My first lost foam casting. Close oh so close.

Discussion in 'Lost foam casting' started by Guitar Bill, Oct 15, 2025.

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  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I didn't know that Bonz!

    Best,
    Kelly
     
    Al2O3, Oct 18, 2025
    #21
    FishbonzWV likes this.
  2. Guitar Bill

    Guitar Bill Silver

    Thank you for the great instruction, I'll look into these for sure as I move forward in the land of LFC.

    Happy Sunday
     
    Guitar Bill, Oct 19, 2025
    #22
    FishbonzWV likes this.
  3. Guitar Bill

    Guitar Bill Silver

    Morning Kelly,

    I am using a 1/32" conical carbide bit with no coolant, it is a 0.0025 stopover and a 0.02 step-down. It was not hard on the bit at all at 15,000rpm.
    I got castings from my mechanic like pistons, housings etc.
    I'm using Sopra-XPS 30 foam. Density is rated at 1.87 lb/ft3 so on the high side. Im not in an area where they carry the pink, next time I'm in a big city I'll grab some.

    So here are the images with some sanding. I do have the tiny pitting. Not sure how deep but still happy with the pour. If I reuse melted pieces from this and other melts it'll be better I hope. As to degassing, still on the fence.

    Thanks for the advice and library of info. I'll keep going with this one and plan more pours next week.

    Happy Sunday.

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    Attached Files:

    Guitar Bill, Oct 19, 2025
    #23
  4. FishbonzWV

    FishbonzWV Silver Banner Member

    It's better to try and prevent the porosity than get rid of it. Tune your burner to a lean flame and leave any oxides/trash on top of melt as a cover. Turn off the burner as soon as you reach pour temp.
    Get a good heel of virgin metal going in the crucible. Drop a piece of this casting in and watch it melt. As it hot shorts and disappears below the surface, you'll be able to see little tiny bubbles pop on the surface. That's the H2 pores being released.
     
    FishbonzWV, Oct 19, 2025
    #24
    Guitar Bill likes this.
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That's a small bit! The photos mad me think it was a little larger diameter and stepover but those might have been roughing. It's good you had no adhesion. Castings can often be gummy depending upon alloy.

    Pistons are typically higher silicon content, which makes them more fluidic in molten state, a little harder as cast, but also tend to be greyer in color.

    Not familiar with that brand. How do you know the density? Do you have the data sheet? Foam board is marketed by R-Factor and Compressive strength. The compressive strength is a good proxy for density. It's a good bet the 30 in the product name is compressive strength. Underground rated foam board usually have higher compressive strength and density. In the Owens Corning (pink "Foamular") product. Foamular 150 is 15psi compressive strength and is 1.3lb/ft3, and Foamular 250 is 25psi and 1.5lbs/ft3. Both have similar R factor, same as your foam for that thickness. Although this is what their spec sheet says, I have weighed both and found them both to be about 1.5lbs/ft3.

    I think you're off to a very good start. Experienced eyes would probably pick up many things from a video. A close up of the flame at your furnace vent (especially at night) would tell a lot about the tune of your burner. Just need some further process development and refinement.

    Best,
    Kelly
     
    Al2O3, Oct 20, 2025
    #25
    Guitar Bill likes this.
  6. Guitar Bill

    Guitar Bill Silver

    Thank you so much!
    I will tune the burner to go leaner, I think the sleeve that vents the air at the nozzle is where I tune it? I'll research that.
    I'll also try watching how the molten al reacts to a piece dropped in.

    Cheers,
    William
     
    Guitar Bill, Oct 20, 2025
    #26
  7. Guitar Bill

    Guitar Bill Silver

    Hi Kelly,

    Yes those other images was with 1/8" and a 0.02 stopover, so a rougher surface.
    I researched the foam and used ChatGPT for the info on density.
    I'll be sure to video my next pour and capture all the steps. I will be sure to get a lean burn too.

    Thanks,
    William
     
    Guitar Bill, Oct 20, 2025
    #27
  8. rocco

    rocco Silver

    rocco, Oct 20, 2025
    #28
    Guitar Bill likes this.
  9. Guitar Bill

    Guitar Bill Silver

    Guitar Bill, Oct 20, 2025
    #29
  10. Guitar Bill

    Guitar Bill Silver

    Hey guys,

    I spent some time sanding, filling and basic polishing to see exactly what I have here.
    If you look closely you can see the pitting. Darn.

    Is there anything I can do to clean it up better or a way to fill them? Any tricks.

    This is just a prototype but still want it to look presentable until I get a better casting done.
    Whats a good cleaner that gets into the pitting?

    Thanks,
    William


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    Last edited: Oct 20, 2025
    Guitar Bill, Oct 20, 2025
    #30
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Many times, if you have H2 porosity, you can polish some away, only to uncover more. You can try hitting spots with a TIG torch and repolishing, but from experience I can tell you that may be ok for gross/larger defects, it can become a tail chasing exercise for fine porosity, and it usually makes it worse and there are too many to make it worthwhile. Sorry, no silver bullet, but as mentioned by Bonz better to avoid it than fix it.

    Melt management is really critical for cosmetics and good material properties. Not many gases are soluble in aluminum but H2 is, and it can be a bugger. The hydrocarbon fuel and the combustion air (which contains water) are H2 sources, and the large volumetric flow of the burner introduces a lot of opportunity for H2, and it becomes much more soluble as the melt temp increases. Clean metal free of oil and paint is also desirable.

    All of this is why I use virgin ingot and melt with a resistive electric furnace.......can't get leaner than that and no fuel or ambient air flow......but don't fret. Good dense castings are possible with fuel fired furnaces and good process management.

    If your foam is really ~2lb/ft3, you really want to get that down to 1.3-1.5lb/ft3.

    I also could make a case for gating into the opposite end of your pattern. That's why I was asking about that feature earlier (but I thought it looked kind of nasty). If you can gate into the most massive section of your casting and have the metal flow to the thinner sections at the bottom of the flask, it directionally solidifies from the bottom up, which is a good thing......but, let's stick to changing one thing at a time......melt management.

    Best,
    Kelly
     
    Al2O3, Oct 20, 2025
    #31
    Guitar Bill likes this.
  12. Guitar Bill

    Guitar Bill Silver

    Thanks Kelly,

    I agree, get the melting process pinned down first. Then test and see. All great advise.

    Cheers,
    William
     
    Guitar Bill, Oct 20, 2025
    #32
  13. FishbonzWV

    FishbonzWV Silver Banner Member

    The sleeve plus gas pressure. I tune by sight and ear. Blue flame and then listen to the pitch, play with the air and gas. Dull roar = rich, go for the highest pitch. It's a fine line between rich and lean.
     
    FishbonzWV, Oct 21, 2025
    #33
    Guitar Bill likes this.
  14. Guitar Bill

    Guitar Bill Silver

    Guitar Bill, Oct 21, 2025
    #34
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    That will likely change with alloy and temper. I cast with A356 which is heat treatable, but big difference in natural frequency of a soft as cast part and one that has been taken to T5 or T6. As cast are pretty dull and low duration. High temper are higher frequency and duration. That's not something you are looking to control on this part, is it?

    Best,
    Kelly
     
    Al2O3, Oct 21, 2025
    #35
  16. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    You can also tune by eye, which I find useful. If there is fire shooting out the vent hole in the lid of your furnace, you are running rich/reducing (more fuel than you can burn with this much air before it leaves the furnace). Add more air or reduce the fuel until the fire just fills the furnace and you're pretty much neutral. Add a little more air or reduce the gas a little more, and you're on the lean/oxidizing side. I don't think it's ever a good thing to let the mixture get too far from neutral; my understanding is you want the mixture just a little bit lean for aluminum casting.

    In practical terms, I know my 0-10 psi propane regulator can put out more gas than my 'hair dryer on a dimmer switch' blower can keep up with, so I usually turn the blower up from barely on to full blast just after the furnace is lit, then adjust the gas regulator dial to suit using these visual cues. If it's winter or I'm doing a long melt session and my gas tank starts to frost over, it's nice to have the fine control of the blower afforded by the dimmer switch so I can turn the air down to maintain the mixture until pouring temperature is hit even when gas pressure drops. Keep an eye/ear on these telltale signs throughout the melt in case conditions change and adjustment becomes necessary - the gas tank frosting over, the furnace coming up to temp, etc.

    Jeff
     
    Tobho Mott, Oct 21, 2025
    #36
  17. Guitar Bill

    Guitar Bill Silver

    Hello guys,

    I picked up some C200 Foamular NGX. Im shipping a guitar and I like to add extra padding. It's going to California.
    So I'll have some scrap left over. Now it's only 1" think and Id like to ad 1/4", can I just glue on a 1/4" slice?
    I am using that white Elmers PVA glue. Would I need to cover the whole area or just a few dabs?

    Made some parts and did some cnc'ing.

    Cheers,
    William

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    Guitar Bill, Oct 23, 2025
    #37
    FishbonzWV and Tobho Mott like this.
  18. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    White Glue PVA/Poly Vinyl Acetate is ok for small surface area joints but they won't dry if laminating large areas. Like any glue, make it very, very, thin. But if you are planning on machining through the glue joint, it will load up your router bit and won't sand evenly at the joint.

    I use PVA for joints where I need longer working time, but prefer low melt point hot melt glue, or foam safe rubber cement.

    Best,
    Kelly
     
    Al2O3, Oct 23, 2025
    #38
    Guitar Bill likes this.
  19. Guitar Bill

    Guitar Bill Silver


    Thanks Kelly,

    I'll be very sparse with the amount and see how it goes.

    Cheers,
    William
     
    Guitar Bill, Oct 26, 2025
    #39
  20. master53yoda

    master53yoda Silver

    I direct fire in my processing furnace, what i have found entrained H2 has a relation to couple of things. One is the higher the pour temp the more entrained H2. also the longer it sites in the melt pool after melting the higher the H2, The richer the burner is set the more H2 will be untrained.
    When i am pouring a casting that needs have as little H2 as possible i use my crucible furnace and degas using Calcium hypochlorite"Pool Shock". I monitor the temp to 1325 -1350 I use a mixture of 25% sodium Chloride, 25% calcium Chloride, and 50% Calcium hypochlorite . Approximately 2 tablespoons of the mixture per 12 lbs of aluminum. This puts off chlorine gas, You must have sufficient ventilation these gases are corrosive. push to the bottom of the crucible with minor agitation of the melt. HT1 is were i got my initial introduction to using Calcium hypochlorite, the above mixture is mine by experimenting.
    Also the actual remelt of ingots etc. releases any entrained H2 from prior melts etc. I am unaware of any commercial foundries that are not sourcing there raw materials from the recycle industry. The difference between the ingots I sell and a commercial foundry is that they test each batch to certify that the alloy is within standards. My ingots meet the standards with the exception of being slightly higher in Fe, it is why I call them NEAR 356. They have been successfully used in most application except for Over the road parts as the DOT requires certification.

    Art B
     
    master53yoda, Oct 29, 2025
    #40
    Guitar Bill likes this.
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