HMS Bellona 1760 by SJSoane - Scale 1:64 - English 74-gun - as designed

[mtaylor]

Mark,

 

Did drilling the trunnion hole first cause any issues with the turning of the gun?   I've thought of that but was concerned about chatter and possible cutter breakage.

 

I've got one of those angle tool mounts on my lathe.  They make doing things like cannon a lot easier. 

[SJSoane]

 

Hi Mark,

 

It worked for me, drilling the hole first. I then turned it at the highest RPM on the Sherline lathe, with a very shallow cut across the area with the drilled hole. I was also using the pointed cutting bit, which presumably has a smaller surface to catch if it would. I was only aware of a smallest change in sound, but no sense of anything catching. It seemed to work without difficulty.

 

Best wishes,

 

Mark

[druxey]

Mark; your method is fine. Michael Mott (Skipjack thread) suggests a centre bit to start the hole on a round surface. The mass of the bit prevents deflection.

[mtaylor]

Mark & Druxey,

 

Thanks for that info.  I'll do that next time I make cannons.    I knew about the center bit and it works a treat but holding the darn cannon without damaging it is a trick.  Doing it before turning would be best.  Hmm... note to self, don't start turning cannons now.

[Siggi52]

Hello Mark,

 

the bark is still in Greenwich. 

 

When I reread your question about what it's in that mold, it's the filling canal. You fill the cannon from the under side, so that the air could leaf to the top.

 

Regards,

Siggi

[SJSoane]

 

HI everyone,

 

Well, I confidently started out trying to make the gun insignia with photo etch. I simplified the George III image, but when I print it out at 3/16" inch scale (about 1/8" long), even the simplified detail disappears. And I am not yet sure how much detail will even show after I sort out the etching process. Not so confident now!

 

Maybe there is a better idea....

 

Best wishes,

 

Mark

 

[michael mott]

 

And I am not yet sure how much detail will even show after I sort out the etching process. Not so confident now!

 

Maybe there is a better idea....

 

Hi Mark, I wonder if the etching process is the best choice?

 

I seem to recall that Doris used the fine Fimo type modelling clay to form the insignia on her cannons, I cannot remember the post but she did do some tutorials on some of this very small detail stuff. I am assuming here(one of my recent failings ) that this is for the mould. I will see if i can find it, I could also be completely out to lunch on this one.

 

And thank you for the kudos regarding the machining.

 

Michael

[michael mott]

Mark I was thinking about this sort of thing

 

 

and this

 

 

michael

[SJSoane]

 

Thanks, Michael, this is a very good lead. I'll look up Doris' log, and track down some Fino in the morning. The etching was beginning to look like major overkill for one master....

 

Your machining continues to inspire me. I worked a little harder on my cannon master after seeing how you approached your project. Thanks!

 

Mark

[druxey]

If you only need one monogram for a master pattern, have you considered building up the detail with thick acrylic and a fine brush?

[SJSoane]

Thanks, druxey, that is a good idea. I spent the day trying fine wire, Fino modeling clay, and then some stick-on thin copper. None worked as well as the copper, which I show in a rough form here. I was thinking about casting a copy of the cannon, then adhering the thin copper to the barrel, and then engraving and cutting while it is in place. But before trying that, I will try the acrylic matt.

 

I am learning that, at this scale, it is an impression of detail, not as defined as I thought at first. The thin wire and modeling clay were way too "chunky" for the scale of the detail and the cannon.

 

druxey, any ideas on how I will transfer the pattern to the brass barrel? Of this this a case of free-handing with a fine awl?

 

Best wishes,

 

Mark

[druxey]

I think free-hand would be the way, unless you can copy the pattern onto very thin paper, glue that to the master barrel and build up over that.

[SJSoane]

Hi everyone,

 

I have managed to cast my first cannon, more by luck than skill. Many thanks to Greg Herbert for the cypher; I have yet to accomplish a photo engraved cypher myself.

 

I learned a great deal, but will have to do this again, since the mould line between the two halves got a little ragged, leading to leakage and also a loss of detail at the join. Here is what I learned:

 

First, I built the initial mould box taller than the clay, which was a mistake. I was digging around from above to try to level the clay, and to push it evenly against the master. In hindsight, I see that the clay needed to be more accurately pushed up against the master. I didn't, and the first pour seeped down into the areas where the clay was not fully against the master, leaving a thin "flap" that prevented the second pour from coming cleanly against the master.

 

Next time, I need to build a first box at the level of the clay, then build higher walls to contain the first pour of rubber (the idea can be seen in the PDF about making moulds in the resources section of this website).

 

Second, I was using MicroMark rubber mould material that was 18 months beyond its shelf life. I don't know what it is supposed to be like within its shelf life, but one of the bottle's material was very stiff to stir at first. Indeed, I did not stir it enough for the first pour, and as a consequence it took overnight to dry and did not capture the detail as well as the second pour. I worked hard at mixing for the second pour, and added some thinner. The fidelity to the master was significantly better. 

 

I used a bottom-up feed on the mould, with the understanding that the trapped air would be pushed out a vent at the top.  I poured resin until I saw it bubbling out of the center vent. That method seemed to work flawlessly, with no captured air bubbles. However, I did notice a couple of pin holes in the top of the muzzle, which i assume were bubbles created when i poured the rubber onto the master. I poured a very thin stream rubber from over a foot above the mould into a corner, understanding that this would remove bubbles thicker than the stream, and that the material would slowly flow over the master. Worked almost, not quite! Perhaps my rubber material is too thick still, and needs more thinning.

 

If I am feeling experimental, I might try a top feed and see if it makes any difference or causes any difficulties. A top feed would certainly reduce wastage on the poured material. (I am in no rush, since I am still backing and filling, waiting for the Colorado humidity to come up in the spring so I can get back to building wales at the same humidity as the internal deck clamps.)

 

Back to the foundry for round two...

 

Mark

 

[Remcohe]

Not bad at all for a first cast!
 

Remco

[Siggi52]

Hello Mark, 

 

it looks great. Casting is always a guess what will come out. But keep trying. I know, sometimes it is frustrating. You would find pewter in every corner of my shop from casting with centrifugal force 

 

Did you forget the touch hole at the cannon?

 

Regards,

Siggi

[SJSoane]

 

Siggi, well spotted. I did forget the touch hole. Good thing I have to start again anyway!

 

So, do you have a centrifugal force casting machine? I have seen those in jewelry catalogs.

 

Mark

[dgbot]

I will be watching and learning.  Eventually I might have to do some casting myself don the road.

David B

[Siggi52]

I'm glad that I'm not the only one who is sometimes faster then it is good for the project 

 

No, I did't have such a machine. But once a friend asked me to cast coins for him. The smaller the projects, the harder they are to cast. So I build something I could put in my drill and then turning it at a slow speed and pour in the pewter. 

 

 

 

 

 

In the middle is the pouring sprout. When I made the speed faster, most of the pewter went out at the side and I had a lot to do, to remove it from the walls and all around me. I hope you understand what I mean, but my english.

 

I think it would't be too hard to build something also for the cannons. But normally it would work as you have already done it. The bubbles are the great problem. If you stir to much, you have bubbles. If you stir lesser it will not harden evenly. 

 

Would you later cast with pewter or stay with this material? Pewter flows better, because its heavier. But also here you could have problems with bubbles. 

 

Keep trying,

Siggi

[SJSoane]

 

Hi David, it is worth jumping into, and easier than I had expected. My initial failure just gave me more encouragement to get it right next time.

 

Siggi, your English well explains the image of pewter flying around your shop! I hope nothing got burned. I have already purchased some pewter from a jewelry supply, and will likely try casting it in the spring, when I can go outside to heat it up. I am a little bit concerned about the weight of pewter guns, and the possibility that they could break away from their mountings long after I can no longer gain access to the deck. But I assume many before me have successfully managed this.

 

Best wishes,

 

Mark

[dgbot]

At one of our meetings we had a member give a demonstration on casting using a low temp pewter. He used a match to melt the ingot. On larger pieces he used a small propane torch. it was a very learning experience.

David B

[druxey]

When I cast (in pewter) I made the mold muzzle up, with relieving vents at the trunnions. I made sure that the pouring vent was large. This helped filling and also provided mass, so that the metal would not solidify before filling the mold. In addition I talcum-powdered the mold to improve metal flow. The first few pours were defective (possibly the RTV mold needed to 'mature'), but after that everything worked perfectly.

[EdT]

Looking good, Mark.  Casting, is an educational journey.  Siggi, I am amazed at your centrifugal casting "machine".  This would scare me to death without a containment to catch the flying molten metal.

 

I invested in a centrifugal casting machine about 20 years ago and have used it many, many times - including on some 1" long cannon barrels.  It has rings around the molds to prevent distortion when spinning and also to contain the inevitable escaping metal.  The spinning mold is contained in a metal box with a hinged lid that has a hole for pouring - also speed control on the rotor.  I have cast maybe 6000 miniature figures in this with maybe an average of 8 different figures per mold.  The machine was about the cost of a Sherline mill so its not a solution for a few dozen cannons, which, by the way, may be too large.

 

Eliminating bubbles from the mold rubber is a major headache.  This was especially a problem for me with the small deep undercuts in small figures- lots of metal baseballs in eye sockets.  I eventually solved it with a vacuum pump of the type used for refrigeration maintenance and a homemade vacuum chamber made from a pot and a sheet of thick polycarbonate- with some tubing and fittings - and an RTV ring gasket.  I think you would be amazed, as I was, by the amount of air that comes out of RTV rubber when under vacuum. This is another investment not worth making unless you do a lot of casting.  Before that I tried using a shop vac with very limited success.

 

I found some success (before having the vacuum) eliminating bubbles in the rubber by using straight mineral spirits to dampen the pattern before pouring the rubber - instead of greasy mold release agents.  Also, tapping the mold or vibrating it when the rubber is first poured may help.  Dusting the mold with talc before pouring metal also helps reduce porosity in the metal castings.  You might also experiment with pouring temperature.

 

I can't offer any advice on casting resins.  I gave up on them rather quickly, because of bubbles and they were too light for me.

 

Good luck, Mark.  The barrel in your picture looks great.  I know you have very high standards.

 

Ed

[michael mott]

Mark your first attempts at casting look great, That said I thought that Druxey's comment about casting the barrel muzzle up was the way I would have approached it, one other thought that occurs to me is to make the bottom of your pouring sprue (gate) a smooth curve rather than the right angles that you have done in your first one. The venting looks good to me. something you might try is to leave the vents off until you start to cast especially with the pewter, and as you test the pours you can use a sharp #11 blade to cut v groove vents from the trunnions and begin with small almost no holes and increase them till the right flow occurs. sometimes a little back pressure helps to fill the area right next to the main body rather than a fast flow.

 

The talcum powder helps a great deal with the metal, I had a small muslin bag that I used to fill with talc and used it to dust the moulds the casting worked best when the moulds had warmed up after a few runs, so you will notice that the casting improves usually with the 2nd 3rd 4th pours and so on until the mould reaches its optimal working temp.

 

I spent many evenings of my boyhood casting costume jewelery in 12 inch circular centrifugal moulds, that were made by vulcanizing them in a metal shell under great pressure. The casting machine had a turntable that was like a record turntable with 6 counterbalance weights that would apply pressure to the steel plate on top of the two halves of the mould, there was no speed control as such but I learned by trial and error what speeds and speed of pour into the central cavity. I used to get paid 3 shillings per gross and there were eight to twelve pieces per mould depending on the particular shape. I used to cast 3 gross per evening (guitar callouses couldn't hold a candle to mine in those days)

 

When I had my own business building models I had the commercial casting equipment but eventually sold it because i didn't use it much.

 

Michael

[SJSoane]

 

Hi druxey, Ed and Michael,

 

Thanks very much for the advice. You have all had a lot of experience with casting, and this is invaluable for me.

 

I will try the top down feed in my next version, and see what happens. I will first order some new rubber from MicroMark. I think the shelf life problem was working against me this first time. It was a little thick.

 

How were you all heating the pewter? With a propane torch, or will a micro-torch do the job?

 

Best wishes,

 

Mark

[michael mott]

Mark in my case it was a commercial melt pot that was electric, the chap I worked for was a bit unscrupulous and would cheap out on the quality of the metal sometimes, I wont go into the details of one event that scared the .... out of me! there was metal all over the room. I went home early that day after giving him an earful.

 

Michael

[SJSoane]

 

Michael,

 

So both you and Siggi have had experiences with metal flying around the room. I am beginning to understand that metal casting is a contact sport!

 

Isn't it fun reflecting on those early life experiences that only later we can call character building...;-)

 

 

Mark

[druxey]

I use a propane torch over a cast iron ladle. Cutting the pewter ingot into smaller pieces and using a small quantity speeds things up.

 

RTV rubber is quite soft, so I recommend an outer plaster retaining jacket to prevent distortion of the casting or leakage between the mould halves. Don't forget to make the vent channels through the plaster continuous with the RTV mould. Please make sure the plaster is completely dry before casting, for safety's sake!

[EdT]

I have always used a hot plate with a metal pouring dish.  An electric casting pot with temperature control is the Cadillac.  Agree with druxey on the plaster support for the rtv but may not be necessary for these small castings.  USe new plaster of paris so the hydration goes to completion and no residual moisture is left.   Micromark sells two varieties of RTV.  One is better for metal -  i.e. harder and more durable - I thinks its called 10 to 1.  I have gotten well over a hundred castings from molds made with it.   A good electronic scale is also recommended for accurate measuring of the rubber and catalyst.  Oh yes, someone mentioned this I think, stir the rubber thoroughly but gently to reduce air entrainment.  Oh, this brings back memories.

 

You're certainly getting a lot of advice here, Mark.  I hope some of it is helpful.

 

Ed

[SJSoane]

 

Hi Ed,

 

Thanks very much for this help. I have 28 castings to do at this gun size, plus a few spares.  I had originally ordered the 1 to 1 four hour set, which exceeded its shelf life by a long time, and I think I need to throw away at this point. I was just about to order some new RTV, and saw that MicroMark has a one to one one hour set; in light of your comments, can I assume that this would be too fragile for my intended run? And do you think I should go ahead and order the 10 to 1? I see what druxey is saying about floppiness with the rubber I tried so far, and perhaps the 10 to 1 would not have that problem.

 

I will try the measuring by weight rather than by volume in a measured cup; it seemed fairly hit and miss by volume.

 

Do you mean a regular kitchen hot plate and metal dish? I somehow assumed I would need more intense heat as in a propane torch.

 

Thanks again, it is always comforting to be walking in the footsteps of great craftsmen who have been down this road before!

 

Mark

[EdT]

Mark, I would go with the 10 to 1, but the other might work as well for the cannons, which are quite simple.  To use the 10 to 1 type, you will need an electronic scale to measure the liquid catalyst - by weight.  50/50 by volume is easier to manage.  The mold tear strength was the problem for me.

 

I found no trouble getting up to temp with the hot plate.  I will take a few pics for you today and post.

 

Ed