Machine tapered hole (spue bushing) for injection molding.

Hello
I want to mill my own sprue bushings for injection molding or mill the channel for the sprue directly into the my prototype molds. I therefore need to mill/drill small tapered holes. The starting diameter will be ca. 1.5mm and then have a 1-3 degree taper (end diameter is larger than starting diameter). The holes will have to be 20-50mm deep.
I know, that I could just buy pre fabricated sprue bushings, but I want to try making them myself so I can make cheap prototype molds. Usually this is done via EDM wire cutting, but I was hopping there would be a way to do this on a 3-axis mill.

So far, I couldn't really find any small tapered drill, any idea where to get them? Not sure if I should drill straight holes and then use a tapered reamer? Any suggestions on that, and does anybody know who sells small tapered reamers?

Any other way I could achieve my goal? All suggestions are welcome.

cordvision said:

Hello
I want to mill my own sprue bushings for injection molding or mill the channel for the sprue directly into the my prototype molds. I therefore need to mill/drill small tapered holes. The starting diameter will be ca. 1.5mm and then have a 1-3 degree taper (end diameter is larger than starting diameter). The holes will have to be 20-50mm deep.
I know, that I could just buy pre fabricated sprue bushings, but I want to try making them myself so I can make cheap prototype molds. Usually this is done via EDM wire cutting, but I was hopping there would be a way to do this on a 3-axis mill.

So far, I couldn't really find any small tapered drill, any idea where to get them? Not sure if I should drill straight holes and then use a tapered reamer? Any suggestions on that, and does anybody know who sells small tapered reamers?

Any other way I could achieve my goal? All suggestions are welcome.

Click to expand...

I used to do a lot of this when I was building molds, I had a local tool grinder make custom cutters for me. If you do this make sure he puts a helical flute in it, it is much easier to get a good finish with a helical flute opposed to a strait flute.

A taper pin reamer or drill has over 1 degree taper.

I always just drilled the hole undersize and used a simple 3D toolpath to cut the taper into sprues rather than using form cutters. Although that approach can be tough with that small of tooling.

PCS & DME make tapered reamers for sprues

cordvision said:

Hello
I want to mill my own sprue bushings for injection molding or mill the channel for the sprue directly into the my prototype molds. I therefore need to mill/drill small tapered holes. The starting diameter will be ca. 1.5mm and then have a 1-3 degree taper (end diameter is larger than starting diameter). The holes will have to be 20-50mm deep.
I know, that I could just buy pre fabricated sprue bushings, but I want to try making them myself so I can make cheap prototype molds. Usually this is done via EDM wire cutting, but I was hopping there would be a way to do this on a 3-axis mill.

So far, I couldn't really find any small tapered drill, any idea where to get them? Not sure if I should drill straight holes and then use a tapered reamer? Any suggestions on that, and does anybody know who sells small tapered reamers?

Any other way I could achieve my goal? All suggestions are welcome.

Click to expand...

.
look for tapered end mills they common on big sites like mscdirect. they are not cheap

cordvision said:

Hello
I want to mill my own sprue bushings for injection molding or mill the channel for the sprue directly into the my prototype molds. I therefore need to mill/drill small tapered holes. The starting diameter will be ca. 1.5mm and then have a 1-3 degree taper (end diameter is larger than starting diameter). The holes will have to be 20-50mm deep.
I know, that I could just buy pre fabricated sprue bushings, but I want to try making them myself so I can make cheap prototype molds. Usually this is done via EDM wire cutting, but I was hopping there would be a way to do this on a 3-axis mill.



So far, I couldn't really find any small tapered drill, any idea where to get them? Not sure if I should drill straight holes and then use a tapered reamer? Any suggestions on that, and does anybody know who sells small tapered reamers?

Any other way I could achieve my goal? All suggestions are welcome.

Click to expand...

Send them out for wire edm. Even if the sprue hole is solid in the mold base. No fuss, no muss. No polishing to deal with, wire & its done.

What kind of machine is this mold going into? What kind of base?
I do a lot of molds and the sprue bushing is in the base. Not the mold.
The runners are cut into each mold half.
Is this a vertical or a horizontal mold machine?
I've made a ton of sprue bushings and always have them EDM'd

Smallest D-M-E sprue bushing reamer I see in my old catalog has a small end diameter of 7/64, or .1094", essentially 2.5mm.

Machinery's Handbook says a 6/0 taper pin reamer has a small end diameter of .0611, or 1.55mm, but the flute length is only 15/16", that's 23.8mm, so should just barely work. Other than that, pop and wire the hole.

You do realize the small end diameter is supposed to be bigger than the nozzle oriface, right? I don't think I've ever seen a nozzle that small, but anything is possible, I suppose.

Dennis

Thanks for all the replies, I'll be checking those options. I own a Boy 50 t2. All the molds are made from scratch and I'll try to keep them as simple as possible. I only make a few hundred parts with each mold, so I'm trying to keep the cost per mold as low as possible. I don't even care if I need to manually remove parts etc. Made already over 1000 parts on another small injection molder for this project. -->
(injection molded the item on the left. It's made of 11 individual injection molded parts)

Didn't have a taper on the sprue which slowed down the process a little bit. Also trying to keep the sprue as small as possible because I'm usually using a dircet sprue gate.

Cost's like $100-$125 to wire a spure hole in a 1.375" plate. You cant do it that cheap yourself if you tried. Hell even the sprue reamers are like $200 & get creamed pretty quick if you are not really careful.

I have made many tiny sprue bushings from S-7, using a DME reamer, then hardening.. Step drill the blank, then ream with oil and low speed. Dwell will dull the reamer... Get in and get out. Never try to open a commercial bushing up with a tapered reamer, it will be ruined. From my experience, taper pin reamers do not have quite enough taper to let the sprue release..

@toolmaker96 I understand that this seems to be "cheap" when comparing to what injection molds usually cost. In my case, I didn't even spend that much on an entire mold. All eleven molds for the product pictured cost me about $500 in materials. Of course they compare in no way to "professional" injection molds, but they do the job pretty well.

Ok, have fun then.

Sorry, hope I didn't come across the wrong way, just wanted to put things into perspective of the type of budgets I'm dealing with. I'm definitely going to try the taper pin reamer idea, not sure if it has enough draft but worth a try at less than $50 per reamer. I might also just give another try to 3d milling it, wasn't really satisfied with the results I got last time, but it might be worth spending some time experimenting with it. Thanks everybody for the input!

One thing to consider... a hot sprue bushing. I've had great success in using a D-M-E Mini Gate Mate in 5x8 M.U.D. inserts. Yeah, the gate mate is pricy (maybe $550 last time I bought one) but you only need one. I have a couple, but still move them from mold to mold. I'm not at work now, but as I recall the hot tip well, from gate to seal surface, is only about .600, so can fit in inserts as thin as 5/8, and can have a gate orifice as small as .020" dia. That's just a pin prick on the surface of the part. And, there is no sprue to regrind, so no degrading fancy material with multiple heat histories, always a problem when the weight of the sprue exceeds the weight of the part.

Dennis

wanted to reply to the thread to add it to my collection. valuable info here!

Hi Cordvision:
You have a couple of options to get properly tapered sprue bushing bores.
Option #1 is to buy a single sprue bushing and use it over and over for all your molds.
On just about every molding machine I've ever encountered, you can move the extruder in and out, so buy a bushing that's as long as you think you'll ever need for the kinds of molds you're making and then just adapt to fit whatever setup you're currently running.

Option #2 is to buy a sprue roughing reamer from DME and learn how to use it.
As Davis points out; it's tricky and you can booger it in a heartbeat if you handle it wrong.

These reamer cut over their entire length, so as you get progressively deeper into the hole, the torque on them goes up and up.
Get just a bit too aggressive, and you'll twist off the tip.
On the other hand, if you get too wimpy, you'll take the edge off it by rubbing, especially if you're reaming into steels like P20.

So; running a sprue roughing reamer properly; here's the technique:
First, as Davis states; STEP DRILL THE HOLE.
Lay it out in CAD so you know what you're doing and go deep enough that you have around 0.005" per side left to clean up with the reamer.

Second, you have to decide if you're going to ream manually on the Bridgeport or if you'd rather try poking it down with the CNC.
Bridgeport reaming is safer but slower.

The secret is to peck with the quill stop; don't try to freehand it.
If you practice even just a little bit you can learn the technique easily.
It allows you to feed hard without taking too big a chip and twisting off the reamer.
You need to be aggressive with your feedrate, but NOT with your DOC, so the quill stop is like magic to keep the whole works under control.

I typically drop in 0.010" increments and feed briskly up to the stop.
Keep the reamer wet with Rapidtap or Moly Dee or whatever you like and KEEP IT CLEAN!!
Leave enough room under the business end so you can shine a little flashlight up through the hole from the underside and see when you've reamed out all the scarf marks from the step drilling.

DO NOT BE TEMPTED TO AVOID THE STEP DRILLING; it's a very common way to overload and bust a reamer.
You want the reamer to take relatively little; twist drills are cheap and easy to sharpen; your sprue reamer is neither.

Budget about half an hour to ream a 2" long sprue bushing bore in P20.

As a last resort, buy a wire EDM and never look back!!
Cheers

Marcus
www.implant-mechanix.com
Vancouver Wire EDM -- Wire EDM Machining
Clarus Microtech

Oh Yeah: you asked for other alternatives:
You could make up split bushings and just 3D mill your sprue bore into each half, then assemble them and pop them into a reamed hole in the mold base.
It's crude and not very toolmakerly but it works just fine.
MC

Wow, since this zombie thread came back to life, let me add some info on small hot sprue bushings.

I had mentioned the D-M-E Mini Gate Mate, which I have used for years; it has a .625" dia. seal surface and can be made to work in an insert .700" or so thick. Recently I needed to retrofit a 5x8 MUD insert and did not have enough room between the existing cavities for that option.

To the rescue came the "Mini Standard" hot sprue bushing from PCS:

http://www.pcs-company.com/viewproduct/hot-runner-products/hot-sprue-bushings/HBM

Overall height of less than 2", I actually had to use the next longer size and still buried the whole thing in the plate. Seal diameter is only .281", and only .220" back from the cavity. I am impressed. Cost is comparable with the older, larger D-M-E product.

Disclaimer: I have no financial interest in PCS or this product, just a satisfied customer.

Dennis