Casting weights from 3D printed molds

[Lemosteam]

Just need a larger well to receive the molten metal above the sprue.

I thought about that and almost printed a new drag. Does that hep to keep the metal hotter longer or is the purpose to act like a pressurized head of water to force the metal into the pattern?

[Maletrain]

The lead casting pot in the link I posted earlier will do both, compared to a ladle.  Taking the ladle of the heat source and pouring the melt through the air into the mold does cost some heat.  And the pressure is really not much more than the weight below the top of the sprue when you use a ladle.  With a bottom valve on a melt pot, the whole path to the mold is heated, and the pressure is close to whatever comes from the depth of the metal in the pot above the mold.

[metalworkertom]

More pressure and keeps the metal molten a bit longer. I think double the weight of the part in reserve in well is the number . But I've used smaller and larger.

[peteski]

More pressure and keeps the metal molten a bit longer. I think double the weight of the part in reserve in well is the number . But I've used smaller and larger.

I suspect if the metal is heated even more (above the melting point) it will stay liquid longer (take longer time to cool and solidify).  But I don't know how the resin form would handle higher temperatures.

[Maletrain]

I suspect if the metal is heated even more (above the melting point) it will stay liquid longer (take longer time to cool and solidify).  But I don't know how the resin form would handle higher temperatures.

Casting lead alloys in steel molds, I have found that letting the molten metal get too hot leads to a frosted appearance on the castings.  There seems to be an optimum temperature, because not hot enough leads to wrinkled-looking surfaces on the castings.

I am not sure how this would play out in molds made of printed resin.  Too much heat against the resin might show issues not seen with steel molds.

[metalworkertom]

Casting lead alloys in steel molds, I have found that letting the molten metal get too hot leads to a frosted appearance on the castings.  There seems to be an optimum temperature, because not hot enough leads to wrinkled-looking surfaces on the castings.

I am not sure how this would play out in molds made of printed resin.  Too much heat against the resin might show issues not seen with steel molds.

You can't go too much hotter with most alloys without problems.With Brass you get zinc burnoff.

[JMaurer1]

Why are you doing this as a two piece mold? Just pour it into the bottom mold and you can make sure that both wings get enough material and any excess material that builds up on the top can just be cut/sanded off.

[cgw]

Hey John L.   Instead of making small molds make a series of patterns and runner trees.  Use the pattern to make a silicon mold.  Take that mold and put it in a spin caster and you will get decent parts all filled up on the sprue tree.    There are a couple of maker spaces that had spincasters for the jewelry folks to play with in the metro area.    I forgot the name of the fellow who was the owner/operator of sunrise details.   He used a spinster to make the detail parts.  Unfortunately he was involved in a nasty car wreck that disabled him.  Armstrong on the west side sell a lot of jewelry making supplies on 8 mile in Livonia. he also has spinsters for sale and sometimes has classes using the spin caster.      check it out.

 

[Lemosteam]

Why are you doing this as a two piece mold? Just pour it into the bottom mold and you can make sure that both wings get enough material and any excess material that builds up on the top can just be cut/sanded off.

1: to see if I could
2: I was trying to create a final part in one shot (no dress up)

I wanted the top to come out perfectly smooth so I could just cut off the gate and vents and shove it into the flatcar.  After realizing that is not possible, then it became just a series of experiments.

[Lemosteam]

Hey John L.   Instead of making small molds make a series of patterns and runner trees.  Use the pattern to make a silicon mold.  Take that mold and put it in a spin caster and you will get decent parts all filled up on the sprue tree.    There are a couple of maker spaces that had spincasters for the jewelry folks to play with in the metro area.    I forgot the name of the fellow who was the owner/operator of sunrise details.   He used a spinster to make the detail parts.  Unfortunately he was involved in a nasty car wreck that disabled him.  Armstrong on the west side sell a lot of jewelry making supplies on 8 mile in Livonia. he also has spinsters for sale and sometimes has classes using the spin caster.      check it out.

@cgw Thanks for that tip.  Like some pewter castings I have seen, it would need some vents to avoid air pockets no? Also, I SUCK at making molds and such or working with any kind of mix that requires accuracy.  I am at my limits with the printer resin!

I also doubt they'd let me cast lead there too...

This is good info though!

[Mark W]

1: to see if I could

And about time!  Glad you finally got a hold of a printer and can do these awesome experiments!

[randgust]

I've been doing low-end metal casting now for about 14 years.

The two-part rubber molds do an excellent job with low-temp metals, really.  I won't use pure lead, I'm quite happy with other premade chunks like Type160, plenty heavy for me.

You make your master out of styrene, and fit that pattern into whatever you're trying to make.   Add air gates and feed gates; I normally inject resin into either an open or multi-part mold but with metal you want a BIG feed gate with a gravity reservoir, and also be able to shake/pound it down.   It's not spin-casting but same rules apply.  Some of these molds are getting into the 10-year old range, unlike with the resin, they tend to hold up amazingly well and tolerate repeated hot metal heating over time.

I'm all in favor of RP, particularly when you can get the surface finish as good as you can with resin casting, but man, what you're trying to do here just looks so much more difficult than what I'm doing on a regular basis with a styrene master and rubber molds.  Weights are kind of tricky to make because you're often fitting them into existing shells or projects, and styrene is really easy to make into shapes and trim to size to fit about anything rather than repeatedly printing something.   My latest test was making cast weights to fit inside the  electric 'critters' with RP-printed shells by Randy Stahl.   Again, not a cut against RP because it has it's place, just seems harder to me.   I've never had any luck with RP-masters in FUD for resin casting, the resins would appear to be much better for surface, but it's a matter of what you're good at I guess.

[Lemosteam]

Hi Randy, I get it.

I suck at two part mixing, have no patience for it whether resin or rubber.

You are missing one big point here.  My CAD is the master and I can iterate many times before needing a mold.  A styrene master takes much time and if it is not what you want, you might have to start over.  I can get a design exactly how I want it and produce a mold, first time through, by only messing with electrons on a computer screen.

Yes the iterations I made to get to a usable solution here were manual, but they were more for learning and experimenting than anything else.

And, I can apply the knowledge I have learned here to apply to later mold designs, again fist time through.

In the end here, the weight was simply not enough to even bring the car close to NMRA weights, but in my mind it was not a wasted effort by any means.

You might think it was a lot of trouble but all I did was use my 3d of the car pocket to make 3D model the mold, save an stl file, and wait for the two halves to print.

All of this used about 1.5 hours of time.

[randgust]

Yeah, all depends on what you are good at.  I could probably equal that time with my method, and I consider myself really good at making molds.  I must have several hundred now for all my kits, most kits have multiple duplicate sets so that if a mold does fail it doesn't shut me down.   When I'm doing a resin mold run I'll probably do anywhere from 15-20 molds at once and since I learned to pressure fill my scrap rates are about zero.  I'm not that good in metal, but if it doesn't look right, at least you can remelt that stuff.

Meanwhile, while I've been successful at doing a couple 3D printing designs, I can shoot a week trying to get it right, very frustrating.   I got pretty tired of arguing with Shapeways on model acceptance and results.   One of my sons is getting really good at resin printing with his own equipment, but he's been having too much fun doing his own stuff to mess with my trains.   I really admire the guys that have got this down pat.

When I look at a pile of styrene and brass to me it's easier to work with tactile real materials than a CAD design, I'm old-school.   It's like the sculptor that looks at a rock and sees a face in it, and is asked how to do it, and the answer is cut away everything that's not a face.   Just different.

[SandyEggoJake]

John, v cool.  Given temp and pressure seem to be issues, wondering if you might see further improvements with a mother mold of some sort?  Maybe with just simple greensand?  Such could then be preheated to keep the mold hotter - and would allow a larger funnel for a bigger pour - to both improve the gravity feed as well as temp retention of the slug.

Could be as easy as a wooden box filled with greensand. Obviously, you'd need to remake the top half of such a sand mother mold prior to each pour, but such is stupid simple to do as unlike true sand casting, you wouldn't even need to take out the part pattern (the mold).... just the patterns for the airholes (pencils?) and pour gate (funnel?) 

And you might consider to try to *briefly* heat the mold by pointing the MAPP gas flame into the funnel just prior to the pour?