Low-cost, easy to build Repstrap for a mechanical klutz

Hello! I'm posting this because I thought someone may be interested in my project. I'll give you a bit of background first.

I'm a computer programmer by trade, and I'm fairly competent at electronics. However, I'm also tight-fisted and, most importantly, completely rubbish at anything that involves mechanics or fabrication. If I attempt to pick up a spanner or wield an angle grinder or MIG welder, the inevitable result is blood, lots of swearing and no useful output.

I've been interested in 3D printers and, specifically, Reprap for about a year now - I'd like to own one for a variety of reasons, the main one being that I'm interested in developing the project further one day (and specifically in the possibility of designing and building extremely low-cost machines using DC servo motors and cheap electronics). However, to do that, I need a starter machine.

The eventual plan is to build a Prusa Mendel, but before I can do that I need something to print my parts on (in other words, a Repstrap). I wanted to build this Repstrap almost entirely out of scrap and salvaged parts, while making as many cost savings as possible.

Here are the basics:

- Stepper motors and drivebelts are salvaged from old scanners.
- Frame is built entirely out of scrap wood.
- Heavy duty drawer slides will be used for the linear movement. These can be salvaged from old filing cabinets; I've bought mine for about £10 a pair (annoyingly, you need three of them)...
- ...and on that, only one slide is used per axis. I have no idea how well this is going to work. I'm just hoping it might be accurate enough to get me going on printing out a set of parts for a better machine.

Primary consideration on this will be up/down play at the end of the slide's travel; there is axial play but I think it should be fairly constant. We'll just have to suck it and see here.

So far, I've almost completed the Y axis. Exactly the same design will be used for the X, except it will be mounted on a pair of vertical supports bolted down to another crossmember added in the center of the Y carriage. Haven't decided what to do for the Z and the extruder yet; I'll keep you informed.

Some pictures of the design so far...





The traditional "great British bodge". Cable ties form a rudimentary belt tensioner; hot glue mounts the optical endstop (which is of my own design).



Electronics. Arduino mega, four Sparkfun Easydrivers (I plan to use a stepper for the extruder, too - I have a large number of spare ones!)



This shows the novel method I devised of mounting the idler pulley from bits of scrap I had around the place. The belt clamp is a piece of sheet metal, roughly cut out with tin-slips and bent using a hammer and some molegrips.

The Y carriage moves smoothly and tracks straight and true. The other advantage to using the single drawer slides is it is only a few second's work to adjust them if any misalignment is noticed.

So, there we go. It's rubbish, but with any luck it may do what I need. We'll have to see. Tonight I'll be adding the middle crossmember, the uprights and some feet so it doesn't wobble

Edited 1 time(s). Last edit at 07/25/2011 05:38AM by TBJ.

Good effort, and fine British bodging! Looks like you are making progress. You already have a couple of the parts that seem the hardest and most expensive source - the electronics and the motors. The frame seems to be one of the easier/cheaper parts to source or repstrap, and there generally seems to be a move away from repstraps as the cost of printed parts continues to fall as availability rises of frame and extruder kits. When I built my repstrap, I assumed the frame would take the most amount of time - but it was actually the extruder and hot end that caused most problems.
Have a look at the wolfstrap, which also uses drawer slides [reprap.org]
When it comes to repstraps built with no printed parts, the most difficult bit to get reliable is the extruder and hot end. There are a few versions around, like mine, which is built from MDF and old printer gears: [www.thingiverse.com] - links to others are on the page.
For the hot end, look at Wildseyed's version, which is perhaps one of the simpler ones to manufacture without a lathe: [reprap.org]
When building the axes, careful you don't put too much weight in it, especially with your small-toothed belt; when it reverses direction (which these do a lot) it will jump if there's too much mass, or you will have to run it at a slow speed.
Where abouts are you based in the UK?

Check out this thread and post on te forums.

... and the Thingiverse entry for the same

It is possible to build the frame without any plastic parts, for about $35 U.S. I plan on fleshing out the design as time allows, but the concept is simple enough for anyone else to follow with.

Hi droftarts, I'm based "oop north", not far from Preston to be precise

A bit more progress - center crossmember and uprights are now on:



Will be building the X axis this weekend.

jcabrer -> Interesting design, though the one that really caught my eye was the one made out of nylon supports from B&Q (it's on someone's sig on here, though whose I can't remember). That's plan B if this machine doesn't work, though it will mean investing in a drill press

Been working on the hot end.

I have no idea if this has sufficient flow or how to increase it if not. It will do about 9mm/sec (output). The nozzle is currently 1mm which I know is probably a lot bigger than normal and won't help the flow rates - meh, we'll see

Video here: [www.youtube.com]

Always fun to build these things for yourself, isn't it?! Well done for taking the harder route.
It looks like you are having to use significant force to get it to extrude out of a large nozzle; with a normal size 0.5mm or less nozzle, it will be need even greater pressure. Is the barrel lined with anything like ptfe? If you are heating most of the barrel, the filament will melt and expand along all of its length, causing lots of friction. High temperature needs to be kept very localised near the nozzle, with a cooler, slippery (ie ptfe) feed. The actual extruding hole needs to taper to a small flat around the nozzle hole, clear of the kapton tape and wire, or these will hit the thing you are trying to build.
Have a look at the many hot end designs here: [www.reprap.org]
Hope that helps!