Sherline tailsock drilling.

[EricB]

I just managed to damage the tailstock on my 4400 lathe while drilling a hunk of C360 brass. I was using a 3/8" drill to enlarge a hole from 5/16". The lathe did come with a 3/8" drill chuck, it should be able to handle it right? Anyway, the drill hogged into the brass and spun the MT0 chuck adapter in the tailstock ram and seized before I could find the power switch. I realize (now) I was trying to remove over .060" of material in one pass which I normally would not do even though the lathe motor can handle it. Since the parts were welded together already I went ahead and finished drilling the hole.


I got the parts separated but the tapers are ruined.

While I wait for the replacement parts to arrive I'm looking for guidance on how not to do that again. I obviously exceeded what an MT0 can hold. It's also obvious that this is the weakest part of the lathe. What isn't so obvious is how do I know if I'm approaching the limits of what the taper can hold.

Thoughts?

Eric

 

[benmychree]

When drilling brass, we routinely dub off the spiral edge of the drill point, this prevents the grabbing; the flat need be only about 1/32" or a little more.

 

[mikey]

Eric, a Sherline lathe typically doesn't like to drill above 3/8" but can do 1/2" with care. In brass, the trick is not to use a pilot drill or try to enlarge a pre-existing hole. Spot or center drill it, then go straight to your on size drill. It will cut without digging in or jamming and you don't need to peck drill. I've drill hundreds of hole in brass on a Sherline lathe and as long as I used the main drill I never had it dig in or bind.

If you must enlarge a pre-existing hole then you have to peck drill it - feed a little, back out, feed a bit more, back out, etc. Or you can just bore it, which is what I do in this situation.

 

[EricB]

So what you're saying is my tool choice was not too aggressive, just that I need to keep it from digging in?

Eric

 

[mikey]

Yes. A Sherline lathe will easily drill 3/8" in brass if you use it to begin with. Pilot holes in brass do not work well.

 

[tq60]

Pilot hole only needs to be size of web of final size.

Long ago folks would preach stepping up but this can chip drill bits if not correct.

We often spot the center then drill up to 1/2 on first pass.

In your machine you are limited, does the tail stock allow a tanged taper?

Brass and other soft materials can cut faster than you feed resulting in the taper unseating.

You also can use boring bar above a minimum size.

Others will provide more ideas...

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[homebrewed]

Brass is evil if you routinely step-drill. And it's an issue for larger machines than your Sherline. I know that for a fact. I knew I had to do something when I saw drill bits try to unwind themselves when they were grabbed by the brass! Yikes. And forget trying to drill to a specific depth.

Dubbing a drill works well, but then it becomes dedicated to drilling brass. I have some cheap HF HSS drill bits I dedicated for that purpose. I needed some fairly accurate holes so didn't trust starting with the final drill size.

I've used 3/8" shank end mills as boring bars for brass when I needed a very accurate ID; and I could easily bore holes less than .5" in diameter. I thought the positive rake would be a problem, but it seems to be OK, at least for small DOC's. Perhaps that's because the EM's are very sharp.

I've been machining brass for making decorative yard sprinklers that spin under the force of the discharged water so have had the "privilege" of learning how to machine it.

 

[EricB]

I guess I'm just going to have to get a set of drills only for brass.

I was able to dress up the tapers in the tailstock ram and on the chuck adapter so I can keep working until the new parts arrive.

Here's the part I'm making. It's the cylinder for a tiny oscillating steam engine. One half inch bore, one inch stroke.


Eric