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Thread: r4z0r7o3's Crucible-furnace lifting mechanism / transport-stand.

  1. #21
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    You have to flip the pictures in a photo editor and save them flipped before you post them.

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  2. #22
    Senior Member caster's Avatar
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    Richard,

    They are displayed right side on my pc, attempted to edit but it came the same.

    Caster

  3. #23
    Senior Member r4z0r7o3's Avatar
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    Quote Originally Posted by caster View Post
    Here is how I did it, maybe it will help. A $20 HF come along and a sliding cartridge using skate bearings.
    It'd be helpful to see the sliding mechanism / bearing arrangement

    Dunna worry abouta the pics, we just can turn our computers sideways instead, eh?

    Have you ever found it necessary to raise the body further than the height of a crucible (plus some maneuvering safety-margin)?

    Have you ever cursed the time it takes to raise/lower?
    (genuine question, not a criticism)

    What I'm considering doing is very similar to what you have there, only shorter: If I extend the the lifting point of the carriage downward (below it's bottom face), that will reduce the height required by the whole mechanism. That's it, dead simple change. As for the actual mechanism, I'm still debating a windlass. I could easily use a come-along or strap-wench in a pinch, but that's more to buy and less to build. Would work well backup/emergency in case it gets stuck in the up-position.

    If in jams in the down position, well, I better have some tongs that can reach in down past the lid. Maybe I'll make my tongs with "hands" that can detach w/ the pull of a pin, and be re-attached 90* for an emergency vertical lift-out.

    - - - Updated - - -

    oh, nvm, that's only 16-in, I was reading your ruler backwards.
    "Things that are complex are not useful, things that are useful are simple."
    - Mikhail Kalashnikov

  4. #24
    Quote Originally Posted by r4z0r7o3 View Post
    Lolz, I hadn't even seen that before I started the thread, but common now, I've already dropped the linear-actuator idea (I think that's even the same brand I was looking at). Look how tall the frickin' thing is though, that's why I was going to (greatly) shorten mine by using a lever/scissor mechinism.
    For me, better upward than outward as far as size. It has a low enough CG that is still very stable. I get a lot of mileage out of it and it has it's advantages......the most important being that it seems to work well for such a tall frickin' thing.

    Good luck with your build.

    Best,
    K

  5. #25
    Senior Member caster's Avatar
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    The slide is made of angle iron riding on square tubes. They are connected to each other, the arms (also angle iron) are extended to hold the furnace. The point where the arms connect to the slide becomes a fulcrum, the front bottom is pressed against the tube and the top is pulled away from the tube. The roller skate bearings are placed so that the rotation of the slide presses them against the tube. I mounted the bearings using a 5/8" bolt and two nuts to lock it into place.

    I like having the extra height, lifting a hot and heavy crucible with little margin can be daunting.

    If you plan on making a windlass, remember that you will need to reel in 2x the height (2 x 12" inches) , the difference between the diameters might be pretty big.


    Caster

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    Last edited by caster; 04-10-2016 at 01:34 PM.

  6. #26
    Senior Member r4z0r7o3's Avatar
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    Quote Originally Posted by caster View Post
    If you plan on making a windlass, remember that you will need to reel in 2x the height (2 x 12" inches) , the difference between the diameters might be pretty big.
    Oh! okay, so you did use Gingery's design, just substituted square tube for 45* angle-iron, and bearings for wheels (with bearings). Thanks for the details!

    According to wikipedia (and mrpete222), it doesn't work that way. It's pi times the difference between the radii that gives the rise distance of the pulley, not travel of the cable. The actual diameters of the drums doesn't matter so much. So it's kind of counter-intuitive, but the way it works is the closer the two diameters are, the more mechanical advantage it provides (more turns required per unit distance of pulley rise).

    What I'm working with ATM is using 1/8in SS cable (4x thicker than required), a 4-in drum and a 4-1/4 drum (or built-up section). That gives a radius difference of 1/8-in, time pi gives 0.3926875-in pulley-rise per turn of the drum. If I give myself 4-in extra height (manoeuvring room), total body-travel is 14-in. The windlass cable would be at a slight angle, so call it 15-in to be safe. Divide that by the rise-per-turn, and you get close to 40-turns needed for that distance. Keeping the math simple, that equates to a drum-length of about 5 in (1/8-in times 40). My furnace is about 17-in diameter, so that gives me roughly 17 - 10 = 7, divide by 2 (sides), or 3-1/2 in. extra per-side for axle support, drum end-flanges, gears/sprockets/motor etc. Finally, depending on how long the crank-handle is, additional mechanical-advantage can be realized there as well.

    Likely the route I'll take is to do up the drawings, then make a scale prototype, adjust plans, then do the for-real thing.
    "Things that are complex are not useful, things that are useful are simple."
    - Mikhail Kalashnikov

  7. #27
    Senior Member caster's Avatar
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    It's pi times the difference between the radii that gives the rise distance of the pulley, not travel of the cable
    The pulley is on a loop so its rise is 1/2 the pi difference (circumference). The prototype will flush this out.

    Caster
    Last edited by caster; 04-12-2016 at 11:28 AM.

  8. #28
    Senior Member r4z0r7o3's Avatar
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    Quote Originally Posted by caster View Post
    The pulley is on a loop so its rise is 1/2 the pi difference.
    Are you arguing with wikipedia and mrpete22? Yep, that's why I want to make a small one also.

    This wikipedia page has more info, but also seems to suggest the lower pulley doesn't matter. In any case, I need to calculate the torque involved so I don't wind up (har har) needing a ridiculously large (or small) motor.

    That article says the mechanical advantage (a ratio) of a differential-pulley setup is 2 / (1-r/R) where the 'r' case corresponds to the smaller/larger size drum. So using the above figures (for now), that equates to a mechanical-advantage of almost 2:1 at the surface of the large pulley. That can be directly converted to torque, then adjusted if the actual lever-arm (crank length) is longer/shorter. Keeping it simple for now, this all means raising the furnace + carriage up 0.4 in would require requires about 50 lb of force, or 25lb if castor is correct. A prototype is certainly needed, but based on those numbers I think I need to reduce the difference even smaller.
    Last edited by r4z0r7o3; 04-12-2016 at 10:50 PM.
    "Things that are complex are not useful, things that are useful are simple."
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  9. #29
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    Quote Originally Posted by caster View Post
    The pulley is on a loop so its rise is 1/2 the pi difference (circumference).
    Quote Originally Posted by r4z0r7o3 View Post
    Are you arguing with wikipedia
    It wouldn't be the first time information on the user developed Wikipedia would be off the mark. However, I believe in this particular case they have it right.

    The equation for circumference is pi x d. The result would be the length of rope (cable) wound or unwound by one full revolution. They already halved the comparison of the two sized drums by using their rad rather than the diameter in the equation.

  10. #30
    Ok just to totally throw in a curve ball, here's an idea I had been thinking about it since all the hassle I had with my lid (if you remember).
    Mobile Engine (crane) hoist, the fold up type. So you mount the lower part of the furnace on a plate and use alignment pegs fitted to it and the hoist legs, this makes the whole lot mobile.
    using a slight shorter reach you mount the hook just behind the exhaust of the furnace using a frame mounted as part of the build. From this frame below the hoists lifting arm you make second arm that mirrors the top one in length hinged at both ends, this follows the top one and stops the furnace swinging back (as the hook is not inline with the CoG) this support arm needed not be to big either as it's only doing enough work as to stop the Furnace from tipping.
    With a little work the hydraulic ram could be powered in one way or other.
    also, if the lower section is able to latch on to the top it would then be possible to move it to it's (not in use storage space) filt it off the hoist's legs, put in props drop it down, de-hook and de-support arm pull hoist out and fold it up. Hey presto all tidy!
    Bonus is you can still use the hoist for it's intended purpose.
    Get what I mean?
    Last edited by wargrade; 04-12-2016 at 07:00 PM.
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