First time foam casting

Discussion in 'Lost foam casting' started by Bruce R., Apr 13, 2019.

  1. Bruce R.

    Bruce R. Copper

    I understand the principles with foam, but I’m having a bit of trouble. How do I put holes in the foam ? Drills and hole saws chew it up pretty bad, I’m using the blue insulation stuff. Also, I can sand nice rounded outside corners, but how to make inside fillets ?
  2. DavidF

    DavidF Administrator Staff Member Banner Member

    Hi Bruce, Kelly (al203) will be on shortly. He is the lost foam guru here :D
  3. ESC

    ESC Silver Banner Member

    There is no simple answer. What is your tooling? Kelly uses a high speed router. I use a dremel with a small stone run really fast. For bigger holes I might use the bandsaw, and glue the two semicircles together.
    There is not a lot of literature for our methods, but by experimenting with what you have and making test pours you will be able to develop a method that will suit your goal.
    Since prep time is so short for simple tests, except for coating, which isn't needed for test pieces, make some holes, cast it and evaluate. Show pictures.
  4. oldironfarmer

    oldironfarmer Silver Banner Member

    Forstner bits on high speed in a drill press works. Drill slowly.

    I use a 50/50 toilet bowl ring was and parrafin mix, brushed on hot to seal joints. Low temperature hot glue gun to glue with.

    For large fillets you can cut the shape with a router and rip it off on a hot wire, then glue it in place. You can also make a 45 fillet then sand it once it's in place. I think commercial fillet wax works also, Kelly will chime in. He's shy but getting over it.

    It would be good to review Kelly's water neck thread.
  5. Bruce R.

    Bruce R. Copper

    Maybe it was my speed using the hole saws, I only used a cordless drill, I’ve milled the stuff in my milling machine at 4000 rpm with great results
  6. oldironfarmer

    oldironfarmer Silver Banner Member

    Well if you've got a mill end mills work great. And a 3D router works like a charm too, especially if you like foam everywhere.
  7. Bruce R.

    Bruce R. Copper

    Got the shop vac parked right next to the mill. Lol
  8. Bruce R.

    Bruce R. Copper

    Gonna try the hole saw again at warp speed !
  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hi Bruce, saw your post over at AA, welcome to THF.

    The short answer to your question would be wood working router bits with a lot of speed. If you have good results in your mill, at 4krpm, I use 15k-20krpm on .5 to 1.5" diameter bits. Woodworking router bits work well because the deep gullets clear foam chips well.

    All my stuff thus far is template guided router foam patterns than are glued to together. You can use wax for fillet but I suggest doing so sparingly. If the fillet is bigger than an 1/8" radius I usually try to machine it into the foam with a round nose router bit. There is wax specifically formulated for lost foam, other wise, some alternatives have already been suggested.

    A sharp Forstener bit will bore a hole with a decent finish. Hole saws aren't great because they can't clear the chip. I use router bits mostly. If you have a CNC router you're set.

    I use 80-100grit sanding drums and belts with good result and then hand dress with finer grits.

    Here's a few of my threads but there are threads by other members with good technique here too. I'd encourage you to peruse the threads in the lost foam forum as answers to many of your questions and examples may already be there. Plenty of help here but also must do your homework.

  10. Bruce R.

    Bruce R. Copper

    When gluing the foam together do you run a bead of glue or just dab it on here and there ? I read somewhere about using spray bomb adhesive but when I tried it, it melted the foam. Got a hot glue gun now.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I use hot melt (low temp, some guns have hi/lo setting) and usually try to have a full coverage joint but using some compression and keeping the joint thin is beneficial. You don't have much time with hot melt so if you have a complex joint, use ordinary white glue or wood working glue. You may find it best to slightly thin it with water but not necessary if you us it sparingly. I use clear packing tape to hold joints in place while they dry and then just peel it off.

    There are spray adhesives made just for polystyrene foam (3M makes one). They are generally latex based products. Most all of the common spray contact adhesives will attack the PS Foam because of the propellants/solvents. People have had success with very thin mistings of common contact adhesives. If you have try to machine or sand such a joint afterward you will curse because it will instantly load/fowl cutters and abrasives.

    Alcohol will not attack PS Foam and on occasion I have used shellac as glue. It doesn't burn out as cleanly as white glue or hot melt but produces a very thin joint.

    Here's a little more from one of the previous links I posted for you.

  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Couple other thoughts for you Bruce:

    Building the foam pattern is one hurdle but how/where you sprue and how you orient the pattern and pack the mold are another learning experience and it doesn't necessarily translate well from conventional sand casting experience.

    When I have a large, new, complex part, I usually build a crude facsimile of the foam pattern to experiment with before I blow up a pattern I have a bunch of time invested in.

    As far as aluminum Buick engines, I know that one well from its early days with Buick to when it was sold to British Leyland and its subsequent Rover incarnations. I had a good friend build a motorcycle around one and another that has a nearly 300CI stroker version with aftermarket heads in his TR-7. He's making 1.4HP/CI normally aspirated. Also had an acquaintance with a boosted version in a Lotus Europa.

  13. Bruce R.

    Bruce R. Copper

    Glued the foam together last night, maybe I’ll post a few pictures later.
  14. Bruce R.

    Bruce R. Copper

    Well, gonna pour some aluminum into this thing tonight after work, it will either work or it won’t !

    Attached Files:

  15. oldironfarmer

    oldironfarmer Silver Banner Member

    It will work!
  16. Jammer

    Jammer Moderator Staff Member Banner Member

    Pour hot and fast, don't stop when the flames come at you... keep pouring.
  17. oldironfarmer

    oldironfarmer Silver Banner Member

    Yes, hot and fast. Nice to have a face shield and hold your breath when pouring so you don't get distracted by a face full of acrid smoke.

    Your sheetrock mud looks a little thick. I like to see a little color through it.

    Tilt it so the sand can flow up into the bottom when vibrating it. A hammer on the bucket does OK for vibration.
  18. Bruce R.

    Bruce R. Copper

    Good thing I bought 2 bags of the stuff, I didn’t know it would set up in the bucket ! I mixed up about 5 lbs of it figuring I could use it as I needed it. LOL.
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    By the non-setting stuff in a pail. You can dilute, reseal/reuse that indefinitely.

  20. Bruce R.

    Bruce R. Copper

    I have a stand I built, a piece of plate mounted on 4 springs with an old electric sander bolted underneath, I use it to clean parts, I put a tub of walnut shells on it with the parts in and vibrate them.
    Tobho Mott likes this.

Share This Page