Wax piston sprue extruder?

Discussion in 'Lost wax casting' started by Zapins, May 21, 2018.

  1. Jason

    Jason Gold

    Looking at some of those machine where you top load the wax, it appears the length of the stroke isn't really that long. Must be because the wax gets extruded through a tiny hole. I can see the need for a hydraulic ram or a seriously geared down electric motor setup. Manual work sucks even when ya got a cold one in your hand.
     
  2. Jason

    Jason Gold

    I'll be your HUCKLEBERRY! Get you some of that!

     
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  3. crazybillybob

    crazybillybob Silver Banner Member

    If you have a lathe and a welder Up-sizing this style of unit shouldn't be a big deal. You could wrap a silicone pad heater around the barrel to preheat everything. A gear reduction drive on a 1/4Hp-1/2HP motor pushing a 1" acme threaded rod...you might have $200 into it if you had to buy everything retail ( if you have steel on hand or a local scrap yard and a motor kicking around it's almost free!) Use 1-1/2" DOM 1/8th inch wall tubing. External threads on both ends. Make a couple end caps on that has a big acme nut welded to it (or internal acme threads) for the push rod. You're going to want 3-4" of thread engagement on the rear cap, I'd guess the cap thickness should be 1/2"-3/4" ish as all the load is going to be there. The other with a recess for some 1/8"-3/16" (1/4" isn't crazy if you want 3/4"-5/8" sprues out) thick steel plates with different shapes in it. Make the piston steel centered with delron seal ring that threads on. You could do a small one on a bench-top lathe but really need one with a 32" or 36" bed at least for a "big" unit. But you could knock out 2 of these in a weekend no problem if you had the stock. (ok for me more like a week because I haven't turned threads on a lathe in 20 years so some re-learning is required. and I would have to put my lathe back together first....so 6 months :eek::D:rolleyes:) But do able. and the whole unit could be 2- 3' long not room sized.
    Hydro piston ones would be faster. But you two are not talking production level units just something to keep you in spures right? Screw machine is "hobby" sized.
    I'm also thinking you two want 1/2" to 3/4" diam sprues out of this thing too.

    If the two of you have any interest in something like this... let me know I could knock together a rough fusion drawing of it.

    CBB
     
  4. Peedee

    Peedee Silver

    Or you could pick up an old meat grinder/sausage maker, adapt the nozzle and heat it up?
     
  5. Jason

    Jason Gold

    CBB... 6months lead time plus a week or two? Perfect, Let me know when I can place my order for 2 of them?:D Screw driven is fine for something like this.

    Did you guys see how much sprue that thing pooped out? When I stretched that out, it was 6 feet long!
    To make fatter sprue, would just require the ability to hold more volume that's all.
     
  6. Zapins

    Zapins Gold

    Hmm. DOM pipe. Haven't heard of it before but it seems like it would work. It is pretty crazy expensive though.

    Would extruded aluminum work as well? The dimensions seem pretty precise from the small pieces I've bought from home depot.

    I'm thinking if we build one of these a 6" diameter 18-24" long tube would be the way to go. That has quite a bit of wax capacity in it enough to make large 1" sprues or small threaders.

    CBB would you machine threads if we got the pipe and payed postage? :)
     
  7. Kurtis Kiesel

    Kurtis Kiesel Silver

    Looks like a great idea!
     
  8. crazybillybob

    crazybillybob Silver Banner Member

    I did! That's what got me thinking that 1 1/2" tubing would be perfect for this application.

    Zapins,
    The reason I said Dom is there's no seam on the inside to clean up. I'm going to guess that you're going to still need to bore the tube to get it smooth but only a few thousands. In other tubes you can have a 1/8"+ seam that needs removed and the bore is more egg shaped.
    Depending on your lathe you could do a fatter shorter tube to simplify the machining. (Shorter boreing bars are stiffer and cheaper) but it will mean more pressure on the die so you might want a 3/16 or 1/4" thick die plate. I'm not sure if aluminum tube would hold the pressure. I don't have any data on the wax viscosity, and it will depend highly on the temperature of the wax. I'm sure my thoughts are over kill...but I don't want to give you ideas that end up getting someone hurt either. Aluminum also fails catastrophically without warning when it work hardens. Expanding and contracting repeatedly sounds like a easy way to get tubing to work harden. Steel will develop cracks, and for the most part handles pressure better. I'm not a real engineer so the subtitles of finite structural analysis Escape me. I just over build for safety. I'm not working for SpaceX or nasa...so weights not an issue.

    CBB

    It's been 20 years and my lathe is a basket case, so I don't know if it will cut threads....but I an't scared I would give it a go they cut just like every other cut on the lathe...0.05" at a time
     
  9. Jason

    Jason Gold

    18" long tube that is 1.5" sounds about right to me. Stainless naturally. Piston disk with either an O ring or scrapper ring.
     
  10. That's a cheap hydraulic cylinder. They have really tough seals. Have you considered a hydraulic cylinder?
     
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  11. crazybillybob

    crazybillybob Silver Banner Member

    Adding a Screw drive to a Hydro cylinder could be done with a welder and a grinder! That would eliminate the need for a lathe!
     
    Jason likes this.
  12. Jason

    Jason Gold

    Now you are talking my language. I'll have to sniff around, I bet I've got an old airplane cylinder laying around. It will be aluminum, but ya can't always get what you, but you get what ya need.
    Song about that somewhere I remember...
     
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  13. Zapins

    Zapins Gold

  14. Jason

    Jason Gold

    Yeah but you know that POS is going to piss and leaky stinky jack fluid all over the place. Plus it's going to need serious modification. Jacking is not the action you would want... A nice smooth steady pressure would produce a clean sprue. Rotating acme thread with a 2 foot handle would get her done. It'd be fun to watch my wife yank my crank in the garage helping on sprue duty.
    Remember that big plate I had that rush job on? I need to find that guy and take him my walnut knob extruder and have him upsize the design. He said he does side work outta his garage. Now where did I stick his phone number?
     
  15. Zapins

    Zapins Gold

    Yeah but for the body of the extruder it would work. It has machined insides and a piston in there.

    A different method of pushing the piston is needed like a screw or an electric jack but for a body it might not be too bad. I think the walls are fairly thick as well so you could thread it if needed to attach the dyes.
     
  16. Jason

    Jason Gold

    That's true. 48bucks is cheaper than machine shop time. Good call. Throw the rest away.
     
  17. Zapins

    Zapins Gold

    Exactly my thought. And it gives good wax capacity being so wide.

    Ebay has the same Jack's but cheaper. I saw an 8 ton for 39 bucks shipped.
     
    Last edited: Jun 21, 2018
  18. I'm sure I've got some hydraulic cylinders laying around I'd ship cheap. Old cylinders usually leak around the rod due to rod corrosion damaging the seal. For what you're doing you don't need a rod seal. I would suggest you put a window in the side of the cylinder close to the rod end for reloading and extrude through the head end hydraulic port. A 1/2" pipe thread is there which would extrude up to 3/4". Then you need to be able to retract the piston. You could remove the extrusion connection to let air in or put a check valve in the piston to let air in.

    Don't waste money on acme thread unless you have it cheap. B7 studs are very cheap and can be had very long. Look at your local bolt company for a 3/4" 36" B7. They will last as long as you'll be extruding wax and cheap to replace.

    I think you'll find a cheap jack is better to drive a cylinder than a screw if you can stand interrupted movement.
     
  19. Zapins

    Zapins Gold

    Thats a kind offer. I looked up hydraulic cylinder schematics, they look a bit different inside to how I imagined. I'm find myself wondering if they can be used the way we want them to as a direct injection/ram setup. What do you think?

    Good tip on the B7 studs. I'll keep them in mind.

    I have 2 alternative sources for a metal cylinder. There's a guy on ebay selling 4, 5, and 6" ID steel pipe at reasonable prices that is 1/4" thick walled (https://www.ebay.com/itm/263251699746?ViewItem=&item=263251699746). Another possible source is there's a local place that had large diameter pipe (5-20" diameters) that might be willing to sell me some for a good price without having to waste $ on shipping. The issue is that part of the tube would need to be bored/cleaned up so a ram would make a decent seal on the wall which would probably be fairly expensive to have it done at a shop.

    To push the wax out an electric car jack is fairly cheap ($80) and they push up to 3 tons with uniform even pressure & speed which would make the extrusion come out nicely without jerking lines. A lot of them seem to operate on 12v though so a car battery charger would probably need to be used to supply power to it.

    For the ram itself, what type of metal and shape do you think is the best? Bronze, aluminum or steel? And a solid cylinder that takes up the entire inside diameter of the extruder? I think a softer metal would be a good idea inside so that the ram doesn't scrape and damage the walls and get stuck as its being forced through. How long do you think the ram needs to be to prevent it from diving into the wall?
     
  20. Obviously I think they would work, even extruding at 90 degrees.

    B7 studs are about the cheapest bolting you can find, and are high quality and good for elevated temperatures (600F).

    All of the tube would need to be bored and preferably honed. The eBay listing is probably not particularly round. Remember if you have wax slipping past the piston you may have to melt the wax to remove the piston. Hydraulic cylinders already have a close fitting piston which would likely wipe the wax as it pushes. Cylinders are bored and honed to an excellent finish, then the piston is fit with seals. A ram without seals to wipe the wax will probably get stuck with cold wax unless you heat the entire cylinder.

    A hydraulic cylinder driving the extrusion cylinder would be smooth if driven by a gear pump. Do you have a source of hydraulic power? (I have tractors with hydraulics so running lines from a tractor would be easy). 3 tons will limit you to a small load, 6,000 lbs is only 477 psi on a 4" cylinder and 305 psi on 5". Will that extrude wax? Certainly it would if the wax were hot, close to melting. Then you have to have means to retract the ram which may take a lot more than you could do by hand.

    I don't think the material would be an issue at low speeds with wax as a lubricant. Steel is the cheapest, aluminum could gall on the cylinder walls. The piston can be short if it has a rigid rod which is guided. If not, length equal or greater to diameter should hold it straight. If you use a cylinder it would need a window cut into it so you can put wax in before you press. Another option would be to pour liquid wax in through a hole. Note if you don't fill the cylinder with wax you will have air in with the wax which may give you the jerky response you might not want as you compress air with the wax (like caulk out of a caulk gun with air in it).

    I was assuming you would just use the piston, rod end, and cylinder from a hydraulic cylinder rather than trying to build those parts. You don''t want $5,000 in the extruder.
     

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