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Author Topic: cast a rearset bracket  (Read 1963 times)

Offline pacomotorstuff

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Re: cast a rearset bracket
« Reply #10 on: Dec 24, 2017, 15:58:32 »
The problem (for me) is, CNC parts just don't have that "old school" look.  I know some builders who have sandblasted the living shit out of CNC'ed / machined parts to get the correct surface patina, which strikes me as bit like shipping coal to Newcastle...
There is also the design issue - most if not all CNC'ed parts are from billet (I'm talking about aluminum alloys and to a lesser extent, other materials), which exhibit anisotropic - ie., directional mechanical properties due to the extruding process, but a properly poured casting won't - it has isotropic mechanical properties.   CNC'ed stuff has its place and so do cast parts and it's up to us to use both properly and safely.
Getting back to subject line, a nice job - still want to see your engine patterns though.
Have a Merry Xmas and a Happy an Prosperous New Year.
Pat


 

Offline J-Rod10

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Re: cast a rearset bracket
« Reply #11 on: Dec 24, 2017, 23:54:48 »
I supoose it has its place. The OP made mention of casting being quicker than machining. That's a simple part. Billet, it would be thinner, lighter, and stronger. If you like the old school dull look, tumble it.

Online irk miller

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Re: cast a rearset bracket
« Reply #12 on: Dec 25, 2017, 09:53:38 »
I supoose it has its place. The OP made mention of casting being quicker than machining. That's a simple part. Billet, it would be thinner, lighter, and stronger. If you like the old school dull look, tumble it.
Thinner, if you cut it thinner, lighter because of density, but not always stronger.  Forged aluminum would be ideal, if you had the means to do it.  Also, not so relevant with a clip-on mount, but cast parts do a significantly better job dissipating heat evenly.  As far as which is quicker:  Typically, with production of one unit, it will be faster to machine one unit from a drawing if you can skip the 3D modeling part.  To cast a part from a master takes thirty minutes to an hour.  To produce multiples, casting is significantly faster.  In production, he's limited only by the size of his crucible. Gang molds can be made to produce hundreds of parts per melt, if he has a crucible large enough. 

Offline themotoworks

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Re: cast a rearset bracket
« Reply #13 on: Dec 25, 2017, 10:42:33 »
milling that part would actually take quite a while, it's not dead flat, so the faces would need contour milling, and the pocket part is a nice bit of programming to rough out and then finish nicely, believe me, I can write the code for it and I can make it on my mill, I've got a 4 axis haas vf-2 at my shop, but there are definitely things that should be cast, most of this project is to refresh my casting skills for a set of ducati racing heads I'm going to make, which are in absolutely no way more efficient to machine from a block

Offline themotoworks

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Re: cast a rearset bracket
« Reply #14 on: Dec 25, 2017, 10:46:07 »
Thinner, if you cut it thinner, lighter because of density, but not always stronger.  Forged aluminum would be ideal, if you had the means to do it.  Also, not so relevant with a clip-on mount, but cast parts do a significantly better job dissipating heat evenly.  As far as which is quicker:  Typically, with production of one unit, it will be faster to machine one unit from a drawing if you can skip the 3D modeling part.  To cast a part from a master takes thirty minutes to an hour.  To produce multiples, casting is significantly faster.  In production, he's limited only by the size of his crucible. Gang molds can be made to produce hundreds of parts per melt, if he has a crucible large enough.

the pour in the video did 3 molds, and I used what I had left of my 356 alloy, the crucible was about half full, and i poured the rest on the ground (I don't like melting 356 more than 2 times).  so I could probably do 8 in a pour, 15 minutes from cold to a full crucible ready to pour, and 9 minutes with a hot crucible, so... yeah, you're right, casting for production is damned fast, I could even cast the part, set up a jig in the haas, and do the finish contour milling only, making them look like a part machined from a block, but with better mechanical properties :)

Offline guzzi850t

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Re: cast a rearset bracket
« Reply #15 on: Dec 26, 2017, 08:59:33 »
Howdy, I work in a bronze foundry. We occasionally pour aluminum for patterns etc. however the bulk of our work is investment casting in ceramic shell. do you know of 3D printing material that would burn out easily? Or if it's possible to print in wax? I've thought about casting some rear sets as well. I am planning some bronze head guards for the Guzzi soon.


Sent from my iPhone using DO THE TON

Offline J-Rod10

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Re: cast a rearset bracket
« Reply #16 on: Dec 26, 2017, 10:30:33 »
the pour in the video did 3 molds, and I used what I had left of my 356 alloy, the crucible was about half full, and i poured the rest on the ground (I don't like melting 356 more than 2 times).  so I could probably do 8 in a pour, 15 minutes from cold to a full crucible ready to pour, and 9 minutes with a hot crucible, so... yeah, you're right, casting for production is damned fast, I could even cast the part, set up a jig in the haas, and do the finish contour milling only, making them look like a part machined from a block, but with better mechanical properties :)

Just out of curiosity, where are you getting sand cast alloy has better mechanical properties than billet? Cast is notoriously brittle, and inconsistent. That's really the main perk of billet, its consistency throughout the stock. Part of the reason there is such a huge aftermarket in both cars and bikes for billet.

Not necessarily arguing it with you, just curious, as pretty well everything I have ever read on the subject is contrary to what you are saying.

Offline themotoworks

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Re: cast a rearset bracket
« Reply #17 on: Dec 26, 2017, 10:50:53 »
cast alloy isn't notoriously brittle, where are you getting your information?  if cast alloy were so brittle, it wouldn't be used in aluminum motorcycle frame sections, aircraft parts, or any other structural applications for that matter, but cast a356.0 is used extensively in those applications, and it's heat treated properties are basically a drop in replacement for 6061-t6.  the nice thing about cast parts as well, is that the flow of the metal into and through the mold can be designed to add directional strength to the part, plus with a cast part you get the added benefit of no leftover stresses from the manufacturing process.  go flycut 1/2" off your 1" billet plate and tell me how flat it is now, do the same thing with cast and you won't notice a deviation.

Offline J-Rod10

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Re: cast a rearset bracket
« Reply #18 on: Dec 26, 2017, 11:27:04 »
cast alloy isn't notoriously brittle, where are you getting your information?  if cast alloy were so brittle, it wouldn't be used in aluminum motorcycle frame sections, aircraft parts, or any other structural applications for that matter, but cast a356.0 is used extensively in those applications, and it's heat treated properties are basically a drop in replacement for 6061-t6.  the nice thing about cast parts as well, is that the flow of the metal into and through the mold can be designed to add directional strength to the part, plus with a cast part you get the added benefit of no leftover stresses from the manufacturing process.  go flycut 1/2" off your 1" billet plate and tell me how flat it is now, do the same thing with cast and you won't notice a deviation.
Frame sections aren't sand cast. They're die cast, under vacuum to remove the gas bubbles.

As for removing material, if you can't cut a part flat, your speeds and feeds are wrong, and you're putting too much heat into the part.

Offline themotoworks

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Re: cast a rearset bracket
« Reply #19 on: Dec 26, 2017, 11:37:28 »
damn dude, you've got me... you must be a mechanical engineer who called me on my bullshit and lack of knowledge, i'll go back to making things that don't work now.  byebye