Draw bar w/shackle for recovery point
- Thread starter Backwoods Rambler
- Start date
ntsqd
Heretic Car Camper
In my first calc's I used the Simply Supported Beam, Point Load model, but in revisiting this I used Required Section Modulus rearranged to yield maximum load for each of the alloys analyzed since the Section Modulus is fixed by the 5/8" pin diameter. Normally the load is known and the Section Modulus is what you're looking for. Here it is the reverse situation. Note that I did not include the AISC 66% of YTS Factor of Safety requirement for beam design, so these numbers are straight up - NO Factor of Safety included. This second set of calcs exactly conforms with the results of the first set. Going about the calcs this way also indicates what the maximum is for the pin regardless of how it is loaded.
Alloy ................. 1018 .. 1045 .. 1060 .. 4130 (855C q)
Max Load (lbs) .... 1719 .. 3686 .. 3369 .. 7718
Shear Strength . 24544 . 47185 . 43136 . 98788
(EDIT: Note that this is a doubled Shear Strength.)
Re: Side contact. There would of course be friction involved, but beyond that there is no sliding force transfer mechanism other than the pin. The advantage of a drawbar is that it places almost no bending load on the pin and primarily only loads it in shear.
So far the real issue that I'm seeing is a lack of information about what alloy is commonly used in the mfg. of these pins, but I highly doubt that they're made from anything more exotic than 1018.
Alloy ................. 1018 .. 1045 .. 1060 .. 4130 (855C q)
Max Load (lbs) .... 1719 .. 3686 .. 3369 .. 7718
Shear Strength . 24544 . 47185 . 43136 . 98788
(EDIT: Note that this is a doubled Shear Strength.)
Re: Side contact. There would of course be friction involved, but beyond that there is no sliding force transfer mechanism other than the pin. The advantage of a drawbar is that it places almost no bending load on the pin and primarily only loads it in shear.
So far the real issue that I'm seeing is a lack of information about what alloy is commonly used in the mfg. of these pins, but I highly doubt that they're made from anything more exotic than 1018.
Last edited:
98dango
Expedition Leader
well ill say this I have never seen a bent hitch pin. I have never seen a sheerd hitch pin. I have seen a hitch riped off the back of a 1ton dodge. We still use the hitch and the pin. You also half to rember the recever dose not fit exact it will rock alowing the force to be aplied to the top bottom and sides of the recever. You also almost never tow exactly stright when in recovery. i would be more worried about the 4 1/2" bolts that hold your typical recever on most times are grade 5 atached to a 3/16 thick frame. So id say thay are maney outher factors to worrie about than a pin that if used corectly for recovery will not get a shock load. So if you u a snach strap or a sampson line you get verry little force on the hitch itself. Now if you are yanking with chain you need your head examined in my opinion. I have been around wheeling all my life and found this to be the safest method of recovery with out a winch.
ntsqd
Heretic Car Camper
When pulling at an angle, would the slider stay in place if you pulled the pin? Will it just flop right out, or does it take a while to be pulled out? That is the direct answer about how much of the pulling force is being diverted from the pin.
To my thinking the fit is loose, but not sloppy enough to allow the slider to wedge under load in the socket. With no wedging there would be minimal force diverted from the pin and assuming that you could pull the pin when under load (doubtful) the slider would slide out.
The slider mostly loads the pin in shear, regardless of the angle of the pull. Note how much higher the shear strength is than the bending strength. The worst alloy choice examined is still stronger, though not by a lot, than the commonly used 20k snatch strap.
To my thinking the fit is loose, but not sloppy enough to allow the slider to wedge under load in the socket. With no wedging there would be minimal force diverted from the pin and assuming that you could pull the pin when under load (doubtful) the slider would slide out.
The slider mostly loads the pin in shear, regardless of the angle of the pull. Note how much higher the shear strength is than the bending strength. The worst alloy choice examined is still stronger, though not by a lot, than the commonly used 20k snatch strap.