Assembly step 9
- 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 nema17 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 you 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 everthing is aligned, tighten the coupler
Here is what your assembly should look like at this point:
Bill of Material
|2||1||SM-H05||Threaded Rod 200mm|
|3||1||SM-S06||Z Mount Plate|
|4||1||SM-M07||Z Axis Bearing|
|5||2||SM-H13||M5 x 16mm SHCS|
|6||2||SM-H03||M5 Flat Washer|
|7||3||SM-H06||M3 x 50mm SHCS|
|8||3||SM-H15||M3 Flat Washer|
|10||2||SM-H10||M8 Thin Hex Nut|
|11||1||SM-H12||M5 - M8 Coupler|
User Submitted Notes
|Note: This is the section to add your own notes pertaining to this sub-assembly) If you run into a problem or find yourself asking a question, please post the solution here to help the next person who has the same problem/question|
- 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 derbies (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 Deldrin 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.)
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.