First casting: opinions sought.

[DonS]

Heya,

This is the first thing I've ever cast and I'm testing out the pressure-casting setup I've put together. Overall, I'm encouraged by the result although there are some flaws. Obviously, I'd like my castings to be perfect and am going to go over my work and attempt improvements...but I'm wondering if the sorts of flaws I've pointed out are unacceptable for a deliverable part. I'm hoping some casters or people who've bought garage kits will chime in with their thoughts. For those who are gracious enough to reply and recognize the part (or the whole from which it came), I respectfully ask that it not named in this thread.

BTW, for anyone who might be concerned, this part is not a recast. I own the original master.

View attachment 36353View attachment 36354

Lastly, I'd like to thank everyone on this board and others who share their invaluable knowledge...without it, I can't imagine what would've come out of that first mold!

 

[XtcofPain]

Heya,

This is the first thing I've ever cast and I'm testing out the pressure-casting setup I've put together. Overall, I'm encouraged by the result although there are some flaws. Obviously, I'd like my castings to be perfect and am going to go over my work and attempt improvements...but I'm wondering if the sorts of flaws I've pointed out are unacceptable for a deliverable part. I'm hoping some casters or people who've bought garage kits will chime in with their thoughts. For those who are gracious enough to reply and recognize the part (or the whole from which it came), I respectfully ask that it not named in this thread.

BTW, for anyone who might be concerned, this part is not a recast. I own the original master.

View attachment 36353View attachment 36354

Lastly, I'd like to thank everyone on this board and others who share their invaluable knowledge...without it, I can't imagine what would've come out of that first mold!

Hi, Are you getting any air bubbles in the piece when you demold it. Normally when i'm casting i place the mold in a pressure container like you stated and sometimes a vibrating pad as this really helps to get the air out of the mold. Are the blemishes such as Where your edge is failing in the pic in the mold or just in the casting. If its just in the casting then i imagine it is because of trapped air. If its in the mold well then your never gonna get a perfect one. I

I hope this helps. I have done quite a bit of molds like th one in your picture so i hope this helps. Also if your using 2 part polyurethane resin make sure the containers you measure out the equal quantities of resin are moisture free as any water can also cause bubbles in the cast. Another handy tip is to pour from a height into the lowest part of the mold and let it fill up rather than sloshing it everywhere. I find this helps make a better cast.


Johnny

 

[DonS]

I was hoping the pressure would be enough but if it isn't, the vibrating pad is an interesting idea. There are some tiny air bubbles in the part near the lowest portion of the mold but really just a very few.

The bad edges are definitely in the casting as the mold is fine in those area. There was some warpage in the part, likely the result of the too-taut rubber bands I used on the mold pulling it slightly out shape (live and learn)...now I'm wondering if the mold being out of shape caused that thin edge to close up to the point where the resin couldn't get in. Hmmm.

Your mention of moisture got me thinking. A few days ago, I filled the mold with water in order establish the amount of resin I'd need. Thought I'd dried it thoroughly but am now wondering if that's really so...the large bubbles I pointed out in the image don't look like air bubbles as much as water droplets.

Many thanks for your reply! I'll definitely try pouring from a height, as you mentioned, and, if need be, rig up some method of vibration.

Cheers,

Don

 

[XtcofPain]

I was hoping the pressure would be enough but if it isn't, the vibrating pad is an interesting idea. There are some tiny air bubbles in the part near the lowest portion of the mold but really just a very few.

The bad edges are definitely in the casting as the mold is fine in those area. There was some warpage in the part, likely the result of the too-taut rubber bands I used on the mold pulling it slightly out shape (live and learn)...now I'm wondering if the mold being out of shape caused that thin edge to close up to the point where the resin couldn't get in. Hmmm.

Your mention of moisture got me thinking. A few days ago, I filled the mold with water in order establish the amount of resin I'd need. Thought I'd dried it thoroughly but am now wondering if that's really so...the large bubbles I pointed out in the image don't look like air bubbles as much as water droplets.

Many thanks for your reply! I'll definitely try pouring from a height, as you mentioned, and, if need be, rig up some method of vibration.

Cheers,

Don

No problem glad i could help. I find that the vibrating pad really helps eliminate the air bubbles. I prefer it to using the vacuum method to be honest. I'd double check about how dry that mold is as well especially after you had water in it as those droplet like formations you mentioned sound like what i said about moisture to me.Sometimes if you have even pin holes in the mold the water can be stored there and when you pour the resin it draws it out. Also i wouldn't recommend using rubber bands as they tend to as you said warp it. I was always taught in college to use duct tape around the seams as it gives a uniform shape throughout. Also if there are any very low points in the mold i sometimes make a needle hole through the silicone in that point as if further allows the air to be released when the resin is poured in and doesn't really damage the mold. I would try some of the other steps first though,

Good luck with it and if i can be of any more help just shout.

Johnny