you can use Autodesk inventor or Auto CAD too but this instructable is for 123 design
if you want to know how to use it here link :
Warring read this: do not start your design before read the full instructable
i hope you enjoy your time
Step 1: Get Started
#1_ Extrude the first shape with length 6 mm, (Extrude is from Construct menu ), now Extrude the rectangle 1.5 mm
now as shown on the figure that is the shape of the solid
Step 2: Forks Inner Side
#4_ move it then rotate it as shown on the figure ( Move is from transform menu ) then place it on the solid as on the figure.
#5_ copy the key hole ( Ctrl+C ) or snap it then past it as on figure at the same high
#6_ check the object if it need to increase or decrease on scale
#7_ now draw this cylinder and mark the center of the key hole and insert the cylinder at the center of the keyhole and don't forget to make it's high more than the high as by one it is 7 mm , this cylinder will allows the fork to move, do the same on the other one or just copy first one and replace with the other as shown
#8_ Optional:you can change the martial as you want you can change it from martial menu shown on the photo.
#9_ now it is time to close the shape by drawing rectangle as on the figure and Extrude it with length 1.5 mm
#10_Optional:you can make the cylinder smooth by using fillet tool from modify menu.
#11_don't forget to Extrude the cylinder as shown on the figure
now we are done the fork inner shape.
Step 3: Gripper
#13_ now Extrude it ( inner part 5 mm high, outer part 6 mm high and it's final shape is shown there on the figure
#14_now add this extra part as shown on the figure
#15_ if u make mistake as wrong direction no problem just mirror it ( from Pattern menu ) and site axes point then do it as shown on the figure.
#16_ place this part ( gripper ) on the fork as shown on the figure and insert another cylinder at it's middle
now it's final shape.
Step 4: Fork Outer Part
#18_ now it is time to insert gears go to online kite then choose gear then 40 degree then " 40CA 36T Spur " place it at the lower face of the second keyhole as shown on the figure and then insert cylinder at it's middle
#19_draw rectangle as on the figure
#20_ now draw 2 circles 1st one it center (where cylinder will place )other one will fill occupation of gear to make 2 sides 90 deg now Extrude 2nd circle by same high of your gear my gear is 0.424 mm and insert cylinder on the 1st one.
#21_ now Extrude the rectangle 1 mm and join it with the shape as shown on the figure.
now it 's finally done the fork
Step 5: Description
note this photo is from Wikipedia not mine one i just share it to show it to you.
lets come back to the project :
Step 6: Join Them Together
Step 7: Position on the Gears
Step 8: Finishing It
#24_ now join them together with this bars on fig 3 you can also Chamfer from modify menu r=2 as shown on the figure
#25_ now Extrude the sheets and bars more as shown on the figure then close the X sign part as on the figure
#26_ now draw this shape with the same length of the arm then Extrude it and finally add to arm as shown on the figure and leave some holes for nails
so it;s over now great thanks to see this instruction and waiting all this time and i hop u like it and follow me to :D