Mark's First investment casting

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dnalot

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Mark's Lost Resin Casting or Old fart learns new tricks.

I have been doing sand casting and lost foam casting for awhile and that works out well for larger parts. But for smaller parts lost wax or plastic works better. I could only do the sand casting when the weather permitted as it needed to be done outdoors on a dry day. I hope to be able to do this bench top investment casting all indoors.

Having sold my 1950 MGTD I found myself with some money burning a hole in my pocket. So I started looking at 3D printers and whatever else was needed to try and do some lost “Resin” casting. Resin printers are now very cheap and they give incredible detail. Today you can get resins that are strong and flexible, resins that can take up to 400 degrees F and resins made for casting that can be burned out cleanly.

To kick off this new adventure I bough an Anycubic Mono resin printer. This is my first 3D printer so I spent hours watching you-tube videos to learn the basics. The first parts I will be making are for an upcoming build. I quickly drew up the parts in Draftsight and then proceeded to make a 3D object in Rhinoceros version 5. And that is where I came to an abrupt stop. Its been years since I used the program and I'm fumbling around trying to relearn it. So I decided sense I was starting over I might as well learn a new program. I will be trying Fusion 360.

So I made a kiln, learned how to use Fusion 360, bought and learned how to use a 3D resin printer and now its show time. I used Siraya Tech Cast resin. It is a wax based resin made for investment casting and is one of the lesser cost resins of this type (but is highly rated). I am simply astonished at the detail my cheap printer and budget resin produced. I used Prestige Optima investment powder. It is formulated for use with 3D printed resin parts.

Despite a comedy of errors My first attempt came out far better than I expected. My impatience was the leading cause of my problems. After waiting weeks for a vacuum chamber I ordered I tried to improvise using a small trashcan. I tested it several times without any problems but when it came time to use it for real it failed. When mixing the investment powder you first put the bowl of plaster in the chamber to remove the air from the mixture. And then after pouring the plaster into the flask you vacuum again. That is where the can collapsed. As I was not expecting to much from this first attempt I went ahead and did the burn-out and pour (brass).

My main failure was tiny little balls of metal all over the parts and some air bubbles blocking the smallest of holes in the parts from filling with plaster. Another mistake was applying the vacuum to the flask to soon during the pour. And my flask cooled down to much before I poured. Despite my problems my parts turned out very well I think. Now I will measure the parts to find out how much shrinkage has affected their size. With that info I can make adjustments to my printed part size to compensate.

I made a considerable investment setting up for this (no pun intended). Now I just need to refine my methods and get my equipment sorted out. For me bench top casting is now a reality. I will be keeping this tree of parts as a reminder of the adventure.

Mark T

Bent trashcan.jpg

Manifold.jpg

parts spured.jpg

Cast parts 1.jpg

Cast parts 2.jpg
 

Scott_M

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Hi Mark
Very nice for the first go. I like the collapsed trash can :)
So how did the burnout go in your new kiln/furnace ? Was your exhaust hole big enough ? Smoke, fumes, residue?
The parts do look good, even with you getting in your own way :oops:

Nicely done !! 👍

Scott
 

abby

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Hi Mark , you have had excellent results for a first attempt !
The little balls sticking to the castings are , as you know , are caused by air bubbles.
The bubbles can be held in place by static and are very difficult to move even with good vacuum and vibration.
They resultant metal spheres are very annoying especially in the case of figure sculptures where a tiny sphere in an eye can be difficult to remove without damage.
I found the cure to be investment mix water temperature.
Dan.
 

dnalot

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So how did the burnout go in your new kiln/furnace ?

Good news bad news. I added a small aquarium air pump that feeds air into the bottom of the furnace and I enlarged the hole in the top a little. The hood did a great job of removing the steam and then the smoke and there was very little smell in the shop. The burn out was very clean, I saw no indication of any residue from the resin patterns. The bad news was the element had to many turns to the coil and so were to closely spaced so the wire got to hot and escaped the pins that held it in place. I am in the prosses of installing a new one with less turns and dropping the voltage to 120 Volts. The original element was 3300 watts and the new one is 2000 watts. I have also replaced the original PID controller with one that has very good documentation. Once I get things sorted out and running properly I will update the Kiln's build page. You should have heard the BANG the trash can made when it collapsed.

Mark T
 
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dnalot

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I found the cure to be investment mix water temperature.

Do tell, I used cold water hoping it would extend the time I had to work. I just completed construction of a vibration table. I am a little hesitant to use it on the flask as I worry about dislodging the part from the tree. I have a long way to go figuring out what works and what doesn't.
 

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Great first try. I'm building up to this myself and have just purchased a resin printer. Next up will be a vacuum chamber, table-top burnout kiln and table-top furnace.

I do have a question for those in the know.
All the videos I've watched on this process seem to show the printed parts being seperately attached to wax sprues/tree. Would it not be better to print the sprues and patterns as one piece?
 

abby

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Investment powders have a worktime and it is very important that the manufacturers stated worktime is adhered to.
The moulds are subjected to great stress during the de-waxing and burn out stages of heating.
The expansion and contraction, that would cause straight plaster of paris (the base of block investment moulds) to crack, is controlled by the addition of very fine, carefully chosen refractory minerals.
If your filled flask is allowed to stand for longer than the stated time the minerals will start to settle and this can definitely result in a weakened mould.
During my learning curve I had many moulds with hairline cracks and I have had the lower half of moulds give way under the pressure of 27"Hg vacuum.
Most investment powders give a gloss over time as 12 minutes at a temperature of 20°C with mixing under vacuum for 4 minutes.
However to achieve this your mix water will need to be at around 45°C because of the heat loss due to vacuuming.
At 45°C the water in the mix will boil and this will remove the annoying air bubbles.
You will also get moulds that can stand the stress without failing.
Imagine the internals of this mould once the wax has gone,

DSCF5022.jpg

For the sake of economy every posible bit of room has been filled with a wax pattern leaving where possible 1/4" between them , with the wax gone it is a honeycomb that has to be heated up to 725°C without spalling or crumbling even when molten metal at up to 1200°C is sucked in by the surrounding vacuum.
Any cracks would prevent the vacuum needed to ensure every casting is complete - so stick to the recommended mixing routine.
Dan.
 

dnalot

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Investment powders have a worktime

A lot to chew on there Abby. I need to organize my equipment into a smaller well organized area. I am wasting time walking about. Like everything else practice, practice, practice. I am using an old vacuum pump I have been using for vacuum bagging composites for 20 years. I think it is to slow for this use so I am looking at buying a new pump.

Mark T
 

ajoeiam

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A lot to chew on there Abby. I need to organize my equipment into a smaller well organized area. I am wasting time walking about. Like everything else practice, practice, practice. I am using an old vacuum pump I have been using for vacuum bagging composites for 20 years. I think it is to slow for this use so I am looking at buying a new pump.

Mark T
Hopefully not hijacking the thread - - but - - - where are you looking for vacuum pump(s)?

I'm finding them devilish hard to find - - - and pricey!!!!!!!!!!!!
 

dnalot

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where are you looking for vacuum pump(s)?

I have been looking at this one on Amazon

Pump

Not certain I really need it so will wait till I have a little more experience using the one I have. My vacuum chamber arrives today and I have been told if I can boil a cup of water in a minute my pump will do the job. We will see.

Mark T
 

ajoeiam

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I have been looking at this one on Amazon

Pump

Not certain I really need it so will wait till I have a little more experience using the one I have. My vacuum chamber arrives today and I have been told if I can boil a cup of water in a minute my pump will do the job. We will see.

Mark T
I'm looking at vacuum pumps for at least a couple different projects.
Thanks for the tip.
Any ideas as to the cfm and 'pressure' you need for your setup?
 

abby

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For investment casting work, vacuum is required during the powder/water mixing stage, and suitable vacuum pump should be capable of reaching a minimum 27"Hg well before the the 4 minute mixing time is finished.
Filled moulds need to be fully vacuumed in less than 2 minutes
It follows that the pump requirements will depend on the capacity of your mixing facility.
If you are casting with vacuum assistance you will also require at least 27"Hg but the investment is only very slightly porous
The pump does not need to be large , many vehicles have vacuum assisted braking with a fan belt driven vac pump, try your auto breakers yard.
Some fridges have compressors which may also work as vac pumps.
The quoted times are typical of most plaster based investment powders.
Dan.
 

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For investment casting work, vacuum is required during the powder/water mixing stage, and suitable vacuum pump should be capable of reaching a minimum 27"Hg well before the the 4 minute mixing time is finished.
Filled moulds need to be fully vacuumed in less than 2 minutes
It follows that the pump requirements will depend on the capacity of your mixing facility.
If you are casting with vacuum assistance you will also require at least 27"Hg but the investment is only very slightly porous
The pump does not need to be large , many vehicles have vacuum assisted braking with a fan belt driven vac pump, try your auto breakers yard.
Some fridges have compressors which may also work as vac pumps.
The quoted times are typical of most plaster based investment powders.
Dan.
Not sure what cars might use vacuum pumps but diesel engined vehicles will have them as there is no manifold pressure to tap into due to the lack of a butterfly valve or throttle plate.
 

dnalot

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How strong a vacuum can one get with a venturi vacuum setup

I have used one and it could maintain very strong vacuum but with low volume of air movement. I would use a large piston pump to draw out the majority of the air and establish a vacuum and then switch to the venturi pump to sustain the vacuum for a long period of time. I don't know if there are practical larger versions of venturi pumps.

Mark
 

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Mark's Lost Resin Casting or Old fart learns new tricks.

I have been doing sand casting and lost foam casting for awhile and that works out well for larger parts. But for smaller parts lost wax or plastic works better. I could only do the sand casting when the weather permitted as it needed to be done outdoors on a dry day. I hope to be able to do this bench top investment casting all indoors.

Having sold my 1950 MGTD I found myself with some money burning a hole in my pocket. So I started looking at 3D printers and whatever else was needed to try and do some lost “Resin” casting. Resin printers are now very cheap and they give incredible detail. Today you can get resins that are strong and flexible, resins that can take up to 400 degrees F and resins made for casting that can be burned out cleanly.

To kick off this new adventure I bough an Anycubic Mono resin printer. This is my first 3D printer so I spent hours watching you-tube videos to learn the basics. The first parts I will be making are for an upcoming build. I quickly drew up the parts in Draftsight and then proceeded to make a 3D object in Rhinoceros version 5. And that is where I came to an abrupt stop. Its been years since I used the program and I'm fumbling around trying to relearn it. So I decided sense I was starting over I might as well learn a new program. I will be trying Fusion 360.

So I made a kiln, learned how to use Fusion 360, bought and learned how to use a 3D resin printer and now its show time. I used Siraya Tech Cast resin. It is a wax based resin made for investment casting and is one of the lesser cost resins of this type (but is highly rated). I am simply astonished at the detail my cheap printer and budget resin produced. I used Prestige Optima investment powder. It is formulated for use with 3D printed resin parts.

Despite a comedy of errors My first attempt came out far better than I expected. My impatience was the leading cause of my problems. After waiting weeks for a vacuum chamber I ordered I tried to improvise using a small trashcan. I tested it several times without any problems but when it came time to use it for real it failed. When mixing the investment powder you first put the bowl of plaster in the chamber to remove the air from the mixture. And then after pouring the plaster into the flask you vacuum again. That is where the can collapsed. As I was not expecting to much from this first attempt I went ahead and did the burn-out and pour (brass).

My main failure was tiny little balls of metal all over the parts and some air bubbles blocking the smallest of holes in the parts from filling with plaster. Another mistake was applying the vacuum to the flask to soon during the pour. And my flask cooled down to much before I poured. Despite my problems my parts turned out very well I think. Now I will measure the parts to find out how much shrinkage has affected their size. With that info I can make adjustments to my printed part size to compensate.

I made a considerable investment setting up for this (no pun intended). Now I just need to refine my methods and get my equipment sorted out. For me bench top casting is now a reality. I will be keeping this tree of parts as a reminder of the adventure.

Mark T

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I worked 30 yrs in aerospace and investment aluminum casting were the bread and butter of our assemblies. I would happy to get these parts from our casters. I do suggest you look into the approach of coating the wax with plaster and build up thickness. There are some Youtube videos on doing this for art sculptures. Saves on the expensive plaster that isn't the stuff hobbyist purchase, need to take higher temperatures without cracking. With a brush on the first layer can seek out and remove air bubbles. And a quick look on later layers. To get more strength for pouring sand around the plaster works. This is from those videos. We got end products.
 

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Any idea as to the specs on said vacuum pumps?
Not sure, I have a couple of Fords with diesels and I'm pretty sure they won't show any specs in the manuals but I'll take a look. I'll also see if I have a vacuum guage I could test one with.
 

TSutrina

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I have used one and it could maintain very strong vacuum but with low volume of air movement. I would use a large piston pump to draw out the majority of the air and establish a vacuum and then switch to the venturi pump to sustain the vacuum for a long period of time. I don't know if there are practical larger versions of venturi pumps.

Mark
They are called a steam ejectors and have been around in the chemistry industry and power plants to remove air from the condensers for a century or more. The biggest is used I assume even today to test rocket engines at very high altitudes up to very close to space. Those ejectors are multi story building with a huge boiler and use water to condense the steam.
 

Joe

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Not sure, I have a couple of Fords with diesels and I'm pretty sure they won't show any specs in the manuals but I'll take a look. I'll also see if I have a vacuum guage I could test one with.
So the manual does have a vacuum system test section. The tests require 18-21 inches of Hg at the idle. Not sure if that helps but it is maybe a starting point.
 

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