DIY Injection moulding by JR Hartley.

[HankMcSpank]

The main 'speed impediment' wrt my cnc 'output rate' is my spindle- basically I chose low noise levels over 'grunt', becuase I live in a terraced house, with no workshop - so I don't want to receive a neighbour induced an ASBO, but do want to be able to use the machine late (it's this one - http://www.google.co.uk/imgres?imgur...26tbs%3Disch:1 - just the router part) it is *very* quiet, but being relatively low powered 250W & a max RPM of 6,00, the max I can push it at - even with feeble acrylic - is about a 3mm depth cut at about 80mm per minute (yes you read that right!)....else the tool wanders off course (I guess it can't get rid of the swarf at any higher rate & takes a path of its own)

So the average bobbin is about 120mm circumference - but being 2.5D it needs several passes ...and holes - plus I make two halves do everything need to be doubled (so tool changing involved...touching off etc)

Roughly the procedure is this (& you need to bear in mind, I'm wet behind the ears & proud!)...

1. cut a piece of acrylic stock to size (I have a mini table saw)
2. Scribe the centre point.
3. Double sided sticky tape to affix the acrlyic onto some spoiler/waste material beneath.
4. Clamp it.
5. Put 4mm drill into tool holder - align tool over acrylic centre, touch off etc.

About 8 mins has elapsed & I haven't started the CNC machine up yet!!

6. CNC machine drills twelve holes (I make two halves of a bobbin & join them in the middle, therefore twice the number of holes/cuts per bobbin!)
7. Tool swap - 3mm flat endmill into position, touch off.
8. Cut bobbin shape around holes to a depth of 2mm (i use 3mm thick material) - this leaves 1mm at the bottom (ie the edge of the bobbin)
9. Now move the cutter outwards a bit & cut the outer perimeter for the whole 3mm depth (ie completely cut the shape out from the acylic stock)

I now have two bobbin halves.

10. clean the parts up (wire wool the rough edges etc)
11. Glue the two halves of the bobbin together.

On a good day with the wind behind me (& no screw ups - which happens a fair bit!) - I can do in about 30 minutes from start to end. A high proportion of that 30 minutes is the tool moving oh so slowly on those numerous 2.5D cuts around the part perimeters!, at the minute this isn't a huge problem (as I don't make that many), but I'd like to be in a position where I could make 20-30 bobbins in 15 minutes or so.

therefore with a moulder...

1. Turn heater on
2. Load plastic granules.
3. Compress
4. Spit part out

About 30 seconds per bobbin?!! It's a compelling argument!