Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I find that with deep cuts, there is some risk of breaking off material
as the endmill reaches the end of the part. Slowing the feed rate near
the end helps, but does not eliminate it. Lots of light fast passes
seems to work.

What _should_ I be doing? Out of curiosity, would it change if the
material were Aluminum?

The part is a little long to stand on end in my bandsaw. With a
suitable jig, that might work. But if it must be roughed on a mill,
what is best approach?

Bill

On Sat, 21 Jan 2006 20:24:52 GMT, Bill Schwab
wrote:

Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I find that with deep cuts, there is some risk of breaking off material
as the endmill reaches the end of the part. Slowing the feed rate near
the end helps, but does not eliminate it. Lots of light fast passes
seems to work.

What _should_ I be doing? Out of curiosity, would it change if the
material were Aluminum?

The part is a little long to stand on end in my bandsaw. With a
suitable jig, that might work. But if it must be roughed on a mill,
what is best approach?

Bill
============================
Woodworking practice would be to put a piece of scrap at each end
to support the edges. The edges of the scrap will chip rather
than the good part.

Uncle George

In article . net,
says...
Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I find that with deep cuts, there is some risk of breaking off material
as the endmill reaches the end of the part. Slowing the feed rate near
the end helps, but does not eliminate it. Lots of light fast passes
seems to work.

What _should_ I be doing? Out of curiosity, would it change if the
material were Aluminum?

The part is a little long to stand on end in my bandsaw. With a
suitable jig, that might work. But if it must be roughed on a mill,
what is best approach?

Rough the part from both ends to the middle reorienting as required to
avoid climb milling, then finish with light cuts the whole length. The
final can be a very light climb, if that gives you the best finish.

Ned Simmons

Ned,

Rough the part from both ends to the middle reorienting as required to
avoid climb milling, then finish with light cuts the whole length. The
final can be a very light climb, if that gives you the best finish.

Dumb question: what happens in the middle? For any given pair of "half
passes", won't the first half of thecut leave the second half breaking
out of the material? Or is the point that when it happens, there is
material under (and in front of) the endmill?

If that is the idea, would you take a large endmill and cut almost full
depth (up/down)? How much would you take front to back on each pass?

Bill

In article .net,
says...
Ned,

Rough the part from both ends to the middle reorienting as required to
avoid climb milling, then finish with light cuts the whole length. The
final can be a very light climb, if that gives you the best finish.

Dumb question: what happens in the middle? For any given pair of "half
passes", won't the first half of thecut leave the second half breaking
out of the material? Or is the point that when it happens, there is
material under (and in front of) the endmill?

Yes, in order to create a defect in the middle you'd have to pull a
divot out of the part, whereas on the end you're chipping off a sharp
outside corner.


If that is the idea, would you take a large endmill and cut almost full
depth (up/down)? How much would you take front to back on each pass?


Depends on how well you can hold onto the part and, especially in this
case dealing with acrylic, how much heat is generated. Unless I was in a
big hurry to make a number of parts, I'd probably use a dead sharp 5/8"
2-flute endmill taking perhaps 1/8" off both surfaces on each pass, and
make adjustments depending on what's happening in the cut. Finish with a
pass of .005"-.010" on both surfaces simutaneously.

Ned Simmons

Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I find that with deep cuts, there is some risk of breaking off material
as the endmill reaches the end of the part. Slowing the feed rate near
the end helps, but does not eliminate it. Lots of light fast passes
seems to work.

What _should_ I be doing? Out of curiosity, would it change if the
material were Aluminum?

The part is a little long to stand on end in my bandsaw. With a
suitable jig, that might work. But if it must be roughed on a mill,
what is best approach?

Bill
Maybe a dado blade on a table saw?
Ken.

Bill Schwab wrote:

But if it must be roughed on a mill,
what is best approach?

To use a circular saw in the mill for removing most of the matl.?
Then none or two more passes with the mill.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

Ken,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

Maybe a dado blade on a table saw?

That would work, assuming the plastic can take it?? I'd want one hell
of a jig though.

Bill

Try using a "for aluminum" endmill. These have, in concept at least, a
greater cutting angle and a greater relief angle than normal endmills.

Bill Schwab wrote:
Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I find that with deep cuts, there is some risk of breaking off material
as the endmill reaches the end of the part. Slowing the feed rate near
the end helps, but does not eliminate it. Lots of light fast passes
seems to work.

What _should_ I be doing? Out of curiosity, would it change if the
material were Aluminum?

The part is a little long to stand on end in my bandsaw. With a
suitable jig, that might work. But if it must be roughed on a mill,
what is best approach?

Bill

Some alcohol in a squirt bottle will help keep the cutter (and acrylic)
cool, Keep your cuts light and perhaps use a roughing cutter for all but the
finishing cuts.

JMiller
"Bill Schwab" wrote in message
news
Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross
section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I find that with deep cuts, there is some risk of breaking off material as
the endmill reaches the end of the part. Slowing the feed rate near the
end helps, but does not eliminate it. Lots of light fast passes seems to
work.

What _should_ I be doing? Out of curiosity, would it change if the
material were Aluminum?

The part is a little long to stand on end in my bandsaw. With a suitable
jig, that might work. But if it must be roughed on a mill, what is best
approach?

Bill

In article . net,
says...
Some alcohol in a squirt bottle will help keep the cutter (and acrylic)
cool,

And make a pretty pattern when cracks propagate thru the part.g
Alcohol will craze acrylic, especially in the presence of stress.

Ned Simmons

I've never experienced crazing and cracks using alcohol.

Forgot to mention that if the acrylic is 'old' it is more prone to chipping
and shattering. Sometimes putting the acrylic in an oven at 150 deg F for a
couple of hours or so depending on thickness will anneal it and reduce the
tendency to chip and shattter. Best to have 'new' material though.

JMiller
"Ned Simmons" wrote in message
...
In article . net,
says...
Some alcohol in a squirt bottle will help keep the cutter (and acrylic)
cool,

And make a pretty pattern when cracks propagate thru the part.g
Alcohol will craze acrylic, especially in the presence of stress.

Ned Simmons

"Bill Schwab" wrote in message
news
Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I'd go for the circular saw (table saw, of course) approach. Full depth,
and very slow feed.
Two cuts - done...

--
Jeff R.

In article . net,
says...
I've never experienced crazing and cracks using alcohol.


It's not always a problem, but when it does happen the effect is
something you won't forget. This document puts a number on the stress
required to start the cracking.

http://www.plaskolite.com/productguide/04.pdf

The stress is up around 900 psi, which is higher than I would have
guessed. My introduction to the problem was when deep drilling a rod
using alcohol as a coolant, which I'm sure causes higher stresses in a
larger volume than milling with a sharp cutter would. But it seems to me
that since a milling cutter is shearing material (i.e., exceeding the
strength of the acrylic) the stresses at the cut point are high enough
for the cracking to potentially be a problem on a micro scale.

Ned Simmons

Hello bill-

Woodworking tools usually work better than metalworking toold in
plastic. try and source a woodworking router ( approximately 20,000 RPM
) and give this a go.
Be careful because the plastic is tough and the workpiece and the tool
both have to be well supported to avoid a dangerous fly-out. If the
router has a vacuum swarf remover them remove that because it will
probably block up
regards fredf




Bill Schwab wrote:
Hello all,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in
cross section) block. The goal is to end up with roughly the following:

+----+
| |
| |
| +-----------+
| |
| |
+----------------+

I find that with deep cuts, there is some risk of breaking off material
as the endmill reaches the end of the part. Slowing the feed rate near
the end helps, but does not eliminate it. Lots of light fast passes
seems to work.

What _should_ I be doing? Out of curiosity, would it change if the
material were Aluminum?

The part is a little long to stand on end in my bandsaw. With a
suitable jig, that might work. But if it must be roughed on a mill,
what is best approach?

Bill

"Bill Schwab" wrote in message
ink.net...
Ken,

Suppose one needs to remove 1/2 inch of acrylic from a 2x1 inch (in cross
section) block. The goal is to end up with roughly the following:

Maybe a dado blade on a table saw?

That would work, assuming the plastic can take it?? I'd want one hell of
a jig though.

Bill

Rather than using a dado on a table saw, I'd use just a very sharp HSS or
carbide rip blade and make one cut that doesn't go all the way thru, then
flip the part 90 degrees and repeat. Use a block of wood to push the whole
thing all the way thru and past the blade.

Mike

Mik,

Rather than using a dado on a table saw, I'd use just a very sharp HSS or
carbide rip blade and make one cut that doesn't go all the way thru, then
flip the part 90 degrees and repeat. Use a block of wood to push the whole
thing all the way thru and past the blade.

That sounds better. I still think it would take a fairly good jig to do
it safely. If the rip fence is involved, it should be on the part side
to avoid trapping the waste between the blade and the fence and creating
a missle. On the up side, the part acts as a guard of sorts, and an
auxillary fence would compensate for the uncomfortable situation of
reaching down between the fence and the blade.

If I end up making a "large" run of these, I'll make a simple jig and
give it a shot.

Thanks!

Bill

--Agreed; don't use the fence. Rather, position the part on a
panel-cutting sled and push that thru..

--
"Steamboat Ed" Haas : Whatever happened
Hacking the Trailing Edge! : to Tom Nelson?
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---