A style/usage question about QCTP - how do you run yours? (question #2, less dumb)

[dbb-the-bruce]

I'm moving to metal work from wood work - although I've got a lot of experience using my Southbend 9 for making mechanical wooden models, I've only done a little metal turning on it.

I recently bought a QCTP - mostly because I want to be able to quickly change out cutters and have them setup exactly where I want them when I swap them in. My observation is that a QCTP is almost always setup square to the lathe axis, however, most of the cutter tool geometry descriptions I've seen assume an angled tool approach to the work. (yeah old books).

In the little messing around I've done with my new QCTP, I've already encountered cases where it gets in the way or requires huge unsupported tool bit overhang unless you rotate it.

So none of this is a big deal: geometry wise, if the bit is set square to the lathe, the shape can just be modified to provide that same approach - as if you are coming in from an angle. If the tool post is going to get in the way, then you just rotate it and go back to a profile that works with that approach.

So I'm looking for comments and advise on how people handle this:

- Is there something like a "standard" set of tool shapes to use when the bit is going to be held orthogonal or parallel to the lath axis?
- How often do you find yourself changing the mount angle of your QCTP?
- How often do you use a spotting drill and tail stock support when turning? (this seems to be mostly when the QCTP gets in the way).

I'm sure I'll come to my own preferred work process given enough time and trial.... but would prefer to start with more "common" practice.

- Dave

 

[RJSakowski]

Maybe coming from the old school, using the lantern style tool post, I modify the angle of the tool post to best suit the work that I am doing and the tool that I am using. There are times when I have to use multiple tools on a part and am making multiple parts where I set the tool post (not necessarily square) and leave it though.

The short answer is do whatever is expedient to the work you're doing. Don't box yourself in by someone else's convention.

 

[Tozguy]

Many tool sets have a variety of angles to the cutting edge so that we can choose the appropriate one for a job. Designed to be held either square to the spindle axis or parallel to it, in a QCTP but with the possibility of rotating the QCTP to some extent to maximize performance if necessary. I have no hesitation to rotate the QCTP either to create clearance for the tool or to tweak the cutting angle.
I don't understand your third question.

 

[Ulma Doctor]

since the name is Quick Change, i quickly change the angles and heights to accommodate any tooling needs i have for the job.
you can change the angle of the compound to the lathe axis too, it doesn't all have to be done at the QCTP


Q1: yes, there are some "standard" shapes of tooling, and grinds for tooling for turning parallel to the axis- Right Hand, Left Hand, and straight tooling exists
even sub-groups like roughing and finishing tools.
there are also tools and grinds for tools that run transverse to the axis as well.
it can be a study upon itself

here is a pic of common tools:


Q2: only occasionally do i find myself changing the angle of the QCTP. i usually have my compound at 30° to the axis for threading or turning
if i change the compound angle, i then change the QCTP angle back to 90° to the axis.

Q3; i use center drills all the time, i have not had much problem there-
but sometimes, when turning, you may need to leave extra length in the stock you are turning to avoid interference of the work, the live (or dead center), and the tooling.


if you are doing it right,
you'll learn something every time you turn some work

 

[Canus]

You mention using a spotting drill and tail stock support. A spotting drill has a 135 degree angle and the hole drilled will not allow the live or dead center to seat properly. You want to use a center drill for this. Spotting drills are great to start a hole that you will be drilling.

 

[Mitch Alsup]

So I'm looking for comments and advise on how people handle this:

- Is there something like a "standard" set of tool shapes to use when the bit is going to be held orthogonal or parallel to the lath axis?
- How often do you find yourself changing the mount angle of your QCTP?
- How often do you use a spotting drill and tail stock support when turning? (this seems to be mostly when the QCTP gets in the way).

I run my post square to the axis most of the time.

I change the post angle when turning/boring tapers to minimize the excess cut on the unturned stock due totheuse fo CNMG inserts. I could get away without doing this is I had Dxxx or Vxxx tool holders with appropriate holding angles and inserts.

I support the part being turned whenever it is longer than 4 times its final turned diameter.
I spot using center drills.

 

[dbb-the-bruce]

You mention using a spotting drill and tail stock support. A spotting drill has a 135 degree angle and the hole drilled will not allow the live or dead center to seat properly. You want to use a center drill for this. Spotting drills are great to start a hole that you will be drilling.

My bad - wrong term for the drills I use. They are the correct ones for matching the 60Deg center.

 

[dbb-the-bruce]

@Ulma Doctor - that's pretty much the same as what I've been looking at ~pg 34 of "how to run a lathe" After taking another look at the book, the only tools that don't approach the work at 90 deg are the facing tools.

So the issue is really just the facing bits.
If the work is unsupported by the tail stock, then I can see how a RH facing tool could be ground and mounted parallel to the axis.

For work that's supported on the tail stock end, looks like you have to change the approach angle of the toolpost, possibly by changing the compound angle, but more likely rotating the QCTP. (seems like no matter how much I try to think a head - something is alway in the way when I'm using the tail stock for support!)

@Tozguy - exactly, if it's a QUICK CTP why am I having to rotate it?

The third question was more about supporting work - do people regularly us dogs and/or a center in the tailstock?

Starting as a wood turner, I'm quite aware of dealing with flex, vibration and thin stock (however we just wrap our finger around the work). I also understand the beauty of the geometry of a lathe - driving work between two points a cutter has to (in a perfect world) cut on a plane that is 90 deg to the axis.

That said, I've never setup a dog to drive a piece of work.

Tailstock center support is clearly needed for anything that starts to get thiner/longer. Almost all of the parts I've made to date (either wood or metal) have been stout enough to not require it.

Thanks for all the input.
-Dave

 

[francist]

I had occasion recently to turn between centres again, I hadn't for quite a while. And I kind of surprised myself, it was oddly "peaceful" for lack of a better word.

I know that probably sounds goofy and maybe it is, but there was something weirdly relaxing about not having to tighten the chuck, not having to dial in, not worrying about if it was still on centre, yadda yadda. I could take the part in and out as many times as I wanted and it went right back in the same way, beautifully true. I can hardly wait to have occasion to do more of it!

So I would encourage you to at least try it, if for no other reason than to know how to set up if and when you really do have no other options. Who knows, you might be surprised too!

-frank

Edit: oh yeah, ex-wood turner here too.

 

[dbb-the-bruce]

I had occasion recently to turn between centres again, I hadn't for quite a while. And I kind of surprised myself, it was oddly "peaceful" for lack of a better word.

I know that probably sounds goofy and maybe it is, but there was something weirdly relaxing about not having to tighten the chuck, not having to dial in, not worrying about if it was still on centre, yadda yadda. I could take the part in and out as many times as I wanted and it went right back in the same way, beautifully true. I can hardly wait to have occasion to do more of it!

So I would encourage you to at least try it, if for no other reason than to know how to set up if and when you really do have no other options. Who knows, you might be surprised too!

-frank

Edit: oh yeah, ex-wood turner here too.

My mentor, Jon Siegel, is a woodturner, machinist and all around amazing guy. One of the things he does (and demos) is turning cue sticks. He uses a dog drive and centers. I've learned a hell of a lot from Jon.

We recently ground the threads on a refurbished dividing head - between centers, with a dog on an absolutely beautifully restored Hendey.

So, I've kind-a done it.
Sooner or later, I'll be doing something on my small Southbend 9 that warrants it.

-Dave