Leadscrew repair by reversing

I am in the middle of some renovation and upgrades on one of my lathes, it is a Raglan Little John fitted with the QCGB.

As ever, one thing leads to another and after starting out with a new motor mounting (the old Gryphon was past its best days ) I have upgraded the cross slide to a home made 'long' one, which is interchangeable with a 'short' one when using the taper turning attachment (required a telescopic cross slide leadscrew! ) and making a new QCTP as a clone of the Dickson but better suited to the cross / compound slide heights.

Any way - eventually with all this going on, I decided to delve into the apron to overall the internals - the leadscrew engagement had been playing up for some time and there was no surprise to find the half nuts full of compacted swarf and old grease, plus the power feed mechanism was on its last legs. The power feed system takes a drive off a keywayed gear which slides along the separate power shaft and this then is turn drives, via another gear a compounded10 DP worm which drives either the saddle or cross slide depending on engagement to left or right.

This lead me to then look at the leadscrew itself (and the point of the thread ), I realised the area just short of the headstock was pretty well 'rounded' (hardly surprising given the gunge in the half nuts! ) - So looking in my spares cabinet I came out with a spare (but used ) leadscrew. Looking at this over a cuppa I realised that it was possible that the shaft could be reversed 'end on end', with a little machining the one end could form the rear end and a new front end could be machined, bored and slid over the old rear end - Loctited and pinned to form the front end. The reasoning is the leadscrew has never seen a set of half nut at the far end in the best part of 50+ years! Has anyone ever successfully done this sort of renovation? If so, is there anything awry with my proposal?

Keep safe, Martin

Thats exactly what I would have done, you have to be prepared to think outside the box with these old machines. What are you going to do about the nuts?

After dunking the nuts in white spirit to loosen the gunge they cleaned up reasonably well, seems the lack of engagement has protected the root of the threads in the nuts. Think it is necessary to point out here to non Raglan owners or past owners, that the half nuts are an interesting experiment in Mazak casting. A replacement for all the parts is being considered, either fabricated or also potentially a 'lost wax casting' in bronze. Seems like a good area to use a 3D printer!!

The engagement cam has broken out so that is being replicated in bronze pinned to a steel shaft, the half nut holder (a square 'box' with T slots which locates the half nuts, could be made in bronze and the nuts again could be fabricated by bronze brazed to a steel plate base.

What surprised me was the wear in the 10 DP worm gear in the power engagement box, the bronze gear had shortened by about 0.15" . Here are some photos of the upgrade work:-

Welded repair to a 'new' power traverse bracket - this bracket had not seen much use but the detent plunger housing was snapped off - Farmer Hedley worked his magic with the electric glue!

The 'new' bracket with the power shaft keywayed gear and new 10 DP worm wheel assembled - original worm wheel at right

Original power shaft traverse bracket showing extent of wear on the thrust face of the bracket along with the original 10 DP worm wheel - this will go back into the 'stores' for renovation at a later date - I never throw anything away!

Half nut assembly after cleaning - enough thread left for the time being but new half nuts need to be made.

Saddle carriage rack pinion - upper unit repaired with a new bronze gear - pinned to the original shaft. Lower one showing teeth damage. I have a new rack to fit to the machine.

My 'long' X slide modification - compare the thickness of the deck with the photo below of a commercially available 'long' cross slide. This X slide is replaced by a 'short' version when utilising the taper turning attachment. The TTA is a story in itself as it was purchased from Myfords many years ago as a part of a collection of unmachined castings for Raglan LJ's they had left over from their take over of Raglan Engineering (1954) Ltd,.

Finally my home made Dickson 'clone' toolpost. Made to suit the tool height of the Little John as it falls between the 'normal' offerings from Bison and others. I made it 2 station as on my Bison model I never found a use for the third station.

View of the second tool station.

or thread away from the chuck in reverse if you can, that should use the unworn flank at least if not the unworn end..

A very ancient engineer used to turn towards the tailstock on critical jobs on an even more ancient lathe as he said the accuracy was better.

regards Martin

Smart & Brown made reversible lead screws.

Martin C

Which Smart & Brown models had reversible leadscrews? The model A, infortunately does not have one.

Model M Mk2. I was careful to word the other statement vaguely as I suspected it did not apply to all lathes by Smart & Brown but did not want to spend time searching all possibilities.

Martin C

Martin,

I expect half nuts are still readily available from the US (Atlas 10&rdquo. They were either a direct copy or (more likely) bought in directly from the US.

I doubt the lead screw is particularly worn - it was only needed in operation while thread cutting. It should have worn away the mazak half nuts a few times over before showing any wear, as well. The half nuts do not look as though they are totally worn - they were only die cast, so likely never had the full ACME profile. I’m confident they woul last a long time after proper adjustment...

The rack and pinion area is a common failure point - a weak part of the apron/machine and beefed up on the 5”. Often exacerbated by operators using the rack as a shaper to cut slots and/or key ways.

I expect (but not sure) the rack is reversible? But it depends on how close to perfect you are doing the renovation - and if you have a good one available, why not change it.

A three phase motor with VFD makes a good improvement to the operation, over a fixed speed motor (the single phase ones, in particular). I rarely alter the variable speed drive on the lathe.

Is this a ‘user’ lathe or a standby? Far better, if in reasonable fettle, than most chinese offerings - especially in the price range.

NDIY,

I think the half nuts are good for now - but I'm always looking to pre-empt any 'crisis' and make parts to stock up with. I will investigate the possibility of obtaining some Atlas half nuts through contacts in the States, thanks for the tip!

The lathe is a definite 'user' - its currently fitted with the Capstan Turret and has been belting out some special shoulder screws for a 1930's early tractor drawn plough (amazing mechanical depth setting system designed prior to the adoption of rear linkage hydraulics on late 1940's tractors). It's also the machine I use with the taper turning attachment when I need some taper pins (usually 'big 'uns' ). My other Raglan LJ ( a change gear model ) has the same Siemens motor but is constrained by the length of the motor (with original TEC) when using the TTA or any work close to the chuck with the long X slide.

The motor was the original Gryphon 3 Phz which has always been driven off an inverter (originally a Jaguar Cub - but now a Tianan, otherwise sold as Westinghouse) - I've fitted a Siemens 1kW motor which is appreciably longer than the Gryphon. As it is an 'enclosed fan' I have ditched the fan off the end and shortened the shaft - at the other end I reduced the diameter of the shaft from 20mm to 5/8th to suit the Raglan pulley system. The motor cooling is now feed from a remote motor and blower (single phase Parvalux FHP motor and centrifugal blower actuated by a relay driven by a temperature sensor mounted on the motor ) which will discharge over the motor from the original fan end but with a more compact arrangement.

The rack will be replaced as the teeth have been 'strained' by the damaged pinion, due I think to people running the saddle too far forward and managing to disengage the pinion from the rack then pushing the saddle back and crunching the teeth. I have a 2 metre length of 16DP rack in stock, I have cut a suitable length off this and drilled it accordingly using the original as the drill template.

I also have two brand new bed shears which I bought from Myfords when they were having a clear out of their old Raglan stocks. This was at the time when I also bought the pile of unmachined LJ castings, in which I recognised several sets of TTA castings, several large diameter fixed steadies, travelling steadies, and the odd tailstock, and compound slide castings.

I really like the Raglan as I found it is an excellent machine and easy to work with. I kept looking for a later 5" but never could bare to sell one of my two stalwarts! But I did finish up with an Emco Maximat Super 11 - an ex school item, barely used, for £150 after being told it was to be scrapped out. The idiotic point of this was that the school initially demanded that it had to be scrapped, as if it was sold to a private individual and they subsequently injured themselves the school feared they would be culpable and liable for damages. I had to produce my Apprenticeship indentures to prove 'I was technically qualified' to assure them I was capable of using the lathe.

Edited By Oily Rag on 12/11/2020 14:50:01