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As others have said, a very old and common approach, one that is especially useful on the floppy lathes of yore. They were often called "gooseneck" tool holders - also commonly used for threading.
The trick is to arrange things such that when the bit is pushed down, it automatically pulls out of the cut, reducing the force.
Another approach to achieve the same thing is to put the cutoff tool upside down in a holder that allows that, and run the lathe in reverse. Again, this eliminates any tendency to dig deeper and deeper until something breaks.
Why run the lathe in reverse?
I routinely use a rear-mounted cutoff tool (that holds the tool upside down at a slight angle) and it works with normal rotation. If the tool starts to dig in it flexes the cross slide and carriage upward, relieving the pressure.
In the 40s these were practically standard equipment. They had shanks to fit the gawd awful lantern tool posts which flexed to dig the tool in. As Jerry says, the spring in the tool holder moved the tool away from the work. Anymore,. with modern inserts, parting is a different story.
Nice work.
Bill
Please explain how "modern inserts" fix this problem.
Do they have a spring built in? Are they sharper? Is it geometry? Is the material more slippery so the chip doesn't stick? Oil feed hole to the tip? How?
I like his tool holder. It looks like a good design. I need to watch the video to see what the dark part is and what it is doing.
Some of that type holder had a place to "gag" it so it would not move, and one could put stiff rubber in there to give more return force, etc.
That button might be a similar thing, I seem to recall that some were made with a thing like that, and no actual "gag".
I've never used one that had the extra stuff, gags, etc, on it.
Please explain how "modern inserts" fix this problem.
One source of trouble is the chip binding on the walls of the cut preventing free exit. Material builds up and chokes. Inserts have a configuration that folds the chip, making it narrower. There are numerous shapes that accomplish it. I do the same thing on HSS blades by grinding a notch in the middle of the cutting edge so it makes three narrow chips.
Bill
the black boton is to give extra strength in the return
I believe it's more a comment on more modern lathes, the type being "carbide capable", being much more rigid.
In the spindle, drivetrain, ways, and tool holders.
Actually no. It is the design of the insert that is key. Insert cutoff/grooving blades can be used on small hobby lathes and work very well. Once sized down for height.
The key is that the insert folds the chip away from the walls of the cut so they exit without jamming in or rubbing on the walls. Of course rigidity is a factor but considering this works in non rigid lathes the insert geometry is most important.
This approach of folding the chip can easily be accomplished with a hss straight blade. Grind a shallow grove ~0.015” on the top of the blade along its length. Leave a little land at either edge about .015” wide. Geometry doesn’t matter too much. This results in a lightly folded and continuously rolled chip. Cutoff speed will normally be 1/2 the turning speed of the particular material. Soft materials even faster.
As a "Hobbyist Machinist" how many cut off tools have you ground ?
And how long did they hold up in production ?
And how many inserted carbide types have you tried ?
I suggest you try over at one of the hobby machining forums.
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