Lathe Tool Post Orientation

[redvan22]

Happy new year to everyone,

I watch a lot of machining videos and most authors of lathe videos at some point stress how important it is to have your qc tool post exactly perpendicular to the centerline of the spindle before doing various operations like parting. Then, the first thing I see them do is face off the end of whatever they're going to turn. Typically, they use a right hand carbide insert tool or HSS but leave the qc tp at it's initial setting and they get a beautiful finish.

A righthand carbide insert tool used for facing has one of it's cutting edges perpendicular to the finished surface and when I follow this method, I get chatter. So, I check the obvious things; insert in good shape, tool extended too far, everything secure and tight, compound not centered over cross slide, etc.

When I use HSS, I grind the usual clearances, front, top and side and then radius the point and still I get chatter, some times.

Am I missing something or doing something wrong?

 

[MrWhoopee]

Perpendicularity of the parting blade (and therefore the TP) IS important. Not so much for most other operations. Assuming an insert that has a face perp to the axis of the lathe, it can actually work against you, creating too much face contact with the work (and chatter). For facing I usually use an insert that does not have that perp face or angle the tool out from the tool holder slightly so there is only the tip contacting the work.

On small, hobbyist type lathes, chatter is always with you, even when you do everything right.

 

[Buffalo21]

I usually set the QCTP with a 3-5 degree angle toward the chuck, just enough to ensure the tip of the insert is cutting, not the insert side.

 

[T Bredehoft]

Or your can mount the facing tool at a 3 to 5º angle to the work in the QCTP holder. It will still turn OK, too.

 

[Tozguy]

for facing has one of it's cutting edges perpendicular to the finished surface

There are more things to consider, like how deep the cut is, feed rate, etc.
Could you provide photos and details of the set up that is giving you chatter?
It is very possible to turn on a hobby lathe without chatter.

 

[cbellanca]

The orientation of the tool post is irrelevant other than for clearance. The position of the cutting tool is most important. Only when parting is it necessary to have the tool perpendicular to the work. Your chatter may be caused by having the tool extended too far. or the improper tool profile.

 

[erikmannie]

I took some machining classes, and they said the default setup is to orient the compound slide at 29.5° & have the toolpost absolutely perpendicular to the faced surface of the workpiece.

They also said to lock the compound when not in use & have the compound slide flush (as opposed to overhanging) for maximum rigidity.

I get some comments from people who come to my shop as to why I keep my toolpost perpendicular to the work if at all possible. They said they see people on YouTube with the toolpost at an angle. I use a RH tool for turning, a LH tool for facing & a neutral tool for chamfering.

I watch a crazy amount of machining videos on YouTube, so I see plenty with the toolpost at an angle, using a single tool for facing, turning & chamfering. This apparently works just as well and must be faster.

When turning, for example, everybody probably knows that having the toolpost perpendicular and thus having only a few degrees of relief between a RH tool & the work makes for a lot of tool pressure. I like to do this because it makes it easier to work up to a shoulder.

 

[Dabbler]

+1 on the advice from @erikmannie and @cbellanca


On my 12" lathe I had a lot of chatter (for years) when parting until I adjusted the top of the tool a couple thousandths below the centreline. It isn't enough for small parts to climb on the parting tool, but enough that the flex in my compound/carriage/lathe bed would relieve the pressure and reduce the chatter. You might also be parting at too fast a speed, start at the slowest speed you can dial, and work up from there.

 

[mikey]

Redvan, the tool angle thing you are referring to is called the Lead Angle of the tool and it differs depending on the type of tool (carbide inserts, brazed carbide or HSS) and the operation.

Most, but not all, inserted carbide tools rely on the geometry built into the tool holder and insert to provide the proper working clearances the tool requires when the tool is oriented perpendicular to the work piece. For example, the ever popular SCLCR tool holder holds the 80 deg diamond insert (CCMT and CCGT inserts) so that there is a 5 deg clearance angle between the side cutting edge and the work when facing and turning. This allows you to both turn and face the work without moving the tool from its perpendicular position. That 5 deg angle contacts the work just behind the nose radius when facing and allows the insert to cut all the way into a shoulder without rubbing at the end cutting edge, like this:



Older style triangular inserts did not have this geometry. Instead, they used different tool holders that oriented the insert at different angles while also placing the shank of the tool holder perpendicular to the work piece, like this:



On the other hand, HSS tools can be ground into different shapes so the orientation of the tool depends on the tool shape and the operation. A single tool with a general purpose shape can face, turn, rough, finish and access shoulders simply by turning the tool to provide the clearances necessary for the operation. Therefore, with HSS tools, the lead angle is often changed by the user and usually the shank of the tool will NOT be perpendicular to the work piece. The angle of the tool has a significant impact on the cutting forces the tool generates and chatter, especially on light lathes, can often be resolved by simply turning the tip of the tool towards the chuck a few degrees. Of course, things are much more complicated than just turning tools but, in general, changing the lead angle of the tool has many benefits when using HSS tools.

Of interest is that an inserted carbide tool does not have to be used perpendicular to the work piece. There is no law that says it has to be oriented that way. By altering the lead angle of a carbide tool, finishes can often be greatly improved. Plus, if using a finishing insert with ground edges, that insert can cut much finer than it normally could if the user knows how to use the edges of the tool.

Much depends on which tools you're using and how you're using them, which lathe you have, what materials you're cutting and what your cutting conditions (feed, speed and depth of cut) are.

Lathes and tool orientation do not cause chatter; the operator does.

 

[redvan22]

Thank you everyone.
Some very good advice and a learning experience for sure.

Thank you all for your time, images and patience.