Thoughts on this sliding hot end mount please.
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One side of the switch would need to be able to move slightly to allow for the slow down at the moment it contacts a sprung loaded pin would probably do the job.
Another option may be a hall effect type sensor ?but I am not sure what the repeatability would be with one of them
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A simple microswitch such as those used on an endstop is probably the easiest. They are rated for a certain number of switch actions where as a probe into copper will have an unknown number of triggers before issues with oxide build up or deformation make it unreliable
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Hi Doug,
That's why I was thinking Pogo pins - because they are spring loaded. You can buy gold plated ones for a couple of quid or 100 "ordinary" ones off Ebay for the same money. That makes a very cheap sensor.
It's too cheap and simple - there must be something I've missed….........
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A simple microswitch such as those used on an endstop is probably the easiest. They are rated for a certain number of switch actions where as a probe into copper will have an unknown number of triggers before issues with oxide build up or deformation make it unreliable
Hi Tony. I didn't think micro switches were all that repeatable or accurate enough??
I can buy Gold plated Pogo pins for a couple of quid and I have some gold plated spade terminals that I could recycle so that would take care of the Oxidisation issues.
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Rather than a microswitch which needs too much movement to trigger, and therefore makes the whole assembly wobbly (or has strong springs and needs to hit the build plate with excessive force). Have a flag on the hotend mount and fix a height-adjustable opto endstop to the carriage. The hotend assembly will only need to move maybe 0.25mm to trigger (still a long way off the 0.01mm of the piezo/ir probe). Then it's a case of chosing the right springs, for nice light triggers with minimal nozzle wobble.
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Yes, plan A is to utilise the mini height sensor that I have - effectively as an Opto end stop. I've taken care of the "wobble" - well there might be 0.1mm or so in X or Y when the hot end is lifted off it's seat but that will have a negligible effect on Z I'd have thought (I may yet be proved wrong of course). When the hot end is fully seated, there is no discernable movement (at least with the mock ups I've printed).
Plan B if that doesn't work is to use the mini height sensor as I do now but it'll be a long way from the nozzle and will be affected (as it is now) buy my use of 3Dlac on the glass build plate.
What I'm talking about is plan C. Similar to plan A but instead of using the mini height sensor above the hot end, effectively just 2 electrically conductive pieces of metal that come together to make a circuit. One fixed to the carriage, the other fixed to the (sliding) hot end mount. No springy switches, no signal conditioning, no amplifiers or any other circuitry involved. Assuming there are no mechanical issues, why won't that work?
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No reason in theory, and I suspect in practice it will work, with a bit of fettling it should be accurate and the assembly should be firm, and the probing force should be low enough to give a trigger without being too violent.
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I've decided to take a modular approach. I've incorporated a smaller dovetail slot, above the hot end slot but inset so that the hot end can still be slid out of the top. Then with the right adaptor, I'll be able to fit either the mini height sensor, or a simple contact probe, or some other type of switch, without having to reprint the entire carriage plate. We'll see what works….......
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@CaLviNx:
Instead of a Mircoswitch. What about a linear slide potentiometer that Increases/decreases resistance as it's moved. Properly attached it could act in the same way as the ir probe but being mechanically activated instead.
It could be a nice test to hook a linear pot to one of dc42s ir boards replacing the ir sensors.
Yes but it's all a bit complicated. DC's probe is specifically designed to sense the top surface of a sheet of glass. I could use it above the mount and it'll probably work (as would a linear pot) but it's still a bit overkill and complicated.
What it all comes down to is that we just need a digital switch that gets triggered when the nozzle is a certain distance from the build plate. It doesn't matter what that distance is (as long as it's not too big), because that is the Z offset that we put into our G31. Any form of analogue input is going to have to be converted to a digital on/off somehow because that's the only thing that processors can deal with. So whether it's hall effect, inductive, capacitive or whatever, the output is going to have to be converted to a digital on/off somewhere along the line.
So, if you think about it, with a (spring loaded) sliding mount all you need is 2 contacts, one fixed to the mount and one fixed to the carriage spaced say 1 or 2 mm apart. When they come together they complete a circuit and when they are not touching, the circuit is open. That's about as digital as it gets and so simple. It the event, I'm having a real hard time finding suitable contacts - they really need to be non- oxidising so probably gold plated.
Of course, repeatability is the main thing and that will come down to how well the mount sits on it's seat or returns to it's seat after it'd been lifted off. With plastic parts, this could be difficult. I've got something printed that feels good but then my fingers aren't sensitive enough to detect 0.1mm of "non-repeatability" so I'll just have to build it and try it. The fall back is to clamp the mount rigidly and use DCs probe under the nozzle as it is now. But as I've said before, this isn't ideal with a Diamond hot end because I simply can't get the probe close to he nozzle and also, my use of 3dlac on the glass means that the offset keeps changing due to (I suspect) variable reflectivity.
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For anyone that's interested, I now have a mechanically functioning but otherwise untested mount. The tool free swapping works a treat. With the part on it's seat and held in place with the springs, I can't detect any Z wobble by hand (whether it prints OK is another thing of course).
To save my typing, I've made a short 2 1/2 minute video that shows how it all goes together (and comes apart). You can view it here https://www.youtube.com/watch?v=I6RoyDuUg7s
The untested part is the sliding, nozzle probing for Z homing feature. With the part off it's seat, there might be 0.1 or 0.2mm of movement but it's in Y and that shouldn't affect Z homing (I hope). I gave up on the idea of just having two contacts but found a positioning switch that might work. It's a Metrol switch (Japanese) but I bought it from Misumi EU. It has 2mm stroke but the switch point is claimed to be at 0.3mm with repeatability of 0.005mm. I don't really care about how much movement there is, as long as the switch point is repeatable.
If the Metrol switch doesn't work out, I have an adaptor that will take DCs mini height sensor (fitted above the hot end). If that doesn't work out either, I'll modify the mount by doing away with the spring retainers and replacing them with a cam action lock to hold it all firmly together then just use the IR sensor as "normal". I have already fitted a second mini height sensor in a more conventional position under the nozzle on grooved mounts so that it can be slid up out of the way initially. It's a fair way from the nozzle but the best I can do due to the bulk of the Diamond hot end. That will allow me to home the printer and print the parts I need to do any further modifications.
Whatever happens, I'll be able to swap hot ends fairly easily and, with the redesigned carriages, my Y travel will have increased from320mm to 370mm and X travel from 348mm to 390mm, and I'll have saved some weight too.
Ian -
I like it. Great work!
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That is a nice design Ian. I am really interested to see what repeatability you get from the switch/movement. Also if there is any perceivable movement in the head introduced by the sliding mechanism (although I doubt there will be as it looks constrained only to Z.
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That is a nice design Ian. I am really interested to see what repeatability you get from the switch/movement. Also if there is any perceivable movement in the head introduced by the sliding mechanism (although I doubt there will be as it looks constrained only to Z.
Hi Tony and thanks. I'm fairly confident about the switch (it cost enough!) but whether the entire mechanism will be repeatable enough is another matter - just have to install it and see. With the mount on it's seat and held there by the springs, I can't detect any "wobble" by hand. With it lifted off it's seat there is a little bit of play - I'd guess one or two tenths of a mm front to back (in Y). So if it pans out, the bit of front to back "play" will only be present while homing and hopefully, that won't have a significant impact on the Z height. During normal printing, the mount will be back on it's tapered seat so there should be no Z wobble to affect print quality. - That's the theory anyway. As I've said, if it doesn't work out I'll do away with the springs altogether, clamp the mount in place and home "normally". I'll have got tool free and quick changeability out of the re-design if nothing else.
It took me about 6 or 7 attempts to get the clearances right. I had it just about perfect but then changed to that gold filament and it all became sloppy. I ended up using zero clearance. That is to say, in OpenScad I simply subtracted the male part from the female part to form the female housing, which should have made an interference fit. ln practice, with a smear of silicone grease, the parts fit perfectly - providing I use Gold for the male part and Black for the female part. If I use Black for both parts, I have to have 0.1 to 0.2mm clearance at the sides to get the correct fit. That of course leads to another concern as to how long the thing will last before wear becomes an issue. Hopefully, as it it'll only slide a mm or 2 and then only while homing, it should last for quite a while before I have print replacements. More "suck it and see".
Ian -
Hi Ian - interesting how different filament prints. how long is the switch travel? you should be able to limit the overall movement to <1mm to trigger the switch reliably.
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Hi Tony,
Yes agreed about the filaments. I doubt it is anything to do with the colour - more likely just a different batch but who knows - there could be something about different dyes? The difference is tiny but then the difference between an interference fit and sliding nicely is also tiny - probably in the order of 0.1mm or less. Printing "normal" parts one wouldn't notice. I think with something like this, the way to do it is to start with no clearance then lap one of the parts with very fine abrasive or a needle file.
The switch stroke (travel) is 2mm but the switching point is at 0.3mm. I take this to mean that the switch action takes place at 0.3mm and thereafter, a further 1.7mm of travel is permissible/possible, but I haven't tested it. In theory, I could preload the switch by say 0.2mm so that it only requires 0.1mm of travel to change state but that might be pushing my luck a bit too far - have to test and see. It could also be that the hot end mount sticks to it's seat in a way that as force is applied, it reaches a point where it suddenly "jumps" which might affect repeatability. In which case, setting the switch a bit higher so that there is 1mm or so of travel might make the repeatability better. - More things to test.
It does need quite a high force to move it. The Diamond assemble alone weights 250gms, then there are the springs holding it on to it's seat. I tested it on a piece of 3mm thick glass and it was fine, so as I use 6mm glass, I'm comfortable with that.
Unfortunately, the switch is normally open so it won't fail safe. However, I have a second micro switch mounted on the frame which will trigger an emergency stop if the bed goes 2mm or so higher than the homing point.
Ian -
I'm interested to see how that metrol switch works out for you Ian. I took your dove tail idea and incorporated it into my hotend mount. I downloaded the CAD file for the switch and added it to my file. I like your idea for the E3D Cyclops mount. Small compact to give me maximum XY travel.
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@Simspeed. I'm in the process of printing the other parts I need for the Y carriages plus some spares now that I know it all fits together. Once that's done I'll convert the machine to the all new XY carriage assembly. Then I'll be able to test the mechanism and report back.
A couple of things. I made the Diamond mount (the male part) so that when it's seated, it sticks up about 1 mm above the female part on the carriage. That's to ensure that the springs are pressing down on it fully to keep it on it's seat. The switch I bought doesn't have the threaded body so I devised a clamping arrangement instead.
Also, when I tried to buy a non LED version of the switch from Misumi EU, it came back as discontinued so I had to buy the LED version. It's no big deal and the LED is a good visual indicator that it has triggered but wiring it to the Duet is not how one would expect to do it. Basically, although it's a digital switch because of the series LED, it has to be treated as an analogue switch with a pull up resistor. I'll maybe write a mini guide and either post it here on on my blog but let's see if it works first.
Ian
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Update for anyone that's interested. I've got his all up and running. It's working well so far but of course it's far too early to be able to say what reliability and / or repeatability will be like. Aside from the new mount arrangement, I've completely redesigned the X and Y carriages giving me an extra 50mm in X, 30mm in Y and saving 560gms in weight. Details are on my blog here https://somei3deas.wordpress.com/2017/03/07/tool-free-swappable-bed-probing-hot-end-mount/
Ian
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Hi Ian thanks for the write up, good to see the machine evolving!
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Hi Ian thanks for the write up, good to see the machine evolving!
Thanks Tony. Yes it's good to be up and running again. I had to take apart far more of the machine than I had originally intended. I even had to remove the 3 Z rods and shorten them by 2mm! I was beginning to despair that I'd ever get it put back together.
I plan to do a little mini guide for using the Metrol switch with Duet, because it is a little unusual in that although it is a digital switch, it has to be treated like an analogue switch because of the built in LED.
I think this was brought up in another thread but if you come up with any Duet stickers, I'd be happy to put one somewhere prominent so that it shows in the pics and videos.
Ian
