Castings trouble machining ??

[david newman 9Participant @davidnewman9]

Just started a new project, got a set of castings from well known supplier and the gun metal castings are to me unmachineable, ruined two endmills and the lathe tools are blunt in seconds. Looks like these castings are impregnated with sand . I can't take deep cuts as they are fairly near to size, so in the bin they've gone, I will make them from some hard brass I have. Never in 50 odd years have been beaten like this. Anyone else had similar problems ? David

ary

[david newman 9Participant @davidnewman9]

[JasonBModerator @jasonb]

I had it once on a statioary engine. The cylinder was the worse get part way along the bore, hit a pocket of sand and the tool goes blunt instantly.

Had it several times with iron castings also but that was just chilling

Don't put them in the bin, get the supplier to change or at least refund as the replacements may be no better

J

Edited By JasonB on 05/07/2012 20:32:18

[John CoatesParticipant @johncoates48577]

If the surfaces you want to machine are flat can you get them to a shaper?

They seem to be able to deal with very tough jobs. I've changed over to using mine whenever I can because they produce wonderful flat surfaces compared to all my milling attempts with none of those swirls that milling seems to leave

[Phil H 1Participant @philh1]

David,

I have not had the same problem as you but I have had other problems with castings. For example, I recently bought some locomotive main horns from a well known supplier and the quality was shocking. The metal was fine but the triangular webs down both sides were inconsistent and way over thickness. My solution was to simply machine the webs away completely.

I am also looking at alternatives such as scratch built silver soldered fabrications.

Phil H

[LambtonParticipant @lambton]

Send them back!

Too many suppliers of highly priced castings send out substandard parts knowing that model engineers are resourceful and capable of "getting round" problems. At the high prices charged they should put in proper quality controls and not send out poor components. I have had lots of experience of receiving, quite frankly, rubbish parts in exchange for my hard earned cash.

We should all make a point of always returning faulty parts this is the only way the message will get home.

[KWILParticipant @kwil]

Phil, why did you not machine the triangular webs to the required thickness? I have machined them from solid before.

As regards sending out poor castings, perhaps they cannot recognise poor castings and are merely selling whatever the foundry sends them, based upon the seller's patterns. Always return poor castings or those you hit sand or large chilled areas. The real problem is the foundry does not allow the castings to cool in the sand, kick the castings out whilst they are still red and wonder why they are chilled.

[nigel jones 5Participant @nigeljones5]

I just tried machining some old brake block castings – nothing short of diamond tip will touch them. Theres hard, then theres too hard!

[Sub MandrelParticipant @submandrel]

Reeves will replace, but will ask for receipt and want you to request change quickly

My advice is check castings as soon as you get home – in the shop its very easy to overlook a dished flywheel or casting that is rough or incomplete.

Neil

[Phil H 1Participant @philh1]

Posted by KWIL on 06/07/2012 18:43:03:

Phil, why did you not machine the triangular webs to the required thickness? I have machined them from solid before.

I tried that approach with one side of the horns but with a 1/8" diameter end mill (1/16" rad) the corners didn't look right at all. Also, the design uses 3/32" rivets which are way over scale size (31/2" gauge). So if the rivet heads look daft – I thought – why bother with the webs? In addition, the engine design uses Stephensons gear hiding one set of horns, the boiler ashpan hides the second set of horns and the valve spindle and gear hides the third set of horns.

I think (my view anyway) machining from solid would be ok at say 5" gauge with 1/16 rivets.

Do you have a picture of your machined versions?

Phil H

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