|The FoR (Front or Rear) Inverted Parting Tool|
|The FoR (Front or Rear) Inverted Parting Tool|
The FoR (Front or Rear) Inverted Parting Tool Holder operates with the blade held upside down and can be used in a front or rear tool post.
It has a number of features that make it ideal to use on smaller less rigid lathes.
2: Minimal side overhang and no front overhang help maximize rigidity.
3: Cutting takes place on the underside so swarf will tend to fall out of the groove rather than pile up on top of the cutting edge.
4: The lack of swarf on top of the blade means coolant is free to get right in to the cutting edge.
5: The horizontal mounting of the blade further reduces the chance of the blade pulling itself into the cut and is especially advantageous when turning brass and bronze.
6: Simple to resharpen as only the front face has to be ground.
7: Wide choice of blade widths to suit a variety of workpiece diameters and situations, all the blades fit the one holder.
8: Once set the blade will stay on centre height when extended or retracted.
9: Fine adjustment system for tool height, no more thin shims needed to get the cutting edge exactly on centre.
10: The versatility to be used in a front or rear tool post.
11: Clamping along the full length of the holder aids rigidity and keeps the blade straight and square.
12: A slight concave radius is ground along the top (bottom) of the cutting edge and this helps curl the chip, assisting in swarf ejection from the cut.
13: Blades can be left with sharp corners to ensure the pip is removed at the end of the cut, or if preferred a slight chamfer or radius can be added with an oilstone/hone to reduce striations in the surface finish and increase the strength of the blades corners.
14: The blades can be resharpened multiple times and if used with care one blade will outlast several packets of indexable tips.
For lathes with a screw on chuck the parting tool must be used in a rear tool post with the lathe running in the normal direction. For lathes that are able to run safely in reverse, ie a camlock, bolt on, or LO fitting, the parting tool can be mounted in either the front tool post and the lathe run in the reverse direction, or in a rear tool post and the lathe run in the normal direction.
The holders take the 1/2" "T" type blades, also known as Empire blades (the original manufacturer)or Luers blades (the German inventor of this design) this design of blade has been used in the USA for decades on production turret lathes and screw machines.
The blades are simple to sharpen as they only need the front clearance angle to be ground, this is easy to achieve on the side of the wheel of a bench grinder. The top of the cutting edge (the bottom in our case) never needs touching, the blades can also be reversed in the holder so they can be ground on both ends to save time between sharpening. The blade design incorporates a small hollow grind along the length of the cutting edge to help curl the chip and avoid chips jamming in the groove.
To aid setting the cutting edge exactly on centre height the holder has a 7° taper cut into the shank and a matching adjusting wedge that can be moved back or forth to give up to 1mm (.040") of vertical movement. This avoids having to use thin shims to pack up the holder to exactly the correct height if you don't have an adjustable tool post.
The wedge can also double as a resharpening guide as 7° is ideal for the front clearance angle, the magnet stops the wedge moving about on the grinding rest when used as a sharpening jig. Just place the wedge on the grinding tool rest and use the side of the wheel to sharpen the blade.
The holders are available in four common tool heights.
For other tool heights just pack up the tool holder to within 1mm (.040") and use the wedge for fine adjustment.
Notes on the operation of parting off in the lathe
If you peruse the internet long enough you will find a huge difference of opinion on the ideal method of parting or cutting off in the lathe.
Indexable carbide tipped tools vs HSS blades.
Upside down tools vs conventional tools.
Fast speed vs slow speed.
Having the cutting edge on centre vs above centre vs below centre.
About the only thing everyone agrees with is to always use coolant and have the blade as square to the job as possible.
Geo H Thomas the highly regarded UK model engineer and author of several books on the subject spent a huge amount of time investigating the ideal way to part off in a smaller lathe and concluded a HSS blade held up side down in a rear tool post gave the best results, an upside down blade held in a front tool post with the lathe running in reverse will also have the same effect.
The FoR Parting Tool Holder has been designed to minimize overhang to make the setup as rigid as possible, maximize versatility with the ability to be used on a front or rear tool post, able to use multiple widths of blade, ease of setup, ease of use, be simple to resharpen, and cost effective. The holder is case hardened to 40HRc for durability, made entirely in Australia and all parts and materials are sourced from Australian suppliers with the exception of the blades.