Dome Patterns

[jscarmozza]

Good job! Castings always look rough when you shake them out of the sand. I'd like to know how the durafix works out, please keep us posted on your progress. John

[optigman]

Can't say I agree that castings come out of the mold rough. Depends on how well the pattern is made and how the mold is rammed and poured. Something is wrong if your castings are not coming out nice. Don't believe me then take a quick peek at any old caboose stove. I'm sure that with modern technics a finish equal to or better than something from the past should be obtainable.

[Adirondack]

Those castings look like a bad pour. Lots of voids inside, and a general roughness indicate a cold pour, turbulence, excess dross, or some other problem in pouring. You might need a larger gate and feeder as well.

Are the yellow pieces your patterns? If so, I would expect to see a smooth, mirror gloss finish on them.

My 2p.

Try again?

Chris

[Dick_Morris]

I've probably done a couple of hundred pours over the years and I'm still only successful about 2/3 of the time. Although I was happy with the final side rod castings I posted a few weeks ago, they were from the fourth or fifth try with two molds each time. Every pour is a learning experience.

If you decide to throw this effort back into the pot I'd suggest you do some work on your pattern. It's a lot easier to smooth the pattern than to smooth the casting. It appears to me that there are inclusions in the casting from sand that broke away in your mold. There are any number of things that can cause that problem, a couple might be inadequate draft or side surfaces of the pattern that are rough.

Casting can be the source of a lot of enjoyment as well as a lot of frustration. Keep at it, you'll get better.

It's not necessary that every casting be perfect, only that it is suitable for it's intended purpose. The casting in the attached photo looks pretty rough, but it served its purpose as a structural part of a locomotive for a quarter of a million miles. As I keep saying, we're building locomotives, not jewelry.

[k36no4862002]

Thanks for the advice re the patterns and resulting castings.
I will keep going with the castings I have with a good quality file! Then I will stick them together using Durafix and hopefully if this works I can use the Durafix to fill any remaining holes that remain.
The patterns are not my best, there is not enough draft on them and yes they could do with being smoother with more shine!!
I have got 1 more dome to make using the same patterns, the Challenger has 2 of these big domes and I need to shorten the centre pattern before I do the next set.
I think the main problem was the ramming of the sand in the box and then pulling the pattern out of the sand following, so I will spend more time making sure the mold is better before pouring the aluminium. I also had problems with sand sticking to the mould so I need to get some more french chalk as I know that was not covering very well.
I'll post pics of the final result, hopefully by Christmas.

[Dick_Morris]

I use talcum powder (baby powder) as a parting agent, but judging by the ambulance chasing lawyers' adds it may no longer be available.

[k36no4862002]

Update.
OK so I have filed down the 3 pieces and made them look more presentable.
Purchased some Durafix and I have managed to 'weld', 'solder' them together. The following evening I decided that I would use the durafix to fill a couple of dodgy holes in the casting so I can file it back.
Happily working away on the end of the casting . . . then I noticed the the seam joint had a crack in it. Upon closer inspection it would seem that enough heat has moved around 150mm from where I was working to the join sufficient enough for the seam joint to let go.

Have used up 20 sticks of durafix and can report my findings of the product as follows:
When it's set it quite hard to file, as in harder than the surrounding aluminium. Don't reheat the job once it's set as there is a tendancy for the existing joints to fall apart, trying to fill holes is not as easy as the video, I tried to fill a hole and the weight of the solder often fell through if the underside was left unsupported.
On reflection, it does work but I would not use it for large jobs and I would only use one heating for each part.
I'll get these parts welded together now properly and file the welds back once done.
Paul

[Greg_Lewis]

Paul:
Here in the colonies we have a product called JB Weld. Dunno if it's available there. It's a metal-filled two-part epoxy. I've used it to fill defects and make fillets and I like it better than the auto body putty that some folks use for that. JB Weld can be machined, filed and sanded and brought down to a feather edge that blends in perfectly. You might have something like that which would work for some of your needs.

[k36no4862002]

Greg,
We have JB weld in the UK too, but I wanted to have a powder coated finish to go with the expected finish on the rest of the loco.

The powder coating process needs pure metal to work and uses heat to bake it, therefore a non metal glue was not my preferred choice.

Moving on... a friend of mine welded then up for me, plenty of grinding, filing and sanding later... well the pictures show the process...