"Gearing of Lathes for Screwcutting"

Re-reading Brian Wood's book prompted me to make two small modifications to the Super 7B quadrant designed to make changing the mandrel gear wheel for metric screwcutting a tool-free operation.

As standard, the gear is retained by a hex head screw cum oil nipple which needs the (gentle) use of a spanner and in order to lower the quadrant out of engagement a 3/8" BSF nut has also to be loosened. I have substituted a knurled nut for the screw which is wide enough to give adequate grip and to contain a standard 2BA oil nipple. For the nut, I have adapted an adjustable handle which allows enough rotation to slacken and tighten the quadrant (further projection would have allowed complete turns of the nut/handle but this would then have fouled the cover when closed).

In his book Brian describes a replacement for the somewhat inaccessible clamp screw behind the wide input gear to the gearbox. I haven't yet tried this as I find that, carefully adjusted with a shortened hex wrench, the clamp screw can be set so as not to need turning when the quadrant is moved to install an alternative mandrel gear.

In the photo the 34T is in place and thus far I haven't needed larger gears or the drop arm also shown in the book. I am, however, still looking for the elusive 21T gear!

I have Brian’s book and have read quite a bit of it, mostly the section relating to the Holbrook B8 as I have owned one of these lathes for the past fifty years. I must admit that I have only flicked through the Myford chapters but seeing your mods I must go and give these chapters more attention. I will certainly be copying your kipp handle modification.

Baz:

If I had a B8 I would certainly have hung on to it, too! Is yours the "polished oak cabinet" version?

Extending the Kipp-type handle was made easier by the fact that the standard spring-loaded nut is hex-shaped, rather than splined, so this just had to be replaced by a short hex milled on the end of the adapter. The hex sits in a bi-hex socket giving twelve adjustment positions.

EGA no mine is the cast iron base with the top planed flat, makes a fantastic surface plate! Apart from the two end plates every part of the base is a two man lift. She was moved around a bit due to house moves when I was a lot younger but has sat in the present workshop for the last 25 years, I shall never move her again, the next person will in all probability be the dealer who clears the workshop. I purchased her from a chap in Ware, in pieces for the princely sum of £176, he charged me £1 for a Jacobs drill chuck. All the lathe bits were bought home in the back of the old mans 850cc mini, a mate went back during the following week and collected all the base bits. According to the makers plate she was built in 1946 and sold to RAE Farnborough.

You are obviously cutting metric threads if you have the 34 tooth gear fitted so why the 21 tooth. By the way they are not that elusive.

I understand the 21 tooth is needed for 2BA threads. I have always cut this with a die but, if necessary, could use the regular metric quadrant.

I should be glad to be told where a 21 is on sale.

If you're stuck for a 21T I could cut you one for a token fee. I did a bunch of 33/34T gears a while back when they were not available.

ega,

You can cut a 2 BA thread using a 20 T driver with the gearbox set to 26 tpi

The pitch achieved will be 0.814 mm

Regards Brian

Aye up ega, I got Brian's book and have done the same as you regarding the tumbler reverse and it fit OK no problem oiling up either. I like your handle idea, as I have a spare one that is the next mod to do. I've made the two gears 33/34 and the 21 so all set up. Glad to have a workshop with the shut down. John

[Repeating so far as relevant my earlier replies to the above which seem to have disappeared; I expect I failed to press the Post button]

Brian Wood:

Thanks for the correction

john fletcher 1:

I'm with you on the therapeutic effect of having a workshop right now.

ega,

Home and Workshop Machinery list the 21T gear as in stock.

Regards,

Paul

Many thanks for the information.

Reviving this thread to show a small, self-explanatory refinement:

I think I first saw the idea of storing change gears inside the gear cover in a post by John Stevenson. Mine sit on small nylon "buttons" retained by 2BA csk screws. The only tool I now need to swap gears is a fag paper to set the clearance of the teeth (I plan to add somewhere here an extract from Roderick Jenkins' table of gear and gearbox settings for the 33 and 34T gears which are the ones I use most often).

ega,

A neat idea.

Brian

Nice work. The quick action lever on the quadrant clamp has upgraded your Super 7 to match the Drummond M-Type!

And Martin Cleeve's ML7!