Changewheel set up

[yorkie_chris]

So on with the very steady improvement of my old denham lathe, it uses changewheels for screwcutting. I've got some of the wheels but not the full set.

At the moment it's a bit of a bodgerama, I didn't get any sort of shaft or anything to hold the gears on the segment arm.

The gears have a 3/4" bore with keyway, the slot on the segment arm is 5/8".


Can anyone recommend a clever solution for this? I haven't seen any old lathes with this setup to copy but there must be plenty on here.

[awemawson]

So you need to turn up a short stub, with a  5/8 diameter and 5/8 thread at one end, a plain 3/4" section at the other with probably a reduced diameter part on the end threaded 5/8". The stub is retained onto the quadrant with a 5/8 nut on the 'far' side of the quadrant, the gear slips onto the 3/4 plain section, with a fat washer followed by a 5/8" nut.

You will also probably want to make up one with a double length 3/4 plain section for pairs of gears pinned together, though sometimes a sleeve is used with a keyway to fix two gears together

[DavidA]

I've just done the same thing with my lathe after getting a gear set that had different bore diameters.
It's just a matter of turning up a set of adapters.

Very satisfying when it is all done.

Dave.

[yorkie_chris]

Do you just run the gears on plain steel journals or make a brass sleeve?

Do you drill the gears on a common PCD to dowel/bolt them together when running a pair and not use the keyway?

[Pete.]

If you turn up a stub at 3/4" diameter with a 5/8" or smaller thread on the end then file or mill flats in the 3/4" bit so it fits in the 5/8" quadrant slot you won't have trouble holding it when tightening the nut that will hold the stub to the quadrant or the retaining nuts for the changegears.

[DavidA]

Being cast iron my gears are happy to run on the steel shafts.

Dave

[hopefuldave]

Yorkie Chris wrote:

Do you just run the gears on plain steel journals or make a brass sleeve?

-------------

Mine has just the one cast-iron stud gear, but it's on a keyed steel carrier sleeve[1] that runs on a pair of caged needle-rollers...

First time I took it apart I thought "Ooh, POSH!" and then "Oh..."[2]

Dave H. (the other one)

[1] To allow for compound gear pairs *if required*
[2] Cos the stud shaft was in a right state!

[DavidA]

Where the gears are just running as idlers I let them run straight on the steel shafts.
Where they are keyed I have made a couple of split 'shells' that fit the shafts and slip past the keys. I filed a matching keyway into the gear to alllow it to drive.

I will have to make up some further spacers to get some sort of standardisation. But for the threads I need at the moment it works well.

Dave.

[Raggle]

An alternative to keyways is to pin the gears



These are a bit smaller and from my Exe 2-1/2" lathe. They are 18DP with a 7/16" bore. The pin is press fitted into the gear and engages with a clearance hole in the gear it is coupled to.

A similar system was used on Drummond lathes I believe.

Ray

[awemawson]

An alternative to keyways is to pin the gears



These are a bit smaller and from my Exe 2-1/2" lathe. They are 18DP with a 7/16" bore. The pin is press fitted into the gear and engages with a clearance hole in the gear it is coupled to.

A similar system was used on Drummond lathes I believe.

Ray

Infact rather like the suggestion in the first reply 

[DavidA]

Pinning them together face-to-face is fine,  my gearset came with such an arrangment.  But won't you still have to key them to the leadscrew on occasion ?

Dave.

[yorkie_chris]

The output from the headstock and input to the screwcutting/power feed gearbox are both keyed.

[Pete.]

Just make a keyed blank gear with pin-holes so you can chop and change the gears on those shafts as you like.