overhauling the lathe - New England Model Engineering Society

overhauling the lathe - New England Model Engineering Society
by B. J. Whitehead
R E A D E R S must be in possession of lathes
and other machinery that have slide wear concentrated in sections of most use. 1 expect that
some have heard of, if not come in contact with,
the old craftsman held in awe because his machine is in such a bad condition that he is the only
one able to produce good work from it. How
much better he could perform on a good machine
where full concentration could be given to the
workpiece rather than the eccentricities and
shortcomings of his machine tool.
An accurate machine is a joy to use. but wear
creeps in insidiously, one day it is found impossible to adjust the gibs to give full travel and yet
be tight enough for accurate work in the section
of most use. When this situation arises it does
not necessarily mean an expensive regrind for
your lathe bed for example, my aim is to show
how small machine tool slides may be restored
by the amateur with a minimum of equipment. In
this age of enormous labour costs few reasonably
priced machines have hand-finished slides, so
owners of new machines may profit from a little
of the work I shall attempt to describe.
Rather than describe the overhaul of a particular make and type of machine 1 shall give
a procedure for a 3-1/2 in. lathe, I am sure readers
will be able to apply the principles and methods
involved to their own make and size of lathe,
also millers, shapers etc.
Some of the methods I use may not be theoretically correct and there may be better ways
given sophisticated equipment but if they are
employed intelligently and dextrously they work;
I don’t want to be jumped by the “Talk in half
thou’s, work in half yards” brigade.
Before stripping, overhaul the headstock mandrel and bearings. I do not intend to enlarge on
this, volumes have been written on the subject,
adjustment is usually built in anyway. Good bearings are essential for letting up the slides later
and the lathe is still intact if new bearings have
to be machined.
Strip the lathe right down to the bed, now
check the mounting onto bench or stand that
the bed is not twisted by the holding down
bolts, this can be checked with a sensitive spirit
level across headstock seating and unworn sections of bed, readings should be exactly the
same, if not shim or adjust the jacking bolts
to correct. Much more care must be taken with
a bed mounted on feet at each end than the
cantilever type.
Clean the bed thoroughly with carbon tet. or
similar solvent and take a good look at it in
conjunction with the saddle, headstock, tailstock and sketches Fig. 1, identify the main guide
faces, these will always be opposite the gib faces.
Now to check the wear present, I doubt if
many readers have a fishback surface plate as
s h i m s some-
Some examples of machine slide and gib design
x denotes main guide face
y - g i b f a c e and z - c l e a r a n c e
Fig. 1.
MODEL ENGINEER 15 August 1975
Jig for measurement
accross vee slides
Jig in use to check parallelism
of main and gib faces of
lathe bed
Fig 2
long as the bed, but a 24 in. straight-edge can,
with care, be used equally well. The thick type
of straight-edge as used in combination sets is
certainly the best and easiest to use. These
straight-edges can be obtained plain without
graduations at a considerable saving In cost.
Try along the top flats of the bed with the
straight-edge, if the headstock seating is on the
same level as the bed, bridge the gap from unworn seating to bed as far back as possible and
try to insert a .0015 in. feeler gauge in worn
section; unless wear is excessive you will probably find that It won’t go. Wear will have to be
detected by holding the straight-edge firmly down
on the bed carefully keeping it vertical and flexing it sideways, a little practice and you will be
able to feel where the bed is hollow or worn.
Check the bed all over including guide edges
in this manner, you will probably be comforted
to find that very little wear is causing all that
trouble. A check on the actual amount of wear
present can be taken by using micrometers,
vernier or ordinary calipers over and between all
bed surfaces. To measure over vee slides a jig or
jigs must be made as shown in Fig. 2. Screw a
1-1/2in. length of ground stock to a piece of 1-1/2 in.
x 1/4 in. flat with one face trued flat.
Before scraping the bed a good surface plate at
least 6 in. x 6 in. will be necessary and also an off
standard one about 2 in. x 1 in. x 8 in. with one
edge machined and scraped flat at about 45
degrees. a piece of old cast iron strip from a
large machine is excellent, see Fig. 3.
Cast iron tends to form a thin but very hard
skin, so a few words on scrapers and the method
of attacking the surface are in order. I have not
yet found a commercial scraper that is hard
enough for use on machine slides, 1 have found
the best is a good quality parallel flat file thinned
by grinding see Fig. 3 and the end hardened right
out by quenching in water; for the work in hand
3/4 in. wide is about right.
Two different methods of sharpening are used,
one for roughing and one finishing. The roughing scraper is flat and straight ended, not curved,
as the book says and the finishing scraper is
for vee slides
Fig. 3
MODEL ENGINEER 15 August 1975
Fig 4.
sharpened as Fig. 3. This scraper is used to
remove the high spots and is worked with a
sort of forward-sideways-rocking motion, like
digging the high spot out. I am sorry, but this
is the best description I am able to give, those
that are able to mottle will understand what I
mean and also the difficulty of describing it, however do not despair if you are not able to mottle,
a very attractive frosted effect may be obtained
quite easily.
Start scraping down the top of the bed with
the roughing scraper. Work at about 45 degrees
across the bed, use long even strokes and put
some pressure on, try to remove metal evenly.
If difficulty is encountered breaking the skin use
a fine 6 in. flat file pressed firmly, again at about
45 degrees across the bed and worked slowly and
evenly. This will score the surface to give the
scraper a bite. With the skin removed use level,
straight-edge and feelers to take the high areas
down evenly to the lowest point of wear. The
scraper should be sharpened frequently on a
medium India stone, do not use anything coarser
as it will cause the scraper to score the bed. Each
pass along the bed should be at 90 degrees to
the previous one.
When you are satisfied the bed is dead flat
to the straight-edge smear the large surface
plate with engineers’ marking blue and slide it
up and down the bed a few times, the high spots
revealed will probably be few and far between,
but if the preceding work has been correctly
carried out no perceptible rock should be felt in
the plate. Still using the roughing scraper, take the
high spots off and repeat a few times until a
reasonable contact is shown all over the bed. By
now smal! bright spots surrounded by blue should
begin to appear, using the finishing scraper take
these off. A word of caution. large areas of heavy
blue do not mean a good bearing, it means too
much blue on the plate, 1 repeat, the very high
spots will show bright surrounded by blue. If you
pick the high spots off with a short forward
and sideways motion working at 45 degrees
across the bed and the next time the plate is
used, at 45 degrees the other way the high spots
will appear in more dense clusters and a very
nice frosted effect will take form on the bed. It
is now up to the individual how much time,
patience and dexterity he puts in to obtain a
bearing surface, the more and closer the high
spots, the greater bearing and flatter surface, but
whenever the work is stopped the bearing should
be even all over the bed. All the low areas surrounded the high spots are “oil wells” which
will help to retain lubrication on the surface.
Locate the main guide face and carry out the
same procedure on it, if this face serves as the
headstock location work on this as well to obtain
a straight flat face right through. The tailstock
is probably guided by the same face as the
saddle but if not, this is the next for attention,
measurements must be taken from the completed
face to ensure parallelism. The secondary or gib
MODEL ENGINEER 15 August 1975
faces for the saddle and tailstock are worked on
next, not only maintaining straightness and flatness but parallelism is of paramount importance.
Working clearances are so small that half a thou
makes the difference between binding and slack
in the assembled machine, so if you can measure
a difference, scrape it out. The top and vertical
faces complete, the bed can be removed from its
stand and turned over for work on the underside
of the shears, make sure these faces are kept dead
parallel with the top of the bed.
It may be advantageous to remove some vee
type beds from the stand at an earlier stage than
this but every effort should be made to get the
main guide faces completed while firmly held to
prevent twist.
The completed bed can be refitted to its stand,
take great care to avoid distortion.
Before commencing work on the saddle you
should look at the consequences of your actions.
Removing metal from the bed means that the
saddle will lie in a different plane from the
original, lower and to one side, this will be
magnified by the time the saddle is trued up,
there will be misalignment between leadscrew
bearings and the split nut. Since the intention is
to deal with a few thou of wear and not a
really “clapped out” machine, there will also be
wear in the nut and bearings and it is doubtful
that the slight misalignment will have any adverse
When wear is excessive and the bed has to be
machined or ground the usual procedure is to
machine out the saddle and tailstock and screw
on plates to come back to standard, other
methods can be used depending on the design
of the machine, bearings can be repositioned,
apron modified etc.
Every individual must use a fair amount of
initiative to apply these principles to his own
machine, so a warning to use forethought and
envisage the consequences of metal removal and
the possible action necessary to correct, look even
further, the consequence of this action. Be s u r e
that curing one problem does not create a bigger
one. Clean the saddle off with solvent and check
for wear on the bearing surfaces by means of
straight edge and feelers, the surface plates can
also be of use here, in addition take measurements as Fig. 4. It is essential to scrape the
bearing faces so that when complete the crossslide or boring table top face will be dead parallel
with the bed. Lathes used for normal work
almost always suffer most wear on the saddle
main guide face, a straight edge will probably
show this face to be bowed, when trued it must
be square with the cross-slide.
MODEL ENGINEER 15 August 1975
Many small lathes have a boring table with
vee slides longer than the mating ones on the
saddle, it is better to work on this first leaving
the saddle until afterwards. The boring table
slides will probably resemble those in Fig. 1d,
except that the gib is more likely to be as Fig.
lc. Scrape the under bearing faces true and flat
to the large surface plate, taking care to keep
measurements to the top face exactly the same
all round. Scrape the main guide face true to
the vee surface plate and dead parallel to the
front edge of the table, use a piece of ground
stock to take measurements, see Fig. 4. Blue the
boring table slides and use as a reference to
scrape the flats and main guide face of the
saddle cross slide surfaces, take the points of
the vees off with a file to give clearance in the
corners if necessary. Using the vee surface plate
and pieces of ground stock for measurement
scrape the gib face parallel with the main guide.
If the gib is of the type shown in Fig. lc, it is
only necessary to scrape the bearing face flat to
the surface plate and the cross-slide can be
cleaned, oiled and assembled. Test by pushing
back and fore by hand, it will be heavy to start
but should then move with an even drag without tight or slack spots.
It is likely that the gib strip is steel, if so, use
a spot of soluble cutting oil on the scraper, this
will prevent pick up and give a bright clean cut,
the scraper will work much more cleanly and
Some machines may have a different type of
gib strip. there are many different designs in use,
a few are shown at Fig. I. The gib at Fig. Id is
retained by screws up through it or down through
the slide, it is a dead fit and to take up slack it
must be carefully filed on the top face to let it in.
Sornetimes peeler shims are fitted to help, a good
bearing must be obtained on both taper and top
face and retaining screws kept dead tight. This
type needs a lot of time, patience and skill to fit
well. The gib at Fig. la may be a dead fit and
have to be treated as Id but it is more likely that
there are adjusting screws behind it and the
retaining bolts pass through clearance holes in the
gib to allow for adjustment. It is unlikely that a
taper key will be met with in small machines but
if so it is fitted to a good bearing throughout
its length on both faces.
To true the saddle main guide face square with
the cross-slide put the saddle with boring table
fitted upright on the surface plate supported on
the front edge of the table, this is parallel with
its slides, use a square between plate and guide
face, file out bow true with the square.
To be continued
A 3-1/2 in.
built by
T. A. Bott
by J. E.
Right: Model steam yacht “Alva” by
the Burrow Ship Model Society.
Ia n
Sharp of
Z-gauge one from the Manchester M.R.S. occupying only 6 ft. x 3 ft.
The Barrow Ship Model Society again put on
a show of ship models, both sail and power.
Perhaps the most outstanding ship model was t h e
steam yacht by Ian Sharp, powered by a Stuart
1OV engine and a spirit fired boiler.
Among the locomotives was the very fine 3-1/2 in.
gauge Vale of Rheidol engine by Alan Green of
Urmston. A. Walshaw of Kendal s h o w e d h i s
model beam engine, a Silver Medal winner at the
M. E. Exhibition, and there were several horsedrawn vehicles, such as a model tip cart by Bill
Whidborne, and an Oxfordshire hoop-raved
wagon and a gypsy straight-sided wagon.
In the School yard, the F.M.R.C.‘s 5 in. gauge
portable track was kept busy, the Club’s S i m p l e x
giving a good account of itself.
Overhauling the lathe
By B. J. Whitehead
Part II
From page 803
FILE AND SCRAPE out any measurable difference
in under-saddle to cross-slide thickness. blue the
bed and bed in the saddle flats and main guide
face to it; it is an advantage to lighten the
bearing in the centre of the guide face keeping
a really good bearing at both ends. True up the
gib, clean and oil saddle and bed, fit and adjust
the gib and push the saddle from end to end
of the bed, any tight spots will be felt, an even
MODEL ENGINEER 5 September 1975
drag will reward accurate work. Remove the gib
and fit the keep plates. this is best done by
m e a s u r e m e n t , stepping will probably be necessary. Fit them one at a time using blue u n d e r
the bed shears to obtain a good bearing. they
should be just making contact with the retaining
bolts hardened up ; again feel the drag.
Assemble saddle. apron. leadscrew. cross-slide
and screw and check that everything i s working
smoothly and correctly. Refit the headstock and
chuck a piece of I in. 1-1/2 in. dia. ground stock
about 7 in. 8 in. long, set it to run perfectly
true through-out its length. fix a dial test indicator
on the cross-slide. a magnetic stand is excellent
for this if you have one, so that it may be traversed over the ground bar by means of the
cross-slide ; take the highest readings at the chuck
and unsupported ends of the bar, any discrepancy between these readings indicates the amount
the headstock mandrel is out of parallel with the
bed. Scrape the underside of the headstock. maintaining a good bearing to correct. With the headstock refitted and the test bar still chucked and
now dead parallel vertically with the bed set the
D.T.I. against the side of the bar at centre height ;
traverse it by means of the saddle along the
length of the bar. The difference in reading end
to end must be corrected by scraping the headstock locating face or using any adjustment
incorporated in the machine.
When you are satisfied that the headstock is
dead true with the bed, make the acid test on
cross-slide squareness. Attach the “clock” to the
faceplate so that by swinging it, it makes contact with each end of the true front face of the
boring table or alternatively each end of a length
of straight ground stock laid in the front vee of
the cross slide with the table removed. It is usual
to set the cross-slide not absolutely dead square
but so that it will face .001 in. - .002 in. concave
in the diameter of the faceplate, this ensures
that faced components will mate together without
rock. You will probably find that it will be
necessary to again strip the saddle etc. and scrape
the main guide face to obtain this setting for the
The next problem is the tailstock. Blue the bed
and scrape the tailstock to a good bearing with
it. Extend the barrel fully and lock, set the D.T.I.
on the faceplate so that it can be swung around
the barrel, lock the tailstock on the bed with
the D.T.I. at the front end of the extended barrel,
take readings around the barrel and move the
set-over device to centralise the barrel with the
headstock; note any discrepancy in height, Now
move the tailstock bodily up the bed and again
lock so that readings can be taken as near to
the casting as possible. If the barrel at this point
is out of centre and a different height the tailstock flats and main guide face will have to be
scraped to correct. The barrel should now be
parallel to the bed but it is probably low in relation to the headstock, the cures for this are either
file and scrape the underside of the headstock
to bring it down in line or machine out and fit
plates where tailstock is split for set over to bring
it up. A quick way out is to use shims instead of
machining out and fitting plates. If the barrel is
badly worn, some may consider fitting the tailstock in front of the saddle, just take up the
lock to bear and bore out using the saddle to
push it along, it is then bound to be in line,
either bush or fit an over size barrel.
The top-slide is dealt with in the same way
as the cross-slide, anyone that has gone this far
will not find it any problem.
I hope these notes will be of some use to
readers who are prepared to use time, patience
and elbow grease to improve their machines,
but are not quite sure how to go about it, I can
assure them that their efforts will be amply
rewarded, I will bet they will think twice about
using emery without precautions on the lathe
The drawings are to scale, key dimensions only
being given. They are all of items accessible at
the public museums, etc.
Two instruction charts are available, covering
tools, materials and methods of construction.
The supplier’s list draws attention to the Model
Horse Drawn Vehicles Club-Mr. J. B. Pearce, 4
Heron Drive, Westgate, Morecambe, Lanes.
New “Braze-Welder”
Kellers Welding Centre of 32133 Cattle Market
Street, Norwich: are manufacturing a new style of
welding equipment designed for brazing as well as
welding. Known as the Kel-Arc Braze-Welder, this
works from the domestic 230-250 volt electricity
supply and comprises a fan-cooled transformer, a
“Chem-Arc“ torch with pencils, a set of welding
leads and electrode holder and earth clip. and an
industrial head mask. A supply of 16 gauge electrodes and flux-coated brazing rods are also
The Braze-Welder is designed to braze or weld
metals from thin steel sheet of 24 s.w.g. up to
1/8 in. plate.
Drawings of farm carts
We have received samples of the “Mode1 Wheelwright” plans produced by John Thompson of 15
Darset Avenue, Fleet, Aldershot, Hants.
The drawings include a sketch of the item to
show the general appearance, information on the
present location of the item, its origin and history
etc., and the correct names of the various parts.
16,000 Official Drawings now available to
model engineers
Many readers of the Model Engineer have already
availed themselves of the opportunity to secure
copies of the authentic works drawines. which have
bekn collected, filmed, and marketed by British Rail/
Oxford Publishing Co. over the past 18 months.
However, as the total number of plans located has
now reached the staeeerine figure of 16.000. and
there are perhaps seevra1 model engineers w h o have
yet to realise just what a chance is here I have
begged space from the Editor to try and indicate
the progress of this collection, and to give some idea
of its coverage.
Briefly-its origin came about through the cooperation of an enthusiastic Public Relations Office
MODEL ENGINEER September 5 1975
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