DIY Injection moulding by JR Hartley.

**Robin Hewitt** · 02-09-2010

Originally Posted by HankMcSpank

Thanks for the mould mft link - Have you had a quote from them for a mould? Your injection mould - being 3 phase would be a problem (I'm low-fi here!)...I'm also envisagening an unfeasibly large contraption!?

That's not a mould manufacturer, they sell the bits to make moulds.

See also http://www.pmseurope.com/

The Americans make moulds from what they call 7075 T6 alloy

But Alumec 89 is available in the UK in cut plate and is wear resistant to a greater depth.

I have a book telling how to make a really crummy lever operated press you could knock up in a couple of days. I can find it if you're interested.

**HankMcSpank** · 02-09-2010

That's proper hard core there Robin - I'm only after making a bobbin 50mm long! (the words crack, hammer & nut a bouncing around my head). A lovely looking machine though (every garage should have one)...but alas, everything I buy has to go into my workshop in the loft (this is London & not many have workshops!) - so anything/everything I buy has to go through a loft hatch!

Re the book ...thanks for the offer, but I'd probably buy something rather than make something - I don't trust myself to build a proper injection moulding machine - anthing over what my car foot pump produces (pressure wise) & I start trembling & having palputations.

**Robin Hewitt** · 02-09-2010

Originally Posted by HankMcSpank

I guess most people aspire to a nicely finished mould (so no machine marks are visible on the end result) - but since these puppies will not be visible, I could probably accept a rough & ready one! I'm hearing that Aluminium loaded expoxy might be the route for the mould for my modest requirements.

I think loaded epoxy may give you a couple of shots before flashing becomes a problem.

After machining the mould you get out your die grinding pencil and polish up the visible bits.

I do have a 4.25" diameter bar of 7075 T6, I could probably flog you a couple of slices off it if you have the means to cut it :naughty:

**Robin Hewitt** · 02-09-2010

I will admit it is a bit agricultural :whistling:

**spluppit** · 03-09-2010

I'm a bit curious why making these items seem to take you a long time to machine if you have a small cnc. Do you think it could be your approach to the way you are machining them? There are many methods that can be used to drastically reduce machining time, it is only plastic after all. If you want to give me a run down of the exact process you are using, may be I can help you reduce your machining time down to tolerable levels or even better than tolerable.

I think even on a home made basis injection moulding will be prohibitive cost wise unless you need to produce these in the tens of thousands. Of course where there is a will there is way, the time spent making the set up and the cost maybe better spent perfecting the machining process.

Kind regards,

Scott

**HankMcSpank** · 03-09-2010

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!

**Robin Hewitt** · 03-09-2010

I got the idea when I was hanging around Travin's shop, they were making some moulds for me

They do two small machines, both close the mould with a glorified G clamp, no ejectors. One air driven, the other using a lever.

They used to do the Travin Eagle which was a fully automatic, air driven, hot pot moulder but they seem to have discontinued it. They usually had one running and it seemed to work well.

http://www.travin.co.uk

**i2i** · 03-09-2010

Originally Posted by HankMcSpank

Thanks for the mould mft link - Have you had a quote from them for a mould?
Your injection mould - being 3 phase would be a problem (I'm low-fi here!)...I'm also envisagening an unfeasibly large contraption!?

I guess most people aspire to a nicely finished mould (so no machine marks are visible on the end result) - but since these puppies will not be visible, I could probably accept a rough & ready one! I'm hearing that Aluminium loaded expoxy might be the route for the mould for my modest requirements.

That's a reasonable idea...I might ponder. It'd certainly make the beard a little bit shorter (more Rolf Harris than ZZ Top), but I'd still prefer unshaven (I'm talking beards here - right?). Also, a quick skeg on the net shows they might be a bit hard to find? (ok, so Argios probably isn't the best! -joke ok!). BTW that second link - he rocks, talk about understated....legend!

C'mon, You know the one (psst: you never heard of tipping?)

PS Not related to injection moulding at all, *but* hot off the press tonight - another 'machine for the home', after much trashing of plastic & flaying of switches & sensors - a 'direct to copper clad board' inkjet printer :-)

Edit: Just seen your post...

We need more details than that - a photo to prove it along with a scan of your driving license etc. Seriously...I need more details - I think I now need the opposite to viagra (flacidagra?)

it's made by the small power machine tool co, and is an sp1.

**HankMcSpank** · 03-09-2010

Thanks (I've heard of it...but they're a bit rare!)

an interesting lo-fi solution to making repeatable, low resolution, small plastic parts...

http://www.instructables.com/id/How-...or-little-to-/

It has all the elements, ie melted plastic squeezed into a mould under pressure!