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A design flaw that has continued from the MK2  

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WildBill
(@wildbill)
Active Member
A design flaw that has continued from the MK2

You can say "I've not had that problem," or "You must be an idiot," or whatever other insults you prefer.

 

For those willing to listen and understand, I'll lay out the issue, and the easy remedy for Prusa.

 

-  The E3D V6 heat sink is round.  Round is a horrible shape for holding anything.  Square, or any other shape with flat sides does a much better job in holding a part.  As such, the round heat sink can spin in the plastic when you're trying to change a nozzle.

-  When you hold the Heating Block with whatever tool you can find that will fit the square block, there is minimal surface gripping area, and inevitably, the block moves a few thousandths one way or the other depending on whether you're loosening/tightening the block.

-  The wire bundle is zip tied to the Prusa's Extruder, not allowing for any fore/aft movement if the heat block twists slightly when removing/installing a nozzle.

These constraints, and allowed movement form a perfect design flaw to allow the wires on the heating cartridge to fatigue crack from nozzle changes and most likely, vibration over time.

A few simple changes to the design would fix this issue.

1.  Change the heat sink from round to square.
2. Create a tool that captures the heat block and heat sink together.  This would constrain everything to the plastic that also retains the wires for the heater cartridge.
3. Make the heater cartridge slightly longer, then attach a strain relief to the heater cartridge and wires to keep the frail wires from constant flexation.

 

Thank you for listening.  Kudos if you understand.

 

-Bill

Posted : 12/11/2020 5:07 pm
PRGeno
(@prgeno)
Active Member
RE: A design flaw that has continued from the MK2
Posted by: @wildbill

You can say "I've not had that problem," or "You must be an idiot," or whatever other insults you prefer.

 

For those willing to listen and understand, I'll lay out the issue, and the easy remedy for Prusa.

 

-  The E3D V6 heat sink is round.  Round is a horrible shape for holding anything.  Square, or any other shape with flat sides does a much better job in holding a part.  As such, the round heat sink can spin in the plastic when you're trying to change a nozzle.

-  When you hold the Heating Block with whatever tool you can find that will fit the square block, there is minimal surface gripping area, and inevitably, the block moves a few thousandths one way or the other depending on whether you're loosening/tightening the block.

-  The wire bundle is zip tied to the Prusa's Extruder, not allowing for any fore/aft movement if the heat block twists slightly when removing/installing a nozzle.

These constraints, and allowed movement form a perfect design flaw to allow the wires on the heating cartridge to fatigue crack from nozzle changes and most likely, vibration over time.

A few simple changes to the design would fix this issue.

1.  Change the heat sink from round to square.
2. Create a tool that captures the heat block and heat sink together.  This would constrain everything to the plastic that also retains the wires for the heater cartridge.
3. Make the heater cartridge slightly longer, then attach a strain relief to the heater cartridge and wires to keep the frail wires from constant flexation.

 

Thank you for listening.  Kudos if you understand.

 

-Bill

So are you saying is Prusa made a mistake in choosing the E3D V6 hotend?  You do know Prusa didn't design the V6 (which is a very popular hotend used by many other printers) that was designed and made by E3D (and cloned by countless others)?

 

Are you then suggesting they switch to something like the Slice Engineering Mosquito hotend which has similar characteristics to the what you state you want? 

 

You could easily convert ("upgrade") your existing Prusa to use one of the several extruders that supports the Mosquito if that's what you really want in a hotend.

 

In any case, I'd describe the V6 as a design choice rather than a "design flaw".

 

This post was modified 3 years ago 4 times by PRGeno
Posted : 12/11/2020 11:10 pm
bobstro
(@bobstro)
Illustrious Member
RE: A design flaw that has continued from the MK2
Posted by: @wildbill

[...] -  The E3D V6 heat sink is round.  Round is a horrible shape for holding anything.  Square, or any other shape with flat sides does a much better job in holding a part.  As such, the round heat sink can spin in the plastic when you're trying to change a nozzle.

Your issue is with the heat sink mount, not the heatsink per se, correct? The E3D V6 is very popular and used by many manufacturers besides Prusa. Remedies as simple as some tape around the top collar to tighten the mount work well. I don't disagree that a round mount with nothing to fix it in place is not optimal. However, I think the underlying issue is that replacing the nozzle torques the entire hotend and fragile heatbreak. Newer hotend designs address this. The Mk3 does date back to 2017, so it's not too surprising things have changed. I'd expect the Mk4 to address this and general hotend maintenance issues.

-  When you hold the Heating Block with whatever tool you can find that will fit the square block, there is minimal surface gripping area, and inevitably, the block moves a few thousandths one way or the other depending on whether you're loosening/tightening the block.

There are tools to provide a better grip on the block. As much as anything, I think this is a documentation and awareness issue. Since becoming aware of it's I've had no issues with a 12mm spanner/open wrench.

-  The wire bundle is zip tied to the Prusa's Extruder, not allowing for any fore/aft movement if the heat block twists slightly when removing/installing a nozzle.

Here again, the Mk3 is a 2017 design. I'd hope for a modular extruder and hotend arrangement in the Mk4. For all it's faults, the ease of hotend maintenance on the Artillery Sidewinder is excellent. 3 screw and one cable and the whole thing pops off.

The state of the art has changed over the last 4  years. I wouldn't call the availability of newer designs a flaw. The Mk3 was ahead of the pack on release and is still a strong design. 

My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Posted : 13/11/2020 3:17 am
locktec liked
towlerg
(@towlerg)
Noble Member
RE: A design flaw that has continued from the MK2

Am I missing something, I don't see any reason to grip the heatsink so what difference does it make. You obviously need to grip the heater block to tighten the nozzle against the heatbreak.

@bobstro thanks for the link, anybody know a supplier in UK? (probably time to put the Molegrips away).

Posted : 13/11/2020 6:04 pm
--
 --
(@)
Illustrious Member
RE: A design flaw that has continued from the MK2
@wildbill

That round mount design solves a very important problem: How do you guaranty all of the threads line up properly after everything is torqued?

  • Heat sink to Heat Break is variable.
  • Heat break to Heater Block is variable.
  • Heater Block to Nozzle  is variable.
  • Heat Break to Nozzle is variable.

Solve this issue, then get back to us.  I guess my choice of responses is #2 😝 .

 

 

Posted : 13/11/2020 6:37 pm
bobstro
(@bobstro)
Illustrious Member
RE: A design flaw that has continued from the MK2
Posted by: @towlerg

Am I missing something, I don't see any reason to grip the heatsink so what difference does it make. You obviously need to grip the heater block to tighten the nozzle against the heatbreak.

I was referring to the extruder housing gripping the heatsink neck after final installation. You don't want to heatsink and attached hotend rotating or the block will be angled, possibly creating issues with the cooling duct. You also don't want it wobbling or vibrating during prints.

@bobstro thanks for the link, anybody know a supplier in UK? (probably time to put the Molegrips away).

No, sorry, not aware of any. There are other similar tools, but I didn't keep any links.

 

My notes and disclaimers on 3D printing

and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan

Posted : 13/11/2020 6:43 pm
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