44767
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Posts: 535
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Post by 44767 on Jun 22, 2018 11:50:20 GMT
With ever more demanding standards by some modellers, there seems to be more demand for very close to scale castings and finishes which require virtually no finishing. Lost wax casting is the ideal process for this whether the waxes are produced from rubber moulds of manually created or rapid prototyped masters, 3D printed patterns in PLA or casting wax or, indeed, from hard tooling.
I'm wondering what sort of premium you'd pay for, say, a driving wheel which was lost wax cast using a CAD model done from the works drawings over a sand cast wheel with the necessary fettling etc.? Let's say a driving wheel sand cast in cast iron sold for £35.00, how much extra would you pay for a lost wax casting knowing the extra effort that goes into producing them?
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jasonb
Elder Statesman
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Post by jasonb on Jun 22, 2018 13:30:17 GMT
I suppose a lot depends on the quality of the finished item. If somebody was knocking them out on a cheap 3D printer with a coarse layer and not doing any additional prep to the surface, followed by not degassing the liquid investment or burning out all the pattern then I would not pay any more for an investment cast item over a sand cast one. On the other hand if it were a high quality print with good surface finish and well cast then might be willing to pay more depending on where the item goes on the model as if it is hidden away then not much point in paying for detail that won't be seen.
J
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44767
Statesman
Posts: 535
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Post by 44767 on Jun 22, 2018 13:59:37 GMT
OK. So here is one example. The pony truck wheel for my class 3 tank project. This is the tool I machined to injection mould the wax. And this is a casting produced from a wax moulded in it. This has not been touched. This is as delivered from the foundry. I have machined a tool for the driving wheel which is to go to the foundry for trial on Monday. And right now I am working on a tool for a 5" gauge Castle driving wheel.
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Post by Deleted on Jun 22, 2018 15:47:42 GMT
Afraid I can't add anything but would like to say, that looks excellent sir...
Pete
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sis
Seasoned Member
Posts: 113
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Post by sis on Jun 22, 2018 20:38:59 GMT
Mike,
Ive sent you a PM.
Steve
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Post by 92220 on Jun 23, 2018 10:35:55 GMT
Hi Mike.
Your castings are 'top of the league'. Anyone building a model that wants the ultimate castings will pay a premium to get the best. Anyone building a model to commercial drawings and wants to get it finished in just a couple of years to be able to pull passengers every weekend, is not going to be bothered if the castings are accurately detailed or not, as long as they look reasonable and don't have blow-holes. Someone who wants wheel castings like that one of yours, I am sure, would pay at least 3 or 4 times the commercial rate. There is one hell of a lot of work, and research, required to produce castings to your standard. The cost of the metal is peanuts. The cost of the time taken to perfect the drawings prior to even making the moulds, is what costs the money and anyone wanting the best should know that and be prepared to pay for the work.
When I had my wheels cast, the casters gave me the shrinkage allowance and it was spot on! I made a mould like you did, but in 25mm thick Perspex instead of aluminium (big mistake because it didn't cool quick enough for the waxes), and eventually got castings that were within 0.003" of scale inside diameter. The casters took a long time sorting out the process because of my use of Perspex for the mould, and the fact that I wanted them in free cutting 316J stainless steel (they have mild steel tyres). When it came to pay, the cost was VERY SILLY money.....even though they knocked 30% off because I was a private buyer not a business!!! Well into 4 figures for 3 sets of wheels. I was happy to pay it for perfect castings. I sold the 2 spare sets for, I think, 3 times the cost (at the time) of bog standard cast iron ones.
Oh. And that wheel?.......superb!!!
Bob.
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44767
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Post by 44767 on Jun 23, 2018 10:57:14 GMT
Bob, Thanks for those words. It is a bit more encouraging to me. I guess if lost wax casting was similar in price to sand casting, everyone would be doing it. I know that a minimum time for the casting process at the foundry I use is ten days which is about five times as long as sand casting. Crudely, that would make them four or five times the price, which is actually not far off the mark. Like you say, "If they want it, they will pay for it".
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jasonb
Elder Statesman
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Post by jasonb on Jun 23, 2018 12:43:17 GMT
Hi Mike. There is one hell of a lot of work, and research, required to produce castings to your standard. The cost of the metal is peanuts. The cost of the time taken to perfect the drawings prior to even making the moulds, is what costs the money and anyone wanting the best should know that and be prepared to pay for the work. There seem to be two different things being discussed here. One is prrducing a high quality pattern like the one shown getting it as close as possible to the original which CNC allows compared to a pattern made form wood and a good coating of body filler which will never be as exact or crisp. The other is how the part is cast, I wonder how good a wheel could have been produced if the pattern were CNC cut from the same drawing and cast in a fine sand with care to get the two halves of the box lined up well. I bought a couple of 8" flywheels from Germany recently and the cast surface hardly needed touching and a couple of mins with a file to remove the fine parting line was all that was needed. On the other hand I've had ones that look like they used gravel not sand! What would have been the cost difference if you had used your CNC to cut them all from solid. How would costs compare to a few slices off a CI bar and a couple of cutters?
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sis
Seasoned Member
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Post by sis on Jun 23, 2018 16:02:06 GMT
Jason,
As I expect you are well aware the issue with making the wheels on CNC is machining time since with either lost wax or cnc from solid you have the wheel modeled. So if you want a fine finish you need a small step over with a small ball nose end mill running at a high RPM otherwise it takes all day. I have spoken with 17d about cnc coupled and driving wheels for my 7.25" 9f project but he has a 4000RPM spindle and he has to pass that cost on. He has experimented with speed increaser tooling but you have a limited duty cycle.
Ideally you want at least 10,000RPM but 20,000+RPM would be better then the wheel is going to be finished within an hour rather than a whole day. I do not know of anyone in the hobby commercially offering wheels from solid at reasonable cost because they don't have enough spindle speed. If they had a more modern milling machine with a faster spindle then they would have to pass that cost on. If someone knows of a supplier that can knock out fine finish limited run parts at reasonable costs please do let me know. In the mean time I think the lost wax casting is competitive.
Steve
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Post by 92220 on Jun 23, 2018 16:44:04 GMT
Hi Jason.
You don't need CNC to make a mould like Mike has shown, though it helps. I machined mine using my Senior vertical mill and my 200mm Hoffmann dividing rotary table. As I said above, I made my mould out of Perspex and so I made up all the cutters in silver steel, on the lathe and then just hand ground them down to half thickness to make them into a cutter like an engraving cutter. I didn't even need to harden them. I should have used aluminium for the moulds. If I had done, I'm sure I would have been able to produce them with exactly the same tools. To ensure the halves lined up I used silver steel pins in reamed holes, positioned with the mill DRO. You just have to be extremely careful to get the spokes cutter started on spoke No 1 (whichever you choose for this) relative to the location pins, as accurate as you possibly can, to prevent offset steps in the sides of the spokes when cast, as well as ensuring the width is accurately matched in each half mould. Really it's just careful machining, but it does take a long time. I think it actually took me 6 months to machine up all the moulds for my 9f wheels. I did have a couple of scrappers in that time though!!
As far as quality of casting goes, there is absolutely no comparison between investment cast parts and sand cast parts. Investment cast parts are cast in ceramic plaster like Plaster of Paris. The surface is smooth. Sand casting, however good will never have anywhere near as good a surface. Also, investment casting moulds for forming the waxes, are much more accurately located mould halves. Here you are talking in thous, whereas with sand casting, the location accuracy between mould halves is lucky to be within 1/64", unless you use waxes to produce the sand mould without any split, but you would still have to make a mould for the waxes. Then the only difference would be in the surface finish of the castings, so if costs were compared there wouldn't be much difference, but in cast surface quality, there would be.
Bob.
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Post by steamcoal on Jun 23, 2018 20:20:32 GMT
The CNC mould for making the waxes would be worth more than the locomotive if commercialy machined I am guessing.
Sort of puts things in perspective.
We were talking at our club the fact that castings are worth more in the raw state rather than turned into a locomotive.
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abby
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Post by abby on Jun 23, 2018 21:45:23 GMT
The fact is that the number of people prepared to pay a premium is very limited ...........in my experience ! To earn better than the minimum wage requires quantity and I would suggest 50 as being the minimum. The only clients that I have found willing to risk their money have been German , willing to finance orders for 50 and 100 off. Orders of this size give you a chance. whether it be rubber moulds or metal dies We call machined moulds dies and here is one I made almost 30 years ago. It makes a casting for a Jaguar XK 120 cylinder head hot water banjo , classic cars are a good outlet for lost wax castings. CNC is the latest thing and I must agree that it takes the drudgery out of machining , it also takes the fun. Try CNC ing a die for these castings. The dies for these were designed on the hoof and required the use of a smooth file ,low temperature alloy , a few Allen screws and a lot of thought. Actually I am just on the last glass of a very good Portuguese red and I can't remember the point I wanted to make. Oh yes ! you can put in a lot of effort , doesn't matter if it's the latest technology or bronze age , you can offer the finest product known to man but you can't make people buy. Model engineers are amongst the most parsimonious of people , I should know , I am one ! Finding one that can afford to buy is akin to finding a patron of the arts. Much more to say but too pissed . Dan.
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jasonb
Elder Statesman
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Post by jasonb on Jun 24, 2018 6:31:33 GMT
Hi Jason. As far as quality of casting goes, there is absolutely no comparison between investment cast parts and sand cast parts. Investment cast parts are cast in ceramic plaster like Plaster of Paris. The surface is smooth. Sand casting, however good will never have anywhere near as good a surface. Also, investment casting moulds for forming the waxes, are much more accurately located mould halves. Here you are talking in thous, whereas with sand casting, the location accuracy between mould halves is lucky to be within 1/64", unless you use waxes to produce the sand mould without any split, but you would still have to make a mould for the waxes. Then the only difference would be in the surface finish of the castings, so if costs were compared there wouldn't be much difference, but in cast surface quality, there would be. Bob. I would not say that investment casting ensures a smooth surface, back to what I first said which is that the resulting part is only as good as the pattern/wax. I have seen investment cast parts made from 3D printed patterns and the investment replicated all the layers that were present on the less than ideal pattern (those two guide castings posted by Dan are what I'm talking about*), likewise if your die has flaws or the wax gets damaged it will be reproduced in the finished casting. It is the whole process that needs to be done to a high standard right from research, design, patter/die, making silicon moulds if a positive pattern, injecting wax and finally the actual casting. If only one of these processes is less than it should be you won't get a premium part just because it was investment cast. Another factor that comes into play with surface finish is scale. I assume the locos being talked about here are approx 1/8th or 1/12th scale whereas most of what I make from castings are 1/2 or 1/3rd scale and some "character" to the surface is desirable otherwise it looks like a machined part that has been painted. Infact when I fabricate my own I will take a die grinder etc to the surfaces and add a little texture and remove the regular look to them. Just looked back at some reference photos of a couple of engines I have done and the casting finish on the full size is quite rough and parting lines have only had a token fettling and are quite visible. So again what I would pay would depend on the part in question, sand cast surfaces don't scale well so the smoother lost wax finish would be desirable on the smaller loco scales but not such an issue or even desirable on a larger project. * Not putting down the castings but just an example that the investment will replicate the pattern surface not ensure a smooth one.
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44767
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Post by 44767 on Jun 24, 2018 7:56:28 GMT
I agree with what you're saying Jason. The investment cast product can only be as good as the master pattern. Certainly, the surface finish will need to be sympathetic to the scale as well so that suggests that a sand casting for a 5" gauge locomotive casting is going to have a very rough finish when compared to the full size since the process uses the same sand. Here is another example. This is a sand casting for a pony truck frame. Not a bad sand casting but necessarily rather crude because of the limits of making the mould and the cores and their assembly. Here is a lost wax casting for the same part, as delivered from the foundry. It was designed from the same works drawing. Everything is scale thickness and has minimal machining allowance as it is geometrically accurate and sizes are precise. And both from the other side: Both can be machined to the same drawing but would you pay a premium to have the lost wax casting and save the time to fettle the casting and all that extra machining time? Mike
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Post by ettingtonliam on Jun 24, 2018 8:07:25 GMT
If I was building a super precise model (which I am not) and wanted super detail (which I do not), or was building commercially where time was money, and significant savings could be made in fettling and machining time (which I am not), then, yes, I would consider a premium based on the savings. For what I actually do, then whilst I stand back in amazement at the results which can be achieved, then I'm afraid that sand casting is going to have to be good enough for me. Does anyone remember Stuart Turner in the 1950s and 60s talking about their shell moulding technique which gave a better finish and more accurate casting than conventional sand moulding? I suspect that this was only viable with the production levels they had to justify the cost of the tooling. From comments I've read on another site recently, the casting quality from Stuart Models seems to have gone down dramatically in recent years. Do they not use shell moulding any more? Does anyone?
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44767
Statesman
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Post by 44767 on Jun 24, 2018 8:16:51 GMT
Hi Mike. What would have been the cost difference if you had used your CNC to cut them all from solid. How would costs compare to a few slices off a CI bar and a couple of cutters? Machining a one of set from solid may be OK for the model engineer, if he had the gear to do it himself. I know I do it and I love doing it. But commercially it makes no sense. The whole idea of a casting is to save all the cost of machining from solid and the cost of material and only leave machining where necessary. It wouldn't take much less time to machine one wheel than it does to machine the die (Abby's correct term) but that leaves you with another five or six to make. I find the limiting factor to machining speed is the controller of the CNC. Spindle speed, I find, is not as important as feed speed. I always say "you cut that speed because you can, not because you have to". The step over distance is much more than the feed per tooth so it will always have a better finish in one direction (along the tool path) which will polish out at the same time as the cusps left between passes. I have a CNC which is over 30 years old (an old one but a good one) but its controller effectively looks only one line ahead. Today's machines look ahead hundreds of lines and work out the fastest way it can move through all of the points without error. This is where you need the high speed spindle. Mike
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Post by 92220 on Jun 24, 2018 8:38:15 GMT
Hi Jason.
You are right about investment casting reproducing all the flaws on the surface of the waxes, whether from the mould or later handling. I suppose I was referring to commercial investment casting, which I have had a lot to do with, and commercial quality doesn't always appear in hobby investment casting. However, Mike's castings do get up there with commercial stuff though, and I, for one, am prepared to pay for his quality. Yes I may be a bit of an oddball but I am sure there are others who want the same quality of castings that I do and are prepared to pay for it. Dan is also right though, in his statement that there is a certain quantity threshold that will make the castings affordable to the mass model engineering market. I think that was really the basis of Mike's original post. He wants to know how much extra someone would pay for top quality castings over mass market quality, and that is probably impossible to answer, as everyone has a different depth of pocket combined with their modelling aims.
Bob.
Bob.
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Post by 92220 on Jun 24, 2018 9:08:58 GMT
If I was building a super precise model (which I am not) and wanted super detail (which I do not), or was building commercially where time was money, and significant savings could be made in fettling and machining time (which I am not), then, yes, I would consider a premium based on the savings. For what I actually do, then whilst I stand back in amazement at the results which can be achieved, then I'm afraid that sand casting is going to have to be good enough for me. Does anyone remember Stuart Turner in the 1950s and 60s talking about their shell moulding technique which gave a better finish and more accurate casting than conventional sand moulding? I suspect that this was only viable with the production levels they had to justify the cost of the tooling. From comments I've read on another site recently, the casting quality from Stuart Models seems to have gone down dramatically in recent years. Do they not use shell moulding any more? Does anyone? I think this says it in a nutshell for many model engineers, but not all. There are lots of superb models seen at exhibitions, where the detail is way above the norm. I am sure these model engineers would pay the premium, and looking at Mike's pics of the pony truck castings, they would have no hesitation in choosing the investment casting. After all, if you look at the detail on it, there is no way that it could be reproduced from the sand casting in the average model engineer's workshop without spending a massive amount of time on it, and for anyone like me, who HATES filing, sand castings are a definite No-No if I have a choice!! Even if the wax that the investment casting has been made from, has 3D printer lines, it is very easy to fettle these down with a Dremel and flex drive, using a mini abrasive flap wheel.
Bob.
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sis
Seasoned Member
Posts: 113
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Post by sis on Jun 24, 2018 10:30:21 GMT
Bob,
Last year I popped in to Reeves when I was nearby on business. I asked why e.g. cylinder castings were so expensive. I was told in no uncertain terms that the castings were a quote "nightmare" to deal with. The foundries Reeves use have such poor results that for example the more prototypical cylinder castings in 5" and 7.25" gauge are priced based on the cost of 4 or more attempts to cast. In 7.25" gauge they are too big for the lost wax foundries Reeves use for other intricate but smaller items. (In addition they have the problem of pattern damage.)
I asked Reeves why they were not modernising to avoid the risks of bad castings and pattern damage. I got the impression that they would rather drop these "problem" castings from their catalogue. If you take for example the Trevor Shortland GWR King they have started to do just that with outside cylinders no longer available.
Steve
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jasonb
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Post by jasonb on Jun 24, 2018 12:53:22 GMT
I can quite understand that on a complicated casting, although the foundry can put the metal from a bad casting back into the pot they can't do the same with the time spend on it so have to add something onto each casting to cover the cost of bad ones. As An example the cylinder casting for some of the larger compound models can take two foundry men a day to get ready to cast as there are many cores to make and place so that is 2 days wages down the pan if something goes wrong and the more complex the more likely that will be. Also with the very small turnover of castings it would take the likes of Reeves a long time to recover the costs of making new or reworking old patterns if they may only sell one or less a year and it's a big investment to have the rest of a batch sitting in storage for years waiting for a buyer. The truck is a good example of where the lost wax method would be worth paying that bit more for though there will always be those who have shorter arms but plenty of time on their hands who are quite happy to spend the time fettling a rough casting as model engineers have done for many years. On the other hand there are those who may still be working who have limited workshop time but more disposable income so the lost wax option would appeal to them more than a retired chap who can spend all day in the workshop. For those interested this thread my be worth reading where I suggested a company that could do aluminium lost wax casting and Mike (Vixens) work making patterns, silicon moulds and waxes that were then sent off to be cast. www.modelenginemaker.com/index.php/topic,7559.msg159628.html#msg159628 Don't know if this guy has cropped up here before but mention was made on ME forum of someone who will do the lot from drawing to casting. www.model-engineer.co.uk/forums/postings.asp?th=136363&p=1
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