Recess

I have a 50 mm stainless steel bar and I need to recess it by 5 mm on the end and dia of 44mm leaving a 3mm edge .. What's the best way of doing this can't use a drill as the point will go beyond 5mm .. Any help most appreciated

Edited By rik arry on 12/11/2014 19:36:08

Edited By rik arry on 12/11/2014 19:36:44

Rik, you don't say how long the 50mm bar is? However assuming it can be supported in your lathe chuck I would use a slot drill to make the initial cut, maybe use two different sizes, a small one to start say 6mm then whatever you have that's larger. Drill less than the fished depth then use a boring tool to remove the rest of the material until you achieve the 44mm bore size then do a facing cut to the finished depth.

Hope this helps

Edited By JohnF on 12/11/2014 20:06:02

Boring bar will do it. It is a bit easier if you drill say a 6mm hole to 4.9mm deep then you can put the cut on with the tip of teh bar in teh hole and turn from the middle outwards, final 0.1mm depth put teh cut on while moving teh tool towards the centre so it ramps in. Stop just short of the 44mm so you can take a finishing cut at final diameter. Have a look at this to save me writing it again

J

Edited By JasonB on 12/11/2014 20:16:49

You don't say which grade of stainless G303 is regarded as machining quality, G304 still highly workable, though G316 can be problematic certainly the S11 and G321.

Best way as above but no need to pilot drill or even drill, if boring is on line it will cut the pip out the centre.

Heres one done earlier about 14 years ago 44.2mm bore x 15 deep from memory. For this purpose using 28mm drill just to create a hole, you cant do that. Angle boring bar in to work not at 90 degrees and drag it out. Face off tot depth no drilling straight in.

For such a large recess, I wouldn't use a boring tool.

I would use a knife tool with a radius ground on the face beneath the cutting edge and greater than usual front rake.

Mounted along the axis of the lathe this will prove surprisingly effective if used as Jason describes, and will be stiffer than most boring bars.

Neil

Since the depth of boring cut is only going to be 5mm, the boring tool can be mounted in the tool holder with almost neglible overhang, without the need to grind any special shape.

Thanks all most appreciated will give it a go

Neil, it depends on the size of your tool, this is a 4" dia recess 3/16" deep in an iron casting, no problem with a medium sized boring bar of 10mm dia, as KWIL says you don't need much overhang.

Agreed, that boring tool is effectively my 'end on' knife tool, my 10mm boring tool has an angled 1/8" toolbit for jobs like this and would take ages, while the bits that suit my boring head aren't particularly good angle for rapid metal removal either.

Neil

Thanks

Neil During my apprenticeship,most of the boring we did was resonably shallow and most of the boring tools used were ground from square HSS toolbits as you described ,we called them boring tools the term knife tool was never used.Bigger boring bars with hss inserts were held in the stores though rarely used. And nowadays despite my having a good selection of boring bars with round HSS bits and bars with carbide inserts, I still prefer boring tools laboriously ground from square hss bits , they are more rigid and cut better particularly when boring recesses for ball bearings where the bore has to be accurate .

I often use a single indexable boring bar for both the internal recess, the outside diameter and the internal and external chamfers. With the top slide at 45 degrees, you can turn and face using the cross and saddle power feeds, then use the top slide for the chamfers. No tool change required and obviously you should minimise the tool overhang as a matter of course.

The technique is to operate the machine in reverse with the tool behind the axis for (external) turning and in forward direction with the tool in front of the axis for boring. You can make both chamfers this way without disturbing the top slide or requiring a dedicated 45 degree chamfering tool.

With the right cutting speeds and feeds you can get excellent finishes. Using the micrometer dials, digital calipers and a bit of practice I can get finished dimensions within a thou or so.

Murray

This is exactly the question I was about to ask about ,since it is something I will need to do soon.

Thanks to all for having offered advice.