12 February 2011

Alternator pulley done

One of the important steps was to make the outer circumference of the bearing as concentric (centered) as possible with the inner bore for the bearing. If the two are off, the bearing will run eccentric and hammer on the belt. To ensure concentricity (neat word eh?), I indicated my 4-jaw chuck on the bored hole to within .001", the most accurate I've ever been on my lathe.

Once indicated, I turned the outer circumference just enough to true it up. Then I mounted it on my rotary table -- that's a cool little tool that lets you mount things to it and then as you turn a handle, it turns a fairly precise number of degrees. So if you want six holes in a circle, you drill a hole, spin your rotary table 60° and drill another one, and so forth. This (theoretically) spaces the holes evenly, which is important for balance if your part will be spinning 15,000RPM.

My rotary table is 3" so normally the largest item I can work with is maybe 2", to allow room for clamping. However, since I had already made a hole in the middle of my pulley, I was able to do some creative clamping to just barely fit a 3" pulley on a 3" table. Here I'm drilling pilot holes -- smaller bits drill straighter, and then when I enlarge the hole with the larger bit it will "follow" the existing hole and you end up with a straighter and more accurate hole.

They say a poor workman blames his tools, well, my cheap Chinese drill press really wanders and worse, is way too fast for drilling 1/2" holes in metal. In spite of my care, some of my holes ended up in significantly the wrong place but oh well, we'll see how badly out of balance it is once the car is running. Once the Jetta is done there are some things I can do to the drill press to improve accuracy (just like you have to do on a Chinese lathe).

Then it was time to beat on it:

This was the most critical part of the whole pulley. Bearings are "press fit" which means that the bearing is smashed into a hole that is slightly (.0005" to .001") TOO SMALL for the bearing. This means the aluminum is actually deformed -- stretched -- and the springiness in the metal itself will squeeze on the bearing tightly so it doesn't fall out. In my case, the hole I bored on my lathe was still smaller than the bearing but not by as much as I wanted, so I used some red Loc-tite (essentially, a special form of super glue for metal) to ensure good grip.

...and here it is, installed on the car. Looks nice, even if I do say so myself.

So, the reason I did this was to push tension on the outer edge of the belt. This increases the "wrap" on the alternator pulley to nearly 180° as seen above. The stock setup I replaced pulls tension on the inner edge of the belt, thus reducing the "wrap" on the alternator pulley, which is then more likely to slip and squeal and eat belts.

I hope this works.

10 February 2011

Jetta update

Haven't posted in a while but I've been busy on the Jetta. Lemontree helped me put the engine in, so I've been busy hooking things up to it. And since I already had the dash apart anyway, I went ahead and did the heater core too since it's a right pain to get to.

Anyway, since I've gone the do-it-better-than-the-factory-did route for the alternator mounting, I need a tensioner pulley for the alternator belt. I got started making it but had more and more trouble until I realized I had to take my lathe all apart and adjust it again. Since I didn't really know what I was doing the first time, I didn't really adjust it right to begin with and then actually using it made things loosen up and move so it was time to start over with the carriage, cross slide, and compound adjustments. I also switched to a different type of cutting tool as the $5 Harbor Freight junk is, well, junk. That all done, I was able to make this:

That's several ounces of aluminum "chips", though aluminum makes such long stringy chips the phrase "bird's nest" comes to mind as a more appropriate name than "chips".

Here's the half-completed alternator pulley:

This 3" aluminum stock is about as big as my largest chuck can handle (definitely too big for the chuck that comes with the lathe). Though aluminum, it's still quite heavy for something going to be spinning 15,000RPM which is why I'm hollowing it out and will follow that with drilling some holes to lighten it further (and make it look cooler).

While I was making lathe improvements, I made a second chuck key for my 4-jaw chuck. Unlike a drill chuck which automatically centers the drill bit, each of the 4 jaws is independent so you can grip irregularly shaped pieces. This also means centering something round is done manually by the machinist one jaw at a time... or better, 2 opposing jaws at a time, which is why I made the second chuck key:

The left key is the one I made and the right key is the one that came with the chuck. By turning them together, I can shift the work piece left or right and that dial you see will tell me when I am centered (then I rotate the work 90° and do it again for the other set of jaws). At first I had tried it with just a single key and it's a real pain since the normal key is short and hits the dial indicator and you have to keep turning the work 180° and measuring again. That's why I made my key really really long so it would stick out beyond the dial without hitting it -- clever, no?

I had a hard time soldering the handle on my second key, too. I swear I am cursed when it comes to joining metal... I love cutting it but I sure hate getting it to stick together.