Reamer Basics

there are some things that every

machinist should know about twist drills

they always make an oversized hole they

generally leave a rough surface finish

on the sides of that hole and the holes

they make are not necessarily straight

in thicker material or round and thinner

material in the case of clearance holes

these things tend not to matter but when

you need an accurately sized round hole

with a good surface finish you should

reach for a reamer

reimers are a fast and relatively

inexpensive way to get a precise

diameter on a hole they are available in

almost any size

most industrial suppliers sell them in

thousandths of an inch

and hundredths of a millimeter

increments so you can get just the fit

you need one of the most used tools many

machine shops as an over-under reamer

set which consists of Reimers one

thousandth of an inch over and under

each fractional size from an eighth of

an inch up to a half an inch this lets

you get either a slip fit or press fit

on dowel pins this is useful for

applications where you have two mating

parts that need to be able to move but

also need to stay in relation to each

other like this by stop or these ball

out molds for rounding out tubing

the most common type of reamer is called

a chucking reamer it has a very long

shank in relation to the flute length

this makes sure it's flexible enough to

follow the pilot hole the flutes are

most often straight but they can also be

spiral either right-handed to pull the

chips out or left-handed to push the

chips forward pay attention to the

direction of the cut though because a

left-handed spiral can still have a

right-handed cut like most tooling

Reimers start to get quite expensive in

larger sizes so large Reimers are often

sold as shell dreamers one shank is used

to hold a range of interchangeable

reamer shells this not only makes the

tooling more affordable but it takes up

far less space than a drawer full of

very large Reimers just like twist

drills reamers come in a wide array of

styles materials and shank types many of

these are the same options you would

have with drills they're available in

high speed steel and carbide as well as

carbide tipped so you get the hardness

of carbide on the leading edge and the

flexibility of a high speed steel shank

they also have both straight and taper

shanks like drills but additionally

there's a variety with a square shank

like a tap these are hand Reimers and

are not meant to be run under power on a

machine instead these are meant to be

turned with a tap wrench hand Reimers

have longer flute lengths than normal

and the flutes are slightly tapered at

the beginning to aid in getting the

reamer straight into a hole there are

also some special purpose rumors that

deserve to be mentioned Morse taper

Reimers are available to either cut or

clean up Morse taper sockets taper pin

Reimers are for cutting a seat for

tapered dowel pins these pins are used

in all kinds of machinery to accurately

locate removable partes there are also

adjustable reimers which use opposing

nuts to slide the reamer blades and

tapered channels to make the reamer

larger or smaller these are always hand

reamers and the surface finish that

create leaves a lot to be desired these

are mostly used to open a hole slightly

rather than trying to

a precise fit there are some rules of

thumb that should be followed when

reaming the most important one is that

riemer's should never be run backwards

either under power or by hand doing so

dulls the Reimer the next thing you need

to know is that Reimers should be run at

half the speed and double the feed of a

similarly sized drill simply put if a

drill of the same size should be run at

1,400 rpm the reamer should be run at

700 likewise your feed rate would be

doubled although on manual machines that

comes down to a sense of feel next use

cutting oil when using a reamer this not

only helps achieve a better surface

finish but it affects the size of the

finished hole reaming a hold dry tends

to leave it oversized and somewhat

rough-looking lastly if you are reaming

a blind hole make sure to stop before

you reach the bottom of the hole Reimers

are flexible but generally continue

straight into a workpiece once they're

started the same cannot be said for the

drill used for the pilot hole which will

start to wander sideways quickly if you

hit the bottom of a blind hole

especially a deeper one the reamer will

immediately center itself on the

depression left by the drill tip and

make the hole oversized

if you have to ream a blind hole make

sure to drill a little deeper with the

pilot drill to give yourself more room

at the bottom and utilize a quill stop

to make sure you don't go too far with

the reamer the flutes of a reamer do not

have much space in them so the pilot

hole needs to be closed to size but

still leave enough material for the

reamer to remove otherwise it'll just

rub and dull the reamer how much stock

leave depends on the size of the reamer

so please refer to this stock allowance

chart I've also put this down in the

description and it's part of my class

handout that's linked down there as well

thanks for watching and I'll see you

next time