Hoist and releasing tong build

Discussion in 'Foundry tools and flasks' started by Melterskelter, Dec 19, 2017.

  1. They are made from two ball thrust bearings so good for up and down forces but not that suited for sideways forces which will be significant at the end of such a long arm carrying a full crucible (lots of leverage).
     
  2. Melterskelter

    Melterskelter Gold Banner Member

    I think the bike or motorcycle headset would work great. I never thought of that. There a plenty of old bikes sitting around waiting to be converted into lifting tongs. A good heavy old cruiser with stout tubes would be a good candidate. One thing that does happen to old worn out headsets is that bearings can become Brinnelled. So you’d want to check that the bearing does not feel like it ratchets. I’ve had a couple bikes like that years ago.

    Denis
     
  3. .

    This is not the cases. There should not be any meaningful sidways (moment) forces unless you are locking the arm with a full crucibles. As long as there is a pin joint at the fulcrum out of axis forces would be the same as riding a bike.
     
  4. Zapins

    Zapins Gold

    I'm planning to bore out a schedule 80 pipe and put a bearing inside, then put a thrust bearing on top just loosely sitting there. This should allow the pilot to rotate easily and probably won't be too crazy to set up and make.
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    Agreed, should not be hard to do.

    I would also comment that bicycle, and even more so, motorcycle head sets have to be capable of taking some pretty significant side loads. Considering a 170 pound riders ride off a curb and expect the headset not to fail despite the lever arms of the forks and the rake of the forks means that a controlled lift of 70 pounds on a 7 foot arm would be well tolerated especially since there is a pivot point involved as Alexander pointed out. I am not advocating the headset idea over thrust and spindle bearings, just saying I am pretty sure that it would hold up fine. My current bicycle has carried me tens of thousands of miles over some, at times, mighty rough roads, curbs, chuck holes and a few falls without batting a spoke.

    Keep us posted on your progress.

    Denis
     
  6. I like to think of worst case scenarios such as the lifting pivot jamming somehow and putting the full weight of the crucible via the leverage of the lifting arm on the thrust bearing as a sideways force: it might handle it, it might fail, pop out and jam leaving the crucible stuck in midair. Besides, bike frames seem to be made of heavy gauge steel foil these days or aluminium, a crack failure would end in tears for sure..
     
  7. Melterskelter

    Melterskelter Gold Banner Member

    If someone asked why I expressed confidence in bike and, even more so, motorcycle headsets which must typically be orders of magnitude stronger than bike headsets, I'd cite personal experience, experience of a large number of friends and acquaintances and internet searches.

    I have ridden steel frames over 70,000 miles and carbon frames approaching 30,000. In one case I brazed up a steel frame from scratch and rode it and it proved to be a lively responsive frame. I have many personal friends and acquaintances in various biking clubs who together have ridden millions of miles. I have never heard of a headset collapse in a steel bike. I Googled headset failures in bicycles and see on report from the UK four years ago which was in fact failure of the carbon forks not the headset itself or the steerer tube. Bike frames have become lighter and alloys and extrusion/butting techniques have improved over the 65 years I have ridden bikes. But frame failure remains extremely rare particularly in steel frames and extremely uncommon in uncrashed carbon frames and similarly rare (I found a reported case in Australia 5 years ago) in aluminum alloy frames. They take thousands of hours of hard use in the typical frame pounding over gravel, concrete, cobbles, you name it. I have further never heard of any headset jamming.

    So, my conclusion is the design, perfected over 200 years since the invention of the bike, has become very robust, reliable, and inexpensive.

    If one uses a thrust bearing, my experience is that if it is used with a deeply socketed pin that may (my case does) or may not have a cage bearing on the pin as shown in the images above, this is a very rugged design. How it might “jam” escapes me. How a bike headset might jam is also not evident to me. After using this setup for hundreds of pours over 3 years’ time it has proven to be trouble free. FWIW.

    Denis
     
    Chazza likes this.
  8. Hi Denis, that's a fair enough experience regarding the strength of bike frames. What I wrote earlier in my opinion only and I do have a tendency to over-engineer things I make. I would be a lousy aircraft designer as they design stuff close to the strength of the materials whereas I have been known to hold a workshop mezzanine floor up with 12" steel beams simply because they were close to scrap price. The two or three steel mountain bike frames I've cut up in recent years to use for projects (in Australia) are around 0.6mm or 1/42" wall thickness and made to be disposable. The scenario of a jammed ball thrust bearing would be where a single preload nut is not set tight enough or manages to unwind so the assembly cocks over suddenly in use and jerks the crucible full of molten material. This could equally happen to opposed tapered rollers though they'd be a bit more tolerant of loose preload, enough to get you out of trouble. At any rate given my different (risky) method of crucible lifting, I probably should not be offering opinions on lifting methods I don't even use.
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    One way to avoid trouble that a preload nut might cause is to not use one. The assembly I use just relies on gravity to keep the pin and bearings in the socket. Gravity has never let me down, so to speak. ;-). How a maladjusted preload nut in a spindle assembly could cause sudden jamming is still not very clear to me.

    Aside: Tubing thickness (thin or thinner) on a bike frame depends on where you cut it. Most modern quality bike frame are double butted.
    “For decades, the standard high-quality bike frame was made of Reynolds 531 tubing. The usual combination was a 1” diameter top tube with 0.8 mm wall thickness on the ends and 0.5 mm wall thickness in the thinner (butted) section in the middle of the tube.“
    I used 531 double butted on the frame I built lo these many years ago. In some ways it is an engineering marvel as it is so light but also amazingly strong. Being high carbon alloy, the user should take care in welding or silver soldering, the method I used. If not properly handled, it can be very brittle and fail under load just chrome-moly tubing used in race cars and aircraft. Used correctly it is great stuff.

    Denis
     

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