Boring bar size

I have a mini lathe with a drill chuck that will hold a 13mm max drill. I want to buy a boring bar that is as robust as possible. If I get a 10mm bar, what size of insert can I use, to ensure clearance at the start of the cutting? I want to avoid needing to do the job in steps - using a smaller bare to start with.

The spec of these tools is a bit bewildering - with a whole list of numbers and letters, describing them. My data book gives a sort of translation but I would appreciate some direct advice.

I will be working with aluminium so am I right in assuming that the right tip would be essential? (Dumb question. probably) From what I can see, the way that the dimensions of the cutter are described with those letters, sort of makes sense, with a high clearance angle for aluminium. I guess that it will all come clear with experience.

Why are you holding a boring bar in a drill chuck? Far from being as robustly held...

I use a 10mm boring bar with 6mm inserts..

Have a look here....  https://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Lathe-Turning-Tools-Indexable/ARC-Indexable-Turning-Tools/ARC-S-SCLC-R-95-Boring-Tool-Holders

Edited By John Rudd on 08/09/2018 12:06:51

I'm not holding the bar in a drill chuck. The drill size seems to be what limits the size of the initial hole (at least I though it did. But perhaps that's nonsense and it isn't necessary to have a pilot hole. That could explain a lot!

Best purchase I ever made for boring is a 5/8" MT2 shank drill.

Neil

Oh yesssss. Of course. I never though of that. Save several more mm of boring time.

You can also buy blacksmith drill with a 12 mm shank that will drill to 25 mm or more.

The best type of insert for boring aluminium is the sharp positive rake polished type. I have used this type for a few years now and they give superb surface finish.

Doug

I would suggest a 10mm shank boring bar that takes comes with a CCMT 06$$$$ inset such as this and also buy a specific aluminium insert with a small tip radius to go with it which will have the code CCGT 060202 such as these

You don't actually need a 13mm hole to start with as it is possible to open up a smaller one or as they are end cutting you can start with a flat surface but it just takes longer.

Use with a bit of paraffin to stop metal sticking to the corner of the insert.

A few drills first can save time as has been said

Edited By JasonB on 08/09/2018 13:35:20

+1 I have 16mm / 22mm blacksmiths drills with reduced shanks that I use to open out for boring.

George.

Not my favourite tooling; I've got a cheap set but try not to use them unless absolutely necessary. On the lathe it's much better to use Morse taper drills. I've built up quite a collection, mostly from Fleabay, over the years. They range from around 3/8" up to 1-3/4". If you buy odd sizes, like 63/64", 1-1/64" or 1-5/32" then they're pretty cheap. Nothing like a drill for ripping out metal. With the bigger drills I'm limited by how fast I can wind the tailstock handle.

Andrew

for the bigger holes I use mag drill cutters in the lathe but only in steel........mine go upto 65mm.........

clogs

Have you thought of using a home made boring bar with a piece of HSS as the cutting edge held in with a grub screw.

David

Get a bigger capacity chuck to hold larger drills or an ER32 collet chuck to hold up to 20mm if you want to reduce the time spent boring to a minimum. The ER32 chuck can be used for mag drill cutters as suggested by clogs (19mm shank). Rorabroach mini cutters are also useful and can be held in standard drill chucks.

Martin C

Thanks.

This is all good stuff; The forum is so interesting for me; I need all this info.

I shall have to take it one thing at a time or I will be spending too much too soon! You will all appreciate that problem, I'm sure.

I'm blessed with more boring bars than you can shake a stick at.

One of my favourites is made from the bent and ground end of a broken drill, jammed in a bit of aluminium extrusion. It's excellent for straight and tapered holes down to about 1/4"

The boring bars that come in HSS sets are generally of two types. The square shank ones are easy to use, with the same shim, as other tools in the set, but need to be ground away for clearance in small holes. 8mm tools will just about work in a 16mm hole with this treatment.

Round shank boring bars need less grinding, but are harder to set. It can be better to use a big bar straight in the toolpost without its square holder, than to use an undersize bar with a big overhang.

I also like the bars that take a tiny 1/8" HSS insert in a 3/8" or 10mm shank. These work well with mini lathes, bit you may have to grind a curve on the fixing screw to get in small holes.

My new favourite boring bar is this S10K-SCLSR06 from Arc. It takes CCGT/CCMT inserts. It has flats on it so the insert 'droops' at about 20 degrees which seems all wrong! With a hefty bit of packing (about 2.5mm) it's cutting rather below centre height in the SC4 toolpost. Not sure how the mini-lathe would handle it.

Overhung by the thick end of 3" I had to limit cuts to 0.4mm in 6082 alloy today, but even with a CCMT insert (and a dab of cutting fluid) it was very free cutting with excellent finish.

Obviously a QCTP with much more latitude in setting height will bring me closer to boring bar nirvana on the SC4 but so far I've largely stuck to the 4-way toolpost.

Neil

That's so you get clearance in a small bore with an insert primarily intended for external turning. Hefty packing equals 2.5mm? Dream on! My 10mm boring bar requires nearer 12mm of packing to get to centre height.

Andrew

That's all I can fit in that tool holder! If I hadn't hidden the QCTP under the bandsaw I would have fitted it and had the tool significantly higher...

Neil

Update... I fitted the QCTP.

The S10K-SCLSR06 boring bar works very well.

Neil

Here's my selection of boring bars, which are all useful:

I find it handy to have four different sizes. The smaller ones are useful for small diameter and shallow holes. The big bars resist chatter and have a deeper reach, but need bigger holes to start.

Viewed from the business end, the heads shows how big a hole is needed to get each size of bar into position:

From left to right:

1. Smallest bar is home-made from silver-steel and hardened. I made it specially to open a small hole out to a non standard size. It needs a minimum 5.5mm hole to start and goes 20mm deep.
2. Next is the small boring bar I bought for my mini-lathe. It needs an 8.4mm hole to start and goes up to about 40mm deep.
3. Third is the small boring bar bought for my WM-280. It needs an 9.8mm hole to start and goes about 50mm deep.
4. Fourth is a heavy bar that came with a set. It's more rigid than the other types but needs a 16.3mm diameter hole to start and only does 45mm deep.

As my biggest drill is only 13mm, in practice I use boring bar number 3 most often, starting by drilling a 10 to 13mm diameter hole with a twist drill and then opening out to size. If the finished hole is to be bigger than about 20mm diameter, I usually switch from bar No 3 to No 4. Not essential to swap but being more rigid the heavier bar cuts faster and deeper while producing a good finish.

Minimising the amount of boring done by twist drilling to the max first is a good idea but there are limits. My mini-lathe struggled a little putting a 13mm twist drill into mild-steel so I'm not sure fitting a bigger chuck to one is a good idea. I usually drilled 1/2" (12.5mm), which it did comfortably, and then bored. The one time I did a big hole (50mm) on my mini-lathe I rough chain-drilled the core out and then tidied the diameter up to size with the No 2 boring bar. Not sure if that was the quickest way or not, but it got the job done.

Inserts and boring bars go well together I think. I found grinding and sharpening HSS for a boring bar quite irksome. Just being able to swap inserts eliminated the fuss entirely.  I confess to being an oik at the grinding wheel.

Dave

Edited By SillyOldDuffer on 16/09/2018 16:45:00

On a small lathe be careful using shanked down large drills,they can put a lot of strain on the tailstock barrel,remember the barrel is only restrained by a relatively small key and keyway,and a worn or damaged tailstock can cause problems when turning between centres.Drills can be held in the toolpost although care is required in getting the drill central ,or make a toolpost block or a cross slide block which can hold a large drill chuck. I have made a cross slide attachment which holds a sleeve parallel on the od with a taper id which can hold up to 4mt on a 6 1/2 inch Colchester plus the availabilty of power feed if required, The hardened sleeves are available from tool companies in a variety of sizes.