My first injection mold and the Rabit HY-4 injection molder

[gavztheouch]

Thanks for the post Robin.

yeah i think a video or picture of the machine might be handy, might be able to do that this morning.

I have a feeling the gate is elaborate because you need the wide 90 angle near the "spreader tip" but if you carried that 90 degree angle back to the sealing face it would be too wide, so I think they went with 60 degrees thereafter and blended the two together with a 4mm rad just to keep things smooth?

I think from Robins description, my machine works by holding/retaining the part in the moving half of the mold, the fixed halve is held against the nozzle permantly. So when the platens open the part is pulled away from the fixed halve and the sprue is pulled out through the 1mm hole, leaving a molten mess of plastic in the gate.

[Robin Hewitt]

To understand gates you only have to remember the good old Airfix model kit. The framework holding the parts are the runners, the narrow bits you snip through to release the parts are the gates. The plastic is injected. Wherever it touches the mould it freezes, but it freezes from the outside in, a bit like a water pipe furring up at super fast speed. So long as the plastic flows it can get heat and keep a channel open, if it stops flowing then it freezes and ends the injection process. The gates restrict the flow locally so flow doesn't stop anywhere until the mould is full. Clever stuff sizing the gates in an Airfix mould, kinda makes you stand back in awe.

[Robin Hewitt]

I have a feeling the gate is elaborate because you need the wide 90 angle near the "spreader tip"

When you say gate you mean sprue. If you hold the mould against the nozzle permanently then you need heated runners, I suggest you start simple.

[gavztheouch]

OK I ordered some tools to make the "sprue"

5mm shank 90 degree spot drill.
16mm 60 degree 3 flute v cutter.
8mm ball nose.

The plan is now.

1. 1mm drill staight through
2. 5mm 90 degree point drill to correct depth.
3. 60 degree cutter to bore out
4. 8mm ball to blend 90 degree into 60 degree section(Just by eye)

The 60 degree cutter needs the tip ground flat to stop it protuding to far into the work piece, apart from that I should be golden.

Will need some way of polishing the tool. Dremel attachment?

[JRR]

Were you successful in making your sprue? I have just purchased a Rabit 2/3 and hope to be able to make molds for it. I am in Canada.

Did anyone ever try contacting MCP Group - Mining & Chemical Products Ltd, to see if they had information on their injection molding machines? They are now part of 5N Plus (acquired in 2011) and are located at 1-4 Nielson Road, Finedon Road Industrial Estate, Wellingborough, Northamptonshire, United Kingdom NN8 4PE and their phone number is 44 1933 225766.

Would be good to save any documents they may still have on these machines for using, archiving or repairs.

Thank you.

John

[gavztheouch]

Hi John,

Nice to see another Rabit 2/3 owner on the forum. I have not made any progress on the mold or machines yet. A machine did come up for sale on ebay a couple of months and I managed to ask the owner some questions on the design of the molds. I shall look out that original email and post it here.

[JRR]

Hi back at ya!

I am taking my Rabit 2/3 apart at the moment and have gotten down to where the injector housing appears to be attached to the main cast body of the machine. It isn't that obvious how it comes apart now. I suspect I have to undo the five 2 or 2.5mm (need to get these hex keys) and then the whole turned heater assembly looks like it will simply slide out the front of the frame.

It looks like it won't be amazingly difficult to increase the capacity of the shot from the original 2 grams. I am hoping to get it up to 8 grams so it will cover a wide range of parts that I hope to reproduce for my business which is restoring arcade (and pinball) games. I expect there will be modifications to the machine, but I'm hoping that will mostly be software/hardware to increase the melt time and the impulse time to allow the increased amount of plastic to squeeze in and set prior to release.

I take it the original manufacturer doesn't have anything left on these machines, not being in the UK it is a bit hard to nip around to their shop and see, but the web site suggests they (Mining & Chemical Products Ltd - MCP Group SA - http://www.bloomberg.com/research/st...capId=27830480 - 1-4 Nielson Road Finedon Road Industrial Estate Wellingborough, NN8 4PE United Kingdom). are now just into geological stuff since being bought out by 5Nplus. Their web site mcp-products.com is broken...