Cutting Metric Threads

[pipeclay]

Chris dont over think the last part of the puzzle,it all makes perfect cense,you need that many variations for the models concerned.

[cba_melbourne]

Chris dont over think the last part of the puzzle,it all makes perfect cense,you need that many variations for the models concerned.

Pipeclay, I suspect the part numbers only differ because they include the appropriate charts to stick onto the cover. Or do you know of any additional hardware that was included in these kits, besides one of the two transposing gears and the chart? Chris

[pipeclay]

Yes.

[cba_melbourne]

This assuming problem with the hercus is a bit of a problem with you Chris.

Pipeclay, I am just one of these persons that like to find out how things exactly work., and why they are made in a particular way. Already as a kid I had to take my toys apart .

The key problem that I described is not an assumption, it is very real. You cannot use a 260 lathe to cut accurate precision threads using either a 60/63 or a 64/63 gear! You can only use it to cut approximated fastener quality threads with an incremental error of 0.8%.

This can be a very important bit of information for anyone already owning, or considering to purchase such a transposing gear set. If the lathe is to be used to cut accurate threads such as leadscrews, in the measurement system other than the lathes own leadscrew, then the retrofit of a 127 transposing gear is an absolute necessity. Chris

[cba_melbourne]

Yes.

Pipeclay, I cannot find a breakdown of these kits in the spare parts manual. Would you mind to share the details of your "yes" above? Thanks, Chris

[pipeclay]

No just look at your books you will work it out.

Assumptions I thought you made were in regards to Hercus spindle thread registers,your shock that a carriage can be raiosed at the front and that your METRIC lathe uses 60/63 compound gears.

[Pete F]

Maybe someone can explain why Hercus choose to use two different transposing gears, it is really not obvious to me why Hercus choose to do it this way. The whole gear train could have been designed such as to use the same transposing gear for both metric and imperial models. Maybe it is historic reasons?

By the way, I just had a look at another Hercus textbook of turning, this is for an older 9x Hercus lathe with sleeve spindle bearings. And there they show two metric thread charts both using an 100/127 changegear for A, B and C models. Go figure as for why Hercus choose not to go with 127 gear in the 260 model.........

Chris

Hi Chris I'll try to answer a few of your questions. Firstly, no it's not so easy to design a gear train to use the same transposing gear. You seem to be forgetting that there is a gearbox involved in all this, and it is only capable of a finite number of combinations. The gearbox on the AM is designed to cut all the common (and probably not so common) metric pitch sizes. Likewise for the imperial model. Many lathes out there cannot cut obscure pitches simply because the combination of gears within their gearbox doesn't provide for the appropriate gears to be selected to enable that to happen. Why 63 is used I'll cover later, but the 64 or 60 (metric/imperial) is chosen as that is the gear that will allow the appropriate selection of thread pitches using the "wrong" gearbox ie using a gearbox designed to cut metric threads to cut imperial or vv. This is why I repeatedly said that if you double the 63 to the correct transposing gear of 127, you also need to double the size of its mate on the other side of the compound. If you don't, then the chart will be wrong and/or you won't be able to select the appropriate combination of gears to cut all the common threads.

As far as why 127 wasn't used, that has already been covered above by another member, but just to repeat what he said, it is cheaper and more compact. The error is so small that for 99% of the work a lathe like this will see it's not significant. However you're quite right, to have a perfect translation then the gear "should" be 127 BUT only if you ALSO changed the other side of the compound to either 128 or 120 as appropriate for a metric/imperial lathe.

Hopefully that all makes sense.

Pete