So I haven't been so active on here for a while, but having started a new project I thought I'd post up a build log for you all to
This will not be a quick build as workshop time is limited, I've already been pecking away at this for over a month to get to where I am today.
For a while now I have had the urge to build a 3d printer, reading around and doing a bit of research I decided on a "CoreXY" style. So the basics of this style is to create a box frame to which the linear bearings and everything else are attached. So a few weeks ago I started by deciding on the outside dimensions, 425mm x 425mm x 500mm high, with the plan that (hopefully) I will end up with a Print capacity of about a 300mm cube.
Over a year ago I had thought about building a 3d printer and had ordered some 400mm x 8mm rods and a bunch of 8mm linear bearings. In my research I found that many found the 8mm rods flex on larger printers, so that made me experiment with deflection and I found that I got about 0.4-0.8 mm deflection on a single 8mm rod with a highly specified weight in the centre (a box of coach bolts). So I got some 12mm rods and linear bearings for the Y axis. I plan on using 3 8mm rods for the X-axis in a "L" configuration, that should minimise deflection.
I have no fancy 3d renderings of what I am building, so that's another reason why this will be a longer build, I will be spending plenty of time thinking before hacking up metal.
So a little more on the design (such as it is). I had a few lengths of 25mm box section steel just lying around waiting to be used, so I cut 8x 375mm lengths for the stretchers top and bottom, and cut 4x 500mm lengths for the 4 uprights. I then set up a vice-stop on the mill and drilled & reamed a 8mm hole through, centered 50mm from one end in each upright. Then I drilled out one side of the 8mm hole to 16mm and then cleaned up the drilled hole with a boring bar to ensure a truly round hole (ended up being about 16.2mm) This was done so that when the whole box was assembled I would have a means of adjusting both the Y-axis bars to get them parallel and flat in relation to each other. I figured I would make bushes for these holes that could be have offset holes in them to carry the Y-axis bars.
It was at this point that I realised that I would need a way of inserting the 12mm Y-axis bars through the frame, so I enlarged 2 of the 8mm holes in the uprights to 12mm.
Then I started to weld up all the stretchers and uprights (after carefully marking each, and also drilling a few M5 holes for potential future use), this called for some thought as the process of welding introduces many stresses and it is remarkable how much it will pull and move parts. I ended up by tack welding only the very outside corners, making 2 sides and then carefully tacked on the stretchers to join the 2 sides into a cube. Then I followed a painstaking process of checking every corner with my 9" engineers square, finding the worst out-of-square culprit and placing a tack weld in the right place to pull it back into square. (it was really surprising how much the metal moves as it cools) Then I would wait until it had cooled before moving onto the next one. Lather, rinse and repeat....... This took quite a few sessions, but was really worth it to get a cubic frame that was less than 1mm out of square in any axis.
Then I made up 3 bushes that were concentric and one that was 0.35mm non-concentric (the error I measured in the holes I previously bored), fitted the arrived 12mm ground bars, and voila (bucket for scale)
Today I started thinking about making sure that the 2 bars were absolutely parallel and also flat with relation to each other. I previously was trying to get them running true in the same plane as the top of the frame, but I realised that the frame has a slight rock to it (about 0.7mm), so it struck me that the most important thing is to get both Y-axis bars true and parallel to each other, everything else can be made true in reference to the Y-axis bars.
But how do you measure any runout when the 2 bars are 400mm+ apart? Then I remembered "Rollie's dad's method" and wondered if it could help in this situation. As I recalled it, Rollies dad's method involved using 2 long bars resting on the ways which would then seemingly amplify any error and make it plainly visible at the 2 ends of the long bars. So I set the frame upside down (the only long bars I had wouldn't fit in the gap above the 12mm bars) and stuck 2 6ft lengths of 25mm box section on the bars and took a few steps back. (parts magnified for clarity) I set it on the seat to prevent me having to crawl on the ground to "sight" along the bars!!
Definitely can see that there is a slight twist to the bars. So I turned up another offset bush to replace a concentric one and tried again. A little better, but not enough, so a 3rd offset bush was made with this result. Much better!!
I made up an extension for my digi-vern so I could check the distance between the 2 Y-axis bars and was very pleasantly surprised to find they were only 0.03mm out!! Here's the easy way I made the offset on my mini lathe, just inserted a shim between one jaw and the work.
Here's an offset bush next to a concentric one
As you can see I have marked the "low" spot on the offset bush, this makes it easy to put a matching mark on the frame so that when re-assembling I can be sure they go back in the right position.
Here's a couple of close-up shots of the insert/bush in place
Next up will be working on the Y-axis carriage's, but I gotta order some ali bar for making those.
Stay tuned for irregular updates.