Casting results and metal candy canes

Here's the polished up results of the aluminium R made during the other weekend's casting session with the flowerpot furnace. I used files to remove any spru and large bumps then a couple of sizes of sanding drum on a minidrill to smooth off surface, finally used wirewool and brasso to polish it.

These funny looking objects are not fake metal candy canes to trick the kids this halloween but some parts for a sculpture I'm making in my welding for artists evening class.



To bend the 6mm re-enforcing bar, I heated the bar about 15mm down from the end of the bar with a butane torch. The bar was heated until it has a bright orangy red stripe across it, then wedged in the vice and bent over. Once I had a "L" shape, I heated the very tip till it was again orangy red and used pliers to finish the hook shape. I then left the hooks on the thermalite hearth to cool down.

One of last week's welds demonstrated it's poor quality by breaking whilst I was bending the rebar. To be honest I should have done the bending before the welding but did not have the time.

Sunday sandcasting

It's been over a year since I last fired up the flowerpot furnace. A multitude of factors have got in the way from weather to needing to work on the gates to being too busy enjoying other things.

The melt was started off with offcuts and scrap from the previous melts, once a reasonable pool was formed a mix of aluminium was added, mainly disk drive cases but also some cans and swarf.

I bought myself some petrobond sand last year as I was not happy with the resuls from the hand made "green sand" and have finally gotten around to using it. The petrobond was easy to use in that it did not fall out of the flask, formed nicely around the patterns but did not stick to the patterns. The mold did not collapse when it was assembled and the surface finish was better than my previous results.

One difference with the Petrobond is that it will smoke and blacken where the sand touches the hot metal. I've quizzed the people of the HomeFoundry and Casting group and they say that I don't need to worry too much about this but it's worth removing the large lumps from the sand before re-using it.

Here's some photos of the greensand vs petrobond sand results.



As I had the furnace running, I thought that it would make sense to melt a second batch. This I poured into open mold to make an ingot and a blob wich can be used to start of the next melt.

Steam Punk Magazine

The other month, Steam Punk Magazine was kind enough to offer me a slot in their periodical, to enthuse about brass and making the flea chariot.

The article should be appearing in edition #6 "The Pre-Industrial Revolution" which is out now.



At a staple-popping 104 pages from cover-to-cover, it's filled with a selection of stories, poems, reviews, interviews, articles, and how-tos.

The theme for the issue is 'The Pre-Industrial Revolution', offering an opportunity for us to begin explore the pre-Victorian aspects of the steampunk ethic, and the many faces of steampunk before and beyond the constraints of the Duskless Empire. It also investigates the ways in which steampunk is often an unindustrial (if not pre-industrial) revolution in its own right. All on top of a glut of regular content, such as features on:

Alchemy;
The Luddites;
Victorian Martial Arts;
Creating your own steampunk sculptures;
Building your own windmill;
An interview with British steampunk outfit 'Ghostfire'.

Issue #6 of Steampunk Magazine is available printed on recycled paper through the mail-order page of Strangers in a Tangled Wilderness, and also (as ever) for free download through the Steampunk Magazine website.



The previous edition #5 had a good article on Metal Casting by David Dowling which is worth reading.

Flying cutting blobs

Earlier in the year, I bought some fly cutters at a model
engineering exhibition.



The intention was to tidy up some of the castings I'd made last year. The first issue was how to hold an irregular shaped piece whilst it was being cut. Given that I was planning on turning this into a handle, drilling and tapping two locations to support it seemed like a good idea. The casting was then bolted to a short length of bar which was in turn mounted in the tool post. One of the problems with machining lumpy items is that it's hard to set the first pass, the problem is that you will be happily skimming off a 1/10mm only to hit a 1mm bump where the cutter justs digs in. To work around this either file the item flat first or make multiple passes over the metal to check for high spots to machine down first.

A couple of other issues were spotted in the process. The size of the item to be machined is limited vertically by the sweep of the fly cutter. The size of the item horizonally is limited by both the sweep and the amount of movement of the cross slide. So the size I can easily fly cut on this lathe is about 60mm square. To machine large areas the bar held in the toolpost would have to be moved. I made the error of flipping this over only to discover my mounting holes were not exactly perpendicular to the work. This produced an approx 1mm difference between the two sides. I've decided to abandon this process and cut this casting up into smaller pieces that can be used for various projects needing aluminium in the future

So in conclusion, yes it it possible to use this technique and it beats manual sawing and filing for quality of results. However, it's not idea for removing large quanties of metal as it takes a lot of time, so I'd be much better off trying to improve the quality of my castings and just fly cutting any critical areas.

I've made some progress with regards to better castings with the petrobond sand, some good quality source metal. I now need to make some better patterns and to practice bedding them in the sand to get better results.

Metal experts

Arthur Ganson Machines


Arthur Ganson has been creating wonderful machines since the 1970s. The video below shows a technique for making wire gears which I think is quite ingeneous.



Arthur Ganson's Sculptures

Eugene Sargent

Whilst looking for some topics on metal casting, I discovered Eugene Sargent's article on sand casting. He's made many of his own tools to help with the casting process and he has an impressive workshop.



A few years back he also made this impressive orrery which he cast out of bronze and then milled using a CNC Taig micro mill with his own hand crafted G code created programatically rather than from CAD software.

More blobs to blocks

At the show earlier in the month I was looking for a 4 jaw chuck but failed to find anything small enough. I managed to get one online for a very good price, one of the jaws is a bit stiff but it clamps very well.

When I was casting the beta last year, I kept the riser (in the middle of the picture below) as a potential aluminium rod that I could use.



This was a very strange oval shape with a taper to one end. Four flats were made around one end and I clamped it in the 4 jaw independent chuck and roughly aligned it to a centre in the tailstock. The rod was turned down until most of the surface lumps and bumps had gone. After swapping back to the 3 jaw self centring chuck, I machined down the other end.



The material machined very well and produced a good surface finish. I'm sure that I will be able to produce an even better surface finish on it when I come to actually use it for a project. The hole in the photo above is from the surface and is not a defect internal to the metal.

Terry Brown's Shed - Casting, Maching, Projects and Gingery Shaper

Today I stumbled across a goldmine of information. Terry Brown's shed stuff pages contain a large number of project he's completed over the last 7 years. There's a section on foundry work making furnaces and melting aluminium, this is complemented with a later section on the gingery shaper which has details of pattern making as well as casting. A section on the lathe with modifications to his 9"x20" lathe, simple addons such as a levers and handles, mods to the compound rest, tailstock die holder, ball turning and more. A smaller section on milling machine modifications with an auxiliary table and how he made that with fly cutters. There's some miscellaneous pages with burners, firebricks and a tiny steam engine. He finishes up with a section on his project of making the shaper.



What is a metal shaper?
For those who don't know, a shaper works a little like an electric hacksaw; it moves a tool backwards and forwards in a sawing motion cutting a slot in the metal. It's the predecessor to the milling machine with some advantages. The first is that it can use the same tools as your lathe, the second is that it can cut shaped slots using tools ground to a particular shape, something that would require multiple operations with different tools in a milling machine. It can also cut internal keyways which is difficult with most other tools. However it has mostly been replaced by the milling the machine in workshops as it removes metal more slowly.

Melt 12th Oct

For the latest aluminium melt, I build a new two part flask and tried casting a couple of letters. After a trial run putting the sand in there was an issue with the sand falling out of the cope (the top half) so additional battons were put on the sides (see below).




This was my first attempt at casting with a two part flask and the problems with the sand lead to the closing up of the gates. The gates are tunnels that join the sprue (filling hole) to the hole left by the pattern. The end results were one half of the pattern did not fill at all. This could also have been that the metal had cooled too quickly but that seems unlikely given that the other half formed correctly.



All was not lost though as my wife took a shine to the droplet formed and has asked for it to be turned into a pendant. The sprue also should have a use once I've machined it into a small rod. I also formed a small ingot with the excess which with either be machined into a block as previously or it may just be used for the next melt.



Here's some closeups of the resulting Beta.

Building the flowerpot furnace

2020 Vision said: "Just wondering how you got the air into the flowerpot? Was it through the holes at the bottom or did you somehow cut a hole in the side? I would have thought the latter could weaken it."

Well the answer is yes, it probably did but this should not actually matter. The reason for this is two fold. The first is that the flower pot does not have to take a lot of weight, a small amount of charcoal and a full crucible are probably still a lot less than it's normal load of wet soil. The second reason is that the whole flowerpot is surrounded with mortar, at this point it's about 30mm thick.



When constructing, I followed the instructions from the Back Yard Metal Casting book on the flower pot furnace. I made a couple of changes. The first was that my outer "can" was in fact a fine wire metal waste paper basket. The second was to do with this hole. I could not work out how it was going to be drilled after the mortar was added so I drilled my first using a tile bit and cut one in the basket using some snips. This gave me a new problem of how to line up the two holes. I solved the problem by adding enough mortor in the bottom of the bin so that the flowerpot could be added, I then used some rolled up cardboard to span the two holds and packed the rest of the motor around then. After a few hours of drying, I removed the card and increase the size of the hole so that the air pipe would easily fit.

The hole in the bottom of the flowerpot is blocked up with mortar and a piece of angle iron with extra holes is laid across the pot so that it can spread the flow of air. A couple of blobs of fireclay give the crucible something to sit on. The air enters from the bottom of this photo.


My other change was not really intentional in that I added a new top to the furnace following the main construction so that it was level. Retrospectively, I'd have made more effort to ensure that this lip was part of the main pour. The top edge has now cracked off in just two melts. I'll give the furnace a good soaking (in water) before I try to put some new mortar on, as that should increase the bond.

Update:

The top edge of the furnace has undergone further repairs and so far is holding firm. The lid has had additional fireclay added when cracks had developped and fireclay has also been smeared onto the small cracks in the flowerpot. This is actually quite a normal process on such furnaces.

Blobs to blocks 2

From my second cast, I produced the following two blobs. The left hand one was much better than previous attempts with a large section of straight sides and a better finish. I expect the right one would have been better if it was a deeper casting and had I not run out of metal for it.



These were hacksawed and filed into rough blocks ready for machining. A little like a famous meal with loaves and fishes, I keep ending up with enough offcuts to provide as starter material for the next melt. Obviously as I get better at preparing the molds this will reduce, as long as I'm melting some large blocks (such as the disk drive casings) then this should not be an issue.



Before I can continue with the larger block, I need to make up some suitable clamps or faceplate dogs so that I can attach them to a faceplate. This block is too large to be held in the chuck. The book Workholding in the Lathe (Workshop Practice Series) has given me some ideas on how to make these, I'm planning to make the faceplate dogs out of hexagonal steel rod with M5 clamping screws.

Machined blob

This weekend I machined up one the castings from last week's melt. Here's the stages from scrap to machined results.

Step 1
Some scrap ali that I found round the back of the shed, sawn up into suitable sized pieces to fit into the crucuible.

Step 2
Molten Aliuminium in Charcoal Furnace

Step 3
Casting in sand

Step 4
Casting removed and sand cleaned off. Following this, I sawed off the rough edges

Step 5
Blob machined in the lathe into a block

Red Hot - Casting

This morning the flower pot furnace was lit and I cast my first aluminium. I'd finally got good weather, all the safety gear and tools were finished and I'd sawn up an old strip of aluminium into small chunks to fit into the crucible.

Safety gear

Full face visor
Cotton overalls
Leather apron
Long leather welders gloves
Steel toe cap boots

Only the boots were of significant cost, the other items were source cheaply from several different suppliers.

Tools

From left to right, crucible lifting tongs, regular tongs for coal and metal loading, pouring shank, skimming tool.


The lifting tongs were made from a pair of domestic coal tongs with the faces ground down and drilled so that bent pieces of "repair plate" could be pop riveted onto them. My workshop was black from the cast iron dust after that job! The pouring shank was made from a fire poker that was hacksawn down the end and then heated in the furnace till red and bent into shape with a large pair of pliers (not shown). The skimmer was a bend barman's spoon with a hand turned wooden handle.


The blower was also an essential component, this was made from an old bilge pump taken out of my Dad's Honeybee with a speed controller found on Ebay and a rewired PC Powersupply all mounted on a wooden frame with some metal tubing to connect it to the furnace.

The molding flask was single part design made from some old wood offcuts and nails.

Moulding Sand

The sand was made by mixing a "fullers earth" brand of cat litter with children's play sand and a little water. It did stay in the flask and it did allow shapes to be made in it. However the detail of the initial patterns was lost as the sand stuck to the patterns (might have been a problem with the pattern being made from unvarnished clay). The latter pieces also spattered a bit when poured so my mix might have been too wet. I've quizzed the Home Foundry and Casting group to see if they know what was wrong.

Lighting and fuel

The first attempt the light the furnace was done with some pieces of wood and some scrunched up brown paper. This the wood started burning but did not light the charcoal briquettes. A second attempt was made using firelighters and this worked fine, after the firelighters were just about out the briquettes were white and smoldering so the blower was started and they quickly turned to glowing red. The blower was slowly turned up over the next 30 minutes and the poker (see tools section) was added so it could be bent into shape. Once I'd finished bending and checked it against the crucible size, I put the poker/pouring shank to oneside to cool

Melting

More fuel was added along with the crucible, the furnace was brought back up to temperature. 10 minutes later the first scrap was added, this was repeated over the next hour as it started to melt. I believe that I was misunderstanding what was happening at this point. I think that there was a lot of crud in the mix which I thought was unmolten metal so it could have been skimmed and topped up more quickly than I was doing. We will have to see on the next melt to see if that is right.

Casting the Aluminium

Eventually I had half a pot of molten aluminium and no scrap left.



The first lift and pour went well but I was a little slow so the metal solidified in the spout of the crucible before I'd finished pouring. So back into the furnace and the next pour was a quicker.





Here's my raw results, the bottom items were very rough and one was slightly brown as the hole had been too close to the edge. However the larger blocks appear to have produced good results, I cut the side off of one and it appear to have no defects running through it. I'll cut the other sides square later in the week to see if this is consistent. the top left piece when machined up will be a handle to hand crank the lathe for tapping and screw cutting.

Because of the long time the furnace was running, approx 3 hours there was quite a lot of ash produced from the 2Kg of fuel burnt. The next burn should use less fuel as I believe it is possible to get it up to temperature quicker and less time will be wasted waiting for the dross to melt when really it just needs removing. The furnace suffered a little damage with some of the top edge of mortar falling off and a crack developing in the flower pot. I've been informed that this latter issue is common and is unlikely to cause issues. I'll try to give the new edge, more of a key when I repair it with fresh mortar.

Thermalite

Not to be mistaken for thermite which is not a suitable building material!!



I was curious to know about these blocks as they are a easy to get hold of in the UK, they are made from recycled material, are a lot lighter than refractory bricks and can be carved using a knife or hand saw.

What is thermalite?

"Up to 80% of the raw material used in the manufacture of Thermalite is pulverised fuel ash (PFA), a stable `by-product' of coal-burning power stations. This recycled material is mixed with sand, cement, lime, aluminium powder, together with processed waste and water, to produce a range of blocks noted for their high thermal insulation."

i.e. These blocks are not just aerated gypsum.

The experts view

What the expert said when I asked him about using these for furnace applications:

"Thermalite blocks in domestic situations are usually serviceable after a fire of approx 900-1000 Celsius, however, exposure is only usually for about 30 minutes and the blocks will have a protection layer of plaster or plasterboard. The protection of your insulating layer is all important, however, asthe blocks dryout they will shrink and crack if they are held togetherby conventional mortar, it would be better to oven dry the blocks priorto incorporation into a structure (to limit their shrinkage potential)and to investigate if a special mortar is required to glue themtogether. We cannot give a definative answer as to wether the blocks will crack due to thermal shock as we have no experience of this type of block used in this application."

Charles from Home Foundry and Casting group suggested that I do a "Myth Busters" on this material.

Experiments:

Blow torch test

A fine flamed butane gas blow torch was held on the block.

The result was that the block glowed red in the area of the flame whilst the flame was applied, the surface of the block was cool a distance of approx 30mm away. When the flame was removed the block rapidly cooled and could be touched with a damp finger seconds after the removal. The estimated temperature for these kind of torches is upto 2400°F / 1300°C.

Blow torch scratch test

In order to determine if the block was softer when hot, a metal rod was used to scratch it. The block is quite soft when cold and the rod produced a medium sized scratch with very little effort. When heated, the block was slightly softer but this was only on the surface for about 2-3mm.

Mechanical Properties

These blocks are quite soft and very brittle, even small bumps and scrapes will cause pieces to be broken off. The blocks can be cut with a hand saw and shaped with tools such as a surform. Don't try to snap a partially cut block as it will break along a completely different line. The blocks are very light and the example shown below can be easily lifted with one hand.

An model makers hearth for small brazing and heat treatment jobs, made from a thermalite block and patched back together with fire cement.

My Conclusion:

I see no reason why this material can't be used for a hearth as above, with no additional treatment, time will tell if it is too soft or if it generates too much dust. It should also be ok as a surround for an aluminium melting furnace. Given that it's a bit soft it needs to be protected with a layer of a harder refractory material on the inside and something such as brick or metal on the outside. For higher temperatures needed for steel and bronze further experimentation is advised to see if it meets your needs.

These results are not endorsed by Hanson the make of these blocks.