Motor Arbor
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If you're using a commercially assembled motor, you need some way to connect the blades to the motor. This comes in the form of a motor abor. Bascially, it acts as a adapter that can grab onto the usually smooth motor shaft. You can find motor arbors online for a little under ten dollars, but I wanted to build my own. This arbor was designed for motors with 5/8" (1.5875cm) shafts, which is fairly standard from what I have seen.

You need just a few things for the arbor:
a rod coupling nut (I used a 1/2" one, but 5/8" would be prefered)
all thread - whatever size matches the rod coupling nut
JB weld
a few small bolts to use as set screws
a tap that matches the set screws
two large washers and a nut that fit on the all thread

This is what the rod coupling nut looks like. It's about 2" long (about 5cm) I marked where the holes for the set screws should go

The largest size of coupling nut I could find was 1/2", so I had to drill out the threads with a 5/8" drill bit. This worked fine, but it would have been perferable to use a 5/8" coupling nut, which wouldn't have required all the drilling.

This is what a tap looks like. It's an incredibly useful tool that lets you add threads to a hole. You can find more detailed instructions online, but the process basically involves drilling a smaller hole and then using the tap to thread it. Generally, tap sets will provide speficiations for what drill bit sizes you should use. It's also reccomended to use some lubrication while tapping a hole. They sell specialized cutting oil, but I found that WD-40 worked just as well.

Tapping the holes

The finished treaded holes. I cut them to fit 8mm bolts. This worked pretty well.

The coupling nut should fit fairly snugly on the motor shaft. I found that it often helped a lot to adjust the two set screws to get the arbor perfectly level. If it is not level, the hub and blades will be rotating off-axis and cause a lot of shaking.

It's nice to have a lot of thread showing, so I cut about 9cm (3.54") of all tread. I cut it with a hacksaw, which worked great, but an angle grinder would also work great. Try to make it a clean cut.

Mix up a batch of JB weld

Try to get JB weld completely covering the part of the all thread that will be in the coupling nut, and put a little JB weld where the all thread exits the nut. It is incredibly important that the connection between the all thread and the nut is secure. Let it sit for at least 24 hours before using it.

I added washers and a heavy-duty nut to connect the arbor to the blade hub. Each washwer was 4.5cm in diameter. Larger washers would have been even better. I sandwich the hub in-between the washers and then tighten the nut as tightly as possible.

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