Thread: problems with cutting off

Some slightly O/T info for franco,
I was doing some work in the inner Sydney suburb Surry Hills recently and at lunch time I was walking around the area and came across the pictured building which was undergoing renovation. It is not that clear but on the front of the building are the words 'BRACKENBURY and AUSTIN. The street name on the pole is Wilshire. I do not know anything else about the company.
Mm.

I have noticed that the long 1/2" cut off blades don't have any positive rake , they sit flat . But the shorter gooseneck style blades have a small section at the tip that gives some back rake at the tip .

Is it worthwhile grinding in a groove to provide back rake on the flat ones ?

Mike

I grind mine to have rake.

Dave

Originally Posted by Metalman

Some slightly O/T info for franco,
I was doing some work in the inner Sydney suburb Surry Hills recently and at lunch time I was walking around the area and came across the pictured building which was undergoing renovation. It is not that clear but on the front of the building are the words 'BRACKENBURY and AUSTIN. The street name on the pole is Wilshire. I do not know anything else about the company.
Mm.

Metalman,

Many thanks for that. Since they stopped manufacturing lathes before the internet age information about the company and its products is surprisingly hard to find. My somewhat hazy recollection (I was 14 at the time) is that my father was doing some work for Brackenbury and Austin or vice versa in 1948, and he bought the lathe straight from the factory. Many of them were sold as Gregco 918 or New Gregco.They were not as common as the Hercus or Myford at the time, but still turn up occasionally.

Frank.

We use HSS part off tools all the time and following the tafe guide book and loads of info on the net and advice from industry.
The students dont seem to have trouble when they observe the following:

• Tool post with minimum over hang of the tool holder.
• Tool holder and hold down clamps properly tight
• Use centre height or the tiniest poofteenth above
• HSS tool over set up projecting a tiny bit past center
• Part off tool checked that it is dead square to the cut
• Use 1/2to 2/3rds of normal spindle speed for diameter parted
• Use just enough coolant to see whats going on
• Feed in at a constant rate.
• Sharpen the pointy bit to the side that's needed with out a feather or tit on it.

The rep from Wallers Precision Tooling ( shameless plug as they helped us) was in and gave them a few pointers.


The cherubs have not busted a HSS part of for ages ( not counting the Richard HEAD who wound the carriage into the non operating job and busted the tool )

Hopefully some of the above may be useful to you.

Grahame

Originally Posted by Grahame Collins

• Use 1/2to 2/3rds of normal spindle speed for diameter parted

Thanks for the checklist, Grahame.
I hadn't realised you could actually spin that fast when parting off.

Jordan

Originally Posted by Grahame Collins

• HSS tool over set up projecting a tiny bit past center

Grahame

Mike

I think he is saying have the cutting blade length a touch over the cetre distance of the job.

I rarely have a problem parting off since modifying my parting tool holder so the blade sits properly vertical. In addition to the points made by Grahame I think the key is to have a SHARP tool. I will periodically touch up my blade with a hand held diamond stone to keep it sharp. Other than that plenty of lube as it's cutting.

Pete

Grahame,

I agree with all the points you mention in post #36, except, in this special case, #3: "Use centre height or the tiniest poofteenth above". The O/P is using a sprung parting tool holder. These are designed to flex in the event of an imminent dig-in, allowing the tool to move down and away from the work to relieve the load on the cutting edge. If the tool is above the centre line of the workpiece and starts to dig in, moving the cutting edge down to a greater diameter when the toolholder flexes will make the situation worse. This type of holder needs the tool to be no higher than centre height, and still works OK if slightly below.

When using a conventional rigid parting tool holder, I completely agree with all the items on your list.

Frank.

Quite often parting off problems are an indication of worn headstock bearings. Rear parting tool posts are better as the spindle is forced down into the bearings. Parting off in the lathe is a science unto itself. Often to achieve success you need to control a combination of variables. If your headstock is above suspicion and your chuck is in good order then the compound slide should be checked to ensure there is no slop or play. The compound tends to tilt towards the rear of the lathe when parting off. A Sharp tool , on or slightly below centre height and slow speeds with plenty of cutting oil help. Also parting closer to the chuck jaws is an advantage. Some materials require widening the slot as you cut. eg Aluminium due to it's tendency weld itself to the cutting tool.