Hello,
I have attempted to understand the strength calculation for a bolt. This is because I bought a product (a cart) that, according to the specifications, should be able to carry 100kg. When I got the cart home, I discovered that the part that 'pulls' the cart feels extremely weak and wobbly; moreover, it is mounted with a 2.5MM thick screw that is supposed to pull and "swing around" with 100kg. I tried loading 20kg and immediately felt that it was about to break.
I contacted the company and demanded to return the product; however, they claim that I cannot return a product for reasons of "perceived quality." Therefore, I thought of demonstrating in black and white that the screw they used at the cart's most sensitive part, where most stress will occur, is far too weakly designed. So that I can prove in black and white that this is not my perceived quality but a direct error in dimension choice.
So, how does one actually calculate what a single screw can handle in "kilos" so to speak?
Vol
I have attempted to understand the strength calculation for a bolt. This is because I bought a product (a cart) that, according to the specifications, should be able to carry 100kg. When I got the cart home, I discovered that the part that 'pulls' the cart feels extremely weak and wobbly; moreover, it is mounted with a 2.5MM thick screw that is supposed to pull and "swing around" with 100kg. I tried loading 20kg and immediately felt that it was about to break.
I contacted the company and demanded to return the product; however, they claim that I cannot return a product for reasons of "perceived quality." Therefore, I thought of demonstrating in black and white that the screw they used at the cart's most sensitive part, where most stress will occur, is far too weakly designed. So that I can prove in black and white that this is not my perceived quality but a direct error in dimension choice.
So, how does one actually calculate what a single screw can handle in "kilos" so to speak?
Vol
Know-It-All
· Västra götaland
· 10 939 posts
2.5 mm?
That sounds like something you would use to assemble Märklin trains, not anything in a wagon that should withstand 100 kilos....
Maybe add some pictures?
That sounds like something you would use to assemble Märklin trains, not anything in a wagon that should withstand 100 kilos....
Maybe add some pictures?
Yes, take some pictures of the whole carriage and a close-up where the screw/axle is located.
It sounds very strange if it is 2.5 mm in diameter. Additionally, when you say that the force is in the middle of the screw? and that it is so thin and 8 cm long... That sounds very strange. I can imagine roughly how it all looks, but I wouldn't choose to have a "pin" at such a place on a carriage.
If you are satisfied with the carriage otherwise, maybe you can drill out the hole/holes and replace it with an M8 bolt that is 10 cm long. Then that part won't be the weakest anymore at least
ex: https://braverktyg.se/frasning/maskintillbehor/spanndetaljer/pinnbult/pinnbult-m8-langd-100-mm/
It sounds very strange if it is 2.5 mm in diameter. Additionally, when you say that the force is in the middle of the screw? and that it is so thin and 8 cm long... That sounds very strange. I can imagine roughly how it all looks, but I wouldn't choose to have a "pin" at such a place on a carriage.
If you are satisfied with the carriage otherwise, maybe you can drill out the hole/holes and replace it with an M8 bolt that is 10 cm long. Then that part won't be the weakest anymore at least
ex: https://braverktyg.se/frasning/maskintillbehor/spanndetaljer/pinnbult/pinnbult-m8-langd-100-mm/Attaching an image below. Measured it now and it's probably more like 3mm and not 2.5 as I first thought. But it's still extremely little. This screw acts as the "axle" for a long handle that should be able to pull 100kg, but also move sideways, meaning the leverage when, for instance, turning the cart will exert large stresses.
I'm not very keen on finding my own solution here but rather want to make my argument for claiming a refund. I can already feel with a 20kg load that the entire screw "deflects" but the company claims it’s my subjective judgment, and perceived quality is not grounds for a refund. Therefore, I thought of coming up with some form of data to support my argument that this will never hold, as I am knowledgeable enough to be sure that this won't hold, so it is rather about 'proving' that this is the case.
I'm not very keen on finding my own solution here but rather want to make my argument for claiming a refund. I can already feel with a 20kg load that the entire screw "deflects" but the company claims it’s my subjective judgment, and perceived quality is not grounds for a refund. Therefore, I thought of coming up with some form of data to support my argument that this will never hold, as I am knowledgeable enough to be sure that this won't hold, so it is rather about 'proving' that this is the case.
I find a lot of information online about strength specs related to M3 and something called fracture force. What I need to understand is how to "convert" this into kilos, because my argument is that the technical specification of 100kg that the cart has is directly incorrect based on the dimension of the material (the screw in this case). If I can clarify this, I think they will have a hard time arguing against a complaint. (I actually wonder why they are arguing at all, but it is what it is)
Vol
Vol
You pull it manually, it's a type of "trailer cart" for transporting things like firewood or other heavy items between two points in the garden. I am extremely dissatisfied with the quality, the wheels squeak, it feels wobbly overall, but in particular, IT WILL break if I load it at the point I've indicated in the picture. It's completely obvious.
I contacted the company because I believed it was better for them to take back the product before it breaks rather than after it's broken (you can claim a product before it's broken if it has defects). This is about supporting my argument with more than subjective assessments. Hence, I want to demonstrate that it is undersized based on their specs on the weight it should be able to handle.
I contacted the company because I believed it was better for them to take back the product before it breaks rather than after it's broken (you can claim a product before it's broken if it has defects). This is about supporting my argument with more than subjective assessments. Hence, I want to demonstrate that it is undersized based on their specs on the weight it should be able to handle.
I might be thinking wrong, I thought M3 is 3mm. (that is what the diameter is). This is an unloaded cart, if I add 20kg the entire axle bends considerably, and then it's not even loaded with 1/5 of the weight it should handle.