Do you have a press?

[NormanV]

Hi, I am looking for someone near to Skegness in Lincolnshire who may be able to help me. I have made an aluminium casting that has warped. I think that it would be possible to straighten it using a press. Is there anybody in my locality who would be prepared to help?  I could still use it but it would entail removing quite a lot of metal in order to achieve a flat surface, if it could be straightened it would save a huge amount of work. It measures 24" x 5" x 1.5"
If you think that you could help please send me a PM.
Thanks, Norman

[awemawson]

Happy to do it Norman but I only fulfill one of your criteria

Can you not place it on a bit of RSJ or similar, spaced off by an inch or so by packing at the ends, and apply a G clamp to the middle ?

[NormanV]

Unfortunately I don't have a piece of RSJ. But it does give me a reason to visit my local scrap yard to see if they have a piece. It will always come in handy as an anvil.
Norman

[awemawson]

Stout piece of timber would probably do it as well

[stig]

I have a 20 ton press thats got 2ft between the rails. I'm in Mansfield Woodhouse in notts which isnt quite on your doorstep. if you have no other options I dont mind helping out

[Pete W.]

Hi there, all,

Is it OK to straighten this casting cold or should it be heated/warmed-up?  It would be a shame to crack it.  On the other hand, once straightened, you'd want it to stay straight!

I suppose that in industry the foundry would know fairly exactly what alloy they'd used but if Norman has cast this item himself in the backyard, the alloy composition might not be so well known.

I've never seen any comments about machining aluminium alloys releasing stresses and causing warping like it often does in steel or cast iron - has any reader experienced it? 

[awemawson]

Norman,

post me a chunk of the sprue and I'll run an analysis on my Analloy Alloy Analyser if you like

[NormanV]

Stig, thank you for your offer, 75 miles, probably a bit too far.
Pete, I hadn't thought about it cracking, I sawed half way through the sprue and then gave it a tap with a hammer. That knocked it off easily! It seemed too easy to me.
The alloy is a mixture of car wheels and gearbox casings. It would be interesting to see what the alloy is Andrew, I will post you a piece.
I am melting some more at the moment for my next casting, fortunately this one is not so critical. I'll post a picture when it is done.
Thanks everybody.
Norman

[awemawson]

The car wheels at least would have been heat treated - probably 'solution treated', not so sure about the gear boxes - probably not I suspect. I'll warn the post man

[NormanV]

I've just taken the second casting out of the mould, this one was slightly smaller than the previous one, 10 lbs. It was an interesting one to cast, I used one of Dave Gingery's ideas to save machining and cast it with a steel tube to form the seating for the same tube on the finished item. I blackened the tube with soot from a candle and it released quite easily with a little persuasion from a club hammer.
MDF is not a good material for the flask. as I was removing the sand it fell apart due to the heat and moisture. I suppose it did the job it was only intended for a once only cast.
There is a large shrink cavity in the bottom of it but that does not affect it at all.
All in all I am very pleased. I have to go to buy a new angle grinder so that I can fettle the castings, my old one burnt out yesterday. Cheap rubbish!

[Manxmodder]

I looks very much like the sink mark is caused by not having a large enough reservoir of metal above the sprue....OZ.

[NormanV]

I am sure that you are right Oz, I did consider building up the sand on top to make the sprue longer to prevent shrinkage happening but decided that it did not matter. In fact I had contemplated making the pattern with a slot down the middle similar to the long casting that I made but thought that it just made one more thing to go wrong. Anyway, I want to build in lots of  mass in order to make it as rigid as possible. I plan to fill the centre with epoxy and mineral filler.
 

[awemawson]

Norman,

Your alloy sample checks out as follows:

Aluminium :  90.40%
Silicon :         7.57%
Iron :            0.33%
Copper :       0.28%
Manganese : 0.02%
Magnesium : 1.19%
Chromium :   0.00%
Zinc :            0.01%
Lead :          0.00%
Lithium :       0.00%

Nearest commercial alloy to that is LM25

[NormanV]

Thank you Andrew.

[Pete W.]

Norman,

Your alloy sample checks out as follows:

Aluminium :  90.40%
Silicon :         7.57%
Iron :            0.33%
Copper :       0.28%
Manganese : 0.02%
Magnesium : 1.19%
Chromium :   0.00%
Zinc :            0.01%
Lead :          0.00%
Lithium :       0.00%

Nearest commercial alloy to that is LM25

                                   

[Manxmodder]

Norman, Are the castings for a homemade lathe?
...OZ.

[NormanV]

Not a lathe but a vertical milling machine. I am using some of Dave Gingery's ideas combined with my own ideas. I am hoping to build something that is more rigid than his designs. It's taken me a while to get set up again for casting but I seem to be there now.

[Dawai]

If it was a "steel" or iron.. you heat one side with a rosebud, throw water onto it.  It'll draw up.. I used to do shafts like that.

Yeah.. good thing you don't live next door.. I got one press 5hp, 3phase that explodes aluminum things till you learn not to put them in there. THE HSM-Metal meet inspired C-press manual one I dearly love.

Cooling warps, as does webs, different thicknesses, or leaving sand on one side in eager anticipation digging it out too quick?? used to be the auto rotors cast in Chattanooga Tn, had sand on one side where they shook them out? a hard-soft spot unless annealed and retempered.  (learned this by cross drilling hot rod discs)

Hang in there friend, things, times are a changing.

[NormanV]

I have cast another one, left it in the sand for a lot longer and I am pleased to report that it has come out straight. Unfortunately I had some sand break away so it means that I have some work to do with the angle grinder but it is going to be ok.
Norman