PDA

View Full Version : Trav-A-Dial calibration?



jdunmyer
07-24-2008, 10:58 AM
I finally got around to installing the Trav-A-Dial that I bought a couple of months ago, and all went well...almost:

When I traverse the lathe carriage rapidly from one end to the other, the red hand (that reads in thousandths) seems to "slip"; it goes off-zero very badly when returned to the headstock end. The strange thing is that the black hand (that reads in inches) does NOT change, it'll be right on zero.

If I wind the carriage more slowly/deliberately, the zero will not change, it seems to work fine. The only problem is when it's traversed rapidly. I'm not bumping the carriage into the tailstock or against the carriage stop, I'm stopping the travel before any limits are encountered, so there's no shock.

This might not be a problem during normal operation, but could be if I just crank it as fast as I can.

Is this normal, or does it need repair?

kap pullen
07-24-2008, 12:59 PM
Trav-a-Dial is alive and well.

They now make CNC equipment as well as the old Trav-a-Dial.

Technical help should be avalible.

Here is their website.

http://www.southwesternindustries.com/swi/prod_measurement1.shtml

Kap

J. R. Williams
07-24-2008, 03:45 PM
The unit is calibrated by tilting the head and changing the contact diameter of the drive roll. The drive roll is spherical on it's surface. If the unit is skipping I suggest you clean the surface and check the carriage as you may be lifting it slightly when making rapid moves. I have one on my lathe that has preformed well for the past 25 years

JRW

jdunmyer
07-24-2008, 03:58 PM
JR,
I have the installation/calibration instructions and have it pretty well complete. This is in spite of the problem of loosing zero.

Although my first thought was that it was skipping, that's not the case. After a couple of full-length passes of the carriage (40+" one-way), the zero will be off nearly .100". The amount of change varies from one pass to the next. HOWEVER! The little hand hasn't moved, it's still coming back to zero, right on the money. If the unit was skipping, it would be off by a full graduation or at least a partial grad. It acts like the Red hand is slipping on its shaft. That's probably not what's going on, but that's what it acts like.

If I crank the carriage slowly, it seems to repeat OK.

Should you be able to crank the carriage as fast as you want, or is there a limit to the travel speed?

J. R. Williams
07-24-2008, 05:41 PM
JD
Check the surface of the flat where the serrated wheel runs and clean it up with a fine stone. Clean the surface of the serrated drive wheel.

JRW

lane
07-24-2008, 07:17 PM
I would bet it is not your set up,but the needle is slipping on its shaft where it is pressed on. .One needle cant be right and the other wrong ,unless something is slipping internally.

jdunmyer
07-24-2008, 07:51 PM
Lane,
An old friend, who worked as a machinist for many years, also in a metrology lab, told me that the needle is pressed onto the shaft, which has a slight taper. He recommended that I remove the lens and use a piece of small tubing to lightly tap on the needle's hub to press it down onto the shaft a bit further.

Of course, he wasn't real clear as to how to remove the lens. :-(

JR,
I did what you suggested, but to no avail. The device works perfectly unless I really crank on the carriage hand wheel. The lathe is a 19" LeBlond, so the carriage isn't rattling around, either.

<<Jim>>

loose nut
07-24-2008, 08:13 PM
Lane,

Of course, he wasn't real clear as to how to remove the lens. :-(


<<Jim>>


HAMMER :D :D :D

JCHannum
07-24-2008, 08:23 PM
Of course, he wasn't real clear as to how to remove the lens. :-(

Jim, The slipping needle sounds right. As I recall, the lens simply slips over the dial, and is removed by lightly prying between the lower edge and the body of the main housing. They are easily replaceable because they get scarred up by hot chips. I think I might have a couple somewhere around here.