Thoughts on this sliding hot end mount please.



  • As part of the redesign of my XY carriage, I wanted to come up with a method whereby I could quickly change Diamond hot end assemblies (preferably toollessly). My other big problem is getting a height sensor anywhere near the nozzle and I also have a problem with 3DLac altering the reflectivity of the glass and upsetting the IR probe.

    So being a woodworker I've designed a carriage mount with dovetail joints down both sides and across the bottom with mating dovetails on the diamond hot end assembly. I printed a couple of mock-ups and refined the clearances so that is is good tight fit and a simple clamp would hold it in place. But now I have another idea. I've eased the clearances on the sides so that the hot end will slide easily but when it is fully inserted, the dovetail on the bottom pulls it against the back part and holds it firmly. So the plan is to use a couple of springs or spring clips to hold it down but it will still be able to slide up against these springs. Then I'm thinking that I could mount the IR probe above the hot end - say 5mm. So when homing, the nozzle touches the bed (similar to what some people are doing with Piezo sensors), then the bed will push the nozzle up against the springs until the probe triggers. This means that the nozzle is the probe (there is no offset) and it gets around my 3dlac issues as well.

    There's a couple of pics here. https://drive.google.com/drive/folders/0B_MwtHtQR_ZvYTlfa0FvM2ZUZjg?usp=sharing. The first one just shows the dovetail "socket". The second shows the Diamond assembly (in red) as it would be if it were pushed up 3mm and the green part is the mini height sensor which is just in free space at the moment but in a position 2mm above the hot end "bracket". I'd need to make a quick release fixing of some sort for the mini height sensor but that's just a detail and I'd print the Diamond mount in Black (or whatever colour DC recommends).

    I can't think of any reason why it won't work but maybe you guys can see something that I may have overlooked so all contributions gratefully received.

    Thanks in advance

    Ian



  • I like the dovetail mounting bracket. I can't see any reason that wouldn't work as a way of holding the hotend in place and being easy to swap. The IR probe idea is a novel approach, but in any of the designs I've seen using hinged systems, or springs to hold the hotend assembly, with switches/optosensors/fsr's the issue is how far the system has to travel to trigger the sensor reliably.

    So if your hotend is mounted so that it is just out of range of the IR probe, and then a tiny upward push triggers it, it will work, but if it has to move just a little bit more you'll have the "dreaded" wobbly nozzle. Which isn't so bad really, but I know you want excellence and therefore it will result in some dodgy overhangs and rougher layers near the bottom of the print where the first layer squashes down and leave ridges that the nozzle has to push through and instead rides over or sideways around as there is enough compliance for it to bump up and down (on the springs). I've seen in the wobblier versions of the piezo sensor, the nozzle moving about as it ploughs through any filament slightly above the current z-height, and I don't like it. If the springs are light the nozzle contact can be gentle, but it will be wobblier, if the springs are heavy the inverse is true. I don't think you will get the assembly to spring back without strong-ish springs, the whole thing running on two printed parts sliding over each other, there's probably quite a lot of friction.

    The reason I'm so into the piezo system, is the nature of the piezo transducer itself, if you can clamp it into something to hold it fairly firmly, which can allow it to bend by just 0.15-0.2mm then the sensor functions and the nozzle is firm. Its just how to integrate that into your setup.

    I'm not saying don't try it, as I'd love it to work I just wonder if maybe there is a way to use the IR probe like this but use leverage, like Moriquendi was saying, so that a tiny movement of 0.2mm, or even less, at the nozzle magnifies up to a 1mm movement at the end of the lever, where the IR sensor is located.



  • While I probably can't contribute much to the issue at hand: I've tried a dovetail joint - albeit a much smaller one - for a part in the delta printer I'm currently working on, and I found it very hard to get it to fit with the required degree of accuracy. When I made the clearance wide enough for the parts to slide into each other without too much force, things got wobbly; when I lowered the clearance, I had to use so much force that I got the angles messed up. That might be partly attributed to the cheap-o printer I'm using at the moment, but I'm not sure whether the surface imperfections of any printed part might not pose a general problem.



  • DJ, (Edit - and vwegert)

    Thanks for the feedback. In the mock-ups I've made, I've eased the clearance on the side dovetails so that they slide easily but there is zero clearance on the bottom dovetail. So when the mount is fully seated, it feels rock solid and only requires a slight downward pressure to keep it on it's seat. There would potentially be some slight back to front wobble when the mount is lifted off it's seat for homing, but I don't think it would be enough to affect the affect the Z positional accuracy of the mount from the probe. For normal (printing) operation, the mount would be fully seated. I don't think I'll need strong springs as I have 250gm of gravity at work and also my Bowden tubes are always under compression which will help. Spring tension will have to be a "suck it and see" exercise. I use 6mm thick glass on 10mm thick aluminium so I could use quite a highish force without risk of the glass breaking.

    I haven't discounted using a Piezo element - it's just that I have one of DCs IR probes in my possession which I know works without any additional signal conditioning boards, so for me this might be a better route.

    The other thing I'm thinking about is that, with this arrangement, I don't need to use a non-contact probe. I doubt that a "normal" snap action micro switch would be accurate enough but something like this would be. http://toolsensor.com/switch/pt5m1wb/?utm_source=metrol&utm_medium=referral&utm_campaign=pt_blog. A bit expensive though - works out at £54 plus shipping…........

    Ian



  • I am quite keen to see if it works and to hear how you solve any issues. I have an IR probe surplus now and the idea of making it essentially an indirect probe works, its a very accurate device but as a direct sensor doesn't maximise the benefits of nozzle based probing. That being said this has been quite delta focused as the benefits of nozzle based probing are slightly less for corexy/cartesian as effector tilt isnt an issue.

    Look at the new UM3 its using the nozzle to press onto spring loaded glass with some sort of sensor under the glass that detects when the glass is pressed by the nozzle. That's what you and I are doing with these ideas, making indirect probes.


  • administrators

    Ian I like the idea of a easily swappable tool mount that seats firmly when fully seated. Potentially this can be adapted for tool changing systems in the future 😄



  • @T3P3Tony:

    Ian I like the idea of a easily swappable tool mount that seats firmly when fully seated. Potentially this can be adapted for tool changing systems in the future 😄

    Hi Tony,

    Yes if the sliding arrangement doesn't work out for homing, I'll print a simple cam action clamp or some such that will hold the hot end rigidly against it's seat. So whatever happens, I'll still be able to do a tool less hot end swap. I'm designing the carriage so that if the "sliding nozzle homing thing" doesn't work out, I'll be able to mount the mini height sensor "conventionally". It'll still be a longish way from the nozzle and I'll still have to make adjustments depending on how the 3dlac affects the reflectivity of the glass, but at least I'll be able to do some sort of homing. (I like contingency plans).

    Ian



  • Hi Ian….I had a similar idea for the hot end mount for my machine. I added an adjustment screw to fine tune the tip offset from the bed. I just used a U shape slot to slide the hotend mount into with threaded brass inserts for the screws.



  • That looks neat. For various reasons, (fan brackets and so forth) I'll have to print my carriage part on it's back, so the reason I went for dovetails rather than slots is that they have sloping sides and I won't have to worry about any printed overhangs.



  • What a coincidence, I have just finished this first draft.


    Simple quick release mechanism for the Nimble.

    The idea for the back is that the intersecting prisms locate the plate both horizontally and vertically. Quick little wedge snap at the front. Same as used on a lot of camera tripods.

    (edit added explain) This idea was requested a couple of days ago by a customer (thanks Bob) who wanted a cam lock type of attachment. I had trouble seeing how it could work until I went to take some photo's. The base plate of my camera tripod has a lockplate with a cam. So I used the concept.
    The base plate will lock down the hot end (E3D V6) in this case using a simple cam. The cam and the wedge shape at the back forces the base down onto the hot end and clamps it.
    (A bit like the French cleat system, Ian. Have a lot of my woodworking tools hanging that way. So why it took me so long to click?)

    The cam is something that can easily be adapted to Ian's slide. Unlatch to measure, latch to print.

    In my configuration, I might be able to fit the peizo sensor in the base plate. Hmm, base plate is a bit too small for that as it is now. Still in CAD so that is an easy fix.



  • Guys. If we have some movement in the Z mount, such as my sliding arrangement why can't we just use a metal to metal contact as a switch? In my case I'm thinking something like a pogo pin fixed to the carriage as as one side of the switch, and a flat piece of copper or some such fixed to the hot end mount as the other side of the switch. The switch would be normally open, then when the hot end assembly is pushed up by the nozzle making contact with the bed, the pogo pin touches the copper, and completes the circuit. It seems so simple that there must be something I haven't thought about so let me know what that is.
    Ian
    Edit. Both the hot end mount and the carriage are plastic parts so no insulation would be needed.



  • 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


  • administrators

    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 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….........



  • @T3P3Tony:

    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.



  • 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.



  • 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?



  • 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.



  • 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….......



  • @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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