Interesting Fact.

You cannot use a lathe to press fit 1/2" aluminum hex shaft into a hex broached aluminum 3/8" gear. Well, actually you can get it partway in, getting out was much harder. It was harder still on the mounting block for the tail stock of our lathe. Cracked that cast iron casting right in half.

Don’t blame the kids. I should of caught this before we got the bigger hammer.

Put me up on the wall of shame.

You were on a lathe, you couldn’t have bored out the 3/8ths hole 1/8th more?
::safety:: ::ouch::

Ouch!

My lathe can’t bore a hexagonal hole. It would be great if it could though;)

http://www.polygonsolutions.com/how-rotary-broaching-works

(It would take some serious attention to be able to widen an existing hexagonal hole, but I’ve seen mention of tool guides that hint that it could probably be done.)

This is the coolest thing I’ve seen on CD in a while. Thanks for sharing!

So you were attempting a .125" interference fit?

Just the other night I had a student ask how to cut a small, square hole in a piece of ploycarb… I told her to go find the “square drill bit” :slight_smile: 30 seconds later we all had a good laugh.

It is highly amusing to discover that a “square drill bit” is actually more triangular in shape.

Amusing, and a very intriguing topic.

Yeah. Wobble broaching is fun.

You can see a much better video of the actual broaching process hereand here

Here is a “square drill bit” better known as a mortising bit or chisel

http://www.bing.com/images/search?q=mortising+bit&id=0C4F098720B36843ADA2262265E5504F893567B5&FORM=IQFRBA#view=detail&id=0C4F098720B36843ADA2262265E5504F893567B5&selectedIndex=0

It cuts square holes. Now the laugh is on you!

Dr. Bob
Chairman’s Award is not about building the robot. Every team builds a robot.