wish i'd never bought a stinkn level

[Tony]

or, the saga of getting the most out of my used lathe.

caveat: I haven't actually gotten the level yet. the mail stinks. but I've
opened a can of worms and am bending my brain into a pretzel hoping to
figure this out.

granted I haven't had this lathe long, but I was much happier before I
started trying to take measurements.

initial test cuts were showing that I was turning a 0.004"/4" taper!
my headstock must be out of line, right? well during the rebuild I noticed
the headstock was shimmed (in 3 locations).. as was the t/s (to raise it).
shims were about 0.010"-0.015".

This scared me. Didn't notice them during the initial survey. Hopefully
it was some misguided soul. If not.. well..

To get the shims out I took the head off. Didn't know how many or where
they were. Plus I wanted a closer look at the head alignment gizmo on the
cholchester student.

Also I figured that, under the head, i must have pristine ways that I could
use to reference the eventual levelling.. er.. untwisting.

Here's the headless lathe:



here are where the shims were (white arrows). Also notice the red arrow
points to the pin that the colchester's head can be spun around:



using this opposing pin / pointed setscrew gizmo. note that right now its
been taken apart, cleaned, and set between the ways for foto shoot.
normally it is pinned/bolted to the bottom of the head:

[Tony]

first thing I did, after cleaning the ways thoroughly was to take my
best (only!) straightedge and some feeler gagues and try to get
an idea for how much wear this lathe has.

note the gap has been removed. (had to do that to get the head off).

also, my straightedge is only good to about 0.003" over 24"

nonetheless,



i was STUNNED to find about a 0.020" mismatch!

don't know if you can see it in this photo, but i could just get a 0.020 feeler
in there .. as I got closer to the T/S end it got a little tighter. 0.018 would
just slip through.. barely.



now before anyone notes that this is the flat for the T/S, I do realize that.
But it was an easy place to measure. How could the T/S flat be 0.020" low?

I checked the V ways as best I could, with the same straight and feelers
and they measured the same, 0.020" low for a consistent 10".. then 0.018"
I couldn't get the straightedge any further.

I tried the same measurement on the back way. both the flat and the
V. THEY were pretty much spot on. ie in the same plane. I could get about
0.002" feeler on the H/S end.

at this point I'm hoping that somone with a colchester could tell me
they're made this way out of the factory. strikes me as odd that only
one piece of way would be 0.020" low, however.

starting to look like bad news.

Decided to take some morer cruderer measurements: micing the ways.

The bottom of the ways, although not ground, are machined flat. I know
this means nothing.. but if I saw the same 0.020" wear.. well .. it'd be
another hint.



I measured the 5 locations I could get a mic on

[Tony]

and here's what I got:



i have one more pic and now I don't remember why I took it but here it is



so all in all the lathe (cosmetically) is pretty good. no broken bits or hammer
blows or jury rigged pieces.. seems to have been used with reasonable care.
the oil everywhere was clean and though I can't say if it was oiled regularly,
all of the oiling holes were clear (not gunked up).

as I said I'm still waiting on the level to be delivered.. but I fear that
if I can't figure out how much wear I really have, and hence can't really
figure out how much twist there might be (I expect little.. its a small
stout lathe).. I don't know how well I could actually align the headstock.

-Tony

[philbur]

It's not entirely clear but it looks like you are comparing the rear flat way with the front V way !!!!

Also you may be over thinking this, take a couple of deep breaths and calm down.

Phil

[aboard_epsilon]

doesnt matter if the thing is at 45 degrees as long as everything is level with itself...treat it like a cylinder head..

idea if it works

put three or more parrallels at equal intervals down the bed - across the bed and level it to them with a good strait edge . using feeler guages

all the best.markj

[Tony]

Sorry Phil, my intention was to compare readings taken from the same way.
So in the back I have three measurements (on the carriage flat). On the
front I only have two (carriage V) as the gearbox doesnt allow my mic to get
in to take the 3rd on the headstock end.

I can't take a deep breath, my measurements would change!


Tony

[philbur]

Your drawing seems to show the flat ways on the outside of the bed, both front and back, which is not the case.

There is no reason why the "thickness" of the flat ways should be the same. You need a good straight edge, a precision level and some suitable size parallels, then you will be able to check systematically.

Phil

[darryl]

From what I can tell, that lathe looks to be in pretty good condition. Your readings using the flat on the bottom of the ways- I'd be more than happy with that, and I'm fussy. The 20 thou gap you're measuring seems to be done with part of the straightedge resting on the flat at the headstock area- I'd have to suggest that this is a meaningless measurement. I'd expect the front and back V ways to carry through accurately ground from end to end, but not the tailstock way surfaces.

I don't see any significant wear on the front V way, though of course just looking at the pictures isn't going to be very definitive. My first intensive measurement would be to see if there's any hollowing or low spots on it, then to determine if there's any overall bow to it. Past that you are basically checking to see if the other ways are parallel to it. For the tailstock ways, it doesn't matter if they are high or low- it only matters that they are parallel. You will find that you pretty much have to shim the tailstock in more than one way to make the bore parallel and on axis with the headstock spindle axis- from my limited knowledge of lathes other than my own, I'd suggest that this is something that's mostly left for the user to do. It may or may not have been properly shimmed from the factory, but it's something you do after the bed has been aligned and the headstock aligned. All I'm saying here is that it wouldn't be unusual to find a mess of shims in the tailstock, and it doesn't represent a bunch of fudging. I made a project of shimming my tailstock one day, and now it sure is nice to have it close- makes using it much nicer.

I won't get into the issue of the stand and its effect on lathe alignment, except to say that you should treat the stand, and the floor where it will be placed, as components of the lathe for alignment purposes. This has been discussed to death before, and I'm sure some searching will bring the threads back. It would be a good read.

You mentioned your 'best' straightedge- hopefully you have a surface plate so you can characterize it. It's still usable if it's bowed, but you would have to know the degree of bow and the shim required to fill that gap- then you can take that to the lathe and use that same shim with it.

[Jim Caudill]

The headstock could be mounted on ways that are an inch(or more) higher than the bedways, it makes no difference. Similarly, it makes no difference whether the bedways are centered with respect to the spindle. Some lathes don't even have ways underneath the headstock.

I have seen lathes modified with spacer blocks under the headstock, just so they could swing a larger diameter.

All that matters is that the horizontal and vertical centerline of the spindle is parallel to the bedways.

As a secondary matter, the tailstock spindle has to be "center-to-center" with the headstock spindle AND parallel to the bedways.

[Tony]

understood and point taken.
I would've just expected that, at least on a lathe this short, the ways would
be consistent all the way across.

just seems easier to machine/grind/finish straight across.

intuitively I thought the headstock ways would be co-planar with the bed
ways and it would've been a good spot to reference as "unworn section"
in checking wear and levelling the lathe.

i'll post some level readings and photos of the (my) process (when I get the level).

Tony

[Nemesis]

Hi Tony

Have you considered that this may be how it was manufactured, the fact that you have a reading close to 0.625" makes me think this is as manufactured and in actual fact your wear is only 0.003" at worst.

It may be the headstock had to be 0.020" higher than the bedways for some design reason now lost in the mists of time.

I personally think you have bought a bargain.

Nemesis

[beckley23]

This may help. It's long, but the results are worth it.
http://www.practicalmachinist.com/vb...update-146913/
Harry

[Tony]

Harry -- superb job on the lathe! I haven't done this enough to undertake
what you did -- and hopefully I don't need it (ie wear is little enough that
I can live with).. but great work.

Nemesis -- yes! thats the kind of wishful thinking I like to hear!


-- we'll see once the stinkn level gets here.

Tony

[Tony]

Ok so my level finally arrived. After some fiddling, the best I could get
was 6.5-7 divisions. This is a 0.03mm/m level.. so that means 0.195 to
0.210 mm or 0.007"-0.008"

Any more "untwisting" just picked my lathe up in the opposite corner.

I assume that what I'm seeing is the wear.

Here're some pics:







One caveat: I am measuring across the flats on the bed. At the H/S end
I'm on the gap piece. With a test bar I noticed a small hick-up when
riding across the gap.. that'll have to be taken care of (reseating or some
stoning).. so that error is in this measurement.

[Tony]

One thing I did find disconcerting with the test bar is that it wobbles.
At the far end (10" away from spindle) TIR= ~ 0.015".

My test bar is in a MT adapter thats in my spindle. I tried to clean it
up as best I can.. no way for me to know if this spindle is krookit or the
stack up through the spindle isn't clean enough.

The test bar checks out perfect on my granite.

So i set the "wobble" to the middle of the reading (average) and measured
a rise in the end of the test bar of 0.008-0.009".

I'm making the assumption here that its the carriage that's dropping..
as it coincides nicely with what the level had to say. However, the
carriage is not on the gap at this point, so that should have read less
than 8-9 thou.



I'll realign the headstock tomorrow with the test bar and take some cuts..
or maybe after I sort out this gap piece.

Tony