Just finished printing another batch of puzzle parts in Faberdashery filament. I had 3.6 metres left and Slic3r was telling me I needed 3.9 metres.
Fortunately, to get perfect results, I use a 90% flow rate setting so I reckoned I should be OK.
This is what I came back to when the print had finished!
Like cutting the bomb timer wire with only 1 second left! 
3,9 * 0,9 = 3,5. fits.
And those are some pretty extruder parts as well
Thanks. It’s a standard Mendel90 with non-standard herringbone gears. @nop_head swears they make no difference but I like them anyway.
I have actually had it closer than that and still rewindable but I have also got it wrong a few times as well. I also once ran out of petrol on a garage forecourt and had to ask my passenger to push it the last few feet!
I have never tried the herringbone gears but I don’t see any problem with the original ones that needs fixing. Also I can just slide out the big gear when the filament is unloaded to examine the hobbed bolt, which I would not be able to do if they were herring bone.
Phew!
Love it!
@nop_head I read they reduce backlash and keep the gears centred so the teeth aren’t just mating on a corner. You can get the gear off easy enough by pulling out the hobbled bolt until it reaches the washers and then remove the gear at an angle, it’s easier than it sounds!
3D printing fascinates me to date.
@Liam_Jackson
Those properties may be true and useful in other applications but I don’t think backlash is relevant to an extruder because it only matters how far it travels when going forwards. When it reverses it needs to be far enough but doesn’t matter if it is a little further. Also the back pressure from the filament keeps the teeth engaged until it drops to zero, at which point it has retracted enough.
I make my bolt head a tight fit into the gear because if it is loose it will rotate slightly when reversing and wear the gear away. I.e., if I force it in and out repeatedly it will become loose and then continue to work itself more loose.
@nop_head interesting, I’ve only seen wear when I changed to ABS gears. I used the same PLA ones almost daily for a good 9 months and they’re still fine now, just not using because the colour doesn’t match my new extruder. I’ve always had the bolt fit loose enough that it’s fairly easy to push out but with no noticeable play.