Hello and welcome to Enots engineering I'm Alan this is the second of the two part
video reducing backlash in the cross slide by making a new cross slide nut
we've used a phosphor bronze bar to rough out and prepare the nuts ready for
screw cutting we'll give you some more tips for the lathe so lets see how we do it
the thread we're going to cut is a 2.5 pitch so we need a 40-tooth gear
on the stud and the 48 tooth gear on the lead screw with the 80 tooth gear between the two
the problem I had with this was that the bar here I'm using to hold the tool
is just under 7mm so I've filed some off the back to get right up to the face
the tool is sticking out 2mm so in fact that the distance of this is bigger
than the hole I've got in there that's an 8.5mm hole push the tool
through and it's just scored a line down the side of the hole that's how tight it
is on there so the next thing I want to do is set the Dial cross slide to zero
I've put the half nuts engage them and if I put the lathe on it should
travel outwards drop speed to the slowest speed I've got on the normal
settings I've not got the bat gear on I've got the right gears for the thread
pitch which is 2.5 so if I turn it on
bring it through and see it's cutting then I need to move the tool in a bit
pull it back through without disengaging the gears return the tool to the cutting
position come back again now what I need to do now is mark the dial or the
thimble so this is my the distance when I come
back to zero I don't want to go past that and then I'm going to come in one
millimetre one point six millimeters that's the depth run now I've got to go
a bit deeper so it'd be about there one point so that's when I need to start
trying the thread size by using the China graph pencils it's easier to see
when you're going backwards and forwards the marks you don't have to start
reading the digits on the thimble that makes it quicker when reversing and
going forward
you have to send it in and out a few times just to make sure its
finished cutting the form as there is a bit of deflection on this
boring bar so as it's going through its pushing it away slightly so by doing it
three or four times you'll clean out the thread.
And now what I've got to do is try the thread now because the ball or the
thread I want to try is in the lathe I'm going to take it off so we'll have to do
do not alter the thimble on here of not on disengage anything now what I'm
going to do is undo the two screws here that hold the cross slide thread
Now I can wind the carriage across out the way
now I can twist this out take the screw out and try to thread in the hole I've
just cut and put the thread in there now turn it around it locks up there
so now I need to put this back
pushing it back in locate it there put the two screws back in making sure
you've got the oil filler on the top as if you put it upside down all your
sizes and references will be out
and this will only work if you've got a single thread if you've got a screw with
two threads two start thread I don't think you could do this but because I've
only got the single start thread you know when you put the across slide back
on it's in the same position so now I need to do is bring it to zero from my
mark off
Go back in put the cut on and you keep doing that trying it until it fits.
use this to check it's not going in perfect yet so I'll still need a bit
more out I know when I tighten the cross slide up back into the back into
there it's on the same thread the same position bring it down to zero check on
that it goes right back into the same part and put the cut back on to where
I was
it's in exactly the same position I've not disengaged the half nuts they're
still same as when I first set them
there that requires a nice fit in there so I'll leave it at that because
it's only going to get looser the more I use it so it's stiff enough to turn
45-degree check that I'm not going into the thread bit more into that nearly there
that just holding on this corner
I'll do another 30 on the other side
to fit the new nut wind the carriage off the screw thread push it back a bit so
it's completely disengaged undo the grub screw which will loosen you can
take out the old you need to remove this little pin from here put it in the new
one to replace your new top slide nut
put the nut in the hole pull it down turn the cross slide till it engages
point it down a half way across the cabbage
so it's centralized on the lead screw and then just tighten up grub screw
which will push that small pin out and lock it
there you got it lets check the backlash okay to check the backlash I'm just holding this DTI against the carriage and push the cross
slide backwards and forwards that is about 0.001"
so job done well thanks for watching I hope you've enjoyed it and we'll see you
next time on Enots engineering