I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm wondering
what sort of abrasive I should try. Given that annodizing itself is very
hard, I don't know if normal compounds will touch it. I'm also not sure
how fine I should start with. This is a one-off, so I don't want to have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

"Doug White" wrote in message
...
I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm wondering
what sort of abrasive I should try. Given that annodizing itself is very
hard, I don't know if normal compounds will touch it. I'm also not sure
how fine I should start with. This is a one-off, so I don't want to have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Anodizing is, itself, aluminum oxide. I think it's unlikely you'll be able
to do anything like *cutting* into that surface using other than diamond.
You probably could *scrape* it off with other abrasives, but you'd just be
tearing the anodizing from the base aluminum.

Just an educated guess...

--
Ed Huntress

On Sep 13, 7:56 am, "Ed Huntress" wrote:
"Doug White" wrote in message

...





I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm wondering
what sort of abrasive I should try. Given that annodizing itself is very
hard, I don't know if normal compounds will touch it. I'm also not sure
how fine I should start with. This is a one-off, so I don't want to have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Anodizing is, itself, aluminum oxide. I think it's unlikely you'll be able
to do anything like *cutting* into that surface using other than diamond.
You probably could *scrape* it off with other abrasives, but you'd just be
tearing the anodizing from the base aluminum.

Just an educated guess...

That was my concern. Somewhere I have some diamond compound I used to
lap a small carbide expander button, but my recollection is that it
was extremely fine. My concern was that it might take quite a while
to lap the aluminum piece, which is about an inch ID and 2 inches
long. I may just have to try that.

Some of the Clover compound is aluminum oxide, and I don't know how
well lapping with an identical hardness compound would work. I
suppose I could try that, and then switch to the diamond if it doesn't
work.

Doug White

"Gwhite" wrote in message
ups.com...
On Sep 13, 7:56 am, "Ed Huntress" wrote:
"Doug White" wrote in message

...





I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm
wondering
what sort of abrasive I should try. Given that annodizing itself is
very
hard, I don't know if normal compounds will touch it. I'm also not
sure
how fine I should start with. This is a one-off, so I don't want to
have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and
possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Anodizing is, itself, aluminum oxide. I think it's unlikely you'll be
able
to do anything like *cutting* into that surface using other than diamond.
You probably could *scrape* it off with other abrasives, but you'd just
be
tearing the anodizing from the base aluminum.

Just an educated guess...

That was my concern. Somewhere I have some diamond compound I used to
lap a small carbide expander button, but my recollection is that it
was extremely fine. My concern was that it might take quite a while
to lap the aluminum piece, which is about an inch ID and 2 inches
long. I may just have to try that.

Some of the Clover compound is aluminum oxide, and I don't know how
well lapping with an identical hardness compound would work. I
suppose I could try that, and then switch to the diamond if it doesn't
work.

Lapping with equal-hardness compound does work (that's how they do
diamond-to-diamond lapping), but it's reported to be slow and sensitive to
pressure. I have no experience with it myself.

Diamond, in general, cuts fast, grit-for-grit.

Please let us know how it works out.

--
Ed Huntress

Ed Huntress wrote:

"Gwhite" wrote in message
ups.com...
On Sep 13, 7:56 am, "Ed Huntress" wrote:
"Doug White" wrote in message

...





I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm
wondering
what sort of abrasive I should try. Given that annodizing itself is
very
hard, I don't know if normal compounds will touch it. I'm also not
sure
how fine I should start with. This is a one-off, so I don't want to
have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and
possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Anodizing is, itself, aluminum oxide. I think it's unlikely you'll be
able
to do anything like *cutting* into that surface using other than diamond.
You probably could *scrape* it off with other abrasives, but you'd just
be
tearing the anodizing from the base aluminum.

Just an educated guess...

That was my concern. Somewhere I have some diamond compound I used to
lap a small carbide expander button, but my recollection is that it
was extremely fine. My concern was that it might take quite a while
to lap the aluminum piece, which is about an inch ID and 2 inches
long. I may just have to try that.

Some of the Clover compound is aluminum oxide, and I don't know how
well lapping with an identical hardness compound would work. I
suppose I could try that, and then switch to the diamond if it doesn't
work.

Lapping with equal-hardness compound does work (that's how they do
diamond-to-diamond lapping), but it's reported to be slow and sensitive to
pressure. I have no experience with it myself.

Diamond, in general, cuts fast, grit-for-grit.

Please let us know how it works out.

--
Ed Huntress

Might be easier to strip and reanodize the part properly. Even then, the
anodizing layer is normally supposed to be pretty consistently .001"
thick, with half of the thickness growing into the part and half growing
out from the part. For your bore, if the anodizing is done properly you
would expect the bore to shrink be .001" total. Was the original part
properly sized to account for the anodizing layer?

"Pete C." wrote in message
...
Ed Huntress wrote:

"Gwhite" wrote in message
ups.com...
On Sep 13, 7:56 am, "Ed Huntress" wrote:
"Doug White" wrote in message

...





I need to lap the ID of an aluminum piece out about half a
thousandth.
It is heavily annodized, and has a matte, frosted finish. I think
the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm
wondering
what sort of abrasive I should try. Given that annodizing itself is
very
hard, I don't know if normal compounds will touch it. I'm also not
sure
how fine I should start with. This is a one-off, so I don't want to
have
to go out & buy several grades of diamond paste. I have a "sample"
kit
of Clover lapping compounds, which includes silicon carbide, and
possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Anodizing is, itself, aluminum oxide. I think it's unlikely you'll be
able
to do anything like *cutting* into that surface using other than
diamond.
You probably could *scrape* it off with other abrasives, but you'd
just
be
tearing the anodizing from the base aluminum.

Just an educated guess...

That was my concern. Somewhere I have some diamond compound I used to
lap a small carbide expander button, but my recollection is that it
was extremely fine. My concern was that it might take quite a while
to lap the aluminum piece, which is about an inch ID and 2 inches
long. I may just have to try that.

Some of the Clover compound is aluminum oxide, and I don't know how
well lapping with an identical hardness compound would work. I
suppose I could try that, and then switch to the diamond if it doesn't
work.

Lapping with equal-hardness compound does work (that's how they do
diamond-to-diamond lapping), but it's reported to be slow and sensitive
to
pressure. I have no experience with it myself.

Diamond, in general, cuts fast, grit-for-grit.

Please let us know how it works out.

--
Ed Huntress

Might be easier to strip and reanodize the part properly. Even then, the
anodizing layer is normally supposed to be pretty consistently .001"
thick, with half of the thickness growing into the part and half growing
out from the part. For your bore, if the anodizing is done properly you
would expect the bore to shrink be .001" total. Was the original part
properly sized to account for the anodizing layer?

Unless this is a "hard anodize," which runs up to 0.003" or so. When he said
"heavily anodized" I wondered about that but didn't ask.

--
Ed Huntress

Doug White wrote:
I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm wondering
what sort of abrasive I should try. Given that annodizing itself is very
hard, I don't know if normal compounds will touch it. I'm also not sure
how fine I should start with. This is a one-off, so I don't want to have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and possibly
aluminum oxide.


I've had to do similar work to the OD of anodized pieces. Hard
anodizing is hard but not *that* hard. Give it a quick rub with
carborundum or silicon carbide, and I'll think you'll find it works out
alright. Go really slow and use a lube. You probably find that the
initial work will make a big change, as you take off the high spots, but
it'll go a little slower after that.

--
Pete Snell
Department of Physics
Royal Military College

---------------------------------------------------------------------
it's spring and the goat-footed balloonMan whistles far and wee

eecummings (1894-1962) Chansons Innocentes: I

Ed Huntress wrote:

"Pete C." wrote in message
...
Ed Huntress wrote:

"Gwhite" wrote in message
ups.com...
On Sep 13, 7:56 am, "Ed Huntress" wrote:
"Doug White" wrote in message

...





I need to lap the ID of an aluminum piece out about half a
thousandth.
It is heavily annodized, and has a matte, frosted finish. I think
the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm
wondering
what sort of abrasive I should try. Given that annodizing itself is
very
hard, I don't know if normal compounds will touch it. I'm also not
sure
how fine I should start with. This is a one-off, so I don't want to
have
to go out & buy several grades of diamond paste. I have a "sample"
kit
of Clover lapping compounds, which includes silicon carbide, and
possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Anodizing is, itself, aluminum oxide. I think it's unlikely you'll be
able
to do anything like *cutting* into that surface using other than
diamond.
You probably could *scrape* it off with other abrasives, but you'd
just
be
tearing the anodizing from the base aluminum.

Just an educated guess...

That was my concern. Somewhere I have some diamond compound I used to
lap a small carbide expander button, but my recollection is that it
was extremely fine. My concern was that it might take quite a while
to lap the aluminum piece, which is about an inch ID and 2 inches
long. I may just have to try that.

Some of the Clover compound is aluminum oxide, and I don't know how
well lapping with an identical hardness compound would work. I
suppose I could try that, and then switch to the diamond if it doesn't
work.

Lapping with equal-hardness compound does work (that's how they do
diamond-to-diamond lapping), but it's reported to be slow and sensitive
to
pressure. I have no experience with it myself.

Diamond, in general, cuts fast, grit-for-grit.

Please let us know how it works out.

--
Ed Huntress

Might be easier to strip and reanodize the part properly. Even then, the
anodizing layer is normally supposed to be pretty consistently .001"
thick, with half of the thickness growing into the part and half growing
out from the part. For your bore, if the anodizing is done properly you
would expect the bore to shrink be .001" total. Was the original part
properly sized to account for the anodizing layer?

Unless this is a "hard anodize," which runs up to 0.003" or so. When he said
"heavily anodized" I wondered about that but didn't ask.

True. I'm working on the assumption it isn't since hard anodize is more
complicated and less common.

On Sep 13, 4:04 pm, Pete Snell wrote:

I've had to do similar work to the OD of anodized pieces. Hard
anodizing is hard but not *that* hard. Give it a quick rub with
carborundum or silicon carbide, and I'll think you'll find it works out
alright. Go really slow and use a lube. You probably find that the
initial work will make a big change, as you take off the high spots, but
it'll go a little slower after that.

--
Pete Snell
Department of Physics
Royal Military College

---------------------------------------------------------------------

I agree with Pete. Silicon Carbide is slightly harder than aluminum
oxide and I think it will work just fine.

Dan

On Sep 13, 11:51 am, " wrote:
On Sep 13, 4:04 pm, Pete Snell wrote:



I've had to do similar work to the OD of anodized pieces. Hard
anodizing is hard but not *that* hard. Give it a quick rub with
carborundum or silicon carbide, and I'll think you'll find it works out
alright. Go really slow and use a lube. You probably find that the
initial work will make a big change, as you take off the high spots, but
it'll go a little slower after that.
snip

I agree with Pete. Silicon Carbide is slightly harder than aluminum
oxide and I think it will work just fine.

OK, I'll start with Silicon Carbide and see what happens. Because the
finish is sort of frosted (it may have been bead blasted before
annodizing, but it looks about as rough inside as out), I expect I
will mostly be knocking off the tops of the frosting.

Any idea what grit I should be trying? I can't find the Clover kit
for sale anymore, and I don't remember what grits it has available in
Si Carbide. I'll dig it out when I get home today and see.

Thanks!

Doug White

"Doug White" wrote in message
...
I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm wondering
what sort of abrasive I should try. Given that annodizing itself is very
hard, I don't know if normal compounds will touch it. I'm also not sure
how fine I should start with. This is a one-off, so I don't want to have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

Silicon carbide is far harder than aluminum oxide and will easily remove the
amount you desire.

If it was up to me, I'd use a Sunnen hone with a fine silicon carbide
stone-----or diamond if I had it available.

Harold

"Doug White" wrote in message
...
I need to lap the ID of an aluminum piece out about half a thousandth.
It is heavily annodized, and has a matte, frosted finish. I think the
reason it is undersized is that the annodization built up more than
expected.

I have an expanding brass cylinder lap that fits fine, but I'm wondering
what sort of abrasive I should try. Given that annodizing itself is very
hard, I don't know if normal compounds will touch it. I'm also not sure
how fine I should start with. This is a one-off, so I don't want to have
to go out & buy several grades of diamond paste. I have a "sample" kit
of Clover lapping compounds, which includes silicon carbide, and possibly
aluminum oxide.

Any suggestions?

Thanks!

Doug White

A paste of brown tripoli, and oil.

Steve R.


--
Reply address munged to bugger up spammers

On Sep 13, 7:38 pm, Gwhite wrote:

Any idea what grit I should be trying? I can't find the Clover kit
for sale anymore, and I don't remember what grits it has available in
Si Carbide. I'll dig it out when I get home today and see.

Thanks!

Doug White

You should be able to find valve grinding compound at an auto parts
store. They usually just have coarse and fine grades for grinding
valves. I would try the fine first.

Dan