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Before beginning to build

Here’s a bit I plan on including in the instructionals. Wrote it today. I’ll likely edit it a few times in the coming week.

Bushing Obtainment and Installation

A very important component of the Ironworker is the pin and bushing connections between parts. These parts will be under up to 120 tons of force, so it is crucial that these connections be secure.

The bushings could either be made from 4130 alloy Chromoly Steel and hardened, or purchased from a supplier such as Regal Bushings. It will be much cheaper to make them yourself (cost us $152 for all bushings, would cost ~$ ___ purchased), but does require a few hours of extra work.

To insure longevity of these connections, we suggest the bushings should be either “freeze fit” or “press fit” into holes bored to exact size for them.  This insures the bushings are perfectly centered in the hole, and won’t be able to move or to twist. However, it is likely that boring slightly oversized and welding them in would work.

Boring the hole will require a boring head for a mill, or a boring machine, capable of boring ~3″ diameter holes. The final diameter of the hole will be determined by measuring the outer diameter of your bushings, and subtracting .001″ per 1″ of bushings. The following video offers a good instructional on the boring procedure: http://www.youtube.com/watch?v=VY2crpjhL3E&feature=relmfu

Preparing the “Big Holes”

Boring requires that a hole already exists to be bored to a larger diameter.  For the smaller diameter holes, either mag-drills or drilling would work for making it. However, for the 3″ holes for the big bushings, making these holes will prove to be a bit more difficult.

The easiest way to do them is certainly with a mag-drill. I recommend a 2 3/4″ or 2 7/8″ bit and boring to size. However, it is a very pricey bit ($252 here for a 2 3/4″). For choosing the proper bit, know the following things:

  • The larger the bit, the less boring you will need to do. Boring is very time consuming (takes 4-5 minutes per .03″ removed from a 3″ deep hole) so should be minimized as much as possible.
  • Bits get more expensive with their size.
  • The maximum size bit you should buy is 2 7/8″, as if you purchase a 2″ deep bit, you will need to drill from both sides of the 3″ thick piece to remove all material. I’ve found that despite drilling a pilot hole, the center of the hole can be off by up to 1/16″ overall. So drilling any larger than that risks oversizing your hole.
  • The minimum I’d reccomend is 2.5″, as otherwise, it just takes too long to bore.

If this is out of price range, torching the holes is an option; this is what was done for the OSE prototype. However, torching really hardens the steel and will make it much more difficult and time consuming to machine. (probably 3X longer!)