The Home Machinist!

Hey Harold.

I rigged up a system to weigh the metal with fish scale and a strainer basket from the kitchen.

will look for a reloader scale in my travels.

also sawed the bad part into to get it into the crucible when I get back.

Will put these two bad parts on the shelf to motivate me when I come home.





I believe you guys did mention a learning curve.

Later

_________________
Charlie Pipes
USMC Retired

Project:

2.5 Baldwin 2-4-4 Conversion
1.6 Southern Railway PS-4

Well, from my perspective, you're doing pretty damned well. Everything I've read about foundry work indicates that pouring copper alloys is far more difficult than pouring aluminum or iron. That being the case, while you've had a couple small issues, you appear, at least to me, to have a firm understanding of the issues that are critical. Wish I could speak from a position of experience, but I can not. My only contact with foundry has been as a spectator, albeit for a long time. It's not quite the same as getting one's hands dirty.

Keep the reports coming. You most likely are saving me a lot of future frustration.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

When it comes to scaling metals, I rob my bathroom digital scale for the duration, as it self sets each time. So I weigh the plastic bucket and put my charge in, and deduct the diference. For additions, I have a $12 food scale, that will read to hundreths of an oz in digital. Quite handy for diets and such things as making piece counts by weight. Like how many rivets left in a bag. Or making two part plastic thingies by exact weight.

Bronze alloys are a bit diferent animal than aluminum, and the working properties of getting pourous castings.

If you work with small wieghts of metals, the variations will swing wider. When dealing with say 20lbs of melt, it is easier to hit the desired conditions, since the additions can be small, but much larger than trying to use a jewelry crucibal, to make one part. Been there, wont go back, without precious metals, that I dont do. I think I tried 6 lbs once, and it did not work well, so I would rather go with wild scrap and pig the remainder for next time than do tiny small lots. I try not to 'cook' my scrap several times making pigs and such, as each melting will have a tendancy to degrade the metal in some way. Keep your virgin metal virgin, and add only what revert you need to fill out ingot stock, to assure quality, and consistancy. Dont do a scrap melt and add virgin, it is a waste of money, without promise of success. Better to do the witches brew, separate from the refined formula metals, IMHO.

Just a reminder: you mentioned losing power. Dont ever let a melt freeze up in a crucible. If you lose your blast or run out of fuel, you only have minutes to dump the crucible, or it may split from expanding the frozen metal upon refiring. I have such a crucible with aluminum in it, and I dont know a way to save it, as it is full to the brim. I know the bilge style will crack before it gets half way to temp.

Just some thoughts and wanderings..

_________________
Big Dave

Be Alert! The world needs more Lerts.

That's true of gold alloys. They can be melted a finite number of times before they require refining. The base metals oxidize with each melting, eventually leading to porosity in the resulting castings. For that reason, most jewelers melt only enough to fill the flask, and leave an adequate sprue, which is then reused for the next casting session. That way a good portion of the previously melted gold is used up with each casting session. Otherwise they have to pay for refining gold that was melted unnecessarily.

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

In the section here for internal combustion engines, there is some pics of just cast bronze pcs for an older auto engine. Just stripped from the sand the shapes and layout of the runners sprue, and venting may be of interest to you.

It is labeled 'casting', and provides some emperical knowledge from a favored semi-pro caster.

_________________
Big Dave

Be Alert! The world needs more Lerts.

Rethinking everything while on travel. How long should the run be to help trap sand?

_________________
Charlie Pipes
USMC Retired

Project:

2.5 Baldwin 2-4-4 Conversion
1.6 Southern Railway PS-4

It is awkward in the explaination, and perhaps hard to visualize.. What you have done so far is right on in most respects. As I said before, the diference now is only in the tweeking of process, as you learn to judge how to control the metals. ( There is no wrong way at this point, only things that work better).

To try to describe this again, look at your pouring cup, that is elevated, in the coffee can. As you pour metal in, some grains may be disturbed and pulled along with the metal. as you make the turn to flow to the runner for the casting, there should be a trap, a widening and deepening of the runner, to allow errant sand grains to settle. In most designs of molds, this can happen in the feed runner too, keeping the 'flaws' of sand grains out of the bottom of the mold. Most casters cast things face down, so that a final cleaning of the mold can produce the best impression. The trap is no more that a cup shape that has two characteristics of note. It provides a widening to slow the metal flow temporarily, and it forces the metal to rise over the hard edge of the cup, that will separate any sand grains carried at that point. Cut in runners that are rough and not slicked over, can be a problem, so attention must be paid to not generate loose sand, able to travel to the mold. That is why runners should end with a upswing and taper or narrowing to slightly choke the metal at that point. That (riffle) effect again will catch any grains.

As you can gather, we are far down the road for good castings, and this is picking fly poop from the pepper. It is details to be aware of, that will allow better and finer castings, rather than a blob of metal to chew a shape out of. Done well, you will know the satisfaction of the first fine casting. You are almost there, and I anticipate your success.

_________________
Big Dave

Be Alert! The world needs more Lerts.

Charlie,
I'm sure everyone here would like to see the image you sent me of your driver pattern (hint, hint).

_________________
Dan Watson
Building IC mikado in 1.5" scale

There will be no withholding of images.

How 'bout it, Charlie?

Harold

_________________
Wise people talk because they have something to say. Fools talk because they have to say something.

Sitting in a slightly boring hotel weekend before last I took a 2D drawing out and went about converting it to 3D.




As I am working with AutoCAD 2002 the process is rather dated along with my inability. There is no auto process to convert. The spokes are an example of the hardest to do as they are not square in any plane.

These photo show the method I followed. I was not working to any detail level. Only a rough order effort to upload to the Shapeways Website for a price quote.

First I worked on the concept of a two part pattern to be mounted on the front and back of a match plate. secondly it would be a complete pattern set made by the Rapid Prototype modeling method.



Inititail effort was on the outer rim models making both of them hollow to cut the cost of the models. On RP work you pay for the Cubic Centimeter for the material. Hollow is cheaper.





I quickly came to the conclusion it is easer to draw the various asemblies and stick them together on the centerline. First was the rims. Then one spoke that I pasted in 17 times. Then the hub and counter weight. Nothing is bonded together or radius for joints in at this point. The AutoCAD 2002 does not do filiting very well and if I went this route I would fillet the patterns with wax



At the end of the day I have a rough order of magantude on cost as being somewhere around 350.00 each for the two different sizes for the drivers. Cost is a little prohibitive at this point. Needing only two heavy drivers and four light ones this project, while a good learning experiance on CAD, will go in the recycle bin for now. I am talking to a modeler in Florida who may have 73 inch drivers that I can use as a casting pattern. While they are not exactly as the Fitt Drawing show, they do match the PS-4 in the Smithsonian. This engine does not have the webbng between the spokes.




If the drivers in Florida do not work out i may have to pursue the pattern route.

If I do I will start from scratch to cover some of the issues that Trainman showed me in my drawings.

_________________
Charlie Pipes
USMC Retired

Project:

2.5 Baldwin 2-4-4 Conversion
1.6 Southern Railway PS-4

In my reading I have come across the act of brushing or spraying graphite onto the mold surface to help metal flow into thin areas of the casting.

Can anyone elaborate on the pros and cons of this? Is this possible with the oil bassed sands and if used what effects does it have on the sand for the next mold?

_________________
Charlie Pipes
USMC Retired

Project:

2.5 Baldwin 2-4-4 Conversion
1.6 Southern Railway PS-4

Back home for a few weeks.

Family was so glad to see me they gave me a new toy for the shop. Sand blasting cabinet next.



I have managed to repair the flask that was burned badly in my metal run out experiance. I have also came up with a spring clamp method to hold them down next time



Last but not least after getting guidance from Trainman on cores I am drawing up the cores for the journal boxes and getting ready to mount them on match plates



Still curious if anyone has used graphite for thin castings?

_________________
Charlie Pipes
USMC Retired

Project:

2.5 Baldwin 2-4-4 Conversion
1.6 Southern Railway PS-4