FlyboyBC
New member
- Nov 24, 2017
- 5
Hello,
I have an issue with trying to find a replacement for 35 x 31, 35 x 25, and 30 x 26 mm DURAL tubing.
I am working with this design:
If you look at the way the Down tube (tube AU4G 35x31 L=500 mm)attaches to the Central frame tube (tube AU4G 35x25 L=420 mm) you can see that an enormous torque is applied to the Central frame tube. Most aluminum materials at these thicknesses would be torn apart. The joint between these two is drilled and pinned with a bolt unlike the normal clamping used to attach Kee Klamps and most of the rest of this buggy. I would doubt that this design could even work if it were not for the pictures of this device in action and the builders assurance that he has put 800 bumpy Kms on this buggy with no issues. In addition the builder reports that at one point he installed a longer axle (20% 1000mm changed to 1200mm) and that the longer axle bent where the 1000mm axle worked fine. This tells me that this design is right at the edge using Dural and therefore is probably as light as it can be using that material.
Dural is an obsolete trade name for the earliest aluminum and copper alloys used in aerospace. The name continued to be used in France but as a result of various evolutions of the designations and standards, it was then called AU4G (Standard NF A 02-104), and then 2017 (Standard NF A02-004 / EN 573-1) and now finally 2017a.
2017a T3 is as far as I can tell a very close match for the properties of "Dural" but 2017a is NOT commonly available in tube form. So despite having found the correct modern replacement material I STILL have to find an alternative that is actually available for purchase as tubes with OD anywhere from 33 to 35 mm. (to fit the Kee Klamps).
6061 T6 has far lower tensile strength(310 MPa)than dural (420-500 MPa) and I can not find 33 to 35 mm 6061 T6 tubing that would have sufficient wall thickness to make it work in this application. Not even close. I have not bothered to look for 35 mm RODS of any Alu material as I believe this would be far too heavy and expensive even if available.
Locally available 1.375 OD x 0.049 WALL x 1.277 ID Seamless Stainless Steel 316 Round Tube Would certainly be strong enough but it's Weight/Lineal Foot is 0.909 pounds! Perhaps I could find thinner stainless (again at 1.375' or 35 mm OD) but would it be strong enough? How thin can I go with these highly strained parts?
I even considered trying Carbon fiber tubes. This page:
compares and contrasts "aluminum" with a reported Ultimate strength of 500 kN · m/kg with CF (and steel) and makes the following cavalier statement "A component made from standard carbon fiber of the same thickness as an aluminium one will offer 31% more rigidity than the aluminium one and at the same time weigh 50% less and have 60% more strength."
This strikes me as useless gibberish designed to sell product with no relation to reality at all. Am I wrong? If I take this information at face value I should be able to bolt together 35x31 CF tubing and end up with a vastly stronger and more resilient frame but I suspect even using 35x25 (5mm thick!) CF tubing would result in an explosive shattering of the material on the first big bump. Do you agree? CF is known to degrade over time and without any indications it can become weaker and weaker over time anyway.
I am beginning to think this design CAN NOT BE BUILT TODAY using any commonly available tubing. At least not using all the same material. The only viable option I have been able to come up with so far is to use 1.375 OD x 0.049 WALL x 1.277 ID Seamless Stainless Steel 316 for the Downtube, Central frame tube, axle and forks and try using 1.375 X 0.058 seamless 6061 T6 for the lesser stressed members in order to reduce the overall weight.
If you were to try to replicate this design what (commonly available) 33 to 35 mm tubing would YOU use?
Thank you in advance for any guidance you can provide.
Gary,
I have an issue with trying to find a replacement for 35 x 31, 35 x 25, and 30 x 26 mm DURAL tubing.
I am working with this design:
If you look at the way the Down tube (tube AU4G 35x31 L=500 mm)attaches to the Central frame tube (tube AU4G 35x25 L=420 mm) you can see that an enormous torque is applied to the Central frame tube. Most aluminum materials at these thicknesses would be torn apart. The joint between these two is drilled and pinned with a bolt unlike the normal clamping used to attach Kee Klamps and most of the rest of this buggy. I would doubt that this design could even work if it were not for the pictures of this device in action and the builders assurance that he has put 800 bumpy Kms on this buggy with no issues. In addition the builder reports that at one point he installed a longer axle (20% 1000mm changed to 1200mm) and that the longer axle bent where the 1000mm axle worked fine. This tells me that this design is right at the edge using Dural and therefore is probably as light as it can be using that material.
Dural is an obsolete trade name for the earliest aluminum and copper alloys used in aerospace. The name continued to be used in France but as a result of various evolutions of the designations and standards, it was then called AU4G (Standard NF A 02-104), and then 2017 (Standard NF A02-004 / EN 573-1) and now finally 2017a.
2017a T3 is as far as I can tell a very close match for the properties of "Dural" but 2017a is NOT commonly available in tube form. So despite having found the correct modern replacement material I STILL have to find an alternative that is actually available for purchase as tubes with OD anywhere from 33 to 35 mm. (to fit the Kee Klamps).
6061 T6 has far lower tensile strength(310 MPa)than dural (420-500 MPa) and I can not find 33 to 35 mm 6061 T6 tubing that would have sufficient wall thickness to make it work in this application. Not even close. I have not bothered to look for 35 mm RODS of any Alu material as I believe this would be far too heavy and expensive even if available.
Locally available 1.375 OD x 0.049 WALL x 1.277 ID Seamless Stainless Steel 316 Round Tube Would certainly be strong enough but it's Weight/Lineal Foot is 0.909 pounds! Perhaps I could find thinner stainless (again at 1.375' or 35 mm OD) but would it be strong enough? How thin can I go with these highly strained parts?
I even considered trying Carbon fiber tubes. This page:
compares and contrasts "aluminum" with a reported Ultimate strength of 500 kN · m/kg with CF (and steel) and makes the following cavalier statement "A component made from standard carbon fiber of the same thickness as an aluminium one will offer 31% more rigidity than the aluminium one and at the same time weigh 50% less and have 60% more strength."
This strikes me as useless gibberish designed to sell product with no relation to reality at all. Am I wrong? If I take this information at face value I should be able to bolt together 35x31 CF tubing and end up with a vastly stronger and more resilient frame but I suspect even using 35x25 (5mm thick!) CF tubing would result in an explosive shattering of the material on the first big bump. Do you agree? CF is known to degrade over time and without any indications it can become weaker and weaker over time anyway.
I am beginning to think this design CAN NOT BE BUILT TODAY using any commonly available tubing. At least not using all the same material. The only viable option I have been able to come up with so far is to use 1.375 OD x 0.049 WALL x 1.277 ID Seamless Stainless Steel 316 for the Downtube, Central frame tube, axle and forks and try using 1.375 X 0.058 seamless 6061 T6 for the lesser stressed members in order to reduce the overall weight.
If you were to try to replicate this design what (commonly available) 33 to 35 mm tubing would YOU use?
Thank you in advance for any guidance you can provide.
Gary,
