Metal Casting Zone

I have no foundry etc as yet, but am willing to do what it takes to put one toegether.

In particular, I'm one of those people who lives by the motto of "nothing is impossible". To this end, I'm looking to replace the old four speed gearbox with overdrive out of my classic car with a more modern five or six speed gearbox.

Now it's easy enough to get a five or six speed gearbox, but of course it won't bolt straight on - and many are FWD instead of RWD.

As such, I'd like to use the internals of a modern gearbox, and manufacture my own gearbox casing and selector mechanism. I currently imagine it similar to my existing box - (basin shaped with a lid on top). I hope to create it so that it can reuse the existing bellhousing, but may also need to cast one of these as well.

My question is will aluminium handle the torque from the input face to the output face? Does the material make a difference? Should I simply replicate my existing casing as closely as possible (with the "strengthening ridges" along the side). Would I need a special process to ensure casting strength (and non-porosity)?

I'm guessing torque might be better handled by a deep cylinder with a cap at each end. Are there any references on casting for torque transmission?

many thanks and best regards,
Guy

your project is quite a task for a new person to casting. for starters the gearbox is a aluminium alloy and isnt just plain aluminium. secondly you would need a suitable pattern and one that has been designed to meet your needs and suitably reinforced.having now made a suitable pattern you will need to make a big!!! casting box (flask) and barrow loads of sand. next you would need to calculate what your finished casting will weigh. a good way is to weigh a similar item. after you know how much metal you will need to fill your mould you can now workout how big a furnace and crucible you will need.keep us posted on what you decide.

Thanks for replying so soon! I was intending using three or four scrap bellhousings / casings for the material as I figured whatever alloy is right, at least I'll be using the right stuff.

I understand that there will be a lot of design work, to use the original sized bearings and shaft positioning, but in the end, I'm guessing all the casing is there for is to provide support for those shafts and bearings.

All I need to work out is to ensure that I provide enough strength in the casing.

I already have a cast-iron casing from the original, so I'm intending to keep the "shape" as close to that as possible, depending on internal size requirements, then simply hope for the best!

I guess I'll just have to add lots of reinforcing "ribs" into the design, just in case.

Need to sort out a furnace first though, I guess, and make some ingots to work with.

As to size, I'm looking around the office here to see if I can see anything of a comparable size. Closest I can see is a box of photocopier paper (containing five reams). Say 8"high x 8"wide x 12"long "basin shape" box - with maybe a 1/2" wall thickness.

What kind of size of containing box would I need - maybe 6" deep all around (so approx 20" x 24" x 18" deep - plus a 3" lip so I can make the casting taller and then trim to size)?

From what I learn from reading books and on the internet you are going to need to make a wooden pattern of some kind, of the outside shape of your original gear box, the wood pattern would be rammed with sand and used as sand cavity to form your outside shape.
And make a core box pattern for the inside shape of your gear box to form sand cores.
Witch will make your inside detail.
Cores are used in sand casting to create hollow cavities in the interior of the part. Sand is mixed with a binder to form a solid "sand core". A core must porous enough to allow gas to escape from the casting, while still blocking the molten metal. It should also be easily removed from the finished casting. Sodium Silicate is used as the binder that "glues" the sand together in cores. To solidify the core, apply CO2 gas from a low pressure source such as a beverage gas cylinder. The gas can be applied using a hose and any convenient nozzle. The nozzle could be just the end of the tube, or a diffuser such as a standard kitchen funnel. The object is to push the gas thru the core from one end to the other, and activate the sodium silicate to bind the sand. You will need to build a fixture to hold all this all together to help form your wall thickness .and you need to add shrink sizes to all
Your dimension. I think this is just one way you could do it. There maybe other ways to cast that may be more easy . Can you post a photo of you gear box?

Will do,
Just heading home for the night (I'm in Scotland) so I'll try to look something out.

The outside of the gearbox will have the strengthening ribs, so I'm not sure hot metal onto wood would allow me to detail the outside correctly.

I'd assumed I was going to need a "sandbox"(?) with the exterior detail and a "plug"(?) Interior detail is pretty plain. I'll put up a photo as is, although obviously modifications will be required.

What I WAS going to do was this...

You know that "aerosol expanding cavity foam" you get? I thought about spraying it onto the existing gearbox, then taking it off once set and coating it in oil before spraying more of it on the inside - recreating the gearbox shape, complete with all exterior detail etc. I would then make the required modifications to this foam "model" before using this as a plug to cast a concrete mold (with a thin sheet of plywood down the middle so I could split the concrete into two "half shells". I could then create a plug from either concrete or wood to form the inner detail and hang it inside the former, before pouring the alloy. Is this a non-starter?

The original is cast iron/steel.
thanks
Guy

the wood would be used to form aa sand casting mold of sand.
sound like what you are doing is good

what your doing to make the forms sounds good but you will need to make your mold
out of sand not concrete?

some basic start suggestions have been posted. so its time to build a furnace ,melt some metal and pour it into a useful shape. "useful shape" thats the key to the casting world! anybody can melt metal and pour it into a block which is fine if you wanted just a block of metal but most want something a little more. im currently wanting to cast the parts to build a lathe. research has shown me on the net that many have started and havent finished and they started 6..8 yrs ago. others have them up and running! most of the "starters" have casting experience so why the delay????my advise is to make a furnace,melt some metal and learn how to make a mould before trying your gearbox. the major point really is that there are "thick and thin" areas in your design and these need to be addressed .(very advanced stuff! )

thanks for the "cavity foam" idea i will get some and experiment with it on some lesser projects.