Throaters

[leftiye]

I have an auction on my watch page (ended) with a bunch of throating reamers that someone made. They have nice long pilots, and square drives on the ends, or a knurled wheel for hand turning. The thing that really grabbed me is that they were of the half round persuasion. Should be simple to make. What's your reaction to this? Any reason to not go this route? Could save one a fair piece of money.

[Wicky]

Yep, easy to make called D bits and probably a few other names as well. I make them from Silver steel (water hardened drill rod) draw and temper them and touch them up on a stone. They cut well as long as the cut is slow and well lubed - same as normal reamers really. Bullshop or one of the other guys who are into machining could probably tell you more - I only dabble, these blokes do some good stuff.

[leftiye]

I've made half round drills for forming cavities in paper patched mold blocks (boolit shaped drill, no lube grooves). These are the type of drill that Randy Brooks got from Fred Barnes when he bought Barnes Boolits (to make his swage dies). What I was having a question about was how these would "like" cutting out rifling.

[bohica2xo]

Leftiye:

Like I said in the other throater thread, the job is only as good as the pilot fit.

Since it sounds like you plan on making some for you own use, you can control the pilot fit properly.

Feeding is where it can get tricky. With this kind of tool it is best used in a machine tool like a lathe. Since you have multiple lands, it is possible to drop the single cutting edge into a groove waaayy too deep when feeding by hand. you want to take .001 or less per revolution for a good finish.

Hand reaming a bore with multiple flutes is easier, especially if your flute count does not match your land count. I have had a chamber reamer that would engage the rifling like a spline drive, and it was not something you want to try by hand.

B.