Boring brass

If you want to see how this is done have a look here. If you're going to do a lot of work with brass it's worth keeping a set of modified drills specially for brass.

Russell.

+1

-2 if it's going to be bored why bother. Drilled smoothly a clean hole will be produced. If the drill grabs don't let it.

One of my first lathe purchases was a set of blacksmith drills. Loads on ebay. They allow holes to be drilled up to 1in or 25mm in stages and all have 1/2in shanks. Mine are the black ones.

Sometimes it's difficult to get a hefty boring bar on a lathe say 16mm dia. My Boxford has a Myford branded qctp. What they did to get the additional tool height was to add a plate to the bottom and use the same 1/2" holders. It's fairly easy to make a separate holder for a larger bar. Block of steel and T bolt to fix it in the usual slot. Drill through it to suit the diameter of the bar and add clamping screws. If you might want to get these screws out after much use make sure they are high tensile ones and just to be sure chamfer the ends a little.

The hole for the boring bar needs to pass close to the fixing hole to help reduce twisting moments. The base of the block area shouldn't be too much smaller than the normal tool post really and do make sure the bottom is flat and well finished. If block turned in a lathe it will be concave so lap it. They can be made out of round bar too.

The cutting edge of some of the indexed boring bars is on the centre line of the bar or better still for boring a few thou above it. In this case the hole for the bar can be formed with a drill from the headstock but it would be best to ream it as well.

Super fancy ones can be made as well. with several hole sizes.

Maybe a bit over the top in this case but twisting moment on the holder is very low as the bar passes though the fixing's centre.

John

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Russ's proposition was "If you're going to do a lot of work with brass it's worth keeping a set of modified drills specially for brass" - a general statement regardless of any boring considerations in this thread. I think he's dead right. Having tried both unmodified and modified drills, I made a modified set years ago and have been more than happy with it ever since. Its easy to do and doesn't really cost anything in the long run. If it doesn't work for you (I make the assumption that you've tested it), then fine.

I do agree that you can smoothly drill a hole in brass with a single drill, because the resistance of the core overcomes any tendency of the drill to pull into the work - the problem comes when you enlarge that hole with another drill. It's not always feasible or desirable to drill to the finished size in one go.

And just to be picky - "if the drill grabs" it's too late to "don't let it".

Once some one has enlarged a hole in brass they will know that the drill might grab and react accordingly next time. The noise it may make could also concern people. If they have a dodgy tail stock they might even tighten the barrel clamp a tiny bit as well.

Or they could modify a set of drills.

John

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In an emergency, all you need to do after drilling the 1/2" hole is to take the drill out of it's chuck and clamp it in the tool post facing the head stock, angle the tip slightly towards you, and have that flute at centre hight, now just use it as a boring bar, it does work, I tried it.

Ian S C

Or use a ½ in end mill the same way for increased rigidity.

Russell.