Wades Extruder Gear replacement

Hey all.
I am just about to get up and running with my prusa, slightly re-engineered as i built her and she is a beauty.
With most of the axis hardware set up, it is time to look at the extruder.

I posted yesterday about my inital build thoughts and mentioned i needed a large gear for the Wades extruder.
I am happy to say someone among us has been kind enough to help me out here.

My thoughts, however, continue to re-imagine every aspect of the extruder design and i wanted to get some feed back while getting the electronics going and waiting for the large gear.

I have a pretty good background in RC cars and was thinking the spur gear and clutch assembly closely matches the sizes of the gears that are in the Wades extruder.

Here is my question(s)
If i were to hypothetically match the diameters of the Wades extruder gears to the gears from the hobby shop and the only difference is the amount of teeth on the gears, are there any changes i would need to make in the firmware?

Just a thought.
i feel that the RC gears would be more precise then those printed out.
But matching the diameters of the gears wouldnt be easy and i would probably need to modify the firmware.

What do you guys think?
-E

I use rc gears on my wades extruder. It was one of those emergency fixes that stuck. I never made changes to the firmware, but skein forge can make the changes you need.

Can you elaborate a bit on what size gears you used and what the settings changed were?

ill be stopping by the hobby store on the way home from work.

thanks jcabrer

You are likely to have to edit the firmware anyway. To achieve accurate calibration it's a necessity. I would try to make your extruder from commonly available parts, and tweak the firmware afterwards, rather than custom parts that will be hard to reproduce.

People seem to be nervous about firmware edits; you're not changing the firmware code, all you are doing is changing the conversion factor the firmware uses to convert gcode movements into machine movements. This does involve re-flashing the electronics with the whole firmware, but usually just to change one figure. There are a number of tutorials on the forum about setting accurate STEPS_PER_MM for each axis and the extruder - set it up for Skeinforge 41 like this [josefprusa.cz]

To be able to do this, you need to install the Arduino software on your computer, and get the firmware for your electronics (usually from the supplier's website, or from the wiki). This page [reprap.org] is the generic explanation of how to install the software and edit the firmware.
It is easy when you follow the steps; hey, I managed it! If you have changed other elements of your build, especially things like sizes of pulleys, you'll have to do this anyway. Get used to doing it at the beginning, and the possibilities going forward will expand, and accuracy of your reprap will improve.

I'm an EE so I know arduino verry well.
Firmware is definatly getting modded either way.
Not a prob.
I just don't quite yet know the ins and outs of comp to duino
And what I would need to mod.
Spur gears are cheap and I got time till the real thing in delivered
Thanks all

You just need to 'mod' the e_steps_per_mm in configuration.h part of the firmware. You hook up your new and improved extruder to your electronics, send a gcode like G1 E10 which means extrude 10mm of filament. If it extrudes 5mm of filament, you double the e_steps_per_mm value, and upload the firmware. Repeat until it accurately extrudes the amount of filament you're expecting. This way any variation of extruder can be calibrated. I did it with my repstrap, which has an extruder built from MDF and random inkjet printer gears.

This is a waste of time when you can just calculate the e_steps_per_mm from the number of teeth in the gears (gear ratio) and the circumference of the hobbed drive. The rest of the adjustment can be done in Skeinforge parameter Filament Packing Density Ratio.

Getting your reprap accurately calibrated is it a waste of time? With your way of doing it, you still have to change the firmware, so taking the extra couple of minutes to get it accurately extruding (especially when it is easy to make a mistake with the maths) is hardly a waste of time. Your method relies on measuring the circumference of the hobbed bolt; any error in measurement is then compounded by multiplying by the gear ratio. Even if it is accurately calculated, it takes no account of the material being extruded. You then correct this by using a 'fudge factor' in Skeinforge. What if you are not using Skeinforge to generate gcode? When I ask for 10mm of extrude, I expect to get 10mm of extrude, not 9mm and have to correct it in software. I'm sure it works for you, but having spent years setting up machinery, I know it is far better to remove such inaccuracy at the lowest possible level. If all repraps were commissioned and calibrated in a very similar way, the software would be simpler and quality prints would be more repeatable.

10mm is not enough to measure accurately. I put a mark 110mm above the extruder, extrude 100mm and measure how close the mark is to the extruder entrance. My measurements are only accurate to about 1mm so that gets it to within 1%. With only 10mm it would be 10%, which is not close enough for good results.

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[www.hydraraptor.blogspot.com]

I'm sorry for not explaining clearly. After setting the e_steps_per_mm in firmware to the calculated value, do the same method as you proposed to measure actual feed length. Then calculate the Filament Packing Density Ratio (FPDR) as the ratio of (actual feed length)/(desired feed length). To first order, the FPDR accounts for the drive gear teeth digging into the feed reducing its effective diameter. Doing it this way means that you can have different settings for different feed (PLA, ABS, different colors, source, etc) without having to reload the firmware with different e_steps_per_mm.

For normal PLA the FPDR should be one, ABS 0.98, or 0.96, soft PLA even less.

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

nophead Wrote:
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> 10mm is not enough to measure accurately.
True, 10mm was an example. Prusa's instruction say 3cm, but better accuracy can be achieved by a longer extrude. I calibrated mine measuring 100mm.
@brnrd - Is your firmware e_steps_per_mm setting still your calculated value, or a value from an observed length of extrusion? I can see why you would just use a theoretical value, especially if you are swapping filament a lot, rather than recalibrating the extruder each time, and fix it using FPDR. Yes, of course you can use FPDR like this, but it feels to me like mixing up two functions; correcting any calibration error and correcting variations in filament. Perhaps this is how people who have lots of different filament work, but I don't think it's ideal when setting up a reprap initially, with so many other variables. I was suggesting to the OP what to change in firmware to initially calibrate a new extruder with potentially different gearing.
@Bob - thanks for your settings. I'm just using PLA at the moment, with FPDR set to 1. I will be trying ABS once I get my Prusa built and heated bed. I'm just waiting for my mendel-parts v9 hot end.
@420e - as brnrd said, you can get a calculated e_steps_per_mm by counting gears and measuring the circumference of your extruder hobbed bolt - handy if you don't have any plastic filament to put through it yet. Then test with filament that it extrudes the length expected, and adjust accordingly for a more accurate e_steps_per_mm setting. Finally, to take account of different types of plastic and how they are affected by running through the extruder, there is the 'Filament Packing Density Ratio' setting in Skeinforge which can be adjusted, rather than re-calibrating the extruder when you change the plastic used. But you will have to remember these adjustments if you use any other software for gcode creation.

The most important parameter to get right is the filament diameter. The e_steps_per_mm and the filament packing density ratio compensates for each other under Skeinforge 40 and 41. It doesn't really matter what the exact values of those two parameters are as long as SF 40 sends the right E values to the printer. You can spend as much time as you want to get the most accurate calibration of the feed length pulled by the cold end, but at the end of the day, you'll still be limited by how uniform the feed is and how perfect your filament drive gear is.

Thanks for the explanation brnrd, and while I agree with you about filament width, the limitations you state apply equally to adjusting it using FPDR. I'm still happy that I set e_steps to at least 99% observable accuracy (like nophead, less than 1mm over 100mm), so I don't have to worry about it when I occasionally let repsnapper make the gcode. Or if any new gcode software comes along. It gives a sensible base to start from when tuning Skeinforge. I guess we'll just have to disagree about what function FPDR is used for.

Thanks all.
Very good information.
I cant help but notice that the wades extruder wiki is starting to rot a bit,
Also i can seem to find an assembly guide for makergears grooovemount wades extruder
throw out a link if you have one.
Thanks

This help you?

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