use some paper or tape around the bearing.

Trap the M3 nuts in the slots. Tip: Use a short bolt (e.g. M3x10) with a washer to pull the nut into the slot.

Print Bottom Plate

• Assembled Y LM8UU holders x 4
• M3x20 bolt x 16
• M3 washer x 16
• Print Bottom thick sheet part x 1

Loosely bolt the LM8UU holders assembled in the previous step to the Print Bottom plate using the M3x20 bolts, each with a washer. They should have freedom to move and rotate slightly, for alignment.

Mounting the Print Bottom Plate

• Assembled Print Bottom Plate x 1
• Assembled Frame x 1
• 404mm Smooth bar x 2

Insert the smooth bars into the linear bearings.

Mount the print bottom assembly on the frame by inserting the smooth bars into the bar clamps on the front and back of the frame. This will required the bar clamps to be approximately in the correct position, and loose. The smooth bars hang below the threaded rod and run below the print bottom thick sheet (wooden) part. The print bottom plate is asymmetrical - the holes for the belt clamps are slightly off-centre. They should be on the same side of the frame as the bearing guide is in relation to the Y motor bracket. When looking from the front of the frame, this is the left hand side. Do not tighten up the bar clamps yet.

Square one of the y axis smooth rods with the frame. Measure from the vertex to the edge of the bar clamp (approximately 43mm here, give or take), or the outside of the smooth bar. The value is not important as long as the print bottom plate will fit between the triangles of the frame. Callipers are preferable to a tape measure - the more accurate the measurement the better.

Ensure the equivalent measurement at the back of the frame is the same.

Secure these two bar clamps, keeping the alignment by tightening the inside nut (closer to the centre of the frame) and holding the outside nut still. Be careful not to over-tighten - make sure the bars are firmly held but go no further.

Slide the print bottom plate backwards and forwards a few times, then tighten the bolts on the two linear bearing holders on the secured smooth bar. This makes sure those two bearings are aligned with each other.

Slide the print bottom plate backwards and forwards a few more times. Measure the distance between the smooth bars at the front and the back of the frame as accurately as possible. Take the average of these two measurements and fix the other smooth bar at this distance from the secured smooth bar. The more accurate you can be, the better. This makes sure the two bars are parallel.

Slide the print bottom plate backwards and forwards a few more times, before tightening the bolts on the remaining two linear bearing holders. This makes sure these two bearings are aligned.

To test if your y axis is properly aligned, tilt your frame to a 45 degree angle. The print bottom assembly should slide along the y axis under its own weight before the 45degrees is reached.

If the print bottom assembly does not slide smoothly or requires prompting, loosen everything up and repeat the process.

Aligning the bearing guides

The path of the belt needs to be straight. Align the centre of the front bearing guide with the centre of the holes for the belt clamp.

Measure the distance from vertex to bearing guide. Align the back bearing guide with the front using this measurement.

Square the Y motor bracket by matching the measurement from vertex to y bracket on the top and bottom rods.

The rest of the Y axis

The next stage in the Y axis assembly requires the belts. These will be included in part 3.

Z Axis

Z Motor Mounts x 2

• Z Motor Mount x 1
• M3 nut x 2
• M8 washer x 4
• M8 nut x 2

Trap the M3 nuts in the slots.

Secure the Z motor mount to the frame. The flat side of the motor mount goes at the bottom, and the side with the captured nuts goes on the outside.

Z Smooth Bar x 2

You can install the Z smooth bar at this point, although it will need to be removed to install the X axis.

• Rod clamp x 1
• M3x20 bolt x 2
• M3 washer x 2
• 350mm Smooth Bar x 1

Insert the smooth bar into the bar clamp at the bottom of the frame, and use the M3x20 bolts and rod clamp to secure it at the top to the Z Motor Mount. Do not fully tighten yet.

Z Motors and Leadscrews x 2

• Motor x 1
• Plastic tubing x 1
• Coupling x 1
• M3 nuts x 4
• M3x20 bolts x 4
• M3 washer x 4
• Z leadscrew (210mm M8 studding) x 1

Put the tubing on the motor shaft and sit the motor on the Z motor mount.

Capture the nuts in the half of the coupling with nut recesses.

Use the M3x20 bolts with a washer each to loosely join the two halves of the coupling together. Slide the coupling over the tubing on the motor shaft until the bottom of the shaft is at the middle of the coupling. Insert one end of the leadscrew into the other end of the coupling, until it meets the bottom of the motor shaft. Tighten the M3x20 bolts evenly, keeping the leadscrew straight and square.

X Axis

• X Motor End x 1
• X Idler End x 1
• M3 nut x 2
• M3x10 bolt x 2
• LM8UU linear bearings x 4
• Cable ties x 4
• M8 nut x 1
• M3x20 bolt x 2
• M3 washers x 4
• M3 nyloc x 2

Use an 8mm drill bit to remove the support material covering the lead nut hole from the x ends.

Capture the M3 nuts in the X Motor End slots. Tip: Hold the X smooth bar vertically and place the nut on the end in the centre. Push the X Motor End down onto the smooth bar until the nut reaches the nut recess. Use an M3x10 bolt with a washer to draw the nut into the recess.

Press the linear bearings into the X ends, making sure they are straight and sit within the notches. Cable tie them in position, trimming off the ends of the ties.

Screw the M3x10 bolts into the X Motor End just until the engage with the nut. (The washers are unnecessary and may cause a rattle when printing, so it is best to omit these despite the picture).

Slide the left Z smooth bar up and out of the bottom clamp, position the X motor end underneath and slide the Z smooth bar down through the linear bearings and back into the clamp. Slide the X motor end up the smooth bar and onto the leadscrew. Screw the M8 nut onto the leadscrew beneath the X motor end and let the X motor end sit on the nut.

Repeat on the right hand side with the X idler end.

Approximately square the Z smooth bars and level the X ends by eye. Insert the X smooth bars through the holes in the X idler end and into the slots in the X motor end. Use the M3x20 bolts to hold the rods in place. Do not tighten the nylocs yet as the X carriage still needs to be added.

Troubleshooting if the X smooth bars are too long:

1. Is the distance between the washers on the inside of the vertices 250mm?
2. Is the distance between the outsides of the z smooth rods 414mm (give or take a millimetre)? If not, do you have washer - nut - washer between the vertices and the z motor mounts?
3. Have you pushed the captured nuts into the x motor end as far as they can go and can the M3x10 bolts be unscrewed any more?
4. Are the linear bearings fully inserted into the x ends?
5. How much off-square are your z smooth rods? If they are even only a little bit wonky, this can make the x smooth rods appear the wrong size

If fixing these does not solve your problem, add extra washers between the vertices and z motor mounts to space the Z smooth bars further apart, if the bottom threaded rod is long enough. Let us know where you get to, if you are still having problems we can arrange to meet up.

X Idler Bearing

• M8x25 bolt x 1
• M8 washer x 4
• M8 nut x 1
• Bearing guide x 1

Attach the bearing guide to the X idler end. The order is:

1. M8x25 bolt
2. M8 washer
3. Bearing guide
4. M8 washer x 2
5. X idler end
6. M8 washer
7. M8 nut

Back to the previous part.