22560 forum posts
Rather than Hijack the "Whatch this Space" thread with further discussion of CNC machines casting kits I'll repost something I wrote on another forum a few months back:
I have mentioned it before a few times about being able to resurrect some of the older designs where patterns have been lost or if they are still knocking about and usable the owner can't find a foundry to cast them. With modern CNC it should be possible to reproduce these castings with the added bonus of none of the usual casting defects such as blow holes, undersize parts, hard spots, over fettling , etc and leaving the builder to do the final work such as finishing bores, drilling and tapping of holes etc. much as they would with a traditional casting
A couple more examples of my own making, a bedplate for a small long out of production steam engine
A flywheel again from a 1930s design long lost.
Crankcases never a commercial casting but taken from a 1936 magazine design
There seems to be a market for part machined barstock kits from the likes of Bengs so it would only be a small step further to have some more shapely parts. I think even Stuarts are supplying some of the smaller items CNC cut these days like the valves for the 10series so it may not be as far away as you think.
22560 forum posts
Leaving the more modern methods to one side there is also the fact that far more home workshops now have milling machines and access to relatively cheap tooling so a lot of parts that were at one time provided in a casting set can quite easily be made by the builder where they may once have struggled to cut the part from solid on a typical Myford or it would simply have taken a long time compared to on a mill.
As an example I'm in the early stages of making my version of a reasonably popular engine that is available as a set of castings c/w materials and fixings. Although I could make all the parts I have opted to buy (well Xmas present actually) the cylinder and flywheel castings as these are probably the two parts many would find the hardest to make themselves and be put off the whole idea. The rest will be from barstock but won't have that chunky polished up final look. Cost will be approx half of less of the kit and mine will have more detail and period features. But you will have to wait for another thread on that one or maybe I'll write it up for ME.
8469 forum posts
Seems sensible to me .
Pouring cast-iron into a mould had many advantages in the past, but the method has largely been displaced by several other techniques. Once every UK town had a foundry, now they're rare. My nearest is hi-tech, specialises in aero-space, and doesn't do small value orders.
Fortunately, casting is only one way of shaping metal. Never occurred to me a CNC program could produce much the same result as a mould, but of course it can!
Maybe in future all 'castings' will be CNC cut from continuous cast-iron, and Model Engineers in 2050 will wonder why we put up with hard skin and blow-holes.
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I’m honestly surprised sand casting kits are still available. At the very least modern casting kits should go the investment casting route. With modern 3D printed patterns produced from very reasonably priced printers there is no reason for an investment foundry to not add a few parts to a tree. Today most engineers would tend towards CNC or investment for components in the size range of model engineering, especially lower quantity items.
Personally I like the challenge of getting the calculations right for the risers and messing around with the chemistry of the melt. I can’t remember the last time I got hard spots or blow holes. Casting has been part of the hobby since the beginning, as an additional skill to be honed. Not sure it makes sense commercially though, especially if the suppliers can’t get the castings right.
Maybe in the future G-codes will be sold instead of plans and little home CNC units used to finish models while watching 3D movies. Can't wait...
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The "castings" that Jason shows above say to me "investment casting".
Perhaps the dividing line is between gray iron and tempered 356 aluminum; ie: tempered 356 cuts pretty well, and would probably be easier on a CNC machine.
Gray iron machines well too, but it seems like more power is required.
From a mass-production standpoint, investment casting is the way to go.
For one or two off production, CNC would seem to make sense as an option to castings.
I have followed one fellow who is using a special 3D printer filament that burns out cleanly with an investment process, and he made some cast iron pieces that looked to be die-cast quality (he sent me one).
I don't have blowholes or hard spots in my iron, but I do understand that some kits have this problem.
CNC is definitely changing the game a bit, but I think in the end, 3D printing will have a bigger effect by printing patterns.
Just my 2 cents.
|Iain Downs||18/01/2022 16:40:59|
|852 forum posts|
I chose to build my first engine out of barstock rather than casting and the reason was cost. What I've built (which may someday run) is roughly equivalent to a Stuart 5A. Castings would have cost me £800. My actual material purchases were nearer £120 - £150 - and spread over time.
Apart from the joy of starting from scratch, it's a lot easier to get a bunch of £50 quid purchases around the missus than one £800.
I expect it's taken me 3 - 5 times longer, but I don't charge for my time.
CNC would have made it much more palatable of course.
|Another JohnS||18/01/2022 18:34:24|
|832 forum posts|
I'm finishing up an old set of castings, from Dave Goodwin back in the late '80s, which is a change from the Kozo Shay (no castings) Most of the castings have been machined already, mostly in the 1990s.
With my CNC machines, I think castings now are more hassle than they are worth, IF YOU HAVE THE CNC MACHINES and know how to use them. Doing the motion plates for this were a pain, would have been much faster to just machine from raw materials. Finding blowholes (one motion plate, a cast angle was holy), and too-aggressive fettling needing building back up (cylinders)...
Jason, most of our club still work in imperial, fractions, and pencil and paper, and are not going to change. There are 3 of us with CNC machines out of 25ish members. Another person just ordered a Taig mill to convert, so 4 out of 25??
There's still a market for castings. Ask again in 10 years.
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My main thought wa sof suppliers providing ready CNC machined "castings" the point about selling or providing G-code came up in the other thread as well as here, I don't think this is a very good option for a couple of reasons.
Firstly it would be a bit like putting your home movies on a VHS tape and then selling them to someone with a Betamax machine. There are many different machines and systems out there and each needs a slightly different code for example the Mach3 code that the post processor in Fusions CAM produces would not run straight off on a machine that was running LinuxCNC. There are probably a couple of 100 options for the different systems that F360 can generate the code for so not really practical to send out so many files.
Secondly even if two machines were running the same software just like in the manual home workshop you would not be taking the same cuts with a small hobby machine as you would with a Bridgeport so the g-code needs to be produced with that in mind. For this reason it is better that the individual enters the size of cutters they have as well as the size of cut they can take and at what rate.
If one was providing drawings and digital files for someone to do all the machining themselves then it would be better to use a common file type such as a STEP file either of individual parts or the whole assembly. As an example that photo of the two crankcase halves are from my Midget engine, I was contacted by someone who also wanted to make on and being the nice guy that I am I just sent him a step file exported from my assembly model. He was able to open this and then access the individual part sin his CAD, a couple of clicks and he had scaled it back up to the original engine size and then he ran the various parts through his CAM and produced the code to make the bits on his own machine. I did not even have to produce a set of 2D drawings, he just made them as he needed.
|308 forum posts|
My 3” Atkinson uniflow engine was entirely from bar stock a very cheap option, the whole engine cost less than two bronze valve housing castings for the standard design. For the diff the grease cover was a £36. Ish casting. I used a plate of 100 mm x100 mm offcut of 8 mm plate Bar stock is often easier to hold
22560 forum posts
Pat, yes the CNC will produce a much better finish than the average sand casting even oil bonded ones so a lot less fettling to do to get a good surface for paint. I think those whippet ones have been bead blaste dto remove the visual machine marks though I expect it is almost impossible to actually feel what can be seen.
That bedplate for example was cut from poor quality salvaged grey iron and what you see is straight off the machine, there is a 3deg draft angle on the vertical sides made with a series of cuts as the CNC ramped the cutter down gently as it went round and round the contour. I just lightly deburred around the tops of the bosses with a bit of Emery and this is it straight after the first coat of primer, the few dark specs are small voids in the iron. You won;t get that straight out of the sand pit.
There is no real dividing line between metals, the bedplate and the flywheel were cut from solid iron, the crankcases from 6082. In much the same way as you would on a manual machine a slower speed and lighter cuts are used on iron and steel than you would with aluminium and non ferrious. This assumes a rigid enough machine, a lightweight router type machine may not cope so well with iron but it's much the same for the home foundry as not many can get upto iron casting temps but aluminium is not such an issue with a small furnace and burner.
For decent investment casting then it's better to print using a wax fillament and melt it out than a plastic that has to be burnt out as it's easier to join them onto trees and you don't risk leaving ash in the mould
22560 forum posts
I would not say there is not a place for castings in the future, particularly on the larger subjects like 6" traction engines where you would be turning a lot of metal into swarf and wearing tools at the same time not to mention the size and running costs of a machine that at least commercially would be tied up for several hours on a single part. That does not mean to say the patterns could not be 3D printed our cut from foam on a large gantry of 3D router.
On the cost front one thing I do find with some of the casting kits is that you get cast parts almost for the sake of it where there is little or no reason for the part to have been cast. Take as a recent discussion on another forum where a member was asking about options for a flywheel to go on a triple expansion engine, another member said a casting would save material and said it might but would not save money.
Having just done a similar disc flywheel for the Simplex I went looking at the cost of a similar sized cast one, a well known supplier had one available for £11.68 just a disc with a recess running around either side which unless the two halves lined up well would end up with one side running off if you set the other to run true unless you also machined the recess to get them concentric. In which case you may as well machine from solid, the bit of CI bar cost £1.74 so for very little extra work and maybe grinding up a tool what is the point of a casting for a part like that. Piston blanks and cylinder covers that are just discs also come to mind with the added higher chance of a thin cylinder cover casting being chilled or is that what you are paying for?
325 forum posts
I have to agree with Jason.
On some (perhaps many) casting kits I have seen, many of the parts are more like blobs of cast metal, with little in the way of detail.
I saw a discussion on another forum the other day about how it is getting more and more difficult to get foundry work done for model engine casting kits.
One of the reasons I learned how to cast gray iron is so that the technology would not be lost to the model makers and others who may want to use it.
As far as cost, I have not really kept up with it, but a few costs are as follows:
(prices are so volatile now that I am not sure how accurate this will be next month)
1. Two bags of Mizzou refractory, perhaps $275.00 shipped
2. Two Sonotubes, $25.00.
3. 2.5" muffler pipe, $12.00.
4. Spray nozzle, $30.00 shipped.
5. sheet metal exterior (used 55 gal drum), ?
6. Miscellaneous bits, steel pipe, fasteners, etc. $100.00
7. Clay graphite crucible, $100.00 shipped.
8. Plastic fuel container $25.00.
9. Fuel line, $25.00.
10. Air line $20.00.
11. Scrap gray iron, one place priced it at $0.40 per pound. I found some motor end bells for free.
12. Metal to fabricate lifting tongs, $25.00.
13. Metal to fabricate pouring shank, $25.00.
14. Metal to make ingot molds, $25.00.
15. Wood to make flasks, $50.00.
16. Foundry sand, depends on what type you use, perhaps $0.20 per lb.
17. Fuel cost, I run diesel at about $3.50 per gallon, burning 2.7 gal/hr, with a melt generally being 1 hour.
18. I have an air compressor, but if you don't have one, you have a few other options.
I did build my furnace and burner to last indefinitely, so spending a little more money initially pays off in the long run.
So adding all the above costs (not including labor), you could build a very nice iron furnace and diesel burner for probably under $1,000.00 US.
I paid $600.00 for a single casting kit (ball hopper monitor), and so you would not have to buy many casting kits in order to make your own foundry.
Of course some would pay good money not to operate a foundry; it can be very hot and dirty, but that part does not bother me; its about saving the technology and preserving it for future generations.
And I love to make my own iron castings, just because I can make castings that cannot be purchased anywhere in the world.
Here is the 3D printer filament that supposedly burns out cleanly (I have not tried it).
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And here is an example of an investment casting using 3D printed parts in PLA plastic (not the good filament I listed above), with the tree and gates also printed in 3D.
|Bill Pudney||19/01/2022 06:11:40|
|606 forum posts|
When cast iron was a new material, casting it into new and previously unachievable shapes was one of the major benefits. Another was of course cost. It's really interesting (to me at least), that now the reducing cost of CNC enables the economic manufacture of previously unachievable shapes!! There's also the increased accuracy that machining a "casting" from solid brings, with none of the side issues of shrinkage, draft angles, inclusions, chill spots etc etc
|noel shelley||19/01/2022 09:57:49|
|1278 forum posts|
Hi Pat, Like you I got into foundry work to keep the craft alive. Having become quite successful at it I then took to giving talks and demonstrating the craft in the hope that others would have a go. My furnace was based on a spindrier casing and most of what I needed was made or recycled. Having a well equiped workshop of industrial gear did put me ahead of many. Since most of the work I took on was decorative I worked in brass or bronze my heat requirements were much lower than for iron, but from cold I could have an A6 crucible up to pouring temp in 20 mins on propane. Using greensand molding and careful pattern and mold making one can produce high quality castings that would in many cases make CNC look slow especially in aluminium, if you are trying to replicate a casting then draft angle is part of it, shrinkage can be controlled and, inclusions largely are the result of poor practice !.Never the lass we must move forward ! Best wishes Noel.
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Noel would that include the pattern making time? The way I see it for a one off the time spent making a pattern would be similar to the time spent just cutting it from solid metal so why do it twice. Buy just cutting it straight from the metal you totally do away with the pattern making time so it would be wrong to just compare the melt and pour time without including time spent making the pattern. Not forgetting that apart from the odd tool change if you don't have ATC then you can be doing something else while the machine is cutting so actual time spent will be further reduced.
And if making the pattern the traditional way you are waiting for glue to dry, waiting for filler and fillets to dry, waiting for paint to dry and then unless you have a well vented workshop waiting for a dry day to fire up the outside furnace. All the while I can be sat in the warm clicking a couple of buttons.
Want a handed pair of castings that would be a whole new pattern traditionally, one click of a mouse and regenerate the paths and you are ready to cut the other hand with CNC and CAD/CAM
CNC cutting the patterns will also be faster than making by traditional methods plus you have a lot more versatility for example take a simple name plate. Traditionally you would be limited to available fonts and sizes of pattern makers letters and then have to carefully space them out by hand. Doing it with CNC or 3D printing you have 100s of fonts available in any height you want and can easily arrange them in evenly spaced lines or to follow a curve
Edited By JasonB on 19/01/2022 10:17:21
325 forum posts
That is an interesting story. I do feel like I need to pass this technology on to the next generation, and so I document everything I do.
Each individual has to find the engine building method that best suits their needs and desires.
I enjoy the foundry side of things, as well as hand-making patterns, although I use a lot of 3D printed patterns these days too.
The biggest advantage I see of casting your own parts as opposed to CNC'ing them is with foundry work, you get to play with fire. My mother would roll over in her grave if she saw me handling molten iron.
She was highly cautious, to the point where I had to hid everythign I did from her, in order to get anything done.
Sometimes my neighbors come over to watch iron pours, and they generally say "Man, this guy is crazy, but this is really cool to watch". The art iron folks over here have huge iron pour shows, lots of spectators, and major iron pouring events, such as at the old Sloss Furnaces in Alabama.
It is more than just casting engines; it is a big "thing" over here for lack of a better term.
Edited By PatJ on 19/01/2022 11:35:27
Edited By PatJ on 19/01/2022 11:36:10
Edited By PatJ on 19/01/2022 11:39:37
Edited By PatJ on 19/01/2022 11:40:07
|derek hall 1||19/01/2022 12:29:27|
|214 forum posts|
I wondered when someone was going to mention some of the useless lumps of "castings" that you get with some kits! e.g Jason mentioning a lump of casting that was supposed to represent a flywheel as a very good example.
So many of these components from a kit can be manufactured from the solid or built up and brazed/soldered.
However I am not going down the CNC route personally, I want to leave computers outside the workshop - all this talk of G -code etc just goes over my head! and have no wish to learn it and convert my manual machines to CNC, but I admire the work that these CNC machines can produce.
Jason mentions and I paraphrase.."click of a mouse" and "get on with something else while the machine is cutting" - I like twiddling the feed screws and enjoy manually making things that are generally one offs. I would sooner do this than sit down in front of a PC and write loads of code to be honest...
But horses for courses and all that, I am sure that if I was younger I would be getting into CNC and 3 D printers etc, but for me now pottering around the workshop is enough !
All the best
|Martin Johnson 1||19/01/2022 12:59:53|
|144 forum posts|
If you are asking "Will suppliers who have sweated the value of the same old drawings and patterns for far too many years already be prepared to invest in reams of G code and all the associated fixtures?" Then the answer is a flat no.
If you are asking "Does CNC have a place in model engineering?. The answer is yes.
Personally, I CAD my own designs, make wooden patterns, buy castings, laser cuts, bar stock and machine it on 60 year old machinery.
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Martin, as I mentioned earlier Stuarts are already providing things like the 10 series engine valves as CNC cut parts rather than lost wax castings so the answer is certainly not a flat NO. On another forum as Pat mentions where a few of the casting suppliers are members they were saying how hard it is to now find foundries that can do the work and may simply not be able to provide castings in the future so it's either give up or think of alternative methods, reducing the number of parts in a kit would certainly help in this respect.
Many suppliers already do laser and water jet cut parts as part of kits or along side their castings, I've also bought CNC machined parts from MJ Engineering for my traction engine so it's not much of a step to have the odd "casting" made by other means
Derek, I was having this conversation yesterday and my comment on the "watch this space" thread also applies as I too was put off by watching a demo where ages was spent manually writing a bit of code to do a simple machining operation, air cutting to test it then altering it. In the end I gave up waiting to see any swarf being produced.
However all is not lost as I can honestly say I have never written a single line of G-code and certainly have not had to learn it. Yes I have had to pick up how to use F360's CAM but it's a lot easier than having to type what would be tens of thousands of lines of G-code that are needed for some of the parts I make.
Yes I still like to twiddle the handwheels too and only use the CNC for things that it is best suited for and could quite happily operate a manual machine while the CNC is running in the background.
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