damn closed it before i could reply with a useful question..... you think boyd would actually sand cast the intakes or valve covers? i think not! they would be machine cut out of billet aluminium, hes not going to spend the extra doller to sand cast them. its cheaper to have a computer knock out 10 an hour.
to build one set, yes billet would be cheaper. any kind of quantity, and sand casting will be cheaper.
how would it be cheaper to sand cast?????? once the program is made for the CNC you just put the chunk on the machine and go.
I've been pricing aluminum plate latley for a CNC project i'm working on. a block big enough to carve valve covers out of would cost $600-700
yeah but the pieces cut off can be remelted to make another chunk right? since when is a chunk of aluminium so expensive? i better start melting pop cans... ill be a rich man!
Do you know anything about machining? How many parts on a production car are CNC machined? Nothing that doesn't have to be, ei. internal engine and transmission parts. Thats because its expensive, casting is far cheaper when you're making any more than a few at a time. A block of aluminum big enough to widdle out valve covers could probably be melted and make 5 or 10 at a time. you obviously don't know what you're talking about, and who the fuck cares how Boyd makes his parts?
why would it need to be such a high grade aluminium???? its a fucking valve cover..... ok what about the billet wheels.... if that was the case then they would cost 10,000??!
i know some- anyway, what about man hours? he would have to pay someone to cast them all. production cars are almost all plastic now and stamped steel. if i knew the answer's i wouldnt have asked in the first place.
Well, a billet is cast and if you look in the racks outside his shop, they are full of pre-cast wheel blanks waiting to be machined. You can cast a valve cover blank and then machine it to add whatever design you want. I like the look of a nice casting myself. Plaster is a good alternative to sand if you want a nice finish and don't want to have to remake the mold every time.
Machining would be difficult on the hollow parts inside such as runners, etc. For this you would put a baked sand core in your mold, which is broken out to get the hollow areas inside the casting. Very simplified explaination, get a book for less than $10, either one on Dave Gingery's books from here http://www.lindsaybks.com/dgjp/index.html or here http://www.backyardmetalcasting.com/ Even if you don't start casting they are interesting to read. Oh, and CNC AIN'T cheap.
it's not like you put a block of aluminum in a machine and 10 minutes later a valve cover comes out, even with the new high speed milling machines you're still looking at an hour per valve cover, plus paying a highly skilled person to program, set-up, run and deburr/finish the part...with casting you pay some schlub to make the forms, and another schlub to pour the aluminum...with large enough production you could easily pump out hundreds of valve covers an hour, verses buying several CNC's that cost a couple hundred grand each to make one valve cover an hour each machine...
Billet = EXPENSIVE I stopped at a exotic metals place while on trip a while back, thought maybe I'd found a place to get some neat stuff. While talking to the guy there was a block of alum. setting on a cart going to someone to whittle out a motorcycle wheel, (maybe 2 if they were super thin, was only about 10" tall) there was an invoice taped to it for $5300.00.
I was just watching the trike episode of Biker Buildoff in the shop while fabbing up my front suspension and they made a mention of one billet wheel they were machining in house that took 50 hours...50 friggin hours for one wheel from a 500 pound block of aluminum...damn that's a lot of money wasted at an average shop rate of 85 dollars an hour if you were to have someone machine it for you...
Don't forget that each one of these covers needs to be set up and finished machined, ie sealing flange and bolt holes, filler hole or whatever.
it gets REAL expensive when you are making a part that requires a lot of surfacing. surfacing is when you program the machine to machine a complex shape, say a typical looking 5 spoke mag wheel. those round spokes will need to be surfaced. first the bulk of the material needs to be removed with ordinary endmills, etc. this point is where most of the stereotypical billet parts are done, very simple squared off shapes, but in surfacing, it's just the start, perhaps 10% of machine time is in roughin out the part. next a rough ball nose endmill will come in and machine the surfaces of the part to within a few thousandths of an inch of the final shape, then the finish ball nose will come in and well, finish the part. this is done by making a whole shitload of very tiny moves, starting at one edge of the part, machining along one horizontal axis, moving up and down as it moves laterally to create an intricate shape, then stepping over a few thousandths, and making another pass, and so on, this process can take many hours for large or complex parts, not to mention the machine memory, it can take hundreds of thousands of lines of information. the end result is a part that only needs very minimal hand finishing, if any, to be a finished part. i work in the tool room of a production shop, we do the special projects, a few surfacing jobs we always have running are medical implants, normally made from forged or formed stainless or titanium, the low volume parts are made by surfacing. a small plate that would fix your jaw or arm can take roughly 4-5 hours of surfacing alone. we also make forming dies to make the formed parts, machined from tool steel, a die block 4"x20" can take a full day(24 hours) or more to surface, but the end result is a part that usually needs no hand work to have a smooth surface. aluminum parts could be machined in about half the time. if you can afford the machines, it's gravy work, a few machines plugging away around the clock @ $75 an hour or more machine rate with minimal human input sends my boss down to Barrett-Jackson every year with a huge wad to blow.
CNC machining takes time, and aluminum is expensive. For starters, lets look at overhead. A decent 2 axis CNC overhead mill will cost in the neighborhood of 40 large. I'm not talkin bargain basement shit here, it needs to work for production, so quality is important. End mills are expensive, and consumable in time. cost to run the machine in electric, large 3 phase motors. also, set up time by a qualifies machine operator is definitely not cheap...and we haven't even begun to make our part yet. A brick of Al large enough to be machined into a valve cover would probably cost around $50, so say $100 for arguement's sake for a set. That means that $80 worth of material ends up a useless chips on the floor...not cost effective Good machinable aluminum, like 6061, is expensive. cheap ass aluminum bricks to be melted down for a casting are considerably cheaper, as it's a much lower grade metal, with far more impuraties in it. This becomes painfully obvious when attempting to TIG weld some cast Al pieces. Also, I don't know if you have any machine experience, but it's not like on American Chopper or whatever in real life. it takes time to run a CNC program, even if you already have the program's events laid out. The piece needs to be indicated on the machine....time consuming shit. quality takes time. some of those wheels you see have 10 or more hours of machine time in them. Valve covers, air cleaners, coil brackets don't have critical dimensions like many CNC pieces get. On my race team, our sloppiest tolerance is +/- .005", those pieces need to be dead on. But there is no difference if one fin on a valve cover is a few thousanth over or under, it just doesn't matter.
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