Extruder drive further questions on the extruder drive.

To All
Having lost the brass blank I made yesterday for he worm drive. No idea how or where so making another one.

I am going to try using some tiny 10mm gears I got from Farnnell.
They have 48 teeth 13 in a quarter (4 x 13)- 4

I will also try the Conrad coupler that is 7.78mm with 8 teeth a 1/4
(4 x 8) -4 = 28 teeth

I may try tapping a Conrad gear into a worm as well.

Any other suggestions as to how to make this drive gear easily I will try.

Has anyone any idea as to what is the optimum pull force required to have a Reliable stage 1 extruder.

By stage 1 I mean an extruder that extrudes 0.6mm good enough to make things like a more complex extruder body and gears + replacement parts?

PS you do not need to buy a drive coupler from Conrad any good Model shop will have these things.
They are drive couplers used in RC boats and possibly cars as well.
Allowing for misalignment of the two parts motor to thing being driven.
You screw one onto each of the 2 shafts the gear shaped part slot into a plastic universal joint.
We only need one brass shaft to plastic part for an extruder.

@ Wade
What are you using if its not a worm gear to get 5.5kg of pull?

@ Dissidence
I have kinda messed up my plan to make a Mendel that any one can build without special parts.

Regarding drilling out the welding tip.
I think this can be done by drilling it out to 3.5mm in 0.5mm steps without needing a lathe.
The same technique for the Peek insulator.
Instead of fixing the peek with cir-clips.
Use 2 small screws at the top going down into the length of the peek using an extra piece of MDF glued above the 16mm will work.

@ AK47
machined the Brass at 1600-2200 RPM it seemed to cut OK at that kind of speed is that the kind of speed I should have used?

The blank I made was 11mm long 10mm diameter I had cut a 2mm wide grove ready to cut the worm thread into. Dose that sound about right?

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Bodge It [reprap.org]
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Aka47 had the interesting idea of using a planetary gear. Are you able to mill an anulus, or just pinion gears? I would be very interested if you're able to test a high gear ratio on the planetary arrangement.

I used a small 11 tooth gear, roughly 7mm diameter to get 5.5 kg of pull. Photos of it are here:

[objects.reprap.org]

Click on the second photo a few times, and you'll get a super blown up version of the photo, or just click here:

[objects.reprap.org]

It's the little brass gear in the middle. The teeth themselves cause a fair bit of acceleration and deceleration as they grip the filament, which might be a problem.

I've made a worm gear style pinch wheel using a piece of M8 rod, a file, and an M3 tap mounted in a hand drill, but I need to redesign my extruder body for M8 ID skate bearings instead of 624 bearings, so I'm messing with that now.

Here's a crappy photo of the M8 pinchwheel in progress:

[gallery.me.com]

So far it seems to grip filament pretty well, but I'm not sure it's as concentric as I'd like. A lathe would work a lot better; I just mounted some skate bearings in a vise and spun up the M8 shaft with my slightly bent hand drill in one hand and had at it with a file in the other hand. Then I abused the rod with an M3 tap mounted in the drill. Messy, but it made something. I'll let you know if it works!

Wade

edit - BTW, this sort of stuff should probably go in the Mechanics forum.

Edited 1 time(s). Last edit at 01/25/2010 03:36PM by Wade.

With a cheap £10 stepper the problem I am seeing is not lack of torque.

I am getting a lack of grip on driving ABS filament.

The maximum pull I get is 1.5 Kg to 2Kg pull before the drive cuts the ABS filament instead of driving it..

So far I have used the splined stepper this will give the highest torque.

As it is the smallest drive diameter @ 5mm it provides us with the highest non-geared resolution. 3mm of 0.6mm extruded plastic

I have tried the Conrad coupler with similar results as this is 7.78mm Diameter

It gives even less resolution at 5mm of 0.6mm extruded plastic.

At the moment for a stage 1 extruder I'm not bothered by having low resolution extrusion as long as it is reliable ie it extrudes.

It just needs to be good enought to print the more complex parts of the next stage of extruder that will have a much higher resolution 0.1mm of 0.6mm filament per step.


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Side issue of resolution calculation example.

By resolution I mean each step is 3mm of 0.6mm extrusion.

If my maths is correct.

(5*pi/400) = length per step

1.5^2*pi = area

(1.5^2*pi) X (5*pi/400) = cubic plastic extruded

7.068mm2 x 0.0392 = 0.278 cubic mm per step

extruder hole = 0.6mm

0.3mm^2*pi =area

0.278/0.09mm2 = 3mm of 0.6 extrusion per step

If my maths is right wich is quite a lot more than 0,1mm resolution

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Bodge It [reprap.org]
=======================================

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BIQ Sanguinololu SD LCD board	BIQ Stepcon	BIQ Opto Endstop
BIQ Heater Block PCB	BIQ Extruder Peek clamp replacement	BIQ Huxley Seedling
BIQ Sanguinololu mounting	BIQ standalone Sanguinololu or Ramps mounting	Print It Stick It Cut it

My rep strap: [repstrapbertha.blogspot.com]

Buy the bits from B&Q pipestrap [diyrepstrap.blogspot.com]
How to Build a Darwin without any Rep Rap Parts [repstrapdarwin.blogspot.com]
Web Site [www.takeaway3dtech.com]

BodgeIt, Nophead has a great post where he tested the pull of various systems using a socket wrench instead of a weak motor. Here's the link:

[hydraraptor.blogspot.com]

Here's a cut and paste of the results:

Quote
Nophead

I tried the M3 pulley and that was better still, raising PCL to 8Kg. Here is a summary of all the tests: -

                        PCL	HDPE	 ABS	   PLA
4mm splined shaft	2.5 Kg	3.0 Kg	 5.0 Kg	   7.5 Kg
13mm timing pulley	4.0 Kg	10.0 Kg	 8.5 Kg	   >8 Kg
13mm knurled wheel	5.0 Kg	10.0 Kg	 12.0 Kg   >12.5 Kg
13mm M4 worm pulley	6.0 Kg	>12.5 Kg >12.5 Kg  >12.5 Kg
13mm M3 worm pulley	8.0 Kg	>12.5 Kg >12.5 Kg  >12.5 Kg
M5 thread	        9.0 Kg	>12.5 Kg >12.5 Kg  >12.5 Kg

As you can see, a small, 4 mm splined shaft had the least grip. The old M5 threaded screw drive had the most, with a 13 mm M3 worm pulley being almost as good, at least for PCL.

Nophead did manage to get 5.0 kg out of the 4 mm splined shaft on ABS; you might be able to do better if you can increase the pinch force (decrease the spacing).

His 13 mm M3 worm pulleys seem pretty nice! Hard to make without a lathe though. I think the trick to getting better grip is to engage more of the filament with the pinchwheel (by using a larger diameter, smoother pinchwheel), and increasing the clamping force.

Wade

Edited 3 time(s). Last edit at 01/25/2010 03:50PM by Wade.

The 4mm splined shaft had lots of shallow splines. They are sharp and stick out beyond the shaft diameter, not like the home made splines done with a Dremel.

I don't have a tool to make splines, I had some shafts with them on already. I believe that they can be made with a knurling tool with the correct cutting wheels but not seen them available. Having said that, knurling works pretty well, I wonder if you could just use a knurling tool on a powered stepper so that it knurls itself. Fit a felt washer or similar to stop swarf going in the motor.

But even with a small shaft and microstepping I don't think you get enough resolution without gearing. Mind you, perhaps we could knurl a shaft in situ in a geared stepper drive. Use the drive and its bearings as a mini lathe.

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[www.hydraraptor.blogspot.com]

i am starting to think that is going to be well worth my time to make a geared exdruder

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[mike-mack.blogspot.com]