Bell sweep

Discussion in 'Pattern making' started by Petee716, Apr 2, 2020.

  1. HT1

    HT1 Silver

    I would have loaned you the clapper assembly for you to copy for the cost of shipping... but as long as you are having fun :)

    V/r HT1
     
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  2. Petee716

    Petee716 Silver Banner Member

    That note is a little weird. There is no way the clapper will be anywhere close to 3% of the bell. I would guess more like 20%. The bell will only weigh 9 lbs and the clapper will be at least 2. As far as the quality of the bell goes, if it isn't right it isn't done.

    Pete
     
  3. Petee716

    Petee716 Silver Banner Member

    I'm absolutely having fun. I appreciate the offer but it wouldn't be the same.
     
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  4. Petee716

    Petee716 Silver Banner Member

    I finally got after this project today. I've actually been making patterns for other parts over the last couple of weeks- clapper, wall mount, and bracket mount. I still have to make the bracket pattern as well as the eye bolt and acorn nut. These parts are a helluva lot bigger than they look in the drawings! That eyebolt for the clapper is 5" long". I'm just going to cast a 7" cylinder and machine that one.
    Anyway the sweeps went well. Other aspects of the procedure were a bit of a bastard but the sweeps themselves turned out great. I made the outer profile as shown on the drillpress. I started with a fully rammed drag. I have a George Forman rice steamer that's about 9x9x8" deep that was just perfect for the job. I rammed it full, struck it off and flipped it onto the drag. Mounted it onto the drillpress table and went at it. The beveled cutting edges worked fine with some galling but easily re-smoothed. (In case you were wondering the drill press was unplugged).
    The trouble came as a result of a design error. As you can see from the drillpress photo the upper portion of the bell had very little draft. In fact, as designed, it had none. Instead of reworking the profile and risking ruining it I canted it a bit when I mounted it to the shaft. That bought me some forgiveness but not much. When I lifted the cope the sand pattern stuck and lifted with it briefly and then fell out. Of course it fractured and was unusable for the second sweep, but the cavity in the cope was good. I just re-rammed the rice cooker, changed out the profile, and swept the interior form.
    Sounds simple. Took most of the day.
    I think I'm going to cast this in aluminum and use it for a pattern.

    Pete




    image.jpeg image.jpeg image.jpeg
     
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  5. HT1

    HT1 Silver

    Your confirming what I have always heard anticdotally. Sweeps are alot of work, every time I have heard it come up in conversation everyone with experience rolled their eyes and started cussing and the patternmakers started glueing up wood to get on the lathe


    V/r HT1
     
  6. Petee716

    Petee716 Silver Banner Member

    As an an experienced molder I'm not surprised to hear you say that. What I wrote above is the short version. I had two dropouts while lifting the cope. I ended up revisiting ESC's post above as well as Ammen's book. For the third attempt I stapled an additional set of lathe strips around the perimeter of the cope at the parting line as well as threaded rods for internal supports rammed in. You can see one of the rods poking through in the picture above. In fairness to the process lack of draft was the primary culprit, again a basic patternmakers error, but ramming against that sand pattern without cracking it was a real nail biter. Fortunately none of my failed attempts broke the sand pattern. That happened at the end but yielded a good cope. Ammen indicates ramming that core as you build up and sweep. It would require superior sand and a much more skilled hand at ramming control than I would ever hope to have to make that work. Sodium silicate would probably be a more sure way of doing it.
    Setting up for a one-off has certainly been a lot of work but I wouldn't write the process off -it obviously works- but it wouldn't be my first choice if given an alternative.

    Pete
     
  7. Petee716

    Petee716 Silver Banner Member

    image.jpeg image.jpeg I'm awfully glad I chose to cast this in aluminum first. I had been concerned about damaging the outer form in the process of ramming the cope and although it didn't break apart it got bruised pretty good. Another rookie mistake in the gating. I gated in 2 places along the bottom edge with a deep runner and gates in the drag only. I wanted to keep the gates off of the exterior edge to make cleanup easier. What I neglected to consider was that the bell was designed with a sharp edge at the bottom. One of the gates froze off immediately and the whole bell filled though the single remaining gate. I haven't cut it off yet but I'll be interested to measure the actual cross section.
    I made a second bell casting in the same pour with a smaller cast iron pattern. Very thin cross section. I had attempted this one before gated from the bottom and it failed to fill completely up near the top. Close but not enough. Today's attempt was from the top and wasn't even close. The pattern is just too thin.
     
  8. HT1

    HT1 Silver

    that bell should weigh 10 Lbs after machining old school bells where sized(pounds) this way as the design only had small variations to try and achieve harmonic tuning . the cheap knock off bells will often include the weight of the mounting bracket in the weight of the bell to convince you you are purchasing a quality bell. remember the DOD instruction being used to make this bell, can be traced back to the 1900's I considdereed making these bells for sale . this is the bell that Navy ships and small boats use for their quarterdeck bell. Submarined use one of these for their ships bell, I contacted Loeffler bell a few years back and got a price quote so I could see where I could realistically price them, My quote was $1543 for bell and all hardware, with a 4 week turn around I could never find a customer base wiling to pay anywhere near that for a bell so I abandoned the project, after 2 I sold one for $500. and still have one that need polished . I'm lucky enough to have borrowed an actual bell to use as a pattern. as I mentioned above I have never met a foundryman that was excited about using sweeps. seems a very specialised technique ...

    Loving this thread
    V/r HT1
     
  9. Peedee

    Peedee Silver

    Note entirely relevant to your project but interesting.

     

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