Thread Dial Indicator

[CrabtreeengineerParticipant @crabtreeengineer]

Hi all, does anybody out there own either a Jet 1660 or Warco 1660 gearhead lathe?

I am trying to get detailed information on the thread dial indicator & the manual is only fit for toilet paper!

These lathes will cut both metric & Imperial pitches directly without the need of changing drive wheels but depending on which lead screw is installed I am assuming that the half nuts shall need to remain engaged when cutting the opposite thread to the thread of the lead screw.

The dial indicator is not marked off with the typical 8 quadrants, but has letters & numerals at various angles but not se metrically marked around the circumference.

There is no boiler plate on the gear head to show which thread TPI & or pitch can be engaged at which quadrant setting or numeral setting shown on the dial indicator.

Of course I could resolve by trial & error but wondered if anybody has been this road before?

I could also just ignore the indicator & engage at a single point for any given pitch that matches the lead, but this may well waste unnecessary time waiting for the single point to arrive again. Alternatively I could just leave the half nuts engaged & reverse out, but this all seems a waste with such a fancy thread dial indicator fitted to the machine.

I have scanned the web for other manuals or info, but all fall into the aforementioned toilet paper bracket!

Any ideas? (Please don't confuse matters by discussing conventional indicators, comments must be 1660 specific.)

Regards R

[CrabtreeengineerParticipant @crabtreeengineer]

Jet/Warco 1660 gearhead

[John Stevenson 1Participant @johnstevenson1]

R?

I know you say specific for 1660 and I don't have one but I have a couple of similar machines in this range that have the same problem as yours.

My dial comes with 3 gears that need changing to suit a given pitch, tide table and also depends on the seasons.

I have now given up, not in frustration but in the fact i can thread faster leaving the half nuts engages and using a swing up tool.

I do so wish i had discovered then 40 years ago, it would have saved so much hassle.

Take a read of this thread.

**LINK**

[davebParticipant @daveb17630]

I don't know if this will help, but the arrangement sounds similar. I have a Warco 1327 lathe, metric leadscrew, also with 3 gears on TDI. The machine is fitted with100/127 translation gears which are switched over depending on whether you are cutting metric or Imperial threads. There is a label attached to the carriage which describes which of the TDI gears to engage for various pitches. The manual is unhelpful. I also reverse the machine when cutting threads.

[Clive FosterParticipant @clivefoster55965]

If no-one has the proper details already tabulated it is relatively easy, albeit tedious to work things out from scratch rather than resorting to trial and error.

With the leadscrew stationary measure the distance the saddle moves for one turn of the dial with each gear fitted. One turn of the dial allows any thread whose pitch divides exactly (ie whole numbers, no decimals or fractions) into the distance travelled to be cut by re-engaging the half nuts at whole turn intervals. The same rule applies for part turns of the dial so, for example, if you want to use three graduations the pitch has to divide exactly into one third of the measured distance.

I suspect that your dial has three sets of graduations one even numbered, probably 4 or 8, one set of 3 and one set of 5. I'm told the simplest metric set-up for one set of graduations is 12 with a 4 mm pitch leadscrew and 4 gears.

Clive

[CrabtreeengineerParticipant @crabtreeengineer]

Hi Boys & Gals, thanks for your comments & suggestions. Some of these have pointed me in the right direction & once I took the TDI off the lathe…well the penny dropped this morning! The boiler plate I was looking for was actually on the TDI but I did not understand it.

The TDI is indeed a three gear jobby, or more to the point can be supplied with any one of three gears, & each gear ratio has a different set of quadrants for auto pick up.

One confusing issue was that the indicator face of the TDI is marked off as O,D, E rather than being numbered 1 to 8.

Hence my 1660 is fitted with a metric lead screw & with a TDI fitted with a 15 tooth gear wheel. (This is the only gear wheel that came with the machine!) This gives auto pick up for 8 metric pitches on points O,D & E. All other metric pitches would have to be picked up on the quadrant point that was used on first engagement of the half nuts.

All Imperial threads would have to be cut using the reverse out method without disconnecting the half nuts.

The only way to understand all of this is to take off the TDI & see which size gear wheel is fitted.

Thanks once again to all who contributed.

Regards

R

[Clive FosterParticipant @clivefoster55965]

Even using whole turns of the thread dial by always engaging the half nut on the same graduation mark won't allow you to cut all metric threads with a single indicator gear. You are still limited to thread pitches that divide exactly into the saddle travel for one turn of the dial.

This problem is inherent to metric threads being rationalised directly by pitch rather than turns per unit length like imperial. The thread dial is an analogue calculator which adds the effects of spindle travel and saddle movement to indicate the point where the tool into alignment with the thread. Obviously if the spindle and feed screw are stationary moving the saddle brings the tool into and out of alignment with the thread. The TDI being geared directly to the screw acts like a mechanical dial caliper where a rack and pinion system converts linear movement to turns of a dial. Hence the TDI dial is effectively calibrated in units of thread pitch which clearly only works for a whole number of divisions on the dial. When the spindle is turning the alignment point effectively moves back and forth along the bed hitting the same point once per rotation. As the spindle drives the leadscrew the dial indictates the distance by which the alignment point has shifted during any fraction of a spindle turn. Again this is only useful if one turn of the dial represents a whole number of pitches.

When actually screwcutting the dial is stationary on whatever mark you have selected. Theoretically you could always start the cut from the same place on the bed and same rotational position of the spindle but that is impractical for a human using the half nuts. In practice you engage the half nuts at a fairly random position on the bed and the dial calculates the rotational offset needed to bring tool and thread into alignment at that point so you can engage the half nuts. Electronic leadscrew drive systems can handle odd fractions of a turn but humans need whole numbers and not too many at that.

Clive

[CrabtreeengineerParticipant @crabtreeengineer]

Clive, thanks for your most comprehensive & detailed response which makes total sense to me. I liked your comments concerning pick up from the same position on the bed! Thats how we used to do it when I was a lad working on an old Dean Smith & Grace cone head driven by flat belt from an overhead line shaft powered by a gas engine. A rule would be clamped to the bed as a dead stop, chalk marks would be placed on the chuck & head stock & on the lead screw bull wheel & another fixed point on the lathe bed. Eyeballing all of these chalk marks the half nuts would be engaged when all were aligned coinciding with an eclipse of the sun. If all went well one cut a half tidy thread & this was cutting Imperial! You should remember that reversing out on a line shaft machine was next to impossible without a figure of 8 in the drive belt, either that or you would back out by hand.

I now conclude that for Imperial threads I shall have to reverse out with the half nuts engaged.

For the 8 Metric thread pitches that match the 15 tooth wheel I can use the auto pick up from the TDI.

For all other Metric threads I shall have to reverse out with the half nuts engaged.

I shall now try to locate the other two gear wheels for the TDI from Warco. Wish me luck with that!

John, thanks for the chart from your Crusader however, its totally different to the 1660.

Thanks for all comments & help to date.

Regards R

[John Stevenson 1Participant @johnstevenson1]

Engage anywhere John ?

[Ian S CParticipant @iansc]

When I learned to cut threads on an old(very) Harrison at school, it was not fitted wit a dial, and we were taught how to do it by marking the lead screw, but I would have to hunt out the exact instructions, Ian S C

[CrabtreeengineerParticipant @crabtreeengineer]

Ian, this is the method I was refering to earlier. When lathes did not have Thread Dial Indicators fitted to the lead screw.

With the lathe stopped & the cutting tool clear at the start of the work the chuck was turned by hand until the half nuts could be engaged. The carriage would then either have a dead stop clamped to the bed or the bed marked with chalk. The chuck & head stock would be marked with a chalk line & the lead screw bull wheel marked along with a suitable mark on the lathe adjacent to the mark on the bull wheel.

You now have all the reference points noted to ensure engagement of the half nuts at the correct point.

The lathe can now be started. & thread cutting commences. At the end of the cut disengage the half nuts & return the carriage to the exact mark on the lathe bed. Await the marks on the head stock/ lead screw bull wheel & corresponding marks to be aligned & then re engage the half nuts.

Yes you had to have your wits about you as you are attempting to eyeball two rotating reference points at the same time….but it can be done…..its all we had at the time!

Regards

R

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