X axis belt tensioning

The X axis as standard uses a fixed bearing mounted on the right-hand Z axis carriage and a 3D-printed tensioner which attaches (at one end only) to the rear of the X axis carriage. One of the drawbacks of this approach in the standard build is that tensioning the X axis belt will lead to deformation of the Z axis rods. Essentially, as the belt is tightened, it will pull the Z axis rods closer, which is highly undesirable. 

If you plan to retain the standard tensioning method on the carriage, then I strongly recommend attaching collars to the right-hand side of the X axis rods against the Z axis carriage. 
8mm collars on X axis








My solution introduces two parts. The first is a clamp which fits to the rear of the carriage using existing mounting holes.
X axis belt bracket


An essential consideration here is that the location of the existing holes predicates the need for the clamping to happen on the bottom of the belt whereas the original was on the top.

This means that the direction of the X axis travel must be reversed in order to use this solution

This is a simple thing to change. It can be done either by a simple firmware change in Marlin or by reversing the cables to the X stepper. I don't propose to go into detail here, though, as it is very easy to find instructions online. 

X axis carriage bracket in situ

The second part of the exercise is to fit a modified bracket to the end of the X axis, on the far side of the right-hand Z axis carriage. 

This bracket includes a fitting for a 5mm ID 20T idler which has performed well in my tests. 


The pictures here show the device before and after fitting. It includes two 6mm tensioning screws which connect to captive nuts held within the body of the bracket. 

Importantly, these screws push against the ends of the X axis rods. This means that the tension on the belt is translated into pressure along the length of the rod and not (now) into the Z axis carriage. This implementation therefore brings two advantages: it provides a much more robust method of tensioning and also removes the problem of the original design in pulling on the Z axis rods. 

You can see that despite the fact that the problem should be resolved, I chose to leave the collars in place. One thing which they did show was the amount of flex in the original design. After the new tensioner was installed, there was a visible gap between the end of the collar and the carriage. A gap which wasn't there before!

These devices are downloadable from Thingiverse and Cults3D

Carriage Mount - Thingiverse  - Cults3D
Tensioner/Idler - Thingiverse - Cults3D

Addendum: When selecting the hardware for this, be sure to choose nylon locking nuts and not plain ones. This stops the tensioning being loosened by vibration.

Comments

Post a Comment

Popular posts from this blog

Update: Mopping up

Image
Today I have been working on mopping up some tasks which need do in preparation for creating the cable looms. This latter task is now a little delayed as I've decided to make the stepper motor cables with shielded cables, just because I don't like the amount of noise which they're pumping out .  Today, I have carried out a number of preparatory and remedial processes.  Installed the ESP01 WiFi module into the TFT35 screen. I had had a number of aborted attempts at this previously (it's more than a little arcane) but this time I have managed to get it working. In practice, I may not use it that often but it could be useful in some circumstances. It does seem very basic, but it does mean that I'm not tied to a cable.  I also decided to replace the IGUS bearings on the X axis with traditional roller bearing ones. While I had the carriage apart, I also replaced the heater block, throat and nozzle.  I also upgraded the X axis belt to a high quality Gates one as I'd b
Read more

Update: delayed but not forgotten

Those of you following this blog will have noticed that I've gone a little quiet for a while. This is due to a combination of factors. First, I am very busy with work at present and, secondly, I have a backlog of things which I need to print for jobs around the house. I can't print with the printer at the same time as rebuilding it. To give an update on progress: I still need to rejig the X-axis cable chains to rotate them by 90° The fanless PSU seems to be working very well indeed and makes a huge difference to the noise of the printer The foam insulation on the base of the HBP also seems to help a lot and works far better than I'd expected. Heat up time is improved significantly and excess cooling between prints is also reduced.  I have a set of Z axis pull-rods to install for extra rigidity but these need to be modded to fit the 350mm Z height.  I also really want to move to the latest version of Marlin to address a few annoying niggles which I know are present in 2.0.5.
Read more

Imminent release: Storage trays are finished

Image
Well, after some ado I have finally completed my storage tray solution. It's in numerous parts in order to remove the significant number of supports it would have needed and the parts just slot together. The whole thing then screws into the frame slots.  It also includes clips for the display ribbon cables.  These parts... Slot together like this. To be installed like this To do this I plan to make this available for download soon.  In other news: I have had another delivery from AliExpress as Which is an automatic case cooling kit. It has a built-in thermistor and will take 24V in and be used for the case for my SKR main board. This means that the fan will only come on when it's needed - part of my silencing scheme. I'll probably replace the fan with a Noctua to help further.  Visit the main content pages
Read more