new bronze

[gulfcoastblackpowder]

Thanks!  Looks like one of many must go to places if I ever go to London.

[RocklockI]

New Bronze took a hit today .

The second of two crumbled B4 my eyes ...... in slow motion . I was nearing the sculpting part of the turning when the wax just broke and the gun rolled off in half and fell on the floor .

Good greif , I gotta find better wax .

The first needs to get cast because it is made from the same crumbbly wax . So it maybe weeks B4 the second one is done .

Gary

[gulfcoastblackpowder]

Is that the same wax you've been using for everything else?  If so, what's different now?  Trying to skip a step somewhere (i.e. doing sculpting of the wax rather than sculpting clay then casting it)?

I'm sure you'll work it out.

[dan610324]

sculpting directly in the wax is a cost effective way if you only are going to make one or just a few of something

the silicone is very expensive

dont know any american prices , but here in sweden it costs approximately $ 130 for 1 liter if you want a high quality platinum cureing silicone .
there is lots of different tin cureing silicones for half that money , but thats not good to use if you want a good result
tin cured shrinks , platinum doesnt
so you can spend several hundreds just for the silicone to a small barrel mold
and a lot of hours making the mold
so in this case it will probably save gary some working hours and certainly a lot of money

[RocklockI]

These first one will go to the casters tomorrow . I have some machinable wax on the way till then it's on hold .

I want to make some one offs not really a bunch of one thing . I have 200 bucks in the silicon for the Morko mold and over 300 in the spudgun .

turning the wax also eliminates parting lines .

gary

[gulfcoastblackpowder]

I figured that was the intent.  Is problem you are having that the wax you had for the other guns was not considered "machinable," but rather lends itself to casting?  Eliminating the parting lines would probably make cleaning up the bronze casting quicker!

[gulfcoastblackpowder]

Stupid question - if you wanted to in the future make additional pieces of the machined wax projects, couldn't you then make a silicone casting of the bronze piece as the master?  Not saying that's in the plan, but it seems like it should work.

[RocklockI]

I figured that was the intent.  Is problem you are having that the wax you had for the other guns was not considered "machinable," but rather lends itself to casting?  Eliminating the parting lines would probably make cleaning up the bronze casting quicker!

Well , yea sort of , the wax I was using is considered candles .

It's not the time required to clean up parting lines in wax that is a hassle . It's the damage you can do to the rest of the gun while you clean up parting lines .

why not do them first ? .....well I do , but inevetably I see something that requires more attention after the dolfins are on , the suface is good ,this dingle ball and that is attatched ... and i start    'handling it agian?'    something will get broken or bent .

It is a cleaner way to do things IMHO .

eta the interiour consistancy of the wax in these candles is snow like , crumbbly just plain %^@)_^*!}>(&%

[GGaskill]

Making a mould from an original will result in the finished piece being 4 or 5% smaller than the original, maybe more.  The wax cast in the rubber mould shrinks, and then the bronze cast in the investment shrinks again.  When you make a pattern for something that requires specific finished dimensions, the pattern has to be made oversize so the finished casting is correctly sized.

For something like a Morko, the shrinkage may be acceptable, although you start getting distortion of details also if there are too many shrinkages.

[RocklockI]

True George , Morko came out @ 1/4 " shorter than I thought .

I was mortified I spent all this time layin new layers of 'clay' over and over . When I checked it for the final OK .......... I couldnt believe I made the thing 1/4 inch short ! I was PI%SS*ED OFF BIG TIME !

then it clicked ! .... shrinkage....the clay I'd been using shinks every time you heat it .  I heated it ....a few times ....

No biggie really but it was kinda a shock as I thought I was nutts on .

[dan610324]

both the wax and bronze shrinks approximately 1,5% each , so the total shrinking is 3%
but if you make a master and a silicone mold from tin cureing silicone you can add another 3% shrinkin

[gulfcoastblackpowder]

I was aware of the shrinkage (both before we discussed it here, and after the numbers Dan posted on here a while ago).  Just thought it would be a possible option should the need ever arise.  For that matter, I know some companies like the Rifle Shoppe make their business around making investment casts of original hardware that is rare and sometimes difficult to duplicate.  Are there any techniques you can use to reduce the shrinkage?  For that matter, is it possible to effectively cancel out the shrinkage you get from these 2 different moulds?  (i.e. silicone mould shrinks out - away from the master, while final metal casting shrinks in - away from the silicone)

[RocklockI]

Short of changing the laws of physics i don't think so .

But , now that is only my humble opinion . 

[dan610324]

thats right , you cant change the shrinking because of temperatures , but if you use a high quality platinum cureing silicone you have no shrinking in that step of production

just add 3% on all messurements on the master and you will come very very close

[carronader]

Dan , did you get me those shares in Central American Silicone ?

[dan610324]

sorry noooo , but I could get you a pair of chinese implants if you need them   

[gulfcoastblackpowder]

thats right , you cant change the shrinking because of temperatures , but if you use a high quality platinum cureing silicone you have no shrinking in that step of production

just add 3% on all messurements on the master and you will come very very close

I'm not sure either of you understood what I was asking.  It's not really important, though, since I'm not trying to get into casting.  Still, I'll try to reword what I wrote to see if it makes any sense.  

I'm not trying to defy the laws of physics, but to apply them.  Shrinkage will occur with any mould making process, but shrinkage in one direction is expansion in the other, if you take my meaning.  As far as I understand it, the shrinking of the negative investment cast actually expands the void where the metal will be cast.  The metal will shrink when it's cast in that void, so if you match the shrinkage factor of the metal to the shrinkage factor of the investment, you'd end up with a net shrinkage near to 0.  Of course, there would be some distortion or loss of detail due to the expansion of the investment and the shrinkage of the metal.  This is the same principle employed in dental casting as far as I understand it, though they use a gypsum bonded silica investment, which may behave slightly different than the platinum cured silicones you recommend.  Does that make sense?

[GGaskill]

What you're looking for is a rubber that would expand upon curing, leaving a bigger cavity than the pattern.  I don't know of anything that would do that and am not sure it is possible considering the processes involved in curing.  It would seem that the cured product would have to be in a higher energy state while most curing processes seem to leave a lower energy state (this is mostly speculation here.) 

In any event, for it to be of much use, the expansion would have to match the contraction of the next material and since there are so many potential "next materials," it's probably easier to make the pattern larger by the known shrinkages.

[gulfcoastblackpowder]

I agree with you that it's easier to make the master larger, but this was a consideration of the specific case of trying to produce an 1:1 scale copy of an existing item.  From what I can find, dental casting does this very thing, though they use a restricting ring on the investment mould to allow it to expand longitudinally, but limit it radially, creating a distortion, but maintaining the desired scale, so that the shrinkage of the metal to be cast is compensated by the controlled expansion of the investment.  I can see how this would be important, since you can't make the original tooth larger to compensate for the metal shrinkage.  I was thinking that the same concept could be applied to bronze casting, but maybe the investment material they use really does perform much diffently.  Would be interesting to discuss this with a dentist familiar with the science behind it.

[gulfcoastblackpowder]

The articles I've read on the subject say they generally use SiO₂ + CaSO₄ which expands when it sets when mixed with H₂O (whatever that is).  I don't know if that helps understand their process and how it may differ from the bronze casting process used for cannon.

[GGaskill]

Did you see anywhere how much expansion occurs?

[gulfcoastblackpowder]

I'd have to hunt down the source of the specific formula of investment I referenced before, but it didn't specify a percentage expansion.  Here are some other sources I found with a quick Google search:

For the gypsum bonded silica investments, here's an abstract that gives some differences based on different suppliers and varying amounts of water:

Dent Mater. 2005 Jun;21(6):573-9.

Expansion of high flow mixtures of gypsum-bonded investments in contact with absorbent liners.
Lodovici E, Meira JB, Filho LE, Ballester RY.

Department of Dental Materials, School of Dentistry, University of São Paulo, São Paulo, Brazil.

Abstract
OBJECTIVES: To evaluate the expansion of high flow mixtures of gypsum-bonded investments in contact with two dry absorbent liners since early setting.

METHODS: Cristobalite-Dentsply and Cristobalite-Polidental gypsum-bonded investments were tested under 10 setting conditions (n=4): Normal and Hygroscopic (controls); four conditions of 'Dry-Lining' (set in contact with 3 different amounts of dry cellulose liner: 0.2, 0.4 or 0.8 g and with 0.1 g of a granulated Super Absorbent polymer liner) and four conditions of 'Dry-Lining with hygroscopic expansion' (initially setting in contact with dry absorbents, as 'Dry-Lining' conditions, followed by water immersion immediately after loss of gloss). The percent of expansion at 2h was analyzed.

RESULTS: The 'Dry-Lining' condition, with 0.4 and 0.8 g of cellulose, for brand Dentsply (1.41+/-0.13 and 1.42+/-0.16) and Polidental (1.14+/-0.17 and 1.01+/-0.22) allowed a significant higher expansion than the controls Normal (Dentsply=0.30+/-0.04, Polidental=0.31+/-0.05) (P<0.05). The 'Dry-Lining with hygroscopic expansion' condition with 0.8 g of cellulose expanded significantly more (3.57+/-0.55) than the control Hygroscopic (2.63+/-0.31) in brand Dentsply (P<0.05). Super Absorbent did not produce different expansion (Dentsply=0.86+/-0.02, Polidental=0.79+/-0.18) than the controls Normal and Hygroscopic (Dentsply=2.93+/-0.17, Polidental=2.12+/-0.40).

SIGNIFICANCE: The water removal with dry cellulose absorbent liner before loss of gloss increased the potential of setting expansion for Normal and Hygroscopic conditions. Thus, when using high fluid mixtures, which are more desirable for investment pouring, it will be possible to obtain enough setting expansion potential in order to adequately compensate for wax and alloy shrinkage in the casting process.

http://www.ncbi.nlm.nih.gov/pubmed/15904701

Here's a bit out of an old dental textbook that I found on the USC website, which may be of interest, though it doesn't give as many details as I would like (it gives the expansion of various golds, and seems to be using wax rather than the gypsum silicone: http://www.usc.edu/hsc/dental/Resources/Courseware/atlas/images/Chapter%206.pdf

Here's another reference to a different investment material, which does give a 2.10% elongation for an unspecified phosphate bonded investment.  It looks like the purpose of this study was to investigate different elongations of different investment materials for this very purpose: http://www.springerlink.com/content/k1174n171g088832/

[dan610324]

Im not sure of how you are thinking here

dont know how they do it in the dental labs , but I would guess that they make a wax pattern of what they want to make , then maybe dip it in another wax with a lower melting temperature than the original pattern
this will add enough much to compensate for the shrinking of the gold
then they of course fit it by hand to get the perfect fit

so I cant understand the need of expanding investment or why you should let it expand in one direction and not the other . even if the investment expand the void wouldnt be any larger than the wax original .
the investment I use is the same as used in the jewelry industry for gold castings , so I guess that the dental labs use the same or at least a similar investment .
that investment doesnt shrink

as long as the molten metal is liquid it fill up the mold totally , but when it sets it start shrinking , its the temperature difference from the set metal to room temp that makes the shrinking , so its already set as an exact duplicate of the mold before it start to shrink , so there is no distortions other than the 1,5 % metal shrinking

but stop here , now you mixed up apples and pears , they aint the same

you compare investment with silicone , that cant be done as they are used for 2 totally different purposes in the castingindustry .
the dentists probably never use silicone as they always only manufacturing one piece of everything .
the only time you use silicone is when you want to make a larger serie of the same thing

this time gary wanted only 2 identical pieces and he turned them by hand , by doing so I guess he saved a few hours compared to make a silicone mold , and for sure he saved a coupple of hundred dollars as he dont need to buy any silicone

you must compensate all 3 dimensiond on the wax to have it work
so if you got a gunpart you want to cast , take the originat part and put on a thin layer of wax before you start making the silicine mold for that part , it will give you an slightly oversized wax piece when you cast the wax in the silicone mould.
but in this case you compensate both for the wax and metal shrinking in the next 2 clomming processes .

then when you cast the wax positives they had shrunk approximately 1,5%
next you put it in the investmentand there you have no shrinking , but when the metalgoes from liquid tohard is nothing happened , its when it starts cooling down as an hard piece of metal the shrinking happened , so I guess it aint that difficultto duplicate a weapon part perfectly if you got a top of the line equipment and lots of different wax qualities to work with .

but in this hobby level of cast bronze cannons I have vever nade any practicalchages on dimentions other then the few chabges I make direkt on the drawing board

what do you mean by this :  seems to be using wax rather than the gypsum silicone:
all those 3 materials have specific functions during the whole process , and none of them can br exchanged to any of the others

[GGaskill]

Regarding casting bronze cannon, I have cast 4 half scale mountain howitzers, three in sand moulds and one investment.  I made a fiberglass mould from my wood pattern and cast a wax pattern in that which was then invested.  But the invested casting turned out smaller than the sand castings, perhaps because the sand moulds expand when filled if not rammed hard enough.  The wood pattern had allowances for shrinkage and machining so it was larger than the finished product to begin with.  One of the nice things about CAD is you can enlarge the drawing by any factor and have the software recalculate all the dimensions.

Here is the thread discussing it in more detail but there aren't any pictures of the fiberglass mould.  I'll try to remember to take one tonight and add it to this thread.

[dan610324]

the fiberglass mould made from the pattern will of course leave a 1,5% smaller wax positive than the original master, and in the other step the bronze will shrink another 1,5%
so it will be smaller

[dan610324]

must go to bed now , its 02 15 am here now

[GGaskill]

I think part of the difference is also that the investment gets fired and becomes a very rigid mould while the sand mould remains somewhat soft, at least softer than the investment, so the filling of the sand mould causes it to expand some that doesn't happen with the investment.

[dan610324]

now I read more here , how can you try to excgange the use of silicone and investment ??
bot parts has its place in this chain just dont try to change place of them
silicone is used to cast wax positives in it  , investment is used to cast bronze in it

are you sure you really know what yu are talking abou ??
or it could be me who are too tired to think
or my lack of eglish skills when it comes to a bit mre complicated discussions
OR A MIX OF THEM ALL

  GOOD NIGHT

[Double D]

Good night Dan, sweet dreams...

[Div Arty]

Well let me be the first to wish you a good morning Dan.  Don't kick your English Skills.  I have been reading your posts since you started and you are almost up to par.  To bad because I kinda enjoyed the old Dan.