Reconditioning a Relmac lathe

[Lee Roberts]

lol, good job on the bargins £2.50 ! Any chance of some pics of your progress and also you doing your bearings !?!

[irving2008]

lol, good job on the bargins £2.50 ! Any chance of some pics of your progress and also you doing your bearings !?!

Oh I plan to do a complete record of this... failures and all (I expect to have to pour this more than once!)

I've worked out how to locate the spindle correctly for both front and rear bearings and I'll do the front one first, using the rear bearing and tailstock as guides, then before removing it I shall fabricate a locating bracket that can be bolted to the rear banjo to retain the rear of the spindle in correct alignment to the front bearing once the rear bearing is removed. I'll cut this out rather than melt it out to avoid potentially moving the locator (melting it out will require me to put the lathe on its end somehow to catch the melt without it going everywhere) but might use the torch to soften it...

Weather permitting (this has to be done outside and can't be done in the rain, water droplets and molten metal don't mix!) I hope to do the front bearing this weekend...

[Lee Roberts]

...rear banjo to retain the rear of...

Banjo ? is that the same as a Dodar? or a real name for a part?

[irving2008]

Banjo ? is that the same as a Dodar? or a real name for a part?

Its a real name... old English lathe terminology for the moveable slotted bracket that supports intermediate changewheels for screwcutting as it comprises a large circular boss attached to a long narrow slotted arm. Also known as the 'changewheel quadrant', particularly if it has multiple radial slots.

[Lee Roberts]

Ahh right, thanks for showing us that.

I have also added this post to the FAQ Section: What is a Banjo

[irving2008]

So - todays plan was to get up to the point where I was ready to pour the bearing...

That mean preparing the spindle, locating it in the housing and sealing the bearing ends... so here's how I got on..

Firstly I needed to polish up the spindle on my improvised polishing jig (see post #5 above)

I used wet n dry, kept wet initially and grades down to 600 which is pretty fine. I wrapped the paper round an 8" length of 1/4" x 2" steel flat which made it an easy 2-handed operation.

Here's the before and after, after 30min or so of polishing...





I then turned my attention to the bearing housing and degreased that, wirebrushed it, and now it looks like...

[irving2008]

Now it was time to do trial fit of everything. I planned to locate the spindle using a MT3 taper and the tailstock in which I placed an MT1-JT6 arbor that was already centre-drilled. This worked well...



The clingfilm is just to keep everything clean until I'm ready..

A quick DTI of the spindle showed 0.005mm runout which is fine!

I then experimented with shimming for the pinch-bolt. I've decided that I should shim it with about 30thou then the bearing will be tight enough to allow the pinchbolt to compensate for wear over a wide range. Not having shims to hand I found that 9 folds of heavy-duty roasting foil from the kitchen gave 32thou so I used that. Here you can see it being trialled...




Now we are ready to prepare for pouring the bearing.

Firstly, coat the journal in soot... this is, apparently, one of several ways of preventing the hot metal sticking to the steel shaft and making it easier to remove - we'll see later if that is true :) A candle provides the soot...

[irving2008]

Now I refitted the spindle into the headstock (it took a couple of attempts to do this without scratching the carbon coating on the journal) and locked everything down.

Now all that is needed is to seal everything with fire-cement. Now i don't know if the proper putty, Babbit-rite, is firmer than the fire-cement I got from B&Q but I just couldn't find a way to stop it getting into the bearing. Eventually i decided to create a 'shield' from ally foil folded 3 times and cut into a ring...



and then cemented up. Same for the rear of the bearing...



and finally we are ready to pour metal, once the fire-cement has dried overnight

[irving2008]

Is the backgear on an eccentric and driven by a flat belt with a locking pin(flathead screw) to engage half speed? I thought I saw the locking "pin" in your second picture, I had a machine of this "ilk" 15yrs ago and sold it to a grasstracker 4 years ago and learned to speak Mandarin (bought a Chinese lathe) Why would reducing the OD of the shaft and then fitting "sized" bearings increase any other clearance between gears? I could understand if it were a case of replacing central bearings with offset bearings....I'm confused help me out.

It wouldn't... what I said was that if I ground the spindle down I'd have to bush the bullgear and the pulleys and the backgear pinion as they all run on the spindle. I couldn't just grind down the journals as then the centre of the shaft wouldn't pass through the bearings.

And yes the backgear is exactly like that, except the ratio is 6.67:1!

Can't comment on the Chinese as never owned one, but from what I've seen and read give me some serious old iron any day :)

[Lee Roberts]

So am i right in thinking you will mould around the fire cement or ?