Lamp hardware test part today

Discussion in 'Sand Casting' started by Mark's castings, Mar 17, 2023.

  1. So I was casting aluminium today and made a test casting of what will ultimately be a brass part for desktop stained glass lamps. This guy's wife wants brass 4" lamp wheels and is willing to trade some C section purlins I need to make some flasks. The mould has a hand cut runner in the lid that feeds into the outer ring and then across to the center of the casting. It's been fettled and sand blasted and will need further machining including a hole in the center and a "brass thread" hole. Retail this casting and the accompanying ring sells for USD$170 each:

    https://www.delphiglass.com/bulbs-caps-hardware/odyssey-hardware/4-wheel

    lamp part 2.jpg

    lamp part 1.jpg
     
  2. Melterskelter

    Melterskelter Gold Banner Member

    Thaat is a nice clean casting, Mark. Green sand? Silicate? Printed pattern?

    Denis
     
  3. Hi Denis, it's resin sand and it was poured hot as the metal texture goes between the sand grains in places, I'm using phenolic urethane resin sand this time round. The pattern ring and hub was hand made out of aluminium on the lathe with 3mm thick extrusion bar for the three arms and sanded to give some draft. The inner hub is held on with a screw and the rest is held on with good quality super glue. The aluminium used is something intended for pressure die casting and gives a beautiful smooth silver finish straight out of the sand but has good machining properties.
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    So, this is a PUNB process? If I missed it, sorry. But a thread on this process might be of interest including how part looked prior to fettling and blasting. Nice part.

    Denis
     
  5. rocco

    rocco Silver

    Poly-Urethane No Bake
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    Yes….I hope he does a thread on it as it is not something I’ve done and I don’t recall anyone else reporting on it.

    Denis
     

  7. I used to call it polyurethane no bake, but HT1 patiently pointed out that that it's actually phenolic urethane no bake. The stuff has three components with the third seemingly a cross linker that speeds up the cure. It's not practical for home use unless you have a foundry nearby that uses it and is willing to sell the various components due to the short life and the cost ~$400 for 40 litres. Sodium silicate/CO2 is cheaper, commonly available by comparison and lasts a long time on the shelf to give virtually identical performance.

    I'll take some photos of the other unused moulds next time I'm in the foundry, I think some graphite brushed on will give it that extra smoothness.

    Edit: I had a trawl though my smartphone and took some photos of the various patterns as constructed:

    This pattern will cast a brass tube to be machined into the rings to fit the lamp wheel.
    lamp ring pattern 1.jpg


    Lamp wheel pattern before priming and sanding:
    lamp pattern.jpg


    Lamp wheel pattern sanded smooth before coating with aluminium powder based release agent:
    lamp pattern 2.jpg


    The mould in the foreground is the brass tube mould, the lid is a generic slab of resin sand sawn to size roughly with a giant power hacksaw blade and then a hole for the pouring cup and runner drilled in it.
    brass tube mould.jpg
     
    Meteor Monowatt and Tops like this.
  8. We had to make some emergency bronze castings today and I brushed a coating of graphite onto a wheel mould and cast one in gunmetal bronze. I cut the runner off with a grinder, you can see some shrink as it fed the casting. I've added photos of the casting still in the sand, after hosing off the sand and finally after fettling and sand blasting. I'll machine the remainder of the runner off in the lathe and machine the critical surfaces.




    PUNB wheel mould with graphite.jpg

    Still in the sand mould, the moulds were stacked as they were made so are not perfectly flat leaving a 1.2mm thick bronze flashing.
    bronze wheel 1.jpg


    Top side of the casting showing the runner detail:
    bronze wheel 3.jpg


    Casting after a hit with water to knock off the loose sand:
    bronze wheel washed 1.jpg


    Runner is cut off and sand blasted:
    bronze wheel fettled.jpg
     
    Tops and Melterskelter like this.
  9. Ok the bronze wheel is fettled, filed and the rim machined to size, just have to drill the center hole and tap it and mask it up and sand blast the non machined areas. I do love machining gunmetal bronze and the casting is sound and flawless. In future the order of operations would be to fettle, file, sand blast and then machine it last.


    bronze wheel front.jpg


    bronze wheel back.jpg
     
    Last edited: Mar 20, 2023
  10. Jason

    Jason Gold

    Nice work!
     
    Mark's castings likes this.
  11. Rocketman

    Rocketman Silver Banner Member

    Beautiful work!
     
  12. Today we managed to cast five of the wheels in brass as well as two brass tubes to machine the rings from. The casting session was a bit fraught in places, the two man pouring shank ring was a bit small so the crucible had the tendency to tumble once the brass level was low and spill excess material. As it was all scrap there was massive amounts of dross and skimming took about three times longer than using ingots but I got there in the end. Also of note was the fifth casting: I forgot the carve a runner so the central part was fed via the three narrow ribs and the only difference is a shallow dimple from contraction in the middle.


    wheel moulds 1.jpg

    no runner 1.jpg

    brass wheels 1.jpg

    brass bush1.jpg
     
    Last edited: Apr 17, 2023
  13. Petee716

    Petee716 Gold Banner Member

    It looks like your fifth one filled pretty well without the fat gate. Aside from the dimple it’ll be interesting to see if there are any fatal defects once it’s cleaned up. It looks a bit course just below the 3 o’clock position in the photo but it’s hard to tell. The point being that it would be nice to dispense with the extra gating or at least minimize it in favor of padding the central hub and maybe even gating from the side of the wheel.
    I feel like I’m sounding critical as I write this. If so I apologize-it’s great work.

    Pete
     
  14. Any thoughts on this are welcome, I did have an interrupted pour on at least one of the castings, and that scrap was filthy with crud, I had coagulant and like a fool didn't use it. I brought my own crucible and lifter for an A25 crucible and the two man shank is for an A20 crucible... it's getting a few vertical steel tabs to prevent tumbling in future and should be fine after that. Peter at the foundry suggested a dual gate aligned with two of the three radial arms and yes I'll add some extra as you suggest for the center shrinkage. I cast two brass tubes and was able to get five rings from one tube, I'll make another two rings for the aluminium and the bronze versions.
     
    Petee716 likes this.
  15. The wheels are fettled, ground, filed, blasted and machined now. The runners were cut off with a 9 inch grinder and thin cutting wheel, then after facing that side off in the lathe there was some thin flashing that a hit with a 4mm carbide burr got rid of quickly. There's a few defects here and there, nothing too serious, except for one wheel with a crack in the outer rim that I'll solder up to repair it. Most visible defects machined right out of the castings. The initial bronze wheel is bottom left corner and it's destined for the foundry sample display cabinet :D.

    lamp wheels complete 3.jpg
     
    Last edited: Apr 21, 2023
    Jason, Rocketman, BattyZ and 5 others like this.

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