How do you indicate on 4-jaw?

[Mosey]

What would be a good, quick way to indicate to a pin-prick on the end of an object in the 4-jaw? I am setting up a rectangular bar in the 4-jaw, and have an accurately located pin-prick scribed in the end that is not in the center of the bar. I thought of setting a pointed edge-finder in the tailstock and drawing it up to the end of my piece, then moving the piece until the prick aligns with the center-finder point. There must be a better/good way of doing this. Help!

 

[bearcar1]

Mosey, one of the best methods that I know of is to mount up a 'wiggler' point in the tailstock and advancing the point into the intersect. Mount a dial indicator on the toolpost or carriage so that its plunger is on center (in either plane, facing up or toward you)_ and in contact with the shaft of the 'wiggler'. Now it is a matter of adjusting the four jaw chuck, just like centering a piece of round, until the DI gives a null reading. It takes a few minutes but is extremely accurate.

BC1
Jim

 

[stevehuckss396]

I thought of setting a pointed edge-finder in the tailstock and drawing it up to the end of my piece, then moving the piece until the prick aligns with the center-finder point. There must be a better/good way of doing this. Help!

Thats what I do but I center drill the piece and put the "finder point" in the hole I made.

 

[ShedBoy]

two chuck keys working opposite each other is also a great help.

Brock

 

[Tin Falcon]

pump center and dial indicator,
http://www.homemodelenginemachinist.com/index.php?topic=608.0


http://www.projectsinmetal.com/free-project-plan-spring-center-metal-lathe-mill/


Tin

 

[steamer]

The spring center works well, but you can use something else also.

Take a lathe center, and put the pointy end in the centerpunch mark, and the tail end supported by the tailstock, and then put the indicator on the the now wobbling center.....when you adjust the 4 jaw, adjusting the jaws in pairs, and the center stops wobbling, your there.

Dave

 

[rmw]

I ground a point on one end of a 1/8" diameter rod, about 14" long. I put this in my tail stock drill chuck, and use an indicator as close to the workpiece as I can get. Very quick and pretty darn accurate..
Greg

 

[Ken I]

Similar to steamer's method but for a very small centrepop mark - take a sharpend bicycle spoke in the drill chuck - push the sharp end into the pop mark and clock the spoke (as close to the pop mark as you can get the DTI).

The sharp end cone does not need to be accurately ground as its not rotating with the work - when it stops wobbling your pop mark is on centre.

This method usefull where you are not going to machine away the centre and want little or no marking to remove or clean up afterwards.

Ken

 

[Mosey]

Thank you all for the excellent ideas! I will surely tackle this one better equipped next time. I especially like 2 of the ideas... 2 chuck keys, and clocking the point center or pump center. Do you run your lathe at low speed to see the wobble, or by hand?
Wouldn't it be nice if you could put a 2 axis micrometer adjustable stage onto a face plate and just dial your work over to center as indicated by one of these methods?

 

[bearcar1]

Hi again Mos', rotate the chuck by hand using either method. The shock of rapid needle fluctuations could lead to damage of the jeweled inner workings of the indicator. Lowest backgear speed at most but not recommended.

BC1
Jim

 

[Mosey]

Thanks, again.
Me thinks it would be great if we could take this thread and others like it, and put them into a little album so the next newbie like me can find them without searching all over the forum.
Now I'm thinking that I should restore the missing parts from my old center indicator and make it go again. What the heck, 100 years ain't bad for a tool is it?

 

[mklotz]

Me thinks it would be great if we could take this thread and others like it, and put them into a little album so the next newbie like me can find them without searching all over the forum.

Great idea. Why don't you get to work on that?

 

[lemelman]

I joined HMEM only a few weeks ago and my trawling around revealed this thread.
A good way to indicate a pop mark or pin prick without the use of a DTI is to push the sharpened bicycle spoke through a rubber eraser with about 1-2cm sticking out. Mount the eraser on the tool post somehow (it's not at all critical) and position it so that the spoke is more or less on the centreline of the lathe. Insert the sharp point of the spoke into the pop mark, rotate the chuck, and watch the other end of the spoke.
Chances are that the far end of the spoke will describe a circle that is a magnified version of the circle the pop mark moves. The amount of magnification is determined by the ratio of the spoke lengths on either side of the eraser.
If the pop mark is dead centre then the other end of the spoke won't move.

 

[Mosey]

My 1965 Starrett catalog shows a No. 65 Center Test Indicator that works exactly that way, mounted in the toolpost, a tiny pointed rod inserted into the pin prick, and a very long rod that waves in the breeze to show the off center condition. I have an old broken one of these that I will someday restore. It even had a ball that slipped over the point for indicating holes or buttons.

 

[pkastagehand]

I joined HMEM only a few weeks ago and my trawling around revealed this thread.
A good way to indicate a pop mark or pin prick without the use of a DTI is to push the sharpened bicycle spoke through a rubber eraser with about 1-2cm sticking out. Mount the eraser on the tool post somehow (it's not at all critical) and position it so that the spoke is more or less on the centreline of the lathe. Insert the sharp point of the spoke into the pop mark, rotate the chuck, and watch the other end of the spoke.
Chances are that the far end of the spoke will describe a circle that is a magnified version of the circle the pop mark moves. The amount of magnification is determined by the ratio of the spoke lengths on either side of the eraser.
If the pop mark is dead centre then the other end of the spoke won't move.

This is the method I use. Maybe not quite as accurate as DTI against a rod but serves me well for what I need. Kozo Hiraoka presents his version of this unit in one of the locomotive books (First Shay maybe?) It uses a ball bearing silver soldered to the rod, trapped in a dedicated holder with tension adjustment for the ball. About 1 inch on the short side, 10 inches on the long side so a 10:1 movement ratio so a thou (.001") movement on the short end gives us a hundreth (.01") movement at the other end; easily visible even to my old eyes.

Paul

 

[workshopman]

If I may be allowed to resurrect this thread, look here for a method.

Harold

 

[Lew Hartswick]

A fwiw (for what it's worth) I'd say if you located the "punch mark" from the sides of the piece, then
should be able to locate the piece by using the sides and a dial indicator on the sides in the chuck .
Haven't tried it but would like to see it tried.