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Hi

How's the fit and finish on that machine? I was thinking of getting
one.

Thanks, Frederick C. Wilt

The actual reference surfaces are the face of the spindle and the
outer dia. of the spindle nose; the outer dia. of the spindle is not
a reference. IIRC, the mini-lathe.com and/or littlemachineshop.com
sites have alignment measuring/adjusting procedures.
It's very easy to get measurement errors in the under .001" range -
everything flexes & sticks enough to make technique critical.
(Another area where you have to screw it up to learn how to do it
<g>) Assuming good meaurements, bearing preload may be the cause.
On the left end of the spindle, there are 2 locknuts; loosen the
outer one, tighten the inner one until the spindle doesn't deflect
under moderate longitudinal pressure in either direction, yet still
turns freely. After tightening the outer locknut against the inner
one (you do have 2 hook spanners, don't you?), repeat the
measurements & adjustments until it comes out right after the outer
nut is tightened (it pushes the inner nut away from the adjustment
point.) [Bicycle shops are a source for thin hook spanners.]
Alternately, since Micro-Mark charges a princely sum for their
merchandise, call customer service and make it their problem.

Roy
--- In 7x12minilathe@..., "roycetool" <royce_martin@e...>
wrote:

Hi to all!

New here [and to machining] and having a great ime learning a new
craft.
I got a 7x14 from MicroMark. Lots of small problems, but my big

one

is spindle runout. I am getting just under .001" of runout on the
face of the spindle AND on the outer diameter! Of course, this

means

that turning anything true is almost impossible.
Anyone have any knowledge/suggestionson this one?

Thanks.

Page 50 of the HSM for Sep/Oct 2002 has an article on making
3-C and 6-K collets with dimensiond drawings and good details. There is
a good discussion of the advantages of the 6-K collet over the 3-C in a
modified MT #3 spindle.

Bill in Boulder "Engineering as an Art Form!"

Hello All
I am looking for the parts to put a collet system on my mini lathe
also. Now one might ask what size collets other than 3c can I use,
well here is a site where maybe some of those questions may be
answered. () along with
other information usefull to the beginner machinest. Thats my two
cents worth.
Thanks to all that have helped me in the past and in the future.
MIKENLN

I'm working from the pdf files of articles written by Exactus:


As you suggested, he has you make the collets in pairs and gives the
order of most of the machining operations as well as methods (which
us newbies wouldn't think of) to improve the accuracy of the result.
His articles are general in that they aren't about 3C collets, just
collets in general.

I would like specs on 3C collets if you can find them, especially the
angle of the steep taper. I calculated it as 11 degrees but it
didn't seem to fit properly so I used 12 degrees. The expanded
nature of my brass collet makes it difficult to evaluate the fit
using chalk or machinist blue because once the collet is in the chuck
it is hard to rotate it while it is tight against the taper.

My conclusion about the hardness of the shock absorber rod is based
on my hacksaw/Sawzall test; I couldn't cut it to fit into the lathe
until it was annealed. I don't have a steadyrest (yet).

Once it is in the lathe I start at the end adjacent to the live
center and make a truing cut which takes the chrome (green after
annealing) off using a carbide tool. Seems to work OK although it
smokes a bit as the cutting oil burns off the chips.

John

--- In 7x12minilathe@..., William A Williams
<bwmsbldr@j...> wrote:

Thanks for the information. Somewhere I have seen a

dimensioned drawing

of a 3-C collet; if I find it I will get it to you. I suspect that

you

are "skating" the tool tip on the chrome plate. You have to cut it

off

with a shouldering tool or one that actually undercuts the plating.
You do know to make the collets in pairs? I think that I have

the

procedure for turning them spelled out in an old English machining

book.

Bill in Boulder "Engineering as an Art Form!"

Collet dimensions:


Roy
--- In 7x12minilathe@..., William A Williams
<bwmsbldr@j...> wrote:

Thanks for the information. Somewhere I have seen a

dimensioned drawing

of a 3-C collet; if I find it I will get it to you. I suspect that

you

are "skating" the tool tip on the chrome plate. You have to cut it

off

with a shouldering tool or one that actually undercuts the plating.
You do know to make the collets in pairs? I think that I have

the

procedure for turning them spelled out in an old English machining

book.

Bill in Boulder "Engineering as an Art Form!"

Thanks for the information. Somewhere I have seen a dimensioned drawing
of a 3-C collet; if I find it I will get it to you. I suspect that you
are "skating" the tool tip on the chrome plate. You have to cut it off
with a shouldering tool or one that actually undercuts the plating.
You do know to make the collets in pairs? I think that I have the
procedure for turning them spelled out in an old English machining book.

Bill in Boulder "Engineering as an Art Form!"

Hi Bill,

The diameter of the shock absorber rod is 0.865 while the large end
OD of the collets is 0.830 so I can't be too sloppy when centering;
the body OD is 0.650. This shock was bigger than most, enough
material for 4 collets. Messy business draining the oil out of the
shock itself.

I use a Sawzall for cutting metal and it removed the outer shell of
the shock very nicely. The turned down ends of the rod cut easily
too. The chrome part seemed very hard; I tried a regular hacksaw to
make sure the Sawzall blade was OK and the hacksaw wouldn't cut it
either. I was surprised that the ends were notably softer than the
rest of the rod. Cooking it in the fireplace for a couple of hours
made it much more workable. However, I still have the newbie problem
of a rough finish on steel so I use a file to remove the last mil or
so, even after using my "finish" tool.

The largest diameter 3C collet seems to be 1/2 inch although in the
7x10 group someone said they had a 3C slightly larger (I've not seen
anything larger than 1/2 offered in catalogs).

Thanks for the info on 5C collet diameter. I don't know why my
collet is expanded along the narrow split part. I'm looking for a
steel collet for use as a standard in place of the brass collet I'm
presently using -- perhaps the steel collet won't have this.

John



--- In 7x12minilathe@..., William A Williams
<bwmsbldr@j...> wrote:

I am surprised that the strut rod steel is hard to turn as it

comes from

the strut! In my experience once you get under the chrome plate it

is

very nice turning. Except of course where it has been spot welded!

I am a

little surprised that the rod is big enough to make 3-C collets.

What is

the maximum diameter of a 3-C? I may need to reevaluate my need for

a

set!

Bill in Boulder "Engineering as an Art Form!"

I am surprised that the strut rod steel is hard to turn as it comes from
the strut! In my experience once you get under the chrome plate it is
very nice turning. Except of course where it has been spot welded! I am a
little surprised that the rod is big enough to make 3-C collets. What is
the maximum diameter of a 3-C? I may need to reevaluate my need for a
set!

Bill in Boulder "Engineering as an Art Form!"

A lot of helpful hints in your post, Roy, thanks. This is the type
of info one would pick up as an apprentice in a machine shop, I
guess. I'm looking around for a new steel collet for use as my
standard.

Meanwhile, I'm roughing out blanks for some 3C collets in steel per
the Exactus articles. I annealed the steel from the rod in a large
shock absorber and can now machine it -- it seemed very hard prior to
annealing in my fireplace; there is a good side to the cool spring
we're having!

Regards, John




--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:

My choice for a "standard" collet would be a pristine steel one,
from one of the suppliers who states accuracy. I'd use it to hold

an

accurately ground test rod - dowel pins are good. I've had

horrible

results with drill blanks not being straight!
I always use indicators on stationary parts; without the cute
little roller point, I don't indicate parts while they're moving.
For a runout check, I'd manually rotate the test piece to 4
perpendicular points. If a tiny bit of reverse rotation causes

large

indicated runout change, it's a symptom of dragging the indicator.
Back rotate or not, just be consistent on all measurements.
It's also better to keep oil away from indicators - sooner or
later, some gets inside. It doesn't take much oil to make an
indicator really sticky & unusable (think millidrops!)
Leaving things .001" or so oversize allows room for
filing/polishing for final finish. When I'm trying to make a new
surface concentric with or blended into an existing one, I use the

4-

jaw. When I've used collets for that sort of thing, they still
needed indicating & gentle persuasion with a small rawhide mallet.

Roy
--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

The collet is a new SB, sk-polishing offers these frequently on

eBay

and I took advantage when one didn't seem to draw many bids. I

have

accepted it as a standard in testing my collet chuck, at least so
far...

Your comment on working to tenths is very interesting. Having no
experience or training in machining I've been developing my own
methods on an ad hoc basis. I've run into the problem you

mentioned

of "noise" on the DTI due to surface finish; my crude solution

has

been to use fine carbide paper to polish the surface a bit prior

to

taking the reading. I then wipe the surface with a paper towel

and

add a little oil. My measuring technique is to run the lathe at

its

lowest speed, about 12 rpm, and watch the DTI. The needle is

still

a

little shivery but watching several cycles allows me to get a

reading

by averaging the maximum and minimum readings. I am open to any
improvements in technique since I am very much a beginner at this.

Your point on accepting a couple of mils of runout is one I have
slowly arrived at in using the 3 jaw. Lately, I try to leave the
diameter on the large side if a part will need to be removed and

re-

installed in the chuck, going to the finish size as the last step
when possible.

Thanks for the info.

John

My choice for a "standard" collet would be a pristine steel one,
from one of the suppliers who states accuracy. I'd use it to hold an
accurately ground test rod - dowel pins are good. I've had horrible
results with drill blanks not being straight!
I always use indicators on stationary parts; without the cute
little roller point, I don't indicate parts while they're moving.
For a runout check, I'd manually rotate the test piece to 4
perpendicular points. If a tiny bit of reverse rotation causes large
indicated runout change, it's a symptom of dragging the indicator.
Back rotate or not, just be consistent on all measurements.
It's also better to keep oil away from indicators - sooner or
later, some gets inside. It doesn't take much oil to make an
indicator really sticky & unusable (think millidrops!)
Leaving things .001" or so oversize allows room for
filing/polishing for final finish. When I'm trying to make a new
surface concentric with or blended into an existing one, I use the 4-
jaw. When I've used collets for that sort of thing, they still
needed indicating & gentle persuasion with a small rawhide mallet.

Roy
--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

The collet is a new SB, sk-polishing offers these frequently on

eBay

and I took advantage when one didn't seem to draw many bids. I have
accepted it as a standard in testing my collet chuck, at least so
far...

Your comment on working to tenths is very interesting. Having no
experience or training in machining I've been developing my own
methods on an ad hoc basis. I've run into the problem you

mentioned

of "noise" on the DTI due to surface finish; my crude solution has
been to use fine carbide paper to polish the surface a bit prior to
taking the reading. I then wipe the surface with a paper towel and
add a little oil. My measuring technique is to run the lathe at

its

lowest speed, about 12 rpm, and watch the DTI. The needle is still

a

little shivery but watching several cycles allows me to get a

reading

by averaging the maximum and minimum readings. I am open to any
improvements in technique since I am very much a beginner at this.

Your point on accepting a couple of mils of runout is one I have
slowly arrived at in using the 3 jaw. Lately, I try to leave the
diameter on the large side if a part will need to be removed and re-
installed in the chuck, going to the finish size as the last step
when possible.

Thanks for the info.

John


--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:

I wonder if the brass collet is part of the problem. Coming

from

e-bay, there's no telling what sort of abuse it may have

suffered.

Steel collets are "spring hard" to avoid distortion during use;

they

eventually wear eccentric. (Long eventual, except in high volume
production.)
Trying to work to tenths is sort of frustrating - surface

finish

of mating parts has a disproportionate effect on readings.

Actually,

surface finish on the part being indicated can "drag" the

indicator

to a slightly false reading. Presumably, your measuring

technique

gives the same reading on return to the same point. There's

enough

flex in these machines to get a measurable deflection from

resting

your forearm on the headstock.
Except for really critical work, ignoring any runout

under .001"

or .002" saves a lot of set-up time.

Roy

--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

Hi Roy,

Thanks for the link. I looked at the site and wrote to the

owner,

Dave Audette, who provided a considerable amount of information

in

a

detailed reply. One key bit of data is that his runout is

about

4

tenths, similar to mine when the collet settles in the chuck
properly. I also found a CNC site which gave collet runout as

5

tenths max so apparently my collet chuck's performance is in

the

ballpark.

However, it is interesting that Dave gets 4 tenths runout with

a

SB

collet holder which I assume is probably concentric to the

headstock

MT3 socket. Makes me think my headstock may be poorer than

most

since I find the following when indicating various points on

the

backplate:

Outer rim = 5 tenths
Land for chuck registry = 2
Inside of MT3 socket = 6+
Inside of 3C chuck = 2
Piece in collet = 2-4 typical, sometimes 10 (tapping with a

block

of

wood causes it to pop into alignment yielding 2-4)

Logically, a perfectly concentric collet chuck's runout could

be

no

better than the socket it is mounted in.I use a witness mark to

align

my collet chuck to the backplate/MT3 socket so the socket

runout

should be cancelled because the chuck was machined in that

socket

and

replaced in the same orientation. That is, my collet chuck is
slightly eccentric but in a way which compensates for the MT3
socket's runout.

The above figures indicate (no pun intended) that the runout of

the

MT3 socket in my backplate is larger than desirable and that

Dave's

machine seems to run truer by quite a bit since he gets the

same

runout without having machined his chuck in place.

Based on the above I would guess that during manufacture the
backplate is turned to size on a production machine with the

chuck

land left slightly larger than final size. The backplate is

then

mounted on the lathe and the chuck land is machined to final

size

in

place to minimize runout.

I intend to polish the inside of the collet chuck in an attempt

to

cause it to register the collet the same way each time so I

don't

sometimes have to tap the work with a block of wood.

John

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:

See if there's anything here that helps:


Roy

The collet is a new SB, sk-polishing offers these frequently on eBay
and I took advantage when one didn't seem to draw many bids. I have
accepted it as a standard in testing my collet chuck, at least so
far...

Your comment on working to tenths is very interesting. Having no
experience or training in machining I've been developing my own
methods on an ad hoc basis. I've run into the problem you mentioned
of "noise" on the DTI due to surface finish; my crude solution has
been to use fine carbide paper to polish the surface a bit prior to
taking the reading. I then wipe the surface with a paper towel and
add a little oil. My measuring technique is to run the lathe at its
lowest speed, about 12 rpm, and watch the DTI. The needle is still a
little shivery but watching several cycles allows me to get a reading
by averaging the maximum and minimum readings. I am open to any
improvements in technique since I am very much a beginner at this.

Your point on accepting a couple of mils of runout is one I have
slowly arrived at in using the 3 jaw. Lately, I try to leave the
diameter on the large side if a part will need to be removed and re-
installed in the chuck, going to the finish size as the last step
when possible.

Thanks for the info.

John


--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:

I wonder if the brass collet is part of the problem. Coming

from

e-bay, there's no telling what sort of abuse it may have suffered.
Steel collets are "spring hard" to avoid distortion during use;

they

eventually wear eccentric. (Long eventual, except in high volume
production.)
Trying to work to tenths is sort of frustrating - surface finish
of mating parts has a disproportionate effect on readings.

Actually,

surface finish on the part being indicated can "drag" the indicator
to a slightly false reading. Presumably, your measuring technique
gives the same reading on return to the same point. There's enough
flex in these machines to get a measurable deflection from resting
your forearm on the headstock.
Except for really critical work, ignoring any runout under .001"
or .002" saves a lot of set-up time.

Roy

--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

Hi Roy,

Thanks for the link. I looked at the site and wrote to the

owner,

Dave Audette, who provided a considerable amount of information

in

a

detailed reply. One key bit of data is that his runout is about

4

tenths, similar to mine when the collet settles in the chuck
properly. I also found a CNC site which gave collet runout as 5
tenths max so apparently my collet chuck's performance is in the
ballpark.

However, it is interesting that Dave gets 4 tenths runout with a

SB

collet holder which I assume is probably concentric to the

headstock

MT3 socket. Makes me think my headstock may be poorer than most
since I find the following when indicating various points on the
backplate:

Outer rim = 5 tenths
Land for chuck registry = 2
Inside of MT3 socket = 6+
Inside of 3C chuck = 2
Piece in collet = 2-4 typical, sometimes 10 (tapping with a block

of

wood causes it to pop into alignment yielding 2-4)

Logically, a perfectly concentric collet chuck's runout could be

no

better than the socket it is mounted in.I use a witness mark to

align

my collet chuck to the backplate/MT3 socket so the socket runout
should be cancelled because the chuck was machined in that socket

and

replaced in the same orientation. That is, my collet chuck is
slightly eccentric but in a way which compensates for the MT3
socket's runout.

The above figures indicate (no pun intended) that the runout of

the

MT3 socket in my backplate is larger than desirable and that

Dave's

machine seems to run truer by quite a bit since he gets the same
runout without having machined his chuck in place.

Based on the above I would guess that during manufacture the
backplate is turned to size on a production machine with the

chuck

land left slightly larger than final size. The backplate is then
mounted on the lathe and the chuck land is machined to final size

in

place to minimize runout.

I intend to polish the inside of the collet chuck in an attempt

to

cause it to register the collet the same way each time so I don't
sometimes have to tap the work with a block of wood.

John

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:

See if there's anything here that helps:


Roy

I measured my 5-C spring collets and found less than .001" taper from
the threads to the closing cone!

I wonder if the brass collet is part of the problem. Coming from
e-bay, there's no telling what sort of abuse it may have suffered.
Steel collets are "spring hard" to avoid distortion during use; they
eventually wear eccentric. (Long eventual, except in high volume
production.)
Trying to work to tenths is sort of frustrating - surface finish
of mating parts has a disproportionate effect on readings. Actually,
surface finish on the part being indicated can "drag" the indicator
to a slightly false reading. Presumably, your measuring technique
gives the same reading on return to the same point. There's enough
flex in these machines to get a measurable deflection from resting
your forearm on the headstock.
Except for really critical work, ignoring any runout under .001"
or .002" saves a lot of set-up time.

Roy

--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

Hi Roy,

Thanks for the link. I looked at the site and wrote to the owner,
Dave Audette, who provided a considerable amount of information in

a

detailed reply. One key bit of data is that his runout is about 4
tenths, similar to mine when the collet settles in the chuck
properly. I also found a CNC site which gave collet runout as 5
tenths max so apparently my collet chuck's performance is in the
ballpark.

However, it is interesting that Dave gets 4 tenths runout with a SB
collet holder which I assume is probably concentric to the

headstock

MT3 socket. Makes me think my headstock may be poorer than most
since I find the following when indicating various points on the
backplate:

Outer rim = 5 tenths
Land for chuck registry = 2
Inside of MT3 socket = 6+
Inside of 3C chuck = 2
Piece in collet = 2-4 typical, sometimes 10 (tapping with a block

of

wood causes it to pop into alignment yielding 2-4)

Logically, a perfectly concentric collet chuck's runout could be no
better than the socket it is mounted in.I use a witness mark to

align

my collet chuck to the backplate/MT3 socket so the socket runout
should be cancelled because the chuck was machined in that socket

and

replaced in the same orientation. That is, my collet chuck is
slightly eccentric but in a way which compensates for the MT3
socket's runout.

The above figures indicate (no pun intended) that the runout of the
MT3 socket in my backplate is larger than desirable and that Dave's
machine seems to run truer by quite a bit since he gets the same
runout without having machined his chuck in place.

Based on the above I would guess that during manufacture the
backplate is turned to size on a production machine with the chuck
land left slightly larger than final size. The backplate is then
mounted on the lathe and the chuck land is machined to final size

in

place to minimize runout.

I intend to polish the inside of the collet chuck in an attempt to
cause it to register the collet the same way each time so I don't
sometimes have to tap the work with a block of wood.

John

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:

See if there's anything here that helps:


Roy
--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

I recently attempted to make a 3C collet chuck to fit the 3MT

taper

in my lathe. This seemed to go OK but the first try was not a

good

fit (rear of the collet fit sloppy) so I made another which fit
better. The chuck is based on an article by Exactus, 2984

found

here:

As a newbie, I've never seen a collet chuck in action so I

don't

know

exactly what to expect from it. What I hoped was that it would
provide simple, non-marking gripping of work with zero runout.

My

chuck may be poorly made or perhaps I'm overly optimistic on

how

it

should work.

I bought a 3C South Bend 3/8 brass collet on eBay as a model to

judge

fit; my goal was to eventually make steel collets to fit the

chuck.

When I put this collet into my chuck I find that the runout

varies

each time I tighten the drawbar, typically 2-4 tenths,

sometimes

up

to 1 mil. When the runout is large it gets larger as I move

farther

from the chuck so apparently it is angled somewhere (the work

or

the

collet itself); if I tap the test piece on the high side with a

block

of wood it generally will settle to the more typical 2-4 tenths
anywhere along the length of the 1 inch long test piece (a

commercial

3/8 D bit shaft.

Ths narrow part of the SB collet tapers about 6 mils, getting

larger

as one goes from the threads toward the steep taper. I made the

chuck

so it is an easy fit for the first part of the collet but I

have

to

press firmly to fully insert it due to the collet's taper.

Similarly,

it requires a push with the drawbar to get enough to protrude

so

it

can be pulled out.

With the above as background, I have a number of newbie

questions

on

collets and collet chucks:

1. What is the expected runout when using a collet?

2. Is the taper on the narrow part of the collet machined in or

does

this happen when they add the slits? Will this also be present

on

steel collets or just on brass?

3. What surface(s) are critical in providing the collet

centering.

That is, is the fit of the chuck onto the rear of the collet
critical? Does the chuck need to be tapered in the narrow bore

to

match the collet? Is there a specification for the steep angle

on

a

3C?

Any help here would be appreciated. I've put quite a bit of

time

into making this chuck and now don't know whether it is useful

or

just a fancy doorstop.

John

Hi Roy,

Thanks for the link. I looked at the site and wrote to the owner,
Dave Audette, who provided a considerable amount of information in a
detailed reply. One key bit of data is that his runout is about 4
tenths, similar to mine when the collet settles in the chuck
properly. I also found a CNC site which gave collet runout as 5
tenths max so apparently my collet chuck's performance is in the
ballpark.

However, it is interesting that Dave gets 4 tenths runout with a SB
collet holder which I assume is probably concentric to the headstock
MT3 socket. Makes me think my headstock may be poorer than most
since I find the following when indicating various points on the
backplate:

Outer rim = 5 tenths
Land for chuck registry = 2
Inside of MT3 socket = 6+
Inside of 3C chuck = 2
Piece in collet = 2-4 typical, sometimes 10 (tapping with a block of
wood causes it to pop into alignment yielding 2-4)

Logically, a perfectly concentric collet chuck's runout could be no
better than the socket it is mounted in.I use a witness mark to align
my collet chuck to the backplate/MT3 socket so the socket runout
should be cancelled because the chuck was machined in that socket and
replaced in the same orientation. That is, my collet chuck is
slightly eccentric but in a way which compensates for the MT3
socket's runout.

The above figures indicate (no pun intended) that the runout of the
MT3 socket in my backplate is larger than desirable and that Dave's
machine seems to run truer by quite a bit since he gets the same
runout without having machined his chuck in place.

Based on the above I would guess that during manufacture the
backplate is turned to size on a production machine with the chuck
land left slightly larger than final size. The backplate is then
mounted on the lathe and the chuck land is machined to final size in
place to minimize runout.

I intend to polish the inside of the collet chuck in an attempt to
cause it to register the collet the same way each time so I don't
sometimes have to tap the work with a block of wood.

John

--- In 7x12minilathe@..., "roylowenthal"
<roylowenthal@y...> wrote:

See if there's anything here that helps:


Roy
--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

I recently attempted to make a 3C collet chuck to fit the 3MT

taper

in my lathe. This seemed to go OK but the first try was not a

good

fit (rear of the collet fit sloppy) so I made another which fit
better. The chuck is based on an article by Exactus, 2984 found

here:

As a newbie, I've never seen a collet chuck in action so I don't

know

exactly what to expect from it. What I hoped was that it would
provide simple, non-marking gripping of work with zero runout. My
chuck may be poorly made or perhaps I'm overly optimistic on how

it

should work.

I bought a 3C South Bend 3/8 brass collet on eBay as a model to

judge

fit; my goal was to eventually make steel collets to fit the

chuck.

When I put this collet into my chuck I find that the runout

varies

each time I tighten the drawbar, typically 2-4 tenths, sometimes

up

to 1 mil. When the runout is large it gets larger as I move

farther

from the chuck so apparently it is angled somewhere (the work or

the

collet itself); if I tap the test piece on the high side with a

block

of wood it generally will settle to the more typical 2-4 tenths
anywhere along the length of the 1 inch long test piece (a

commercial

3/8 D bit shaft.

Ths narrow part of the SB collet tapers about 6 mils, getting

larger

as one goes from the threads toward the steep taper. I made the

chuck

so it is an easy fit for the first part of the collet but I have

to

press firmly to fully insert it due to the collet's taper.

Similarly,

it requires a push with the drawbar to get enough to protrude so

it

can be pulled out.

With the above as background, I have a number of newbie questions

on

collets and collet chucks:

1. What is the expected runout when using a collet?

2. Is the taper on the narrow part of the collet machined in or

does

this happen when they add the slits? Will this also be present on
steel collets or just on brass?

3. What surface(s) are critical in providing the collet

centering.

That is, is the fit of the chuck onto the rear of the collet
critical? Does the chuck need to be tapered in the narrow bore to
match the collet? Is there a specification for the steep angle on

a

3C?

Any help here would be appreciated. I've put quite a bit of time
into making this chuck and now don't know whether it is useful or
just a fancy doorstop.

John

--- In 7x12minilathe@..., "mikeaita1" <aita1@a...> wrote:

7X10 is not on the server :(
mike

<

ead.txt>

Download it, print out a copy, and take it to the lathe.

The link got broken by Yahoo. Its a common problem. I'll try to
rejoin it here, but if that doesn't work (I won't know for sure until
I see the new message on the web site) you can cut and paste it back
together.



ad.txt

Hope that helps,
RA

See if there's anything here that helps:


Roy
--- In 7x12minilathe@..., "John" <moran03@e...> wrote:

I recently attempted to make a 3C collet chuck to fit the 3MT taper
in my lathe. This seemed to go OK but the first try was not a good
fit (rear of the collet fit sloppy) so I made another which fit
better. The chuck is based on an article by Exactus, 2984 found

here:

As a newbie, I've never seen a collet chuck in action so I don't

know

exactly what to expect from it. What I hoped was that it would
provide simple, non-marking gripping of work with zero runout. My
chuck may be poorly made or perhaps I'm overly optimistic on how it
should work.

I bought a 3C South Bend 3/8 brass collet on eBay as a model to

judge

fit; my goal was to eventually make steel collets to fit the chuck.
When I put this collet into my chuck I find that the runout varies
each time I tighten the drawbar, typically 2-4 tenths, sometimes up
to 1 mil. When the runout is large it gets larger as I move

farther

from the chuck so apparently it is angled somewhere (the work or

the

collet itself); if I tap the test piece on the high side with a

block

of wood it generally will settle to the more typical 2-4 tenths
anywhere along the length of the 1 inch long test piece (a

commercial

3/8 D bit shaft.

Ths narrow part of the SB collet tapers about 6 mils, getting

larger

as one goes from the threads toward the steep taper. I made the

chuck

so it is an easy fit for the first part of the collet but I have to
press firmly to fully insert it due to the collet's taper.

Similarly,

it requires a push with the drawbar to get enough to protrude so it
can be pulled out.

With the above as background, I have a number of newbie questions

on

collets and collet chucks:

1. What is the expected runout when using a collet?

2. Is the taper on the narrow part of the collet machined in or

does

this happen when they add the slits? Will this also be present on
steel collets or just on brass?

3. What surface(s) are critical in providing the collet centering.
That is, is the fit of the chuck onto the rear of the collet
critical? Does the chuck need to be tapered in the narrow bore to
match the collet? Is there a specification for the steep angle on a
3C?

Any help here would be appreciated. I've put quite a bit of time
into making this chuck and now don't know whether it is useful or
just a fancy doorstop.

John

Based on building a 5-C adaptor I believe that the bore should be
straight to align the collet body coaxially with the lathe axis.

Bill in Boulder "Engineering as an Art Form!"

Did you try the above? Works for me.

Charlie

7X10 is not on the server :(
mike

<

ead.txt>

Download it, print out a copy, and take it to the lathe.

Useing

something that is easy to machine like PVC pipe or aluminum

conduit,

practice, practice, practice. At first, read each step as you

go.

Then when you feel more comfortable, do a few steps at a time,

until

you can do it in your sleep.

The method works. I learned to thread using it.

You can buy ER4/5/6 or EL4/5/6 (size to fit your lathe) as

cemented

carbide or you can grind your own HSS tools. I recommend you

grind

your own bits for practice, using one of the carbide ones as an
example. Don't forget to leave clearance for the helix angle

of

the

thread. Don't try to cut threads using one of the el-cheapo

carbide

bits. You will be frustrated because they seem to have no

clearance

on any edges.

Hope that helps,
RA