Is this a bad hobbed bolt?

notice theres no cuts in the middle.

I'm blaming all my extruding problems on this

The picture is too big, I don't see anything but threads!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Right click, 'view picture'. Curse author of forum software for not scaling pictures or allowing the forum to scroll.

Anyway. That bolt should work, the teeth are sharper and deeper than the M4 insert Im using.

I personally don't like that style of hobbed bolt because the filament can wander really easily.

Edited 1 time(s). Last edit at 07/09/2012 03:32AM by Sublime.

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I wonder, what das filament wonder about?

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

It looks like a nice bolt to me, as a matter of fact it looks like my design, could even be one of mine.
After personally processing a little over 3/4 of a ton of ABS and a couple of hundred Lbs. of PLA through that bolt design without issue and with well over 1000 of my own bolts out in the wild I can safely say that the bolt is not your problem ( As long as you have it installed properly) Installation

One of my customers did have a problem a few months back with filament wandering in a Greg's accessible extruder but that wasn't the fault of the bolt. Using a bolt as a filament guide is....um..... not the smartest way of going about things. Once he exchanged the original idler with the updated guidler the problem went away.

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Sublime
I personally don't like that style of hobbed bolt because the filament can wander really easily.

Sublime, would you mind posting a picture? I'm curious to see what kind of setup that you witnessed allowing this to happen.

Bruce Wrote:
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>Using a bolt as a filament guide is....um..... not the smartest way of going about things. Once he exchanged the >original idler with the updated guidler the problem went away.

Actually it is the only good way unless you like squished filament. A deep groove hobbed bolt like I use on Tantillus and almost every other good hobbed bolt (and the new Hyena) grabs the filament around about 35% of the filament and keeps the filament round even when applying enough force to break extruder gears. If you tighten down the idler on your hobbed bolt the amount need to push 3mm filament through a 650mm long bowden tube and be able to retract at 55mm/s (10,000mm/s^2 retract accel and max E accel) you will see the filament gets squished and is no longer round enough to fit through the bowden tube that is only .1mm larger in diameter then the specified filament diameter not even taking into account the fact that a lot of 3mm filament is over 3mm in diameter.

> Sublime, would you mind posting a picture? I'm
> curious to see what kind of setup that you
> witnessed allowing this to happen.

I don't have any pictures but feel free to read through all the posts on the forum about the filament wandering on this type of hobbed bolt and or knurled bolts when used with a Gregs extruder. Also you already confirmed it happens on a gregs extruder without the guidler which is made to fix the problem that this style of hobbed bolt has and is not a problem with Gregs design but a problem with this style of hobbed bolt.

I have never had filament wander on a Gregs extruder with a deep groove hobbed bolt and do not use a guide of any sort.

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It nearly looks like the hobbed part is larger (in diameter) than the rest of the bolt. Good luck fitting that through a bearing !

And I agree it's suboptimal :
- It's probably going to squish the filament.
- It's more prone to grinding the filament as it needs to plunge the teeth deeper to push it (less contact surface, less grip).

I have one that looks like this - it has a groove actually, but not deep enough, more like some little sanding.
I had to change my idler for one with a guide "guidler" otherwise the filament would just wander around and mess up my actual E_steps per_mm - varying quantity of plastic being extruded is not good for nice prints.

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

Didn't realize this thread was about bowden extruder's. How do you even get wander on a bowden extruder? It doesn't move. Try angling the filament at 40 degrees or so where it enters the hobbed bolt on your accessible Greg's extruder with no guidler and see how it works. I can run kinked filament through a wades.

Now..... You're telling me.... That if I tighten down the idler on my hobbed bolt the amount needed to push 3mm filament through a 650mm long bowden tube it will get squished to much?????

I have no idea how much pressure it takes to push filament through a bowden tube, I've never found the need to use one, but from what you wrote I imagine it must be huge! I know (for a fact) that I can lift a 25 Lb Sells Mendel off the bench with my hobbed bolts while extruding through a .5 nozzle at rate of 8 rpm on the hobbed bolt with (to use use your terminology) less than 1% squish on ABS which leaves it “on the worst of days” a full .1mm smaller than 3mm, so if it takes more force than that to push 3mm filament through 2 feet of bowden tube then I think that maybe you should rethink your bowden tube. That's most likely what's causing your gears to break.

I'd say that your filament is the main culprit to your friction problem, 3mm to 3mm plus is way out of spec. According to the chief engineer at Village Plastics the industry standard for 3mm filament is 2.85mm plus or minus 1%, and their shipments always come in within spec. Maybe you should consider changing suppliers.

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Sublime
Also you already confirmed it happens on a gregs extruder without the guidler which is made to fix the problem that this style of hobbed bolt has and is not a problem with Gregs design but a problem with this style of hobbed bolt.

Don't twist my words around It happens intermittently only on a Greg's accessible extruder, predating the guilder upgrade when the filament is fed on an angle into the extruder.

"Also you already confirmed" that your argument is flawed, you show no actual expertise in the use of my bolt. You have no idea of how my hobbed bolt interacts with plastic filament or even how to set the idler tension, so let me just ask you this: What came first the hobbed bolt or Greg's accessible extruder? What did Greg do when he found out that his new design was causing issues, of which there were more than one? The answer. He fixed it. He didn't say “Oh it's the hobbed bolts fault” He fixed it!

We have been working with a Canadian plastics manufacturer for the past several months in developing a high quality home grown solution for filament supply (2.85mm plus or minus 1%). Not sure that I'd want to sell it to you though, you would probably blame the filament when your accessible Greg's funnels in enough airborne particle contaminants to foul your nozzle.

Drawing a comparison between my hobbed bolt and a knurled bolt is....... how should I put this....... WRONG. Do you even know the difference? How does an apple compare with an orange?

As for the pictures

I figured you didn't have anything, that's why I asked for one. You haven't written or demonstrated in any factual way that have any first hand experience with my bolt. I have been reading this forum for a long time and I haven't seen a post about filament wandering on my hobbed bolt since I first posted about it http://forums.reprap.org/read.php?1,61437,62970#msg-62970 nearly two years ago. Obviously if you are telling the truth you must have seen something that I missed so please save me the time of relentless searching through obscure posts and point me to one of these posts that you are using as reference on the subject. That would be real evidence to back up your claim. Keep in mind that you are referencing “hobbed bolt” and not “knurled bolt” as they are distinctly different in nature.

I did take the time to Google the subject using several variations like this, forums.reprap.org "filament wandering" and I did find one thread ...... This one.

DeuxVis, I like your signature, it's good advise. Case in point. This thread! Hope you mind the critique.

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DeuxVis
It nearly looks like the hobbed part is larger (in diameter) than the rest of the bolt. Good luck fitting that through a bearing !

Wrong. It's hobbed between two 608's and it doesn't come with one installed....... You should be able to figure the rest out for yourself.

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DeuxVis
And I agree it's suboptimal :
- It's probably going to squish the filament.

Wrong. Unless you over tighten it, in which case the same problem will occur with any bolt, or anything else that you over tighten for that matter. It's the flat surface of the idler that does most of the squishing, by the way.

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DeuxVis
- It's more prone to grinding the filament as it needs to plunge the teeth deeper to push it (less contact surface, less grip).

Ever so wrong. There is no visual scuffing on the filament, not to say there isn't any hidden inside the grooves and over long periods of time I do notice a small accumulation of dust in the bottom of our extruder housings but that's over period 50 Lbs. or so. If you google the eckertech hobbed bolt and search relentlessly through the results you will see a comment here and there like “I rarely have to clean it” People like it so much because it doesn't scuff and it doesn't slip.

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DeuxVis
I have one that looks like this

No you don't.

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DeuxVis
it has a groove actually, but not deep enough, more like some little sanding.

Not sure what you are describing but it certainly isn't anything like my design......... which of course invalidates your next statement.

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DeuxVis
I had to change my idler for one with a guide "guidler" otherwise the filament would just wander around and mess up my actual E_steps per_mm - varying quantity of plastic being extruded is not good for nice prints.

Double checking what people write is a good rule of thumb for this forum, but double checking an opinion can be a daunting task for a newcomer with little understanding of the art itself or even the terminology used. With little or no personal experience to rely on, how does one even know where or how to check or who to trust. We've all been there. Until we get our feet wet we tend to rely on faith and trust in others. The eyes generally wander to the top right corner of the post. Volume of posts on any forum is taken as general indicator of knowledge. “If he writes a lot chances are pretty good that he knows what he's talking about.

If more veteran members took a note from nopheads handbook and verified their opinions before posting them to the forum and provide backup when queried rather than saying “go find the proof of my statement yourself” the forum would be much less confusing and provide a better learning environment for all.

We should have a hobbed bolt tug of war.

@ bruce TL/DR

Once you reach my level of quality then you can speak until then its just BLAH BLAH BLAH




To see more read [forums.reprap.org]

Also I started talks with Drader a few years ago about making filament but it was a dead end because we can buy "good" filament from China finally for so little you can't even get it extruded for that price in Canada.

EDIT: I have 7 machines total and not all of them are Bowden machines. And I can pull the filament over 90Degrees on a gregs without the filament coming out of the deep groove hobbed bolt.

Edited 1 time(s). Last edit at 07/12/2012 03:54PM by Sublime.

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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

Ah Bruce, let me guess, would you happen by any chance to be planning about selling those hobbed bolts of "your" design ?

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

By only looking at the orginal photo the diamond pattern appears to be either ground with a small cutting wheel or made from a series of impressions. It does appear that the outer diameter was ground level to the orginal bolt diameter. Probably so it would go thru the bearings.

I've only worked with 3mm filiment and, don't think I've ever experianced squashing of the filiment, but know that the objective of this bolt is to drive the filiment downwards. Ideally you would want only the downwards force with no squashing. Aside from the alignment question, which could be managed with the extruder body, this design seems to lack the sharp teeth required to dig in to the filiment which provided the driving. So because the teeth arn't sharp you would have to increase the pressure on the filiment in order to dig into what is left of the teeth.

I'm not seeing the advantage of this design over the convential bolt made from a tap. I've thought the same for hobbed bolts as well.
With the right setup and correct tap (i found that sprial fluted taps work far better then straight flute) I could cut a bolt in about 15 min. The other advantage of the convential bolt is that the tooth pattern is far greater, resulting in constant downward force throughout the rotation of the bolt.