Originally Posted by
JayneV
Hi everyone,
This is a long post (TLDR - CAD model has been tweaked, nearly finished)
Mactec, thank you for the pivot pin and grub screws idea for the left/right tramming adjustment. It didn’t occur to me to make the forward/back adjustment at the linear bearings either side of the gantry. I was thinking making the adjustments more locally around the z plate. I will think about your suggestions and how to implement them into my design.
I also, understood what you meant about the grease nipples on the carriages potentially robbing some travel. I downloaded the HIWIN models for the linear rails and carriages, since they have the same dimensions as the BST parts. The models included the grease nipples and I discovered the Y and Z axes range of travel are not affected by the grease nipples, but the X axis is. A couple minor adjustments will sort this out.
The last couple of days I have been busy tweaking the model and repeating several hours worth of work after Fusion crashed with lots of unsaved changes. It was a rookie mistake where I got carried away with making the changes and forgot to save along the way. Oops!! The changes were mostly related to swapping out the generic linear guides and ballscrew assemblies with more accurate models, and then tweaking the surrounding structure so everything fit together nicely. The entire gantry assembly is now about 95% complete. Some mounting holes still need to be created for mating parts. I still need to finish swapping the ballscrew assemblies on the base for the Y axis, but it is partially done and have simplified how the ballnut attaches to the gantry be removing one element from the load path. The ballnut now bolts directly to the gantry mounting plate and two of the bolts also capture the lower plate of the gantry beam itself.
I just noticed the constraint that mates the gantry beam to the mounting plate is slightly misaligned in the attached photos. I’ll fix that tomorrow so ignore how the right side bearings are not aligned with the rail. Looking at the second attached image (with the blue bottom plate of the gantry beam) it seems to make sense to extend that plate out to the edge of the mounting plate so all 4 bolts of the ballnut bracket pass through the plate, as was suggested some time back in this thread.
Would there be any benefit to adding a top plate to the saddle assembly as shown by the red markup in the last image to offer some added stiffness?
Our lockdown restrictions were eased today, which means we are now permitted to freely travel within the city limits if we have had both vaccine shots, so tomorrow I will be going to my brother’s shop to make a part or two. The parts will just be some spacers for the linear bearings on the x axis so I can finally hold a physical part in my hand. Hopefully that will boost my motivation because I feel like I am getting stuck in the CAD model suffering from analysis paralysis.
I will also have a chance to go over the model with my brother to figure out how to machine the contact surfaces for the linear rails. The z axis should be easy because it is not that big, but the X and Y axis might be larger than the working envelope of his machines. I’ll know more tomorrow.
Have a great evening/day.
Jayne
PS. The first image, in full colour, was a screen shot captured from my computer, the rest are screenshots from the Fusion 360 app on my phone. There doesn’t seem to be an option in the phone app to turn on colours or edge visibility.