How to Calculate Lifting Capacity of a Partially Engaged Lifting Eye Bolt

[c_marsh]

I would like some help calculating the lifting capacity of a partially engaged lifting eye bolt. The specifics...

We have a part that weighs approx 1,100 lbs and has three threaded M12x1.75 holes that are 11mm deep. The holes are on the top of the part and the eyes would all be lifting by chains in the vertical postion.

McMaster Carr sells a lifting eye bolt (part # 3040T15) with a capacity of 2,270 lbs and a threaded length of 24mm. The hole actually is 17mm deep but only 11mm is threaded. I would like to cut down the bolt to 16 mm so the bolt shoulder engages during the lift. I'm not sure of the bolt material (the specific steel grade) but have emailed McMaster requesting this info.

Is there a formula I can use to calculate the lifting capacity of this reduced length lifting bolt? I had been trying to manipulate the following formula... but I'm basically stuck. Thanks.

LE = [Allow Tens / (Allow Stress)(TSA_I)(N)]+(1/N)

Edit Note - I would use all three holes to lift the part. We typically design lifting devices with a factor of safety of 3x or 4x the actual weight of the part. So if the part weighs 1,100 lbs we deisgn it to 3,300 or 4,400 lbs depending on the situation.

[JAlberts]

Based upon my experience the following is an appropriate statement and solution for this problem; but, anyone viewing this post should feel free to add any comments or concerns regarding the appropriateness of the information and procedure given.

Generally, eyebolt lifting capacity is based upon the tensile strength of the bolt at the bolt top end thread inside minimum diameter, which not effected by bolt thread length engagement, with the assumption that a standard size and class nut specified for the eye bolt has sufficient thread length engagement will be used with the bolt.

As a result, your first step should be to determine the height of a standard M12x1.75 threaded nut. Once you have this data you will know the required bolt thread engagement length in a material of equivalent strength to that of the lifting eye bolt. (I appologize for the bold text but this is a critical element in determing your minimum required tapped thread engagement length)
Your next step is to determine how the strength of your tapped hole material compares to the strength of the lifting eye material. The required minimum thread engagement to achieve the full lifting rating with the eye bolt in your threaded hole is based upon the inverse ratio of your material's strength to the fasteners' material. i.e Lmin hole = Lmin Nut X Bolt material strength / Threaded material strength.

I hope this helps, but if you have any questions or concerns please post them.

[Macgyver]

Here are the dimensions for a standard metric M12x1.75 nut. It looks like you should be able to get approx. 5 full threads on the eye bolt! What is the material you are lifting, (Steel, Aluminum, Plastic?) In my experience with rigging and lifting, my rule of thumb is if the lifting eye has the capacity to lift the work piece and is lifted vertically, not at an angle, the eye bolts are threaded into the piece deep enough to mimic the effect of a nut, you most likely are safe. You have 3 lifting points which is better. If this is a part you make a lot of, then it is in your best interest to make a dedicated lifting harness / fixture that lifts at the points vertically. Yes, cut the eye bolts down to the length you need and thread them in until the shoulder is flat on the surface you are lifting, I have done this many times and never had a failure on any part of the lift. Cut the bolts down using a saw that will not impart too much heat on the eye, you do not want to reduce the capacity by using an abrasive saw or a torch (HAZ)! Now for the disclaimer!!

Never stand too close to or under a load that is supported by temporary lifting hooks.
Utilize your maintenance department and ask them for advice, they probably have an answer for you?

Good luck and be careful!