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Essential Machining Skills: Working with a Lathe, Part One



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the basic components the lathe the

headstock the tailstock the bed the

saddle the cross slide and the compound

the headstock of the lathe is used

supply power to the machine to turn the

part and also supply a point of

attachment for fixtures for holding the

workpiece the tailstock

is used for supporting long work pieces

or for making features in the ends of

work pieces for example we have a drill

chuck in place here used for drilling

holes in the ends of work pieces riding

on the bed of the lathe is the saddle

this allows us to move tools along the

sides of a part the cross slide allows

us to move tools across the face of a

part the compound is held down with two

or more bolts loosening these bolts

allows us to rotate the compound to a

desired angle and then allows us to cut

tapers in parts I'll review the parts of

the lathe in this illustration here's

the bed of the lathe the headstock is at

one end of the bed the tailstock shown

here can be positioned anywhere along

the bed the saddle also rides on the bed

of the lathe the cross slide is built

into the saddle it moves perpendicular

to the bed the compound is mounted on

the cross slide the direction of motion

can be set to any angle tool holders are

usually attached to the compound with a

T slot shown here all of the axes of the

machine can be operated by hand but for

many operations it's desirable to use a

power feed demonstrate that feed now

with a machine on have a lever somewhere

on the machine you'll often on a new

machine that you're not familiar with

have to look for this lever there are no

standards really associated with a

position these levers or how they

operate I'll now do is engage the saddle

feed you can see by the motion the wheel

saddle is moving along the bed

put the lever into neutral on this

particular machine of a knob here that

allows us to change the direction of the

feed

have a similar lever with a cross slide

engaging that is a cross slide out again

changing direction and we can drive the

cross slide in

the third axis of the machine does not

have a power feed

the compound is often used for machining

tapers on parts the base of the compound

is marked off in degrees allowing to set

desired angle on the compound tighten

the compound in place and the compound

is then fed by hands with some practice

using both hands a compound it's

possible to maintain fairly constant

speed and get a smooth cut the cross

slide can be accurately positioned the

use of this dial but on most machines

the saddle does not have an equivalent

dial what you generally use with a

saddle is a dial indicator like this

with a stop bring the dial indicator in

contact with the stop so you know where

you are on that pass you can then adjust

the micrometer so you can take a deeper

pass for example we want to go another

10 thousandths of an inch on the next

pass set the stop there come down and

our machining carefully bring the saddle

down until the indicator indicates zero

an alternative to the dial indicator

mounted on the saddle is what's called a

saddle stop which is generally

micrometer adjustment like this that is

clamped directly onto the bed many

different types of

tools are commonly used on the lathe

this is a standard lathe tool these

tools are commonly held in lathe tool

holders install the tool make sure the

tool holder clean tool in place

and lock the tool down securely

what I have here is a typical array of

tools a prototype shop you have the tool

I showed you which is a general-purpose

turning tool tool used for cutting

plastic cutting in this direction and we

have a couple of boring tools very small

boring tool for making very precise

holes here's a larger boring tool

another turning tool this odd tool is

for knurling for roughening the surface

of a tool typically so you can get a

better grip on it this tool is a cut off

tool or a parting tool it's long thin

blade is used for cutting off pieces

that you've made from a larger piece of

stock this tool very similar to say

these tools the difference is the angle

the face of the tool the top of the tool

here you can see it from the side it's

tilted this way instead of this way this

allows you to cut in this direction

this tool holder is used to hold

tungsten carbide inserts these

triangular inserts be used when the end

gets dull remove them rotate them and

you have another fresh tool to work with

all of these tools are held in this tool

holder place together like this there's

a cam lock you can see it's moving up

and down as I turn the handle bring it

into the up position put the tool holder

in place turn the lever expands inside

the dovetail and locks everything in

place this is very convenient because it

allows you to do work with one tool

remove that tool put on another tool

remove that come back to the original

tool and this tool will consistently

return to within two or three ten

thousandths of an inch of the position

it was in the first time you used it

to set up with a t-nut

we slide the tool post in place in the

compound

lock it down

and lock the desired tool in place on

the tool post I have just cut this piece

of stock from a larger piece of bar

stock used a bandsaw so you can see here

that I've cut it reasonably square to

the sides of the stock the surface is

rough and it is not completely

perpendicular to the side of the stock

so I'm now going to put this in the

lathe and face the end of this part and

in doing that I'll produce a very smooth

flat surface that is also perpendicular

to the sides of the part I'm going to

make sure you've got the piece locked

securely in the Chuck

I have here a facing tool you see the

top of the tool is angled like this so

that when I cut across the face of the

part the chips slide off the tool nicely

lock the tool onto the tool post

bring the tool in front of the part

bring the tool close the part turn the

Chuck just to make sure that nothing is

going to collide with anything else that

may be the tool hitting some part of

piece you've just put in here because

the cut was irregular it may be parts of

the Chuck often the Chuck jaws hitting

other parts of the lathe so always turn

the Chuck to make sure there's no

interference before turning on the

machine

now bring the tool down you can hear

it's just contacting the part and back

the tool off the part and then move the

saddle down this case we'll be taking a

roughing cut on aluminum so it's

reasonable to take a cut of 50

thousandths of an inch or even as much

as a hundred thousandths of an inch the

first cut

you should always at least start the cut

by hand to make sure that nothing

surprising is going to happen you may

have forgotten to tighten the tool

properly the person before you they have

not tighten the tool properly

now you can see this surface even though

that was a roughing pass is now much

smoother and flatter it was before

before removing the chips that you've

just made from the machine always stop

the machine these chips are essentially

like little razor blades in fact

Gillette makes razor blades in just this

way but with a machine off then it's

relatively safe come in and remove the

chips however for example some of the

chips are hung up on some part of the

machine if you pull too quickly

you're still likely to get hurt so be

very very careful with chips like this

now that we've finished a roughing pass

we can come in just another few

thousandths of an inch

take a finishing pass this pass will do

with the power feed

gives us much better control over the

speed of the cut which results in a

flatter smoother surface than we would

get by feeding by hand the last

operation involved in facing apart is to

break the edge you produced a knife edge

here it's very dangerous a couple ways

of dealing with this one way is to turn

the tool

and just bring the tool into contact

lightly with the edge breaking edge and

making it safe this can also be done

with a file

be very careful with the file with

shorter parts it's very easy if you're

not careful to get part of the file

caught up in the jaws of the Vice I have

a piece of stock here slightly larger in

diameter than the finished diameter of

the part that I'm going to be making so

what I'm going to do now is put this

part in the lathe and turn down the

outside diameter of the part to the

desired dimension

start by locking the piece firmly in the

Chuck

tool I'm going to be using for this

operation it's called a right hand

turning tool you can see that the top of

the tool is tilted to an angle this so

that as you're cutting in this direction

the chips come down onto the tool and

slide off the tool nicely

start by bringing a tool close to the

part then turning the Chuck doing this

to make sure there are no interferences

either between the tool and the part or

between parts of the Chuck and the rest

of the machine start the machine you can

hear the tool has just made contact the

part bring the tool off the end of the

parts and then using the dials on the

hand feed and dial in the desired depth

of cut now I'll be taking a roughing cut

here taking off about 50 thousandths of

an inch

I'm feeding this first pass by hand to

make sure that nothing very exciting

happens on first time you take a cut

you may bump something something may

have moved and the cut you thought you

were taking turns out to be much deeper

and by feeding by hand you can much more

quickly stop the feed than you can with

the power feeds now I made one roughing

cut the finish is reasonably good but

there are grooves remaining in the part

because I was feeding by hand and was

not able to control the speed very

accurately

now take a finishing pass on this part

just a few thousandths of an inch I'll

take five thousandths of an inch in this

pass and I will use the power feed and

bring the tool away from the parts

engage the power feed again to make sure

nothing very exciting happens make sure

that the feed is going in the right

direction and the speed that I thought

it was going to be moving it now you

assured myself that the machine is set

right I can bring the tool up close to

the part and engage the fee

you can see by the difference in surface

finish and also even here that the cut

is proceeding much more smoothly using

the power feed than it was when I was

feeding by hands

the last operation you want to perform

is called breaking the edge the process

of turning down a piece of stock you've

left a very sharp edge on the part

convenient way of turning down this edge

by bringing a tool up the contact with

it with the edge of the tool roughly at

45 degrees to the side of the part that

breaks the edge leaves a nice smooth

surface there that's quite safe

alternatively

you can use a file break that edge when

using a file you should be very careful

especially with short parts that you

don't bump the file into the jaws of the

Chuck

now how this part turned down to a

desired diameter this is a parting tool

very long narrow tool used for cutting

deeply into a part typically used for

cutting grooves in parts or cutting

pieces off of the end of a larger piece

of stock this tool is held a special

tool holder you always want to make sure

that you minimize the overhang of the

tool using just enough to get through

the part that you're working on so if

you need to you're cutting off a large

piece of stock you'll be forced to put

the tool out further and this makes a

tool very weak you're very likely to

break it so for the piece that I'm going

to be cutting off part of this

demonstration I need about 3/4 of an

inch of the tool hanging out so set the

tool to a length just slightly larger

than that to make sure I get all the way

through the piece lock it in place

and lock it in to the tool post it's

very important that this tool will be

set perpendicular to the axis of the

part several ways of doing this most

common way to simply bring the tool into

contact with the part

and rotate the tool until you see that

the tool has contacted the part over its

entire length you then lock the tool

post in place an alternative if you are

using this type of tool holder is to

simply bring the tool holder in contact

with the face of the part

and lock the tool post down

another alternative is to use a dial

indicator

we place the dial indicator near the

tool

you can run the tool back and forth and

adjust the tool

until the dial indicator reading does

not change while removing the tool and

then lock the tool into place

yet another alternative is to bring the

tool all the way down

here either in contact with the face of

the chuck or depending on the type of

jaws you have into contact with the top

of one of the jaws

again you just a tool until you see it

coming into full contact with the face

of the jaw and lock it into place

this adjusts the angle of the tool

relative to the axis of rotation in the

machine it's also necessary to adjust

the vertical position of the tool

this is particularly important when

you're cutting off a piece of stock

that's solid in order to cut off a piece

of stock that's solid you must have the

tip of the tool exactly coincident with

the centerline of the part

this type of tool post and tool holder

comes with a very convenient way of

setting the height of the tool loosen up

the tool the holder

and adjust the height of the tool so

that the tip of the tool is coincident

with the centerline of the part lock

this in place very lightly

this adjustment sees no force during the

cutting operation simply here to set

this position now that we have that

position set you can lock the tool down

we are now ready to cut off a piece of

this stock

turn the Chuck to make sure that nothing

interferes either between the tool or

the part or between the Chuck particular

between the Chuck jaws and the rest of

the machine turn the machine on and feed

the part slowly it's reasonable to cut a

groove of about this depth dry cutting

any deeper puts more and more of the

edge of the tool into contact with the

sides of the groove generating heat so

as you go deeper into the part it's more

and more important to use some cutting

fluid

I'll stop using the cutting fluid a

moment and you can hear the kind of dry

squeaky sound coming out of the cut that

means that the tool is getting close to

binding in the groove and breaking off

you can hear the sound the machine is

making change a little bit right there a

little squeak what's going on there is

that I've stopped turning the crank

change the position of my hand on the

crank and during that time very little

cutting goes on and chatters a little

bit I'm feeding this by hand so that if

something unexpected happens such as the

tool binding up I can very quickly

withdraw the tool from the part now you

can hear the pitch the chatter go up

slightly that's usually there you can

use that as an indicator it's just about

the time when you have completed the cut

you can see here the finish the cut but

halfway down you can see that the cut is

a little rough and not as shiny that's

the part of the cut where I was not

using cutting fluid it's very clear from

this the benefits of using some cutting

fluid while you're using the cut-off

tool drilling a hole in a part on the

lathe

it's done in very much the same way that

a part is drilled in a drill press or a

milling machine start by putting part

securely in the chuck before turning the

machine on spin the Chuck making sure

that there's no interference in

particular this is very important when

you're drilling because often when

you're drilling you have the compound

down very near the chuck make sure that

you avoid this sort of interference

between the jaws the Chuck and parts of

the lathe now it's safe to turn the

machine on

going to be putting the drill chuck in

to the tailstock the lathe and see

there's a taper here that inserts into a

matching taper and the tailstock there's

a little tang the two flats on it the

end of the taper that walk-in to the

inside tailstock keeping this from

rotating you rotate this until the tank

fits in place push down until it seats

and then with a soft hammer with the

jaws of the chuck that are normally

extended drawn back inside the body of

the chuck very lightly tap the chuck to

seat the taper in to the tailstock

now we're ready to start drilling the

hole we start by using a combination

Center drill

this is a very short stiff drill by

using this drill first we guarantee that

the beginning of the hole is concentric

with the centerline of the spindle we

bring the entire tail stock up near the

part and then lock the tail stock in

place on this particular machine this is

done with a lever at the back of the

tail stock other machines may have a

lever that operates in this direction

still other machines will have a lever

that's in the front of the tail stock

here

when using a center drill it's almost

always a good idea to use a little bit

of cutting fluid

this drill doesn't cut as well as a

regular drill because it's a compromise

between cutting like a regular drill and

being very stiff the result is that the

chips that it produces don't clear out

of the drill as well because these

flutes aren't as deep nor do they have

as much of a twist as a regular drill

now we have a good accurate start to the

hole you can see here if you look

closely did I move the center drill deep

enough into the part so we have a small

pilot hole plus a taper that taper works

like a funnel to draw the drill into the

center of the hole

it's important to start slowly here the

drill is slightly off-center and it may

be because the tailstock may be slightly

out of adjustment one flute may catch a

little bit before the other and pull the

drill to the side so if you start slowly

you can see the drill jump just a little

bit as I brought it in contact you start

slowly the funnel will draw the drill

accurately into the center of the hole

now that the drill is well into the hole

it's drilled down to the bottom of the

hole left by the center drill we can

proceed at a much faster rate

the first pass with a drill I'm going in

about four or five drill diameters you

can hear now a squeaking sound that's

being produced by the drill and the

chips because the chips are having a

very difficult time riding up through

the flutes of the drill and out of the

hole and are starting to bind in the

hole producing heat and chattering so

now that I've drawn the drill out and

cleared the chips before I go in again

to introduce a little bit of cutting

fluid into the hole and onto the drill

now we continue this way removing about

one or two drill diameters of material

each time we run the drill into the hole

the squeaking you hear there is often a

very good indication that you've gone

far enough with this pass and it's time

to remove the drill and clean the chips

from the hole and from the flutes of the

drill after you finish drilling the hole

drill chuck can be removed by drawing

tailstock back all the way until it

stops

turn the handle back a little further

and a pin inside the tailstock is there

it will press the taper out of the

tailstock and release the chuck

you