Wednesday, September 2, 2020

Baby Needed Another Counterweight

 The crackle finish black round thing is the counter weight that came with the EQ-1 mount.  Unfortunately, it was not quite enough weight to counterbalance Baby:

I needed about another pound.  If I had a chunk of round aluminum lying around, I would have used it.  But I had a block of aluminum.  I was pleased to see that my math skills and knowledge of aluminum's density (2.7 g/cc) were sufficient to cut a 15 oz. block, square it, then drill an 1/2" hole for the axis.  

How to hold it in place?  The lazy way would be a 1/4"-20 bolt in a threaded hole, but the bolt would have marred the axis each time I tightened it.  So I tapped 1/4"-20 through the side to the bore hole and looked for a piece of acetal rod that I could turn down to .2".  This would go between the end of the bolt and the shaft.  

No luck on acetal.  I did find a .125" diameter brass rod in my odd scrap collection.  No turning required.  No risk of scarring the axis.  Just dropped a short piece down the hole and put in the bolt.  

When I took off the factory counterweight to install the new one, I discovered it used the same technique, and like my design, it was not captive: when I removed it, the rod slid through to the bore hole, but it was long enough to not fall out the bore hole.  I am about to run to the pharmacy, so I will buy a 1/4"-20 thumbscrew at Star Merc, and probably cut a longer brass rod so that it does not fall out the bore hole when I remove the counterweight.

Counterweight perfectly balances Baby.

I found some knobs with 1/4"-20 threads to replace the hex head bolt pictured above.  I had hoped for a knurled head thumbscrew,  but this multiple lobed knob provides much superior locking over any hand tightenable bolt or screw.

1 comment:

John in Philly said...

Next time you need to thread a long deep hole, think about figuring out how much length of thread you need, add a bit more, and only tap that much.
You can drill the rest of the hole as a clearance for the fastener, and the time needed and the risk of breaking a tap are reduced.

The finished counterweight looks nice.