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Casting a 3D Print


regme
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Hi

 

I want to make a casting of a 3D print, and I think I'm going to answer my question since this is the first casting I'm going to do but here goes anyway.  I was going to place the model (top down) on a glass plate and surround the model with plasticine to the level of the buffers.  Since these are the smallest part I'm worried they will break off, unless they are form by both parts of the mould.  So where the white line would be the where the two haves of the mould would meet.  I hope that makes sense.

 

Is this the right way of looking at it.

 

 

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That would work ok. I presume you are casting in Resin with a silicone mould.  

 

One way I have done a 2 part mould in the past is to make up a box then roll out some plasticine and lightly press the wagon into it so it is just near to the join. I then make up some silicone mould and pour it in until it gets to the point where you'd like the mould to join. Let it set then cover this silicone in vaseline/mould release, place your register marks/cones/tabs into this and then pour the next lot of silicone so it covers the wagon. When it has set you can open the mould carefully and remove the plasticene and first pour (discard this), this leaves a lovely flat face. Put the mould back into the box and cover with vaseline/mould release and pour the bottom part of the mould.

Don't forget your airways so you don't get trapped air and decide how you are going to fill the mould.

 

@gr.king is much more eperienced with resin than I am and produces some lovely items.

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  • 3 months later...

Hi

 

Well it's taken it's time but I have done my first casting, needless to say it will be a labour of love before I get it right.  Apart from air bubbles, need to make a vacuum chamber (new topic I assume).  So here are few pics sorry about the focus hence the 3D versions.  I'm using pinkysil to create the moulds and procast for the resin.

 

Issue number one - I do not have a bottom or a top of the mould, as I have the half at the buffers so they would not break off when taking it out of the mould.  Which means I can't get enought resin in before it starts to overflow and panic sets in.  I'm thinking to place the whole model so that the bottom is up, the split line is at the top of the wagon and the top part of the mould becomes a plug that gets pushed into the bottom part.  The only concern is the buffers breaking off when trying to seperate the casting.  I've been playing with the mould that creates the sides to see how much give it has and I'm half thinking the casting may come out without breaking the buffers.

 

Issue number two - I want to include the steps and air tank as part of the model. I can place a small infill in the steps and break them out later, which I did for this mould but found out that air gets trapped (I considered this to be the top part) and the hole I put in to let the air escape is too small so the steps did not come out very well.  With the air tank I have made it part of the underside so there's no air gap, I'm just not sure how much to fill the gap without making it look to out of sorts.  

 

I can 3D print these and get a reasonable print, but I would like something a bit less brittle and being a iron ore wagon I would like just a few :) without killing the 3D printer.

 

The more I stare at it the less I see the negative space that I need to create so I can get the resign in without it going all over the place before I bring the two peices together.

 

I guess I can break it apart and cast it as parts then glue it back together, but I don't know how to cut the ends off to make it look clean when you glue it back together.

 

Any thoughts would be great.

 

Cheers

 

 

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Definitely break it down a bit, your small details should be mounted on a sprue ideally, link each part to the sprue via a gate (narrowing of the sprue) to make it easier to remove, you actually need two sprues the bigger feed line and a smaller exhaust to make sure no air is trapped, cast plenty of spares of the small parts, I'd make a 3D Print of multiple small parts all attached to the sprues , if you need to make split moulds for the little parts set the parts out like a clock face from the central sprue, the volumes of each part on a sprue should ideally be similar when using resin, then they will all be filled at the same rate, try to align the split so that its at a location where cleaning the inevitable flash off the part will be easy and not result in you sanding off fine detail

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After 20+ years of resin casting using silicone moulds and fast setting poly urethane resins, both of various makes over the years, I would suggest making the body and chassis as two separate pieces. Try to give yourself a split that allows for one flat surface on each part. Preferably the bottom of the body and top of the chassis so that you only need a one piece, open, mould for each.

My method using these open moulds, is to pour the resin, slowly and carefully so that you don't trap air in the detail pockets, and slightly overfill the moulds. I then cover the mould with a piece of flat clear plastic which displaces the excess resin, don't press hard or as you ease off air will be drawn back into the mould, and leave this on until the resin has cured (ideally "Javis" brand 40 thou clear sheet, as it does not stick to the cured resin though after a few uses it may pay to give it a wipe over with a WAX polish, clear plastic packaging often works as well).  Peel the plastic off and remove the castings from the moulds, with a little luck, and a following wind, you should be able to glue the two flat surfaces together to form your wagon. If you find you have an air trap on the same point each cast you can usually give that point a prod with a piece of wire to displace the air bubble before you put the plastic cover plate on, I've got several moulds that need this treatment, just some thing that comes with experience.

 

Unlike some of the "experts" who may pop up to tell you how, this method is derived from experience of making and selling several thousand items over the years for myself and other suppliers. I'm not an expert and get annoyed if some one calls me one, merely had a lot of experience and no few failures in learning, and you may not wish to use my methods but they are there for you to consider. You will no doubt find a method that works best for you. Incidentally, using low viscosity  fast setting resin I have never found need for a vacuum chamber, and I don't think that with the short pot life after mixing I would have time to use one before the resin becomes unworkable.  If you have any questions you think I may be able to answer please feel free to PM me.

Phil Traxson

Port Wynnstay Models

Edited by Phil Traxson
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Thanks for that, I hadn't come across that method.  I guess that each method would have it's own benefits. 

 

I'm not sure about splitting the body and the chassis because of the buffers, maybe I can split the ends of the wagon as well so there would be 4 pieces.

 

Could I create one open mould rather than four separate ones?

Edited by regme
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14 hours ago, regme said:

Thanks for that, I hadn't come across that method.  I guess that each method would have it's own benefits. 

 

I'm not sure about splitting the body and the chassis because of the buffers, maybe I can split the ends of the wagon as well so there would be 4 pieces.

 

Could I create one open mould rather than four separate ones?

No reason at all why you can't just make one open mould. I tend to find making separate ones uses less rubber, particularly if I'm making a one piece body as that will need to be deeper than the mould for the chassis, but that's just the commercial side of things! The beauty of a one piece body is that, apart from the flat base, all the surfaces can have detail put on as well.

 I used to demonstrate casting alongside my trade stand at some exhibitions but we don't have those at the moment. I've toyed with making a video but would need some one else to help as I haven't enough hands and that's a no-no at the moment. It would need some one who was good at editing sound too to put in the bleeps when it doesn't quite go according to plan. Some one did offer to help some years ago but life got in the way and it didn't happen.

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This is what I was thinking, if I split the ends off then it's just a matter of gluing them back on.  No doubt there will be a mtach line but a bit of filling, sanding and paint should cover it up.

 

My only concern is the coupler box, maybe it would be better to keep that as one piece, even though it is an overhang (not sure if that's the right word).

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  • 2 weeks later...

Hi

 

Trial 2, I decided to go for a piece hoping that the buffers won't break on the way out, after de-moulding the buffers didn't come out.  I think it's an air bubble issue, I'm also a bit gutted that there was a big air bubble just near where the bogie is attached.  I was thinking I could fix that by using either wax or plasticine.  I'm suprised that the air tank came out, thought that was going to fail for sure.  I didn't bother to clean the model up as it wasn't very good

 

Fastening the model down

I used a piece of exposed x-ray film and glued the the model down using super glue, peels off easy after the inital pour, however the excess super glue needs to cleaned off, which more than likely caused me some issues.  I did see somone use bee's wax, but a slight touch and it came loose.  Is there another way to hold the model down?

 

The sides, for some reason, came thicker is some spots, maybe because I used a book to hold the top piece down and squashed the mould a bit, shall try with rubber bands next time.  Also the clean up on the excess glue my also be a contributing factor.

 

How you push the two halves together may have a effect on the outcome the casting, I think I did it a bit too quick, maybe a slower approach required.

 

The instructions say you can de-mould from 1 to 3 hours, I did it after 1 as the left over resin was hard, but when the model came out it felt soft, next time I'll leave for 3 hours

 

So what did I learn don't mix for too long, less time to pour, choose the time of day, the warmer it is the quick it goes off.  Holding the casting up the light shows up all the air bubbles and lack of resin.

 

The master needs more sanding also.

 

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You’re definitely making good progress but... Wouldn’t some less brittle 3D resin yield better results for less effort and expense? Siraya Tenacious is great, even mixing in 10% with your normal resin will help. 

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That is pretty ambitious for a first attempt, but a good try. I still some times have the same results with the first casting off a new item, some times needing a complete rethink on either mould or casting method, though after 20 plus years I like to think that I have met most of the problems and overcome them, but there is still the odd one that catches me out. Like wise I am sometimes surprised how easy some, apparently difficult ones at first glance, are to cast.

  I think that, like I did at first, you are perhaps trying to pour too quickly, both rubber and resin and trapping air. I had the same problems when I first attempted a two part mould. Pour from one end and let the mix make its own way, you've plenty of time with the rubber when making the mould and longer than you think with the resin. Experiment with coating the plug top in the awkward corners too, a couple of drips from the mixing stick often helps.

 Try not to be tempted to push the plug in too quickly, rather assist it to sink than force it down, if you follow my meaning.

 I'm dubious about mixing any thing else with the resin as the two parts are made to react with one another and adding anything else is an unknown and in extreme cases may even make a dangerous mix (poisonous or explosive fumes), there are many different types of resin and they are not all compatible. A lot of the 3D resins are actually more brittle than the fast cast ones you are using, in fact development of them seems to be paralleling what happened in the mix and pour types 25 years ago, going from shattering if you dropped them on a carpet to bouncing back if you throw them at a wall, fortunately the improvements happened much faster with 3D.  

Sorry for the long diatribe but I really wish I could either be there when you cast, or demonstrate one to one, as you are definitely on the right track and I would hate you to give up in despair. After my first attempts failed I almost gave up, and that was with much less complicated flat cast items items, but it came right in the end. 

  Just to justify my advice,(and brag a little!!) if any one bought resin kits in the years between 2000 and 2017 from Mercian Models, Invertrain's Highland Castings Building range, Alphagraphix or Ten Commandments then there's a fair chance that I cast them, plus my own Port Wynnstay Models range, (which I still produce). I only stopped most outside casting in 2017 due to life throwing me a couple of curved balls, and the realisation that at 70 years old I ought to be slowing down a little, so I retired to Porthmadog, and set up a smaller workshop there.

Phil T.

 

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On 12/12/2020 at 06:47, njee20 said:

You’re definitely making good progress but... Wouldn’t some less brittle 3D resin yield better results for less effort and expense? Siraya Tenacious is great, even mixing in 10% with your normal resin will help. 

I have gotten better results with 3D printing, however at 9 plus hours per print, I thought casting would yield quicker models, plus I want a lot of wagons :) and didn't want to hammer the printer.

 

So same mould, slow pour and let the plug slide in with a little pressure, a better result but still lots of air bubbles.  However when I first pour the resin in I do not see any air bubbles so I'm not sure what's going on there.  The sides feel rough even though the mould doesn't.  The photo of the end has two bubbles that seem to be in a very odd spot.  I would expect to see air bubbles trapped against an overhang.

 

I used a toothpick to open up the smaller openings abit more so my side steps can out better (well one side).  I guessing it's developing a technique when pouring.

 

Phil, thanks for the advise it is really helpfully, hopefully the penny will drop soon.  When you do an open mould what to you stick the master down with so it doesn't move when you pour

 

Cheers

 

 

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2 hours ago, regme said:

I have gotten better results with 3D printing, however at 9 plus hours per print, I thought casting would yield quicker models, plus I want a lot of wagons :) and didn't want to hammer the printer.

 

I get that conceptually, but "hammering" the printer is really just the LCD, which for a Mars/Photon type printer is £20. Even a Saturn 9" mono screen is only £80 or so, and those printers will let you print 8-10 bogie wagons at a time.

 

Not that I find the failure rate any lower - here's about a quarter of my "prints that were nearly good enough but not quite"!

 

50447653832_faffc00bcc_z.jpgGraveyard of 3D prints by njee20, on Flickr


Still, not my place to tell you what to do, just can't quite get my head around not using what appears to be a more suitable tool for the job! Unless it's just because you can and to add another skill to the toolbox, in which case crack on! :good_mini:

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Agreed, this was something I thought I could add to the tool bag, to increase production.  I too have a graveyard of almost there but no cigar prints, was thinking about using them as a train wreck :)

 

I have also learnt that everyone has something to contribute, it's whether you choose to take that on board or how you take that is another thing :)

 

I shall crack on, maybe with both methods running parrallel.

 

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  • 3 weeks later...

Great work so far on the silicone moulds, I'm also getting into resin casting myself. The problem you have with the air bubbles affecting the Resin I'm certain is down to the mould design. I'd recommend adding a runner tube to any future moulds that you make, feeding resin to the pattern cavity from the bottom, allowing air to escape out of the riser vents. I've attached a picture of a ram pattern from work to help explain what I mean. I've censored any information that may be deemed sensitive by the company. 

 

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Although this is an industrial pattern for producing sand moulds for Casting Iron, the basic principles are transferrable. The runner system is visible towards the bottom of the picture on the parting or datum plate, running from the 'cup' at the top, down to the bottom of the cavity. Although its not essential when producing models, I've highlighted the choke point of this casting in the green box. As the name suggests, the choke point is the smallest part of the runner system and restricts the flow of liquid into the cavity, increasing the time taken to fill it, for air to escape and reduce the chance of the core cracking and vapourising before the Iron has set. There is a formulae for working it out but I wouldn't worry about it unless you plan to add cores to your silicone mould.  

 

On this particular pattern there is only one riser, centre top on the pattern and next to the runner cup. I have seen as many as four risers on a single cavity before, though it all depends on how much air you plan to displace. Your best bet is to have a riser in every location you are likely to suffer air pockets. They don't have to be large risers, I use 1.6mm styrene rod as my riser pattern.

 

Something I should also mention is that there is no particular orientation that a mould should have a runner or riser in. If I was to cast a hopper from a Hornby MGR 'HAA' wagon, I would cast it upside down and have the runner and riser like so. This is one of my CDA hoppers I've just stripped, in the picture the red represents the runner (with choke point) and the various green lines are riser tubes to prevent air pockets forming.

 

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It may be worth positioning all the risers at a slight angle and on the corner of the edges of the surfaces chosen, so a pour can be done with one end of the mould raised up, reducing further chances of air bubbles. Just remember that there is nothing wrong with having half a dozen or more risers. The more complex the design, the more risers you may require. 

 

Hope that helps, I'll be following the thread.

 

Jordan

 

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20 hours ago, Bearwood West Yard said:

 

 

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It may be worth positioning all the risers at a slight angle and on the corner of the edges of the surfaces chosen, so a pour can be done with one end of the mould raised up, reducing further chances of air bubbles. Just remember that there is nothing wrong with having half a dozen or more risers. The more complex the design, the more risers you may require. 

 

Hope that helps, I'll be following the thread.

 

Jordan

 

Absolutely spot on Jordan. I too worked in a foundry for a number of years and my next suggestion was to be runners and risers. The only thing with these and resin casting is to remember to keep them as straight as possible as they have to have the resin poked out of them after each cast. Easy enough with a piece of wire, so the red runner should at least be curved rather than a sharp corner if you cannot make it straight.

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Thanks to Jordan's prompting I'm going to take some photo's, next time I'm in the workshop, of a two part mould I use for making a body for the Leek & Manifold transporter wagon. This is cast on end rather than flat, with the two halves clamped together, and the casting is set on the diagonal so that you have one corner as the high point for the riser and the runner is at the lower of the top corners. By pouring slowly, controlled by the choke point, and having a reservoir cup at the top of the runner, the resin runs down one corner of the inside and fills the mould. There is just time to do this before the resin becomes unpourable (does that word exist!) so long as I'm not interupted mid pour! I have a much higher success rate than I ever hoped for with this, in fact I'll tempt fate by saying I can't actually remember my last failure. At the moment I'm staying at my daughters place, a few miles from home, as I normally live on my own, but I visit the workshop every couple of days for an hour or two so will make the photo's a job for my next visit, but don't hold your breath waiting.  I have a suspicion that this may possibly help with this wagon although it would mean making a new mould. 

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Clicking on the photo' will take you to my Flickr page and under "Albums" you should find Resin Casting with these photo's and others with explanatory captions

Phil T. 

Edited by Phil Traxson
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I've just added 4 more photo's to My Flickr "Resin Casting" album to fill some of the gaps between prepping the mould for pouring and the finished casting. Can't show the actual pouring as I haven't enough hands to pour and take photo's. That will have to wait until we are allowed to gather again so some one else can work the camera.

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Excellent work Phil, the results are brilliant. Perfect example of having the mould cavity at an angle as well! 

 

I’ve attached a picture of some new tooling that I unpacked on Monday, ready for commissioning. I couldn’t resist taking a picture to better show how it all fits together. On our Disa machines, we have a chamber that fills with sand and every mould that is pushed out, is patterned on each side. A clever mass production technique so you always have a ‘drag and cope’ on its side.

 

The large plate the patterns are located on is always the datum face. If you were to take the patterns off and stick them back to back, you would have the rough shape of the product, plus the depth of any pattern recessing into the large mounting plate. 
 

The patterns get more interesting than this though. I was working on some earlier that have two discs per mould, with the runner being guided between the two. 

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That makes more sense, it seems you need to have a method to do this, from making the mold to pouring the resin.

 

In regard to the resign, what type are you using?  I'm using a product called Procast, it only has a pot life of 5min, the guy at the shop also said to try Easycast pot life 2min.  I think this is too fast, I could not even put it in a vacuum chamber (if I had one) to get the air bubbles out.

 

Is there a method to mixing so as not to introduce air bubbles.

 

I might butcher my mold to be able to pour the resign in rather than plunging the top part of the mold into the bottom.

 

 

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https://flic.kr/p/2kqCab4

https://flic.kr/p/2kqyd9J

https://flic.kr/p/2kqWxj2

https://flic.kr/p/2kqWxuH

I managed to take some video of pouring some castings by using a tripod to hold the camera. As you will see there is nothing special about mixing. I'll try and put some captions up tomorrow. (or today even!)

I took them a bit late in the day as a tryout. Being a very amateur cameraman who had not really tried this properly before, I now realise that if I had waited until my next spell in the workshop I could probably, perhaps,  have managed to put some sort of commentary on as well. I'll redo the resin label pictures in focus too.

The first video shows my method of mixing and pouring "Fast Cast" polyurethane resin into silicone rubber moulds. The resin is a 50/50 (ish) mix of resin & hardener, once thoroughly mixed you have around 3 minutes to get it into the mould. You will notice that despite beating it to death with a stick there are no air bubbles, a property of these low viscocity resins. The deep mould block is for a railway van body & floor, the resin is poured gently and evenly, using the mixing stick to pour it down and guide it into the mould starting with one corner and allowing it to flow at it's own pace into the mould cavities. The plastic cover plate is then placed over the resin, pushing out the excess, to give a level base making sure not to squeeze it down too hard as if you do air will be drawn back into the casting as you release finger pressure.  The mould next to it is the chassis for the van, same technique again.  The other casting at the top left is a partition to separate the saloons of a coach, parts of which feature in the second video

The second video follows on to the previous one and shows the next mix being poured into the van roof mould, the ends of of the roof are in the undercuts which the resin flows into quite easily if poured gently. the other castings being made are for the brake gear and brake handle(the small moulds) and, out of sight at the top of the picture, the van sole bar/ axlebox castings. The other castings are parts for a coach, sides, ends,and a pair of doors. During this video the van body and chassis, poured previously, can be seen turning opaque and beige colour as they begin to cure.  They can be removed from the mould in an hour or so's time but will be done tomorrow now as dinner awaits.

Edited by Phil Traxson
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Phil

 

Great to see your videos and only sorry that I had missed this topic until today. Of course I have seen your demos many times, right back to the early days. I recall one time at the NEC when you had a crowd around the table and I was at the back trying to explain to others what you were doing as they couldn't see properly. There was a guy there from Skytrex and he said they used exactly the same method and same resin except they were probably producing hundreds more castings than you were.

 

The 7mmNGA are thinking of having a virtual show in June instead of our usual visit to Burton and those videos could be used to remind members that you are now back in business - especially as you are no longer spending most of the time casting for others.

 

Mike

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