Boring aluminium - What am I getting wrong

I acquired ( for another problem) the 30mm boring head from ARC which came with a couple of tools.

I wanted a 22mm hole through a 25.4mm square lump of aluminium, so thought it would be a good project to try it out on. The hole came out well in the end, but I was clearly doing something wrong. Not sure if t was speeds ( tried several from 500 - 1500), feed rate - I was feeding the boring head into the work using the quill, or the setup of the tool.

But I was making some very odd swarf even though the hole was all the way through the work (I started with a 10mm drill), and I was taking 0.25mm cuts, I was getting round disks every pass.

The tool used was the carbide on supplied with the set. I couldn't get enough depth with the HSS one.

Although the hole came out fine in the end, could someone suggest how I might modify my technique for next time?

Peter,

You need to show us a view from the boring tool slide axis (a 90 degree shot to the current one) to allow us to judge how the tool is set with regard to centre line. Normally for boring operations I set the tool slightly 'high' as you would when boring from a lathe toolpost. The other question is what is the tool top rake like, if set slightly high you need a good positive top rake when working with most aluminium otherwise you can get tip welding.

Was the tip brazed on by a passing seagull? Not a good boring tool in my estimation - just a general purpose item. I use either Boremasters, Criterion (solid carbide), or a reputable insert tip boring tool with a decent polished high rake insert for a good quality bore in aluminium. Plus, of course, a little white spirit / WD40 / or Russian Fat.

The final thing is did you have a lose gib or one that was nipped?

Martinl

The tool is in the incorrect orientation, it should be in line with the slide on the boring head and having a little axial twist to give some rake The tool should move radially in relation to the hole when increasing the cut. By the way, how much are you trying to cut, and did you ore drill the hole?

just think about it as a boring tool in the lathe the tool as shown is angled about 45degrees to the lathe cross slide and is elevated way above centre Thus it is rubbing all the time

Hi

It looks to me that you have the tool in the head the wrong way around, the clamping screw usually clamps down on the top of the boring bar and pushes the bar down into its seat, you feed the bar out to the right as we are looking at it, you have the tool upside down and facing the wrong way also the cutting tip needs to be on centre to the feed out axis if that makes any sense, a high speed steel tool will cut well on this material at the speeds stated with cutting fluid as mentioned above.

cheers Colin.

As Colin says you have the tool the wrong way round as you are reducing the numbers on the dial when increasing the cut. Also it looks like it is dragging. Also The tip of the tool should be pointing slightly forwards as in the picture below, as you have it the tip is dragging not cutting.

This is a different ARC boring head but one of their bars, cut fine when fitted correctly

Edited By JasonB on 22/04/2021 20:17:34

Edited By JasonB on 22/04/2021 20:19:10

Were you going from 10 to 22 in one go?

I've had that effect with a drill bit in very soft alloy.

Colin I have a similar Japanese boring head and if you use in a tailstock the fixing screws are underneath.

Clue in the original post "I was taking 0.25mm cuts"

The 30mm ARC head has grub screws on both sides but tool tip should be facing other way so it advances away from the adjustment screw which can be seen top left wound almost right out.

Edited By JasonB on 23/04/2021 08:27:24

Another thing which caught me out, is that these brazed carbide tools seem to come unsharpened.

I had issues with boring with a similar head until I read this in the forum previously. Sharpening them on a green wheel and then touching up with a diamond hone from time to time has made all the difference.

I also found that if you don't tighten the grub screws up well, the tool tends to rotate, so even if you have it aligned correctly (as described above) after a couple of passes it's twisted out of alignment and rubs rather than cuts.

Iain

I get that, but how else do you make swarf that wide unless the 0.25mm cut is put on with the quill?.

And speaking of the original post, none of the above answers, although they have merit have explained the op's question :- But I was making some very odd swarf even though the hole was all the way through the work (I started with a 10mm drill), and I was taking 0.25mm cuts, I was getting round disks every pass.

Having melted the aluminium on a cutter in the past learning the CNC to the point where it becomes "plastic" I would say that as the cutter looks to have about 45deg of negative rake it has scraped/pushed the metal off the stock rather than cut it and what you see is in effect one big burr that has been pushed out the bottom of the hole

I recently acquired the same boring head as Peter and the carbide tool was terrible. The tip was covered in braze and had a chip out of the cutting edge. Fortunately I prefer using HSS so was able to proceed. I tend to use HSS on aluminium in most cases.

Thank you to everyone for the help. I am now much more prepared for my next foray into the boring head. In particular OilyRag for reminding me (politely) to think about the comparison with boring on the lathe, and that the angles required being the same. In my defence I would say that I was too concerned with the operation of the boring head itself - first time I have used one - and consequently didn't pay enough attention to the tools. Just assumed that they would be ok out of the box.

Jason was correct about the swarf. The carbide tool has about 25 (rather than 45) degrees of rake, and a couple of experiments showed that at 0.25mm cut depth the point was digging in first and then folding the resulting thin wall inwards towards the centre of the work. Down the 25mm depth it more than created a flat saucer of aluminium.

Thanks Paul for confirming it's not just my one. Why the carbide tool is the way it is I have no idea - I am not sure what operation or material would need that degree of rake. For comparison I have mounted the HSS tool (about 6 degrees) and the carbide tool in the head. (I will NOT be using them that way!)

Now I just need to find a source of 6mm shank HSS boring tools suitable for the head in a couple of lengths and/or a couple of 6mm shank insert boring tools suitable for the head.

Peter, if you must the ones Jason is demonstrating are ok once they are sharpened up. Used to use them daily until 8 years ago and do thousands of holes in 14mm thick.
Now use the only Glanze tool i have kept but shortened it and bought decent inserts from Sandvik, big difference.

Hard to tell from the piccies, you cant allow aluminium to get hot and its also dependant upon grade.
With the shape of the hss and Jasons you will get a better finish on the up cycle and spin it much faster.

When setting up a boring bar put a 6 inch rule edge on the face of the cutting edge and look at its relationship to the bore and center line, with the face of the boring bar square to the center line. You can see the top rake of the cutting face and adjust to give appropriate angle for material ie very little for brass and much more for aluminium. You can then look at the back clearance of the radius to be cut and grind a bit more if necessary to prevent rubbing. This is how I set up.

David

There is something that is not clear to me in the photo above with the 2 boring bars. The cutting edge on the HSS tool is facing the front which is normal. But if the brazed cutter is meant to rotate in the same direction, the carbide tip appears to be brazed onto the back of the spindle. (brazing under tension). They are normally at the front and supported at the back with the braze under compression. (or am I seeing things). 

Note: If the boring head is screwed onto the spindle and has a side mounting hole for cutters an opposite handed tool has to be used otherwise it could unscrew while cutting.

Edited By Paul Lousick on 24/04/2021 10:58:29

The first photo views the tool as if looking from the left of the second photo, so the tip is mounted normally, it just has an unusually large lump of braze doing nothing behind it.