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  • Help with a reverse handbreak.

    Discussion in 'The main mechanical design forum' started by Ambroas, Jul 3, 2014.

    1. Ambroas

      Ambroas New Member

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      Hello,
      I've just recently designed a part holding rack for someone that will be placed through a furnace, after finishing it they asked for a simple cart to put it on to take it to and from the furnace. The rack is 62 L, 23 H, 31 D. Fully loaded the cart and rack will weight an estimated 1,500 lbs and will rest on 8" casters. Now this is all easy until they ask for a brake, what they'd like is a handbrake on the bar that works in reverse. You must squeeze the handle of the brake to release it allowing the cart to be pushed. If at any time the operator trips/falls/stops paying attention and releases it the cart will stop moving. I considered a spring loaded system but stopping 3/4 of a ton from moving may be too much for my original design. If at possible they also requested the handle be almost like the throttle handle of a push lawn mower. A smaller bar running parallel to the cart handle that would be squeezed to it. Does anyone have suggestions on how to make this, or of a part that already exists? Thank you very much in advance!
       
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    3. srdfmc

      srdfmc Well-Known Member

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      Hydraulics is there to help. Check the basis of break design .Then look at parts on the web;

      You will end up like this (In the case I didn't mistaken you obviously ;) ):

      [​IMG]
       
    4. Lochnagar

      Lochnagar Well-Known Member

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      Just my "two pence worth" - but a 750Kg trolley in a foundry environment - with the usual dirt on the floor and possibly "damaged" concrete floor - appears a lot for one man to push this cart over? (The fact that you are thinking about 200mm diameter wheels - makes me think my best guess about the condition of the floor might be right).

      Don't suppose you can make a pallet - and move the pallet into position with a small electric forklift - which the foundry maybe already has?

      http://www.gmdu.net/product-27448.html

      Hope this helps.
       
    5. Ambroas

      Ambroas New Member

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      I completely agree with you Lochnagar, I would've much rather made a forklift cart that could be used however the customer has been very specific about what they're wanting. A forklift wouldn't fit into the area they're moving it too, instead they use these carts to transport it, and a small fixed crane system to load and unload the carts. It was originally a smaller project, here's an image of it before they increased the capacity and weight. Only difference now is I've had to reinforce the frame of the cart for the added weight. [​IMG]
       
    6. Lochnagar

      Lochnagar Well-Known Member

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      Hi Ambroas,
      Ah well - I just hope they have got a competitor from the "world's strongest man" competition on their payroll to push this 750Kg "trolley":)

      If there is dirt on the floor - or the floor is uneven - then it will be difficult to push - and some form of "simple" suspension may be needed - to aid in getting over the "bumps".

      As for the braking of the wheels - well you can buy off the shelf "braked castors" - where you just put your foot on the top plate (see picture below) - and that brakes the castor. However, it is not a dynamic brake - and it should only be used on a level floor (i.e. zero gradient).
      I don't know about the "acceptable" frequency of use of the brake - but on all our workshop platforms - on which we built our products on - we had braked castors - and they were fine - but then we weren't using the brake 10 times per day (if you know what I mean) - maybe just 2 or 3 times per week. (I think high frequency use - might be an issue - because I have come across defective castor brakes which have been damaged - but have a chat with the suppliers).

      http://www.atlashandlinguk.co.uk/Br...ameter_upto_350kg_capacity--product--481.html

      Hope this helps.
       
    7. Jcb

      Jcb Member

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      I think you should use a hand break that breaks if you stop holding it, like in luggage trolleys at airports. A 750 kg trolley would be difficult to stop if it goes somewhere you don't want it to go. So I agree with Srdfmc above.
       
    8. Lochnagar

      Lochnagar Well-Known Member

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      Hi Ambroas,

      You might be interested in these pneumatic castors - with brakes - you might find them a bit easier to push over minor dirt on the floor - though usually any dirt on the floor is an immediate brake to a trolley of that sort of weight that you are looking at.

      http://www.grainger.com/product/Swivel-Pneumatic-Caster-w-WP98261/_/N-ir4?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/1ULH2_AS01?$smthumb$

      Hope this helps.
       

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