Drilling into a brass bar

[Geraint WilliamsParticipant @geraintwilliams68288]

HI all – my first proper beginners question!

I'm just trying various procedures to get a feel for tools machines and materials. Among other ideas I have a project in mind to suspend a pin vice using a couple of bearings in a DTI magnetic base so that I can drill at a consistent height into a plastic model. I can set the base and model on a flat surface, drill a hole one side and drill at the same height on the other side with the bearing helping me spin the pin vice.

I took a piece of 25mm stock brass round bar, hacksawed it down to about 40mm in length, faced the end and turned a shoulder on one end down to about 8mm so that it could be clamped in a magnetic base arm. So far so good. Next was to drill a hole through the bar from side to side, Fortunately I have an old pillar drill and heavy machine vice I can use. I took it very carefully starting at about 3 mm drill then increasing by about 0.2mm each step. As the drill diameter increased, I reduced the speed of the drill. All good until I got to about 10mm and the workpiece began to vibrate in the vice. Just a slight shudder but came more noticeable the wider the drill so I increased diameter by 0.1mm at a time. I eventually stopped at 12mm (bearing o/s diameter) and pushed the bearings into the ends. Then it became obvious that the bearings were not in alignment and that the hole had somehow deformed (not to the naked eye but something had gone wrong!). It doesn't need to be 100% to work but that's what I'm here to find out as I'd like to get it 100% correct o learn and improve, Questions are:

Is Brass suitable as I've read it is a relative soft metal and can deform? If I think about it I am drilling a large diameter hole compared to what's left!

Any Advice re drilling. Should I have drilled the hole in a bigger bar first then turned it down etc.

Any beginners advice no matter how basic welcomed

Thanks

G

[Geraint WilliamsParticipant @geraintwilliams68288]

Drilling a 12 mm hole into the side of a 25mm brass bar

[Anonymous]

If I've understood correctly you are drilling across a round bar, not along the axis? If so then the larger drills will tend to chatter as the initial surface is not flat. I wouldn't pussyfoot about. Going up in small increments means the driils are more like to be rubbing than cutting. Clamp the work in the vice and then clamp the vice to the drill table. For a conventional drill with a chisel edge I'd spot drill at 10mm, drill though at 3-4mm and then drill 12mm. If the drill is 4-facet, so the end is a point, I'd miss out the smaller drill. Ideal would be to use a slow helix drill to reduce snatching at breakthough, but going up in a large step can also help to reduce snatching.

Drilling brass is generally ok dimension wise. It's bronze and gunmetal that move, close round the drill/reamer and deform.

Andrew

[Geraint WilliamsParticipant @geraintwilliams68288]

Thanks Andrew – I'll give it a go, Was nervous clamping the vice to the drill table. Not sure why as it does make good sense. Thanks again G

[Nigel Graham 2Participant @nigelgraham2]

I like the idea of what seems a type of "pillar tool" for the pin vice.

Ah,,, brass is a tricky material to drill. It is not as hard as steel, but it's not "soft" in a plastic sense, not to ordinary machining operations anyway. There are several points here…

1) A twist-drill with its normal geometry, including a large rake angle behind the cutting edge, will tend to dig in, causing the chatter you noticed, and likely to spoil the accuracy… as you found.

A cutting-edge for brass should have no rake, or more precisely a rake of 0º; often gained on a twist-drill by very carefully easing the edge back with a small oil-stone. (Same as the lathe tool for brass, where the cutting-edge goes away horizontally from its contact line along the centre of the bar.) It still needs the clearance, but the cutting action is more scraping than slicing.

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2) If I understand your description correctly, you were cross-drilling a round bar. That can be a bit awkward, but you were correct to make the set-up as rigid as possible. (I assume you bolted the vice to the drill table.) Even with that, a twist-drill with its normal edges that will try to screw itself into the brass is even more likely to chatter and wander when you need it enter and leave the work-piece on cylindrical surfaces.

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3) You may have used too many, too fine increments in opening up the hole. Each drill would have gained little support and guidance from the previous hole, especially as you were drilling a large hole in a round bar only twice the largest bore diameter.

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4) Bearings are fussy. They are made to fine limits and the hole for them is best reamed, from a hole drilled to maybe 0.3mm smaller than the finished size. On a workpiece like that the reamer will need a bit of guidance so you don't end up with a mis-shapen hole.

I would use the pillar-drill either with a machine-reamer, or to guide a hand-reamer.

12mm reamers are readily available, but you could also make one of the type sometimes called a "Toolmaker's Reamer " for brass. It consists of a length of silver-steel of the intended diameter, with the end cut at a long angle, hardened and tempered. I have not tried them but you see them recommended occasionally on this forum.

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5) You might in fact have been better boring the hole on the lathe, with the brass held in the 4-jaw-chuck; but this will entail very careful setting-up so the hole goes truly across the diameter. You'd also need ensure the boring-tool has space to exit into so it won't hit the chuck.

I use a simple saddle-stop when I carry out operations like that. It's a just a bar with a hole in the middle, clamped across the slide-ways by the clamp borrowed from the steady. (This is on a Myford 7, which has wide flats on the bed – you'd have to modify the idea to suit other bed-profiles.)

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6) Starting with over-diameter bar will help but is a bit wasteful of rather expensive material, and gives a horrible interrupted cut with a risk of the tool catching and ruining the work. (A fine self-acting feed with light cuts will overcome much of that problem.)

hope this lot helps!

[HopperParticipant @hopper]

You dont need bearings to spin a pin vice 180 degrees. Just drill a small hole through your brass and stick the pin for the vice mount or whatever through the hole. Drill the hole first then turn your pin to fit the hole nice and firmly.

Run your drill press at full speed for drilling small holes in brass. Drill your small pilot hole then go straigth to your full size drill bit. Small increments increase grabbing and carrying on it brass. For holes under maybe 3/8 inch, no pilot should be needed.

[Chris GunnParticipant @chrisgunn36534]

If I were doing it, I would start with the long piece of bar stock, and mill a 12mm plus wide flat where you want the hole. put a good centre dot in the middle of the flat, then I would hold the section of bar in your vice, you will hopefully have a decent chunk to hold on to, and then clamp the vice down, drill the 12mm hole in one go, with no pilot hole, if your drill is big and heavy no problem at all. Then I would cut the blank off the bar, and then carry out the turning required. to make sure the blank runs true, make a split bush to hold the blank to avoid damaging the hole edges, and Bob's your uncle!.

Chris Gunn

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Hopper on 09/03/2021 22:04:01:

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You dont need bearings to spin a pin vice 180 degrees.

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I think Geraint means to spin the pin vice several turns, to drill the plastic.

MichaelG.

[Geraint WilliamsParticipant @geraintwilliams68288]

Thanks for the comprehensive advice Graham…yup a kind of pillar tool that can be used horizontally/vertically and at any angle is the idea, As soon as it's firmly clamped in position on a flat metal surface using the magnetic base i just insert a pin vice which can then be used repeatedly to give the same result (for example drilling symmetrical holes on both sides of a model ship, tank, car etc)

I'm also following some proper Harold Hall model engineering projects and have started a Stuart 10V but I also want to come up with some of my own "quick win" useful projects where I can see an immediate benefit to in some of my other hobbies. That should give me some momentum to keep going

I have much to learn, but that's the plan

Thanks again

G

[John HaineParticipant @johnhaine32865]

If the small drill you started with wanders, which it might do especially if it is slightly misaligned with the axis or the bar, once the hole is off centre it's hard to recover especially if the bar isn't firmly clamped. I would take care to get the drill exactly over the bar axis and start with a 10mm drill actually which isn't going to bend. I usually use "pilotpoint" drills to start a blind hole, they drill fast and true and can make big holes in one go.

[HopperParticipant @hopper]

Posted by Michael Gilligan on 09/03/2021 22:12:36:

Posted by Hopper on 09/03/2021 22:04:01:

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You dont need bearings to spin a pin vice 180 degrees.

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I think Geraint means to spin the pin vice several turns, to drill the plastic.

MichaelG.

Ah ok. That type of pin vice. Was thinking more a small toolmakers pin vice made from two pieces of flat bar. Even so, it should work ok in a hole drilled through brass. Presumably its being spun by hand not under power so the brass would make a suitable bearing material.

Either way, seems like it might be easier to make the part out of square material so drilling and reaming or boring the hole is more controllable on a flat surface.

Edited By Hopper on 09/03/2021 22:26:38

Edited By Hopper on 09/03/2021 22:27:17

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Hopper on 09/03/2021 22:25:01:

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Either way, seems like it might be easier to make the part out of square material so drilling and reaming or boring the hole is more controllable on a flat surface.

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Now that’s a good idea

MichaelG.

[Author]

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