Lapping seems to be a term that encompasses several different processes of
similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve this:
From dedicated lapping compounds obtained in Auto part stores (which here
nobody has heard of) to mixing up a scouring powder with oil to make a
lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)?
2) What is the maximum/minimum grit suitable for lapping?
3) Why isn't using ultrafine steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings. Not
having anything "lapping-like" to hand I mixed up Fast Orange with oil and
used that. It contains pumice and GOK what the grit of that is. The shaft is
smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes which
contain abrasives. Would they be suitable? Too harsh?

--
Michael Koblic,
Campbell River, BC

Michael Koblic wrote:

Lapping seems to be a term that encompasses several different processes of
similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve this:
From dedicated lapping compounds obtained in Auto part stores (which here
nobody has heard of) to mixing up a scouring powder with oil to make a
lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)?
2) What is the maximum/minimum grit suitable for lapping?
3) Why isn't using ultrafine steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings. Not
having anything "lapping-like" to hand I mixed up Fast Orange with oil and
used that. It contains pumice and GOK what the grit of that is. The shaft is
smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes which
contain abrasives. Would they be suitable? Too harsh?


How about the old stainless steel cleaner, 'Barkeeps Friend'? It
says it is abrasive, but not how much. I've seen it used in kitchens
for years to keep old stainless steel sinks & tables clean and looking
good.

http://barkeepersfriend.com/products.htm

http://barkeepersfriend.com/BKF_MSDS_01_09.pdf


--
You can't have a sense of humor, if you have no sense!

On Sun, 17 May 2009 21:21:33 -0700, Michael Koblic wrote:

Lapping seems to be a term that encompasses several different processes
of similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve
this: From dedicated lapping compounds obtained in Auto part stores
(which here nobody has heard of) to mixing up a scouring powder with oil
to make a lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)? 2) What is the
maximum/minimum grit suitable for lapping? 3) Why isn't using ultrafine
steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings.
Not having anything "lapping-like" to hand I mixed up Fast Orange with
oil and used that. It contains pumice and GOK what the grit of that is.
The shaft is smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes
which contain abrasives. Would they be suitable? Too harsh?

Where's "here" for you?

In the US you can get lapping compound (and diamond grinding/lapping
compound) from McMaster and from Small Parts, Inc.

--
www.wescottdesign.com

On Mon, 18 May 2009 00:45:01 -0500, Tim Wescott
wrote:

On Sun, 17 May 2009 21:21:33 -0700, Michael Koblic wrote:

Lapping seems to be a term that encompasses several different processes
of similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve
this: From dedicated lapping compounds obtained in Auto part stores
(which here nobody has heard of) to mixing up a scouring powder with oil
to make a lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)? 2) What is the
maximum/minimum grit suitable for lapping? 3) Why isn't using ultrafine
steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings.
Not having anything "lapping-like" to hand I mixed up Fast Orange with
oil and used that. It contains pumice and GOK what the grit of that is.
The shaft is smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes
which contain abrasives. Would they be suitable? Too harsh?

Where's "here" for you?

In the US you can get lapping compound (and diamond grinding/lapping
compound) from McMaster and from Small Parts, Inc.

IIRC, Michael's in BC.

I haven't done any myself since engine rebuilding on the farm days
(decades), but usually it means charging abrasive to a softer metal
form to lap a harder metal. The abrasive embeds in the softer metal,
then the lap (softer is moved across the harder material to improve
finish and fit.

This implies that you wouldn't want to lap a babbitt bearing because
you'd never get the abrasive out, and it'd continue to wear the shaft
it was supposed to protect. Very deformable laps also wouldn't be
effective because they wear the low spots almost as fast as the high
spots.

Brass makes a good lap for cast iron or steel. I intend to use lead
bullets charged with abrasive to fire lap a rifle barrel. There's
lots of other combinations.

The abrasive must be removed completely from the lapped part after
lapping. I have read of abrasives that break down quickly so they are
not a problem, don't know how effective that is.

As far as obtaining lapping compounds, I'd google Clover compounds
British Columbia. Hmmm. Just tried that, there's a supplier in
Ontario, and the stuff is pretty easy to ship. They also have some
info on grit sizes and uses. http://www.newmantools.com/clover.htm

Pete Keillor

Michael Koblic wrote:
....
FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings. Not
having anything "lapping-like" to hand I mixed up Fast Orange with oil and
used that. It contains pumice and GOK what the grit of that is. ...

Uh oh ... that wasn't a good idea. The pumice will embed itself in the
bronze and continue to lap the shaft, even when you think that you have
cleaned it out. Or, maybe pumice is soft enough that it will break down
- I dunno.

Bob

On Sun, 17 May 2009 21:21:33 -0700, "Michael Koblic"
wrote:

Lapping seems to be a term that encompasses several different processes of
similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve this:
From dedicated lapping compounds obtained in Auto part stores (which here
nobody has heard of) to mixing up a scouring powder with oil to make a
lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)?
2) What is the maximum/minimum grit suitable for lapping?
3) Why isn't using ultrafine steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings. Not
having anything "lapping-like" to hand I mixed up Fast Orange with oil and
used that. It contains pumice and GOK what the grit of that is. The shaft is
smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes which
contain abrasives. Would they be suitable? Too harsh?
Greetings Michael,
It's too bad you used pumice to lap your shaft. This is because the
pumice will embed itself into the softer bronze and continue to lap
the shaft. For lapping plain bearings (AKA bushings) the stuff to use
is called "TIMESAVER". You can find it online. It is an abrasive that
breaks down completely and will not keep cutting. It is available in a
sampler kit that contains several different grits of two different
types of compound. One for soft metals like bronze and babbit and the
other for steels and the like. Unlike regular lapping compounds when
this stuff is used the softer material is lapped, just the opposite
when using, for example, Clover Compound.
ERS

wrote in message
...
On Sun, 17 May 2009 21:21:33 -0700, "Michael Koblic"
wrote:

Lapping seems to be a term that encompasses several different processes of
similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve this:
From dedicated lapping compounds obtained in Auto part stores (which here
nobody has heard of) to mixing up a scouring powder with oil to make a
lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)?
2) What is the maximum/minimum grit suitable for lapping?
3) Why isn't using ultrafine steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings.
Not
having anything "lapping-like" to hand I mixed up Fast Orange with oil and
used that. It contains pumice and GOK what the grit of that is. The shaft
is
smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes
which
contain abrasives. Would they be suitable? Too harsh?
Greetings Michael,
It's too bad you used pumice to lap your shaft. This is because the
pumice will embed itself into the softer bronze and continue to lap
the shaft. For lapping plain bearings (AKA bushings) the stuff to use
is called "TIMESAVER". You can find it online. It is an abrasive that
breaks down completely and will not keep cutting. It is available in a
sampler kit that contains several different grits of two different
types of compound. One for soft metals like bronze and babbit and the
other for steels and the like. Unlike regular lapping compounds when
this stuff is used the softer material is lapped, just the opposite
when using, for example, Clover Compound.
ERS

Ah. Live and learn. Though the stuff washes off my hands fine. Maybe the
shaft will live...I honestly do not know how much effect it had in the first
place. Anyway, calling it a "shaft" requires a fit of enthusiasm in the
first place.

Now I am still confused: Why go to all this kerfuffle to smooth out a bit of
metal, particularly if it is flat. I see the grits available are anywhere
between 50 and 1200 so one can take pretty big chunks of material. Why can't
you achieve the same result (on a flat and accessible surface at least) with
steel wool/Scotchbrite pad? Or just plain old sand-paper for that matter (if
you are using the coarser grits). How is the lapping compound behave
differently from these other gizmos?

But thanks for the references - I have been able to bookmark the web site
that sells both Clover and Timesaver just in case I decide I cannot live
without it.

--
Michael Koblic,
Campbell River, BC

On May 18, 5:17*pm, "Michael Koblic" wrote:
...Why can't
you achieve the same result (on a flat and accessible surface at least) with
steel wool/Scotchbrite pad? Or just plain old sand-paper for that matter (if
you are using the coarser grits). How is the lapping compound behave
differently from these other gizmos?
--
Michael Koblic,

Lapping implies a rigid guide holding the abrasive. You could use a
flat steel block behind sandpaper but the paper has some give and the
relatively thick abrasive layer wears down unevenly. I wrap sandpaper
around a form such as a dowel to clean up rounded inside corners and
such if the geometry isn't critical.

I suppose you could burn sandpaper to separate the abrasive. Caustic
soda dissolves alumina to some extent, without damaging metals except
aluminum.

jsw

On May 18, 5:17*pm, "Michael Koblic" wrote:
wrote in message

...



On Sun, 17 May 2009 21:21:33 -0700, "Michael Koblic"
wrote:

Lapping seems to be a term that encompasses several different processes of
similar nature.

I am interested specifically in the recommendations to lap the ways of
lathes and mills. There seems to be a variety of ways people achieve this:
From dedicated lapping compounds obtained in Auto part stores (which here
nobody has heard of) to mixing up a scouring powder with oil to make a
lapping paste. It brings up several questions:

1) When does lapping stop and grinding starts (Permatex make a "valve
grinding compound" which some people use for lapping)?
2) What is the maximum/minimum grit suitable for lapping?
3) Why isn't using ultrafine steel wool/Scotchbrite pad "lapping"?

FWIW I tried to make a 3/4" shaft turn more smoothly in bronze bearings..
Not
having anything "lapping-like" to hand I mixed up Fast Orange with oil and
used that. It contains pumice and GOK what the grit of that is. The shaft
is
smoother. I think.

BTW it is now virtually impossible to get the old scouring powders for
cleaning - everybody is so proud that their product is "scratch free".

While browsing in the Auto part stores I found several cleaning pastes
which
contain abrasives. Would they be suitable? Too harsh?
Greetings Michael,
It's too bad you used pumice to lap your shaft. This is because the
pumice will embed itself into the softer bronze and continue to lap
the shaft. For lapping plain bearings (AKA bushings) the stuff to use
is called "TIMESAVER". You can find it online. It is an abrasive that
breaks down completely and will not keep cutting. It is available in a
sampler kit that contains several different grits of two different
types of compound. One for soft metals like bronze and babbit and the
other for steels and the like. Unlike regular lapping compounds when
this stuff is used the softer material is lapped, just the opposite
when using, for example, Clover Compound.
ERS

Ah. Live and learn. Though the stuff washes off my hands fine. Maybe the
shaft will live...I honestly do not know how much effect it had in the first
place. Anyway, calling it a "shaft" requires a fit of enthusiasm in the
first place.

Now I am still confused: Why go to all this kerfuffle to smooth out a bit of
metal, particularly if it is flat. I see the grits available are anywhere
between 50 and 1200 so one can take pretty big chunks of material. Why can't
you achieve the same result (on a flat and accessible surface at least) with
steel wool/Scotchbrite pad? Or just plain old sand-paper for that matter (if
you are using the coarser grits). How is the lapping compound behave
differently from these other gizmos?

But thanks for the references - I have been able to bookmark the web site
that sells both Clover and Timesaver just in case I decide I cannot live
without it.

--
Michael Koblic,
Campbell River, BC

Lapping is about getting two parts to fit each other, as in lapping
valves into their seats, or pins into holes. Scotchbrite is about
getting parts clean and shiny.

In article ,
"Michael Koblic" wrote:

Now I am still confused: Why go to all this kerfuffle to smooth out a bit of
metal, particularly if it is flat. I see the grits available are anywhere
between 50 and 1200 so one can take pretty big chunks of material. Why can't
you achieve the same result (on a flat and accessible surface at least) with
steel wool/Scotchbrite pad? Or just plain old sand-paper for that matter (if
you are using the coarser grits). How is the lapping compound behave
differently from these other gizmos?

If, by some miracle, it is "flat", then using scotchbrite or sandpaper
will render it not flat - on the microscopic precision scale one cares
about with lapping - areas where the stuff is pressed harder will wear
down more, etc.. If it's not flat to start with, scotchbrite or
sandpaper won't do any thing to improve it, as they conform to the
surface (removing material form both low and high spots) and also have
the above behavior of possibly putting new gouges (on a fine scale) into
the surface.

A lap only grinds at the high points of contact between the rigid (soft)
lap and the rigid (harder) item being lapped, where the (even harder)
abrasive trapped in the soft lap scrapes the high points of the item
being lapped. Thus, it makes the surface flatter, or rounder, or more
whatever shape the lap is.

--
Cats, coffee, chocolate...vices to live by

On May 18, 8:05*pm, Ecnerwal
wrote:
In article ,
*"Michael Koblic" wrote:

Now I am still confused: Why go to all this kerfuffle to smooth out a bit of
metal, particularly if it is flat. I see the grits available are anywhere
between 50 and 1200 so one can take pretty big chunks of material. Why can't
you achieve the same result (on a flat and accessible surface at least) with
steel wool/Scotchbrite pad? Or just plain old sand-paper for that matter (if
you are using the coarser grits). How is the lapping compound behave
differently from these other gizmos?

If, by some miracle, it is "flat", then using scotchbrite or sandpaper
will render it not flat - on the microscopic precision scale one cares
about with lapping - areas where the stuff is pressed harder will wear
down more, etc.. If it's not flat to start with, scotchbrite or
sandpaper won't do any thing to improve it, as they conform to the
surface (removing material form both low and high spots) and also have
the above behavior of possibly putting new gouges (on a fine scale) into
the surface.

A lap only grinds at the high points of contact between the rigid (soft)
lap and the rigid (harder) item being lapped, where the (even harder)
abrasive trapped in the soft lap scrapes the high points of the item
being lapped. Thus, it makes the surface flatter, or rounder, or more
whatever shape the lap is.

--
Cats, coffee, chocolate...vices to live by

Actually, what I should have said is that "lapping" with Scotchbrite
will make your previously flat surface conform to the shape of your
fingers,

Jim Wilkins wrote:

Lapping implies a rigid guide holding the abrasive.

OK, now I get it. This was the critical element I was missing. So to lap,
say, a lathe way, you would spread the paste on a flat piece of brass or
aluminium and rub it on the ways?

I won't even ask how they lap the automotive valves...

--
Michael Koblic,
Campbell River, BC

Ecnerwal wrote:

If, by some miracle, it is "flat", then using scotchbrite or sandpaper
will render it not flat - on the microscopic precision scale one cares
about with lapping - areas where the stuff is pressed harder will wear
down more, etc.. If it's not flat to start with, scotchbrite or
sandpaper won't do any thing to improve it, as they conform to the
surface (removing material form both low and high spots) and also have
the above behavior of possibly putting new gouges (on a fine scale)
into the surface.

A lap only grinds at the high points of contact between the rigid
(soft) lap and the rigid (harder) item being lapped, where the (even
harder) abrasive trapped in the soft lap scrapes the high points of
the item being lapped. Thus, it makes the surface flatter, or
rounder, or more whatever shape the lap is.

This brings up all sorts of follow-up questions, like what should be the
nature of the flat surface that does the lapping. Does it need to be lapped
itself? Or would, say, fly-cutting a piece of soft metal such as brass or
aluminium be sufficient. If the lapper has to be softer than the lappee then
a plate of glass would presumably not be suitable.

Revisiting the shaft affair, what should one have done? The profile is
round, not flat. Would you apply the lapping compound to the bushings and
spin the shaft in them? Would the bushings still be useable afterwards?
Should one have a set of "lapper bushings"?

Anyway, this has been very helpful to me. Thanks.

--
Michael Koblic,
Campbell River, BC

P.S. I have jsut become a proud owner of the Machinery's Handbook. It has a
fairly extensive section on lapping yet even they assume the basic
understanding of the concept. So all I need now is some fine, soft,
close-grained cast iron, flour of emery and some sperm oil...:-)

On Mon, 18 May 2009 20:06:35 -0700, the infamous "Michael Koblic"
scrawled the following:

Jim Wilkins wrote:

Lapping implies a rigid guide holding the abrasive.

OK, now I get it. This was the critical element I was missing. So to lap,
say, a lathe way, you would spread the paste on a flat piece of brass or
aluminium and rub it on the ways?

I won't even ask how they lap the automotive valves...

I learned this way: apply lapping paste to valve seat, insert valve,
stick rubber suction-cupped, hand-crank egg-beater/drill thang to
valve face, and turn handle. like this: http://tinyurl.com/pdscsu or
http://www.goodson.com/store/product_images/b1_imgshop_528.jpg
I have no idea what grit we used in 1971/72.

Here's another semi-manual way:
http://fly.hiwaay.net/~langford/corvair/valvejob.html

And a VERY manual way: http://tinyurl.com/r6ab8a or
http://www.holtsauto.com/images/products/repair-and-maintenance/maintenance/holts-valve-griniding-kit-hi.jpg

--
No matter how cynical you are, it is impossible to keep up.
--Lily Tomlin

On Mon, 18 May 2009 20:34:34 -0700, "Michael Koblic"
wrote:

Ecnerwal wrote:

If, by some miracle, it is "flat", then using scotchbrite or sandpaper
will render it not flat - on the microscopic precision scale one cares
about with lapping - areas where the stuff is pressed harder will wear
down more, etc.. If it's not flat to start with, scotchbrite or
sandpaper won't do any thing to improve it, as they conform to the
surface (removing material form both low and high spots) and also have
the above behavior of possibly putting new gouges (on a fine scale)
into the surface.

A lap only grinds at the high points of contact between the rigid
(soft) lap and the rigid (harder) item being lapped, where the (even
harder) abrasive trapped in the soft lap scrapes the high points of
the item being lapped. Thus, it makes the surface flatter, or
rounder, or more whatever shape the lap is.

This brings up all sorts of follow-up questions, like what should be the
nature of the flat surface that does the lapping. Does it need to be lapped
itself? Or would, say, fly-cutting a piece of soft metal such as brass or
aluminium be sufficient. If the lapper has to be softer than the lappee then
a plate of glass would presumably not be suitable.

Revisiting the shaft affair, what should one have done? The profile is
round, not flat. Would you apply the lapping compound to the bushings and
spin the shaft in them? Would the bushings still be useable afterwards?
Should one have a set of "lapper bushings"?

Anyway, this has been very helpful to me. Thanks.

Essentially a "lap" is a piece of material in which abrasive can be
imbedded. Think of it as similar to a grinding wheel. A "diamond
hone", diamond particles imbedded in a steel plate, is a lap, for
example.

Normally a soft material is not lapped as the abrasive grains will
imbed in the softer material and you will essentially make a lap.
Babbet bearings, for example are scraped to fit. Not lapped.

A "lapping plate" is traditionally a flat cast iron plate and is
"charged" by spreading abrasive on the plate and imbedding it by using
a hardened roller like a rolling pin to force the abrasive grains into
the cast iron. The plate is then washed free of loose abrasive before
use.

Regarding the shaft in bushings you mention the traditional method was
to polish or grind the shaft to size and then ream the bushings after
installation.

Generally a lap is used to provide a certain surface finish rather
then to provide a certain surface dimension, although that is not a
iron bound description.

The O.P. question about "lapping" a lathe bed seems almost a
contradiction as nearly all lathe beds are finished by grinding and
sometimes scrapping to provide oil retention.

Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

On May 18, 11:34*pm, "Michael Koblic" wrote:
...
Revisiting the shaft affair, what should one have done? The profile is
round, not flat. Would you apply the lapping compound to the bushings and
spin the shaft in them? Would the bushings still be useable afterwards?
Should one have a set of "lapper bushings"?

Michael Koblic,

High-speed internal grinding attachments for lathes were once made
with extremely close hardened steel-on-steel bearings without oil that
reportedly would coast for a long time although they seemed to stick a
little at rest. They were fitted by lapping with fine diamond dust,
which didn't embed in the steel. I think I saw that in one of Fred
Colvin's books.

I fit pressed-in bronze bearings with a reamer and make slight changes
to the drag with an adjustable reamer. Mine are mostly the cheap
imports and they begin to chatter if asked to remove more than a hair.

I've read that a half-round or D reamers works well and you can make
one to any size on your lathe.

jsw

On Sun, 17 May 2009 21:21:33 -0700, "Michael Koblic"
wrote:



I am interested specifically in the recommendations to lap the ways of
lathes and mills.

It is most strongly recommended that you do not lap the ways of lathes and
mills.

If the flatness obtained from the surface grinder on a hardened way is
insufficient and if you have the use of an autocollimator and if you are
working in microns or less, then you might consider lapping. Otherwise, use
scraping or surface grinding.


Mark Rand
RTFM

On May 18, 10:02*pm, Larry Jaques
wrote:
On Mon, 18 May 2009 20:06:35 -0700, the infamous "Michael Koblic"
scrawled the following:

Jim Wilkins wrote:

Lapping implies a rigid guide holding the abrasive.

OK, now I get it. This was the critical element I was missing. So to lap,
say, a lathe way, you would spread the paste on a flat piece of brass or
aluminium and rub it on the ways?

I won't even ask how they lap the automotive valves...

I learned this way: apply lapping paste to valve seat, insert valve,
stick rubber suction-cupped, hand-crank egg-beater/drill thang to
valve face, and turn handle. like this:http://tinyurl.com/pdscsuor
http://www.goodson.com/store/product_images/b1_imgshop_528.jpg
I have no idea what grit we used in 1971/72.

Here's another semi-manual way:http://fly.hiwaay.net/~langford/corvair/valvejob.html

And a VERY manual way:http://tinyurl.com/r6ab8aor
http://www.holtsauto.com/images/products/repair-and-maintenance/maint...

--
No matter how cynical you are, it is impossible to keep up.
* * * * * * * * * * * * * * * * * * * * * * --Lily Tomlin

And no matter what they call it, it's a GRINDING operation, not
lapping. The abrasive doesn't embed in the valves or the seats, it
just rolls around between(at least you HOPE it does).

Stan

On Mon, 18 May 2009 21:02:36 -0700, Larry Jaques
wrote:

On Mon, 18 May 2009 20:06:35 -0700, the infamous "Michael Koblic"
scrawled the following:

Jim Wilkins wrote:

Lapping implies a rigid guide holding the abrasive.

OK, now I get it. This was the critical element I was missing. So to lap,
say, a lathe way, you would spread the paste on a flat piece of brass or
aluminium and rub it on the ways?

I won't even ask how they lap the automotive valves...

I learned this way: apply lapping paste to valve seat, insert valve,
stick rubber suction-cupped, hand-crank egg-beater/drill thang to
valve face, and turn handle. like this: http://tinyurl.com/pdscsu or
http://www.goodson.com/store/product_images/b1_imgshop_528.jpg
I have no idea what grit we used in 1971/72.

Coarse then fine if you bought the double ended can from Canadian Tire
for $2.29 that has the yellow label painted over with black paint. I
suspect I bought this one in 1958.

Here's another semi-manual way:
http://fly.hiwaay.net/~langford/corvair/valvejob.html

And a VERY manual way: http://tinyurl.com/r6ab8a or
http://www.holtsauto.com/images/products/repair-and-maintenance/maintenance/holts-valve-griniding-kit-hi.jpg
That's similar to the tool I had - a section of broom stick with one
of the suction cups from an electric defroster screwed into a hole in
the end.
Gerry :-)}
London, Canada

"Michael Koblic" wrote in message
...
Ecnerwal wrote:

If, by some miracle, it is "flat", then using scotchbrite or sandpaper
will render it not flat - on the microscopic precision scale one cares
about with lapping - areas where the stuff is pressed harder will wear
down more, etc.. If it's not flat to start with, scotchbrite or
sandpaper won't do any thing to improve it, as they conform to the
surface (removing material form both low and high spots) and also have
the above behavior of possibly putting new gouges (on a fine scale)
into the surface.

A lap only grinds at the high points of contact between the rigid
(soft) lap and the rigid (harder) item being lapped, where the (even
harder) abrasive trapped in the soft lap scrapes the high points of
the item being lapped. Thus, it makes the surface flatter, or
rounder, or more whatever shape the lap is.

This brings up all sorts of follow-up questions, like what should be the
nature of the flat surface that does the lapping. Does it need to be
lapped itself? Or would, say, fly-cutting a piece of soft metal such as
brass or aluminium be sufficient. If the lapper has to be softer than the
lappee then a plate of glass would presumably not be suitable.

Revisiting the shaft affair, what should one have done? The profile is
round, not flat. Would you apply the lapping compound to the bushings and
spin the shaft in them? Would the bushings still be useable afterwards?
Should one have a set of "lapper bushings"?

Anyway, this has been very helpful to me. Thanks.

--
Michael Koblic,
Campbell River, BC

P.S. I have jsut become a proud owner of the Machinery's Handbook. It has
a fairly extensive section on lapping yet even they assume the basic
understanding of the concept. So all I need now is some fine, soft,
close-grained cast iron, flour of emery and some sperm oil...:-)

Lapping of a shaft would typically be done with a split bushing kind of lap
with some method of holding and adjusting the split. It would be worked
along the rotating shaft, lapping the tightest parts mostly, until the shaft
was uniform. Lapping can provide very good accuracy and finish. Gage blocks
are finished by lapping.

Don Young

"Mark Rand" wrote in message
...
On Sun, 17 May 2009 21:21:33 -0700, "Michael Koblic"


I am interested specifically in the recommendations to lap the ways of
lathes and mills.

It is most strongly recommended that you do not lap the ways of lathes and
mills.

If the flatness obtained from the surface grinder on a hardened way is
insufficient and if you have the use of an autocollimator and if you are
working in microns or less, then you might consider lapping. Otherwise,
use
scraping or surface grinding.

1) The instructions that come with the Taig lathe specifically recommend
lapping the ways before use. This is where I got the scouring powder/oil
paste mixture from. I did not do it. The ways seemed smooth and the carriage
moved like silk. I was concerned (justifiably it seems) that I was more
likely to screw things up than improve them.

2) Many owners of mini-mills have reported improvement in properties of
theirs X and Y axes' movements after lapping the ways. I was considering it
for various reasons but wanted to make sure that I understand the process
first. I seem to remember that there was a thread on this very group
discussing it some time ago.

I am beginning to wonder if these sources freely confused "lapping" with
"polishing". I certainly was.

--
Michael Koblic,
Campbell River, BC