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.

More Gearing Up, and more to come.

This was 4 days ago.
Today. Re the gears on the right, bottom row…. one was machined from bar stock, the other was cast, had the outer ring removed, and a new ring soldered on, then the teeth were cut. Can you pick which is which? And all of the round gears have spent 3 hours in the gemstone tumbler to remove sharp edges. The tumbling has reduced the surface oxidation on the large gear castings, but some more time required to totally remove it.
CNC milling the spokes in one of the intermediate gears. Neat job, but the internal corners with fillets are not really kosher. This gear is barely visible in the finished model.

And the gears with ratchets attached need 2 mates. I tried to make them yesterday, but we had a wild day with thunderstorms and high winds, and my machines were playing up. I might get back to them today. (the ratchets can be seen in the header photo).

In country Victoria we are out of level 3 lockdown! Hooray! Still can’t see family from Melbourne, and minor restrictions on visiting local friends, and need to wear masks when out and about. But things are on the improve. I doubt that we have seen the last of the virus however.

Rack Off

As in, not yet installed.

I spent few hours finishing the racks today. But not yet installed. Some photos.

Firstly the racks were surfaced…
… then drilled, then given an outline using CNC.
….then tested against their corresponding circular gears. But not yet installed.

For once, a job proceeded without a mistake. Hooray. Hmmm. Look at that big gear. Thinks… “I quite like that blackened inner area with the polished bronze hub and teeth”.

(p.s. For non-Australian readers, “rack off” is an expression sometimes used in Oz, when telling someone to leave or desist, in a forcible, but not quite foul manner. Used in the post heading in a hopefully, mildly humorous effort to be eye catching.)

On the RACK

The final gear in the cannon carriage positioning train is a rack gear. It is 198mm long, 7.2mm wide plus tabs for bolting it to the carriage of the model Armstrong cannon.

A rack gear is a flat gear, and it is cut with the same cutter (number 8) which makes a circular gear of 135 teeth or more.

The teeth of a circular gear are cut by dividing 360 degrees by the number of teeth. But the pitch of the teeth of a rack gear is determined by a formula found in Machinery’s Handbook. rack gear pitch = module x 3.1416. Which for my module 1.25 = 3.927mm. Hmmmm. 3.1416. That is a familiar number. Light bulb in brain switches on! A rack is just part of a circular gear of very large diameter.

At first I thought that I would use the same mill arbor which I had been using for the circular gears, but as soon as I started to set it up I realised that the stick out of the arbor would be ridiculously excessive. So, reluctantly, I set up the horizontal milling attachment of the mill. Reluctant, because the attachment is heavy, fiddly, and time consuming. Luckily, I had a 22mm shaft for the attachment, the correct diameter for the cutter. I had never used this shaft before, and it was missing the nut, and bronze bush. Bought it on Ebay years ago. Found a suitable nut and made a bush.

This is the setup. The 350mm shaft was not long enough to make the rack in one setup, and it took a bit of trial and error to work out the best compromise.

The horizontal attachment on the vertical mill. Setting it up takes me a couple of hours.
No CNC here. Just lots of calculations using 3.927.

I need 2 racks, so I will split this one down the middle.

Did not have a piece of bar stock big enough for this job.

So I joined 2 pieces end to end with silver solder. Will that be strong enough? My friend Stuart T insists that a well made silver solder join is stronger than the parent metal, so we will see.
It meshes nicely. The mounting holes (which I did not use) will disappear when the outsides of the 2 racks are shaped.

A bit of a story about that heavy horizontal mill attachment. When I bought it some years ago, I put it in the rear compartment of my SUV. But on the way home my SUV was T-boned by an idiot at an intersection. No injuries, but a big expensive dent to the passenger side of my SUV. Air bags activated. And the rear window was smashed. I could not figure out why the rear window was broken. After the police and fire engines had finished, and the tow trucks arrived (my car was out of action for 2 months, the other vehicle was a write off), a by-stander approached me with a familiar object which he had found in the gutter on the OTHER side of the 8 lane highway. Yep! It was the horizontal mill attachment. Been flung through the rear window by the violent impact of the collision, and across 8 lanes of the road. It was scratched, but otherwise intact. And thank goodness, it had not hit me or anyone else in its trajectory!

Gearing Up

I have been making gears.


The big bronze gears on the bottom row were cast, had M1 teeth cut, had the teeth machined off, a bronze ring silver soldered on, and M1.25 teeth cut, which is what you see. They are almost finished. Above them are an almost finished M1.25 pinion and a pinion which will be parted from the stock bronze shaft tomorrow.

The right hand smaller gears are M1, with teeth cut. The right hand one started life like the ones on the left, but was a reject. I machined off the outer ring, and part of the spokes. and silver soldered on a new outer ring, and machined the M1 teeth. The similar solid gear has been made from bar stock from scratch. The spokes will be CNC machined, maybe tomorrow.

The bar at top has M1 teeth machined, ready to be bored for the shaft, and gears parted off.

The pinions for the big gears have a 4 tooth ratchet. This will allow the gear train for carriage movements to be disconnected for firing.

Gears. Modularity Counts!

Making the big spur gear which pushes the gun carriage up and down the inclined chassis has been a bit of a saga.

For a start, I decided that fabricating it with lathe and mill was going to be very difficult, and it was an obvious candidate for casting. In bronze. After making a model with 3D printing in PLA.

So, I drew up a 3D model, saved it as an STL file, and printed it. But did not take into account shrinkage of the PLA part. Or shrinkage of the cast bronze part. So instead of 58mm diameter, the blank gear was only 57.4mm diameter. By reducing the number of module 1 teeth to 57, I could get a reasonable gear, and the teeth were duly cut.

But, module 1 teeth looked skinny and pointy and not correct. Plus, 3 of the cast gears were total casting failures and were discarded (remelted).

So, I machined off the module 1 teeth, made some bronze disks, and silver soldered them onto the cast central hubs and spokes, and machined the blanks to 60mm diameter. By this stage I had decided that the big gear teeth should be module 1.25. Chunkier. Looked the part.

But I did not have 1.25 module gear cutters. And no-one in our club had them for loan. So I ordered a set from China. Delivery any time up to the end of November!! Then I found 2 of the set from an Australian dealer, but they were priced almost as much as the full set of 8 cutters from China. But, thinking that they would arrive more quickly I bought them. They were Chinese. It is a seller’s market.

Then today, at our GSMEE meeting Swen P said that he had a set! And I could borrow them! So, gratefully, I did. And I cut the teeth this afternoon.

The module 1.25 gears at bottom. The module 1 gear top. Please tell me that you can see a difference.

While the teeth were being cut, I tidied up another bronze T rex.

Two of them now face off on my Trevithick engine. They should amuse the kids.

Next to cut the M1.25 rack. Should be straightforward.

Blood Sacrifice

My brother Peter, on reading my tribulations regarding the making of the big gear in the Armstrong RML cannon, reminded me of a saying of our father regarding any difficult job. That the job would not go well until some blood had been spilt.

My brother has not responded to my invitation to visit, in order that some some blood be spilt.

And to be frank, I have many so cuts and nicks and embedded splinters, that Hephaestus, the god of blacksmiths, should be happy….And, I have made some progress on the big gear…

Today I machined off the module one teeth, and silver soldered on a bronze blank disk ready for the module 1.25 cutters when they arrive. Yes, it was painful. Not sure if Hephaestus will be satisfied. But the invitation to my brother stands. If he will risk the Victorian Covid 19.

The module 1 teeth on the left gear has been rejected. So I have ground off the teeth on the middle gear and silver soldered on a blank disk ready for the module 1.25 teeth. Same with the gear on the right.
and these are the big winding handles, with the defects repaired. I silver soldered in some segments from the reject handle to replace the defects. Can you pick the handle which was perfect? Not quite finished, but looking pretty good?

Casting Bubbles

When bubbles occur inside a casting, the cause is probably in the design of the pouring system, or the way the melt was poured. If you watched the video a few posts ago by Prof. John Campbell you would think, as I did, that our pouring funnels and sprues should be more complex and more carefully designed. Difficult at an amateur level. I have made some changes in this direction, using a side reservoir to tip the melt into, and trying to avoid the gurgling and glugging.

With the sort of castings which I have been making for the Armstrong cannon, I am not so concerned about internal voids. The scaled down model always has an advantage in strength of the part, compared with the full size part, within limits.

But, bubbles which stick to the exterior of lost PLA/wax models are replaced by solid bronze, or whatever metal is used, and these metal bubbles can be tricky and difficult to remove.

I decided to remake the big gears, which were the subject of the last few posts, and the cause of a lot of bad language. I decided that the gear teeth were too skinny and pointy, and redesigned the part using larger module teeth. To compensate for PLA shrinkage and metal shrinkage I printed the PLA parts with a 2mm machining allowance.

The gears with the narrow pointy teeth.

I printed the PLA blanks, leaving the gears and brake drums as a blank lump which I will turn to shape after casting. But the internal decorative holes and ribs will be cast. And they are the site of many bubbles in previous castings.

So, to avoid the bubbles, I am trying something different in the current casting session. I am trying a method which was suggested by a GSMEE member, and that is to PAINT the first layer of investment material thinly on the tree components, making sure that no bubbles stick to the parts, then to pour the rest of the investment filling the cylinder. There might be some bubbles in the main volume of the pour, but they should not be sticking to the parts. That is the theory anyway. I am waiting for a bigger vacuum pump to arrive by post, which should be more effective at sucking out the bubbles, but meanwhile, I will try this…

The gear blanks, painted with investment, particularly in the bubble prone areas between the spokes.

Today, I heated 2 cylinders/moulds in the investment oven, and melted some bronze.

For the pour I tried the negative pressure apparatus.

I did not notice any change in the level of the molten bronze in the reservoirs when I applied the negative pressure, so I doubt that it added much to the process.

The results were like the curate’s egg… some good, some bad.

This was one cylinder. The reservoir/funnel at top, then 4 rather spindly round handles. The top one had a defect, the second was perfect, the third had a couple of small defects, and the fourth was unusable.
The bottom one will be used to repair the 2 with small defects. There were 4 tiny parts in addition. 2 were excellent, 2 must have broken free from the tree and disappeared into the ether.

There were 2 big gears in the other cylinder. The one at the top did not fill properly and is not usable. It will be remelted. The bottom one was close to perfect.
Note the absence of bubbles. I think that my pre-painting the investment into the recesses must have worked. The failed gear again was near the top of the tree. It seems that even bronze requires a bit of head to create filling pressure.
These are the tiny 20x19mm fittings. Some time in the gemstone tumbler should polish them up nicely.

I am waiting for a more powerful vacuum pump to arrive by post. The 1/4hp one that I am currently using is too slow, when time is critical. I have a 1hp pump on order. No more casting until it arrives.

And then got better….

When my workshop activities mainly involved woodworking, I realised that concealing mistakes was a major skill of the craft.

As an amateur metalworker/model maker, the same principle applies.

So, today, I took a long hard look at yesterday’s disaster. (and apologies for my bad mood, and worse language. Actually, I toned down the language for the post.)

It was pretty bad. Huge gash, bent brake drum, damaged teeth.

And what I did is as follows….. first, a bit of amateur blacksmithing to bend the bent brake drum roughly back into shape. Then….

I found a bit of brass, and roughly fitted it in the big gash. Some belt sanding improved the fit. Then silver soldered it into place. I rested the brass shaft on a piece of brass as a heat sink. I really did not want that join to let go yet.
… then bandsawed and belt sanded and turned it closer to shape…. then recut the teeth.
… and it turned out pretty well, no?

Still some work to be done on the reverse face, but it is looking useable.

This time I wrote my own CNC gear cutting program. And it worked perfectly. And I used the same program to cut another gear.

Repaired gear on right. Some further filling, filing and machining required. But, nothing can go wrong now. OK?

It got worse

After yesterday’s post my readers were very supportive and nice. Made the post worthwhile. Thanks readers!

So today, I machined off the bent shaft, silver soldered on a new bigger one, and re-machined the damaged brake drum. It looked resurrectable.

Silver soldering a new, bigger (13mm dia) shaft. Note the damged teeth, filled with silver, and the brake drum, hammered roughly into shape, and filled with silver.
and then machined the shaft to 12mm, perpendicular to the gear face.
And then milled new gear teeth….
and it looked really beautiful. Ahhhh!

BUT!. There was a line in the gear cutting program which I had checked, but not noticed. It said Y0. 3 lines earlier the program said G0. If you program CNC you might make the connection. With 3 lines difference, I did not spot the problem. But this was the result….

Fuck, Fuck, Fuck.

The CNC mill did what it was told to do. Really buggered about 3 days effort. NOT impressed with Mach 3 Wizards for gear cutting.

I will look at it again tomorrow, to see if it is fixable, again. Excuse my French.

Learning from MISTAKES

It is said that you learn from your mistakes.

Actually, I think that you TRY to learn from your mistakes.  It makes you feel a bit less stupid when you make mistakes.  Or, at least, it puts a bit of worth into having made a mistake.

At the rate of my mistakes in recent days, I should be turning into an Einstein.  Somehow, I doubt that is happening.  I think that I will stick with my motto of avoiding making the same mistake more than 3 times in a row.

Yesterday, I was cutting gear teeth into the big gears which I had cast a few days earlier.  Due to the mistake of not allowing for shrinkage of the castings, the wheels were almost 1mm smaller diameter than planned. (#1.). That meant that the wheels would have 55 teeth, rather than the planned 56 teeth.  Not a big problem, just an annoyance.

Also, I had not cast a shaft in the gears, or any method of holding the castings for teeth cutting, (#2) so I had to drill a central bore, insert an 8mm shaft, and solder it in position.  I should have used steel for the shaft, but for some reason I chose brass. (#3.)

Then, I could not find my module 1 gear cutters.  The  cutters, I knew, because I had seen them recently, were in a small cardboard box.  I went to where they were usually stored, and they were not there.  OK.  I must have put them somewhere else.  Then spent 2-3 hours searching every shelf, drawer, bag, box, floor, machine…. you get the picture.  And could not find them.  So I searched my vehicle, the other shed, and could not find them.   Had I loaned them to someone else?  Surely I would remember that?  So I went and had a cup of coffee.   Hmm.  What next?  OK, start searching again, going over previously searched spots in case I had missed them.  So, first to the cupboard where they were usually stored.

And there they were.  Exactly where they should have been.  Well bugger me!  (#4).  There was a small upside to this long and frustrating search.  I had found a few other tools which I had not seen for quite a long time.

So then I commenced the gear cutting.  55 teeth into the bronze wheel.  The setting up of the CNC rotary table on the mill, attaching the cutter to the arbor, cutting teeth marks onto the circumference to check my calculation of the number of degrees per tooth (360/55 = 6.545454º….).  All going well.   Each tooth required a cut 2.66mm deep.  But I was a bit concerned about that 8mm brass shaft.  Would it bend under the pressure of the tooth cutting?

So, I cut the teeth in 2 stages.   1.5mm deep for the first cut, 2.66mm for the second.  The first cuts went well.  Looking good.  After a complete circuit, the partly cut teeth were all even, and gleaming.  So, onto the full depth of 2.66.

DISASTER!  (#4.). When I attached the cutter, I had carefully placed it on the arbor so that the securing nut would tighten, rather than loosen with the cutting process.  But I had got it wrong.  Totally wrong, and it loosened!   BAANG.  I hit the big red button.  The mill spindle stopped, but the now loose cutter was still spinning wildly.  What if it comes off while spinning like that?  Would it fly across my workshop, cutting whatever it hits? Like me?

When I bought a woodworking spindle moulder many decades ago, an uncle advised me to NOT use it.  He had seen a co-worker die, when a cutter flew off a spindle moulder, slicing into his abdomen.  I did use the new spindle moulder, but with great caution, and never had any problems.  

Visions of the gear cutter slicing into my belly.

But, the cutter slowed, then stopped, to my relief.

A quick look at the workpiece was disheartening.

The brake drum attached to the gear was bent .  A spoke had a big gash.  The tooth which was the culprit for this disaster was gashed too deep.  and the shaft was bent to a crazy angle.

First thought.  “Bin it and start again”.   Steps to make another big gear.   1.  3D print a new PLA gear (with machining allowance this time, and include an oversize shaft).  2. Make a casting tree. 3. Mix and pour the investment. 4. Dry, burnoff, and bake the investment. 4. Melt the bronze and pour. 5. Machine the gear blank, cut new teeth.  2 days estimated, if all goes well.

Oh well.

No photos of the damaged gear.  Not in the mood.  But I did take a closer look.   I wonder if it can be repaired.  Maybe the distorted brake drum could be bent back into shape?  Or cut off totally, and silver solder on a new one? Fill the defects, and tidy up the damage.

I decided to call it a day.   But first I used a hammer on the damaged bronze gear brake drum.  Somewhat to my surprise, it went back into reasonable shape, without cracking.  So, a bit more tapping, and it looks quite good.  It will require a bit of filling and filing, and machining, but maybe it is resurrectable.

After a sleep, and fresh look, I relented and took a couple of photos.



But what about finishing cutting the gear teeth?  It will need a new shaft.   My plan is to machine off the bent shaft, insert a new steel shaft while holding the external circumference of the gear in the lathe chuck.  Might just work.  If the over-gashed tooth looks too odd when I finish cutting the teeth, I will fill the void with bronze or silver and re-machine it.  Watch this space.


BRONZE POUR- everything went wrong!

Just to recap, I made the trees and investment powder moulds about 2 weeks ago.

The biggest gears on the Armstrong cannon. Some with cast teeth, and some with blanks for teeth to be cut. And some brackets in red on top.
And the 2nd tree has 6 brackets on top, and another T rex to fill the spare space.

The first problem was that when I was adding the carefully weighed and expensive investment powder to the carefully weighed water, the f***cking scales timed out and shut down. So I had to guess the amount of powder to add. Then mix furiously. Then a briefer than normal degassing. All to be completed in 10 minutes. 10 minutes sounds like a long time. But it is all too short when there is any hick-up at all. (read.. “stuff -up”). #1.

I knew that the scales had a shut down timeout, and following the Chinglish instructions, I thought that I had turned the timeout off. But apparently I had not. After that I ordered some new scales.

Then I had to wait almost 2 weeks for the 15% phosphor copper to arrive.

Yesterday, after installing a new heater element in the melting furnace the day before, I fired up the investment oven and went through the drying, burnout and baking cycles, about 8 hours. And prepared another tree and mould for the next pour, in a few days time.

The melting furnace with its new element took a lot longer than previously to melt the bronze ingots, about double the time. But that was OK. Just had to ring SWMBO to warn her that I would be very late. (Got home about 9pm. She had organised take away.)

I added the 15% phosphor copper in approximately the recommended amount. And poured the first cylinder. But I forgot to wait the recommended 2″. #2.

Then I poured the second mould. And there was not enough melt!!!! #3. I had underestimated the amount of bronze! Those 4 big gears were guzzling the molten bronze! So what to do? Abandon the second cylinder? Or melt another ingot and just pour it on top of the first one after another 30-45″?. Nothing to lose, so I plopped in another bronze ingot, and waited for it to melt. Meanwhile I put the mould half filled with bronze back in the investment oven to keep it warm at 710ºc. Then, for some reason, the electronic controller of the investment oven shut down, and the element stopped heating. #4.

When the extra bronze melted I added bit more phosphor copper and completed the pour into the now substantially cooler mould which was already half filled with bronze which presumably had solidified. I assumed that the join between the 2 pours would be a problem. And it was.

Forgot my camera. Some photos to be inserted here later.

Somewhat surprisingly considering the guessed amount of investment powder at the original mix, and short duration degassing, the first mould was, apart from a few bubbles, completely successful. The second mould, with its 2 pours, was not a total disaster.

Today I sawed apart the trees, removed the bits of sprue and vents, and partly machined the parts. These are the bits.

The toothed gears and non toothed gears are the biggest gears on the cannon. And they include the drum brake, I was unsure whether the cast teeth would be adequate, or whether I would need to cut the teeth. It was not a fair test, in view of the interrupted pour, and the brief degassing. But I will cut the teeth from the blank wheels to the right. The toothed gears were probably the join between the 2 pours and total failure and will be remelted.

Even the blank wheels are not without problems. I did not allow for shrinkage, #5. and the diameter of the wheels is 57.5mm instead of the intended 58mm. So I cannot cut 56 teeth per wheel. I can cut 55 teeth on the smaller diameter. Still pondering that one. Do I repeat the entire exercise with a machining allowance? Or just be satisfied with one tooth less? I have not decided definitely, but am tending towards accepting a slightly smaller tooth count.

But, at least the brackets to the right came out well. This photo was taken after some belt sanding….not perfect, but not bad at all.

Incidentally, the T Rex is quite good. substantially less surface oxidation, and the oxidation layer that was present came off much more easily. Next pour I will add a bit more of the phosphor copper. And I will wait the recommended 2″.

2 steps forward, one step back. A familiar dance.

15% Phosphor Copper-2

It arrived today. Rather uninspiring small grey bits of metal about the size of rice grains.

But how much to add to the melt?

So I searched the net and found this.

15% Phosphor Copper Shot is use as a deoxidizing agent for copper, brass & bronze alloys. It will also increase fluidity and inhibit gas porosity. The shot we carry is approximately 1/8″ x 1/32″ in size.

Melting of brass, bronze and copper should be done quickly in a slightly oxidizing atmosphere. The crucible is removed and surface is skimmed, then phosphor copper shot is added by simply dropping it onto the surface. The reaction is very visible. The metal will become fluid and bright. Allow a minute or two for the reaction to complete, and pour. 

The phosphorus is a reducing agent (deoxidizer). This product must be carefully measured so that enough oxygen is removed, yet a small amount remains to improve fluidity. Too much phosphor can cause the melt to be so fluid that it leaks from the mold and penetrates the sand. A little goes a very long way! 

The primary reason to use the shot is because the molds aren’t filling well or have gas porosity problems. The literature suggests that 1 ounce of 15% copper phosphor shot be added to 100 lbs of metal. A teaspoon of shot weighs about 1 ounce. 

Start with these amounts: 100 Lbs add 1 Tsp. 50 Lbs add 1/2 Tsp. 25 Lbs add 1/4 Tsp. 

For lesser amounts start with about 1 to 4 granules per pound of metal

At that rate the 1kg will last a lifetime.

Metal Casting Research

The video featured in this post is fairly recent, and will probably be of interest only to those who are actively involved in casting, and those who like to keep up with developments.

While aimed mainly at industrial level casters, there are lessons which amateur casters can apply.

Thanks to GSMEE member John Bernoth for sending me the link.

As a very amateur beginner, the video made me aware of how little I know about the subject.

You can watch the video on the small screen here, or find the YouTube link to watch it full screen. The video quality is pretty ordinary, but the message is, I found, very interesting.

ps. waiting for the 15 phosphor copper to arrive by our very slow post before I do any more casting. Still in level 3 lockdown. I am making a negative pressure pouring apparatus, almost finished, but after watching the above video I wonder if I am on the wrong track. Maybe I should be thinking about bottom filling, spinners, and restricting the flow rate.

The heavy plate with the hole is connected to the water chamber on the left. The mold cylinder will sit on a silicone pad which will have a corresponding hole. The hot air will pass through a copper coil in the water chamber to the left, and the cooled air will then go through a tube to the evacuation chamber and then the evacuation pump. The filler and drain plug positions were determined by pre-existing holes in the copper tube.

15 Phosphor-Copper Shot.

Never heard of 15 phosphor-copper?

Neither had I.

T Rex, in bronze.

My bronze castings had been coming out of the investment mould looking like this. I had been expecting to see a wonderful shiny golden bronze colour, and was a bit disappointed in the irregular black coating. But the casting itself was complete, with no voids, and having fine details like fingers, and 3D printing marks showing up clearly. And after laboriously attacking the black coating with Dremel wire brushes, files, sulphuric acid (ineffective), a lot of the black was removed.

This baby T Rex has found a home on my model dredger engine. The variegated skin colouring is reasonably convincing, but was not the shiny bronze colour which I wanted.

Maybe a problem with the LG2 bronze ingot? Something else?

So, I telephoned the supplier, Clingcast Metals, Sydney. Paul answered the phone, and he knew exactly what I was describing. “copper oxidation. Did you add 15 phosphor-copper shot to the charge? (The “charge”, I gather, is the crucible loaded with bronze pieces, for melting?)

“No. What is 15 phosphor-copper shot?”

“Small metal balls. If you add a tiny amount to the charge you will avoid the surface oxidation which you are experiencing, AND it will make the bronze melt thinner and run more freely.”

“Great. Where do I get it.”

“Oh. We have heaps here.”

“Would you post some to me?”

“Sure. How much do you want?”

Quickly thinking….”Maybe a kilogram”.

“That will last you a lifetime. $15, plus postage”.

“Fantastic.” – but I can’t find my credit card. Darn.

Paul. “I will post it. Just pay us when you get around to it.”

So, no more casting sessions until the 15 phosphor-copper shot arrives.

And big kudos to Clingcast Metals.

Meanwhile, I am making up trees and moulds.

Another T Rex, and some cannon parts.
The transparent PLA disks are the biggest gear with brake drum. I have not yet decided whether to cut the teeth on this part. And the red PLA parts are brackets for the cannon chassis.

Also meanwhile, I noted that Banggood have a special on melting furnaces which seem identical to the one for which I paid $425, and I have seen advertised at up to over $500. Banggood are asking $AUD290 + $20 p&p. So I have ordered one, as a spare. If you are interested I suggest that you check out this special, ASAP.

p.s. 2 Sept 2020. The 15% phosphor copper arrived today. I found this info on how much to add. I think that my 1kg will last a lifetime.

15% Phosphor Copper Shot is use as a deoxidizing agent for copper, brass & bronze alloys. It will also increase fluidity and inhibit gas porosity. The shot we carry is approximately 1/8″ x 1/32″ in size.

Melting of brass, bronze and copper should be done quickly in a slightly oxidizing atmosphere. The crucible is removed and surface is skimmed, then phosphor copper shot is added by simply dropping it onto the surface. The reaction is very visible. The metal will become fluid and bright. Allow a minute or two for the reaction to complete, and pour. 

The phosphorus is a reducing agent (deoxidizer). This product must be carefully measured so that enough oxygen is removed, yet a small amount remains to improve fluidity. Too much phosphor can cause the melt to be so fluid that it leaks from the mold and penetrates the sand. A little goes a very long way! 

The primary reason to use the shot is because the molds aren’t filling well or have gas porosity problems. The literature suggests that 1 ounce of 15% copper phosphor shot be added to 100 lbs of metal. A teaspoon of shot weighs about 1 ounce. 

Start with these amounts: 100 Lbs add 1 Tsp. 50 Lbs add 1/2 Tsp. 25 Lbs add 1/4 Tsp. 

For lesser amounts start with about 1 to 4 granules per pound of metal

One to 4 granules per pound of melt! It really will last a lifetime. My crucible will melt a maximum of 3kg/6.6lb.

Spur Gears -1

The model Armstrong cannon has 7 gears, 2 of which are bevel gears, and 5 spur gears, including one quadrant gear.

4 of the original spur gears. These position the carriage on the chassis for loading and firing. There is also a decoupling mechanism on the second shaft. (Portland cannon)

The spur gears will be machined and cut from bronze, brass or steel. I have a set of module 1 cutters, which are close in 1:10 scale to the originals which are close to module 10.

The bevel gears I have made by casting them in bronze, teeth and all, and they are pretty darned good. Not perfect, but they will be hidden from sight in the gear case. They seem to mesh pretty well, but, if they are not up to the job of elevating the barrel I will cut some replacements.

The biggest gear is a spur gear, and it has a brake drum as part of the casting. It is a bit more complicated than a simple cut spur gear. Apart from the brake drum, the gear teeth have flanges at each end of the teeth, which will make them difficult to cut, unless I add the flanges later. I guess that the original was cast, teeth and all.

From below, the biggest gear with the brake drum on the left of the picture. The brake band is a steel band. (Port Fairy cannon)

I have decided to cast this gear also.

You can see the flanges more clearly in this photo. (Port Fairy cannon)
So I have 3D printed casting blanks with teeth and flanges (left) and without teeth and flanges (right). I will cast both, then decide which to use. 58mm diameter, 25mm wide. The prints are colourless PLA. I have had problems with plate adhesion with this PLA.
The bevel gear case. Cast bronze. Some more finishing required.
The cast bevel gears. Since this pic I have machined bores and improved the finish. PLA blanks.
And can you guess what this fingernail size piece is? It will cast in bronze.

Bronze Casting. Can You Bake the Investment Twice??

I found out the answer to this question today, unfortunately.

This is the PLA + wax tree which I wanted to cast. There are 3 bevel gear cases, for the Armstrong model cannon.

There are internal cavities for the bevel gears, holes for the shafts, and external/internal surfaces, quite a complex shape.

Yesterday I mixed the investment, and poured into the flask, around the tree. It was a tight fit in the flask. I had miscalculated the flask diameter, and some parts were probably touching the metal cylinder. So I was not too confident about a good outcome. But I went ahead and commenced the drying out, burning out, and baking cycles. About 7-8 hours altogether.

Then started the bronze melt in the electric melting furnace.


The temperature was not rising.

Usually, 1100ºC was reached in 30 minutes or so.

But it remained at 19-20ºc. Ambient temperature.

Penny dropped. Bummer. The Melting furnace was RS.

6 months old, still under warranty. But how long would it take to get parts or replacement from China? Email sent.

And what to do about the already prepared investment flask, happily baking away? So I turned off the investment oven, and let it slowly cool down.

Discussed the situation with Stuart. Probably burnt out the heating coil, but could be the relay or the control unit. Whatever, it will take days/weeks/months to sort out. Bummer.

Stuart: “You can borrow my spare unit”.

Me: “you have a spare melting furnace?”

Stuart: “sure”. “you can borrow it”.

Me: “wonderful, thank you”

So today I wondered if the investment flask could be reheated to 710ºc, and accept the molten bronze. Stuart: “Don’t know. Never done it”.

So today, I reheated the investment flask to 710ºc, over 3-4 hours, held there for an hour, melted some bronze in Stuart’s loan furnace, and poured.

Here is the result.

3 almost perfect gear cases. I have removed the sprues and funnel and most of the investment. Not showing up well in the photo, but I have demonstrated that the investment mold CAN be reheated. I will machine off the unwanted bits and surfaces tomorrow.

Casting with bronze seems a bit more forgiving than with aluminium. And Investment mold, at least with Goldstar Omega Plus, CAN be cooled and reheated without cracking up.

And a replacement heating coil will be sent from China. Maybe I should buy a spare melting furnace.

Japanese Knife

In common with every modeller, woodworker, metalworker, boat builder, surgeon, “hands on” person that I have ever met, I love tools, particularly tools made with thought and care and passion for quality.

And, although I have never been a knife maker, I have been a frequent watcher of “how to” make knife videos. Who knows, maybe I will branch out into that hobby one day.

This post was prompted by my purchase of a new knife. Undoubtedly the sharpest knife I have ever used. At first glance, it has an attractive, basic shape, and I thought, “that will make a good kitchen knife”. It is long and slender, not for chopping sweet potato or pumpkin, but more for fine slicing of tomato, or coriander. (or meat/fish if you are a Neanderthal).

And sharp! It is sharper IMO than a surgeon’s scalpel. It passes the paper held at one edge slicing test with ease. I could shave with it, except with a 8″/200mm blade, that would be a bit terrifying. Even cutting up vegetables is an activity to be approached with caution. A touch on a finger would end up as a trip to the casualty department for stitches.

The knife is Japanese. Of unknown age. Probably handmade.

It was offered to me by GSMEE member Neil, who has a substantial collection. One glance at the photo he sent to me was enough for a “yes please”.

The knife, and its wooden sheath.
Can anyone translate this?
The handle, ferrule and blade are asymmetric. The grip is quite positive. Previously I have rejected asymmetric blades because they tend to deviate sideways while cutting, but this one, for some reason, cuts straight.

The wooden sheath is not Japanese. It was made by Neil, and the blade snicks perfectly into place. The pattern on the sheath is unique, and random. Looks the part, no? Considering the terrifying sharpness of the blade, the sheath is an absolute necessity IMO.

Japanese knives, chisels, saws and other implements are available from Tetsu, Ocean Grove, Victoria, tel 0403 549485. If you want a knife with a fitted wooden sheath (strongly recommended), contact Neil McMeekin at tel 0491 212 258.

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.


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


 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…


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.


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


Soft Jaws

The bronze gears which I cast yesterday were cut off the tree with small bolt cutters, band saw and hack saw.   Then a belt sander to reduce the daggy bits.


The gears, and the tree trunk and branches which will be remelted.


The faces needed to be flattened in the lathe, but how to hold the rather thin, delicate, irregular gears?

Soft jaws.

Soft jaws made of aluminium, and exactly machined to match the external diameter of gear teeth, so there are multiple contact points, and minimal chance of damaging the teeth.  I made these soft jaws ages ago, for just this sort of job.


The soft jaws are machined to exactly fit the workpiece.

The soft jaws may be used multiple times, machined to shape each time.  Very handy in this situation.


The larger gears are good.  I silver soldered some extra material on one of them for the shaft, then turned the shaft to size .  But, holding the small pinion gear is more problematic.  I will need to machine a soft jaw with a taper to hold the teeth.  Next session.  I should have anticipated this situation and designed the gear with a shaft to be PLA printed as one piece.



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”.


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.



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.


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

Totally delighted with this result.  Beginner’s Luck.