Small Iron Casting

Discussion in 'Request casting service' started by Matthew Chapman, Sep 24, 2019.

  1. Hello Everyone, I have been sent this way from reddit because someone there suggested that you may be able to help me. I'm looking to have a small part (90x90x70mm) cast in iron as a tool post riser for a lathe. From my limited knowledge of casting (and I would love some feedback on my understanding here as learning is good) I believe that this could be done in an open sand mould.

    I have attached an image of the part, please keep in mind that this is currently designed as a fabricated part (hence all of the undercuts which will be filled with weld bead). If someone here is able to help me I will de-feature it and make it a smooth continuous outer surface so that it has a single pull direction and no holes. Further, if it is useful, I can provide a 3D printed pattern and even labour on the day off to make it all easier on you and so I can learn!

    I hope someone is able to help me, otherwise I'm going to have to fabricate the part (as designed) or buy/make my own foundry and learn a new skill.

    Regards,

    Matt
     

    Attached Files:

  2. You could buy a chunk of iron Durabar and saw the sides to close to that shape and then get the base and top machined parallel. Durabar is continuous cast material so it's much more consistent than a casting in terms of porosity. If you were to cast it, then making it hollow will eliminate some issues with casting it in iron, not to mention making it lighter.
     
  3. Mate, you are inside my thought cycle at the moment. I just replied to you on the other thread.

    I had considered purchasing a piece and machining it down. Either manufacture from billet, fabrication or casting is going to require finish machining, I have access to do that (if I didn't this project wouldn't be getting anywhere).

    As for making it hollow, the more mass in this the better for me. so hollow isn't something I'm keen on. I don't think that porosity is actually going to be much of an issue in this case, the loads will be very low and the mass is more about vibration absorption and general stiffness than anything else.
     
  4. Casting the riser in iron is still going to require at least machining the top and bottom surfaces parallel with the other surfaces looking non critical. There will be some patternmaking involved to have it cast by somebody. The other ways I can see to make such an object with the desired dampening properties of cast iron is to make it from durabar: Judging by the truncated pyramid shape of the tool post, you could use a power hacksaw to cut off most of the excess if you had a jig to clamp it in the hacksaw vise at the correct angles, you could get it fairly close to net shape. You mention having a mill too so a face mill could then take it to net size.

    The other alternative is to fabricate it from welded steel plate and then fill it with epoxy granite composite which I understand has even better dampening properties than cast iron.
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    I agree that porosity should pose no problem for this part cast in iron. From my reading on this site, I understand porosity is a major problem in aluminum. From my experience, that should be an easy part to cast solid in iron but it will need a modest riser as there will naturally be some need to feed the casting as it cools. Top center a 50mm round by 50mm high riser should do it.

    Denis
     
  6. PatJ

    PatJ Silver

    The part could be pretty easily cast in gray iron.
    I would use a follower board, and ram the top first, then the bottom, making the casting hollow.

    I have not been having any porosity problems with my iron castings, and the last ones I made were pretty thin, much like that part.
    There is plenty of burner and furnace data here to allow you to make consistent iron castings, if you choose to go that route and stick with proven designs.

    I generally create a solid shape in 3D, and then use the "shell" command in Solidworks to hollow it out and give it a thickness.

    Don't forget to build in shrinkage to your pattern (about 1.015 multiplier), and add a bit of machining allowance on every surface that needs to be machined.
    Looks like you have plenty of draft angle, so the pattern will pull from the sand easily.

    For the base plate, I generally extrude it upwards with a draft angle, to that it will not have a straight edge on it. It looks like you many have done this.

    Use a generous radius on all the edges/corners so that you don't create high-stress points in the casting, and you are good to go.

    Sometimes I print out a 3D pattern, and then fill the corners/edges with filler, and sometimes I just incorporate the fillets in the 3D model (easier to incorporate the fillets in the model if possible).

    .
     
  7. Tobho Mott

    Tobho Mott Gold Banner Member

    If I understand the drawing, it looks like it has a flat parting line at the bottom of the pic - I'm curious why a follower would be needed to ram it up?

    Jeff
     
  8. Melterskelter

    Melterskelter Gold Banner Member

    BTW, I would recommend not casting it as an open sand mold. Better quality of casting with less machining would be needed with conventional cope/drag configuration with very little additional work compared to open. I would simply place the pattern with added riser on the table oriented as shown, place a flask around it and then ram it up, flip the cope over and cut a sprue and then ram up a drag. Split it open and cut the runner and gate right into the bottom flange. 10 to 15 minutes and ready to cast.

    I would definitely cast it solid to maintain maximal rigidity in use. I can tell you that similar parts on my Monarch EE are solid for that reason as well as my Bridgeport. If shipping weren't a killer, I'd do the part for you for a small fee. But shipping would be 100 dollars or so....

    Denis

    Denis
     
  9. PatJ

    PatJ Silver

    That is a very good question, and the answer is "because that is the way I have done it in the past".
    But the fact is that Tobho is correct, you don't need a follower at all.
    I guess I have "follower on the mind" syndrome, similar to "hammer syndrome", where if you buy a hammer, everything starts to look like a nail.

    Edit:
    I am beginning to think I could omit using a follower board for almost everything.
    I have been leaning that way for a while with one-piece flywheel patterns, but the trick is to be able to get the sand rammed tight enough around an irregular shape, so that when you flip the mold and excavate down to the pattern, and are still able to pull the pattern, and the mold does not have any void spots in it.

    More experienced folks are offering some very good advice.
    If it is cast solid, it may take a significantly sized riser to prevent shrinkage.

    I wish I had thought of these great suggestions, but that is why I post here (to learn from others).
    .
     
  10. Melterskelter

    Melterskelter Gold Banner Member

    Pat,
    Since you are printing your patterns, just make a split pattern. No cutting in a part line. Easy to ram cope, flip, add drag pattern half, ram, split, done.

    Denis
     
  11. PatJ

    PatJ Silver

    In the past, I have made split patterns, but with small engines, this means that split patterns may be very thin, and I have had an expensive ($100) commercially printed flywheel pattern shatter on me because it was thin as a two-part pattern.

    Some of the parts I make are much smaller than the flywheel pattern that broke.

    And in researching the old Cretors Popcorn steam engines, I have found that they used one-piece patterns for apparently all their engine patterns, and they made many thousands of engines, so I am guessing there are advantages with one-piece patterns.
    One advantage is that the parts are not so prone to breakage, and another advantage is that there are no parts to get separated and lost.

    Generally I am forced to 3D print pattern halves, but I do that with double shrinkage, with the intend of making one-piece permanent patterns cast in aluminum.
    The 3D plastic is not stable over time, and it can start to fail over several years time.

    Basically the intent it to set up for patterns and perhaps matchplates for steam engine kits.
    Whether I ever offer kits remains to be seen, but I would like to get set up for kits of all the engines I have under design, such as the one in my avatar.

    If nothing else, one day I could sell the match plates and permanent patterns to a kit company.
    I don't think there is a lot of money in the steam engine kit business, which is why I still keep my day job.

    Edit:
    Hopefully this is useful information to Matthew.
    If not, the mods can break this out to a separate thread, so we don't derail this one.
    .
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    I guess I’ll have to be careful with the 12x30 split pattern I’m making! ;-)

    8935F0A3-330B-43C1-8FD6-1ED637ECE5E2.jpeg D8149435-4AC0-4BA2-B9FF-8853E49BF327.jpeg 79D064E3-1F78-4E2E-8607-F2DFB73AD7F1.jpeg

    Denis
     
  13. Thanks for all of the replies everyone.

    Mark, I am tracking that some machining will be required. My thoughts were if it was open cast it would only require two setups to finish machine (cast with a small riser would require the riser cut off then the two setups). Regarding fabrication and filling with epoxy granite, that is the current plan and current design. I could do it, in fact I could do that this weekend; the negative is there is 14 individual components in that riser that require cutting (angle grinder) and then welding before the machining of the final weldment starts. In my mind this is not an ideal situation for fabrication and while for a one off part I could just buck up and do it, it's the principle of the matter and I think this is a perfect candidate for casting. Additionally, while epoxy granite has better vibration absorption properties than cast iron, a solid chunk of iron will be stiffer, stronger and likely have better vibration absorption than the fabricated epoxy granite (due to the the relative volume of the granite vs steel weldments).

    Dennis, thanks for the advice. For my education, why do you recommend not using an open mould? I understand that this would lead to increased shrinkage, follow my thought pattern here for a minute and let me know if this makes sense. The shrinkage would cause the open surface to "cup" and create a depression, if the part was cast inverted from the picture shown at the top, that cup would occur on the bottom (cross slide mating surface) of the tool post riser. This means that with minor machining the outer perimeter of the riser would be flat and in contact with the riser while the center would be off by 1-2mm [40-80 thou]. To me this is the perfect solution, trying to mate two "flat" surfaces, particularly non ground surfaces, often has issues due to sub mm flatness deviations, having the center inadvertently retracted a minor amount saves an additional machining step to provide relief in the centre. Let me know your thoughts.
    Speaking of shipping, you may be onto something. I will be in the midwest (Duluth, MN to be specific) for two weeks from 18 Oct to see my fiance. As I haven't seen her for 3 months she wouldn't be too keen on me heading your way to lend a hand, however I can pay for the work and she doesn't mind me using her place as a mailing address for the various tools I buy from the states and bring home when I visit her (or she brings me when she visits me). By my reckoning this would easily fit in a medium flat rate box, which would be far cheaper than shipment to Australia.

    PatJ, while slightly off topic this conversation is fascinating, and I mentioned at the top that I wanted to learn, so I am keen for it to continue.
     
  14. PatJ

    PatJ Silver

    One word......wow.

    Well golly gee, come on down and bring the pattern, and we will fire up the furnace, and make some molds.
    .
     
  15. Melterskelter

    Melterskelter Gold Banner Member

    I think you are generally right about the cupping likely to occur somewhere in the mid portion of the base if cast oriented as you suggest. Where and how much is an open question. And that may be OK.

    However, random bits of floating sand, slag and other crap may also contaminate the surface and also subsurface of the casting as open casting tends to pull those material into the casting rather than leave them in the pour basin. I guess I like clean castings for machining. Centrally relieving the bearing surface by machining it should be a relatively trivial operation so that hoping to get that relief by casting shrinkage (the depths of which may harbor sand and debris) seems like going at it the hard way, in reality. So, that is the reason I suggested conventional closed casting.

    You can do it open if you want.

    As far as my casting that piece in October that might be possible IF you have a clean, shiny-smooth, well-designed pattern with proper draft that won't require fettling. I am pretty absorbed in casting straight edges and hoping to cast a large master square, so I might lack patience for cleaning up a pattern so that it will draw cleanly. But we can correspond off line about the particulars of getting this part cast.

    Denis
     
  16. Whenever someone who knows things says this it's usually a good time to do what they suggest! I fully acknowledge your points about the debris and slag and "crap" this is why I've come here to ask for advice / help.

    Ill drop you a message directly, I do really appreciate the offer. I will say though, if there is anyone who is Brisbane based here who would be keen please let me know, I would love to learn how to do this in person.

    Pat, I'm not sure if that was a genuine offer or not, but looking at your location I do not think I would get away with flying to across the world to the US, saying hello to the better half and then heading south to "play with my toys" (though the weather would be far better than MN). If I did that it would may well be my last trip to see her....
     
  17. PatJ

    PatJ Silver

    I use to talk with one of my wife's younger cousins when I would see him at parties, and he had gotten into metal working, and was making all sorts of cool things.
    Then he got a girlfriend.
    I saw him at a wedding party, and we started the man-metal-chat, and the girlfriend came up and said "COME ON............", and drug him away to dance.
    He had become like a dog on a leash, YIKES !

    But what can I say, then my wife came up to me and said "COME ON...........".
    I said meekly "Yes dear".

    So the trick is to be able to make good iron castings AND have a girlfriend/wife.
    My suggestion would be to make up a ruse where you have an urgent business engagement down south for a day that must be dealt with immediately for the good of humanity.
    That should do it.
    I will get the furnace ready. :D

    .
     
  18. Pat, I must say I very much appreciate the offer and I'm going to entertain this idea for a minute... How far south are you? My knowledge of the geography of the USA is slightly limited (I did live in SoCal for a while and now I visit quite regularly), but last I checked Duluth, MN is right at the top of the country roughly in the centre, there is a very long way between there and the south and east extremes....
     
  19. PatJ

    PatJ Silver

    Looks like it would be a 15 hour drive time (one way).
    Well, if you ever get a bit more time, do stop in.

    .
     

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