Reconditioning a Relmac lathe

[irving2008]

Hi all (is anybody is here... do I hear an echo...)

Anyway, thought I'd use this location as a sometime record of reconditioning a Relmac lathe. Bought for a song a few weeks ago (oops, that should have been a clue) it seemed fine. It lacked a chuck but had a suitable faceplate for a 3.5" one and I had one for another lathe I am recondtioning (eventually, but thats another story) so just had to drill the mounting holes. Also lacked a toolholder but a economy QTC holder, a bit of 1/4 plate and a T-bolt from Chronos sorted that Got it all bolted down in its new home on a specially constructed welded angle iron bench but an inability to turn things in a round fashion and a nasty vibration suggested all was not right... see the next post for the story...

Here's how it looked when I got it:


And heres the install with nice new drip-feed oilers from Adams Lubetech


The list of things to do grows daily

• Polish the spindle

• Remove the inside burr on the spindle rear end

• Replace main bearings

• Fit 3 speed v-pulleys insted of the 2 speed flat pulleys (maybe)

• Sort out backlash on cross feed (nasty 0.4mm 'jump')

• Sort out backlash on leadscrew (less critical)

• Figure out how leadscrew dog clutch should work and sort out

[irving2008]

This post was copied from the Antique machines forum on http://www.practicalmachinist.com where I am getting a lot of help from some very knowledgeable guys

Well I went back and did some more measurements, tests, etc. and convinced myself that the spindle wasn't bent. I DTI'd the inside of the spindle and discovered a lump which I previously hadn't noticed when I cleaned it up. Took some removing but eventually it was gone. Retried the taper and the runout was now a much more reasonable 0.04mm (2 thou) average (rotating the taper in the spindle), max .06mm, min 0.02mm. DTI'd the inside of the spindle and got .03mm (1.2thou) runout.

So then went back to the issue of the eccentric cut. Set it all up again, tried bar test for bearing movement and put more effort into it and was getting .2mm (8 thou) movement lifting vertically, but .4mm (16 thou) pressing down. I also discovered 0.4mm end play on the cross-slide (at certain positions of the handle you can physically move the slide - with a clunk!) that will have to be dealt with as well but still felt the problem was in the bearing.

Decided to take the plunge and get the shaft out. In the end it came out surprisingly easily... here are some pics of what I found...




can you see whats wrong yet :roll:

[irving2008]

I think I know whats happened... the bullgear is keyed onto the spindle but to get the shaft out you have to turn it so that the mark on the spindle lines up with a mark on the headstock casting, that puts the key at the 3-o-clock position looking into the headstock allowing it to move through the bearing (you can see it out of focus on the left in 1st pic). If you don't line it up and try bashing it out with the bullwheel at the 'normal' position (i.e. the locking pin at 12-o-clock) the key tries to cut through the bearing - hence the partial slot at the 6-o-clock position in the 2nd pic. Sometime in the past someone has tried to remove the spindle and gave up, smashing the bearing in the process... this also probably explains why the back end of the spindle is burred over and wont admit a 3/4" bar (fortunately the thread for the changewheel retainer doesnt run right to the end).

Here are the spindle journals...

Front


Rear

[irving2008]

I think these need regrinding (I would if this was a car crankshaft, but maybe a lathe is different), at least the front one does, its well pitted.

Here's a view of the broken up bearing , note the small pieces of my carefully tapped oiler hole :(, the bearing material went right up through the headstock casting. Does this suggest they might have been poured in situ??



and a view of the headstock with front bearing removed. Is that an oil well in the bottom? If so I dont see how it works as theres no hole in the bearing and it wasn't full of oil. Also I notice the bearing is offset in the headstock - there's considerably more metal to the right where the pinch bolt is than to the left. I have no idea how to specify this or replace it...



Finally, the rear bearing. Its intact, but do I need to replace this? Its a bit scored but otherwise doesn't look too bad.



The last pic shows clearly how offset these bearings are... would these have been manufactured/bored in place? How would I go about specifying or making new ones? have I bitten off more than I can chew? All answers gratefully received...

[irving2008]

Wel I've decided to pour new bearings and have read up all about it in various places and I am now collecting what I'll need. I have some white metal bearing alloy coming, as well as a ladle and some fire-cement. Watch this space :)

I've rigged up a temporary arrangement to polish the spindle as a precursor to pouring the new bearings



After a few minutes with 80, 120, 150 and 360 grade abrasives it looks like this for the front journal



compared to


Clearly some way to go but improving...

my concern is whether I can take too much off this way? Currently the spindle is 31.62mm - 31.72mm dia (about 4 thou variation) and there are some noticable hills and valleys on the front jounal through wear. Where the bullwheel sits, just inboard of the front bearing is where is measures 31.72mm as this would have had the least wear (nothing turning at that point). Nominally its a 1.25" - 31.75mm - shaft. The rear journal and where the backgeared pulley runs are about 31.68mm. If i don't even it all out this means that the front bearing must be able to open up to 31.72mm+ from 31.62mm to allow the spindle out. My theory is that if I don't shim the front bearing and lock it down when I pour it then 0.15mm - 0.2mm shims will give suitable clearance on the bearing and they will open up to maybe 0.5mm overall which will give clearance to remove the spindle in the future.

Should I just aim to get the worst of the scoring out (that pitting is quite deep), or should I aim for a mirror finish?

Is wet n dry the right way to go, or should I be using something more esoteric like an abrasive paste (in which case with what and how do I apply it?)

[irving2008]

Hi, If you're pouring new bearings why not have the shaft reground and re hardened for a few quid? Failing that I'd try and make sure there were no high spots rather than using w&d to gain the appearance of smooth/round/ground etc.

Are you going to use the lathe or is it ornamental?

Hi Kip, Oh definitely for use... got several projects planned... including the restoration of two other lathes...

My original thought was to get it reground but was advised by others with greater knowledge that this wasn't a good idea as it would increase the play in the bearing surfaces for the pulleys and back- and bull-gears which could introduce chatter... and that a good polish was sufficient with white metal bearings as long as they were well scraped after... a regrind would take at least 10thou off and this would mean the pulleys running with the backgear would have >15thou bearing clearance which is not good for a oiled bronze bearing IMHO

[Lee Roberts]

Log is looking good keep it up, also if you have a look at the link below we do have Bronze bushings for sale and can source alot of diffrent sizes.

If you wanted to take it down more i could have a look for you and see if we can get the right size bushings to fit.

Link: Bronze Bearings
http://stores.ebay.co.uk/MYCNCUK_Oil...QQftidZ2QQtZkm

[irving2008]

Log is looking good keep it up, also if you have a look at the link below we do have Bronze bushings for sale and can source alot of diffrent sizes.

If you wanted to take it down more i could have a look for you and see if we can get the right size bushings to fit.

Link: Bronze Bearings
http://stores.ebay.co.uk/MYCNCUK_Oil...QQftidZ2QQtZkm

Well the spindle is 31.75mm OD, 22mm ID so I'd not want to take it down below 30mm OD, which means I'd need to bush the 2 main bearings plus the bullgear plus the small backgear and pulleys so I'd need 4 bushes about 60mm long approx, 30mm ID, 31.75mm OD. To be honest I'd only bush it if the shaft was so bad that it was impossible to get a reasonable life out of white metal bearings, but given its likely workload I think thats a whole lot of pain I dont need right now. Also might be just as cheap to get a new spindle manufactured from 32mm OD, 20mmID stock...

[Lee Roberts]

Ok well ill bookmark this log and keep an eye on you.

[irving2008]

How will that help?

Anyway, today I picked up a kilo of V1-A best bearing alloy from GWN, a family owned business who were happy to do a small quantity 'cash in hand'. Also today I picked up a 1.5hp 3-phase motor won yesterday on eBay. Chatting to its previous owner (a Myford owner BTW) mentioned I was planning to pour a bearing but was having problems finding a suitable melting ladle. To my surprise he rummaged in his garage and produced an old but servicable 6" dia leading pot with a spout and wooden handle, ideal for the job, so that changed hands for a further £2.50!