What is your experience with dual hotends? Are they worth the trouble?

Last one I priced was in the 175-200k range.

*drool*

I want me some toys like that. Oops, sorry, I think my enthusiasm is showing again...

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JamesK
*drool*

I want me some toys like that. Oops, sorry, I think my enthusiasm is showing again...

Job perks. All kinds of toys and they pay me too.

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JamesK
I don't think I'd want to try and use a lock nut to set the final height of a threaded throat.

Do you expect that one will not be able to fasten the nut without moving the threaded barrel just enough to invalidate the level of the 2 nozzles?
Do you expect vibrations to affect such fastened jam nut?

Is there any other reason? I fail to see any difference with regards to set screws in the final result aside from aspect and having the nozzle further away from the heatsink which I also don't know how/if it affects anything. And a tad more difficulty but considering that most of the people out there have this kind of hotends and they'd prefer to keep thaer carriages as they are, this seems like a very minimalist approach.

Thanks.

Edited 4 time(s). Last edit at 05/09/2016 09:06AM by realthor.

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Just based on the practical difficulty of tightening a lock nut sufficiently without moving the throat. Like you say, once tightened it should be fine, but it might be quite hard to get it in the right place. The vertical alignment of the nozzles really is quite finicky. A lot depends on how often you expect to change hotends. If the answer is almost never then you could probably make a jig and set the nozzle heights away from the printer where it would be easier to tighten a lock nut. I change hotends frequently, so I was hoping for a system that is quick and easy to do in situ.

The other minor disadvantage of a thread throat is that adjusting the height means rotating the hotend, so you can't rely on any particular orientation of the heater block without also having to adjust the nozzle/heatblock relationship. Smooth throats seem to be a more natural approach for a dual extruder setup.

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realthor

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JamesK
I don't think I'd want to try and use a lock nut to set the final height of a threaded throat.

Do you expect that one will not be able to fasten the nut without moving the threaded barrel just enough to invalidate the level of the 2 nozzles?
Do you expect vibrations to affect such fastened jam nut?

Is there any other reason? I fail to see any difference with regards to set screws in the final result aside from aspect and having the nozzle further away from the heatsink which I also don't know how/if it affects anything. And a tad more difficulty but considering that most of the people out there have this kind of hotends and they'd prefer to keep thaer carriages as they are, this seems like a very minimalist approach.

Thanks.

I dunno, over a decade machining things for a living and experience adjusting things by .0005" or less.

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JamesK
Just based on the practical difficulty of tightening a lock nut sufficiently without moving the throat. Like you say, once tightened it should be fine, but it might be quite hard to get it in the right place. The vertical alignment of the nozzles really is quite finicky. A lot depends on how often you expect to change hotends. If the answer is almost never then you could probably make a jig and set the nozzle heights away from the printer where it would be easier to tighten a lock nut. I change hotends frequently, so I was hoping for a system that is quick and easy to do in situ.

The other minor disadvantage of a thread throat is that adjusting the height means rotating the hotend, so you can't rely on any particular orientation of the heater block without also having to adjust the nozzle/heatblock relationship. Smooth throats seem to be a more natural approach for a dual extruder setup.

I agree with all you say. However I am thinking it for a retrofit solution. I have already played a bit and designed a sort of a tool to quickly lock the jam nut without modifying the height of the threaded barrel.
The minor issue you see is quite annoying to me but there is no way around it with a threaded barrel .

Here's what I have in mind for a quick locking tool:



This tool does two jobs, one is the wrench part that is used to fasten the jam nut and the other side pushes apart, via the spring, the heater-block with the threaded barrel on one side and the heatsink on the other side, achieving what is crucial for an error-free locking: that is having the threaded barrel always keep contact and rest on the lower side of the threads inside the heatsink. This makes sure that when the jam-nut is fastened the barrel has no room to be pulled out of the heatsink (which the jam-nut tries to do), because the threaded barrel is already at it's lowest possible position inside the threaded hole of the heatsink.

All this is highly speculative atm but I believe the tool can be 3d printed and used to lock the nut quite tightly ...

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Koko76

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Koko76
Look at existing work. E3d is nice enough to publish drawings of already working designs.

Which designs did you have in mind?

Me personally? None. I strongly considered building my new machine around a dual extruder design, mainly for the purpose of printing dissolvable support material. I ultimately decided against designing around it for a number of reasons. Mainly that to me the compromises needed to make dual extrusion happen would impact print quality with a single nozzle in ways I didn't want.
The E3D designs are the Chimera and Cyclops (the Kracken also uses a similar arrangement). They use a smooth walled heatbreak tube instead of the v6 threaded version where the heatbreak attaches to the heatsink. They use a set screw, to fix the tube in the hole and allow adjustments. They seem to hold reasonable tolerances, so I imagine the fit is fine. Were I to do it, I would wire cut a clamp block, but consumers are typically unwilling to pay the price that wire edm part would cost, so I can see why they did it that way. Something similar to a one piece shaft collar could work here. They do make aluminum ones.
Theory is one thing, but actually adjusting something like this to work in the real world is a different matter. Tightening threads against each other is generally very very fiddly.

Please to read that.

Although I wouldn't dismiss "theory" while in fact it is misunderstood theory and total lack of practice the problem.
When you see people here using set screws to squeeze and block linear or ball bearings outer cage, it is wrong both theoretically and confirmed by practice isn't it ?

Note that an amateur with a jeweler saw could do what you propose as clamp. It is just Al.
I am making a new hotend and of course I will not use a threaded tube (and not the absolute horror, a set screw against a thread). For clamping, eventually the usual slit (shaft collar like) or yours as it is neater.

Edited 3 time(s). Last edit at 05/12/2016 07:56AM by MKSA.

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realthor

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JamesK
I don't think I'd want to try and use a lock nut to set the final height of a threaded throat.

Do you expect that one will not be able to fasten the nut without moving the threaded barrel just enough to invalidate the level of the 2 nozzles?
Do you expect vibrations to affect such fastened jam nut?

Is there any other reason? I fail to see any difference with regards to set screws in the final result aside from aspect and having the nozzle further away from the heatsink which I also don't know how/if it affects anything. And a tad more difficulty but considering that most of the people out there have this kind of hotends and they'd prefer to keep thaer carriages as they are, this seems like a very minimalist approach.

Thanks.

Why not simply do a prototype and try ?

Not at home for a few months... I would ask anyway even if I were home for experienced people's opinions are usually useful along the way..

PS: don't assume people have the same resources or garage or situation as you have. You know what's said about assumption .

Edited 2 time(s). Last edit at 05/12/2016 08:02AM by realthor.

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RepRap Lander concept on Concept Forge
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My Things, mostly experimental stuff