Boring in the lathe - imbecile question

I've got a chunk of round aluminium bar of 60mm diameter, 100mm long. I want to bore this out to make a cup shape with 5mm walls (so
removing a cylinder 95mm long by 50mm diameter). I have bought a Glanze indexable boring bar (from RDGTools or Chronos, can't remember which) that fits into my toolpost and is shimmed to the right centre.
Am I right in thinking that in order to use this bar I first have to drill/ream a hole big enough in the bar to take the whole tool? My tailstock chuck only holds up to 10mm bits, although I suppose I could invest in a blacksmith's drill bit.
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Robin,
There is nothing imbecilic about asking for help when you are doing something unfamiliar!
You do need to be able to get the whole boring tool into the starter hole, preferably with a bit of space at the back of the tool (otherwise the hole will rapidly fill up with swarf and may even jam).
Your options are (a) blacksmith's (reduced shank) drill bit or (b) start with a smaller boring bar - you can get ones that fit into pretty small holes, 4-5 mm is not hard to find. They do though tend to have round shanks, and are best used in a boring head in the tailstock. (a) is likely to be much cheaper.
If the boring tool you have will only just not fit, and if you were desperate to save money (usually a mistake) you could start with the topslide set round to an angle (say 10-20 degrees) and start boring a tapered mouth, then when you have made enough room to get the tool in all the way (sounds vaguely filthy) you can revert to parallel boring. This is made more feasible by the fact that the bore you are aiming at is so large, giving you plenty of time to fiddle about and get it right; the offset means that the back edge of the tool is not trying to enter the hole until it has been enlarged. I haven't tried this, and I simply offer it as an idea to try, preferably on a piece of scrap rather than a valuable workpiece.
In general terms, you should always use the largest diameter boring bar you can get in; the bending of a cantilever beam of round cross section is, IIRC, proportional to the fourth power of the diameter, and even a small increase reduces the tendency to bell-mouthing of the hole. Also, if the diameter is important, be careful getting to the final size, running the tool through again (or running it outwards) will often take off a surprisingly large amount, especially with a narrow springy tool.
David
--
David Littlewood

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So I hope no one will mind if I go off at a tangent, as my question is about a large through hole in aluminium rather than the blind hole that Robin wants help with. Would it be possible to use a diamond edged core drill, as used by builders cutting through brick etc, to cut a hole through aluminium and then finish to size with a boring bar? eg http://www.machinemart.co.uk/shop/product/details/marcrist-dcu750x-28x400-12f-dry-core/path/diamond-drills-and-core-bits Although they are expensive to buy I noticed that they can be hired from our local hire shop for a one off job at a reasonable cost.
If it would work you would be left with a waste chunk of aluminium, all be it with a guide hole through it, that could be used for another project rather than lots of aluminium swarf.
I guess the problem would be the difficulty of removing the swarf and the heat efficiently so that the aluminium didn't stick to the cutter and jam up.
Alan
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On Sun, 28 Mar 2010 11:43:55 +0100, Alan Dawes

I would just use a standard hole saw small bites and continual clearing to remove cuttings. Limited on depth but possible to cut from both sides. Do not forget to remove the slug eject spring if fitted!
Richard
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Some great replies to my original question (and the hijacked one!!). Regarding the "sanding" - I wouldn't have done this with the piece rotating in the lathe, so don't worry too much about my fingers...
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Had a play this afternoon, bored out about 10mm depth to about 45mm diameter, using facing cuts and then finished up with longitudinal boring. Whenever the gas runs out in a can of WD40, I pierce the tin and pour the remnants into a container so I brushed some of this on to lubricate the cut. Set the gears to 350tpi (the smallest pitch I can get) and used the power feed - gave a beautiful finish. It's going to be difficult boring to the full depth but think I'll buy a blacksmith's drill tomorrow as I can pick one up for a few pounds locally, whereas getting a small boring tool is going to take time.
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Here's the results of this afternoon's practice:
http://i277.photobucket.com/albums/kk76/richardspandit/Lathe/DSC_0283.jpg
http://i277.photobucket.com/albums/kk76/richardspandit/Lathe/DSC_0282.jpg
http://i277.photobucket.com/albums/kk76/richardspandit/Lathe/DSC_0281.jpg
There's something wonderful about a nicely engineered piece of metal, or is it just me?
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It is not just you.
--
Nigel

When the only tools you have are an X3 mill, a
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I'd second Richards comments. I have used this technique in both alloy and cast iron. You will need some lubricant/coolant with alloy and clear the swarf regularly.
Once the hole saw is about 1/4" in, you can carry on without the pilot so if you keep it very short inthe first instance, you do not necessarily have to end up with a hole up te middle of the slug you are removing. Don't go too fast, don't be too agressive.
Richard (another one)
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Thank you to both Richards, if only I had asked last year I wouldn't have wasted so much aluminium. I've filed the info away for future use.
Alan
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My aluminium stock arrived today. I decided to go for 60mm OD tube with 10mm wall thickness, so no problems with tool clearance. Had to teach myself how to use the 4-jaw chuck as it is too large for my 3 jaw - not sure if I'll ever go back now!
The problem I have, though, is when I increase the inner diameter from 40mm to 50mm, for a 20mm section, it leaves a step (which is good - it's what I want) but when I feed the tool in automatically, when it gets to this step on each cut, a horrid squealing noise ensues as the tool is trying to cut on 2 faces. I generally disengage the dog clutch on the leadscrew and have offset the compound slide by 15 so I can wind it away from both faces at once - is this the right technique or is there something different I can try?
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wrote:

I hope that I have understood correctly. Basically in my mind you are traversing too far! It sounds as if you have little or no clearance on the front face of the tool and you are hitting the step that you are producing, each time full face. In my mind you should be power traversing to a carriage stop and changing to manual feed before hitting the stop. Alternatively depending on your tool profile you may be better facing out to the required radius then power traversing away from the chuck.
If you want to end up with a 50mm THROUGH bore then just traverse all the way through on each cut. The original statement suggesting 20mm at a time was based on a solid bar. Given hollow bar you have bags of room for chip clearance so cut all the way through.
But maybe I misunderstood. <G>
Richard
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The original post was about using a solid bar but the tool clearance problems and enormous amounts of swarf I'd be producing made me go for a thick tube instead with 40mm inner diameter. The workpiece is 80mm long and I need actually a 23mm section bored out to 50mm. Perhaps I'd better build a carriage stop or just disengage the power feed earlier and, as you suggest, manually feed the rest. I do love watching the lathe power feeding - find it very therapeutic.
Not sure how I'd face out to the required diameter and then power away from the chuck and don't think my tool profile is really designed for cutting in that direction but will have a play!
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Easiest way is power feed out from the chuck. Set up a stop which can be as simple as a bit of bar resting on the lathe bed up against the headstock. Set the tool a bit shy of the depth you want to finally bore to - say 22mm in your case. Position the tool in the bore and wind out manually to the depth of cut you feel you can handle. Power feed out, rinse and repeat. When you get close to final diameter you can take things a bit slower and then just finish the base to depth.
--
Dave Baker



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Yes, you will have to drill a hole big enough to get the boring bar in.
Assuming that your boring bar needs more than a10mm hole to start with:-
It is quite reasonable to use a drill press or hand held drill to do the hole (remembering not to go too deep!). So long as the hole is big enough and close enough to centre that the boring bar either has clearance or is taking a reasonable cut at the most off centre part. This nay allow you to drill a large enough hole without needing to buy blacksmith's drills.
Another option is to invest in one of the smaller boring bars to open out a 10mm hole to the size where your other boring bar will fit. This is a good option, because the small boring bar will prove useful for other jobs in the future. In time, you may end up with a range of them DAMHIKT :-)
You can use the boring bar to face the bottom of the hole, just try not to take the tool too far past centre, there is a real danger of the edge being snapped off the insert when the metal is moving past the edge in the wrong direction.
Mark Rand RTFM
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No, you can also use a boring bar to "face" in towards the centre from the rim and just gradually work deeper. Clearly you have to be able to do this to finish the bottom of the hole anyway. However it would certainly be faster to get the bulk out with a drill and having at least some sort of central hole prevents you "facing" in past the centre and knocking the tip of the tool off when the stock changes direction of rotation on the far side (facing over centre). However at least aluminium is less likely to do this to a carbide tip than steel is but it'll still probably happen. Personally I'd drill as large a hole as you can, just 10mm if that be the limit, and "face" in towards that. It's slower than boring because you can't take very deep cuts but it's certainly quite feasible.
You can also "face" out from the centre instead of in towards it. Then you only need a central hole big enough to get the tip of the boring bar into for whatever depth of cut your machine can stand. The biggest worry here on a manual lathe is you'll lose concentration and go out too far on diameter on a cut and wreck the job. On a CNC machine that's not an issue and in fact it's a better way to use a boring bar from in to out than from out to in as it makes proper use of the cutting geometry of the tip. You're pushing the tip into the stock rather than out through it. Remember a proper facing tool will have a tip pointing inwards towards the axis whereas a boring bar being used for facing will have a tip pointing outwards and so works better moving in that direction.
In fact I suppose I could summarise that a normal turning and facing tool has a tip designed to go from right to left when turning and from out to in when facing. A boring bar has a tip designed to go from right to left when boring and from in to out when facing. Hold the two side by side and you'll see what I mean.
What I tend to do on such jobs is work out from the centre leaving a very safe allowance on diameter - the cock-up allowance, and then bore the sides in the normal direction to finish the job so you can gradually work to your target size allowing for any spring in the tool and the cut.

There's nothing to stop you turning down the end of the shank on an ordinary bigger drill to 10mm so you can hold it. I have a few up to 1" modified like this with 1/2" ends to go in my drill chucks. There's obviously a limit on how big a drill you can do this to before the cutting forces make it slip in a small chuck. Usually you can get away with twice the gripping diameter quite easily, especially in something soft like aluminium.
--
Dave Baker



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Funnily enough, that was going to be my next question - that's probably what I'll do, then

There's my competence!!
Here's the tool I bought, I think the way the tip is aligned it is equally good for facing and boring
http://i277.photobucket.com/albums/kk76/richardspandit/GZ6.jpg
I have found that I'm getting a bit of chatter with the tool but the project doesn't actually require that much accuracy so I can probably sand those imperfections out
Thanks for reply - great help!
Robin
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The tip is aligned the same way as any other boring bar. When the shank is held in the toolpost parallel to the lathe centreline (for normal boring ops) then it bores from right to left and faces from in to out. However if you turn it 90 degrees so the shank is perpendicular to the lathe centreline it becomes a turning tool and can be used for outside turning from right to left and facing from out to in. The only real differences between a boring tool and a turning tool are rigidity and shank clearance which of course you don't need for turning.

Chatter is always a problem with boring tools which are obviously not very rigid when you have most of the length stuck out from the toolpost. What you may find is you get less chatter if you bore from left to right on the final light cuts. Try it while you still have some stock to play with.
The reason is you're pushing the tip away from the stock now which takes some spring out of the tool albeit leading to a smaller cut diameter for a given setting than if you were pushing the tip into the stock. The other advantage is you can just let the feed run the tool right out of the job without having to worry about stopping it before you hit the bottom of the bore.
Speeds and feeds can also help. A fast cut on a coarse feed might not generate an ideal surface finish but is often more predictable and less chattery than light fine cuts.
The other trick is stick a small lump of plasticene on the shaft. This can help damp out vibrations.
The best trick obviously is use a bigger boring bar once you've got most of the stock out.
The right tip is crucial. The generic tips that come as standard might not be ideal for non ferrous metals. You want the sharpest tip edge you can find for those which is why some people still swear by HSS. However the right carbide tips are every bit as sharp as HSS I find and last many times longer. Usually the right tips for aluminium are silver in colour not gold or grey.
Finally the best cutting lubricant for aluminium is paraffin (kerosene). I keep an old glass cleaner squirty bottle of it by the lathe and mill and just mist the job over with it every now and then. Diesel is a similar substitute and also central heating oil. Basically any light hydrocarbon that's a bit greasy. WD40 is also ideal but expensive of course.
When I'm flycutting aluminium cylinder heads on the mill I generally run dry which on my very rigid setup gives a perfectly smooth but slightly matt finish. However with a mist of paraffin or WD40 you can get the job to come out mirror shiny which looks pretty but is not the ideal surface for keying to a gasket. It does however highlight how paraffin helps the cut.
--
Dave Baker



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wrote:
Snip

Snip
Be very wary of "sanding out" a bore. Fingers up holes in rotating bits of metal can result in lost fingers!
A few other points.
If you do not have a carriage stop it is worth fabricating something. Even some scrap and a toolmakers clamp or G-clamp will give you a fixed position to stop your carriage at.
No need to drill the whole 95mm in one go drill say 30mm first.
No need to have the boring bar hanging out 100mm from the start. Again initially say 30mm. Bore out to say a 6mm wall in any way of the methods suggested. Shorter bar overhang will mean you can take bigger cuts and work quicker. Also working in this way will give maximum chip clearance room.
Extend the bar to 60 mm drill again and repeat. Zero the tool on the existing bored diameter to give an easy reference.
Repeat this with further bar extensions until you have 100 mm sticking out. Set your carriage stop to suit the bar extension to give the required depth. Watch it when you do your last drilling better to short than too long. Use the topslide to achieve your final depth when hard on the carriage stop.
One thing you might try before you start drilling. Set the bar at the 100mm extension and try facing the material. This will give you a feel for speeds feeds and finish where you can see what you are doing, not down a 95mm deep hole. Note your results and use them at the end. You will definitely be able to work harder with shorter extensions.
Good luck.
Richard
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Why did you not make a boring bar out of steel and put a hole in the end at 45 degs to take a bit of HSS you could have then ground some top rake on which is what you need for Aluminum and boy would you have saved money. You would have only had to drill a small hole as well.

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