Reconditioning a Relmac lathe

[irving2008]

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

The fire-cement is just to seal the holes to retain the metal inside.

Well I tried a pour ths morning - not very successful :(



- couldn't get enough heat into the pan (maybe its a bit big for small amount, but the burner is only 1kW as well), so it starts solidifying as soon as I start to pour
- you're supposed to scrape the 'slag' off the top, but its hard to tell whats slag and what isn't... it doesn't seem to scrape
- you're supposed to heat up the bearing housing/shaft to about 100deg to help the flow, but I found it hard with a blowtorch to get any heat in there...
- I carefully forgot to leave any air holes in the seal. As a result after about a third of the metal went in the pouring hole solidified and clogged up and that was it... no more pour! I need to leave a way for the air to get out at the top of one of the dams



So need to find a larger gas ring and a smaller ladle.

Next job is to clean it all up so i can start again... :( going to try removing the rear dam and melting it out...

[Lee Roberts]

Ok mate sorry it didnt work out so well, keep going tho you will sort it i'm sure...

Dinner time, SUNDAY ROAST !

[irving2008]

Removing the remains of the 1st attempt was easy - didnt even have to melt it out as there was hardly anything in there, but what was there showed promise - nice n shiney and clean surfaces



So cleaned it all up and re-assembled with a blowhole this time and left it out in the hot sun for 4 hours while I popped down to Argos for a better burner - the new one is 2300W and a much wider burner so it melts the metal in about 6 minutes against 18 or so before.. so much hotter (and you can buy the canisters for it too!)

So the fire-cement appeared to be set, it was rock hard and the whole lathe was hot to the touch from being sitting in 26degC sunshine for 4 hours so thought I'd try again...





As you can see, not a great success

Two mistakes... firstly my impatience, I assumed it had set but clearly was only on the surface and not right through - it needs that 24h or so... and secondly, I made the end dams not from ally foil but from pieces cut from an ally foil dish 'cos its thicker and easier to handle. But to get it round the shaft I cut fringes and bent them over. Big mistake, because it prevented the fire-cement sealing to the shaft properly. As a result when the pressure built up the fringes lifted and allowed the hot metal to spurt as you can see - it was quite a loud bang and fortunately I was standing on the other end... The third pic shows the 'hole' where the pressure built up, probably due to water vapour from the fire-cement. the air blow hole worked ok till it blocked up tho :)

[irving2008]

So we live and learn...

I now had 3/4 of a bearing, but obviously needed to do it again (but hey, I expected this)

Next problem was to get the spindle out to clean up again... now I had a full circle of bearing metal I encountered another problem... the centre section of the spindle is about 2thou bigger than the journals. The soot 'release agent' worked fine, I could turn the spindle OK although it was tight, but I couldnt extract it. It took some serious work with a rubber hammer to get it out. Whether this would damage the bearing surface is hard to say, the pics suggest not (see below).

Next time I might try the oiled paper suggestion instead of soot as this will give more clearance. Also this time I didn't put the foil shim right through to the journal as the first time it seemed to act as dam, but if I did it might allow the bearing to ease when the pinch bolt is undone. Trouble is all the examples I have found on the web are for fully split bearings not side split like these so I don't have any information on this.

Here is a pic of the bearing surface, sooty but smooth, before I chopped it all out again :(.



Here is the bit that goes into the keyway.. a nice impression and shiney too :)




I am wondering whether to put the lathe on end and try pouring into an open well rather than use the pouring hole (if indeed that what it is). It would certainly be less likely to fail. Or maybe I need multiple airholes in both dams that would 'plug' as the level rises so improving the 'venting'. Clearly this is going to take more than a couple of goes

Oh well... lets hope the weather is good next weekend!

[Lee Roberts]

Wow, you’re not wrong. I tried having dinner alfresco today with the family but it was just too hot I couldn’t stand it.

I’ve just done a wiki on “white metal” so now I understand what it is a bit better, now I know you’re going down the route your going down because you are enjoying what you’re doing and so on but would the bronze bushings not offer a better service to you in this situation and get your build along a bit faster? Or is this not a time sensitive build and your happy to take your time with it?

No offense meant and I’m not trying to just sell you some bronze bushing as it doesn’t matter to me, I’m just trying to understand if you’re giving yourself more problems than it is worth.

Now I’m also thinking maybe you just want to restore this machine back to how it was originally, if that’s the case then fair-play to that mate. Hopefully next weekend and the rest of the week to come are nice so we can all get lots done!

I think you could be right about turning the whole thing on end though then pouring. Does this mean we’re going to have to wait till next weekend for an update? Cheers, Lee

[irving2008]

Lee,

No offence. But there is a good mechanical reason why I want to use the right material... when the oiling fails in a Babbitted bearing its the Babbit that wears. When it fails in a bronze bearing its the spindle that gets chewed up... now I know thats unlikely while its running, but lathes are very stop-start and have long gaps between usage where there is the possibility that the oilways dry out. A Babbitted bearing will survive better under those situations.

And there's something about making like the original. While I plan some mods to this lathe, like an adjustable top-slide, nothing will be done that can't be returned to the original.

And time is not a huge criteria (not sure that a bronze bushing will be any quicker, I'd still need to find someone to grind down the spindle and machine the bushings).

[Robin Hewitt]

If you want to get it hot you will need to lag it :D

Silly question... Are you faffing about casting because you don't have another lathe to cut the new bushing on? Do you need help?

[Robin Hewitt]

If you want to get it hot you will need to lag it :D

Silly question... Are you faffing about casting because you don't have another lathe to cut the new bushing on? Do you need help?

[irving2008]

If you want to get it hot you will need to lag it :D

Silly question... Are you faffing about casting because you don't have another lathe to cut the new bushing on? Do you need help?

Robin,

Well I wouldnt call it 'faffing' as such... there is an element of learning a new skill here too :) but you are correct in that currently I dont have access to another (working) lathe.

Even if I did, I don't entirely see how to create a bronze bushing as the spindle is offset in the casting. It would need to be turned down from a solid 1.75" round and bored out to 1.25" approximately 3/16" offcentre. But then the castings would need to be line bored to ensure they are concentric and parallel with the bed as the advantage of a poured bearing is that it isn't dependent on the alignment of the external casting as long as the spindle is in line. Thats not true of the bronze bearing.

Irving...

[Lee Roberts]

when the oiling fails in a Babbitted bearing its the Babbit that wears. When it fails in a bronze bearing its the spindle that gets chewed up... now I know thats unlikely while its running, but lathes are very stop-start and have long gaps between usage where there is the possibility that the oilways dry out. A Babbitted bearing will survive better under those situations.

And time is not a huge criteria (not sure that a bronze bushing will be any quicker, I'd still need to find someone to grind down the spindle and machine the bushings).

Ok thanks for teaching me somthing today!, i see the bronze bushings are not really an option then.