replicating a motorcycle intake

Discussion in 'Lost foam casting' started by GJL, Sep 8, 2021.

  1. GJL

    GJL Lead

    Hello Home Foundary

    I am a long time follower of this art and hobby. As a machinist I'm always looking to advance my skills. I seek the forums advice on how to proceed with this small project.

    Looks simple, but I'm sure the devil is in the details......it's aluminum, approx dimensions 1.5" x 4" (image)

    I am thinking the lost foam method would be the best approach.

    What say the forum?

    Thank you!

    GJL

    [​IMG] intake.jpg
     
  2. GJL

    GJL Lead

  3. Melterskelter

    Melterskelter Gold Banner Member

    First, welcome!

    These parts come complete with parting lines from when they were cast. Lost foam might be a good way to go. But, I’d think Petrobond and a wood box would be a far simpler way to get started. And it should work fine. I’d use the original part as a pattern realizing I’d lose about 1-2% size. There are ways around that if that’s an issue. You will need a core, of course. Make core box by 1) splitting an original part and adding on bits to index in the core print or 2) use a replicating rubber from Smooth-On or Freeman to make a core.

    There are some great lost foam folks here and they may see it differently. That my take as a sand caster.

    Denis
     
    GJL likes this.
  4. GJL

    GJL Lead

    Hello Denis
    Thank you for the welcome and responding!
    Am I correct to understand that you're suggesting making a two part mold and abandon the lost foam approach? (see attachment)
    Petrobond instead of sand?
    Does the replicating rubber remain in during the pour? My readings are that the replicating rubber is limited to 600'ish.

    Thank you again!
     

    Attached Files:

  5. DavidF

    DavidF Administrator Staff Member Banner Member

    Lots of ways you could cast them. Just depends on what you have on hand equipment wise and how many you plan on making...
     
    GJL likes this.
  6. GJL

    GJL Lead

    The hollow part aspect is what confuses me................
     
  7. DavidF

    DavidF Administrator Staff Member Banner Member

     
    GJL likes this.
  8. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    As mentioned, there are multiple ways to do it. The recommendation sort of depends upon what you are already set up to do and how many you want to make. Assuming it is one set or a handful and.....
    1. You are adept at CAD or already have models and 3D printing capability, printing them and investment would be practical.
    2. If you can except 1.3% shrinkage, and already have bonded sand of some type, MS' suggestions is viable, but you still need to make a fairly complex core. If you want to make many copies, a hard pattern and sandcasting is probably the way to go.
    3. If you are just starting out, and basically have no molding equipment, lost foam is probably the easiest way.......but, you have to be capable of fabricating a foam pattern. The methods for doing so can range from hand carving, hand/pattern guided wood working tools, cnc router.

    If you are interested in pursuing lost foam I'd suggest you read these threads.

    http://forums.thehomefoundry.org/in...ssions-of-a-lost-foam-caster-5-years-on.1650/

    Here's a very similar tubular foam casting:

    http://forums.thehomefoundry.org/index.php?threads/tubular-lost-foam.11/

    Best,
    Kelly
     
    GJL likes this.
  9. rocco

    rocco Silver

    I don't want to speak for Denis but I think he suggested the rubber not as the actual core for the casting but so that you'd have a positive model off of which you could create the core boxes. Are you looking to replicate the pieces you have as closely as possible or will your casting be a modification of the originals?

    BTW, my first serious casting project was also a manifold, one to fit a single 2-barrel side draft carb to an inline 4 cylinder engine. In my case, I was not replicating anything, I was creating a brand new design, I started by carefully measuring the ports on the head and carb, those were the two most important constraining factors of the design, from there, I made a positive model of the interior of my manifold, used that to create my cores box, then added carb and head flanges to my model, decided on the wall thickness and fleshed out my pattern design from there.

    Cores are what create the hollow space inside a non-lost foam casting. To make the cores, sand with a binder is packed into a mold called a core box which duplicates the desired internal shape of your part, once the binder has set up, the core is removed from the core box and placed inside your sand mold. If you do a search on youtube for "making foundry core", you'll come up with lots of examples, including this one, mine which shows me mixing the binder into the sand, packing the sand into core box and curing the binder. The binder is sodium silicate which sets up in the presence of CO2, that's what you see me injecting into the sand with the orange hose.

    I also have images of the mold just before I close it up to pour the aluminum but they're on an old computer, if I can recover them, I'll post a few picture it should help to de-mystify the molding process and how the hollow shapes are created.
     
    Last edited: Sep 8, 2021
    GJL likes this.
  10. GJL

    GJL Lead

    It's all coming together now. The videos and responses really helped. My intiention is to duplicate the original parts (that I already have) as closely as possible. Have to agree the sand cast with a core is the way to go. Already have a furnace, need to make the box, get some more petrobond and the core material. It's ooking like "lining up" the core accurately would be the challenging part
    Thanks to all for the advice!
     
  11. Melterskelter

    Melterskelter Gold Banner Member

    If you snad cast, you will need to make a core to keep metal out of the hollow center of the part.

    Here is avideo that talks about the general concept of core making. I do not think his method of using sodium silicate is very good (actually terrible), but there is a lot here on the site concerning silicate cores and there are a number of people here who use linseed oil, molasses and you can also use other binders like epoxy.



    Take some time to look at various youtubes on cores and look at some written pages as well. There is nothing very technical about making them.

    Here is a guy making molasses cores---an easy way to make a core with no exotic materials needed.


    Just as I was about to post this, I see Rocco made a very good reply.

    Denis
     
    GJL likes this.
  12. myfordboy

    myfordboy Silver

    I did something silmilar a while ago.

     
    BattyZ and GJL like this.
  13. rocco

    rocco Silver

    The molding process Myfordboy uses is probably a pretty close approximation of the one you'll end up using, at about 11:30 minutes into his video, he places the core into the mold and you can see how the features at the ends of the core, called core prints positively locate the core within the mold.

    Regarding binders for the core, Denis is correct, there are several viable options for binders, use whichever you think is most convenient for you. I chose sodium silicate because it was convenient for me, I was able to source a small quantity locally, I liked the fact that it is a very quick process and that it doesn't require heat to cure so a plastic or in my case, plaster, core box could be used.
     
    GJL likes this.
  14. rocco

    rocco Silver

    On a related note, I've seen several youtube videos with people using epoxy resin as a core binder, does anyone here know if normal polyester resin could be used in the same way? I've never seen it used and I'm wondering why, it's cheap, universally available, you'd think, if it works, it would be near the top of the list of preferred binders for the hobbyist.
     
  15. I'm waiting for more replies to this thread. I have only seen epoxy used as a core binder, maybe polyester is too flammable? I've sent a few emails to companies here in the UK concerning an addative to harden sodium silicate without using CO2.
     
  16. Melterskelter

    Melterskelter Gold Banner Member

    If a new caster is going to cast aluminum, I would suggest Petrobond. I’ve used both green sand and Petro for AL and both work well enough for me. Petrobond is very easy to ram up right out of the box. Green sand has a definite learning curve. For a new guy making his first core, I think I’d lean toward polyester or epoxy resin simply because they are so available. Cobett recommends about 2 to 4% by weight of resin in the sand. Flammability should not be a concern. A central vent is generally said to be important to help allow gases to escape the core.

    Denis
     
    GJL likes this.
  17. rocco

    rocco Silver

    So, we know that polyester resin works like epoxy for this application? Did Tom say that?
     
  18. Ironsides

    Ironsides Silver

    I tried polyester resin once, it hardens too quickly for using as a binder for sand cores. I have been using epoxy resin for cores for about 25 years and would not use anything else.
     
  19. Melterskelter

    Melterskelter Gold Banner Member

    I've been toying with making epoxy and polyester cores for some time now. So, I just tried making a simple core with both epoxy resin (West System 105 resin and 205 hardener) and common polyester resin plus catalyst. I mixed each small batch of 8 oz sand with 3% epoxy resin and 3% polyester resin. I used standard mixes for the epoxy A+B and polyester drops of catalyst per ounce of resin as specified for the ambient temp of 78 deg F environment. Both binders mixed into their respective sand batches nicely and produced the same "feel" of mixed core sand as I get with the silicate I mix at 4 to 5%. I would expect a similar feel as the binders all are very similar in viscosity and density.

    I used a five inch length of a simple split tube of plumbing 1" nominal plastic pipe as a core box cutting nearly through lengthwise on one side and all the way through on 180 degree opposite side. This produces a conveneint clamshell box like I have used on many occasions in the past.

    Neither mix "kicked" prematurely and after a couple hours in the sun and warmed to probably 90 degress F, I can feel that they are solidifying. Had I mixed too much catalyst with the polyester I know from plenty of experience laminating with it that it would kick off very quickly. (Large quantities on the order of a half pint to pint can easily catch on fire due to their exothermic qualities and many a boat building shop or larger business has burned down do to careless handling of epoxy and especially polyester mixed containers.) I'll open the the cores in the morning, even though I am tempted to open them now.

    Given the very similar chemistry of the polyester and epoxy resins it would be very unlikely they will behave differently when in contact with molten metal.

    Denis
     
  20. Thank you for taking the time to carry out this experiment Denis. If I try this way of using resin bound sand it won't be just for the cores, it will be to create a "shell" impresion of the part to be cast. The shell will consist of 6 seperate parts that will have to be glued together with core glue. It will be interesting to learn how strong the cores are, do the edges feel weak, surface finish etc.
    Lee
     

Share This Page