Constant high-speed printing

Quote
richrap
'm getting less convinced hobbed bolts are a good idea, certainly my experience is now that this is the main problem area I need to resolve.

My most reliable and best filament drive system to-date is still the old style Brass fitting Adrian used to use before also moving to a hobbed bolt, I have never had any jamming or filament stripping using this style.

I just switched to a hobbed bolt (actually 5/16" bolt) in a Wade's extruder from the toothed pinchwheel Adrian's extruder. I started having problems with the pinchwheel slipping and digging into the ABS feed after putting my Mendel in a box. Increasing the tension on the springs in the Adrian extruder flattened the feed and it didn't help. After switching to a Wade extruder, I haven't run into the problem. I just hobbed the bolt using a hand drill so the threads aren't as deep as they should be but it already beats the pinchwheel in Adrian's extruder probably because it doesn't flatten the feed and it makes contact over a larger surface area.

richrap Wrote:
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> I read back Nopheads blog post on Knurled v
> Hobbing and it may actually be worth using
> Knurling rather than hobbing when you use a bigger
> drive wheel, the contact area will be much greater
> and as long as you can apply idler pressure across
> a section or a few points the knurling may cause
> less damage to the filament, and be less likely to
> strip or gouge the filament.

The new mendel-parts.com V9 direct drive extruder comes with a knurled pulley almost exactly like in your picture. I've managed to strip the filament with it many times, though, but lately I seem to have found the right settings. Just cranking up the extruder drive current and idler tightness to maximum wasn't really the right approach. Happy medium with both and enough temperature has worked much better. Still, I think I'm getting much deeper teeth marks in the filament than in your pictures, but they don't seem cause any resistance when extruding.

You could also replace the idler with a circular groove which leads the filament into the extruder. That's the sort of setup they use for extruding copper (I read somewhere). You'd get much larger contact area from this and could also completely block the filament from buckling. You'd need pretty beefy mechanics if the drive wheel was much larger than the current ones (and it would need to be, since the filament has to curve around it for some distance), though. That would be a pretty interesting project.

richrap Wrote:
-------------------------------------------------------
> I read back Nopheads blog post on Knurled v
> Hobbing and it may actually be worth using
> Knurling rather than hobbing when you use a bigger
> drive wheel, the contact area will be much greater
> and as long as you can apply idler pressure across
> a section or a few points the knurling may cause
> less damage to the filament, and be less likely to
> strip or gouge the filament.
>
> Many of the hobbed bolts just seem to dig into the
> edges of the filament and the small teeth on the
> sides do most of the transport, if you have too
> much idler pressure or resistance from the hot-end
> it just starts cutting the filament, slipping and
> making a mess.
> I'm getting less convinced hobbed bolts are a good
> idea, certainly my experience is now that this is
> the main problem area I need to resolve.
>
> My most reliable and best filament drive system
> to-date is still the old style Brass fitting
> Adrian used to use before also moving to a hobbed
> bolt, I have never had any jamming or filament
> stripping using this style.
> [www.mendelfactory.com]
>
> It had dull teeth, not sharp and you can apply
> high pressure to the idler without stripping the
> filament, you just need to make sure the filament
> is constrained otherwise it just slips off the
> side of the drive. I'm thinking that a much larger
> version of this drive wheel would be really good.
>
> This is 1.75mm filament, it grips well and is
> uniform -
> [3.bp.blogspot.com]
> AAAAAAAAAPA/MfNQYXBTdF4/s400/1_75_filament_micro_d
> riven4_with_Richrap_Bowden.jpg
>
> [4.bp.blogspot.com]
> AAAAAAAAAO8/MCBE1YHXAxw/s400/1_75_filament_micro_d
> riven2_with_Richrap_Bowden.jpg
>
> When I get a chance I will take a look at what
> filament driven with a hobbed bolt looks like
> under a microscope, unless anyone else has already
> done this?
>
> Maybe it's also time to think about doing
> real-time torque measurement on the gear so we are
> aware in firmware when things are about to strip
> the filament or if the temperature is too low for
> the plastic/speed etc?

i have that combo set of parts i just dont know where its supposed to go and i cant find any instructions
plus my other question is, is a hobbed bolt needed why cant i just use the bolt as is?

The hobbed section is what grips the filament.
A plain bolt would have no grip and would not feed the filament smoothly.

---

Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
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