Best value parting tool for mild steel?

You might find this useful: https://en.wikipedia.org/wiki/Speeds_and_feeds

Parting is generally done at about 50% of the usual cutting speed. You might find use of a rear tool post advantageous.

Thank you Chris!

I'd probably be starting at around the 450-500rpm mark and wind up the wick a bit more as the diameter left reduces. Keep some paraffin on the job to stop tip build up.

Even with the wrong speed and feed you should not have blunted the insert that quickly

I am wondering if I weakened it with the method I used to install the tip. I could not find anything online about the correct way to install the inserts, so I placed it in the lathe, then held a small cylindrical piece of stock between the insert and a workpiece I had in the lathe. I had the cyclindrical piece sitting well below the tooltip and then applied pressure on the cross slide to push the tip into the holder. Could this have weakened it?

I bought the holder and insert from RDG: https://www.rdgtools.co.uk/acatalog/Indexable-Parting-Tool-3mm-x-19mm-blade--12mm-shank--2535.html

Cheers

Ross

Edited By Ross Lloyd 1 on 17/01/2019 12:23:23

Since Ive used the inverted parting tool from Eccentric on my Myford rear tool post I found parting off a lot easier, could seem to get it right with other methods !

H

Although I use this type of holder and get on well with them, I've broken two. It is possible to bend the holder by pushing the insert in too hard during fitting or - more likely - by applying excessive cutting pressure, or during a dig in.

In the photo (edited from the RDG link), the red circle shows the amount of metal under the lower stress reliever is rather small. As the triangular wedge above is stronger (less leverage, better stress distribution), I thought I might have the insert upside down. But all the web photos suggest the way RDG show it fitted is correct.

Parting off is and always has been notoriously difficult. The problem is that any lack of rigidity, misalignment in the set-up, build up of swarf, or failure to lubricate is liable to cause a dig-in, which puts severe stress on the job, tool, and lathe. I think the holders are deliberately designed to fail when the cut gets too brutal. And in implementing the design it's possible the steel used in cheaper holders is somewhat weaker than that in the full-blown product.

When these tools are working correctly I find them about 50% better than the alternatives, they're fast and can take deep cuts. But they're not immune to the kind of foul ups you get on manual machines. My biggest problems are failing to maintain a steady feed rate and swarf jamming in the slot. The two issues are related because when cutting is interrupted by the need to clear swarf I might struggle to recover the 'feel' of a good steady cut.

Aluminium is more difficult to part than Brass, free-cutting Steel, or cast-iron because it tends to stick and then melt covering the cutting edge.

Practice is necessary. When I first tried parting-off something would go wrong almost every time. Learning was slow because the natural reaction to chatter and other cutting difficulties is to slow down. This is usually correct book advice and practical experience for HSS. Unfortunately what's good for HSS is often wrong with carbide!

Don't despair, now I've got a feel for the tool I get much better results despite not being a gifted machinist. If I get a dig-in it's most likely because my attention wandered...

Dave

I doubt if it did. That said, both brands of which I have experience - Sandvik and Iscar - provide insertion/removal tools. I think you may find that the bottom hole in the holder in your link is the fulcrum for such a tool.

When fitting a parting insert I just place it by hand and give it a light tap with a nylon faced mallet. I definitely wouldn't use anything hard. To eject an insert I give it a quick tweak with the supplied tool - looks a bit like an Allen key. I find that coolant is essential on all materials other than brass and cast iron. Feedrate is critical too; I never use less than 4 thou per rev.

Andrew

Ross, the bluntness or maybe apparent bluntness of the insert may be down to the tool height setting. Having the tip only a little bit high will cause problems. This picture shows some waste from using an insert on stainless steel with a slight angle on the tool. Getting the tool correctly perpendicular results in tight coils. Power feed is pretty much essential for happy parting in work hardening material like stainless steel.

Martin C