I've been turying to turn down a part in aluminium today and have
found a somewhat serious issue with my C3 lathe.
With the saddle locked to the leadscrew, the simple act of turning the
handle on the cross-slide moves the tool closer to or further from the
workpiece, resulting in a ridged finish on the face of the work.
This is confirmed by moving the saddle hand wheel - it's possible to
see the wole saddle moving on the bed.
I can't see any way to adjust the clamping system to improve the
Is this a known problem with lathes at this end of the market ?
The lathe was purchased including the strip down and set up service
from ArcEuroTrade, so I have no reason to believe that the initial
setup wasn't precise.
isn't it supposed to do that?
resulting in a ridged finish on the face of the work.
probably - locking the saddle with the leadscrew is a bad idea though,
you want a proper saddle lock which locks to the bed, not the leadscrew.
There are lots of home-made ones on the 'net, or if you can't find
anything suitable I can post a picture of mine - made with one nut and
bolt and a bit of scrap.
-- Peter Fairbrother
From my interpretation of the C3 construction, vertical play will affect
lateral play. If it doesn't, the saddle lower surface would need
re-scraping/re-machining. I'm assuming that the saddle actually locates on the
dovetails, not on the top, flat, surface of the bed.
I'll have to take my magnifying glass to the leamington show and crawl all
over one of Ketan's examples:-)
Some mini lathes have a tapped hole in the front end of the saddle, at
the middle. That's what I first used in my Conquest. It's meant for a
travelling steady. Perhaps not as good as a hole at the back, eg
but it can be used without any modification to the lathe.
BTW, that's the best type of carriage lock, by *far*. Don't bother with
any type which doesn't jam the carriage down on the ways, and which
doesn't do the jamming from in the middle of the ways.
If you have a H-shaped carriage (I think these are pretty rare in the UK
tho') you may need to add a bit of metal in the gap of the H,
If you decide to drill and tap, it's not hard to do - the cast iron is
nice and easy to work with. Just use some method to get the hole and the
tap vertical. M6 is about right.
-- Peter Fairbrother
Yes, the carriage locates on the V at the front and the flat bit at the
back. The rest - eg the flat bit at the front - shouldn't touch the
The OP's problem however is that he is using the half nuts and the
leadscrew to lock the carriage, and there is just too much lateral
backlash and general slop for that to ever work well.
It's a design lack of the minilathe, and probably the first and/or most
important mod most people do is to fit a carriage lock (the next most
important one is a lever-action tailstock).
IMO you cannot face properly on the minilathe unless you fit a carriage
There will be some vertical play in the carriage, and it may well affect
lateral play, and also twist - but there won't be nearly as much play
from that as from the slop in the halfnuts/leadscrew, and a good
carriage lock which will jam the carriage onto the ways will stop both
(the play and the slop) dead.
You can get the vertical play down to almost zero for when the carriage
lock isn't in use, but it's quite a job - the bits which hold the
carriage down need to be shimmed (from the factory they have
pushme-pullyou bolt systems which do not work well and need to be
replaced by shims) and while you are at it you need to work on the
bottom outside edges of the ways - scraping or the like - as well.
As I say, it's quite a big job. Good for normal use, but not absolutely
necessary if you have a good carriage lock (unless you are doing a CNC
A good carriage lock, on the other hand, is IMO essential.
-- Peter Fairbrother
Whilst this will make it more rigid, there is play in the lead screw so
this will not stop some sideways movement as you observe. You also need to
lock the saddle onto the ways. The simplest is to just use an engineers
clamp with the edge of the lower jaw under the ways and the top jaw
clamping onto the saddle. If like me you have the older H shaped type of
saddle with a cut out you will need to span the cut out with a piece of
metal - I've even used an Allen key which was to hand. In the long run the
best thing is to make a simple clamp that fits onto your saddle, I
designed my own although there are various designs available eg on the
Yahoogroups for the minilathe or 12x7 and 14x7 lathe.
Originally I was going to drill and tap an M6 hole near the back of the
saddle and use an Allen screw tipped with a piece of brass so as not to
mark the ways srewed down onto the ways. Although this is the method that
is found on the college lathes which are much more rugged on a lighter
lathe it will raise the saddle so is not a sensible thing to do.
As others have said, you can add a saddle lock but in the mean time you can
improve things a bit by applying some pressure to the saddle hand wheel with
the half nuts closed while making your cut. It is not ideal but better than