johnsmachines

machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most.

Category: metal casting

Bronze Tyrannosaurus Rex

Actually, I had some spare space on the tree which I used to make some more small gears, and I had some PLA T. Rex’s, so I added one.

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And this was the cast result, in bronze.  Yet to be cleaned up, tree bits ground off, and polished..

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 Again, the gears are close to perfect.  I like bronze.

And the gears have a short length of shaft, printed in PLA and cast in bronze, which I will be able to hold in a chuck for tidying and turning.  Lesson learned.   Think ahead, how the cast part will be machined….

And at our society Zoom meeting, Frank M  asked about the colour of burning Borax.   I could not remember, so took a shot today…

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I would describe the colour as white-gold, with a touch of green.  Like a volcano.   Maybe I overdid the Borax?

Oh.  And I had a brainwave.  When degassing the investment mix with negative pressure, add some vibration.  I tried applying my sanding machine once, and filled the room with old fine sawdust.  But for this session, I placed the vacuum pump on the vacuum chamber, and could hardly believe the volume of air which came out of the mix.  The best degassing to date.

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and it takes less bench space.   A no-brainer.  Try it!

 

First Bronze Castings

Bevel gears seem to me to be rather difficult, even with CNC control of X,Y,Z and A axes.  The bevel gears on the model Armstrong cannon are rather small, being 32mm and 14mm outside diameter.

I read Ivan Law’s book on the subject, and I think that I understand the requirements, and I was prepared to try and cut the gears.  But, first, I decided to try to cast them.

That involved…

  1. Using “Gearotic” to design the gears, and save them as an STL file which was able to be imported into the 3D printer.
  2. Made PLA gears with the 3D printer.
  3. Attached the gears to a wax “tree”.
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3 pinions and 3 gears.  I need 2 of each.  1 spare of each.  Plenty of venting sprues.  And a head of about 70mm.

4. Then mixed the investment, poured it into the flask.  At least that was the intent.  The investment makers specify exactly 40:100 by weight of water:powder.  But the bloody scales switched themselves off while I was adding the powder to the water, so I had to guess the quantity of powder.   This was not looking promising.  First bronze casting pour not off to a good start.

5. Dry the mold flask in the potter’s oven for 2 hours, then 2 hours of burning out the PLA and wax, then 2-3 hours of baking at 750ºc.  A few minutes into the burnout phase, the oven died.   ?heating coil failure, ? control box failure?, ?thermocouple failure,  something else?    So I replaced the control unit and thermocouple (I had a spare of each), but problem persisted.  I rang my expert friend for advice.  “sounds like a broken wire” he says.  Suggested 3 or 4 things to try.  And the 4th suggestion worked!  The oven was working again!  Brilliant!   Thanks Stuart Tankard.  So I restarted the oven at the burnout temperature (400ºc) and continued.  Nothing to lose, after all.

6. Melted a couple of bars of LG2 bronze at 1100ºc in the melting furnace.  Added a pinch of Borax.  Let the investment oven cool to 710ºc for 1 hour to let the core of the mold cool to 710ºc.

7.  Without any great expectations of success, considering the various problems, I poured the molten bronze into the mold flask.  It seemed a bit more viscous and thick than I was expecting.  Oh well.  It is experimental.

8.  When the mold flask had cooled to 150ºc, I plunged into cold water, and flushed out the investment.

THE RESULT….

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Unbelievable.  No voids.  Hardly any surface bubbles.  ALL teeth intact and complete.  6 good gears!   You can see the head of molten bronze between the funnel and the top gear.  It did not need vacuum or positive pressure.

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I will turn the faces, bore the shaft holes, and if necessary file the teeth.

Totally delighted with this result.  Beginner’s Luck.

 

 

Casting Aluminium. It is just too light.

When doing my aluminium castings  for the model Armstrong cannon, I noticed that the objects in the wax/PLA tree which were closest to the funnel (i.e. the topmost ones) were the ones which were most likely to have significant deficits, and I wondered whether the pressure of the molten metal at that level was the problem.  The objects at the bottom of the tree were most likely to be successful.

Well, my friend Stuart Tankard is working on a positive pressure system, and I am working out a negative pressure system, to increase the pressure at the higher levels within the tree.

An interesting number is that for every 1″ / 25.4mm increase in the head of molten aluminium, the increase in pressure forcing the molten aluminium into the casting voids, is only 0.1 psi!!!  Bronze, being much more dense (x3 – x4)  would be less problematic, but still less than 1psi.

Some casters use a centrifugal system to increase the pressure on the molten aluminium.  Frankly, that idea frightens the shit out of me.  One episode of molten metal flying around my workshop was enough.

Stuart T is working on a positive pressure system, using approximately 5psi on the melt, to force it into the tree spaces, and he is well along the path of manufacturing the hardware to accomplish that.

I am inclined to use negative pressure to suck the melt down.  I already have a vacuum pump, and I think that it might be easier to seal the hot steel cylinder to the silicon gasket which is required.  There is a YouTube video on the subject.

(oops.  I pasted the wrong VOG video.  The one below is the intended one.)

I have ordered some 3mm thick Silicone sheet.

VOG, in the above video, allows the surface of his casting cylinder to cool to 100ºc before pouring the aluminium melt, so the silicone gasket does not burst into flame, and he has had some excellent results.  It is casting heresy, and he should be burnt at the stake.  But if it works…. hey?!  (maybe the core of the casting cylinder is still closer to the molten aluminium temperature of 710ºc?).

So that is the path which I am following.  Not exactly.  But using the principle.  Watch this space for my results.

Actually, molten bronze is my next pour.   I doubt that it will require vacuum or pressure.

My Daughter Has Caught the MetalCasting Bug

For some reason which I do not really understand, my youngest daughter has become interested in my metal casting activities.

First she watched me do a molten aluminium pour.

Then she rang me a day or two later and asked if she could have a go.  She really wanted to do it in brass or bronze, but as a relative beginner myself, and with only one episode of molten brass, and that one did not go so well, I demurred, and said that her first effort would have to be in aluminium.

So I prepared 3 flasks, printing the plastic parts, and gluing them into a wax tree, then slowly heating the flasks in the potters oven, up to 750ºc over 8 hours.  Then lowered the oven temperature to the pouring temp of 710ºc.  And preparing the aluminium melt at 710ºc.

When Eleanor arrived, we had a couple of practice runs with flasks full of sand, so she could get used to the weights and handling the tongs, and the various movements while wearing the protective gear.

Then the pour.   This is Eleanor’s video of the event.

 

I admit to some substantial reservations about this exercise, but Eleanor listens carefully, asks intelligent penetrating questions, and follows instructions precisely.   Full marks.

And, a very successful pour!

The (non) gripping power of rubber

In order to increase the head pressure of molten aluminium during my casting pours, I increased the height of the casting cylinder to 250mm (previously 100 to 150mm).

That meant that the weight of the casting investment mix increased to 5.25kg. per 250mm cylinder.

This was the result today, when I poured the investment mix, then moved the cylinder with the rubber cap at the bottom.  It would have been OK if I had waited for the mixture to set. (about 20″).

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The rubber end cap slipped off, the investment mixture came out, the 3D printed parts tree fell apart, and an horrendous mess resulted.

After a barrage of unprintable expressions, I hosed the 3D prints down (outside), and washed the cylinder and end cap (outside).

By then the mess on the bench and floor had set, so I was able to scoop most of it up with a BBQ spatula.  Then multiple wipe downs to get the very fine powder off the surfaces.

I still wanted to prepare the moulding cylinder(s), and for some reason I had lost my desire to use the 250mm cylinder, so I made 2 trees with the parts, and split them into two 150mm cylinders.   Without further incident.

While waiting for the investment mixture to set, I did some further work on the previously cast parts.

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Applying some JB Weld  onto one of the cast rear wheel bracket and column assemblies.

Lost PLA Casting – 3rd pour

Today I attempted another aluminium casting session with trees that I had made 2 days ago.  More wheel forks, and barrel trolley brackets.  16 parts altogether.

And this time I installed air release vents, following my previous poor results, and at the suggestion of reader Rob R.

I also made some 50mm extensions of the pouring funnel, to increase the head of melt pressure.  The extensions were “add ons” rather than designed into the system, and the molten aluminium leaked between the extension and the main flask with the tree, so I doubt that they were very effective.

BUT!  Of the 16 parts on the trees, 14 were good to excellent, and only 2 showed any voids, and I assess one of those as repairable.  So, 15/16 is very pleasing.  I feel that I am closer to getting good results every time, if I can make an effective system of increasing the delivery pressure of the molten aluminium.

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These are the extension pieces to the funnels on the investment flasks.  The shape was made with the plastic funnel.  If I had positioned them before the investment plaster had set hard they might have worked better, but as they just sat on top of the already hardened plaster, the join leaked molten aluminium rather badly.  I have a different system in mind for my next pour.

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Previous failures were cut up and thrown into the melt.

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See the tiny silver dots surrounding the central funnel.  That proves that the air vents functioned as intended.

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The aluminium trees.  Not very pretty, but delightful to see.  10 parts on the top one, 6 on the other.  It is odd to see the wax spaghetti turn into aluminium spaghetti.   I will separate the parts tomorrow.

And while the investment burnout and baking was proceeding, I worked on previously cast parts.

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The centre columns have beep painted with etch primer.  A little more filling required, then I will use the best 2 on the models.   The 2 bracket and column assemblies on the right were initially considered unusable due to large voids, but I used some aluminium solder to fill the defects, and they might possibly be OK.  The 2 on the left just need some tidying, machining removal of  melt tubes, and minimal filling.

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I will probably remake this one, but will continue to salvage it and see how well it comes up.  Note the solder fill on the RHS.   That will not be seen on the model.

One more melt and pour, and that should be the last of the castings made for the model Armstrong cannons.  It has been a challenge, and lots to learn, but very interesting and very satisfying.

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Finally for today’s post…  I noticed some black marks on the normally pristine white wall above the casting bench.  They extend about 4 meters above the floor.  Do you know what they are?  The paint has been melted off the wall by bits of flying molten brass, resulting from the steam explosion 2 days ago!

Many thanks to Rob R for his spot on suggestion about the air vents.

Brass Melt. Dangerous!

Today I received by mail 2 new crucibles for my furnace, so I tried a melt of brass.

The source of the brass was machining offcuts, machining failures (quite a few of them), and machining swarf.   The swarf was not very clean, probably containing some aluminium, cutting oil,  dirt and grunge.

It was an interesting experience.

Firstly, the temperature had to increase to 1000ºc.  Later increased to 1050ºc.  It is very hot.  And the impurities came off as smelly fumes, and dross.

But, I poured some ingots.

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And I made another remelt.  And later remembered something which I had read somewhere…..   molten metal and water is dangerous.

After making a few brass ingots, and quenching the moulds so I could remove the ingots, I proceeded to another brass melt.

When I poured the molten brass  into the mould, IT EXPLODED!

IDIOT!!!!

FU**ING IDIOT!!!

I had caused a steam explosion.  Probably the mould was still damp.  And when the molten brass entered the mould, it EXPLODED.   I kid you not.  It went BANG.  Luckily, none hit me, but some of the molten brass had landed up to 2 meters away.

OK.  Lesson learned.  Molten metal must be treated carefully, with respect.  And NEVER put it in a container which is not thoroughly dry.

And after inspecting those brass ingots, I will never try to melt dirty brass, or any other dirty metals.

Meanwhile, preparing for another aluminium pour.

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Here is the next tree.  You might note that there is a spaghetti appearance of wax tubes added to the tree, to allow efflux of air from the cavities, as the melt enter them.

Next aluminium pour on Thursday.  Fingers crossed.  Stay tuned.

Video of Casting Small Complex Cannon Parts

This video was taken and edited by my daughter Eleanor.  I was doing an aluminium pour of some parts for the Armstrong RML cannon, explaining the process to her.  I was hardly aware that she was videoing, so the interaction is conversational.

Although the pour was not a success because none of the parts were good enough to use, it does show the process as seen by someone who previously knew nothing about it.

 

 

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There is also a 20 minute video of the whole process which I will add to this post when it is available.

Reader Rob has suggested that the positions of the defects suggests that air entrapment is the cause of the voids and that the fix is to position some vents at the positions at risk.  I will try that with my next pour.  Thanks Rob.

Here is the 22 minute video.  Just as recorded.  Not planned or edited.

 

 

 

 

 

 

 

Second Pour.

One definition of stupidity  is repeating a set of actions and expecting a different outcome.

Well, after my partly successful first molten metal pour, I repeated the same steps, (with some minor corrections), and hoping for a more successful result.

The day was entertaining, with one of my daughters videoing the exercise.  But this was the result…..

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The aluminium melt has not properly filled the cavities at the top (nearest the funnel).  The bottom cavities have filled nicely, with good definition of the printing details.

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The second flask with the same  result.

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My daughter found the exercise very interesting, particularly the pour and the boiling out of the investment material.  But she was a bit disappointed that the end result was not better.

So, I am considering how to change the process.

I believe that I need to increase the filling pressure in the upper half of the flasks.

Possible methods:

  1.  Install a vacuum system for the melt pour
  2. Use a vertical extension for the melt funnel, to increase the height of the column
  3. Increase the diameter of the funnel tube
  4. Increase the number of the funnel tubes
  5. Don’t place tree branches close to the funnel

I had previously considered 1. as recommended on YouTube by several contributors.

The investment powder is a significant cost, so I would prefer to use as much of the volume of the flask as possible, which makes 5. an unattractive proposition.

There are difficulties with instituting 2. but I am thinking about this one.

And possibility 6, is to try bronze or brass, which has a much greater density, and probably less viscosity than aluminium.  I am waiting for some more furnace graphite crucibles to arrive before I can try this one.

Meanwhile I have to 3D print some more PLA parts.

 

A Closer Look at the results of yesterday’s Metal Pour

Yesterday I made some cast aluminium parts for the model 1:10 Armstrong RML cannon. It was the first time I had done lost PLA casting, and seeing the castings emerg from the investment mixture was thrilling.

Today I had a closer look at the parts, band sawed them from the trees, and tidied them up with some belt sanding and filing.

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There were 3 central columns.  In each case the vertical side flanges came out almost perfectly, but the bases contained some voids.

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The undersides of the bases shows that the voids match the internal structure of the original 3D print.  This indicates to me that the fault arises from the 3D print, not from the molten metal pour.  Those columns were among the first 3D printing that I had done, and I remember that the surface layers were only 3 layers thick.  Since then I print substantially thicker surface layers, which I believe are more water tight, and less likely to let the investment material leak into the structure of the print.

Although they look very ordinary, I will fill these voids with JB Weld, then paint them with automotive filler primer, then the final paint coat(s).   If they are still substandard I will start again with new 3D prints,

I also poured 6 wheel forks.  2 were so bad that I have melted them down into ingots for re-use.  The other 4 looked resurrectable.  Unfortunately I had a mishap when bandsawing the parts from the tree.  The tree was flung across the workshop, and one of the forks snapped.  Of course it was the best one.

So 3 of the 6 forks were put into the re-melt, and I did some tidying up on the other 3.

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This lot was remelted into an ingot for future re-use.

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The 3 on the left after some tidying.  Same problem with the voids in one base, but structurally OK and can be fixed.  I scrapped the one on the right.   I might eventually remake them all.

So, although I ended up with 6 use-able parts out of 9 made, and most of those require filling, I am still reasonably happy with this first attempt.  I think that the 3D prints were the weak link in the chain, and with that assessment I will try another casting run in a few days.

Meanwhile, back home I printed a Tyrannosaurus Rex.  I think that it is my best 3D print so far.  It is 250mm long, and the level of detail is excellent, even the vestigial arms are intact.

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About the colour.  No one has any idea what the original T Rex skin colour was.  So even this red is possible (but unlikely).   Nor do the scientists know what noises the T Rex made.  Could have been a reptilian hiss, or a roar, or a porcine grunt.   Whatever, I am glad to never hear it.

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The print took over 24 hours.

Metal Pour

50% preparation of the PLA originals, 45% preparation of the investment, and 5% management of the pour.   You have seen making the trees with the PLA originals.  Today I melted metal, poured, and held my breath.   First metal pour.   I also made some videos, but the autofocus on the Panasonic LX100-2 is so crap (or maybe it was the operator who was more focussed on the metal pour), that I have scrapped the videos. But some stills are OK, as you will see.

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I purchased an ingot of casting aluminium, and bandsawed some pieces to fit into my melting crucible.  Then I washed and wirebrushed the pieces in hot detergent.  There was minimal dross in the melt, so this step was worthwhile, and the ingots must have been fairly free of contaminants.

Next, was measuring the investment powder and water, using kitchen electronic scales.  After mixing there is a 10 minute window for thorough mixing, removal of air bubbles in the vacuum chamber, and pouring into the investment moulds, which had been prepared beforehand.  (see last post).

10 minutes sounded like lots of time, but this was a real time and motion study, having everything ready, with no delays.   But when I saw the clouds of silica dust I remembered that I should be wearing a mask.  So, quick dash, pull on mask, find hearing aids dislodged by the mask, and back to mixing the investment mixture.

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Then, 1.5 hours for the moulds to set hard, and remove the rubber caps with the pouring funnels built in.   That exposes the bottom of the wax trees.  The hose clamps were to assist security of handling the steel cylinders with flask forceps.  Next time I will position them closer to the funnel end.

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The moulds, after removal of the rubber ends, are placed in the investment oven, for 4 hours at 250ºc, 2 hours at 400c, and 2+hours at 750ºc.  The wax and PLA plastic is burnt out and the investment powder sets really hard.   The steel cylinder is red hot.  The wax and PLA comes out as smoke, with no other remnants seen.

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The aluminium ingots are melted at 710ºC, and any dross is scooped off the surface.

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Meanwhile, I have placed a sheet of cement sheet on the floor, a tray of dry sand, and moulds for any excess aluminium melt.  There is a bucket of cold water ready.

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when the mould has been at 750ºc for at least an hour, and the aluminium has melted at 710ºc, the mloten metal is poured into the moulds, which have been removed from the investment oven.  Made a video, but not showing because very poor quality.  After about 30 minutes, the still very hot mould is plunged into cold water, which blows out much of the investment.

And here is the result……

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These are the rear wheel forks.  I need 4.    2 were unusable, and will be remelted.  4 are good to OK, and after some filling with JB Weld, and painting, will be fine.  The 2 failed forks were those closest to the funnel.  Not sure why.

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These are the centre columns.  I need 2.   All 3 are repairable.  One is very good.   Again, the top one, closest to the funnel, (RHS) will be remelted. I did not vacuum the melt into the moulds, and the weight of melt is lowest at that level.  (maybe the cause for the poor result there?)

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so, when I had a closer look at home, none of the pieces are perfect, but they are not too bad.  For a first run, I am really pleased.

With many thanks to Stuart Tankard for his advice and encouragement.

 

 

Making a Tree

The adequately sized vacuum chamber arrived today, much more quickly than I expected.   Initially it would not seal and I could see no holes or leaks.  But when I removed the silicon gasket I found a small silicon flake which was the problem.  Thorough cleaning, and all was well.

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The 1/4hp vacuum pump on the left.  The new 5 gallon chamber hooked up.  And the too small 3 gallon chamber on the right.  I have an idea for using the smaller one, so will hang onto it.

With this arrival I am almost fully equipped to start casting.   So today I built 2 trees.

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The first tree has no branches, so it is more like a tree trunk.  The red items are plastic models of the central pivot column on the Armstrong model gun.  Glued together with wax which I melted with a soldering iron.  (soddering iron for American readers).  And attached to a wax stick which inserts into the rubber flask end at the bottom.  The actual steel flask is behind.

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And here is the “tree” trunk in position inside the flask, ready for the investment plaster to be poured around it.  After pouring it sits and sets for a couple of hours.  Then after removal of the rubber end, about 8 hours in the kiln to melt out the plastic and wax.   Then the molten metal pour. 

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This is the second “tree”.  Wheel forks for the cannon chassis.  Wax glued to the central wax tree trunk.  The 4″ steel cylinder behind. 

Preparing the moulds, and the metal pour will probably occupy about 10 hours, so I will need a totally free day.  Maybe Thursday.

Getting Ready for Casting

Setting up for casting molten metals into shapes for my model Armstrong cannon.  Still getting ready.

Today I made some moulds for dealing with any left over metal melt.  Not a big deal, but it does have to be done before the first melt.  No point realising that there is nowhere to put the left over aluminium or bronze during the pour.  It has to go somewhere.

So today I made some ingot moulds, in readiness.

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The ends of the moulds are sloped to allow easy ejection of solidified aluminium or bronze.

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4 ingot moulds.  Made from 40mm ID thick wall pipe, with long handles.  The diameter of my crucible is 48mm ID, so any ingots made should fit into my crucible later for remelting.

It seems a long time since I have done any welding, and the welding of these items was pretty ordinary.  But the joins seem water tight, so hopefully they will be OK.

Today I fired up the casting oven, to 850ºC, and the load was some ordinary food tins.  They are the correct diameter for investment moulds.  I wanted to see if the tins would cope with these temperatures. (after removing labels of course).

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3 ordinary food tins, at 850ºC.

It became apparent, that the tin joins were welded not soldered.  And the inside and outsides of the tins were covered with some sort of paint or plastic, because it flaked off.  But the metal cans remained intact.  Admittedly, when hot they were VERY soft, but when cooled they retained their shape, and were quite stiff.   I would be prepared to try these for single use moulding projects.

I have realised that my investment plaster mixing bowl is too big for the vacuum chamber which I had bought.  So I have ordered another vacuum chamber, and waiting for it to arrive before starting a mix.  I am using the delay to gather items like the ingot moulds above.

It will probably be another couple of weeks before I am ready to cast.   Meanwhile my 2mm rivets have arrived at last, so I will get back to the riveting.

TURKISH BOMBARD – a-post-script. And metal casting setup ready.

I made this 1:10 scale model of the Turkish Bombard which currently resides in the Royal Armories Museum, Portsmouth, in 2016.  I specify “currently” because I originally saw this cannon in 1979 at The Tower of London.  And long before that it was used in Turkey, guarding the Dardanelles.  Quite likely used in anger in 1805 against a British fleet, approximately 340 years after it was made for Sultan Mehmet “the conquerer”. 

And I re-visited the original in May 2019. It seems like half a lifetime ago. Mainly I visited the UK to see the Trevithick dredger engine in the London Science Museum, but the Turkish bombard was the second reason. I could not find a photograph of the touch-hole in the bombard anywhere. And my requests to the museum went unanswered.

The original bombard in the Royal Armories Museum, Portsmouth, UK.

So, here is my photograph of the touch hole, in case anyone else is inclined to make a model. I guarantee that this is the only photo of the touch hole which you will find, with my hand anyway.

The Turkish bombard touch hole
My 1:10 scale model of the bombard. I still have not added the touch hole.
The Arabic script around the muzzle. Not as good as in the original. But as good as I could manage in 2016.
and the large thread between the barrel segments


So, I made this model, in wood, as a practice run, intending to make a bronze model eventually.

The reason for this post script is that I had a question from a reader about a remark which I had made in 2016. And I could not find my original photographs. So I took some more, as you have seen.

And……… very excited to announce that I now have a foundry setup, and could possibly make a bronze example of the bombard. But first I intend to obtain some casting skills, by making parts for my 1:10 Armstrong cannon.

I replaced the analogue controller with a digital type in the potter’s oven which I had recently purchased, and today my wiring was checked by an expert before we ran a test run. (thanks Stuart!) All good, up to 750ºC, which is enough for preparing the investment molds.

Here is a shot of the oven, and the metal melting furnace.

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from the right, the melting furnace which should be adequate for 3kg of brass/bronze,  and the investment oven. The oven might also be useful for metal tempering. Note the Hebel bricks behind the oven.

Hopefully, the first attempt at a casting session in a couple of days.

 

Bronze Casting -2

When I looked closely at the rifling cutters which I had lasered out of a broken Brobo saw blade, I realised that I had boobooed.  I had measured the thickness of the blade at 2.5mm, which was actually a bit thinner than I wanted, but would have been acceptable. But when I measured the cutters, they were only 2.2mm thick.   Reason?  The saw blade had been hollow ground, and the blade inside the teeth was thinner.   Too thin, I decided.

So after some wailing and teeth gnashing I have ordered some 3mm thick tool steel in the form of planer blades, which I am pretty sure will not be hollow ground, and I will ask the laser cutter to cut me some more blades.  So waiting waiting.

And I am setting up the cannon barrel for rifling.  The CNC rotary table (stepper motor hidden behind) will be bolted to the CNC mill table.  The barrel is held in the jig which is held by the mill quill.  The cutter, (not seen in this photo) will be drawn out of the barrel by the mill X axis, while being rotated in the A axis by the rotary table.   That is the plan anyway.  But still waiting for bits to arrive so I can finish the cutting tool.

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The Armstrong cannon barrel held to the mill quill, and the rifling cutter will be held by the CNC rotary table.

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The rifling tool which I will not be using because the cutter is too narrow.  The cutting edge just peeping out of the slot will be dragged and twisted through the barrel bore.  The cap screw adjusts the degree of protrusion.

 

BRONZE CASTING

Meanwhile, I am accumulating various bits of gear to do some bronze casting.   An electric furnace with graphite crucible from China, Some jewellery investment material for the moulds, and a second hand pottery kiln for preparation of the moulds, and melting out the PLA 3D printed parts.   I will take some photos when it is all here.

And SWMBO has conscripted me to assemble and install some kitchen cupboards for a property which she is renovating.

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These are flat pack units.  Kaboodle.  Well designed and CNC cut and predrilled.  Not quite finished.  Waiting for the stone bench tops to be made and installed, and for appliances to be wired and plumbed.  Frankly I would prefer to be tidying up my workshop, but hopefully I am gaining some “Brownie Points”.

Bronze Casting. 1.

My model Armstrong cannon has some components which will be difficult to machine, and would involve silver soldering many tiny pieces.

For example, the steel brackets in which the wheels are supported, and the centre column.

rear trolley

There are 4 trolleys like this.  Each one has 2 or 3  wheels.  It is a Z shaped profile with 3 gussets visible and 2 more inside.

IMG_8411

The centre column.  It could be fabricated.  

But being basically lazy and always looking for the easy way out, I have decided to investigate the possibility of casting these parts.  And some others.

So I have printed them in PLA filament, with a view to a “lost wax” type of casting process.  It will be “lost PLA” of course.  Maybe doing the casting myself.  But also checking the possibility of having it done professionally.

The PLA printed parts which will be melted and burned away in the casting process, have to be as well finished as possible.  So I have been experimenting with various settings in 3D printing.  One problem is that the molten plastic thread has to be supported.  Overhangs up to 45º or even 60º can self support.  And even horizontal overhangs can self support if the gap is not too big.

print unsupported threads

But this gap, about 20mm, proved to be too big…

print unsup oblique

The threads are partly bridging the gap…

print unsup end

Horrible.  It is the underside, but even out of sight, it is unusable.

So, I am printing up some supported versions, even as I type this.  And I am going to look at some casting equipment which I might be able to borrow.  Apparently the gas furnace is very noisy, and it needs a home with no close neighbours.   List…. a furnace capable of melting bronze, a crucible, investment casting powder,  protective gloves, helmet or face mask, leather apron, tongs, slag ladle, a casting box.   There are many YouTube videos on the subject of lost PLA casting.    Watch this space.  But if the quote for professional casting from my printed molds is not too fierce, I will probably take that path.