1 Topic by elmoret (edited by elmoret 2013-01-29 05:49:26)

  • elmoret
  • Filastruder
  • Offline
  • Registered: 2012-10-11
  • Posts: 6,048

Topic: Hotend Fail...

This one's my fault:

https://dl.dropbox.com/u/1786359/Photo%20Jan%2028%2C%2010%2042%2008%20PM.jpg

I came home after starting an hour long print, to find the thermistor had come untaped from the hotend. That caused the printer to send max power to the resistor, while stopping extrusion at the same time ("cold extrusion prevented"). Ironically, had the extrusion continued, it is unlikely that any damage would have resulted - I'm at 90% average power while printing, so 100% would have likely just bumped it up 15 degrees or so.

Anyway, looks like the PEEK melted, then it got so hot that the resistor actually burned up, or went open circuit. Its resistance is >2Mohms now. In fact, it looks like it got so hot that the acrylic (?) ring around the PEEK started to bubble.

So, my question for you: If you had to start from square one on a hotend, where would you begin?

I've been looking at this PEEK:

http://www.mcmaster.com/#1595A13

It's self lubricating (with PTFE, so I wonder if I could get away with not using the liner. At $28/foot, I could make 12 for what I pay for one from Solidoodle.

It seems like every hot end I find has PTFE. Why? Is PEEK really that sticky?

EDIT: Did some research:

http://research.me.udel.edu/~dlburris/papers/JA9.pdf

The second author on the paper is actually a professor I know here at UF. Small world!

Anyway, it looks like the friction coefficients for plastic/metal look like this:
100% PTFE: 0.135
50/50 PTFE/PEEK: 0.11
100% PEEK: 0.36

Interesting. So, at least for contact with metals, PTFE is 3x slipperier. McMaster rates PEEK at 0.18-0.40, and carbon filled PEEK (what I'm suggesting) at 0.21. They rate PTFE at 0.05-0.10.

I bet it'll work. especially with a stainless barrel like the one from QU-BD, instead of the brass (?) one from SD.

Filastruder - the robust, inexpensive filament extruder
E3Dv6 All Metal Hotend - the premier 3D printing hotend

2 Reply by danny

  • danny
  • Member
  • Offline
  • Registered: 2012-08-09
  • Posts: 322

Re: Hotend Fail...

If I were designing a hot end, I'd use a nichrome wire wrap, after all the nichrome wire is meant to heat, power resistors are meant to be allowed to get hot. Not that they don't work we'll, (they do work very well in extruder hot ends.

As a material I'd use brass or aluminium, instead of peek I'd want to use stainless steel. With heat sink fins on the stainless...


Back in the real world,
I don't have the means to machine a new hot end, I'd buy the all metal construction that josef Prussa released late last year.

3 Reply by solijohn

  • solijohn
  • Member
  • Offline
  • Registered: 2012-08-07
  • Posts: 1,465

Re: Hotend Fail...

danny wrote:

If I were designing a hot end, I'd use a nichrome wire wrap, after all the nichrome wire is meant to heat, power resistors are meant to be allowed to get hot. Not that they don't work we'll, (they do work very well in extruder hot ends.

As a material I'd use brass or aluminium, instead of peek I'd want to use stainless steel. With heat sink fins on the stainless...


Back in the real world,
I don't have the means to machine a new hot end, I'd buy the all metal construction that josef Prussa released late last year.

In reality, the wider printing community has had a hard time getting away from PEEK insulators. They are cheap, and they work, but there are obvious limitations.

Former Solidoodle employee, no longer associated with the company.