Wednesday, May 27, 2009

 

Sourcing low-cost parts for RepRaps/RepStraps

The key to finding RepRap or RepStrap parts: keep your eyes open, and don't be afraid to ask: experiment, try things out, and tweak your design to what you can find. I've found a few useful bits over the last couple of months.

I wanted to add an encoder to my GM3 drive motor, but I've previously blown my three spare opto-switches.
Asking around at work, I found an old ball mouse with a broken USB plug, and got permission to take it home from sysadmin.
Logic dictated that running off USB (5v) it might contain some opto-switches that I could recycle. Taking it apart, a quick inspection revealed two components either side of a slotted wheel that looked right:
From RepRap_bits


I desoldered them, ripped out the broken IR sensor from the x-max endstop board, and just soldered them in.

From RepRap_bits


Hooking it up to the arduino, it works perfectly! (even the pins are the same)

Other extruder bits:

I found some thin-walled alumininum an brass tube in a Model shop in Westbury. It's imperial (5/32) but the internal diameter is exactly right for my 3.1mm filament. (£4.50 for a pack of 4)
From RepRap_bits

I think it might work well to make vik's no-lathe/ariel extruder, or to make a Nophead-style thin-walled extruder. I've got a large heatsink from a core2 CPU to go with it.

I've been looking for a block of metal to make nophead's resistor heater for a little while - it's not something you can buy in B&Q, and I don't happen to have aluminium bar stock in my garage. :-)

In the middle of Bath, down by Sainsburys, I walked past a little tool shop that was selling scrap metal outside. I went in and asked, and...
From RepRap_bits

Hey presto, the chap disappeared out the back and came back with a 10mmx30mm bar - and cut me off a couple of 30mm lengths from it. The best bit : cost 25p. So, a shout-out to the guys at Avery Knight and Bowlers, Bath - thanks guys. They've been consistently helpful and the shop is full of tools and other useful bits. I also grabbed some m6 coupling nuts (50p)- might be useful to attach nozzles - and a 7.5mm drill (£3.24), which is the right size for my resistors.

I've thrown a few quid away on some tattoo tips from a dodgy overseas company (like these ones). I wanted to have a look to see if they would be useful to turn into nozzles. When (if) they arrive, I'll post some measurements and photos.

Edit: half-hour after posting this, I noticed a big split in the mains cord insulation for my wife's hairdryer. 'It's not safe, we'll have to you get a new one' - of course, nothing to do with the fact it's full of nichrome wire....

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Comments:
I see that you found the 5/32nds copper tubing. I built my extruder barrel around that stuff some years ago and it worked very well. Precision Metals makes it for K&S metals in the US. If you want to see how I did it you can look at...

http://3dreplicators.com/New%20Front%20Page/Documentation/Extruder/Mk%201%20Extruder%20Barrel.htm
 
Nice! I took apart the exact same mouse to use as an extruder encoder; it worked, but I never got around to writing the software for it; I just used Zach's magnetic encoder instead.

Here's a pic:

http://picasaweb.google.ca/wbortz/OldExtruderShot#5340932570448195922

Great source for opto switches though! I think there's actually two detectors for each wheel to run the quadrature output, but either one will work for an end stop sensor.

Will be checking the hobby shops for thin walled tubing; I've found some very thick walled stainless tube at Metal Supermarkets, but it'll take a lot of machining to make it work.
 
Thanks for the links!
Forrest - Nice post describing the process! I was planning something along the lines of the ariel drilled grubscrew, or possibly a drilled welding tip nozzle that takes the barrel.

Wade, yep, they're great sources for opto-switches. You only need two mice, and you could get 4 switches - enough for the min stops and an encoder.

I didn't check the outputs at all, and the boards and pins were unmarked - I just trusted that they were the same!
They fit directly into the 2 and 3-hole spaces on the existing endstop boards. I've no idea how to get quadrature, but hooking the board to an arduino gives the high/low when blocked, which is all I needed.
 
I've tried to thread that 5/32" tubing. The wall thickness is just too thin. :-(
 
http://www.aquabacon.com/wp-content/main/2009_05/cordless-mouse.jpg

:-p
 
Don't forget you can use surplus nicrome wire from the hairdryer (mine had oodles of the stuff) to make an acrylic bender.

https://sites.google.com/site/mechatronicsguy/acrylic-bender
 
I've just spent 2 days straight playing wit hthe insides of PS/2 mice, for pretty much the same reason... I wanted a quadrature encoder for my pinch-extruder ( not stepper driven, DC driven ). In the process I've discovered that the 20KHz PS/2 protocol is stupid, and the Arduino PS/2 lbraries are not designed for background-processing, as they bind the arduino CPU down to doing just that one task. I've also re-implemented 80% of the protocl myself as interrupt-driven ( reads are asyncronous, writes are synchronous), and then I've finally decided to scrap the entire thing, and I'm using a HP/Agilent quadrature encoder from a printer hooked into two inrterrupt lines, much easier, and no *frigging* PS/2 protocol. :-)
 
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