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NeoMiller
10-19-2003, 02:05 AM
I am a novice in machining so please dont laugh at my questions.

I want to make a simple mold out of mild steel for a hollow plastic cylinder used as a spacer for mounting PCBs. Size 3/8inch dia, length 1.5inch hole 5/32inch. The injection molding will be done with a hand molding machine. The surface quality of the product is not an issue and nor is the production speed. The mold will only be used to make a few hundred pieces in all.

The only machine at disposal is a Taig CNC micromill. I dont have any lathe mahine which might seem necessary for this but I think the job might be done using only the mill.

Questions:
Can I use aluminum or brass to make this mold.
Which software should I use to design the mold.
Are ther any simple reference design files for moulds avaialable on the internet or can anyone share one.
Are there any videos avaialable that show machining being done on a mill.

thanks for any help. rgds. NeoMiller

HomeCNC
10-19-2003, 03:05 AM
I'm going to be making me a home built injection molding machine to do small plastic parts. Make your mold out of aluminum. It will be much easier to machine and will be fine for 100 or so shots.

Don't know about you last three question.

ullbergm
10-19-2003, 09:26 AM
Originally posted by HomeCNC
I'm going to be making me a home built injection molding machine to do small plastic parts.

that sounds interesting, do you have any plans already or any websites with examples of home made machines?

ToyMaker
10-19-2003, 09:43 AM
NeoMiller:
For the a short course on home mold making, check out "Of Runners, Gates and Cold well plugs:" at

http://www.seattlerobotics.org/encoder/mar97/mold_art/molds.htm

robotic regards,

Tom
= = = = =
When religion was strong and science weak, men mistook magic for medicine; now, when science is strong and religion weak, men mistake medicine for magic.
- - Thomas Szasz, American psychiatrist

NeoMiller
10-19-2003, 11:18 AM
Great article for beginners like me. Thanks ToyMaker.

ullbergm, I have seen a couple of home built molding machines. Dont have any pictures of them though. In fact, they had appeared so simple and the molds that they used for small jobs were so straight forward (without any alighnment or ejector pins), that this is what initially got me intersted to enter this field. I am basically in small scale manufacturing of customized electronics and often require project specific plastic hardware for fittings and stuff.

HuFlungDung
10-19-2003, 11:44 AM
While I applaud your initiative to get into molding thermoplastics, for this particular app, would it not be easier to get some plastic rod and drill the hole through it? I suspect that you might have a fair bit of a tussle to pull the mold core out of the part?

ullbergm
10-19-2003, 11:48 AM
Originally posted by NeoMiller
Great article for beginners like me. Thanks ToyMaker.

ullbergm, I have seen a couple of home built molding machines. Dont have any pictures of them though. In fact, they had appeared so simple and the molds that they used for small jobs were so straight forward (without any alighnment or ejector pins), that this is what initially got me intersted to enter this field. I am basically in small scale manufacturing of customized electronics and often require project specific plastic hardware for fittings and stuff.

please let me know if you find some links to pictures/drawings of some examples.

thanks,
magnus

NeoMiller
10-19-2003, 01:04 PM
HuFlungDung, how about if I make the plastic rod in a bit of a taper. The mold will have the cavity in plate A and the pin for center hole in plate B. The hole pin can also be made into a little lesser taper. So when I open the mold, the piece is sticking on the plate B with the center hole pin. That should be easy to remove. Wouldn't it.

HuFlungDung
10-19-2003, 01:40 PM
Oh certainly, Neomiller, those are ways to do it. But, I would select the easiest method of production, and save your mold making for parts that are not as readily produced from barstock.

cadcam
10-19-2003, 02:15 PM
I would say the aluminum die would work well. i have done this with complexe mold shapes and able to get 500 plus part from glass filled plastics..

So I say have at it.

hardmill
10-19-2003, 02:19 PM
Originally posted by HuFlungDung
While I applaud your initiative to get into molding thermoplastics, for this particular app, would it not be easier to get some plastic rod and drill the hole through it? I suspect that you might have a fair bit of a tussle to pull the mold core out of the part?
Gonna have to agree with hu on this one.
Seems pretty straight forward.

PEACE:D

HomeCNC
10-19-2003, 02:47 PM
Ullbergm,

Yes I have a book called 'Secrets of building a plastic injection molding machine'. By Vincent R Gingery

http://www.lindsaybks.com/dgjp/

It shows you how to build the machine, make a simple mold, and gives you instruction on the injection process.

High Seas
10-19-2003, 07:01 PM
Background - I'm getting into the smal cnc application 'cause everyone I spoke with wanted an arm and a leg to build me some molds for low pessure IM. Figured I'd build the machine and the molds for the price they wanted for the molds.

My original pieces are a bit larger, more like the size of a hockey puck or a pack of cards - but a bit more intricate. Thought I'd do the molds of delrin and hand cast resin ('glass fiber renforced - carbon won't work in this app)

BUT - a home made injection molding machine - who'd-a-figured?!

So, for HOME CNC - have you started building it? Look any easier/harder than putting a home built cnc together? Is the book informative useful - would you recommend a purchase of the book? Estimate on costs? Source of materials for molding listed too? SIZES - are they scaleable? What size are you making?

For NeoMiller -- could you do a master "plug" and build several molds from silicone, then finish as needed - drill the hole for example? Silicone is easy (especilly the 1:1 stuff but won't get the life so build a few molds. Or do 'ya need a reason to use the mill? [I know once mine gets builit I GOTTA! -- or I'll be sleeping outside!]

Appreciate your thoughts - y'all can do it thru the forum or direct via the email side.
:cheers: Jim

NeoMiller
10-20-2003, 01:39 AM
I agree that drilling a hole in a plastic rod is much easier but it is no fun. I want to make this mold (my first one) as a hands on experience.

Can anyone please post some pictures and/or drawings of simple molds.

HighSeas, can you please point to some more info on "silicones". It does seem interesting.

High Seas
10-20-2003, 08:43 AM
No worries!
The nice thing they are easy - if not messy a bit - but hey let the chips fall.
RTV - room temp vulcasning (cure)and casting resinss are a great boon to modelers and there are heaps of sites out there that give more specifics. You can cast just about anything as you'll see from the following pages:
First, a good text intro - but no pics -are at this long thread from somewhere:
http://www.ravensforgeminiatures.com/faq20413.html

These are 2 well thought of outfits:
http://www.smooth-on.com/moldmaking.htm

and:
http://www.alumilite.com/

Some of the companies have trial kits you can order that might be a good size for your project. But then after that the sizes get a bit bigger but they seem to be ok size-wize. I haven't yet ordered from these 2 - but while I'm here in the 'states I will - I use folks overseas when there (ATI and Nuplex).

I bumped across the "materials" web site the other day haven't spent much time looking at it yet:
http://www.matls.com/index.asp?ckck=1

Basically, you need a mold [cnc built], PVA (release agent and wax), the RTV, and something to cast with [resin, foam, whatever]. BTW, there is a site that shows how to use LEGOs as the mold box and even has a calculation for how much molding material you need to fill it.

If you need some more I'm sure other modelers will chime in too - I bet balsaman has some links from the rc pages too.
:cheers: Jim

HomeCNC
10-20-2003, 10:49 AM
So, for HOME CNC - have you started building it? Look any easier/harder than putting a home built cnc together? Is the book informative useful - would you recommend a purchase of the book? Estimate on costs? Source of materials for molding listed too? SIZES - are they scaleable? What size are you making?

No I have not started building yet. I did order two of the heating elements called out in the book.

The book looks very informative. It is basic enough for a novice in this area. It shows the machine, and how to build it. It sources the heating element. The book uses one element but I wanted a larger volume shot so I am going to use two elements in the heating block.

One of the projects of this book is to make the crank knob for the machine. The mold is held against the injection nozzle by a screw jack. This screw jack needs a knob for your hand to tighten with. Your first mold will be to make this knob.

The book says you can use many different types of material, like milk jugs, plastic bottles or even a place to get REAL material like the big boys use.

I would get the book if you are not too good at designing from scratch. The machine is simple. It's a frame that will hold the mold against the injection nozzle (screw jack) and the nozzle sticks out of a block of steel that has the chamber for melting the plastic. There is a piston rod that is attached to a long handle at the top.

Operation: You place the mold on the screw jack platform and raise the mold up to the injection nozzle. Apply pressure to hold the mold together and keep the nozzle from leaking plastic.

You turn on the heating element to heat the melting chamber and the mold. Raise the handle to lift the piston rod and fill the chamber with plastic chunks. Let it melt. When ready, pull the handle with enough force to fill the mold with plastic.

ullbergm
10-20-2003, 12:09 PM
Originally posted by HomeCNC
No I have not started building yet. I did order two of the heating elements called out in the book.


is there a estimated cost in the book or do you have any ideas based on the parts list?

HomeCNC
10-20-2003, 12:53 PM
They don't place a cost in the book. That would not be smart because the book ages and costs change.

The material for the frame is standard angle iron I think it's 1 x 1. It's bolted together so you don't have to know welding. The rest is just steel material that can be had from a scrap yard.

The heating elements and oven thermometor are two thing that need to be purchased. I can't remember how much the heating plug was but I think they are around $25.00 each.

DLMACHINE
11-24-2003, 11:56 PM
How about you guys showing off some of your mold work. Post some pics of your favorite pieces.

peter
12-23-2003, 12:29 PM
:) hi neomiller
in this country we call them manumoulds
there good for getting a few hundred components
you can make it out of aluminuim
then i would make a sleeve ejection to get it off
ejection pin to create hole then sleeve to eject it off
best regards
peter

cadcam
12-24-2003, 12:56 AM
How about you guys showing off some of your mold work. Post some pics of your favorite pieces.
Here is one http://www.ppcadcam.com/html/tounge_scraper.html

eintnl
12-24-2003, 07:01 PM
For a single cavity, molding a cylindrical shape will be quite interesting for you in terms of gating.

Cheers.