David,

Not sure if "my cross slide moves at an angle away from the work" means that facing cuts tend to leave the surface concave or convex (the terms are used loosely, because the shapes involved are really conical) but I had a similar problem and measured the amount of dishing as shown here .

After making the test facing cut, a dial indicator mounted in the toolpost should show no deflection as it is run from the near side of the work to the centre, because it is following the same path as the tool took. But (assuming the facing cut has a bit of concavity/convexity) when the DI is run from the centre to the far side, its reading over that radius of the workpiece will represent double the amount by which its centre is up or down in relation to its circumference.

Dead flat would be perfect, but it is better to be cautious and aim for a bit of concavity rather than convexity. The latter would mean that a faced item would rock when placed on a flat surface, whereas a slighlty concave item wouldn't.

I didn't find this an easy fix….

Andy

Nobby, if the out of perpendicular cross-slide is a manufacturing fault, David can't true up a faceplate. Sort of chicken and egg situation.

Gray, if the owner of the mini-lathe you mention is who I think it is, he emailed me about it before saying that he was lucky enough to have put it in your capable hands. It would be good to see details of how you sorted it out.

Andy

Edited By Andyf on 12/05/2013 20:50:00

"Perpendicular" usually means the same as vertical, Nobby. But in geometry it means, to quote from my big (20+ volumes) OED, "Of a line or plane: having a direction at right angles to a given line, plane or surface." In my schooldays, when dinosaurs roamed the earth, we were taught how to use compasses to construct one line "perpendicular" to another. Verticality didn't come into it; the paper was flat on the desk.

Thus, I was meaning that the motion of David's cross slide was not perpendicular to his spindle axis, resulting in concave or convex facing cuts.

Andy

Hi Woody

It will help if you put a (tested straight) bar in the four jaw chuck, then firmly but no more tighten the bar in the chuck. It is very important not to over tighten and distort the bar.

Then rotate the chuck and bar testing against an indicator mounted on the cross slide or the lathe bed touching near the end of the bar, If the indicator measurement is not the same when the bar is rotated end for end lightly tap the bar until both ends have the same indication.

Once this is done you know that the face of the bar is at 90 degrees to the axis of the machine, and you have eliminated any error that may have been introduced by the chuck or face plate.

Then once set rotate the bar until it is horizontal, and move the cross slide with an indicator fitted touching the bar it in and out You be able to see any errors at any point along the bar.

It is accepted (By some) that if there is an error it should make the lathe face slightly concave. maybe .0002" over a foot but never convex.

Cheers
John

Hi David ,

(1) Lathe BED is primary reference .

Cross slide line of action needs to be at right angles to the lathe BED .

Spindle axis needs to be parallel to lathe BED .

Facing off true should then happen automatically on test . If it doesn't investigate further .

(2) If your lathe has rectangular bedway shears then a basic test of cross slide alignment can be done with a large engineers square . Put square to sit true on any shear and use cross slide to traverse dial gauge aginst it . Note readings . Change square to locate on other shear and repeat . For both tests have stock facing the same way on lathe – towards headstock both times or towards tailstock both times . Observation of both sets of readings will tell you exactly how far cross slide is out of alignment .

Usually worth doing test more than once on different bed locations .

If not convenient to run dial gauge against square directly then use an intermediate parallel .

A slightly more sophisticated version of same test will work with raised V ways but you need to make a square with a stock that will engage the V's true . Easiest to make this one more like a T square .

(3) If you just want to do the simple test you asked about in first posting then :

Do all nescessary checks to ensure spindle is parallel to bed first .

Fit any reasonable face plate and draw a diameter line across it .

Set diameter line horizontal and use cross slide to traverse dial gauge across complete diameter of faceplate (or as much as you can reach) . Note readings at several points in traverse ..

Rotate faceplate by 180 degrees and repeat test . Observation of the two sets of readings will tell you exactly how far out of alignment cross slide is . 

Drawing a graph is useful but not essential .

Optionally repeat with another randomly chosen diameter line .

(4) Cross slides and other slide actions can be not just out of line but crooked as well – its quite common for a cross slide to be properly aligned in one place and not in another . It's actually quite common for slides on worn machines to run in a very large radius curve rather than straight . Needs to be checked before doing any alignment tests .

There is as usual a lot more to this – ask any questions you like .

Regards ,

Michael Williams .

Edited By MICHAEL WILLIAMS on 13/05/2013 17:27:19

Hi Gray,
I think that is a very clever technique using very simple equipment. It only relies on the bar being a uniform diameter over its length to give accurate results.

Les.

I'm with John on that, and I would add it is better to disengage the leadscrew and push the slide by hand to feel the resistance. Hopefully the steel gib strip will wear faster than the cast iron slide so replacing the strips with new ones may offer some improvement, otherwise it will be necessary to get the parts re-ground. If you're in the habit of using a slide locking screw (which presses against the gib strip) then this is often a source of localised and uneven wear.

Thanks for showing, Gray. I bet the owner will be as pleased as punch.

Andy

Hi Gray,

As you probably know, these minilathes are made by one or other of the Chinese firms Sieg and Real Bull (!). There are detail differences between the two versions, but most parts are interchangeable. I believe the current Sieg machine comes with a plastic spacer but your photos show that you are dealing with a Real Bull, so it may have a metal one.

Andy

PS I have never owned either machine. My knowledge of them stems from my being (for reasons which have always eluded me) a moderator of the Yahoo 7×12 minilathe group, so I see a lot of comments about their idiosyncracies (to put it politely). I agree with your earlier comment that basically they are soundly designed little machines. But, being at the budget end of the market, many examples are let down by poor standards of fit and finish, and things like plastic spacers.

Hi Guys
As Martin sugested On my 40 years old plus super 7 over 3" concave .0002 Nobby

HI

My mate rang me and said there is a lathe next door rusting in a coall bunker > I went round a gave the guy £5 to take it away. It needed dials A handles.. there no tailstock and no motor bracket no cover for belt etc . That That was about 20 years ago As you can see its like this now
Nobby