Boring brass

Hi

I need to bore a piece of 2 inch brass with a 1.25 inch hole. Never done this large size before so need some advice. I have made a pilot hole of 13 mm, the only drill I have next size up after 13 mm is 21 mm. Would it be safe to go ahead with the 21 mm drill only I have had some nasty surprises drilling brass with pilot holes. Once I get the size to 21 mm I intend to buy/ use a boring bar.

Many thanks mike

Never done this large size before so need some advice

I would use the boring bar all the way from 13mm

By the time you get to 1.2 inches you'll be getting good and be ready for the critical bit

Try for a spot on 15mm hole and a spot on 20mm hole and test it with a roundbar to see how good your work is

Thanks for reply.

I did not know boring bars could start from a small hole like 13 mm , that's why I was going to enlarge it to 21 mm. I will look on the auction site to see what is available.

Mike

I looked on the auction site, but not sure what size boring bar to purchase. As the hole is only 13 mm at present do I need a tool that is smaller than this size to fit into the hole. Or is it possible to open out the hole from the start with a larger tool. As my cylinder is 80 mm long I was worried about a thin tool flexing to much as it reaches the bottom of the hole.

Mike,

how long/deep is the bore you intend to make? I ask because anything over 3" long/deep with a boring bar that will fit inside a 13mm hole is going to be very difficult and it might just be as easy to drill it to 21mm. I reckon you should be able to drill it without it grabbing too much.

Mike

Nip to your local Machine Mart (usual disclaimer ) they stock jobbers drills to suit your needs... I have bought from them 16 -20 - 22 mm with machined stem (12 mm ) to fit into 0 - 13 mm drill chuck, all at reasonable prices.

George

Would not a drill this big grab and pull the chuck out of its taper. I would have thought that the cutting edge should be stoned to take the edge off.

Frank

You can make your own boring bars, a length of silver steel and a grubscrew do the job

They are especially useful if you need a hole that's not a standard drill size

To get the job done quick just drill it and get a boring bar, be careful though, 21mm is a big big drill for a hobby lathe, I've never used anything bigger than 12mm

A lot of purchased boring bars to fit 13mm hole would be small and flex as you say. However there is a type that is a bar with a small round tool bit in the end held by a screw gong in from the end and the bar is held in a piece of square section with a longitudinal slit to be held by the force of the lathes tool clamp. You could use a 1/2 in bar so quite stiff but your lathe might not be big enough to hold the square part.

I have one I made by turning half inch square stock to round at the end a tad under the half inch Then I had to cut part of the remaining square down to fit it in my toolholder, while keeping the mid point of the round bit at centre height. It is cross drilled at the end for a 1/8 round bit of tool steel. The tool bit only has to project a tiny amount so I think I made this one for boring a half inch hole after trying to bore with a smaller flexible commercial bar.
The tiny bit is sharpened while held in the bar, with more projection for convenience. It can be rotated to present the top to the grinding wheel, and then rotated again to set top rake so quite a helpful set up.

Pictures above found by web search for illustration only.

Hi,

I'm very much a beginner to this game so take what I say with a pinch of salt

I bought one of these about 3 weeks ago (first time I'd ever used a boring bar) and can't fault it.

**LINK**

I know it's only a budget tool but for the price it works fine and only needs a 12.5 mm hole to start of with, although to be fair I think 14mm is a bit more realistic.

Peter.

The biggest drill I own is 21 mm, I have used this in the past on my Super 7 but I think this is about the limit for my lathe. As I need a finished hole of 30 mm by 80 mm deep I think I will have to chance using the 21 mm drill to open out the hole so that I can then use a thicker less flexible boring tool to achieve the 30 mm I need. If I use back gear and take it real slow I might get away with it.

Mike

the link below shows boring bars that can be used down to 11mm (usual disclaimers) but I guess you'ld be going up a second boring bar size for rigidity. Or you could use the first bar as a pattern to make a second larger DIY tool once the hole has been started...

**LINK**

Sorry, I didn't realise you were going 80mm deep, the tool I mentioned will be of no use.

Given the hole size, rather than use a drill to open up the hole, you might consider using an end-mill instead if you have one long enough. You will need a suitable holder that will fit in your tailstock, though. Don't even consider using a drill chuck.

If the brass is 2' round being held in a 3 jaw chuck, and the hole is a through hole, drill to 13mm, use a small boring bar to about 1" bore but only 50mm depth, then re-chuck the brass piece the other way around and bore the other end the same way. Then keeping the same setup in the chuck, use a large boring bar to bore to size for the full depth.

This obviously won't work if the hole is not a through hole.

Andrew

Its at times like this that hollow cast bronze has more than just a cost advantage if its a cylinder you are machining.

It is possible to open out the 13mm hole with a large boring bar but a bit time consuming, basically you have to take a series of cuts from the hole outwards to increase the dia but as you will only be able to take 1.5mm depth of cut at best thats 50odd cuts that would be easier with a blacksmiths drill or second smaller bar.

If you are looking at indexable tools then a 10mm shank boring bar is about as large as you can get down a 13mm hole. 16mm shank would be about right for that depth of hole to avoid flex and not have to spend excessively.

I used a home made bar in the chuck and tailstock centre with a broken drill ground as a cutting tool, then put the work piece on the cross slide. The bar is well supported though it's a bit more faff shimming the work piece.

Made a 1/2" UNC left hand nut today, cut the thread in the lathe with a home made boring bar, It was one that I'd made years back. The bar is drilled though at right angles 3/16", and a bit of an old centre drill is used as the cutting tool. Ground to form for UNC (60*), it protrudes from the bar just a few thou greater than the thread depth. If you are making your own, use old centre drills, end mills, HSS taps, then all you have to do is drill the right size hole(drill it at an angle, and the tool will be ahead of the bar), drill and tap a hole for the retaining screw, and you'v made a boring bar, you can make what ever size you want, aim for as fat as you can use. You can use quite a reasonably large bar to open out a 1'2" hole to 1 1/4" by going in at an angle, by the time you'v opened out the front to a tapered hole to 1 1/4" the hole will be open right through, you can then cut it parallel.

Ian S C ps  sharpen the tool with a flat top for brass.

Edited By Ian S C on 18/07/2015 12:16:41

Hi all

Nearly there now, managed to open up the hole to 20 mm using a short narrow boring tool and attacking it from both ends , Made a heck of a lot of chatter noise but got there in the end. Just a case of finishing of now with a heavy boring bar with the cylinder centered in the four jaw chuck.

Many thanks for your help, Mike

Once you've modified the cutting edge for brass on the 21mm drill, you should have no problems drilling in the lathe. Just steady turning at a slower speed, don't try to tear***e. Have regularly step drilled up to 2" (50.8) in the lathe. Tain't a rush, you're not on piece work.

You haven't said what size lathe.

Regards Ian.