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Thread: Looking to calculate the mechanical advantage of a toggling lever (t-shirt press)

  1. #1
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    Looking to calculate the mechanical advantage of a toggling lever (t-shirt press)

    I've spent a decent bit of time perusing mfg sites and forums and not a single one specifies the force generated by this style of lever:





    It seems to be some sort of compound lever and I'm not sure how to apply the formulas I've found in Machinery's Handbook. Here it is in action: LINK REMOVED Any insight is much appreciated.
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    Last edited by Kelly Bramble; 08-15-2015 at 08:22 PM.

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    Technical Fellow jboggs's Avatar
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    Look into the products mfd by Destaco. They make all kinds of toggle clamps and all have max force ratings. Also, regardless of the force the toggle could generate, the only force on the pad is a result of the amount of spring compression.

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    Administrator Kelly Bramble's Avatar
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    Good Job

    Quote Originally Posted by jboggs View Post
    Also, regardless of the force the toggle could generate, the only force on the pad is a result of the amount of spring compression.
    Oh the simplicity! Brilliant!

    Spring Force and Compression Calculator
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    Kelly, really, you are giving Boggs high marks for stating the obvious. What is this site coming to! (Only joking)

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    Technical Fellow jboggs's Avatar
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    Jalberts, you forget! We are engineers. We always overlook the simple or the obvious. I think its in our basic training somewhere.

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    Actually, I think this skill is in our DNA, our education and training only refines it; but, without it how would keep the uninitiated confused. If we didn't make things complicated then anyone might think they could be an engineer; and, where would be the fun in that.

    Of course, we are only a distant second class in this skill since the medical profession clearly outpaces us in it.

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    Boggs,

    For some reason after entering the above post my mind would not stop thinking about the mechanics of the machine; and, as a result I came to realize that there is a techinical error in your statement.
    While it is true that the amount of spring compression determines the force applied by the pad, the amount of spring compression is dependent upon the amount of force that the machine operator can, by way of the toggle mechanism apply to compress the springs. Basically, the springs don't determine the pad force, it is determined by the force applied to the springs by the toggle assembly at its maximum travel point.

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    Technical Fellow jboggs's Avatar
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    Jalberts - I get your meaning, but my response is based on the assumption that the operator moves the toggle all the way to its lock position, which is the only way I have seen them used in industrial environments, and which is also the position mfrs. use for their force ratings. That locked position is a known fixed geometrical position. Assuming the work surface is also in a known position, the spring compression will also be known, thus their force.

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    Administrator Kelly Bramble's Avatar
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    Confused

    Quote Originally Posted by JAlberts View Post
    Kelly, really, you are giving Boggs high marks for stating the obvious. What is this site coming to! (Only joking)
    I have a confession - when I first looked at the post I thought the op wanted the kinematic solution and resulting forces of the mechanism. Which I then rejected the idea of doing the complex math for the op because I'm busy.

    So, when I seen Boggs simple answer I thought the following (in relative order):

    1) I'm getting old.
    2) Why didn't I think of that?
    3) Those springs are cool!
    4) I could use one of those.
    5) Good answer
    6) Think I'll kudos Boggs cause I didn't get it.

    So there ..... you have my confession!
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    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by JAlberts View Post
    the amount of spring compression is dependent upon the amount of force that the machine operator can, by way of the toggle mechanism apply to compress the springs. Basically, the springs don't determine the pad force, it is determined by the force applied to the springs by the toggle assembly at its maximum travel point.
    So, if the op places a thin weight scale or similar device that can measure force between load pads... Then place/secure a scale ruler such that they can measure spring compression, they could then create a force to compression curve to be utilized for whatever...

    Nyuk, nyuk... am I being useful yet?

    BTW, what's that wire coming off the second larger picture?
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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    Technical Fellow jboggs's Avatar
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    Yeah Kelly. Ignore everything your wife tells you about that. You ARE useful!

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    Boggs, I understand what you are saying but, in reality we don't actually know why ScotT5 wants to determine what the loading forces by the mechanism.

    If he intends to use the calculation for an alternative machine design of some type then the relationship between the operator's required handle operating force and the resultant spring load throughout the spring compression travel is an important factor regardless of the final force at the maximum spring compression point. If the force at any point during the handle stroke is too high then that can lead to operator fatique etc.

    I know I am nitpicking on this issue about this issue, but that is also included in engineer's DNA. That is how a person knows they are supposed to be an engineer.

    At any rate, I am glad to have created a discussion with some give and take because, sadly, our site has gotten to be a bit boring lately.
    Last edited by JAlberts; 08-18-2015 at 10:33 AM.

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    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by jalberts View Post
    because, sadly, our site has gotten to be a bit boring lately.
    What! Not boring here...

    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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    Quote Originally Posted by jboggs View Post
    Look into the products mfd by Destaco. They make all kinds of toggle clamps and all have max force ratings. Also, regardless of the force the toggle could generate, the only force on the pad is a result of the amount of spring compression.
    uuuummm.... unless the springs bottom out before the handle is fully pivoted.
    Like when a 'thick' object is clamped.
    Then the pad pressure can get quite high.

    (just jumping on the nit-picking bandwagon. )

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    Technical Fellow jboggs's Avatar
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    Speaking of which, where did the OP go? We must have scared him off. Curmudgeons can do that.

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    Dale, well said, and appropriately added.

    Kelly, Boggs puts on partial post response and gets your kudos; and, I make a more detailed response with one small statement about the low current volume and complexity of of resent posts and I get the ugly "bored pumpkin". No telling what you might have posted if I failed to do careful spell checking on my post. There is simply no fairness in this world.

    On the other hand, I have to admit that there have been a couple of interesting threads added today.

    As for your "not boring here" I suspect that you are not yet a retired engineer with this forum as your only real opportunity toexercise your engineering ******s, other than your own self generated projects.
    Last edited by JAlberts; 08-18-2015 at 11:58 AM.

  17. #17
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by JAlberts View Post
    As for your "not boring here" I suspect that you are not yet a retired engineer with this forum as your only real opportunity to exercise your engineering ******s, other than your own self generated projects.
    Actually, I'm quite busy doing training and consulting GD&T per. ASME and ISO standards as well as DFM/DFMA. I'm off to Urbana, Ohio next week followed probably by NASA AMES and have three other customers on the calendar. I've been around the world five times in the last three years. In fact, I've been in your neck of the woods (Houston) at least forty times over the years training and consulting.

    Also, I do engineering drawing reviews for both GD&T and DFM practices for a variety of customers. - So, I'm practicing design and engineering pretty much all the time - like 50+ hours a week.

    In addition to the above - I founded, maintain and operate this website (15+ years). I'm a busy boy and don't know if I'll ever retire..

    I do agree we (I) could try to be more interesting around here - all facts and no fun makes for a boring forum..

    p.s. - I thought the video was funny....
    Last edited by Kelly Bramble; 08-18-2015 at 09:59 PM.
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    Everyone, thanks for the replies and I apologize for not getting back sooner. It seems my example has unintentionally derailed the thread, as I'm interested in the lever force sans spring, however the resultant discussion was an interesting read nonetheless.

    Quote Originally Posted by jboggs View Post
    Jalberts - I get your meaning, but my response is based on the assumption that the operator moves the toggle all the way to its lock position, which is the only way I have seen them used in industrial environments, and which is also the position mfrs. use for their force ratings. That locked position is a known fixed geometrical position. Assuming the work surface is also in a known position, the spring compression will also be known, thus their force.
    This is the rating I was looking for ideally- lever fully toggled and locked down. However since the lever is in a fixed position, force will vary depending on the height of the object being pressed. An object tall enough and rigid enough will resist the input force by the operator and prevent the lever from toggling (or possibly break the press). I was hoping to calculate the mechanical advantage of the lever so even if toggle/full lock isn't reached, I'd have an idea of the load on the plates. Just to be clear, I am removing springs from the equation entirely.

    Quote Originally Posted by dalecyr View Post
    uuuummm.... unless the springs bottom out before the handle is fully pivoted.
    Like when a 'thick' object is clamped.
    Then the pad pressure can get quite high.

    (just jumping on the nit-picking bandwagon. )
    This is what I was going for- a fully rigid design. So for the sake of discussion one could assume the springs are fully compressed prior to toggle.

    Quote Originally Posted by jboggs View Post
    Look into the products mfd by Destaco. They make all kinds of toggle clamps and all have max force ratings. Also, regardless of the force the toggle could generate, the only force on the pad is a result of the amount of spring compression.
    Thanks for the Detasco tip. I'll check out their website.

    Quote Originally Posted by Kelly Bramble View Post
    So, if the op places a thin weight scale or similar device that can measure force between load pads... Then place/secure a scale ruler such that they can measure spring compression, they could then create a force to compression curve to be utilized for whatever...

    Nyuk, nyuk... am I being useful yet?

    BTW, what's that wire coming off the second larger picture?
    This would be ideal but I don't actually have this press in my possession. I'm exploring options for a product design and trying to get an idea of the force generated to see if this lever style is a viable option. Do you know any manufacturers of the type of scale you mentioned? Something that can withstand 2,000 lbs would be an awesome resource once I move into the prototype stage.

    The wire in the 2nd pic is either a power supply for a strip heater and/or a transmitter from a pressure sensor (detects when the press is closed and activates a timer).

    Quote Originally Posted by JAlberts View Post
    Boggs, I understand what you are saying but, in reality we don't actually know why ScotT5 wants to determine what the loading forces by the mechanism.

    If he intends to use the calculation for an alternative machine design of some type then the relationship between the operator's required handle operating force and the resultant spring load throughout the spring compression travel is an important factor regardless of the final force at the maximum spring compression point. If the force at any point during the handle stroke is too high then that can lead to operator fatique etc.
    Ding ding ding...we have a winner here. I'm looking to design a handheld press with an output force of ~100 psi (probably between 900-1600 lbs) and an input force of around 50 lbs. I'm wondering if this lever design is capable of a 20:1 mechanical advantage [or greater] as this is one of the simpler lever systems I've seen and simple means cheap to manufacture.


    So going back to the OP- who has the engineering chops to determine the force generated by this lever? General formulas, links to similar problems, or precise calculations; all will help.

  19. #19
    Lead Engineer Cake of Doom's Avatar
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    I'm sure there is a spring calculation spreadsheet on this site. Using this, could you not calculate the size/spec of the spring to deliver the required force at full compression and then calculate the minimum length of lever required to aid in the compression?

    What is it you are looking to clamp?

  20. #20
    Technical Fellow jboggs's Avatar
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    "I'm looking to design a handheld press with an output force of ~100 psi (probably between 900-1600 lbs) and an input force of around 50 lbs. I'm wondering if this lever design is capable of a 20:1 mechanical advantage [or greater] as this is one of the simpler lever systems I've seen and simple means cheap to manufacture."

    Again I will refer you to Destaco. They have made these things for decades. No one knows them better. We could give you theoretical forces just based on geometry, but the actual real world force output near the final clamping point is mainly affected by miniscule deflections and bending in the individual components. They eat that stuff for lunch. Ask for Application Engineering assistance.

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