All squared away.

[DavidA]

Will,

I didn't mention the saddle.  Clearly that follows the bed ways and it is an imaginary line down the middle of the bedways that we are trying to get everything lied up with.

If the cross ways are not dead square to the bedway then you are screwed right from the start. You may be able to line the headstock (and tailstock) with the bed, but will never get a square facing cut across any job as the tool will be traveling at an angle to the idealised centre line of the bed.

VT,

What I mean place your dial indicator on one of the bedways (or maybe on a bar clamped across the bed) then clock against a straight edge that is clamped to the cross slide.

If the cross slide is square to the bed than you will be able to find a position of zero dial movement when you move the cross slide in and out.

If you can't fins this point then it is either wear or you are measuring a slight angle in the cross slide ways.

I also have heard this about the cross slide deliberately being left out of true. Sounds rather odd to me. According to that theory you an never cut a truly flat surface.

Dave

[philf]

VT,

...Assuming the saddle slide is square to the ways...

That's the easiest bit.

Stand your clock on the bed and traverse the cross slide from side to side.

Maybe clamp a good straight edge to the cross slide table first and clock against that.

My own cross slide shows less than a tenth of a thou' over it's five inch of travel. That is my reference for everything else.

Dave.

Dave,

I have to disagree.

The cross slide could be 15 degrees out of square to the bed and a clock fixed to the bed would only show the out of parallelism between the cross slide dovetail and the side of the cross slide (which may be zero).

Taking a cut on the faceplate isn't the 'approved' way of doing things. According to Connolly or Schlesinger (which Norman quoted as the bibles) the method is to clamp a substantial parallel lightly in a 4 jaw chuck. With a dial mounted from the cross slide take a reading with the gauge at one end of the horizontal parallel. Without moving the cross slide rotate the chuck through 180 degrees and take another dial reading. Keep repeating this, lightly tapping the parallel, until you get identical readings at both ends. Then you can move the cross slide scanning the horizontal parallel to get an out of square reading.

You still don't know however if it's the cross slide or headstock which is out of square.

There are many checks and adjustments to make before the above. The first being to level the bed to ensure there is no twist. After all (as Will pointed out) a Myford is adjusted to turn parallel by twisting the bed (or perhaps more accurately untwisting it).

Cheers.

Phil.

[philf]

I have heard that the cross slide is deliberately not set at exactly 90 degrees to the bed! That way when you face a large piece the centre of the work is concave by a tiny amount. Concave is better than convex when facing!

Will,

There was a detailed discussion on this subject some time ago:

http://madmodder.net/index.php/topic,7066.msg75763.html#msg75763

Phil.

[DavidA]

Phil,

You're correct, I described it the wrong way around.

You use a square to position a straight (preferably a parallel) edge across the bed. Then fix the clock to the cross slide and traverse it across.
If there is an error then the clock will move either towards or away from the fixed bar.

Sorry about that. Old age setting in.

Dave.

[vtsteam]

Like I said.....
 

[Fergus OMore]

Centrecam anyone? It had only one fault and that was computer programme.

The rest was a poor imitation of what professional car body repairers were doing with laser alignment.  Car chassis were being made with Off Centre alignment- not straight lines as of yore. Anyway, I did a bit of this- hence my interest in Mike Trethewey's Centrecam and also Peter Rawlinson's excellent articles in ME.

It was- and is a lot, lot simpler than first believed.

Norman

[philf]

A few days ago there was a discussion about testing the parallelism of a lathe spindle to the bed.

Fergus mentioned two books by Schlesinger & Connelly (which I'm very fortunate to have hard copies of). I've just found pdf copies of the two books as well as two more very interesting looking machine tool testing books on: http://totallyscrewedmachineshop.com/documents/documents.html.

The Connelly book gives a huge amount of info on scraping and correcting all sorts of errors on many different types of machine tools. The Schlesinger book is more about testing than remedy.

I thought Vtsteam might find them of help with his 'New Lathe' project.

Phil.

[vtsteam]

Thanks Phil! Yes I will. 

[Fergus OMore]

Thanks Philf!

Two( I think) points arise. When these worthies did their thing, there was no such thing as easily available and cheap laser stuff.
Somewhere in my laughingly called workshop are two or is it three lasers. One is a a plastic affair which is almost a baby rotary table with the ability to send a beam at an angle.  I bought it to supplement my machinist's spirit level whilst aligning my lathe. OK, it somewhare with cheap surveyor's laser level etc.

So going back to CentreCam, it was in its infancy. Trethewey WAS going to bring out a new program or update it- but hasn't.  Peter Rawlinson wrote a lot about lasers in ME or MEW but I forget which. However, he sort of ran into problems of getting the laser pinpoint- to be a pin point.
OK, I'm rambling a bit but another issue is that cars 30 years ago were being re-aligned after collisions with lasers going through clear plastic graticules and being turned- with prisms.
It is 30 or so years since I was being taught as a manure student by Alan Robinson who wrote the Repair of Vehicle Bodies- I had the first or second edition at Gateshead Tech. Of course, this was all part of City and Guilds qualification.

OK- can all this be modified to a cheap alignment system for --us?


Phew!

Norman

[Fergus OMore]

Just unearthed these laser things.

One is Strait-Line laser level 120 and the other is a Laser Straight. Both switched on after yonks( Geordie- meaning for ever) but I am getting straight lines. Any bright( oops) ideas to tuurn them into a round pinhole, please?

Norman