1/8 Rider Ericsson - Home build

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Pat
Many thanks for the information on Petrobond and its equivalents.
Personally, I have remixed the burnt sand back into the mix and Luckygen of Youtube also says he does the same. I am guessing I may need to rejuvenate my batch but I will try on a sample bucketful first.
I do not have a muller as I really am only a casual foundry enthusiast and that often means I never really get to master the art but I do finally get what want when there is a project on the go .
All I do is rub the whole batch of sand through a garden sieve with quite small mesh and hand mix it together.
Cheer
Rich

 

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Today was 'bitting and bobbing' day.
The small brass parts have been invested and vacuumed to reduce entrained bubbles (not always successful I add).
The baseplate was invested in an old butter carton, something I have not done before. I was hoping to remove the print after the plaster set but there is no way it's coming out so I will burn it out and do a combined investment and sand casting. Not something I have tried before but Myfordboy has demonstrated the technique.
All the investment plaster moulds need to rest overnight before entering the burn out schedule.
In the meantime I started machining the flywheel which was tricky to hold and my chuck does not open wide enough so I clamped it to a diy mini face plate and did my best to get it running true which is tricky on a casting.
Very small cuts were required to ensure it didn't disturb the alignment but the wheel is now mounted on its spindle.

 

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Not a lot to report today as I visited my Mum. She's 91 but still independent and active.
This afternoon I started to burn out the PLA patterns.
Prior to putting the cylindrical flasks in the kiln/furnace I now burn out the sprue with a blowtorch to aid breathing of the pattern.
I say 'breathing', the fact is on two occasions I had flasks explode and because I simply have ceramic wool over the furnace this offered no resistance and the workshop ceiling was covered in plaster debris. In fact the whole workshop was covered with bits.
I am guessing moisture had found its way into the pattern during vacuuming of the plaster and then built up vapour pressure in the pattern itself.
I tend to print patterns with low infill to reduce the amount of ash and allow the pattern to flex more easily during melting. Small prints are not usually any problem.
The moulds are too hot to show just now after the 4 hour process and will be examined in the morning.

 

[GreenTwin]

I seem to recall some folks warning that plain plaster of paris can contain water trapped internally and explode.

I guess if the pattern itself had a bit of moisture in it, that could also cause problems, expecially if eveything got very hot, and then the moisture was released from a pocket somewhere.

I have seen people use concrete as a refractory for a funace, and that will explode (there are some videos out there of this happening).

People tell me constantly to never pour over concrete, but it depends on the concrete.
I have tons of photos of where I spilled aluminim, brass/bronze, and cast iron on my concrete, and have never had an explosion.
Some concrete will explode if you spill molten metal on it, so don't assume that spilling molten metal on bare concrete is necessarily a good or safe thing.

From a practical standpoint, if you have a nice concrete driveway (I don't have very good concrete), then you don't want to ruin it by spilling molten metal on it.

And steel ingot molds can have residual surface moisture on them, and those must be taken up to perhaps 500 F, else they tend to eject molten metal violently in your face (don't ask me how I know this, but I have some good burn photos if anyone is into backyard casting gore).

The low infill is a great idea, and speeds up printing a lot too.

I have been very impressed with the lost-PLA process, and I have seen it work very well with both aluminum and gray iron.

How difficult is the breakout?

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Breakout couldn't be easier. After quenching in water the refractory simply disintegrates and goes like soft putty. I just use an old toothbrush and water to finish them off.

 

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Well, not an encouraging day.
On cooling I inspected the open moulded baseplate. It was a pretty clean burnout as you can see but a couple of very cracks and flakes on the thinner sides. Not too serious.
I am not convinced the small lettering will fill though due to surface tension.
Second fail was on a flask cast which I decided to vacuum test and due to lack of support the base failed under the vacuum and pulled free. Oh well!

 

[GreenTwin]

Seems like you could band or clamp the mold to keep the cracks closed long enough to pour.

The only way to learn how to cast things is to have failures.
I could win some sort of major failure award for my past blunders.

I would guess the letters would fill, depending on your pour temperature.
I generally pour aluminum at 1,350 F.

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[creast]

Well, things couldn't get worse as I dropped the damn mould and broke it badly so it's start again.
This means printing another base and so I have decided to go back to petrobond casting so at least I have a pattern for future errors!
This will not have the lettering which I may add as a separate lost PLA plaque on the base.
However, The lost PLA linkages came out good. Just a few micro bubbles which is quite normal and knock off easily.
Attached is also short video showing how permeable this plaster is.

 

[GreenTwin]

Luckily resin-bound molds are quite sturdy, and they can be transported long distances in a car without damage, since they cure in a hard state.

I guess that is one downside to the lost-anything methods, is that you lose the pattern with each casting.
Its a fair trade if you need the accuracy, have a very complex shape, or can make multiple castings on a tree.

The parts look great.
Are those bronze? They look more like brass.

I have seen folks 3D print their own letters, but a plaque with letters sounds like an every better idea, since that would fix the letters and keep them from shifting around or getting glued on crooked.

The video is very interesting.
I was not sure exactly how that was done.

I have seen some centrifuge demonstrations, which I guess accomplishes about the same thing.

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[creast]

Pat,
The parts are brass as per the plans.
The video shows just how well the plaster can allow a vacuum to pull the melt in.
Yes it is a more compact method than centrifugal equipment.
At the moment I get away with vacuuming from the base but I hope to use perforated flasks soon. This will improve fill but will require new vacuum vessel.
The cheap Chinese vac pump works ok but it would be better with one that pulls a bit harder . I work on a skinflint budget

 

[GreenTwin]

I envy the convenience of a tabletop furnace.
If they did iron, I would definitely build or buy one one.
I have seen the smaller induction units, but they are very complex, and so would be prone to breaking down.

My mini iron furnace will be more convenient, but I still plan on using outdoors.
I guess I could build an outdoor fireprooof metal box to contain the mini furnace, and use a powered respirator to avoid carbon monoxide poisoning.

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The revised base pattern was printed with ingates and not sanded or filled for the first cast. I had problems with the sand core in the boss and it started to break away when removing the pattern so I reinserted the pattern and pressed some screws into the sand.
It was only partially successful but this bore detail has to be machined anyway,
Likewise some sand lift at the base of the circular boss too.
There are a few but minor anomalies of surface skin on and near the square boss.
I admit I went a bid mad with riser feeders but I was wary of the thick and thin areas.
All in all its a workable part and the finished part will be painted.

 

[creast]

I have just noticed that my last photos when viewed and zoomed seem to zoom in massively. Any ideas how to prevent this?
Should I check image size etc or attach in a different way?

 

[GreenTwin]

The photos look fine, I don't see a problem.

The pour temperature looks to be on the money.
Nice shiny finish with no burning into the sand.

Everyone has their favorite sprue/runner/gate configuration.
I will mention how I would do it for comparison purposes.

I would use a U-shaped runner with sprue at the center of the U.

One knife gate at the center of the pattern on each side (total of 2 knife gates).

Maybe a small riser over that thick square part.

Vents out the high points in the cope to assist with mold fill.

Knife gates would be maybe 2.5" long, 1/4" tall (not sure exactly how thick your piece is, so maybe not so tall).

Looks like you got a very good casting.

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[aka9950202]

Love your work.

Are you using the plans published in the Model engineering magazine?

Will you be making the 3d printed files available?

Cheers

Andrew in Melbourne.

 

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Hi Andrew.
Thank you for your kind comments.
Yes, eventually I will publish the files as I usually do on GrabCad when I have completed the project.
Because I am casting a lot of parts I have to create patterns slightly oversize but I will include finished parts.
I am working from those plans but they are 1/4 scale and mine is 1/8th
Cheers
Rich

 

[creast]

The photos look fine, I don't see a problem.

The pour temperature looks to be on the money.
Nice shiny finish with no burning into the sand.

Everyone has their favorite sprue/runner/gate configuration.
I will mention how I would do it for comparison purposes.

I would use a U-shaped runner with sprue at the center of the U.

One knife gate at the center of the pattern on each side (total of 2 knife gates).

Maybe a small riser over that thick square part.

Vents out the high points in the cope to assist with mold fill.

Knife gates would be maybe 2.5" long, 1/4" tall (not sure exactly how thick your piece is, so maybe not so tall).

Looks like you got a very good casting.

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Pat,
Thanks for the input.
The part is roughly 4x2 inches and the sides 1/4" high. The recessed area is 0.16" thick.

 

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Today I printed the main bracket as a split pattern. Some light sanding but no filler or paint as I am a bit impatient
As usual I got lifting of the Petrobond at the edges...grrrrr. It is so fragile at the edges no matter how hard I ram the damn stuff!
Oh well just a little more flash to file off!
Opening the flasks after casting looked encouraging but as you can see the cope side wasn't great.
Guess a re-cast is in order.

 

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Forgive me Father for I have sinned!
But in sinning I actually got a great result for the Rider crank bracket
Yesterday I spent countless hours revisiting greensand and in the end gave up, sand slightly too moist and evidence of tiny steam bubbles on the drag side. Avoiding the moisture simply made removing the patterns without breakout impossible so I resorted to Petrobond.
Again I had incomplete fill at the exact same point as the first casting.
I modified the patterns to give slightly more draft and printed them off.
This is were I sinned. I simply used one sprue/feeder with an extension to give more head as per Myfordboy.
Now, Olfoundryman on Youtube would scream at me for doing this as it encourages turbulence and air entrainment but I thought if Myfordboy gets such good results then it's worth punt.
I will let the pics speak for themselves

 

[GreenTwin]

Everyone has their favorite casting methods, and while I see a lot of debate online about the "right way" to do it, the fact is that a lot of ways work, and so it is about getting good casting results, and not pleasing someone on youtube.

I am in the John Campbell camp, mainly because my sand is not reuable, and so I have to nail it the first time.
I err on the side of caution, and I don't take chances with iron, since a defect in an iron casting would cost me a lot of time and effort, not to mention expense. I can melt aluminum in 12 minutes. A typical iron melt is 1 hour.

Aluminum seems to be more tolerant of sprue/runner/gate layouts, and it would seem that most anything will work.

I have found iron to be not nearly as forgiving, for whatever reasons.
It is not that easy to get superheat with iron like you can with aluminum, and aluminum seems to be more fluid generally than iron.
I am not sure if the 3X mass of iron (compared with aluminum) causes more turbulence and air entrainment, or what, but the mass may come into play.

Foundry and pattern work has been a lot of fun for me.
It is exciting to see folks casting engine parts.

In the end, the proof is in the pudding, and your pudding looks really good !
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