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RepRap Pro Ormerod Spring-loaded extruder

by MasonStonehenge, published

RepRap Pro Ormerod Spring-loaded extruder by MasonStonehenge May 2, 2014
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Summary

After problems with inconsistent filament diameters in my RepRapPro Ormerod I made an extruder block that includes a spring for tensioning.

It uses a long 3mm screw, nut and a tension string on a long lever arm. I've implemented this one with great results - it handles variations in filament with ease.

This works well with variable filament diameters. Smooths out the action of roughly printed gears. Makes cleaning the hobbed insert a snap - Undo the bottom spring screw, flip the back up and clean away! :)

As mentioned on forums.reprap.org it makes the mounting of iamburny's Herringbone gears (http://www.thingiverse.com/thing:242536) a bit easier because you can mount the gears separately, then mesh them together once complete.
The spring I've used came from a fairly strong action ball-point pen - the lever action increases the effect of the spring, so it works well for me and others.

EDIT: Some discussion on the RepRap forums indicates that there is a large difference in spring strength in pens and that they can be under strength for this purpose - A suggestion is the springs that can be found in the plunger of products like soap dispensers - refer to http://forums.reprap.org/read.php?340,524181,page=2 for the ongoing discussion. :)

The STEP files are included in case you want to make a modification - in which case share & share alike (and keep me informed - I'd like to know) :)

PTFE version

In this version the Feeder part has a wider feed pipe to allow for the PTFE insert to run all the way up to just before the hobbed insert. This is supposed to decrease the resistance on the filament and stop wear on the extruder.

Instructions

Print the version you want - Most people will only use the 'Extruder' files - either the PTFE liner version or the standard - that has all the parts necessary. The 'With support' files include simple support that should print well with most slicers and should be easily removed.
Whichever files you use, you'll need a 'motor' part, a 'feeder' part and probably the 'tongue' part.
Screw the feeder to the motor using an M3 screw and nut through the hinge at the top - optionally using thin washers between if your print has the space.
I found that I had to work the hinge a little bit before it was a smooth action, but don't need the washers myself.
Build the extruder as per the original RepRap plans. Make sure that the tongue is properly inserted and anchoring the Bowden tube correctly, then optionally anchor that in place with a cable tie or screw.
Insert the long M3 screw at the bottom with the spring between the head and the bracer near the filament entry point. Tension the spring by sending through filament - can be done by hand by turning the large gear. Specifically try to stop the filament to make sure the hobbed insert doesn't slip on the filament.

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I had problems feeding plastic through the small hole at the hobbed nut so i made a remix with a larger hole and it solved all my problems :)

http://www.thingiverse.com/thing:1747676

MasonStonehenge's Ormerod Spring-loaded extruder with larger holes
by Victhor

Hi Victhor,
I wonder if you've perhaps got a bit of over-extrusion if the hole was too small? Either way, looks like you did a good job with the derivative.
Looks like you're using Cura to slice - doesn't look like it copes very well with the built-in support :(

Comments deleted.
Sep 12, 2015 - Modified Sep 12, 2015

Thanks for this. I've just made and installed one on my Ormerod 2. I think I'll make one modification when I get round to it: lengthen the straight part of the hook/cable tidy part so that it enters the slot in the x-axis-rib just a little more than at present.

Treito: I use the (free) DesignSpark Mechanical (RS) just because it's fairly intuitive. It happily imports STEP files.
Bob

Hi BobM, thanks for the comment. This was designed for the Ormerod 1 which didn't have the gaps in the x-axis arm for the 'crook'. If you have a look at the remixes you'll see that there's a remix for the Ormerod 2 that has the longer crook you speak of! :)

Thanks. the Ormerod 1 version is doing sterling service at the moment but I will print the other soon. Sorry for delay, short holiday!

Which software did you use for the design? maybe you can provide other files so it would be easier to remix this great part.

Thank you for the kind words. I would be willing to put it up in various formats - I'm not sure what formats would be the most popular however. I find the .step files to be quite popular, but find limited use for them myself..

Thanks for the reply. The first thing is -> what software do YOU use?

Hello,

great idea. I have made one combined of two remixes (Ormerod2 motor side and Feeder with pneumatic connector) but I have a problem with the base design especially the spring. I used a spring from a ball pen but I cannot get the tension right. If the hobbed insert slips for some reasons the filament will not extruded anymore. If I tighten the screw more the filament cannot pass the heater. If I loose the screw the filament slips more easily and the extruder cannot pull the filament (1kg spool, laying on an spool holder which can easiliy be moved).
What is wrong?

Comments deleted.

Thanks for posting the stp file, but as I indicated my skills are in electronics and software programming - I'm pretty useless at the moment with any CAD tool.
Would anyone else be kind enough to add 5mm to the shepherds crook tip length and then repost?

There are so many versions of this now - So you're looking for an Ormerod 2 version with the PTFE all the way through the part or the standard 2mm feed hole?

i would also be interested in Ormerod 2 version if there is any plan for it :)

May 28, 2015 - Modified May 28, 2015
MasonStonehenge - in reply to darathy

Hi Darathy & Merlincode,

The item below is a remix by Amsterdamman which includes the longer tongue for Ormerod 2
http://www.thingiverse.com/thing:504722

Hope that sorts you out! :)

Amsterdamman's remix for Ormerod2 of MasonStonehenge's Ormerod1 Spring-loaded extruder

Brilliant design.
As an electrical and software engineer I must take my hat off to you CAD/mechanical engineers.
I am using two of these extruders with the alternative gears you mention on my dual colour Ormerod 2,
and it solves all my previous extruder problems.
The only issue is that for this particular model of RepRapPro your extruders main body's shepherds crook is not quite long enough
to fit in the lower slot on the acrylic X-rib. Any chance of lengthening the tip by 5mm in version 3?
I can send you an original Ormerod 2 extruder if you would like to examine it - or send you the stl file.
Thanks

Thank you for the kind comment. I presume that you're using the Ormerod 2 which has a slightly different x-rib to the Ormerod 1. I have posted the .stp files for those inclined to make the relevant changes, but as yet haven't got around to looking into what is involved.

I like this extruder very much, however I have a recurring problem, which is that the filament breaks overnight in the inlet duct, often in more than one place. I think this is because of the small radius that the filament has to go round. Any chance of doing a variant with more height between the inlet hole and the holes for the drive bolt and bearing? I think the inlet could be moved down at least 10mm without danger of fouling the print, which would allow a greater radius of turn.

Mar 1, 2015 - Modified Mar 1, 2015
MasonStonehenge - in reply to dc42

hey Dave. I hear you on the filament breaking problem - as I mentioned before I haven't experienced that before and I'm quite interested as to how it occurs - the end of the filament is wrapped around a fairly small diameter when on the reel and doesn't break when pulled off, so I'm still baffled as to what would cause it to break. The only breakage problem I've had has been with the 'transparent' ABS, which is not very flexible, and that was with a Prusa with a direct feed, no bends and a less than ideal feed system. Does it possibly get very cold where your printer is at night?
I don't mind making changes - I just don't get around to design much at the moment..

EDIT: The radius on the curve that you're talking about is 24mm, which is at least the same as the Reprap stock, but I wonder if it's to do with that radius going straight into the bearing and hobbed insert and being forced straight from then on..

Are you still interested in the pneumatic connector?

I've no evidence that breakage is more likely in your extruder than in the stock RRP one - I've been using yours for so long that I can't remember how it was before. The room the printer is in does get cool at night, probably down to 10C. I really do need a solution. Could you please increase the radius to 30mm or 35mm, if that's not too difficult? And yes, I am still interested in using the pneumatic connector - the two on my Mini Kossel have given me no trouble. That said, if the filament breakage problem is fixed then I won't need to disconnect the Bowden tubes from the extruders very often.

Can you give me the length of the thread on your pneumatic connector? I'm not convinced that there is enough space for a trapped (slide in) nut - tapping might be the only way, but then the length of the thread must be such that it will hold and not just damage the plastic.

It's 4.35mm. On the Mini Kossel, the connectors are screwed in to the plastic, which has been printed in ABS and then tapped.

Let me know when you've tried the latest design I posted for you. I might release it here if there is sufficient improvement in the breakage issue you have and no major issues.

Works brilliant! Thanks for the upload! At first it wouldn't extrude at all, but after I thickened the bearing opposite of the powered wheel with kapton tape I could just let it go, where as before I had to constantly help it extrude.

Hi there, I've had this mentioned in a previous comment. There is a slight size difference between the two bearings that sandwich the hobbed insert (9mm diameter) and the one that mounts to the motor (10mm), so check that you have those the right way around.
if you use the smaller bearing by accident you will have problems like you mention above.

Well, thats probably what happened. Thanks!

Another thought. One of the problems I find with the Ormerod is that if I leave the filament in the extruder for a few days without printing anything, when I next come to print it breaks off (or has already broken off) in the extruder. So how about a quick-release mechanism that I can use to release the pressure on the filament when I finish printing? In its simplest form, this could be a slot for the screw instead of a hole in the front part, along with a circular recess for the spring to seat in. Alternatively, a slot in the back part, retaining the hexagonal nut trap. Either way, the tensioning screw could be disengaged without the use of tools.

That's an interesting problem. I've never had my filament break inside the extruder - even after a while of non-use. I wonder if it's to do with the humidity in the UK?
I think I get what you're talking about, but if you email me a simple drawing or something to masonstonehenge at gmail.com it might make what you're suggesting a little clearer. I'm not sure if I'll get a chance to make that sort of change in the short term, but I might be able to do a tappable hole for the M5 thread - a little something in exchange for the excellent work you do on the firmware!
I'll send it to you directly though unless there's a lot of extra interest in the idea.
Cheers Vorty/MasonStonehenge

Have you considered modifying your design to accommodate a push-fit pneumatic connector for the Bowden tube? These are used on the Mini Kossel printer, and I find they are great! The connector is for 4mm tube and has an M5 thread, available on eBay.

Nov 17, 2014 - Modified Nov 17, 2014
MasonStonehenge - in reply to dc42

hey dc42 - don't suppose you have a link for that part?
Something like this?
http://www.thingiverse.com/thing:275029

Ultimaker Rp 1/8" Bowden Push Fit Connector

Yes, similar to that one. There is a picture of the one included in the Mini Kossel kit at http://www.think3dprint3d.com/extruder-parts/extruder-hardware-set. I just found them on Amazon here http://www.amazon.co.uk/SODIAL-Thread-Pneumatic-Connector-Fitting/dp/B00HUHC00Y/ref=sr_1_2?ie=UTF8&qid=1416240906&sr=8-2&keywords=4mm+pneumatic+fitting, although it says they are dispatched from Hong Kong so it could take a while to get them.

I'm thinking about how to implement it. The plastic wouldn't be able to print thread that you can screw into, so the option I'm thinking of would be to put a nut embedded into the top of the extruder. That should be fairly easy to do - what do you think? Would you be willing to be the guinea pig if I give you a version that can do that? Unfortunately it takes forever and costs the earth to get anything posted to where I live.

A few months late, but I use a screw-in push-quick fitting as in the picture on an ABS extruder on my Rostock. You size the hole a little smaller than the threads, and it screws in nicely and holds its place. With your extruder, I Got one that the threads were just a little too small and used a thick ABS/acetone slurry to bridge the gap between the threads and the exit hole in the extruder. Works well, I vastly prefer the pneumatic fittings over the 'tongue' method of Bowden retention.

Separate note: I love your extruder! Thanks for thinking it up and posting it here!

Nov 20, 2014 - Modified Nov 20, 2014
dc42 - in reply to MasonStonehenge

I'd prefer a nut trap to a nut that has to be embedded during printing. If the hole goes all the way through the part, then I'd be happy to buy a 5mm tap so that I can tap the hole in the plastic instead. This is what they do with the parts in the Mini Kossel kit.

My last filament purchase turned out to be around 1.73 on average, and would simply stop feeding on the Ormerod. After printing this extruder with the last of an old filament spool, it seems that I'm back to being productive.

Great job! :-)

Do i need a wider bearing for the one which bolts to the top right of the stepper motor? my PLA filament doesnt get trapped between the bearing and the knurled bolt. the bearing on the knurled bolt part hits the stepper case before the PLA is pinched

Oct 29, 2014 - Modified Oct 29, 2014
MasonStonehenge - in reply to PaulHam

The construction of the extruder is exactly the same as the Ormerod 1 extruder, using the same parts - There is a slight size difference between the two bearings that sandwich the hobbed insert (9mm diameter) and the one that mounts to the motor (10mm), so check that you have those the right way around. See https://reprappro.com/documentation/ormerod/extruder-drive-assembly/

what is the spec for the spring?

Jul 31, 2014 - Modified Jul 31, 2014
MasonStonehenge - in reply to antlvk

A mild compression spring like those found in some ball-point pens seems to be perfectly sufficient. The lever action increases the grip from the spring a lot, but some springs you would tighten the screw more than others to get the desired grip.
Do a couple of test prints and tighten until all slipping stops.

Added breakway support for the PTFE Feeder and Motor side hinges. Shouldn't need to print with support as long as your printer can bridge smallish gaps. Let me know if you need this done for the non-PTFE version.
Also slightly strengthened the join between the motor side and the axis cross piece as requested by Ezwul.

Hi Mason
Wonderful part, forgot to print with support, so will have to print again :)
A small problem, the joint between the spring clip and the stepper motor where it joins the point with the rightmost single stepper motor screw hole is rather thin and after printing, the upper surface has cracked and weakened the print. This is the point which bridges the Ormerod laser cut X axis plate. Is it possible for you to fill the space from the top of the screw hole and the last upper point on the clip, I know this is not as aesthetically pleasing as the current part.
This will increase the amount of material forming the joint strengthening the part.

The various V2c files now contain an anchor for the Bowden tube clip as requested by Ormerod168

Bobtidey - I've made that change - "Feeder V2b PTFE.stl". Give it a whirl and let me know?

Ahh OK, well if you look at the original extruder design, there's a VERY thin part that I could imagine on some prints could be worn through.
I'm making the changes I spoke of and will be updating the model soon. If I get a chance I'll look at making that hole big enough for the PTFE liner as an additional download.

Yes. The feeder tube was enlarged up to close to the hobbed insert to allow a PTFE liner as some including myself were experiencing significant wear as the filament goes round the bend. One can use the PTFE like in the bowden tube but I found that a little stiff so used a tube with a thinner wall but same OD and that works really well as a liner. http://forums.reprap.org/read.php?340,313967,316416#msg-316416http://forums.reprap.org/read....

I hadn't looked at that. Do you mean increasing the size of the curve feed so that the PTFE goes right up to the hobbed insert? Interesting, though I've removed my PTFE and replaced it with another pipe, so wouldn't work all that well for me. I must make the mods I mentioned, but I'm still very happy with this extruder block - works like a charm!

Very interesting. Have you considered also extending the wide bore of the filament inlet through most of its length like the Mr Burns extruder mod? That then allows a ptfe tube liner which reduces wear and make the filament slide though better.

I've been using V2 of this extruder for a couple of weeks now, and am very happy! 2 things I'm going to change:
1) The top hinge on the large gear side should be countersunk so that the spacer nut for the large gear isn't required. This will allow other gears like the interesting helical gears.
2) Where the feed tube for the filament enters at the bottom, I think I should have a guide to keep the two parts aligned, rather than relying on the screw hinge at the top for alignment.
I was worried that moving the large gear closer and further away from the small gear wouldn't work well, but I'm happy to say that this isn't a problem - I've managed to feed filament that varies between 1.5 and 2mm with no problems.

Will post the step (.stp) files if anyone is interested

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