The effect of the length of the extrusion hole

On reading Wades comment some where here regarding the length of the narrow part of the extruder I made sure my extruder had 0.8mm of length at 0.6mm.

As I know my extruder has easily have enough umph to push throght a longer length of hole will I gain a smaller sizer of extrusion if I make the length of this hole longer say twice as long a 1.6mm long?

Curently I get a 0.99mm extrusion from my 0.6mm welding tip thats a die swell of almost 50% of the hole size...

Coments and sugestions welcome.

Here is my feed rate calculation.. using the formula from Nick brokentoaster

Description Value Unit Name Formula
filament diameter (3mm) 3.00 mm FD
extruded diameter (0.5mm) 0.99 mm ED
pinch wheel diameter, outer diameter of teeth on my custom brass splined gear is 7mm 6.50 mm PWD
drive gear ratio (1 normally, 5 for 55:11 drive) 25.00 - Worm GEAR_RATIO
number of steps per revolution (I'm using a half steps drive ) 400.00 - STEPS_PER_REV


pi 3.14 - PI PI
length of filament drawn into extruder in one revolution 20.42 mm FL (PI * PWD)
radius of filament entering the extruder 1.50 mm R1 (FD/2)
radius of extruded filament as it exits the extruder 0.50 mm R2 (ED/2)
length extruded in one revolution of pinch wheel 187.51 mm EL ((FL*R1*R1)/(R2*R2))

number of steps needed to extrude a length of 1mm of plastic. 53.329148623715100 - E_STEPS_PER_MM (E_STEPS_PER_REV * GEAR_RATIO / EL)

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Hi BodgeIt,
I get about 0.8mm - 0.9mm ABS from a 0.6mm welding tip. I recently use one to print large objects with 0.75mm filament / 0.6mm layers. Somebody posted that 0.6mm tips are for 0.6mm wire and actually have a bigger hole than that for clearance. It also depends on the type of ABS and how fast I extrude.

I am not sure what effect the length of the hole has. On the one hand a longer hole increases the pressure, which increases the die swell. On the other hand the plastic may get more used to being the hole diameter and swell less when released.

A welding tip would be a good way of experimenting with this as one could start with a long hole and then keep filing the tip away.

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[www.hydraraptor.blogspot.com]

Cool I will have a go at trying that out as I have a spare extruder now and spare extruder controller boards and several packs few of the 1" long welding tips from B&Q before they discontinued them.

Your right I had not thought of it being a clerance hole... ;-O

I think I will just drill out a pack of tips to diffrent depths to start with from 3mm to 1mm to get a feel for the effect it might have.

I gues It will take several iterations at each size if the size changes to change the number of steps required for 1mm of length extruded.

For printing higher quality prints what size extruder tip are you now using and how long is your extrusion hole for ABS?

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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]

> I gues It will take several iterations at each
> size if the size changes to change the number of
> steps required for 1mm of length extruded.

The nozzle size or length doesn't make any difference to the amount of plastic that flows through it, so you don't need to change any settings. All that changes is the size of the filament when extruded into mid air. When it is being laid down it gets stretched to match the travel. I.e. the size of the filament laid down is determine solely by the flow rate / feed rate.

The effect of the nozzle diameter and die swell is that it sets the maximum and minimum filament size you can lay down. It has to be less than the size extruded into mid air so that it is stretched rather than compressed. If you try to extrude filament too big it wont span gaps and will tend to squiggle rather than form straight lines.

You can extrude smaller filament simply by reducing the flow rate / feed rate ratio. As you go smaller you are stretching it more, which helps it span gaps, but it tends to cut corners and holes shrink more. The limit is when it starts to snap as it it laid down.

>
> For printing higher quality prints what size
> extruder tip are you now using and how long is
> your extrusion hole for ABS?

I use 0.4mm on HydraRaptor and 0.5mm on my Mendel but I have used from 0.3mm to whatever size a 0.6mm welding tip is. If you want to print gears 0.3mm is great. But if you want to make large strong things, bigger is better.

I generally extrude with diameters from the nozzle diameter, up to the die swell limit. So die swell is somewhat beneficial in that it increases the usable range from a single nozzle.

My guess would be that for the best accuracy one would extrude at the same diameter as the nozzle in which case you want just enough die swell to cause the filament to be stretched a little, but not too much that it cuts corners.

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[www.hydraraptor.blogspot.com]

Thank you from your comments I think I must make it possible to change the extruder tip at the moment they have all been using Nichrome wire wraped around the welding tip. May be having a corse and a fine extruder would be another way to do it.

That would require some kind of Extruder selection process in the firmware;
Im just starting to get to grips with the firmware so it may not be too much of a problem to solve.

Midge also has been having a look at the firmware and Host Software with ideas of making some changes though she is more interested in extruding acrylic paint with a Mendel or Darwin as soon as I have a spare one for her.

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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]