Thank you for your kind words Green Twin. My miscast defects could probably be repaired but I’ll just likely use this one for machining practice. I won’t stop until I get a couple of good ones. I will definitely use your suggestions. THANK YOU. Norman
Aluminum sand casting for Chenery Gnome Rotary
- Thread starter albd5a
- Start date
Help Support Home Model Engine Machinist Forum:
Roger Taylor
Member
- Joined
- Apr 9, 2023
- Messages
- 19
- Reaction score
- 25
I would use a single, large center sprue with three large gates at 120-deg intervals, so the sprue acts as a riser.
Another option, especially if you get into using bound sand, is to turn the mold on edge, and then you could use a single larger riser at the top of one cylinder, with the sprue feeding a runner into the bottom of one of the cylinders.
.
.
Richard Hed
Well-Known Member
- Joined
- Nov 23, 2018
- Messages
- 2,637
- Reaction score
- 678
That is such a good casting that I would consider filling in the hole with a bit of tigging.
That is the beauty of making your own castings.
If it does not turn out exactly like you want, just ram up another mold and pour again.
.
If it does not turn out exactly like you want, just ram up another mold and pour again.
.
So far my miscast to usable, casting ratio is not very good! I have a feeling maybe it’s a difficult pattern… I do have one crisp completely usable one so far out of about four attempts; a few of my other attempts where porosities or that same shrinkage problem area as before, but they are all very small defects, Really small. I was hoping that somehow they could be just repaired- add on. I don’t have a TIG or a welder but I’m able to braze with MAPP gas if I knew of a solder rod with flux or without flux that would work. Also, this thing is a pretty big heat sink . Would love to repair a couple of them.
Attachments
These photos are in a rather random order, taken during a couple of different casting attempts just thought that some of them were cool looking.
I have a mold, ready to go made up with a large central riser with some spokes going out to the perimeter. However, I kept the other sprue and Riser idea . will try to cast this tomorrow although it’s supposed to rain in the morning. I’m looking for a pattern, sprue riser gate system with a high success rate . right now it’s rather hit or miss. Although, green twins, advice of really enlarging my gates did work. That is my best casting so far; it’s perfect.
Richard Hed
Well-Known Member
- Joined
- Nov 23, 2018
- Messages
- 2,637
- Reaction score
- 678
You're int the USA, your friends or neighbors will have a TIG machine.
I had all sorts of problems when I first attempted to cast aluminum.
I did not understand the process, and so it was trial and error, with lots of error.
I had flask halves separate because I did not use weights on top, aluminum too hot, too cold, sand and slag inclusions, porosity.
You name it, I had problems with it.
Once I figured out what was happening, mainly by listening to Bob Puhakka's videos, and following John Campbell's 10 rules for good castings, my success rate went from perhaps 10% to basically 100%.
Using bound sand with a ceramic mold coat is a game changer too, especially with iron castings, but bound sand is not really necessary with aluminum castings.
Petrobond makes some great castings with aluminum, and it gives an excellent surface finish if you pour at around 1,350 F.
Petrobond can be used with iron, but is subject to mold failures due to the extreme heat, and I don't recommend it.
Your setup is good; you just need to tweek your method, and then I think you will have a very high success rate.
There is nothing quite as fun as pouring molten metal, in my opinion.
It makes my wife a bit nervous, but she has gotten use to the fire show, and she knows I can do it safely.
Edit:
I use a sheet metal heat shield on my pouring shank, and that allows one hand to be within a few inches of the crucible.
Having one hand close to the center of mass of the crucible/molten metal makes it much easier to handle the crucible, and gives a much better fine control over pouring.
Another trick is to use a piece of steel pipe, perhaps 2.5" or 3" diameter, and 1" tall, and place that at the top of the sprue, so that you don't have overflows that can run over and burn the flask.
.
I did not understand the process, and so it was trial and error, with lots of error.
I had flask halves separate because I did not use weights on top, aluminum too hot, too cold, sand and slag inclusions, porosity.
You name it, I had problems with it.
Once I figured out what was happening, mainly by listening to Bob Puhakka's videos, and following John Campbell's 10 rules for good castings, my success rate went from perhaps 10% to basically 100%.
Using bound sand with a ceramic mold coat is a game changer too, especially with iron castings, but bound sand is not really necessary with aluminum castings.
Petrobond makes some great castings with aluminum, and it gives an excellent surface finish if you pour at around 1,350 F.
Petrobond can be used with iron, but is subject to mold failures due to the extreme heat, and I don't recommend it.
Your setup is good; you just need to tweek your method, and then I think you will have a very high success rate.
There is nothing quite as fun as pouring molten metal, in my opinion.
It makes my wife a bit nervous, but she has gotten use to the fire show, and she knows I can do it safely.
Edit:
I use a sheet metal heat shield on my pouring shank, and that allows one hand to be within a few inches of the crucible.
Having one hand close to the center of mass of the crucible/molten metal makes it much easier to handle the crucible, and gives a much better fine control over pouring.
Another trick is to use a piece of steel pipe, perhaps 2.5" or 3" diameter, and 1" tall, and place that at the top of the sprue, so that you don't have overflows that can run over and burn the flask.
.
Last edited:
Before you spend much more time with this part can I suggest taking a look at your pattern. From what I can see the two edges are almost flush with the bases of the cylinder mounting bosses. As these two edges need to be machined it is usual to include a machining allowance. If you were to machine your casting as is then the width of the main body will be less than the diameter of your cylinder bases. If it is not that then your cylinder mounting bosses are too large a diameter which th elack of space for webs seems to suggest..
The bonus of having that extra machining allowance is that your areas of shrinkage may well be limited to what has to be machined off so may not even be a problem with a correctly sized pattern.
And As Pat said earlier those thin gates are cooling fast and not allowing the riser to feed metal back into the part as it cools which is the likely reason for shrinkage.
The bonus of having that extra machining allowance is that your areas of shrinkage may well be limited to what has to be machined off so may not even be a problem with a correctly sized pattern.
And As Pat said earlier those thin gates are cooling fast and not allowing the riser to feed metal back into the part as it cools which is the likely reason for shrinkage.
Attachments
Last edited:
