Sunday, August 14, 2005
Threaded guide rods
I haven't made much progress on things for a bit because I've been busy building myself a house. Here's the basic setup I'm using for lathing the threaded rod.
I'm using a drill press here, but a regular drill will work just as well (see Vik's Afhgan Lathe documentation). The only real difference with this is that I'm lathing vertically rather than horizontally.
At the opposite end to the drill head there is another drill chuck to grip the other end of the rod (this is essential). What makes this different from the Afghan method described for drilling a centred hole is that this is a rotating chuck. I took this off a dead rechargeable drill that I picked up for $2 from the junk yard. I just removed the internals and then cut it with a hacksaw so only the front part of drill remained. After putting the first gear back into the drill (which includes the greased bushings, etc), I end up with a smoothly rotating chuck. As pictured, I clamped this to the bench. You can quite easily adjust the position of this by hand while the drill is spinning. Any wobble in the rod should be eliminated and you can also easily see if the rod isn't straight.
The platform serves as a good tool guide, and I use this to help position a metal file. I lathe it as described in a previous post. I chose 6.0mm as a good diameter for the end of the shaft. The rod is M10 (10mm outer diameter) so 6mm will give enough room for adjustment in the bushing and will still be strong enough. Care needs to be taken to ensure the lathed part of the rod is parallel. If it widens towards the tip, it won't be able to be removed from the bushing later on. If it tapers at the tip, it is more likely to jam. Still given a choice, it'll be better to taper slightly than become wider. Using callipers, I lathed to 6.0mm at the tip and 6.05 towards the thread.
The lathing happens slightly away from the end of the rod (because part of it is held in the chuck). After lathing and polishing, I cut the threaded end off. You repeat for each end, ensuring the total length is correct. The only thing that remains is to polish the end of the rods when the excess thread is cut off. This is fairly important because if it's not rotationally symmetric it will dig into the back of the bushing which will add unwanted horizontal play into the shaft.
I have a method ready to try this but haven't quite got there yet.
Also, as shown in the picture, the rod I'm trying to lathe is too tall for my drill press, so I've raised it up onto a base supported by some blocks, and I had to rotate the drill head away from the base.