|Scott's Atlas / Craftsman 101.07403 12x36" Lathe, modifications and projects. Stone Mountain, GA||Unique Visitors:|
This is one of those things that everything was wrong/
This is the "wonderful" Zamak pulley that was on the lathe. It was just weird. Wobbled and did not fit the hub right.
I measured the bore and it was a bit oval. So, I decided to weld it up. I had tried TIG welding the Zamak cross-slide handle and it was near impossible. I decided to try aluminum brazing.
It was a mess. The stupid Zamak melts at the same temperature as the low-temp brazing rod. I managed to build it up enough to bore it.
Ok, what do you use as a reference for center? Whatever your answer is, you are wrong. I decided to center on the inside of the V-belt groove. That would have the pulley always keep the belt at the same radius.
Well, then the outer hub center was off one way and the inner hub was off another. Both had an obvious angle off of each other from being on axis. I decided to persue.
Ok, center bored the hub that was filled with aluminum braze (Alumniweld.) Turns out the hub was so off center, that I could not bore it to 0.75" without one part uncut. I decided to bore to 1" and make a sleeve.
You can see the pits in the center of the bore. This Zamak has bubbles in it. A Piss-poor casting.
Another thing that was very odd was the V-grooves were not in the center of the casting. You could see the rim moving side-to-side but the V-groove stayed in the center. This you could see as a visible side-side wobble. The diameter of the pulley was off too. You could see it moving up and down but the belt did not move. I faced the pulley and the hub and the outer edge. Now everything was referenced to the same center.
For the first time, I could see the pully turn with the hub, belt groove and outer edge not visibly wobble in reference to each other.
I knew the opposite side was thin, but it just blew out when boring. As you can see the left side is much thicker than the top right.
I can't believe how off everything was. I originally thought it was bent, but that would make the V-groove non-circular; that was the only thing that measured perfectly round. I would say the hub and outer ring were .040" off in both the center point and the angle offset of the ring on the axis.
I'll need to find some aluminum and make a sleeve. Then I'll braze the sleeve in. Maybe I'll try TIG brazing.
Why? Well, I had thrown this in the trash twice but kept pulling it out. I kept saying, "why not try and fix it?" Was a chance to try the brazing rods again. I have used them many times before with sucess.
The stuff is horrid to work with. I tried TIG welding the cross slide handle. It must have some zinc in it as it flared up and made the arc very instable. Also has magnesium that makes a black mess everywhere.
I had heard it was "unweldable", I did not expect it to be so hard to braze too.
Just can't believe how off this casting was. Ok, this is just a hobby lathe, but they must have really not cared how some of thes zamak parts came out. The gears are fine, as are some of the other castings.
|Faced the opposite side and cut off the lump left of the old hub. Now just need to turn a piece of bar stock for a new hub; just waiting for some aluminum stock.|
Here's the adapter cut from 1.5" 6061 aluminum ready to be cut off. It was bored after being installed in the pulley.
It was turned to be a force-fit into the pulley. The set screw will go through both the pulley and adapter to lock them together.
Finished pulley. It works well and no longer wobbles. It still looks a bit odd as the inside of the outer rim moves while the outside and hub stay centered.
Will probably need to be rebalanced. There are 23 holes drilled in one side, probably to correct the hub being off center.
Actually, the pulley is on backwards, it lined up with the motor pulley better.
You can see the pulley operatae n the Variable Speed Drive page.