Setting lathe QCTP tools on centerline

[mikey553]

How do you set your lathe cutting tools on centerline? I used to do that visually with a small steel rod in the chuck and aligning the tool height to the center of the rod. The accuracy of this method is .010-.020", which is fine in most cases. Unfortunately my eyes are not getting any better and sometimes you need better accuracy. In addition when you need to setup a new tool while you have a part in the chuck, this method is no longer an option.

After a lot of thinking I came up with a new (for me) method. I put a drill rod of known diameter in the chuck and set an indicator on top of it. Indicator plunger was set perpendicular to the spindle axis and indicator was set on zero using a half of the rod diameter. So now indicator zero will be my centerline. After that I can put all of my holders with tools on the post and set them accurately on height.

It is difficult to set an indicator in the correct position, but I have to do it only once. One of my tools will be a master and I can use it in the future to setup other tools with indicator mounted anywhere on the lathe bed.

What do you think about it? It is a big help for me and I would like to share it with you.

There are cases where you should intentionally set your tool below or above centerline. There was a discussion about that, bit I cannot remember the details. Can we talk about that again?

[sid pileski]

If that works for you, that’s great!!

Sid

[Rich Carlstedt]

I think your setup is nice, but there is a faster way that dates back to lantern Tool post days.
Just hold a ( Aluminum Preferred) 6 inch scale between the work and tool point.
bring the tool in and gently touch the scale to both workpiece and tool ( Clamping it so to speak.
If the scale tilts away from you, you are too high
If it tilts towards you, Too Low
If the scale is vertical, you are on center

Rich
This is one of the reasons old time machinists wore aprons, with the scale pocket in the center of their chests

PS Your method works great if you have multiple tools to set up at the same time using the DI !

[Galaxie]

How do you set your lathe cutting tools on centerline?

I made a center height gauge. Set it on the ways and adjust the tool to the same height as the pointer. Your method offers much better accuracy of course.

[Dan Dubeau]

I think your setup is nice, but there is a faster way that dates back to lantern Tool post days.
Just hold a ( Aluminum Preferred) 6 inch scale between the work and tool point.
bring the tool in and gently touch the scale to both workpiece and tool ( Clamping it so to speak.
If the scale tilts away from you, you are too high
If it tilts towards you, Too Low
If the scale is vertical, you are on center

Rich
This is one of the reasons old time machinists wore aprons, with the scale pocket in the center of their chests

PS Your method works great if you have multiple tools to set up at the same time using the DI !

Hey, I still wear an apron*. And I use a scale, just as mentioned. And will adjust if I'm leaving a tit after facing.

It is a neat indicator trick though.

*I'm down to may last apron at work as the boss doesn't get them in the laundry service anymore, as only a few of us wore them. The last one I have doesn't have a hanging pocket like I've always liked and I'm close to giving it up, as every time I bend over to get something it dumps the contents if I don't remember to cover it. Quite annoying. I might be on the hunt for something new...

[BCRider]

That certainly works and would be accurate and no guessing. But it takes a fair bit of time to set up each time you need to set a tool height.

Some folks have come with bars or other style gauges that rest on the bed and are the exact height of the spindle axis. Then they just offer up the tool and feel across the top of the gauge and tool.

In my case I installed a wide chip catcher on the front of my cross slide to stop the finer swarf getting into the dovetail way of the slide. So I'd need a lot of overhang for such a gauge. Instead I opted to just turn the tool post around and use a short gauge resting on the flat top surface of the compound that you can see in this picture. A finger rubbed over the two can feel a pretty small difference.

Another improvement I've seen is to add a top piece to the gauge that catches on an edge which is too high.

.... Actually in taking this picture I got to thinking that a new gauge that rested on the flat top of the cross slide would not need all that much extension. And it would mean I didn't need to spin the tool post around each time.... Might be a Mark II version soon....

Yet another option would be a simple and dedicated dial gauge stand with one of the low cost gauges. No joints to slip at all. Just a solid base a fixed rod and a fixed arm that holes the dial gauge and put a flat ended shoe on the finger.

[BCRider]

You asked about tools above or below center? I tried that with boring bars where I'd set the cutting tip just a whisker high. I think the idea was that it would spring down and take less of a cut and should reduce chatter/singing? A couple of years ago I went with the boring bars dead on center and found that I got less chatter or none at all. So now I set the boring bars to center height with the same gauge seen above.

[rdfeil]

My High School machine shop teacher showed me Rich Carlstedt 's way many decades ago and it still works well for me. Like Dan said I adjust if there is a tit after facing or if there are cut/finish issues. Your way is great, just a little time consuming and not good if you have work in the chuck, as yo said.

[Randy]

Just as Rich and Dan mention, I wear an apron and use my 6" flexible rule for tool height setting. Have for decades. That is, until I recently saw a post or video or something showing a setter made with a dedicated dial indicator amd a magnetic base, and decided I just have to have one of those. I need to improve mine though. Needs a stronger magnet in the base. I have a spare on-off mag base to try. I keep it in a drawer under the headstock, just a foot from its point of use.

As for aprons, I sew my own, usually cotton-poly poplin with nylon webbing and fastex buckles rather than strings, and pockets however I like. Guys are surprised when they find out I can sew, but I just tell them "I'm a machinist. I make things, using machines." My mom was a seamstress, and I practically grew up at Jenny's Yardstick, the fabric store where she shopped. She taught me a fair bit. The sewing machine I use was my grandmother's, which she won at a grocery store grand opening in 1965. (Remember those?) It's a Brother, made in Japan and built like a tank. They make CNC machines too. But I wonder, if it's my grandmother's brother, does that make it my great uncle?

[Lew Hartswick]

Here is what I came up with, after seeing similar idea on the net, for a bunch of beginners in a high school metal shop. Even had a bunch of them do a miniature production run for enough for the classes. :-) All the tools have positive rake of course .
...lew...

[mikey553]

Thank you guys for the feedback. Maybe I failed to explain my idea properly. It is only for QCTP because this is what I have. There are 28 holders in my collection and most of them are setup with tools - ready to go on the post. This is what QCTPs are about - quick change without any adjustments. I have checked my tool post for repeatability, the vertical tool position is easily maintained within .001". I have also checked most of my tool holders and many tools were off vertically by as much as .010-.020". This much for the visual setup accuracy...

I did not reset the tool holders yet, but I am sure it will take me less than an hour for all of them. After that I can designate one of the least used tools as a master and use it with an indicator on the lathe bed to transfer vertical position from the master to any new tool. It would only take a minute or so per tool.

BCRider, I was thinking about a short gauge on top of the compound similar to yours, but decided against it. Although my compound has a flat top like yours, there is no guarantee the top is parallel to the machine ways. When you rotate 5" long boring bar 180 degrees, even a slight tilt of the compound top would result in a significant error on center height. That is if a bar this long would fit on the compound. In addition not all lathes have a flat top compound.

I do not intend to keep a designated indicator with base for this purpose. It is not reliable and not really needed. I can set my base with indicator anywhere on the machine bed and just zero the indicator off the master.

When you machine a 3" shaft journal, .020" error in the tool centerline position is not a big deal. But if my journal is .060" in diameter, I cannot afford to make big mistakes.

[jimsehr]

Most of the time I just use a 6 inch scale.
But if I need to be real close to center I use a depth mic . I collet a 1 inch bar with about 3 inches extended out from spindle. Then I place my depth mic with base alined along top of 1 inch bar and depth mic down half of bar dia too tool tip and I have center.
Any dia will work as long as you mic down to top of tool using half of stock dia.

Another way I check center is to put a flat plate across lathe ways and then use my height gage to check top of 1 inch bar then get a reading on top of cutting tool . Then set tool half inch down from top reading.

Jimsehr

[Tobias-B]

I just chuck up a centering pin and use the tip of that.

t

[MrWhoopee]

I made this height setting gage a while back, based on a Hardinge design (I think). Rare earth magnet in the base holds it securely to the flat way.
It lives on the taper attachment until needed.

[nickel-city-fab]

Ooo Nice! I wish thought of that!
I was taught to use the dead center in the tail stock
just line things up by eye and use a magnifier...
but my eyesight is not to be trusted any more
A dial gauge gets it right on.
I have to try your method.