Resin Casting

[JMaurer1]

Maybe I missed the answer but I was a sucker not a blower. Other than ease (which blowing seems to be), what are the advantages? I always thought the best way to do this was to suck the bubbles out (but according to my ex, I am always wrong).

Jeff Maurer
Sacramento Valley NTrak

[zephyr9900]

How do you guys handle casting parts that go beyond one mold's lifetime?  Do you pull a mold from your master and save it for "secondary masters" and then pull production molds from them?  Or do you mold a series of secondary masters right away and save them for production mold making?  (I'm assuming that the original master might be damaged in the initial moldmaking).  Or do you do something else?

Part of my extremely-long Flying Yankee patternmaking delay has been in trying to develop techniques to make "bulletproof" masters--I'm on my second generation of CNC equipment...

I recently did some Shapeways 7.5" gauge detail part patterns for a friend in California, and his caster used them to investment-cast brass patterns to use to make wax-injection molds.  Lesson learned--FUD burns out pretty well...

Randy

[LV LOU]

Maybe I missed the answer but I was a sucker not a blower. Other than ease (which blowing seems to be), what are the advantages? I always thought the best way to do this was to suck the bubbles out (but according to my ex, I am always wrong).

Jeff Maurer
Sacramento Valley NTrak

A lot of resins to goofy things when you vacuum them.If there's any kind of moisture whatsoever in some of them,you pretty much get a horrible,foamy casting,looks like spraycan insulation.The resin also sometimes hardens well before the normal working time.Also,sometimes,bubbles that would easily show up in a casting simply are too small to rise to the surface,pressure mashes them to nothing.

[LV LOU]

How do you guys handle casting parts that go beyond one mold's lifetime?  Do you pull a mold from your master and save it for "secondary masters" and then pull production molds from them?  Or do you mold a series of secondary masters right away and save them for production mold making?  (I'm assuming that the original master might be damaged in the initial moldmaking).  Or do you do something else?

Part of my extremely-long Flying Yankee patternmaking delay has been in trying to develop techniques to make "bulletproof" masters--I'm on my second generation of CNC equipment...

I recently did some Shapeways 7.5" gauge detail part patterns for a friend in California, and his caster used them to investment-cast brass patterns to use to make wax-injection molds.  Lesson learned--FUD burns out pretty well...

Randy

When I make a mold I never want to lose,the first casting that comes out of it is a master of the inside of the entire mold from resin,including the core of the mold,base and all.I pretty much do that for the core,too.I make a box from MDF board for each mold,that box gets used for ever process I do for that particular mold,the original pour of the first master,the core,and then the resin master copies.

[DKS]

How do you guys handle casting parts that go beyond one mold's lifetime?

My strategy varies depending on what is being cast. For starters, I always try my very best to make masters that will survive more than one mold-making cycle. One reason is that it's rare when I'm satisfied with a casting that isn't first generation. When the object can survive dropping a generation, it almost always stops there; I think I have only one product that's third-generation.

Example. For things like tie piles and other low-detail-level objects, I will make a master mold and pull first-generation castings for a production master, from which I'll pull as many production molds as I need. The advantage of this is that the production master, being all castings, is virtually indestructible, so it'll essentially last indefinitely.

Example. The crawler absolutely would not survive dropping a generation; every crawler kit is a first-generation casting. To keep up with the demand, I made three masters, from which I've pulled ten molds and counting. Thankfully the masters are still in perfect shape, because I'll probably have to pull another ten molds.

If the master does not survive past the first mold, I'm faced with a couple of options. If the final product can drop a generation, then all is well, since I can make a whole bunch of castings to stockpile for production molds. If first-generation castings are required, then it becomes a limited-run of very expensive castings, with the hopes of being able to make a new master.

[johnh35]

I just received a quart of Hydrospan that I ordered and was taken aback by the packaging. I  know that people have noted that resin now ships as hazardous, but this is a new level to me.

The quart bottle (like a quart of oil) arrived in a box the was 16x16 and stapled together. After prying the staples out and opening the flaps, there was a smaller 10x10 box inside encased in blown in foam. After chipping away the foam to get to the flaps of the inner box, I finally get it open to reveal the bottle inside wrapped in a plastic bag and encased in more foam.

The company where I work ships hazardous items all of the time (ie: aircraft fuel system components containing preservation oil) and the requirements are not that crazy. Do the other companies like Smooth On and MM now package their resin in a similar manner for shipping?
BTW, i know someone was talking about twenty dollars to ship resin from somewhere. I paid fifteen from Texas to CA

[DKS]

Do the other companies like Smooth On and MM now package their resin in a similar manner for shipping?

Not with Smooth-On at least. The product arrives in a single, taped cardboard carton, and the containers inside are packed in air pouch packing.

[LV LOU]

I just received a quart of Hydrospan that I ordered and was taken aback by the packaging. I  know that people have noted that resin now ships as hazardous, but this is a new level to me.

The quart bottle (like a quart of oil) arrived in a box the was 16x16 and stapled together. After prying the staples out and opening the flaps, there was a smaller 10x10 box inside encased in blown in foam. After chipping away the foam to get to the flaps of the inner box, I finally get it open to reveal the bottle inside wrapped in a plastic bag and encased in more foam.

The company where I work ships hazardous items all of the time (ie: aircraft fuel system components containing preservation oil) and the requirements are not that crazy. Do the other companies like Smooth On and MM now package their resin in a similar manner for shipping?
BTW, i know someone was talking about twenty dollars to ship resin from somewhere. I paid fifteen from Texas to CA

It was me.I got stuff from Smooth on,two bottles of resin.I only live 50 or so miles away,same state,it was something like 18 dollars..

[zephyr9900]

David and Lou, thank you.  My first choice is to have durable masters, and that is where my sticking point has been.  For the Pioneer Zephyr masters, the skins were .010" etched brass, with the window/side area being two sweat-soldered thicknesses.  I machined the "cores" from various pieces of acrylic and glued them together, and then applied the skins to the cores with thinned contact cement.  Dick later said that he had to do maintenance on the masters becuase of the brass delaminating from the cores at the corners.

That has been the sticking point for me.  On the Flying Yankee I have destroyed two skins due to the contact cement sticking prematurely (looking back, I must have had beginner's luck on the PZ masters) and I have tried multiple alternatives, from .002" acrylic film adhesive to various cynaoacrylates to various epoxies including Golfsmith shafting epoxy, which is supposed to be good for metal-to-carbon fiber plastic.  Nothing sticks acceptably to brass--it is easy to peel a corner on my test pieces.  I have yet to try Loctite Black Max (should stick but has limited working time) and, of all things, JB Weld which was just suggested to me recently.

My other alternative is to go all brass and solder.  My difficulty there is to attach the pre-sweated skins (three layers now with the side doublers and .002" shim window blanks) to a relatively thick brass core piece without disturbing the alignment of the skins, which on the nose and tail cars wrap around in two directions.  I am thinking an aluminum mandrel with embedded cartridge heater, and an enveloping aluminum shell lined with silicone rubber, which starts in nominal contact and which will expand with soldering temperature to apply even pressure all around as the solder reflows.

Or, abandon all that and go with the very fine resolution RP that is now available, have primary masters investment cast in brass and use them for the multiple RTV production molds...all with significant expenditure to other people when I have perfectly good CNC and photoetching capability in my own garage...

That is why I've been paralyzed from action for all this time, Peteski...

Randy

[LV LOU]

Randy,if contact cement works as an adhesive,you could just ignore the directions,and apply the sides to the cores while it's still wet.Instead of using the regular method of apply to both sides,let it dry,ETC.I use water based contact cement on my foam for my railroad,I just brush it on,and screw it together..GOOD LUCK getting it apart.Also,clear silicone ADHESIVE,not sealer,is one nasty glue that is easy to work with.It will say "adhesive sealer" right on the tube.DOW is the best,but Permatex is good,also.I use it to glue tire on RC cars and slotcars,it takes TERRIBLE abuse,and is the only thing you can use to glue silicone tires to wheels..It can,however,be removed quit easily..

[DKS]

If you are sweat-soldering two layers of brass together for the skin, think about cutting/etching bend-out tabs near the edges of the bottom layer (such that the tabs face away from the edges, towards the center, when they're flat so that there are no notches in the edges). Then, drill holes in the core to accept the tabs, and fill them with epoxy before applying the skin to the core. Alternatively, solder pins to the backs of the skins along the edges, and continue as above.

[Sokramiketes]

What is stopping you from machining a block of brass into a full shell?  It looks like you've graduated from Sherline to some serious CNC firepower.  And milling would allow a more accurate replication of Budd corrugations rather than the flat look of photoetched overlays.  And keep it in house versus rapid-prototyping.

If you do decide to play with a high-resolution RP to lost wax brass, let me know and I can share some insight and recommend a company to try. 

This Z scale flat car was done via that method:

[johnh35]

My local hobby shop has started carrying casting supplies! Now I don't have to pay the high cost of shipping when I want to order a small quantity and their price is competitive with buying online. It's the little things....

[peteski]

Randy,
thanks for the detailed explanation of the problems - it is finally clear that the decade-ling delay was due to technical issues (rather than you simply doing other projects).   

And for couple of OT replies:

John: My HydroSpan, also quart, was packaged the same way as yours. It took me some time to chisel my way through the double boxes with all the urethane foam!  And those boxes used a double layer corrugated cardboard.  The packaging actually weight more than the product!  That's why the shipping was so pricey. I have no idea why the extra packaging was needed for a quart of a substance which is not even all that hazardous.

When SmoothOn ships me urethane resin and RTV, they just come in a standard single cardboard box with some plastic "pillows" as a filler.  In the last shipment, I ordered 2 trial sizes of resin and the (UPS Ground) price was around $15. And the shipment originated about 15 miles from my house.

The shipping costs have gone up in the last few years (probably doubled).  So $15 for shipping is really not that high. Just last week I shipped a package, which was just under 4 lb., from MA to CO. It cost me around $12 for shipping (and that was with a discount for doing the transaction online).  It was shipped USPS Priority Mail. In my experience, Priority Mail price is pretty much in-line with the UPS Ground price.

[randgust]

Wow, in many ways I'm glad I never read any of this and just went ahead on my own and started making stuff... This would have talked me out of it.  Chris333 got me started and I evolved separately on my own little island.  Pretty much the Edison approach, try everything, throw out what doesn't work.   

I've always made my masters out of styrene and brass, and early-on had the problem of laminating layers and master durability.  But I've learned, sometimes the hard way, that if I design a mold that's so difficult to get off the master that I destroy it, I'm going to have the same exact problem with the part and the mold will get torn and have a relatively short life.   The more you design for low-stress mold removal the longer the master and the mold lasts.

If you laminate masters with styrene and use a solvent for it, most evergreen-type material will warp, at least over time.  I'll use a bit of solvent for structure, for for sealing I use watery ACC.  No more problems with leakage of the mold rubber into the part master, no more warping.  But it's so rigid that you can't go honkin' & tearin' the mold off the master either.

I also deliberately design my sprue gates and air bleeds to be breakaway off the master with just a touch of ACC, that stuff fractures before the solvent glue will and doesn't damage the surface as much.  Those are expendable and are easily reattached.

I have some masters (like the V&T ore car frame) that are just miserable to mold, and those have evolved over to mostly brass for strength.

I'll often re-insert the master back into the damaged/spent mold, and redo one half or piece at a time against the master again with new material.  That's been a big time and money saver.  I've now got many 3-4 part molds and it can take days to make a replacement if there is a real mold failure, this allows to just replace the one section that has a problem and also makes molds interchangeable against each other.