Hello welcome to Enots engineering Im Alan this is a two-part video for reducing
backlash in the cross slide by making a new cross slide nut we take these
phosphor bronze bar and make 2 nuts and have plenty left for a compound slide nut if needed
will also give you some more tips for the lathe so let's see how we do it
just checking the backlash in the cross slide I just hold it on there
it's about 17 thou the back lash
This is the cross slide nuts off the boxford lathe
and as you can see when it was first machined they didn't set the
casting central this is the cross slide thread you can see looks like an ACME
thread 3.5 millimeter pitch and that gear is for the cross travers
I've changed the screw thread or I will change the change screw thread in the top here from
5/16 BSF Im now doing it 8mm which is virtually the same size but
metric and I've got this phosphor bronze bar so I can get two as of this at least
maybe three
right I finished that there so I roughed the outside out just to get it running
true cut it off the main bar because it was it was too long
sticking out I can't go any further in so I just rough it out and cot it off
held it in the chuck machined this down to fit the hole in the lathe
which is point six eight seven five I'm going to drill the hole in the end and tap
it for an 8MM thread
so that's so far is the blank I've got put a quarter inch hole in the
side here and little pin goes in so as you tighten that down the pin pushes
out the side and that's what grips it into the cross slide
I will put a flat each side at the moment this is too wide to fit into the cross slide
It goes in between this gap there it's just a bit too wide.
What I'm doing at the moment is just machining some some of each face-off the nut so it will fit in this slot.
So what i've done is put it in a four jaw chuck it's not critical.
Im going to face 2 mm of the side
Turn it around and face 2mm of the other side
and I've just put that spacer bar behind so I can get it square.
Touch it on the bar Zero the cross slide
just check in the thickness of the face that's just over 2mm off that
so that should be okay spacer bar in
Now it's got a flat on you can push that flat to the bar
that's just a to give me a start when I put the hole in for the thread.
What I need to find out now is how far it is from the face down to the
center line at the hole so I'll put this in this small Vee block on the serface
plate and you put that up there
with my height gauge I come to the top that the height gauge should level off
the brass on the phosphor bronze bush
Zero it move over to the shaft come down on the shaft and its 0.190 the information I need to find out is
the angle and the thread it looks like an ACME thread but it's slightly different.
okay I'm marking now the position down
from the top of the hole if you remember we measured that earlier it was 4.075
touch it on the top
zero scribed the line
and that line is a position of the hole from the face down
I centre punch the mark that we made from the face to this to the center of the hole
I've put the centre in there supported it on the back so this is free to move and now I'm just
adjusting the jaws of the chuck to bring that centre punch mark to the center
of the chuck so the way I do that is to pick on a pair of jaws get the reading
at the Jaw rotate 180 degrees you can see that's virtually zero so I know the
adjustments got to be on the other jaw putting that back down zero it
rotate that 180 degrees and you can see the difference in the reading.
and tighten up the jaw so that it halfs the distance
zero that there check this one
keep adjusting the jaws until thats running true
less than 0.001"
I'm using a overhead projector to protect the image onto a wall the small bar
you can see is a reference bar so when I've got the image I can trace
around it and that reference bar gives me an idea of how how much the
projector has magnified it so I can refer the other size to that
this is the drawing which shows some of the calculations I made.
on the right you
can see the tool form I used this is a three millimeter carbide bar with two
seventeen and a half degree angles on
By putting a piece of plastic here this reflects the light and then you can
see easier between the the edge of your square and the boring ball what sort of
gap you've got this is important to get your square because it will affect the
the profile of your thread now with this profile
it's a strange thread this is it's not it's not a metric and it's not an
imperial it's a cross between the two it's 2.5 pitch and as far as I can work
out the angles of each side are seventeen and a half degrees so that's
what I've ground the tool to with a slight flat on the front
I've got to go in square to give the proper form.
the next job is to set up the gearing
I continue making the nut in part two