View Full Version : My first injection mold and the Rabit HY-4 injection molder

23-09-2014, 06:31 PM
This Machine arrived yesterday and now the challenge of constructing a mold can begin. I think something simple will do for starters but I would like to maybe add an injection system to make the mold cycle automatically.


23-09-2014, 07:20 PM
was it on ebay a week or two back,i was gonna bid myself.i got scared by the lack of info on it.
hope it does the job,show us it in action when your going.

23-09-2014, 07:38 PM
Good spot deisel most probably is the same machine, I didn't actually win the auction but the winner went awol and I was the secound highest bidder so I thought I would take a punt and accepted the secound chance offer. Its 240v for the heater and logic controller and 3 phase for the hydraulics. Took me a while to figure out how to wire it all up as the 240v supply was cut off inside the controller and I had the hydraulic pump motor spinning the wrong way. Seems to cycle ok now, there is even a small air cyclinder that activates the ejector pins and a light gate to sense wether parts have stopped exiting the machine. All in all pretty pleased but if I find Im not up to making a mold or have no need for the machine Ill let you know and maybe I can pass it on to you.

What is the easist material/plasic to use in an molder like this. I would like to get some granulated plastic purged through the nossel, before I commit to making a mold.

23-09-2014, 09:49 PM
Thanks for bearing us in mind gav should you move it on,at the minute though im still stuck on building one,but you never know so..
hdpe seems to be favourite as a purge material for the more common plastics used
click on this link below, theres method to purging so depending on what plastics stuck in there?best to be safe ;)


24-09-2014, 10:19 AM
Looks great but with a name like 'Rabit Hy-4' you'd better watch out for vibration :hysterical:

Robin Hewitt
24-09-2014, 11:46 AM
Excuse me if I am stating the bleedin' obvious, but have you discovered www.dms-diemould.co.uk (http://www.dms-diemould.co.uk) ?

24-09-2014, 08:51 PM
Excuse me if I am stating the bleedin' obvious,

Only Bleedin Obvious if you Bleedin know about it Robin! Bleedin hell man that's the Bleedin dumbest Bleeding thing I've heard you Bleeding say Ever.! . :joker:

24-09-2014, 09:14 PM
Only Bleedin Obvious if you Bleedin know about it Robin! Bleedin hell man that's the Bleedin dumbest Bleeding thing I've heard you Bleeding say Ever.! . :joker:

Well it might be, but there are numerous instances where people ask for information when a simple search reveals everything.

24-09-2014, 11:48 PM
Well it might be, but there are numerous instances where people ask for information when a simple search reveals everything.

Grow a sense of humour Eddy I was clearly having a Bleedin Joke.!! . . . . . . Clue was at the End. .:joker::joker::joker::joker:

Robin Hewitt
26-09-2014, 09:57 AM
Well, gavztheouch seems to have left the premises so we will never know if it was bleedin' obvious or whether I should have pointed him at the other one :whistle:

26-09-2014, 03:28 PM
Cheers Robin, I have seen that site from a previous post you made on another thread. Ebay is also a good place to find parts for molds there are a few chinese sellers selling ejector pins, springs and bushings, I dont have a link but they should be easily viewable.

Thanks for the heads up on purging deisel I was not aware of how toxic some plastics are when burnt or that you should not mix certain plastic together for safety.

The rabit takes molds bases that can be made on the lathe ie. cyclindrical not square, at some point someone has modded the machine to also accept bigger square or rectangle molds. The machine came with a manual with some basic dimensions and mold making tips. I will try and scan some important pages and see if anyone can help me work out how to cut the injector gate on the rear of the mold.:beer:

08-10-2014, 07:01 PM
http://i59.photobucket.com/albums/g282/Gavztheouch/IMG_20141008_18465_edit_1412790428485_zpsnqmfpy26. jpg

Any ideas on how best to machine this gate entry in the mold, the mold is cylindrical so I can use a lathe.

I can see 4 components to the operation,

1. 1.1mm hole
2. 4mm radius
3. 60 degree bore?
4. 90 degree bore?

08-10-2014, 08:38 PM
CNC lathe would be the simplest.
However, with a selection of drills, boring bar, 90deg countersink, and an 8mm radius ballend mill it could be acheived on a manual lathe.

Robin Hewitt
09-10-2014, 10:48 AM
Hard to see what is going on, is this where a plasticiser nozzle connects to a mould parting line?

I would not have thought it would be critical if there is no other inlet (insert "beats me, shrug" smiley here)

09-10-2014, 12:39 PM
Robin - This is a diagram of the nozzle/injection entry on the rear of the mold. The 'small internal cone' I think is hot metal cone that keeps the plastic from setting in the entrance to the injector point. Is this what you call a plasticiser?

I think you are right that this is not so critical to get all the angles and rads just so. I think the only critical point would be the depth that the hot cone pokes into the mold specifically the 1.1mm diameter hole that feeds the mold cavitiy. If it goes in too far it will block the mold and if its too far away it might allow the plastic to set?

09-10-2014, 01:59 PM
If you can get an engraving bit with the 60 deg angle you should be able to do it.
If you go over to http://www.model-engineer.co.uk/ and look up "D" bits this will show you how to make one from silver steel, drill your hole go in with the "D" bit to the required depth then tickle the hole with the engraving bit.
Good Luck

09-10-2014, 02:21 PM
Thanks Mike,

Most center drills are 60 degree I think? Shame they have a that little drill point on the end (Maybe I could turn that down to continue the 60 degree shape?). Anyway I should be able to pickup a 60 chamfer or engraving tool.

So I think the plan would be.

1. Drill 1mm hole straight through. (Hopefully easy in alu?)
2. Use 60 degree tool to hog out material and form 60 shape.
3. Use a small 90 degree tool widen the 1mm hole entrance
4. Use 4mm rad ballnose to blend the 60 and 90 degree shapes by eye?

09-10-2014, 03:55 PM
Yes first op is drill the hole, you then want to remove the bulk of the material as you would probably break the engraving tool if you tried to open it out with that, also just checked the angles the 60 deg is refering to the larger opening that blends with the 45deg, the taper that opens out the hole has an included angle of 30 deg so you need an engraving tool that size, so remove the bulk machining the 45deg taper then go in with your 8mm dia ball nose cutter then just blend out with the 60 deg taper and tickle out the 30 deg taper with the engraving tool. FYI a "D" bit is just a form tool you basically turn the required profile with the drive dia slightly offset then machine away the profile leaving it flat topped to the centre line of the driving diameter, this gives the profile a "D" shape and a cutting clearance.

09-10-2014, 05:32 PM
the taper that opens out the hole has an included angle of 30 deg so you need an engraving tool that size,

I think the 30 degree taper is not part of the mold but instead part of the machine that injects the plastic. My thoughts are this is a heated tip and the plastic will flow around this?

09-10-2014, 05:39 PM
That makes it relatively easy to make then, carry on number one.

Robin Hewitt
09-10-2014, 08:53 PM
I'm still not understanding what I am looking at.

The plasticiser is the bit that converts granular plastic to melt. This has to connect to the mould, inject the melt, hold the pressure until something freezes, gates, sprue, whatever, disconnect from the mould and melt more granules.

Generally there are 3 ways in to a mould. On the mould parting line, through a sprue bushing, through heated runners where the melt never sets.

I thought that sprue bushing was usually a flat on flat seal with maybe a puff of cold air if stringing got too bad.

I thought I saw something like a countersunk screw head shaped cavity in your picture which would be fine and dandy if it was on the mould parting line because you wouldn't have to worry about getting it all out before the next shot.

09-10-2014, 08:59 PM
Original scan is a detail view from this sheethttp://i59.photobucket.com/albums/g282/Gavztheouch/IMG_20141008_184751_zps8baasdjr.jpg (http://s59.photobucket.com/user/Gavztheouch/media/IMG_20141008_184751_zps8baasdjr.jpg.html)

Robin Hewitt
09-10-2014, 09:24 PM
So you have two tie bars 4" apart. The platens have 3" indents presumably to locate the mould halves. The moving platen (top) has a 2" hole through which the ejector pins pass.

Can we assume the fixed platen (bottom) has a similar hole, which isn't shown, and the nozzle comes up from below, the drawing Y axis, through that hole. It does not come in from above, the drawing Z axis, to hit the parting line.

09-10-2014, 09:31 PM
Yes the nozzle does come up from below in the diagram, but I have it round the wrong way, it needs to be rotated 90 degrees. This is a horizontal machine.

10-10-2014, 09:25 AM

Bought this 40mm long bar from ebay, hopefully I will be able to chuck it up in the lathe and still get enough material sticking out to make a blank for the injection molder.

Robin Hewitt
10-10-2014, 10:34 AM
IIRC I have about 4 or 5 feet of 4 1/4" 7075 T6 somewhere in my workshop.

13-10-2014, 04:37 PM
Sounds tempting Robin but I don't think my myford will be able to work something that big.

18-10-2014, 07:24 PM
Anyone got any ideas as to what a custom made carbide or hss tool would cost to cut the profile for my injection mold "nozzle gate" as per drawing?

19-10-2014, 10:17 AM
Can you make one of these


Robin Hewitt
19-10-2014, 10:43 AM
I am still not understanding, isn't this shape ground into steel perfection for you as part of the sprue bushing?

19-10-2014, 01:51 PM
I am still not understanding, isn't this shape ground into steel perfection for you as part of the sprue bushing?

As far as I know you cannot buy sprue bushings for this machine, you have to machine them yourself into the fixed halve of the mold.

23-10-2014, 02:03 PM
Can you make one of these


Would this be possible to make on a standard myford ml7-r?

Im guessing it would need to be quite high quailty steel? Hss?

23-10-2014, 06:43 PM
Hi Gav
Yes it's made from silver steel which is a high carbon steel available in metric & imperial sizes and is ground finish and readily available. The bar is in it's annealed state and you manufacture your required tool then heat it to cherry red and quench, then polish the tool and apply heat to the end of the shaft and you will see the polished surface change to a straw color as this works it's way to the cutting part of the tool quench in cold water and that's it tempered.

Looking @ your drawing that profile is situated in the sliding part of the jobby that the mould goes into,is that correct ?

23-10-2014, 11:43 PM
Making those kinds of countersink bits in silver steel on a Myford is fine - done it plenty of times myself. The biggest issue is machining the half-diameter; you can file it, but I used my Myford milling slide to machine it. Even easier if you have access to a milling machine. If you make a slight undercut just where the cutting surfaces meet the full diameter, you end up with a flat surface that is easy to touch up on a stone if needed. Hardening is one of those odd things that sounds very difficult and technical but is actually very straightforward when you do it. Main thing, as Mekanik said, is to heat the shank. not the tip, and watch the colours travel towards the cutting edges, but don't use too much heat as the travel can be a bit too quick. If that does happen, you can always try rehardening (cherry red and quench) and then have another go at tempering. Silver steel properly hardened and tempered actually cuts mild steel surprisingly easily; what it can't take is heavy/fast cutting which overheats the cutting edges and destroys the tempering. That's one reason HSS was invented - holds its temper even when pushed hard.

24-10-2014, 06:07 PM

I dont know if this drawing makes it more or less confusing?

Robin Hewitt
24-10-2014, 09:53 PM
Let me go through the theory so that anyone here who is not au fait with sprues can keep up.
The mould is in two halves which bolt to two plates in the moulder. The plates are called platens.
There is a fixed platen which you can move by handscrew to allow for different height moulds.
There is a moving platen which winds back when the moulding operation is complete so you can get the part out.
The fixed platen has the ejector pins coming out through it to free the part when the mould is open. So it is very important that the part stays with the fixed platen on opening or everything is going to go horribly wrong.
Coming up through the middle of the moving platen is the injection nozzle which has a whole mess of molten plastic behind it and some kind of piston arrangement that is going to force it out. It's a bit like a hot bicycle pump.
So, the mould closes, the nozzle connects, the plastic is injected. It has to get to the heart of the mould to form the part.
The initial pipe that carries it will end up full of cold plastic. The plastic in that pipe forms the sprue.
If you are still reading, well done, you will now appreciate the problem, the sprue is moulded on the moving platen side but it must stay attached to the fixed platen side when the mould opens. Obviously anything that helps it slide out is good.
First thing you do is make the sprue using a tapered hole and polish it inside.
Next thing is to make the injection nozzle big and hot so the mould never manages to chill it. If the plastic strings a bit when the nozzle retracts that is good. If it strings too much you might need a puff or air to freeze it.
If the sprue connects to runners rather than directly in to the part you can fit a sprue extractor to the fixed platen side of the mould. A sprue extractor is a conical dent widening in to the mould with a monster ejector pin at the bottom to force it out once it has done it's bit. You have to make sure that the whole sprue comes out. If the sprue breaks and leaves anything of itself behind then we have to hope the machine can detect it.
If you are still reading you should be up to speed.
The European nozzle is usually hemispherical and goes in a hemispherical sort of dent. There is no flat end to the nozzle because that would mould a nail head on the top of the sprue and make it hard to pull. That is why I don't understand why this machine seems to have a flat.
This machine has a relatively tiny nozzle diameter so is there a real risk of it freezing? Perhaps it is supposed to freeze, pull the nail head and the remelt it? Perhaps the nozzle is floating and the conical cutout is to guide it? Obviously it must work or they would have done it differently, but I am still puzzled.
This needs to be understood before trying to make a mould.

24-10-2014, 11:24 PM
Excellent post Robin.
Perhaps a picture or two of the actual nozzle may help clarify things. I can't get my head around why the gate is quite so elaborate, unless the machine relies on it to actuate something as part of the injection process.

25-10-2014, 09:46 AM
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
25-10-2014, 12:00 PM
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
25-10-2014, 12:17 PM
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.

28-10-2014, 05:54 PM
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?

22-03-2016, 06:52 PM
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.


12-04-2016, 02:40 PM
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.

02-05-2016, 11:42 PM
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/stocks/private/snapshot.asp?privcapId=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...

05-05-2016, 12:03 AM
Would this be possible to make on a standard myford ml7-r?

Im guessing it would need to be quite high quailty steel? Hss?

I've made molds for my Rabit 2/3 out of aluminum. Nothing magic there.

07-08-2016, 02:26 PM
Hello Tenaja, would you be willing to show some pics of your machine and molds, maybe some parts you have made?