Linear Rail Z Axis Mod for Ender 3 by bamoore01

Last crawled date: 3 years ago

Note: Check out the 1.22.21 update for this mod below.
8.5.18 - I've re-designed this mod completely from the original version that I had out here. That version had the X gantry attached to the linear bearings with printed plastic adapters. I was worried how stiff that set up would be and it turns out I should have been more worried. It quite literally was crap. All of the original design is gone.
The way I did this mod was to mount the linear rails to the front of the vertical posts and attach then directly to the metal plates that hold wheels and X gantry. Since there are no soft attachments with plastic it makes for a solid mod. You will have to print the right and left templates to drill the bearing block mounting holes and a new Z limit switch holder.
The result of moving the bearings out to the front of the vertical posts is that the X gantry, X gantry mounting plate and the hot end are moved out by 9.25mm. Moving the hot end may require moving the Y axis limit switch. For me that was not problem since I did the Y linear rail mod and could simply move the Y limit switch to accommodate for the shift in the Y. To maintain the geometry of the Z lead screw, the back X gantry mounting plate needs to stay in the same place. I did this by removing the three axle screws and replacing them with screws that were 10 mm longer leaving the ability to adjust the position of the back plate.
On the original Creality design the X gantry is fixed at both ends to the mounting plates with no allowance for adjustment. That works fine but I changed the right side a bit to allow a final adjustment to be made on the X gantry to right X gantry plate with T-Nuts. It simply allows for a little error in measurement and execution since we all don’t have CNC machines to make holes exactly where they should be.
Notes;

All of the positioning of the right and left front X gantry plates is pretty much fixed by the geometry of the linear rails and bearings when they are connected and fastened to the vertical rails. That’s not the case for the left side rear plate that is connected to the Z lead screw. That plate needs to stay in its original place and since the front plate moved by 9.25mm the space between the left plates needs to increase by that much. That is not a problem on the right side since there is no rear plate. I thought the best way to handle that was to simply make the spacing adjustable. If you look at the pictures you will see that I used the extra Nylock nuts that came off of the axles to clamp each plate. This way I can fairly easily adjust the space between the two plates. The front plate is fixed so the adjustment nuts can be used to move the back plate forward or back to make sure that the lead screw is the same distance from the vertical post at the top and bottom of the screw and that the two plates are separated equally at all three axle points. I think that using the spaces as I did helps stiffen the entire front/back assembly so use them if you can. Notice that I used the eccentric nut on the back of the inside axle on the right side of the left plates. This is because that hole is bigger that the rest for the eccentric nut on the original design and the eccentric nut works perfectly.


As I mentioned, I did the other two axis mods already so I had a lot of spare parts to use for this. You may or may not have to get more parts.


Left Drill Template. You have to remove the left side front plate from the printer. Use the 5mm axle screws to attach the drill guide to the plate using the two holes marked A. Drill out the four B holes through the left front metal plate with a 3mm or 1/8” drill bit. The result will be that the bearing block will attach to the plate just below the X gantry. It is best if you can use a drill press to help guarantee that the holes are straight.


Right Drill Template. Remove the right side font plate and attach it to the template using the three 5mm axle screws through the holes marked A. Drill the right plate through the B hole with a 5mm drill bit (3/16” may work, if not use a 13/64” if you don’t have metric bits). Drill the holes marked C with a 3mm or 1/8” drill bit.


Limit Switch Adapter. This is easy to replace. Just unscrew the original and put this one on. It will move the limit switch out 9.25mm. Obviously it will have to be adjusted before you retram you plate.


Taking it apart is easy. Just unscrew things. Putting it back together can be a challenge. Things have to get put together in the right order or you take it back apart again. The most important one is the two screws that hold the X gantry to the left front plate. They go on and get tightened first. You can’t get to the after the plate is attached to the bearing.


Adjustment. There are some things to watch for here. On my machine the vertical posts were turned a little. It didn’t bother the wheels much but the linear bearings don’t like it. The best way to handle that is after everything is nice and snug and with the gantry at the bottom of its travel, loosen the bottom two screws and top two screws on the left side only. While the four screws loose, loosen the three 5mm T-Nuts on the right X gantry plate to X gantry and retighten. Then retighten the 4 screws at the top and bottom of the post. Then do the same to the right side including loosening and tightening the 4 T Nuts. That should square the posts and set the bottom spread. After that is done, move the gantry to the top of travel and loosen all 4 of the top screws only and tighten. This should set the post spread.

After the posts are set you should make sure the X gantry is square to the posts. The best way to do this is to loosen the four 3mm screws holding the left front plate to the bearing block and the three 5mm T Nuts on the right side of the X gantry. Then clamp a square to one of the posts and the X gantry. Then tighten the four 3mm screws and the three 5mm T Nuts.
Parts List;
Rails
2 x 350mm mgn12 Linear Rails with mgn12H blocks. I got mine from Amazon.
24 x M3x8mm Hex Socket Cap Screws. Attaching linear rails to upright posts.
24 x M3 T-Nuts. Attaching linear rails to upright posts.
Left Side
4 x M3x6mm Hex Socket Cap Screws. (Attach left plate to bearing block)
3 x M5x50mm Screw for the three Wheel Axel Spacers
9 x M5 Nylock nuts ( I had plenty of these as spares from the linear rail mods)
5 x M5 spacers (These came from the linear rail mods also. Could use a washer)
1 x eccentric nut (from the inside Wheel Axel)
Printed Left Plate Template
Right Side
4 x M3x6mm Hex Socket Cap Screws. (Attach right plate to bearing block)
3 x M5x6mm Screw
3 x M5 T-Nuts
Printed Right Plate Template
Limit Switch Adapter
Printed Z Axes Limit Switch Adapter
Rev History;
8.12.18 Added Limit Switch Adapter V2. Moves the limit switch out 10mm so that it hits on the metal Left X Gantry Plate instead of the rubber wiper on the end of the bearing block.
8.13.18 V2 of the Limit Switch Adapter had problems. Replace with V3.
12.17.18 Replaced V3 of the Limit Switch Adapter with V4. Some people were having trouble splitting/printing the adapter. There was a problem with the STL so I rebuilt it. There is no difference in the final size and shape so if you printed the V3 file there is no need to print the V4 file.
4.6.20 I've had some requests for a CAD file of the drill plate so people could use it to cut new plates so I've included a DXF of that drawing.
1.22.21 I just added a dual z drive kit to my printer. I used the kit from BCZAMD on Amazon. It's a little over priced for all the parts but I guess I didn't feel like hunting down all the parts separately. A while back I added direct drive to my printer. I was never really happy with the results. It seemed like I was getting more banding with the direct drive mod. So.. I finally did a little checking. I disconnected the drive screw so the gantry moved freely on the z axis. What I found is that lifting the gantry from where the screw lifts the movement was noticeably smoother when the print head was on the left side of the gantry compared to the right side of the gantry. This really isn't that surprising if you think about it.
I can't say what the same experiment would be with a stock print head. So I installed the dual drive kit. This is the one that has a belt across the top connecting the two Z screws and uses the original motor only. Prints are noticeably improved. No more banding. I think I finally got this printer printing how I want. One note about the kit. The Ender 3 is not a perfectly aligned machine (huh??????). On mine the right side lift screw from the kit did not align with the top support bearing from the kit. I was bad enough that the gantry would not travel all the way to the top before binding. I had to file the top bracket holes into slots so I could move the bracket to the left a little more that 1 mm. Not a big deal but not the fault of the conversion kit. I also tried the aluminum bearing blocks you can get separately. They are close but also can be a little off in the Y direction so you might have to shim them out or file them down (maybe).