Wade extruder hobbed bolt

Hi all. I bought a hobbed bolt for my Wade's extruder and I am now noticing that there are moments when the filament slips in between the bearing and the hobbed part of the bolt. I observe the slippage happen when the large gear (which is attached to the bolt) is at a specific position. When I open up the extruder I notice there is a lot of material in between the teeth on the bolt. It's as if the bolt just starts chewing on the plastic without pushing it. How can I fix this? What tools would I need to do so? I have looked around online and I find that some hobbed bolts have larger and deeper teeth than others (at least mine). Are larger deeper teeth better?

Also, besides one seller on ebay (who is out of the US), does anyone know were I can get another hobbed bolt from? If I decide to make it myself, what tools do I need? I have a drill press, a dremel, and a screwdriver. I don't have the jigging stuff to hold the bolt as it is being hobbed.

Thanks a bunch! I've had my machine built already for a few months, and this is the last step in getting it to work!

Once it has slipped the teeth get clogged and it will always slip in that place again. The easiest way to clean it it with a wire brush.

It might slip because you don't have enough spring tension, or the plastic could be too hard to push due to too low a temperature or other problems with the hot end. Or you might be trying to extrude too fast.

I have found M4x0.7 teeth sufficiently deep. They are only 0.35mm deep each side.

To make a hobbed bolt you need the jig from Thingiverse, an electric drill and an M4 tap. It is much easier with a lathe.

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[www.hydraraptor.blogspot.com]

Is there a downside to having too much spring tension?

Too much and you can flatten the filament, or break the idler bracket. That would take quite a lot of force though.

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nophead Wrote:
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> Once it has slipped the teeth get clogged and it
> will always slip in that place again. The easiest
> way to clean it it with a wire brush.
>
> It might slip because you don't have enough spring
> tension, or the plastic could be too hard to push
> due to too low a temperature or other problems
> with the hot end. Or you might be trying to
> extrude too fast.
>
> I have found M4x0.7 teeth sufficiently deep. They
> are only 0.35mm deep each side.
>
> To make a hobbed bolt you need the jig from
> Thingiverse, an electric drill and an M4 tap. It
> is much easier with a lathe.


I was under the impression from here: [reprap.org] that Wade uses an M3 tap. What's the downside to an M3 as opposed to an M4?

or too much tension can stall the extruder

You need a lot of force to push a hard 3mm filament into an M3 thread. I found it tends to sit up a bit, so the effective drive diameter varies according to the filament diameter and how much force you apply, making the feed rate a bit uncertain. Also, when it sits up it only contacts on two edges rather than a full semicircle.

M4 allows the filament to rest in the bottom of the groove, so the feed rate is more defined by the minimum radius.

I have used both M3.5x0.6 and M4x0.7 successfully.

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[www.hydraraptor.blogspot.com]

I had the same problem with my bolt. I found that I had to clean the bolt frequently. I purchased a bolt and it did have bigger teeth. I have no idea what they cut them with but this bolt does not slip. I haven't had to clean the threads but maybe once in a few weeks. I have not tried making one of my own.

I never need to clean the threads unless I have some mishap that causes a filament jam.

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[www.hydraraptor.blogspot.com]

Hi Nophead,

can you estimate how deep the slit in the bolt needs to be??

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regards,
Tom

I make it about the radius of the filament so with an 8mm bolt I have an inner radius of about 5mm.

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[www.hydraraptor.blogspot.com]

ok, that's deeper than I've imagined. I thought it should be about 50% of the filament size, to have the bearing on the opposit site play it's role too. Anyway, thanks!

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regards,
Tom

I think you misunderstand. The radius of the filament is 1.5mm, so I make it about 1.5mm deep so that half the filament goes into it. That makes the inner diameter 3mm less than the outer diameter, i.e. 5mm.

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[www.hydraraptor.blogspot.com]

ah, my bad! Thanks

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regards,
Tom

I made my own hobbed bolt by filing some slits in an M8 bolt, this gives a lot of power, enough to push the filament.

Though this is on a shapercube

I have had the same problem with non-round ABS filament (cheap stuff) switching to round PLA filament and the problem went away - but not for round ABS. I used the thingyverse holder to make my hobbed bolt using a lathe and M4 tap but had to cut into the bolt thread which isn't nice as the groove is uneven (the bolt holder is plastic and does give way during turning even at 100% infil)- waiting for an ordered hobbed bolt to try that. What I have found is that black ABS is dryer/brittle than white/natural ABS and this leads to a dusty build up on the bolt - anybody else confirm this?

I was able to pretty reliably make a hobbed bolt without the printed jig. I just put two 608 bearings in a bench vice and stuck the bolt through them. Seemed to do exactly the same thing as the jig.

Turn down the current on your extruder driver, way down, then turn it up just enough so that it back lashes but does not slip when the hot end is cold. This should eliminate the clogging problem. You will recognize the backlash as a quick , intermittent counter-rotation of the large gear as the stepper turns.

jcabrer Wrote:
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> Turn down the current on your extruder driver, way
> down, then turn it up just enough so that it back
> lashes but does not slip when the hot end is cold.
> This should eliminate the clogging problem. You
> will recognize the backlash as a quick ,
> intermittent counter-rotation of the large gear as
> the stepper turns.

If you need to turn down your current to allow the stepper to skip steps you most likely have your E_steps_per_mm set to high. Once I got mine set perfectly I can extrude at more than 200mm/s and reverse at 600mm/s. At the same time this also solved the issue with stripping the filament which causes the clogging. As Nophead pointed out it is can be caused by trying to extrude to fast. You can tell you have it set right when your feedrate and flowrate match in skeinforge (39 and older at least) and you get the correct dimensions being printed. If you've had to lower your flow rate to get it to print right then the E_steps is to high. These effect become more noticeable the faster you try to print.

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I'm not talking about extruding here. I'm suggesting running the extruder motor with the tip cold, as a method for setting current at a level that will not strip filament to dust.

jcabrer Wrote:
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> I'm not talking about extruding here. I'm
> suggesting running the extruder motor with the tip
> cold, as a method for setting current at a level
> that will not strip filament to dust.


My point is if you do not have enough power to strip the filament then you don't have enough power to extrude fast either. If the E-steps are set correct you can almost never strip the filament unless you have a jam somewhere else.

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver