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  1. #1

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    Machining a funnel

    Hey guys, I’m new to machining so be gentle. I recently converted a small mill to cnc and bought a 5 ton injection molding machine. The time has come to make the first mold. With the purchase of the machine I was given a sample mold so I could get an idea how to make one.

    The injection machine has a special extruder which has a spike runner through the center which keeps the plastic hot when it’s injected directly into the part. The fixed mold half needs some special machining to accommodate this. Basically a .5” cone with 60 degree taper, into a 90 degree taper into a .050 office.
    Anyway before I spend $100 on tooling, I wanted to ask the pros how they would go about doing this operation. I do have a manual mini lathe but I figured this would be easier and repeatable down the road for making new molds to program this in my cnc. (Has an 11k spindle small cutters are no problem).

    So what do you suggest? Would a 60/90 degree tapered 1/16 end mill work by chamfering down? Should I drill the .050 orfice first then use an end mill? I have little experience with what tools would work best.

    Forgot to add, the bottom of the cone where it meets the orfice needs to be sharp for the part to seperate properly, and the cone finish is important for plastic to flow nicely. Thanks for any advice! Please see pics!

  2. #2
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    Re: Machining a funnel

    Quote Originally Posted by ypmcnc View Post
    Hey guys, I’m new to machining so be gentle. I recently converted a small mill to cnc and bought a 5 ton injection molding machine. The time has come to make the first mold. With the purchase of the machine I was given a sample mold so I could get an idea how to make one.

    The injection machine has a special extruder which has a spike runner through the center which keeps the plastic hot when it’s injected directly into the part. The fixed mold half needs some special machining to accommodate this. Basically a .5” cone with 60 degree taper, into a 90 degree taper into a .050 office.
    Anyway before I spend $100 on tooling, I wanted to ask the pros how they would go about doing this operation. I do have a manual mini lathe but I figured this would be easier and repeatable down the road for making new molds to program this in my cnc. (Has an 11k spindle small cutters are no problem).

    So what do you suggest? Would a 60/90 degree tapered 1/16 end mill work by chamfering down? Should I drill the .050 orfice first then use an end mill? I have little experience with what tools would work best.

    Forgot to add, the bottom of the cone where it meets the orfice needs to be sharp for the part to seperate properly, and the cone finish is important for plastic to flow nicely. Thanks for any advice! Please see pics!
    This is normally a lathe job do you have a photo of the sprue bush, you can get and use a sprue cutters and reamers, so post a photo you may have something different
    Mactec54

  3. #3

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    Here are the photos!

  4. #4

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    And another for depth
    Attached Thumbnails Attached Thumbnails mold 5.jpg  

  5. #5
    Community Moderator Jim Dawson's Avatar
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    Re: Machining a funnel

    Jim Dawson
    Sandy, Oregon, USA

  6. #6

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    Thanks Jim! Should I first drill the .050 orffice and then use the chamfer mills to cut down to the bottom? It’s important that the bottom of the funnel stays sharp and maintains orfice diameter. Would there need to be a cutter with a tip smaller than .050?

    Would this work? https://www.the-carbide-end-mill-store.com/m5/TC32004--tc32004-1-16-drill-mill-90.html

    Thanks, I appreciate your help!

  7. #7
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    Re: Machining a funnel

    Quote Originally Posted by ypmcnc View Post
    Here are the photos!
    Are that is where the nozzle of the machine has to seat this should be to the shape of the machine nozzle which is normally just a radius

    The nozzle has to seat /seal off when it is pushed up against the sprue, so this shape you have is incorrect, that is more to the shape of what a hot tip would need

    Post a photo of you machine injection nozzle this will determine the shape you need
    Mactec54

  8. #8
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    Re: Machining a funnel

    Quote Originally Posted by ypmcnc View Post
    Thanks Jim! Should I first drill the .050 orffice and then use the chamfer mills to cut down to the bottom? It’s important that the bottom of the funnel stays sharp and maintains orfice diameter. Would there need to be a cutter with a tip smaller than .050?

    Would this work? https://www.the-carbide-end-mill-sto...l-mill-90.html

    Thanks, I appreciate your help!
    Not if your Machine nozzle is round on the end

    Here is what you Sprue and nozzle should be like
    Attached Thumbnails Attached Thumbnails Sprue and Nozzle Design.PNG  
    Mactec54

  9. #9

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    Quote Originally Posted by mactec54 View Post
    Not if your Machine nozzle is round on the end

    Here is what you Sprue and nozzle should be like
    Thankyou for the replies mactec, this machine was designed to allow plastic to be injected directly into the part eliminating the need for a runner, hence the special sprue shape, and the metal spike that keeps the plastic hot. Please see pics, hopefully you get the idea.
    Attached Thumbnails Attached Thumbnails 392FF4D8-128A-4345-A82D-8E44AABFCDC2.jpg   B8735BCE-ADAF-4AF8-BC62-D3A9EF804F30.jpg   12F0BED8-D9EA-4BFF-9318-843CAFBA0BFD.jpg  

  10. #10
    Community Moderator Jim Dawson's Avatar
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    Re: Machining a funnel

    Quote Originally Posted by ypmcnc View Post
    Thanks Jim! Should I first drill the .050 orffice and then use the chamfer mills to cut down to the bottom? It’s important that the bottom of the funnel stays sharp and maintains orfice diameter. Would there need to be a cutter with a tip smaller than .050?

    Would this work? https://www.the-carbide-end-mill-sto...l-mill-90.html

    Thanks, I appreciate your help!

    Yes, I think that will work. And yes, you would need to drill the 0.050 hole first. Maybe more like a 0.032 hole first then cut the chamfer. Maybe a #1 center drill would be a good place to start. https://www.grainger.com/category/ma.../center-drills.

    That part is going to be tricky to keep that edge sharp.

    EDIT: I guess I would make a carbide or tool steel ''button'' that had the proper shape, and just drop it into a pocket machined into the part.
    Jim Dawson
    Sandy, Oregon, USA

  11. #11

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    Quote Originally Posted by Jim Dawson View Post
    Yes, I think that will work. And yes, you would need to drill the 0.050 hole first. Maybe more like a 0.032 hole first then cut the chamfer. Maybe a #1 center drill would be a good place to start. https://www.grainger.com/category/ma.../center-drills.

    That part is going to be tricky to keep that edge sharp.

    EDIT: I guess I would make a carbide or tool steel ''button'' that had the proper shape, and just drop it into a pocket machined into the part.
    Jim, thankyou for sharing your thoughts, what would I do without you? Would that be something you would have to make? Guess there’s no place to buy a custom tool like that?

  12. #12
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    Re: Machining a funnel

    Quote Originally Posted by ypmcnc View Post
    Thankyou for the replies mactec, this machine was designed to allow plastic to be injected directly into the part eliminating the need for a runner, hence the special sprue shape, and the metal spike that keeps the plastic hot. Please see pics, hopefully you get the idea.
    That explains it, you have what is called a Pin Point Tip or could be a modified Hot Tip, which I mentioned before, this pocket has to be very precisely machined, this is normally done with an EDM or turned, this has a profile that you need to machine not just the angles, it is quite unusual the way they have done this

    You need to clean it up to see what you have, you can warm it up with a torch and brush off the plastic with a brass wire brush
    Mactec54

  13. #13
    Community Moderator Jim Dawson's Avatar
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    Re: Machining a funnel

    It's a pretty simple piece to make if you have the tools. It could be done in a mill, but a lathe would be easier. Might be a good excuse to buy a lathe Carbide would pretty much require an EDM, not common in the home shop. But annealed tool steel machines easily with home shop tools. Some O1 or A2 drill rod would be my starting point. You can harden it with a torch.

    For small parts like that, you can easily turn your CNC mill into a CNC lathe, Just use the spindle to hold the part, and hold the tool in your vice. I used to do this occasionally before I bought a CNC lathe.



    An alternative would be to have the part made by a commercial vendor. Dayton Lamina might be able to make that at a reasonable price, they do stuff like that all the time. https://www.daytonlamina.com/sites/d...Kommercial.pdf
    Jim Dawson
    Sandy, Oregon, USA

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