Hello all,

I am starting to notice the time it takes to square blocks for some of
the larger parts that I makes. Large seems to be 2x8 inches.

Clearly I can save time by making more accurate rough cuts. My Delta
bandsaw is working out well for both acrylic and Aluminum. My layout
technique could be better, and I end up leaving larger margins than
necessary as a result.

So far, I have been using mostly a combination square for layout, but
that does not work well for irregular stock. Are there any particularly
good ways to draw rectangles on stock with no clean edges?

For reasons unknown, I have not yet purchased layout fluid - that will
get fixed in my next order.

Just for laughs, suppose you had to clean up a 2x8x1 piece of acrylic.
The thickness varies from 0.94 to 0.98 inches with some cupping. It is
to be milled down to 0.900 inches. To keep things simple, suppose the
final dimensions are to be 2.000x8.000 inches. How big would your rough
cut part be? Would you start with an endmill and then switch to a
flycutter? How long would it take you to get it square and to thickness?

Don't worry - I won't try to race you.

Bill

Strive for accuracy on every thing you do, even if it is not a critical
part. Roughing techniques can be learned any time. If you haven't yet used
layout fluid, you're already roughing it!

Bob Swinney

"Bill Schwab" wrote in message
k.net...
Hello all,

I am starting to notice the time it takes to square blocks for some of the
larger parts that I makes. Large seems to be 2x8 inches.

Clearly I can save time by making more accurate rough cuts. My Delta
bandsaw is working out well for both acrylic and Aluminum. My layout
technique could be better, and I end up leaving larger margins than
necessary as a result.

So far, I have been using mostly a combination square for layout, but that
does not work well for irregular stock. Are there any particularly good
ways to draw rectangles on stock with no clean edges?

For reasons unknown, I have not yet purchased layout fluid - that will get
fixed in my next order.

Just for laughs, suppose you had to clean up a 2x8x1 piece of acrylic. The
thickness varies from 0.94 to 0.98 inches with some cupping. It is to be
milled down to 0.900 inches. To keep things simple, suppose the final
dimensions are to be 2.000x8.000 inches. How big would your rough cut
part be? Would you start with an endmill and then switch to a flycutter?
How long would it take you to get it square and to thickness?

Don't worry - I won't try to race you.

Bill

"Bill Schwab" wrote in message
k.net...
Hello all,

Just for laughs, suppose you had to clean up a 2x8x1 piece of acrylic. The
thickness varies from 0.94 to 0.98 inches with some cupping. It is to be
milled down to 0.900 inches. To keep things simple, suppose the final
dimensions are to be 2.000x8.000 inches. How big would your rough cut
part be? Would you start with an endmill and then switch to a flycutter?
How long would it take you to get it square and to thickness?


Feed and speed as fast as possible, with these exceptions:

Don't wreck the part.

Don't break the cutter.

Don't stall the spindle.

Use the flycutter for squaring/sizing, not the endmill. DOC will be limited
by the length of the toolbit's cutting edge, feed will be limited by the
rigidity and power of your machine, RPM will be limited by the cutter
material.

It's important to experiment. Keep feeding harder and running faster until
you have some type of failure.

Also, keep the sawed edges as close to finished size as possible. Ideally
you want one finishing cut on the mill and that's it, but in reality one
roughing and one finishing cut is more likely.

Regards,

Robin

Robin,

Feed and speed as fast as possible, with these exceptions:

Don't wreck the part.

Don't break the cutter.

Don't stall the spindle.

So far, wrecking the part seems to be the limiting factor, at least with
acrylic.


Use the flycutter for squaring/sizing, not the endmill. DOC will be limited
by the length of the toolbit's cutting edge,

Interesting. I will check some things and follow up with some dumb
questions. Sadly, I probably can't do so today given a hard deadline.



feed will be limited by the
rigidity and power of your machine, RPM will be limited by the cutter
material.

It's important to experiment. Keep feeding harder and running faster until
you have some type of failure.

It must be true that I can cut faster than I am at present. Your point
on the cutting edge might be an important key. The grumbling (didn't
push it to failure) might have been less about DOC and more about the bit.

What might be the max DOC you would expect with an ideal flycutter in Al
and acrylic, respectively?


Also, keep the sawed edges as close to finished size as possible. Ideally
you want one finishing cut on the mill and that's it, but in reality one
roughing and one finishing cut is more likely.

I would expect to make a separate finishing cut, if only because it
simplfies getting a good measurement to know how much to remove to get
to size.

There is no doubt that I need to start sawing closer to final size.
Better layout will help me do it reliable - I hate to make something
enough under size that it ends up as scrap before the tricky stuff. Of
course the good news is that scrapping early leaves a rectangular block
that will be good for something in the future.

More later. Thanks!!

Bill

"Bill Schwab" wrote in message
nk.net...

So far, wrecking the part seems to be the limiting factor, at least with
acrylic.


I assumed it would be. I worked with it in high-school and I remember it
cracking and chipping a lot.


It's important to experiment. Keep feeding harder and running faster
until you have some type of failure.

It must be true that I can cut faster than I am at present. Your point on
the cutting edge might be an important key. The grumbling (didn't push it
to failure) might have been less about DOC and more about the bit.

AFAIK plastics suffer from issues relating to heat and pressure. You can run
into trouble melting your part, cracking it from localized heating, or just
placing too much pressure on it because of your feed/DOC.

Grinding your toolbit correctly is very important. I believe you want
agressive positive rake, a *very* sharp edge, and lots of clearance on the
front face. Consider carefully honing the edge with an oil stone. I believe
the sharper the edge, the less heat generated.

Others will have much more experience than I.


What might be the max DOC you would expect with an ideal flycutter in Al
and acrylic, respectively?

Assuming a Bridgeport mill (or similar) in aluminum you can get away with
..2 - .4" DOC. Perhaps deeper, but you'll find the motor will have trouble
keeping up as the DOC increases. I'm really not sure about acrylic. You may
be able to look up some values in Machinery's Handbook.


I would expect to make a separate finishing cut, if only because it
simplfies getting a good measurement to know how much to remove to get to
size.

Very true. If you're making more than one of the same part, you can get away
with setting the Z height (using the knee) and just using one pass to get to
size. Depends on your tolerance and how much material you have to remove.
You're right about one-offs however. You pretty much always need a roughing
and a finishing cut.


There is no doubt that I need to start sawing closer to final size. Better
layout will help me do it reliable - I hate to make something enough under
size that it ends up as scrap before the tricky stuff.

With experience I've found you tend to trust your own eyes and judgement
more. On a properly setup bandsaw, I'd cut within 1mm (.04") of the line.
You have to adjust this figure if your bandsaw doesn't cut squarely, or if
you have trouble keeping the blade on the correct side of the line.

Regards,

Robin

"Harold and Susan Vordos" wrote in message
...

You're learning, Robin! That's always a good policy.


Harold,

Just as I've been getting better with the machines, I now spend a lot of
time with disk grinders, die grinders and polishing stones. I think I'm
going to be in *heavy* learning mode for another five years. I know it
should never entirely stop, but I'm pretty sure that feeling of ignorance
which all apprentices should have eventually goes away...

Regards,

Robin

For layout, start with a surface plate or something similar. (I have a chunk
of flame cut 3/4 thick plate which was blanchard ground both sides. Not
perfect, but very usable) Size of plate should be large enough to put your
work piece on and then some room to use a surface gage, or whatever.

To layout your 2 inch x 8 inch rectangle from stock with no regular edges,
the objective will be to hold it stationary in reference to your surface
plate (on edge). Basically, the surface plate becomes your known straight
edge.

Use the surface gage to layout two parallel lines (2 inches apart) and
parallel to the surface plate. No surface gage? Use a HS tool bit
sharpened on end for a clean scribe mark for the first layout line. Then
set this same bit onto the 2 inch side of a 1-2-3 block and scribe the
second line.

Use an accurate square ( I often end up using my 1-2-3 block) to layout a
vertical line. Then measure 8 inches from the first vertical line, mark it,
and use the square again to layout the final 8 inch length.

Finally, perfect your skill at band sawing to line, but actually leaving the
line. A bit of practice and you'll be able to clean up in one 'finish'
pass.

Hope some of this helps,

Good luck!
"Bill Schwab" wrote in message
k.net...
Hello all,

I am starting to notice the time it takes to square blocks for some of the
larger parts that I makes. Large seems to be 2x8 inches.

Clearly I can save time by making more accurate rough cuts. My Delta
bandsaw is working out well for both acrylic and Aluminum. My layout
technique could be better, and I end up leaving larger margins than
necessary as a result.

So far, I have been using mostly a combination square for layout, but that
does not work well for irregular stock. Are there any particularly good
ways to draw rectangles on stock with no clean edges?

For reasons unknown, I have not yet purchased layout fluid - that will get
fixed in my next order.

Just for laughs, suppose you had to clean up a 2x8x1 piece of acrylic. The
thickness varies from 0.94 to 0.98 inches with some cupping. It is to be
milled down to 0.900 inches. To keep things simple, suppose the final
dimensions are to be 2.000x8.000 inches. How big would your rough cut
part be? Would you start with an endmill and then switch to a flycutter?
How long would it take you to get it square and to thickness?

Don't worry - I won't try to race you.

Bill

Ace wrote:
For layout, start with a surface plate or something similar. (I have a chunk
of flame cut 3/4 thick plate which was blanchard ground both sides. Not
perfect, but very usable) Size of plate should be large enough to put your
work piece on and then some room to use a surface gage, or whatever.

To layout your 2 inch x 8 inch rectangle from stock with no regular edges,
the objective will be to hold it stationary in reference to your surface
plate (on edge). Basically, the surface plate becomes your known straight
edge.

Of course!!!!!!! Would a square mounted over some 3/4 inch plywood
and some type of clamp work? The idea would be to use the square as a
reference surface for a comination square that sets the directions, and
use some notched rods or something to get point contact of the work
against the square.


Use the surface gage to layout two parallel lines (2 inches apart) and
parallel to the surface plate. No surface gage? Use a HS tool bit
sharpened on end for a clean scribe mark for the first layout line. Then
set this same bit onto the 2 inch side of a 1-2-3 block and scribe the
second line.

Use an accurate square ( I often end up using my 1-2-3 block) to layout a
vertical line. Then measure 8 inches from the first vertical line, mark it,
and use the square again to layout the final 8 inch length.

Do you visually align the block with the first line, or is it pressed
against something?

Something else I have considered is to scribe a couple of circles and
the scribe tangent lines. But having an external square reference
should be easier if not more accurate.


Finally, perfect your skill at band sawing to line, but actually leaving the
line. A bit of practice and you'll be able to clean up in one 'finish'
pass.

There's that word "skill" again Humor aside, that is clearly
essential. The other thing that bothers me is that if I cut too closely
and the rough part does not sit well in the vice, it could tilt such
that it ends up being under sized. A visual pass of an endmill next to
the top line would reveal big errors. Is there a better way?

One cheat I've used is to rough a little large, clean up one edge, and
then saw the other edge again before milling it. The idea is that the
second saw line is easy to find thanks the clean edge opposite it.

As I expected, you guys saw closer and take deeper cuts than I do.
Better layout will help. I'll probably have some more questions about
tool bits in the next couple of days.


Hope some of this helps,

It does - thanks!!

Bill

"Bill Schwab" wrote in message
...

Of course!!!!!!! Would a square mounted over some 3/4 inch plywood and
some type of clamp work? The idea would be to use the square as a
reference surface for a comination square that sets the directions, and
use some notched rods or something to get point contact of the work
against the square.
It sounds as if you are still wanting to work on a horizontal plane. What I
have suggested is to work in a vertical plane. I guess I left out the part
of holding your workpiece against a 90 degree angle plate (or a reasonaby
clean & square piece of angle iron/alum/??)

Do you visually align the block with the first line, or is it pressed
against something?

Something else I have considered is to scribe a couple of circles and the
scribe tangent lines. But having an external square reference should be
easier if not more accurate.

If working in a vertical plane, you can use an two (2) items with a
difference in dimension of 2 inches to layout exactly the 2 inches without
any visual reference. Remember, you are working from your 'surface plate'.

Then for the horizontal dimension, (a vertical line) the line is simply on
the work piece, but is square to the horizontal line due to the sqaureness
of the 1-2-3 block, which by definition has all surfaces square to each
other in addition to being 1x2x3 inches.


Finally, perfect your skill at band sawing to line, but actually leaving
the line. A bit of practice and you'll be able to clean up in one
'finish' pass.

There's that word "skill" again Humor aside, that is clearly
essential. The other thing that bothers me is that if I cut too closely
and the rough part does not sit well in the vice, it could tilt such that
it ends up being under sized. A visual pass of an endmill next to the top
line would reveal big errors. Is there a better way?

If your mill vise is of reasonable quality, the top of the solid jaw should
be parallal to the bottom of the vise. As such, simply line up your part
visually so your layout line is equal distance above the vise jaw. Use your
'scale' to measure it....

Good luck!

"Robin S." wrote in message
...
snip----

Grinding your toolbit correctly is very important. I believe you want
agressive positive rake, a *very* sharp edge, and lots of clearance on the
front face. Consider carefully honing the edge with an oil stone. I
believe
the sharper the edge, the less heat generated.


Good observations, Robin. One more thing that is very important is the
direction of feed and cut. It's a good idea to always cut into an edge,
never away from one, and to climb mill. That way you don't chip the
material, particularly at the corners, which generally require particular
care (brittle plastics).

Harold

Harold, Robin,

Grinding your toolbit correctly is very important. I believe you want
agressive positive rake, a *very* sharp edge, and lots of clearance on the
front face. Consider carefully honing the edge with an oil stone. I

believe

the sharper the edge, the less heat generated.

More toy$ - I knew this was coming. Is this a job for a bench grinder
and set of oil stones? Is there a better way?

I did a quick experiment last night with a 0.1 inch DOC. There was a
little more vibration than I might have liked, but the machine handled
it. It's not a bridgie[*]. On one such pass, I found cracks in the
remaining material, so I don't know that I'll be repeating such a cut.
Still, it is nice to see that some of the cuts I thought were too deep
were probably ok. I can revisit it once I have a proper sharpening
setup. However, better layout and sawing will probably save me more
time than deep cuts.


Good observations, Robin. One more thing that is very important is the
direction of feed and cut. It's a good idea to always cut into an edge,
never away from one, and to climb mill. That way you don't chip the
material, particularly at the corners, which generally require particular
care (brittle plastics).

Cutting into an edge makes sense, and I have been doing that with
plastic whenever possible. I have not deliberately tried to climb with
a flycutter, though thinking back I probably did it once on Al.

With Al, I simply back off if the machine seems not to be enjoying its
work. Plastics are the problem, because an aggressive cut can turn into
a broken part.

To avoid cutting away from an edge, are you suggesting that I take two
climb passes for a deep cut? That still ends up "leaving an edge", but
as somebody said a few weeks ago, to do damage, the bit has to take a
divot out of the part (or crack it as I have just learned) instead of
merely breaking away part of an outside edge. Fair?

Thanks!

Bill

[*] I can say that - nobody else can

If working in a vertical plane, you can use an two (2) items with a
difference in dimension of 2 inches to layout exactly the 2 inches without
any visual reference. Remember, you are working from your 'surface plate'.

I see what you are saying. We definitely were 90 degrees apart. One
potential snag is that your method depends on having an object of a
suitable thickness. A mix of parallels would probably cover most things
I would need to do though.

If your mill vise is of reasonable quality, the top of the solid jaw should
be parallal to the bottom of the vise. As such, simply line up your part
visually so your layout line is equal distance above the vise jaw. Use your
'scale' to measure it....

Got it - thanks!

Bill

"Bill Schwab" wrote in message
k.net...
Harold, Robin,

Grinding your toolbit correctly is very important. I believe you want
agressive positive rake, a *very* sharp edge, and lots of clearance on
the
front face. Consider carefully honing the edge with an oil stone. I

believe

the sharper the edge, the less heat generated.

More toy$ - I knew this was coming. Is this a job for a bench grinder
and set of oil stones? Is there a better way?

A bench, or pedestal grinder, is all that is necessary, but it should have a
good wheel---one made for grinding HSS-----aluminum oxide, and not too
hard----something in the H-J range-----vitrified bond, and maybe a 60 grit.
It should be dressed either with a star dresser (I don't like them) or a
diamond to true it, then followed up with the sharp edge of a silicon
carbide
sintered dressing stick. The diamond isn't necessary, but makes dressing
the wheel easier. Diamond dressed wheels don't make for a good off-hand
grinding surface, however, -----thus my recommendation to follow up with a
dressing stick. As far as stoning goes, the usual shop stone works fine,
nothing special necessary. It's all in technique, however. You can destroy
a tool's ability to cut by improper stoning. It's very important that you
do not round the cutting edge, regardless of the material being machined.

The typical aluminum oxide grinding wheel that comes as
standard equipment on small grinders tends to be bonded way too hard to
successfully grind hard materials (think HSS). As I stated today when
discussing this
very issue, privately, by email, it can be challenging to find the right
wheel for grinders that mount wheels with small fractional bores, 1/2",
5/8" or even 3/4". The greatest selection of wheels is available with
1-1/4" bore, wheels that are commonly used on cutter grinders and small
surface grinders. A standard grinder can be easily converted to that wheel
size by machining new wheel arbors, although you may have to remount the
wheel guards because you extend the wheel. If you can work without a
grinding rest, and I do, that isn't a problem. Just discard them. Wheel
arbors should be properly configured to avoid breaking wheels, so don't jump
in blindly if you decide to make the conversion.


I did a quick experiment last night with a 0.1 inch DOC. There was a
little more vibration than I might have liked, but the machine handled
it. It's not a bridgie[*]. On one such pass, I found cracks in the
remaining material, so I don't know that I'll be repeating such a cut.

Very unlikely the depth of cut was instrumental, although not
impossible-----more so the tool design. A properly sharpened tool should
be able to remove a huge amount without chipping when machining acrylic
plastic. Speed and feed play a serious role, too, so you have to balance
the tool configuration with the other variables for success. What's very
important is that the tool be very sharp, and have ample clearance and rake,
as Robin suggested. You don't want the tool to do any pushing, just
shaving, so to speak.

In order for you to be successful in machining, it's quite important to
learn proper tool configuration, and to be able to generate the forms as
needed. That includes grinding chip breakers. At first it may appear to
be a daunting task, but don't allow it to discourage you. Practice makes
perfect, and once mastered, it's no big deal. As I've stated time and again,
learning to grind proper toolbits will set you free.

Cutting into an edge makes sense, and I have been doing that with
plastic whenever possible. I have not deliberately tried to climb with
a flycutter, though thinking back I probably did it once on Al.

When fly cutting, it's not a big problem like it can be with an end mill.
By climb fly cutting, and walking around the perimeter of the part in
question, you can always take cuts towards the inside, which will almost
totally eliminate edge chipping. The only exception is outside corners,
where you have to sort of back off as you approach the corner, diminish
cutting feed rate, and gently round the tip of the corner. Again, piece of
cake.


To avoid cutting away from an edge, are you suggesting that I take two
climb passes for a deep cut? That still ends up "leaving an edge", but
as somebody said a few weeks ago, to do damage, the bit has to take a
divot out of the part (or crack it as I have just learned) instead of
merely breaking away part of an outside edge. Fair?

See above. It would be so much easier to demonstrate this instead of try
to discuss it. More than one pass may or may not be necessary, depending
on many variables. When you fly cut, it's usually more than desirable that
the tool have not only decent rake, but have a lead angle on the tool as
well, assuming you're not trying to establish a shoulder. That way the top
of the cut is first to see the tool, and the bottom the last. You machine
a bevel, in other words. That minimizes the chance of chipping. Does that
make sense?

Harold

Harold,

See above. It would be so much easier to demonstrate this instead of try
to discuss it. More than one pass may or may not be necessary, depending
on many variables. When you fly cut, it's usually more than desirable that
the tool have not only decent rake, but have a lead angle on the tool as
well, assuming you're not trying to establish a shoulder. That way the top
of the cut is first to see the tool, and the bottom the last. You machine
a bevel, in other words. That minimizes the chance of chipping. Does that
make sense?

On the latter point, I think so. This is one of those posts that I will
have to read several times. I will do so and follow up.

Thanks!!!

Bill