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- About steel materials
- Use steel for making frames and jigs which need strength. Steel is very cheap and very available. In addition to them, it is strong and easy to weld. The following table shows various uses of steel materials.
No
Name
Symbol
Tensile strength
Kg/mm^2Uses
1
Hot Roll Steel
SS400
Over41
Jig,Handle stopper,Bracket, Handle lock bracket (out of angle and flat bar)
2
Machine Structural Steel
S25C
Over45
Collar,Boss,Frame joint, Shaft (out of round rod which needs no heat treatment)
3
Machine Structural Steel
S45C
Over70
Shrinkage fit break liner with heat treatment(out of round rod)Indicated strength can be obtained after heat treatment.
4
Machine Structural Steel Pipe
STKM13A
Over38
Front fork,Swinging arm
5
Structural Steel rectangular and square Pipe
STKR400
Over41
Simple surface table(out of square pipes)
- S45C which contains much carbon get hard and strong after heat treatment. But richness of carbon makes it fragile so it can't be weld and we can't make a frame out of this material. Usually, high strength materials including alloy steels are not available for welding. They are used with heat treatment for the machined parts which need strength. When you weld them they look to be welded firmly but many invisible cracks exist and they decrease the fatigue strength of the parts so it is extreamly dangerous. Many magazines introduce chrome-molybdenum steel is available for frames but it is not for amateuas. If you use this material without any knowledge of materials or heat treatment it may kill you while riding. It gets heat treatment after welding naturelly and the fatigue strength decrease very much. On the contrary, steels with non-rich carbon are avilable for every purpose. They are not strong compared with alloy steels or rich-carbon steels but they can't be hard or fragile after welding. They are the steels for amateurs with poor tools,machines and equipments.
- About aluminum materials
- I use aluminum alloys for the parts to make light or to show the aluminum ground color. Compared with steels, aluminum alloys are expensive and not easy to get except certain kinds of them. And they need special welder for welding so it is difficult to use aluminum alloys satisfactorily for amateurs. The following table shows various uses of aluminum materials.
No
Symbol
Anti-
corrosivenessMachin-
abilityWeld-
abilityTensile strength
Kg/mm^2Uses
1
A1100
Best
Bad
Best
9.1(16.0)
Tank,Side cover
2
A2017
Not Good
Good
Not Good
18.0(43.6)
Steering stem,Engine mount bracket,Step bracket,Disk break inner rotator
3
A2024
Not Good
Good
Good
19.0(52.7)
Steering stem, Engine mount bracket,Back step plate,Disk break inner rotator,sprocket,Disk break floating pin
4
A5052
Best
Not good
Best
19.7(29.5)
Tank,For sheet metal,Swingingarm take up bracket,Engine mount bracket,Back step plate
5
A5056
Good
Good
Best
29.5(44.3)
Steering stem pipe,Swinging arm pivot bracket
6
A7075
Not good
Good
Bad
23.2(58.4)
Steering stem,Engine mount bracket,Back step bracket,Disk break inner rotator,Sprocket,Disk break floating pin
7
A7N01
Good
Good
Best
35.0(37.0)
Welding parts such as frames which need strength
Attension:Numerical values in ( ) can be gotten after heat treatment or cold working. Other values are for materials after annealing.
- Aluminum has two groupes. One groupe is weldable and another groupe is unweldable. Generally speaking, high strength aluminum such as A2017 or A2024 or A7075 are used after heat treatment, so they are not suitable for welding. We get them with heat treatment and machine them. A5052 which is relatively strong and anti-corrosive is very easy to get in many shapes. It is strong when you get because of plastic hardening after cold working but after welding the strength go down because of annealing. So it is easy to work on the sheet metal after annealing by means of a burner. A5056 is available in the shape of a round rod. For instance, I use A5052 for a tank body and A5056 for a lathe-made boss to which gas cock is attached and I weld them together. A7N01 is developed in Japan but it is not easy to get it in many shapes. It depends on the dealer's stock. It has a marvelous nature that the strength returns gradually after welding. The strength is close to steel and it is available for frames. A1100 is pure aluminum and used for electric chassis. It gets very soft after heating. I don't recommend to use it for a gas tank.
- About calculation of strength
- When you make a force on metal, inner force occurs to bear the force. We say this force stress. For instance, if we pull the plate in the force of P, the material lengthens a little in directions of the axle and stress value becomes P/A in the area of a-b.(A shows the area of a-b) we use unit of Kg/cm^2 and this is the base of calculations. Strength value in the upper table means this value. If you pull the material over this value it will break.
- Compared with pulling, stress is not constant while bending. If you bend a square rod as shown in the figure, commpressed stress occurs inside of the rod and tensile stress occurs outside of the rod with the boundary of center line. The length of the arrows mean strength of stress and you can see the biggest stress at the surface of the rod. Compared with pulling,the calculation for the biggest stress is not easy but you can calculate the stress by using section modulus Z which is calculated from the shape of the material. For instance, Z=b*h^2/6 is for a rectangular shape rod and Z=PI*(d2^4-d1^4)/(32*d2) is for a pipe. we use unit of mm^3. We make almost all motorcycle parts using these two materials only. If you want to know the biggest stress using the section modulus you should know the bending moment of the material. Moment means external force for bending a material and we use unit of Kg*mm. For instance, if we make force to fall the post down on the top of it which is driven in the ground, the post will bend. If the force is 10 Kg and the point is 1000mm from the ground, the moment is 10*1000=10000 Kg*mm at the border of the ground. Moment is caluculated by force*distance.
- If you support both sides of a beam as shown in the figure and make force W on the beam, the shape of moment is a little different. The strength of moment is different in every section and the shape is like triangle. The strongest moment occurs at the forced point and the value is Mmax=W*L1*L2/L. If you think of a backbone of a frame and W means man's weight and the supports are two wheels, the formula is very adaptive. You can calculate the best stress against bending with the following formula. Sigma max=Mmax/Z. This formula is the base of every strength calculations. The unit of stress is Kg/cm^2.
- The basis of stress calculation is very simple so I always calculate when I design a motorcycle. But the frames are not simple like this so I simplify the shapes of them before calculation. Then I insure the strength of the frames after measuring the stress which I'll tell you the methods from now on. Recently the technique of FEM is extreamly progressed and the calculations get very accurate but measuring is still important.
- When you pull a metal, the metal lengthen in the direction of the force and internal force occurs, as mentioned before. There is a law between stretch and stress and every metal has its own value. So we calculate the stress by measuring the stretch with electric devices. We use a strain gauge as shown in the figure to measure the stretch of metal by pasting it to the measuring points. Thre is a patterned line in the strain gauge and the line streches or shrinks with the metal. It causes variation of elctric resistance and we can read the magnified voltage using Wheatstone bridge. If you use gauges like this at every place you want to measure and measure the stress in many test patterns, you can understand the strength of the frame.
- You should consider fatigue strength in addition to tensile strength. If you bend a thin steel plate over and over it will break before long. This is caused by fatigue strength. If a work break after a while without breaking quickly, it should over the fatigue strength. The value of fatigue strength is around a half of its tensile strength. Furthermore, the value of the portion welded is around a half. The fatigue strength of high tension steel is reduced by welding than the strength of normal steel. It is why amateurs can't use high tension steel such as chrome molybdenum steel. If you make force over the fatigue strength, materials don't break quickly, but the value defines the time to break. We call the diagram S-N curve. N means a number of cyclic stress and S means strength of stress. Upper figure shows an exanple of S-N curve. The curve gets horizontal at the point of around 10^6 so the value of the stress at this point means fatigue strength. If you use materials under this value they don't break forever.
- About welding
- There are three types of electric welders. Covered electrode arc welder is the cheapest. We use this for welding steels. Welding rod is covered by flux to prevent the welding point agaist oxidation. The rod is clamped by a holder and arc is made by touching the rod to the matelial and heat melts both the rod and material. There are many rods in thickness and the thickness defines current of welding and thickness of steel. And there are many rods for welding direction. A kind of rods helps downward welding. Cheapest welders use alternating current so they are hard to arc. I think they are not available for amateurs. Some kinds of Tig welders have the same function but they use direct current so they are very easy to arc and available for amateurs. Like Tig welder, battery welder uses direct current. It is very easy to make a battery welder with a few batteries but I don't recommend it for your safty. If the batteries catch fire they will suddenly explode. If you want weld a thin metal it needs extremly high technique. It needs intermittent arc so you should move the welding rod close or far to the material alternately. If it can't succeed the material will melt down. Once it occurs, it is very difficult to close the hole. Welders sold at D.I.Y. shops use current in 100V and it is very hard to weld finely by using them. You can't expect its welding power and can't use common welding rods so I can't warrant the strength if you use these welders. If you dare to use them use them for the parts which is not dangerous when they break.
- It is a Mig welder that sends a thin wire out of the torch by means of a motor and blow argon gas around the welding point. It is expensive compared with a covered electrode arc welder. It is available for steel and stainless steel by changing the wire. You have to choice the thickness of the wire considering the thickness of material and welding cyrrent. If you convert plus and minus you can weld aluminum but it is very difficult to weld it. You don't need to strip off the slag because the wire is not covered by flux. It combines the materials firmly because it welds deeply. And its welding speed is very fast so warp is very small. It is available for thin metals for instance gas tanks or mufflers. The bead is not fine compared with a Tig welder. It is like a welt. Production frame is made by means of a Mig welder. Imported Mig welders are very cheap compared with Japanese ones. The fault of this welder is that this needs inert gas so you should set a cylinder somewhere and connect a hose to it. Another fault is that it uses a coil of wire so it needs a driving mechanism of the wire. So it needs wider area than a covered electrode arc welder. But if you once use a Mig welderyou can't go back to a covered electrode arc welder. It is really comfortable to use. Moreover it doesn't need to change welding rods so you can weld continuously and efficiently.
- You feel it like a gas welder when you use a Tig welder. It blows argon gas from the torch and arcs from the tungsten electrode at the middest of the torch to material and you drive a 1-2mm welding rod using your fingers carefully when welding. It builds beautiful beads. It is not available for thick metals. Welding speed is not fast compared with other kinds of welders but it makes welding easy. If your welder is for both direct current and alternating current, you can weld steel or stainless steel in direct current and aluminum in alternating current. If it can add pulses in the current, welding aluminum gets extremely easy. Many books say that welding aluminum is very difficult but I doubt it. Unfortunately, Tig welders cost very high and I don't know cheap ones you should pay much. Moreover, inert gas is argon and it consumes far much gas than a Mig welder so it is not economic. So I mainly use my Tig welder for welding aluminum. When you weld steel or stainless steel the light is brighter than that of a Mig welder, so use a darker lens in your welding mask.
- About drawing
- I don't explain external form lines and dimension lines because you can see them at a glance. The mark phi is used for the dimension of diameter and dotted lines are used for hidden lines.
- A letter C expresses planing off the corners. If there is a figure it expresses the size of chamfer. A letter R expresses making the edge round. If there is a figure it expresses the size of radius.
- We use a letter M for a metric screw size. The figure following M expresses the size of the screw. For instance, M6 means 6mm screw. If X with a figure is follwed after the screw size the figure expresses the pitch of the screw. For instance, M8X1.25 means 8 mm screw with 1.25mm screw pitch. We usually use coarse thread but we sometimes use fine thread if the screw is apt to loose. We usually use fine thread like M8X1.0.
- Dimensions enclosed () are reference dimensions.
- Reversed triangles express the level of surface finishing. Increasing number of triangles shows finer surface. You can get two triangles using a lathe but you can get three triangles by carefull finish. Coarse finish is one triangle.
- An alfhabet followed after an axle or a hole size expresses its tolerance. It is impossible to make a thing just in size so if the size is in the tolerance we think the work is finished. We use big letters for an axle and small letters for a hole. The standard gets bigger about an axle and smaller about a hole if the alphabet goes from A to Z. The next figure expresses the width of the tolerance. If the number becomes big you can make things with a little carefulness.
- The letters t= expresse the thickness of the plate. The figure fallowing = means the thickness of the plate. For instance, t=3.2 means a plate in the size of 3.2mm thickness.
- I omit welding symbols in this recipe. Even if you forget to draw the symbols you may have your works built in a welding factory. Maybe they know how to weld your works. If you have some interest in these symbolse, see mechanical books.
- You may understand my drawings if you read this recipe. Please watch previous recipes again.
- Use steel for making frames and jigs which need strength. Steel is very cheap and very available. In addition to them, it is strong and easy to weld. The following table shows various uses of steel materials.