Hobbed Bolt comparisons

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Hobbed Bolt comparisons

Postby RetireeJay » 2016-Jan-Tue-20-Jan

I was having difficulty using my E3D because it exerts much more back-pressure than the original ceramic Ubis. The Printrbot-supplied hobbed bolt was often losing traction and simply scraping the filament instead of feeding it properly. So I ordered two replacement hobbed bolts to try out.

The first one that arrived today is an Airwolf3D "Concentric" Hobbed bolt, 60mm. It took me a while to realize that it's 8mm diameter, threaded 1.25mm pitch instead of 5/16 - 18 (they look a LOT alike). And the location of the hobbed portion is not directly compatible with the Wades extruder, so I installed it "backwards" with the threaded part extending through the drive gear. Then I used two metric 8mm nuts to get the hobbed part lined up properly and "jam" the location in place. The bolt seems to hold its position pretty well without an effective spacer on the other end (I tried a tie-wrap, but it hangs up on the nearby bolt for the idler wheel, so the tie-wrap is not really effective).

Result: now the motor would skip instead of the bolt chewing into the filament. So I turned up the drive power, and of course got it to the point where it would chew the filament. However, when the over-powered motor drive would cause the hobbed bolt to chew into the filament, there was always a curlicue in the space below the driving point - so in this case it's not really the fault of the hobbed bolt, but rather the fault of the filament itself not being able to withstand so much longitudinal force without buckling. (Maybe I should try to do that "soda straw" thing to support the filament better between the hobbed bolt and the entry to the extruder body.) In other words, the new hobbed bolt is doing its job perfectly. It's visibly much more aggressive than the older Printrbot bolt.

I've backed off the motor drive now. I'd rather have a few rare "thin" parts of the extrusion due to motor skipping than completely lose an entire print because the filament gets chewed and stops moving at all. I've had to crank the "manual" extrude speed in Repetier all the way down to 1.5mm/sec. However, that's still about twice as fast as I normally print parts (a printhead moving at 50mm/sec, 0.25mm layer, 0.4mm wide trace pulls about 0.8mm/sec with my 2.76mm diameter filament).

The E3D is still very frustrating to me with T-Glase. I've got the temperature up to 250 now (on the old Ubis I was using 230). It just has so much back pressure! Here's praying that when I start a big print tomorrow that nothing will fail.

I've also ordered an Arcol Hyena, and I'll post results about it after it arrives. Once you get shipping included, the two different suppliers cost about the same, but the Airwolf3D delivered a lot faster to me because it ships from the US instead of Hungary.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
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Hobbed Bolt comparisons

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Re: Hobbed Bolt comparisons

Postby RetireeJay » 2016-Jan-Thu-12-Jan

The three hobbed bolts are quite different. I was surprised to see that the Arcol Hyena is brass; had I known that, I would have ordered the chrome-plated version. Brass is a lot softer than steel, so it will wear out faster; chrome plating is actually pretty hard, so it will extend the life of the Arcol. I thought the chrome was just for bling, so I didn't order it. :oops:

From top to bottom: Printrbot, Airwolf3D, Arcol Hyena
HobbedBoltsTopViewsm.jpg

HobbedBoltsLineupsm.jpg


Here's a closeup of the Printrbot version (granted, they may have changed the design; this one was made in 2013). Note that the "teeth" don't necessarily end in sharp edges.
HobbedBolt-Printrbotsm.jpg


Here's a closeup of the Airwolf3D Concentric. They claim that the grooved area is concentric with the axis of the bolt, meaning that there should be a consistent quantity of filament delivered with each fractional revolution of the bolt because the radius stays the same. BUT - notice how the grooved area is very wide, and the "slope" pushing the filament to the center of the groove is relatively gentle. I observed my filament riding not in the center but a bit to one side. That completely negates the "concentric" benefit, and in fact I found that calibrating the Extruder steps per mm was frustrating because of inconsistent quantity delivered.
HobbedBolt-Airwolf3Dsm.jpg


Finally, here's the Arcol Hyena. Note that its groove is narrow and deep - the filament stays very well centered in this groove. I got very consistent extrusion quantities when calibrating the steps per mm with this hobbed bolt. Also notice the unique pattern of fine and coarser grooves. It seems to drive the filament very well.
HobbedBolt-Hyenasm.jpg


So overall, I'm happiest with the Arcol Hyena - but the next one I order will be chrome plated.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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Re: Hobbed Bolt comparisons

Postby Mooselake » 2016-Jan-Thu-13-Jan

I didn't know that mine was (maybe...) brass under the chrome, as the chrome version is the only one I've used. I also ordered a direct drive version, but haven't tried that one yet.

My comparison set is smaller, being only the PB 2013 well worn original, and the Hyena. The Hyena wins hands down.

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Re: Hobbed Bolt comparisons

Postby thawkins » 2016-Jan-Thu-13-Jan

Have you guys looked at the "diy" hobbing systems like

http://www.thingiverse.com/thing:21782

Should allow you to create your own bolts to your own specs.
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Re: Hobbed Bolt comparisons

Postby RetireeJay » 2016-Jan-Thu-14-Jan

thawkins wrote:Have you guys looked at the "diy" hobbing systems like

http://www.thingiverse.com/thing:21782

Should allow you to create your own bolts to your own specs.


Just looking at that system, it seems like it will create the broad, shallow grooves like the Airwolf, and without the "teeth" coming to a point. There's another person who has written up a somewhat similar-looking system that uses a standard thread cutter instead of a Dremel disk, which should create a better profile, more like the Printrbot but you could go deeper and get something more like the Hyena. I think there's a thread about it somewhere in this forum.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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Re: Hobbed Bolt comparisons

Postby Mooselake » 2016-Jan-Thu-15-Jan

There's also the original DIY reprap hobbed bolt, which can cut sharp teeth like the PB version. Hobbing is a method of making gears with a notched multi-toothed cutter, and if you squint and look through a glass, darkly, you can kinda draw a comparison between a thread cutting tap and a gear hobb. An electric drill, a jig, and a bit of luck and you can make your own hobbed bolt. Google a bit an you can find directions.

You could take that jig, shape your abrasive wheel into a sharp edge, and perhaps make something that looks pretty close to a hyena. It would likely cost you as much, take quite a bit of your time (whereas the shipping will take more time, but you could use it for something else), and the result would likely not be as good. Or you could just go buy a Mori Seiki and some tooling and go into production, if you can get that past your SO and banker.

Personally I'm getting pretty fond of gear drive extruders, like the one I made from the PB beta parts. Bondtech makes one for the much better 3.0 mm filament, an area that PB appears to have abandoned.

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Re: Hobbed Bolt comparisons

Postby RetireeJay » 2016-Jan-Wed-15-Jan

Having now finished a 14-hour print, I can definitely say that I'm happy with the Arcol Hyena. There was never a hint of jamming, and the quantity delivered was extremely consistent; I've never before seen such smooth vertical walls on my parts.

The other part of the puzzle was to insert a tube leading from the driving point to the entry of the extruder, to avoid kinking (this is not a problem with most of the newer extruders, but the old Wade's extruder had a relatively open gap between the hobbed bolt and the top of the extruder). viewtopic.php?f=84&t=10634
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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Re: Hobbed Bolt comparisons

Postby Richy_T » 2016-Dec-Tue-19-Dec

Jay, would you say the hobbed bolt was the biggest improvement you've seen? I only get my LC out occasionally and it's still pretty much stock and I would like to improve it. At the moment, I'm looking at the stock bed levellers as possibly being the source of some of my issues. My layers are pretty rough but each layer is itself pretty straight.
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Re: Hobbed Bolt comparisons

Postby RetireeJay » 2016-Dec-Tue-22-Dec

Oh, everything works together; there was never any "magic bullet" that suddenly took my printer from difficult to easy or suddenly made my prints fantastic. But I will say that the Arcol Hyena hobbed bolt really has eliminated that particular part of the total printer as a source of problems.

Besides the things mentioned in my signature block, I do NOT use a probe for leveling but instead shim my bed so it's trammed (aligned) with the X-Y plane of the nozzle's motion. I use a dial gauge indicator, clipped onto the horizontal rods on my Plus with a clip I designed to measure the clearance precisely. (All the projects, both in the signature block and in this note, are documented on the forum). The "Injection Molded Gears" are because I'm using a Wade's Extruder and "3mm" filament instead of a direct-drive extruder and 1.75mm filament.
For safety's sake, I replaced the wiring to my heated bed with heavier-gauge wire; on the Rev D board I soldered this heavy wire directly to the connector pins; on the Rev F board they have good screw terminals instead.

I tune my speed and accelerations to avoid excessive vibration.

Whenever I go to using a different material (e.g. NinjaFlex instead of T-Glase) I find that I must re-tune not just the temperature but also the speed - and these interact with the size of the nozzle and the layer height. So sometimes I can just pull up good settings that I know work, and sometimes I still have to experiment because I haven't used that particular material with that nozzle and that layer height before. It can be frustrating, but when you eventually get the machine tuned in perfectly for what you are doing the results can be great.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
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Re: Hobbed Bolt comparisons

Postby Richy_T » 2016-Dec-Wed-10-Dec

Thank you. The printer does pretty well, I just need to dial it in to get things a bit smoother.

I remember you did some work on tuning the Z-steps so that the layer heights were actually the same. Then I think you changed your mind. What was your final conclusion on that? Looking at my layers, it seems like that might be an issue for me, there is a regular "beat" to the roughness in the Z direction. I really should just go back through your posting history. I'm sure there's a lot of good stuff in there.
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Re: Hobbed Bolt comparisons

Postby RetireeJay » 2016-Dec-Wed-11-Dec

Yeah, this post has the math if you care to give it a try - but don't expect too much! viewtopic.php?f=20&t=4596
There's a post somewhere out on the wide world of Internet that gives half a dozen reasons for Z ribbing, and the integer layer height thing is a relatively minor one in the whole list.
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Printrbot Plus operational January 2013
Brass threaded rods (5/16" X 18) & nuts for Z axis
GT2 belts & pulleys
Cable chain to reduce probability of fatigue failure in wires
E3D V5 Hot End, 0.4mm nozzle, also 0.8 and 0.25 in use occasionally
PB fan mount + 40mm fan -- using printed mount adapter, not the E3D supplied fan
Injection molded extruder gears
Optical Z "endstop" (custom designed and built)
Have used many pounds of T-Glase filament. Now also doing some work with Ninjaflex SemiFlex
Print on glass with Scotch Craft Stick or other glue stick
User avatar
RetireeJay
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Re: Hobbed Bolt comparisons

Postby Mooselake » 2016-Dec-Wed-14-Dec

An average error of around 1/5000th mm isn't going to amount to much, especially when dealing with full and micro step tolerances are far greater. Don't get me started on stepper cogging when the default PB firmware turns the motors off. Pick a convient step size, not the mythical perfect one.

Likely that regular beat Is related to full screw turns. Measure it and see...

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