Assembly step 9
These are the instructions for the SO1 and are here for historical reasons only.
If you are building an SO2, please see the instructions at http://docs.shapeoko.com/
The Z-axis both holds the spindle and moves it up and down. There are a number of alternative ways to assemble it, as well as several replacement / upgrade options. While it's arguably better to assemble one's machine in a stock configuration, one could install an ACME Z-axis upgrade at this point instead of the stock threaded rod.
- Slide the M3 bolts through the z-axis mounting plate
- Place the 3/4" nylon spacers on top of the mounting plate
- Bolt the motor to the spacers
- The thread depth on NEMA 17 motors is notoriously unpredictable. Although datasheets spec 4mm minimum depth, we've run into some that are only 3mm deep and others that exceed 5mm. It’s a crap shoot.
- If your thread depth is shallow, you won’t be able to bolt the motor firmly to the spacers. In that case, use an extra M5 washer to make up the space.
This is the only time you will have to measure in the whole assembly process :-) Also, make sure your jam nuts and delrin nut run smooth before starting this assembly step. See the User Submitted Notes below for more details.
- Thread 2 M8 jam nuts onto the end of the M8 threaded rod.
- When the top jam nut is 5mm-6mm away from the end of the threaded rod, tighten the two nuts together.
- These nuts give the assembly a place to rest on the bearing, they also provide a positive stop for your z-axis coupler.
Now it's time to put your two assemblies together.
- First, slide your coupler through the motor mount hole until it's pushed up on the stepper motor shaft
- the coupler is transparent blue in the pictures below to help see the motor shaft and threaded rod
- Your shaft will be just short enough to *not* stick out the end of the coupler, but you'll probably be able to see it
- Keep note of the orientation of the coupler. one end accepts M8, the other M5. Put the M5 side up first, so the M8 is exposed on the bottom.
- Slide the assembly from step 2 (threaded rod with two nuts) up through the Motor mount plate.
- Slide the z-axis bearing onto the rod and press it into the hole of the z-axis mounting plate.
- this is going to be a little difficult because the bearing is a friction fit inside the hole. Once you get it close, just use your thumbs, or the edge of a work surface to help push it through. Make sure the edge is deburred. Try not to push on the shaft of the stepper motor.
- While sliding the assemblies together, make sure the M8 threaded rod makes it up to the stepper motor shaft.
- Once those are lined up, slide the coupler back down until it's resting on the M8 jam nuts.
- After the coupler is resting on the M8 jam nuts, verify the jam nuts are resting snugly against the bearing.
- Verify the bearing is flush with the bottom of the motor mount plate. The top of the bearing will be protruding from the top of the motor mount plate. That's OK.
- Now that everything is aligned, tighten the coupler
Here is what your assembly should look like at this point:
Bill of Material
|8||3 (or more)||SM-H03||M5 Flat Washer||(Optional, use if necessary to achieve correct spacing and to allow motor bolts to seat completely)|
|11||1||SM-E01||NEMA 17 Stepper Motor|
|14||3||SM-H15||M3 Flat Washer|
|16||6||SM-H02||3/4" Nylon Spacer|
|23||1||SM-S06||Z-Axis Mount Plate|
|24||2||SM-H13||M5 x 16mm SHCS|
|25||1||SM-M07||8mm x 22mm x 7m Bearing (Z-Axis)|
|26||2||SM-H10||M8 Thin Hex (Jam) Nut|
|27||1||SM-H12||5mm -- 8mm Coupler|
|28||1||MSK01-03||Makerslide Extrusion - 200mm|
|29||1||SM-H05||Threaded Rod 200mm|
|30||3||SM-H06||M3 x 50mm SHCS|
User Submitted Notes
- Threaded rod too small. Wrapping the rod in some sort of metal foil or tape was suggested on the forums if the coupler does not hold it securely.
- Use the ring end of a 5/8ths inch combination wrench to press the bearing.
- I found that when putting the lock nuts on the rod that they did not turn smoothly. By running the nut up and down the full length of the rod by hand, this was cleared up. Unfortunatly this was not enough to make the delrin nut smooth also. Run the delrin nut up and down the threaded rod until it is smooth. Keep an eye on the thread and clear any black delrin traces from the thread and also blow out the delrin nut regularly to clear debris that has come loose inside the nut.
- If the delrin nut is still not smooth after running it up and down the screw several times, file a small angled flat on the end of the screw. Put the nut in the freezer for a few minutes, then run the screw through the nut again. It should run much smoother.
- If you have problems pushing the coupler up on the stepper motor shaft just take a knife and clean the edge on the coupler.
- I found that some delrin came off and created a blockage and I had to screw it in and out several times (I guess I went for 5 to 10 mm each time) to remove the debris (by blowing in the hole and on the thread) or it would get stuck...
- My stepper motor shaft was too long, and I ended up only using one of the jam nuts, I used some threadlock and jammed it against the coupler.
- NOTE: If your Delrin Nut is stiff and is not easy to move. Use your hand held electric drill and attach it to the short side of the stepper motor shaft that is exposed. Just run it up and down a few times to fix the problem.
- NOTE: For an alternative assembly method, see this post from the forum:
If the z-axis assembly wobbles the problem is likely caused by the way the coupler lock screws have cut into the threaded rod along with the threaded rod being undersized. Try having the rod go 2mm farther into the coupler. (If the motor shaft is too long it might be hitting the threaded shaft. You can use a Dremel tool with a cut-off wheel to cut about 4mm off the shaft end. Cut the shaft with slow bites, don't let the shaft heat up. Chamfer the motor shaft end. Protect the bearing and wire opening of the stepper from grinding dust by covering it with blue painters masking tape.)
For a wobble free coupling you need two things: 1) the coupler's inside diameter should be just big enough that you can barely slide it over the shaft. 3) the shaft needs to go far enough into the coupler that it goes 2-3mm past the set screw locations.
To make my coupling work wobble free I had to cut 4mm off of the stepper motor shaft (it was too long and was forcing the threaded rod to barely reach the set screws). Then I locked the nuts together with about 8mm of length on the rod. Then I carefully ground the threads off the rod (the rod was undersized and the threads made shimming the rod hard - ymmv). I worked it slowly (using a Dremel with a cut-off wheel to slowly grind down the rod while I rolled the rod on a table). Keep it concentric. Then I rolled shim stock around the end to shim it up the correct diameter for the coupling. I made it a very tight fit. Now it's wobble free.
A separate note: I found it easier to change the order of assembly here. I pressed in the bearing first. It is a lot easier this way to make the bottom side of the bearing flash with the mount (where the Z slider will be screwed on). Then I dropped in the threaded rod from top, and then put everything together there.
Also I would recommend NOT to cut the threaded rod. The length of the rod as coming in the kit fits tightly, and I set them so that the threaded rod is touching the shaft of motor (when all the mounting screws on motor tightened). The two locked nuts provides reference point for when the spindle is pressed down. The touching of the rod and shaft provides the reference point on the other direction. Without it, the weight of the spindle would compressed the coupler spring and have the tool head extended down further than you thought.
- NOTE: Further observations about the flexible coupling for builders having problems with apparently undersized lead screws. In step 2, you are supposed to tighten the two jam nuts so that there is 5-6mm of the lead screw extending into the coupler. IMHO, this is far too short an extension into the coupler especially for an 8mm threaded rod. It should ideally be approximately twice the diameter of the rod meaning about 16mm insertion. Then the coupler will grab tightly. But this is NOT possible because the NEMA stepper motor shaft extends too far into the coupling. Take a look above at the Section D-D part of the Assembly 2 drawing (PDF). You can see that the motor shaft extends well past the small bore part of the coupler. It does not need to be this long. This limits how far the lead screw can extend into the coupler and hence how securely it can be affixed.
So the obvious solution is to shorten the stepper motor shaft appropriately. Apparently stepper motors have varied shaft lengths from the factory. So you need to measure how long the shaft needs to be to just reach the end of the small bore in the coupler with the coupler pressed onto the shaft to about 1mm of the motor housing. You can see the small gap between the coupler and motor housing on the Assembly 2 drawing above. The gap is required so that the coupler does not rub on the motor, of course.
You can verify these measurements (like I did) by loosely assembling the components and measuring the gap when the M3 bolts with spacers are tightened. Just make sure that the bearing is already pressed into the Delrin mount and the 8mm lead screw is not hitting the end of the motor shaft. Measure the gap and then take the assembly apart. Now you can cut the motor shaft to be length of the small bore in the coupler PLUS the measured gap.
OK, now you can extend the 8mm lead screw much further into the coupler and adjust the location of the lock nuts accordingly. Now everything should be tight and secure (so at least in my kit).
Modified Z drive Assembly
I've always thought that the Z drive design was a weird oversight, so I assembled my Z as follows:
- Insert the bearing into the Z plate, making sure it is flush with one side of the plate. It is important that the bearing lines up and sits horizontally. The side that's flush is the bottom, the side where the bearing sits proud of the plate is the top.
- Find the cleaner end of the threaded rod. Thread a nut on the other end. Thread it until 19-20mm of rod sticks out.
- Slip the bearing, with the Z plate, on the short end of the threaded rod, bottom (flush) side toward the nut. If it's not a tight fit, take it off and put some tape on the rod until the bearing fits snugly. Aluminum tape works very well (I needed two turns of that); plumber's PTFE tape is good too. Tape only the 7mm of rod that goes into the bearing. Work the tape in with your fingers, then try the bearing again. The tape helps keep the rod centered in the bearing during assembly.
- Thread another nut on the end of the rod. Tighten the two nuts firmly, trapping the bearing between them. You should have 8-9mm of rod sticking out of this last nut.
- Slip the flexible coupler on to the end of the threaded rod. If it's not a snug fit, again, tape the end of the rod. Do not tighten the coupler grub screw(s) yet.
- Mount the Z motor to the Z plate.
- Thread the Delrin lead nut about three quarters of the way on to the threaded rod.
- Bring the Z plate and the Z rail together. You'll see that the bottom nut touches the Makerslide. Using a file, notch the inside top end of the Z Makerslide enough that the nut can rotate freely, even with the rail in the closest position to the threaded rod. You need a notch about 12mm wide and 4mm tall, and it's not a problem if you remove a little more material than that.
- Attach the Z rail to the Z plate, but do not tighten the screws all the way yet.
- Mount the four Z V-wheels on the standard carriage plate, put the Z axis assembly in, and adjust the eccentric spacers.
- Line up the lead nut with the respective holes in the carriage plate, and screw it in. Temporarily tighten the screws.
- Looking from the side of the assembly, find the position for the Z rail on the Z plate that makes the threaded rod run parallel to the Z rail. This is easiest if you look from the angle where the edges of the Vs on the rail seem to overlap. The small space between that edge and the threaded rod should be the same at the top and at the bottom of the assembly. Tighten the Z rail screws.
- Loosen the lead nut, then tighten it back again.
- Tighten the grub screws on the flexible coupler.
- Continue with the assembly of the X carriage as in the original instructions.
This configuration has the advantage that up and down forces on the Z axis are both applied to the Z bearing. The flexible coupler does only its intended work, that of compensating misalignment of the end of the rod and the motor shaft; it doesn't have to support the weight of the entire Z axis. Potential problems are a threaded rod that's not straight, and M8 nuts that are not quite perpendicular to the rod. Unfortunately, the latter is a frequent occurrence, but it seems that most of the wobble gets taken by the flexible coupler, and the Z axis itself is steady.