Parting off problems

[Bob PerkinsParticipant @bobperkins67044]

Hi Petro

my two penneth…. I have a "mini lathe" and a similar parting tool to the one in your picky. I to had the same problems your having. Convinced I was doing every thing correctly and deciided rear tool posts and parting tools with inserts must be the way to sort out my parting…. Lets throw some cash at it. I took a step back and went back to basics. There is some excellent advice above. As a start, and don't laugh but my parting tool was in the holder upside down. I reduced the overhang, made sure the tool was square to the work and set to the correct height and locked up all the slides, correct speed and a constant feed. I even turn of radio 4 so I can listen to the cut, as you can hear when things are not right. Parting is now fine and I've even ground up a few parting tools for some fine grooves in my latest project. Keep at it.

Bob..

[Steve WithnellParticipant @stevewithnell34426]

The parting-off problem is quite often in the set up and actually difficult to resolve without using a rear toolpost. I think the geometry of a rear toolpost is more important than it being at the rear, but that's an opinion.

If you take a standard parting off tool and holder in the toolpost, the cutting forces can have two quite big levers to play with. One is the distance between the centre of the tool post to the tip of the tool (across the bed) and the distance from the centre of the tool post to the axis of the tool measuring up the bed.

A rear tool post eliminates the latter of these levers, and can minimise the former. I haven't tried a rear tool post at the front! Anyone done that comparison?

Steve

[egaParticipant @ega]

Someone experiencing parting off problems would do well to start by reading the relevant passage in George H Thomas's book. My own experience improved radically when I built his rear toolpost some years ago. More recently, I invested in a Greenwood KIT-Q-CUT and had very good results using it in a custom turret on the GHT toolpost on a Super Seven.

The Greenwood tool is based on a Sandvik p/o blade and insert and appears to be half a standard double-ended blade fastened by two countersunk screws to a rectangular block intended to be gripped in a clamp type toolpost. This design works but is not as robust as the standard Sandvik arrangement, the shear strength of the screws being the limiting factor. At some stage I added a third screw and later still three dowels. The beefed up tool also worked very well in the standard toolpost on my larger lathe until I had a major seizure and succeeded in breaking both tip and blade (I will aim to post a photo of the result).

This happened shortly after I had bought two replacement tips including one of the new ones with an angle to reduce the pip. When I learned that the standard, double-ended Sandvik blade, costs about £70, I decided to try the Front or Rear tool advertised on this site and find it excellent. If anyone wants to take the two Sandvik inserts off my hands at cost less 10% they are welcome to message me. There are cheaper versions eg the Glanze but this is not as effective as the Sandvik in my experience.

Happy parting!

[Danny M2ZParticipant @dannym2z]

>>> The parting-off problem is quite often in the set up and actually difficult to resolve without using a rear toolpost. I think the geometry of a rear toolpost is more important than it being at the rear, but that's an opinion. <<<

For minilathe owners (or anybody else with a bolted on chuck).

A parting off tool may be mounted upside down in the front toolpost and the lathe run in reverse for the advantages of this method of parting off. You will probably need a quick change tool post to drop the cutting edge to centre height.

Regards from the land ofd the kangaroo

* Danny M *

[mechman48Participant @mechman48]

I have the same parting off tool but have fitted it to the rear toolpost that I made from Hemmingways kit (disclaimer) & it works fine, have parted off Brass & 1" MS under power without any probs but ensured that I had neat cutting oil dripping on the mild steel.

The tool, being horizontal, had some top rake ground on to approx 5-7* to help curl the cuttings,you can just see it in the pic (tool is upside down).

Much more rigid & no flexing of blade or convex/concave washers.Just ensure that the blade is square on to the work.

Cheers

George

[jason udallParticipant @jasonudall57142]

George..your photos show one other secret of parting off…have a hole up the part…
When the part off reaches the smallest radius the surface speed falls off dramatically. Of course with constant surface speed turning this particular problem goes away..

[Author]

Posts