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# smaller filament by stretching?

Posted by o_lampe
 smaller filament by stretching? May 14, 2016 03:49AM Registered: 8 years ago Posts: 5,232
I want to make my own 1mm dia filament from 1.75mm filament.
Can I use a heating element and a geared spool drive to stretch the hot filament with a given gear ratio?

The spool for the thin filament would run 1.75 times faster.

ASCII art:

o__________O
***** ~~~~~

o= small gear
O=big gear
*= cooling
~= heating
 Re: smaller filament by stretching? May 14, 2016 05:50AM Registered: 9 years ago Posts: 550
Never tried it but don't think it will work. There is a thread on this forum somewhere where someone build a 3mm to 1.75mm filament converter. He used a nozzle Can't find the thread but did find this [www.thingiverse.com]
 Re: smaller filament by stretching? May 14, 2016 06:04AM Registered: 12 years ago Posts: 2,470
You will be very hard pressed to get a constant diameter. Any specific reason why you want to use 1mm filament?

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 Re: smaller filament by stretching? May 14, 2016 04:54PM Registered: 8 years ago Posts: 978
I think you would need to run the 1mm spool 3 times faster than the 1.75.... cross-sectional area is proportional to diameter squared.

Except that this depends on both spools having the same diameter. If you're planning on unwinding 1.75 off one and winding 1mm onto the other, then the spool diameter of one decreases and the other increases over time. So you can't just drive the spools... you have to control the filament speed.

But I suspect that it wouldn't work, although I don't know. I suspect that strength (and therefore "stretch") of the filament is inversely proportional to diameter. So once a thin point develops, it just rapidly gets thinner until it breaks. Maybe if you cooled it immediately that it was down to 1mm, so that it regains its strength, it might work.
 Re: smaller filament by stretching? May 14, 2016 05:49PM Admin Registered: 11 years ago Posts: 1,063
could use a normal extruder and hotend but make the nozzle hole somthing like 0.8/0.9mm and simply wind up the extrusion from that

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 Re: smaller filament by stretching? May 15, 2016 06:13AM Registered: 8 years ago Posts: 5,232
The idea is to stretch the hot filament without melting it. That's how copper wire is made, so I think it will not rip apart.
I also believe some ingrediences will disappear by melting it.

The idea is to feed the filament through a wider tube ( say 10mm inner dia ).
Air is blown through the tube from the 1mm side. A heating element in the middle of the tube will heat the air and also the filament. That way I get a continuous temp gradient.

My math was wrong, I took the circumference formula instead of the cross section

Edited 1 time(s). Last edit at 05/15/2016 06:14AM by o_lampe.
 Re: smaller filament by stretching? May 15, 2016 06:18AM Registered: 8 years ago Posts: 5,232
Quote
Srek
You will be very hard pressed to get a constant diameter. Any specific reason why you want to use 1mm filament?

The reason is to be able to use smaller extruder motors for direct drive. I have the idea to use a diamond powder coated dremel tool as drive gear, which has a very small diameter.
 Re: smaller filament by stretching? May 15, 2016 06:35AM Registered: 9 years ago Posts: 550
If you need custom filament imho it's easier and cheaper to start from pellets and use a extruder.
 Re: smaller filament by stretching? May 15, 2016 06:47AM Registered: 9 years ago Posts: 550
This reply below is based on my experience with filament extruders:

You can not use the spools. You need rollers that will not slip or skip steps otherwise you will get inconsistent width. From the feed side you might need multiple rollers to counter slippage. The filaments needs to be cold enough before reaching the puller rollers otherwise the puller will flatten the filament. As [frankvdh] mentioned you really need good (correct) cooling.

You might also need filament width sensors on both ends to control the process.
 Re: smaller filament by stretching? May 16, 2016 03:32AM Registered: 8 years ago Posts: 5,232
I'd wind the filament a few times around the spools until there's enough friction and then feed it to a final spool. This way I wouldn't have to use filament sensors.
The heating tube would be off aluminum or copper and the heating element ( Ni-Cro wire ) would be on the outside. It would be movable to find the best suiting temp-profile.
I don't want to start a mass production, just produce enough filament to test my extruder ideas.
[VDX] mentioned somewhere else, he had 0.5mm filament ( from toothbrush production?) at hand. I'd like to experiment with that too.
 Re: smaller filament by stretching? May 16, 2016 03:36AM Registered: 8 years ago Posts: 5,232
I've seen a few very cheap 3mm filament offers on the bay ( probably old stock?)
A filament stretcher to convert it to 1.75mm would come handy, if one would have a huge demand for filament.
 Re: smaller filament by stretching? May 16, 2016 08:42AM Registered: 7 years ago Posts: 62
Quote
o_lampe
Quote
Srek
You will be very hard pressed to get a constant diameter. Any specific reason why you want to use 1mm filament?

The reason is to be able to use smaller extruder motors for direct drive. I have the idea to use a diamond powder coated dremel tool as drive gear, which has a very small diameter.

I gave a diamond coated dremel bit as a drive gear a chance some time ago:

- Diameter 5mm, grit size 252 (MAFRA d-s109 Diamond grinding bit)
- Did nicely push the material (3mm filament), very constant feedrate resulting in smooth printed surfaces
- After some time one of the grits seems to have detached from the bit and clogged my nozzle (0.4mm)
- Subsequent grinding did fill up the diamond coating with plastics. Material did not fall off by itself - missing taper angle of the grits and undercuts kept the material sticking
- Cleaning the nozzle and the bit was quite a pain...

Improving the grinding bit parameters could probably solve these issues - please keep going on and let us know.

PS: See also the No-hob extruder using a Dremel bit #196

Edited 3 time(s). Last edit at 05/16/2016 05:49PM by powdermetal.
 Re: smaller filament by stretching? May 16, 2016 08:58AM Registered: 8 years ago Posts: 5,232
Thanks for the insight info.
Was it 1.75mm filament with a 5mm dremel tool? With smaller filament and a smaller grinder tool, the job would be much easier, I guess.
I think, with a quick release bit holder, we could put the diamond bit in acetone over night to keep it clean.

Edited 1 time(s). Last edit at 05/16/2016 08:59AM by o_lampe.
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