TDS 1/1GB gears and gear pitches

[davidsbthomas]

My TDS is metric and has a gear box. It has a "fixed" gear train including the In/Out slider, and a set of stud change gears Lettered (rather than numbered) A to G (actually 16 - 35 teeth).

I have a conversion quadrant, which should allow me to cut imperial threads if only I had the right change-wheels and studs.

But all second-hand change gears I have ever seen appear to be of a different pitch from the gears in my lathe's train. I have a couple I bought separately from the lathe, which are painted in Denford red, and which are "imperial", having a 9/16" bore, and by my measurement are 18 DP.

BUT the gears in my "fixed" In-Out quadrant are, by my measurement, 16 DP (and of course lead to a 16DP gear into the gear box itself). The shaft into the gearbox is 1", so even if I installed a whole train of 18DP gears, I'd still need one with a 1" bore.

By eye, though I haven't dismantled it to check, the tumbler reverse and the mandrel gear are of another different pitch -- perhaps 20 DP (would that be the same as Boxford gears ?).

Does anyone know if Denford changed gear pitch at some point, or perhaps just used a different pitch on the gear-box lathes from the change-gear-only models ? ... and if so, why are 18DP Viceroy gears quite common but the 16DP conversion gears rarer than hens' teeth ?


dt

[Andy B]

From all the drawings I have seen (dating back to the 1950's) the end drive gear chain has always been 18DP, with the reverse tumbler set being 20 DP.
This continued through to the 280 series lathes in the 1980's too.

So the O/D of the 66 tooth gear on the gearbox input shaft should be:
pitch dia + 2 x addendum
66/18 + 2 x 1/18 = 3.778 in.
Is yours different?

Conversion gears for most lathes are, in my experience, rare second-hand.
Tony Griffiths (lathe.co.uk) can supply new I believe.
See this topic for drawings, etc.

I understand Boxford gears are 14.5 deg PA, not 20 degress which all the Denford gears are - caveat emptor!

Edited: note for anyone reading this thread later (see below for when we found out the differences) - the 280 series have 16DP 'standard' end drive gears, carried over from the 5" gearbox models. The conversion gears for both (metric -english or english-metric) are 18DP, which was the pitch used for all the changewheels on the non-gearbox models.
Unless anyone knows different........

[davidsbthomas]

No, it seems to measure at 4.25" -- which is 66/16 + 2*(1/16). ...and it is stamped '66'

Have I discovered a hitherto unheard of piece of kit ?

[davidsbthomas]

... but you're right. Whatever the gears on my "fixed" quadrant, the conversion quadrant is made for 18DP wheels.

The distance on the conversion quadrant between its (fixed) bushed bolt and the gear-box spindle centre is about 5.1", which would accommodate the size of an 18DP 135-tooth and an 18DP 48-tooth screw gear. But it's not long enough for the equivalent in 16DP (for which the distance between centres would be about 5.7").

I still don't understand why my lathe in metric setup is equipped with the only 16DP Viceroy gears in the known universe.

[davidsbthomas]

If I've understood this correctly, a metric lathe needs the following to cut imperial threads:

: ML105 129 54-tooth stud gear (9/16" bore) (and Thank you Andy, yes I have found the drawing of this)
: the quadrant, stud bolt etc which I think I have
: ML114 9 127/135 compound (9/16" bore, and thank you again for the drawing)
: ML114 10 -- a 48-tooth gear with a 1" bore to mount on the gear-box spindle.


I don't suppose there's a drawing of ML114 10 is there ?

[Andy B]

I don't suppose there's a drawing of ML114 10 is there ?

I just happen to have a copy....! Now added to the downloads thread mentioned above.

Now, we need some pictures of your 16DP set-up. Are there any 'ML..' numbers on any of the castings? The CI gears larger than about 50 teeth normally had.

[davidsbthomas]

Thank you Andy.

Here are some pictures. From the first you will see that my workspace is small, and full-frontal gearnography is not possible with the gear train in place on the machine. So the second is a general view of it in place and the others of the quadrant and gears off the machine.

As I think is standard, the gears are:
Stud
Compound 64 / 22
Compound 24 / 66
66

In the last three photos, of course, the stud gear is not there but still back on the machine.

Sadly, although all four larger gears are stamped with their teeth ("64", "66") there are no ML... numbers.

DavidThomasLathe 1.jpg (300.94 KiB) Viewed 8251 times

DavidThomasLathe gears.jpg (264 KiB) Viewed 8251 times

DenfordTDS metric gears back.jpg (245.41 KiB) Viewed 8251 times

DenfordTDS metric gears front.jpg (364.37 KiB) Viewed 8251 times

DenfordTDS metric gears side.jpg (221.92 KiB) Viewed 8251 times

[Andy B]

I was wrong, and assumed incorrectly!
Apologies for any confusion caused.

Your pictures prompted me to look closer into some of the files that Admin sent me recently, and there I found drawing ML115-903 which shows a quadrant like yours. The pitch between final idler and gearbox shaft is shown as 4.125", which is right for a 66t gear pair at 16DP.
The geartrain schematic (ML115-900B) states that the end drive gears are 16DP also.

These dimensions tie up with the pitch on the quadrant for the 280 lathes - I had never actually measured my gears but will certainly do so this evening (edit note - I checked and they are 16DP). I had only ever looked for the drawings for the conversion gears for my lathe, which are all shown as 18DP. So I assumed (incorrectly, as it turns out ) that standard and conversion gears were the same pitch.

The drawings for a non-gearbox lathe are definitely 18DP for all versions.

So it does now appear that:
'Standard' end drive gears for gearbox lathes are 16 DP
'Conversion' gears for gearbox machines and all idler / drive gears for non-gearbox lathes are 18DP
Tumbler reverse gears are 20DP.

I'll add this info into the thread on conversion gears.

[Andy B]

If I've understood this correctly, a metric lathe needs the following to cut imperial threads:
: ML105 129 54-tooth stud gear (9/16" bore) (and Thank you Andy, yes I have found the drawing of this)
: the quadrant, stud bolt etc which I think I have
: ML114 9 127/135 compound (9/16" bore, and thank you again for the drawing)
: ML114 10 -- a 48-tooth gear with a 1" bore to mount on the gear-box spindle.

You'll also want 48T, 49T & 52T stud gears to cut the whole range available between 4 & 28 TPI.