View Full Version : Lathe bit cross section, NOT A GRINDING QUESTION

08-01-2011, 08:49 PM
Bought a fair number of various sized HSS lathe tool bits this past winter, everything from 3/16" to 1/2" and "plain" HSS to fancier cobalt mixes.

IIRC in every catalog or thread the bits had either a square profile or in some cases a rectangular profile. Point being: 90* corners.

In looking more carefully (hoping by late Wed some actual use :D ) I found one batch that the profile is parallelogram, point being:
NO 90* corners.

Anyone seen/used such a shape?
And if not, is there anything I should be aware of in terms of action of forces ?

IF I turn the parallelogram the "correct" way, much of the grinding of a typical right hand lathe tool bit is done (exception being the top surface). And, I think logically (? my logic most days) if you flip it end to end it works as left hand. The way I am looking at it, with the factory angle at the ends and the parallelogram shape, there is almost nothing left for me to grind.

The bits in question are labeled "DOW Mechanical" 'Supreme' and on an adjacent side, 'Top Right Hand'

08-01-2011, 09:00 PM
If you mean the bit allready has side relief, And you tilt the toolpost a few degrees, then yea, all you really need to do is grind a nose radius and maybe polish it a little. Cool bits. (That or happy production grinding accident?)

Might need to grind more if you want to use them at 90 degrees to the work however. (Some front relief)

08-01-2011, 09:37 PM
Hmm, I have never seen tool steel cutters in a parallelogram shape. You are correct in assuming one end would be a left and the other a right hand turning/facing cutter.

What is the side angle of the cutter? If it's around 10 deg it would work nicely.

08-01-2011, 09:55 PM
Interesting. Sort of makes me wonder why that is not more common, really.

08-01-2011, 10:01 PM
Well, the reason is the side relief is different for different feed rates. The less side relief you can get by with the better the cutting edge will hold up. After a lot of time grinding cutters I decided a 10 deg side relief works good for me most the time. I seldom feed hard enough to need more than 10 deg. but I have a bunch of cutters ground to different angles I can use.

08-01-2011, 10:38 PM
Yea.. I would however like to point out that side relief really depends on feed rate / Diamiter.

Smaller diamiter will need more side relief since a given feed per revolution results in a steeper angle of cut. This effect can be seen most in threading bits (Fastest feed rates)

08-01-2011, 11:03 PM
Possibly intended for a tangential tool holder. Depending on the various ways you hold your tongue, the alignment of the planets, the mood of the gods, and the angle of the grind, one could be used as a tangential thread cutter.

Or a cutter for both turning and facing in one setup as Airsmith was attempting to explain.

08-01-2011, 11:52 PM
I think the tangential cutter is a square cutter with the end cut to form a diamond shape.

Naw, nothing like what airsmith was saying.

08-02-2011, 12:06 AM

Estimate angle of "relief" between 9* and 10*.

FYI: If you want to see something "neat", I got the above angles by using this link, its an interactive parallelogram.


The face grind/cut from the factory is pretty typical of other untouched bits I have, perhaps a bit steeper angle.

The only bad thing I can find so far is if one uses the typical "square" bit/round holder (its one the usually comes in set of holders) one of the corners is right on the edge of the "v" and it wants to roll a bit.

08-02-2011, 12:24 AM
Yes, that may be a problem and you may have to use the holder without the V in it.

08-02-2011, 12:40 AM
I think the tangential cutter is a square cutter with the end cut to form a diamond shape.

A parallelogram can be ground to the shape of a diamond, too. In fact that's pretty much how they start out.

Here's a tool holder project:


Another example: http://www.youtube.com/watch?v=xUAPrkC7Q-Q

They can also be held horizontal in a properly made QCTP.

08-03-2011, 10:03 PM
Put a slight relief (?) on the top, added a radius and after the first attempt put more of a fine finish (polish?) on all sides and works nice.

Spiraling blue chips, slightly smaller bits with no colour or even crumbly ones depending on how fast the feed and DOC.

FYI, since I supposed it makes a difference, thought I would start simple so other than the way the tool bit itself was ground all else was "square" i.e. bit held 90* to work and as close as I could get to on center.