Delta End Stops
I think that printers “End Stops” are the second most important thing on a 3D printer. Not sure what the first most important thing is, but end stops, are definitely the second most important thing. End stops, tell the printer what it’s working dimensions are going to be. Every time you turn on your 3D printer it has no idea of its place in the universe. It doesn’t know how much room it has to print in. It doesn’t have a clue about the dimensions of the X, Y, or Z axis, until you send that G28 (home) command.
The sending of the G28 command, allows the printer to see its dimensions, once this is done, it knows how much room it has to move around in. You could say, that the end stops are the printers birth place, it’s centre of being.
There are a few different sorts of end stop, as explained below
- Mechanical End stop – Mechanical end stops are the simplest and most commonly-used type of end stop. The switches are placed on each axis. At the start of each print and after a G28, the 3D printer moves each axis until the carriage hits the switch.
- Hall-O – The Hall-O is a “Hall Effect” Sensor PCB that reacts to magnetic forces. It is a non-contact proximity sensing device. It measures the distance to a magnet. Therefore, it is ideally suited as a precise end stop measurement.
- Optical Endstop – Optical end stops are a precise non-contact proximity sensing device. The end stop is activated when the light beam is broken
There are others, but these are the main ones. I guess you’ll be asking which is the best type to install? Well, that’s up to you. I tend to go for the Mechanical type, I have seen these types on CNC machines, costing thousands. If it’s good enough for them, it’s good enough for me. They are also cheap and affordable at least to be able to carry a few as spares in case you need one.
In this post, I will concentrate on the Delta style printer. Not that this doesn’t apply to the Prusa style ones. But in my mind the Delta is really reliant on the end stops being set up correctly.
I have a Kossel Plus. I have a 250mm build plate, and I have 380mm in the Z axis. This is good if I need to go any taller. Saying that, I have noticed that it doesn’t take that long to lose its edge, after it’s been printing for a couple of weeks. I should add, that I am a little “over the top” when it comes to calibration. I tend, not to use a probe. Only because, I feel that calibration should be done by hand. I have tried to get on with a probe, but they seem to be more trouble than there’re worth. Don’t get me wrong, I can see the sense of a probe, but I would rather trust the printer’s setup, to me. Rather than leaving it to a probe. Also, it allows me to keep learning, and getting better at setting up my printer. Which is never a bad thing.
With a delta printer, you have three towers, these towers should be the same height. They should also be the same when it comes to degrees between the towers. My printer has its towers at 120 degrees. Three of these makes 360 degrees, a full circle. If you want to check yours. I suggest you head over to www.thingiverse.com and look for thing number 745523 and have a look, print it off, and you will get an idea of how close your Delta printer is, in regards to its calibration.
From each of these towers, is attached a carriage, from that carriage is attached some rods, called “Diagonal Rods” one end is attached to the carriage, that, travels up and down the towers. The other end, is attached to the “Effector” the effector, holds my hot end, and cooling fans.
Now you understand, everything leads back to the beginning, and the beginning is the actuation of the end stops. Once these have been hit, they tell the printer how far it is to the build plate. That finite mm measurement where the hot end first goes, when it starts printing. Therefore, it must be spot on. Imagine a 20-hour print? All you have between you and disaster, is the first layer. That first layer must be put down perfectly. In fact, the first layer is the most important layer, of the whole print.
What determines all of this, are those small end stops. It goes without saying that they should be set up correctly. Not only that, but you need to make sure they are fixed to the chassis properly too. Now, on a delta printer, the end stops are used a little more than with the Prusa style, of 3D printer. On a Delta printer, you have to, physically move the end stops, while you calibrate your printer. I found this to be a little troublesome, if only because of the way the end stops were nailed to the towers. Lots of faffing about, trying to get a small allen key, into a hole that wasn’t accessible enough. Couple that, with the fact that these blasted end stops, had to be adjusted tens of times each. You will quickly see, why I wanted to take up knitting.
So, I redesigned some new end stops brackets, that went in place of the ones I already had. Very good, so I thought. But I soon realised, that they were not wide enough, and after a few hits with the carriages, when doing G28 (home) command. One started to move, very slightly. In fact, it was getting pushed up, and out, a little. This slight movement up and out, and hardly noticeable to my eyes. Manifested in some of my prints not looking quite right. Mainly in the way of bed adhesion. I finally stumbled upon the problem when the carriage missed the end stop completely and lots of grinding noises were heard. It’s only then, that I realised, the end stop had been pushed too far out and the carriage wasn’t hitting it. So, the printer didn’t know when to stop on that particular axis.
Back to the drawing board. This time, I made them wider in the front edge, I also, cut in a 2mm x 20mm depression so that they were held in place and couldn’t spin at all. Also, I printed some gnarled head covers for the bolts, this was to make them easier to tighten with my fingers.
I was wondering how hard the carriages hit the end stops. What I did to measure this, was to get a small piece of “BlueTac” and place it on top of the carriages, then see what the indentation was like, when I called G28. As it happened it was negligible to be fair, hardly leaving a mark. But it did answer a question, I had often wondered. In as much as, when the printer homed itself, was the act of hitting the end stops, moving them at all? Come on, I bet at some point you’ve though the same thing?
Anyway, I re-calibrated my printer, getting it all setup. A couple of test prints later, and I was happy. Then, as an added precaution, I adjusted the carriage rails, so that they were touching the bottom of the new end stop brackets. I knew that way, they could never be pushed down too far. Also, this would act as an easy visual check, to see if they had moved at all. If they had all I needed to do was to loosen them a touch, and pull them back down to the tops of the carriage rails.
What then, was knocking the end stops out after a few prints? Well, at first, I wasn’t sure. I had after all, done the BlueTac test, and it looked like, it was hardly touching them. But then, as I was calibrating the printer. After fitting the new end stop brackets. I noticed that in certain positions, like when the hot end is all the way over to one tower, when it homes again, there is a bit more force as it hits the end stop on that particular tower. Not sure why, maybe it’s the angle of attack, as the carriage comes up, but something, definitely worth keeping an eye on.
Things to do. I am happier with the end stops now, and I have a way of knowing if they are moving at all. But this doesn’t really fix it long term. My main goal is to have an end stop that you can move up or down, using a long bolt, so I can adjust it in a more finite manor. Plus, the bolt holding in place will be the downward force required to keep it in position in a more definite way, against the top of the rail. But for that to happen, I need to print off some new corner brackets. My current brackets are too fussy, and don’t allow me the space to add anything like that. But, it’s something to do as the nights draw in.
End stops are vitally important when it comes to 3D printing. They need to be nurtured and cherished, looked after and fussed over. Perhaps that going a little too far, but you can see my point.