How do I ensure stock is square in the chuck ?

[JohnS]

If the depth of the material you put into the jaws of the chuck is greater than the depth of the jaws I can rely on the face of the chuck to ensure that everything is nicely squared up. If, however, the depth of the material is less than the depth of the chuck jaws how do I ensure that it will be square ? I have tried using parallels during set up but clearly these have to be removed before turning begins and I am left wondering if I am leaving squareness too much to chance. Any advice for a novice lathe operator ?

John

 

[rake60]

If I'm using a 4 jaw chuck I indicate the piece in round at the chuck with the jaws
using a dial indicator, then move the indicator to the end of the piece and
use a slug of brass to bump it around so the indicator reads the least
run out. I do the same with a 3 jaw, but it is only necessary to indicate
the end farthest from the chuck by bumping it to get it round.

At work I use the exact same procedure, but the pieces are often over
100 pounds in weight. Instead of a slug of brass it's a 4 pound hammer
adjusting the outboard run out.

A heavy out of balance part turning at a moderate speed in a big lathe can
be dangerous. A small out of balance part turning at high speeds can be
just as dangerous. If your just starting out you want to keep everything
as square and safe as possible.

As your experience and confidence grows you will find yourself trying
other things. If we didn't a part that took 3 days to make in 1923 would
still take 3 days to make today. But that's a whole different subject. :wink:

Rick

 

[JohnS]

Thanks Rick, after reading your explanation three times the penny (dime ?) dropped. The fact that I had to read it three times is more a reflection on my slowing brain cells than your ability to describe the process. Many thanks your help is much appreciated.

John

 

[Cedge]

The human eye can detect some incredibly small deviations in a rotating part so you can get surprisingly close with visual cues. If the piece is being rechucked, I use a dial test indicator near measure the end of the stock and shoot for as close to zero runout as is possible..

I've also discovered that a tap or two on the end of the slowly rotating stock, with my brass hammer, tends to equalize the chuck's grip and often centers things up quite nicely. Gently as you go... the chuck's scroll doesn't like large impacts, no matter how satisfying they might be. Not a good idea with hardened metals as they can score your jaws.

Steve

 

[rake60]

Very good point Steve!
How can I describe the force involved in "bumping" ? LOL
Rapping it hard can not only damage the chuck. The spindle bearings of
a small lathe wouldn't take that as a compliment either.

Rick

 

[JohnS]

Thanks Cedge, I can imagine a gentle tap with a brass hammer would tend to settle the object square within the jaws. The piece I have in mind is rectangular so visual clues may not quite be quite as apparent but I think a settling tap with the hammer followed up with a check using the dial indicator will bring me a good result.

John

 

[rake60]

Ok John
If the sides are true. (ie: if it mics the same width at both ends.)
Indicate it at the chuck then run the indicator down the flat using the
carriage. That will show you where you stand for square.

Many of Elmer's Engines cylinders are made from 1" square stock that
has to be offset in a 4 jaw. Once it is offset the only way to check it
for square is to check one side laterally with an indicator.

Rick

 

[JohnS]

Hello Rick

Now how on earth did you know I was making one of Elmer's engines ? Guess you guys in the States are psychic, or else your Google Earth looks inside workshops ! Next stage is to machine the width of of the cylinder bock down to 5/8th which brought up the problem of squaring up in the 4 jaw.

Thank you all for your help.

John

 

[rake60]

Oh I'm one of Elmer's greatest fans!

Which engine are you building?
The only one with a 5/8" dimension on the cylinder block that I can think
of at the moment is the Horizontal Mill Engine.
Mine runs very well but it was not exactly a pretty build.
Marv did a beautiful build of that one!

Rick

 

[JohnS]

Hi again Rick

Yes you're spot on my Elmer is the horizontal mill engine. I really am taking my time over this one (you'll never guess how many attempts I made at making the steam chest before I got a half decent result). I am not on a learning curve with this one, more like a sheer vertical wall, but I'm enjoying every minute - and how those minutes fly !

Yes I've seen a pic of Marvs engine, looks a real treat. In fact I have the picture in my build manual as it helps me visualise what each component should look like. Saw one running nice and slow, on air, at a vintage machinery country show at the weekend and this has added fuel to my enthusiasm for the project.

John

 

[rake60]

I built that engine before I had a milling machine.
All the mill work was done using the lathe.
It's a nice little project.
Now you have to share your progress pictures!

Rick

 

[mklotz]

Thanks for the kind words but I have to admit to feet of clay with that engine.
If you look carefully at the picture, you'll see a curious short cylinder sticking out of the block under the crosshead. Refer to the drawing and you'll see that such a fitting is not called out anywhere.

You see, I carefully lined up the block in the milling machine and very carefully drilled and tapped the exhaust hole...into the wrong side of the block. Fortunately, said errant hole didn't interfere with the engine's workings so I made a nice little decorative 'cylinder drain cock' simulant to hide the mistake.

I now make it a habit, when drilling holes into complex parts with big time investments, to carefully mark the location with a felt tip marker while referring to the print. Can't tell you how often that practice has saved me from a stupid error.

One of the unadvertised benefits of this hobby is the insight one obtains about how one's mind works - or, more to the point, how it misworks. After you've built a few things you'll understand much more about where you're likely to make mistakes and will develop personal regimens to help you to avoid making those mistakes.

Work long enough and you'll become so thoroughly self-regulated that you'll need to take a day off now and then and botch up a few things just to avoid becoming swell-headed.

 

[rake60]

No one world have ever noticed Marv.

No one has ever noticed that the inlet of my version of the Mine Engine
is on the wrong side.

One end of the cylinder turn out perfectly. The other end had a one
cylinder head hole out of location. To hide the flaw I mounted the
cylinder upside down so the screws missing from the misaligned hole
would not be visible. It still works fine and unless you turn it over you'll
never notice the missing bolt. Just have to keep the air line elevated
high enough to clear the flywheel. :wink:

Rick

 

[Cedge]

Work long enough and you'll become so thoroughly self-regulated that you'll need to take a day off now and then and botch up a few things just to avoid becoming swell-headed. Very Happy

ROFL... Marv I'm right on your frequency, dude. I've noticed a few new idiosyncrasies taking hold of late myself.

Steve

 

[JohnS]

It sure is a helluva relief to hear that you guys are human and make occasional mistakes - and not only that, you are happy to admit to them. Maybe there is hope for us beginners after all. I particularly like Marv's idea of marking any relevant features from drawing to work piece before diving in with a cutter, a simple notion but potentially saving hours of reworking.

John

 

[mklotz]

Make the marks with some crude degree of accuracy (e.g., measure with a 6" scale)
and they'll save you from the dreaded

"Ah, s..., I forgot to allow for the radius of the edgefinder"

mistake.

(I almost never lay out features directly on a workpiece, preferring to work from a datum established with an edge finder and using the machine dials (and 2" DIs on my mill) to locate to the proper spot.)

This becomes even more important when working in two dimensions - e.g., drilling a six hole bolt circle by coordinates (as opposed to using a rotary table). Laying out the hole locations by eye is accurate enough to save you from accidentally interchanging the x and y movements needed to reach the next hole.

 

[JohnS]

Hello Marv

Used my edge finder for the first time and as I didnt have a collet of the correct size I put it in the drill chuck on my mill. Establised my centerline (on steam chest !) - used a small center drill to scribe a line - zeroed my dro on the centerline then was able to take off the required measurements. I felt that using a centre drill was rather unkind on the centre drill but it did the job.

As for drilling six hole bolt circle by coordinates can I leave that until next week ?

Silly question coming up - if I use the axis turn wheels to bring the edge finder up to the edge I don't see that I need to have the edge finder spinning - surely as soon as I see the edge finder displace then I have hit the edge - right ? Previously I used the damp cigarette paper technique and that worked quite well.

So much to learn and so little time

John

 

[mklotz]

Why bother to scribe a centerline at all (and, yes, you shouldn't use a center drill as a scribe)? Once you've located to the (unscribed) center line, zero your DRO and take all further measurements as offsets from that datum.

When you get around to doing bolt circles by coordinates, have a look at the BOLTCIRC program on my webpage. It will calculate all the coordinates you need for the holes automatically. Here's a sample of the output it generates for a five hole circle:

--------------------------------

Boltcircle specification:
Radius of bolt circle = 3.0000
Bolt hole diameter = 0.5000
Spacing between hole edges = 3.0267
Angular offset of first hole = 0.0000 deg
X offset of bolt circle center = 0.0000
Y offset of bolt circle center = 0.0000

HOLE ANGLE X-COORD Y-COORD

1 0.0000 3.0000 0.0000
2 72.0000 0.9271 2.8532
3 144.0000 -2.4271 1.7634
4 216.0000 -2.4271 -1.7634
5 288.0000 0.9271 -2.8532

--------------------------------

If you don't yet have a rotary table, this program can help a lot. (Many of Elmer's engines call for bolt circles on the cylinder ends.) Even if you do have a RT, the program will save you the hassle of swapping the vise out, mounting the RT, then reinstalling and rezeroing the vise just to make one small part.

You want your edge finder spinning because what you're interested in is the spin axis of the spindle, which may not be coincident with the mechanical axis of whatever is grasping the edge finder. Using the edge finder in the drill chuck is acceptable, but you really do need to have it spinning.

Observe the edge finder from a direction orthogonal to the direction in which you're moving the table. You'll be able to pick up even a slight offset more easily.

Not all edge finders are made equally. A good one will snap off a considerable amount as soon as it goes slightly over center. Poor ones may be sloppy and displace only a very small amount.

 

[JohnS]

Hello Marv, I see what you mean about it being unnecessary to scribe the centre line - it was just that I wanted the satisfaction of seeing the result of using my edge finder for the first time. Have downloaded your Boltcirc software - at first I thought I may be able to use it when drilling , for example, the bolt holes on my steam chest but as these are not set on a circle I guess not. Shall certainly use it when the situation is right, like on the cylinder head fixings. It sure beats trying to position centres by eye.

John