I am making a couple of parts from cast acrylic, with a "large" run [*]
probably going to happen in the near future. Rough cutting was more
trouble than I remember, probably because of my cheap Craftsman buzz saw.
The main problem with the cutting was that the plastic melted and
partially re-attached. Some repeat passes with some cooling breaks
removed enough of the excess that it finally separated. Am I correct to
think that a bandsaw will eject the material and (largely?) avoid the
problem? Is there a preferred speed and tpi to try on the buzz saw?
[*] that means more than five sets of them ;)
"Bill Schwab" wrote: (clip) Is there a preferred speed and tpi to try on
the buzz saw?
What do you mean by "buzz saw"? Obviously, as you realize, your problem is
heat. I would play around with speed, and feed pressure, to see whether can
stop the chips from melting back to the sides of the cut. Sometimes it
helps to "pulse" the feed pressure, so the chips have a chance to clear
before they get hot enough to melt. It might also help if you direct a
stream of air directly into the cut, to clear and cool the chips.
A band saw works great. You MUST have a high speed blast of air at the
cut area to cool and clear chips. Run it slower than for wood
(1500-2000 fpm), tooth count is not too fussy as long as the surface
finish is acceptable.
Bill Schwab wrote:
I spent the majority of today on my bandsaw cutting acrylic sheet of
various thickness from 1/8 to 3/4" and never once had a heat or
melting problem. I can['t tell you what speed its running at as my
speed control is history so it only runs at one speed which is pretty
darn fast. I have been using a bimetal blade of 14 TPI even for the
thinner stuff and it has not caused any chipping, nor did it gum up in
the thicker stuff....
I also use a table saw with a blade made specifically for cutting
acrylic on and it too works like a champ. I have used regular carbide
tipped baldes (40 Teeth) before and they worked fine, but not as good
as a balde made for acrylics.....
I cut both cast and extruded types, as well as polycarbonate all with
the same blades. Use no coolant of any kind.
I will keep that in mind. Dumb question: what about a circular saw?
For the time being, I will be chipping away at a corners of a big slab.
For any long cuts, my ts should be a great way to go.
However, the thought of deliberately shutting down with the blade
surrounded by material is a little disturbing. Of course, a circular
saw might be unusually inclined to kick if it gets stuck in melting
I'll try a piece of scrap in my Jet "bandsaw" (at least it has some
value as hacksaw), and if that goes well, I might take this as yet
another sign that I need to buy that Rigid bandsaw that is getting near
the top of my wish list.
That's pretty much what I recall from the good old days on a really nice
bandsaw we had. My troubles with a reciprocating saw are not
surprising. An air jet is a possibility. Any recommendations for a nozzle?
I did some milling on the piece I rough cut, and it could be going a
whole lot worse. A corner broke off, JUST as I was reaching to stop the
feed to take over manually :( The part will likely be salvageable.
Seeing the nearly finished product leads me to think it should be a
little beefier in a couple of spots, so it might be just as well.
There is some weirdness however, either in the form of movement as
stresses are relieved, or maybe the stock isn't as flat as I thought.
While I'm certainly no expert, things generally get thinner when milled,
right ~:0 I checked the vise alignment before starting work, so I know
that's not the problem.
Several years ago I had to make 4 parts out of 2 inch thick cast
acrylic. These parts were 23.5 inches in diameter. I rough cut them
with a circular saw out of a 4' by 4' plate. 1 pass for each cut. I
used a carbide blade and a spray bottle filled with water. I sprayed
the water on the leading edge of the blade. It worked well. Slow, but
well. If things seemed to be getting too hot I would back the saw out
of the cut. It was easy to tell when the plastic got too hot by
looking at the chips. When they looked kind of melted it meant that
the saw was feeding too fast. I did think constantly that using water
might electrocute me. A good strong cold air blast would probably have
been better. Whatever you do, keep all oil away from this plastic. The
slightest crack or scratch, one you can't even see, will develop into
a big crack if any oil is present. Even the oil off oily hands will
cause acrylic to crack.
Another option might have been a cordless saw. 18-24 V probably would
not be all that threatening, though I am told a 1.5 V cell can kill
under the correct (one might say extreme) cirumstances. Air does sound
The plan is to take another look at the bandsaw I have been planning to
buy. Any of the suggestions given in this thread will be safer and
easier to realize on it, and I have many other uses in mind for it.
> Whatever you do, keep all oil away from this plastic. The
Did somebody say "crack"? :( Chemistry is a possibility, but I suspect
I did it with the vise. I milled a couple of parallel slots and then
created an L-shaped shelf by milling over one slot and "around" the
other. There are a couple of counter sunk holes more or less between
I made a point of clamping near the bottom to avoid hitting the vise
while making the shelf, and to allow room for a round-over pass on the
edges of the shelf. The slot "under the shelf" had the potential to put
some of the material above it in tension, and given the apparent
location of the crack, my guess is that's what happened.
How nutty would it be to make a fixture/sub plate that exploits the two
holes? They are designed for 8-32 machine screws and no abundance of
strength. My concern is that it might be difficult to ensure that they
hold their relative position during the machining.
I made the slots early on because they seemed like the easiest things to
get wrong. However, it is fairly clear now that they weaken the part
and complicate clamping. The round over endmill worked very well, so I
will probably do that step last. I think I see how to make a plate that
would use the holes to connect to slots so the "back edge" of the plate
could be stop-aligned with the edge of the part.
Back to chemistry: if oil is the culprit, how does it work? Can I clean
it periodically and be ok, or is the damage done as soon as it gets hit?
BTW, I think I just proved that the stock is warped. That would explain
some of the weirdness on tolerances. Should I bother with the cheap
facing cutter that comes with mill/drills? Fly cutters scare me as yet.
Is there something else I can use, or will I simply need to make a
bunch of passes with a 3/4 inch end mill?
Happy New Year!
I dunno about the other stuff, I'm just too tired to think. But the
oil thing may just be that it is like water in rock cracks when it
freezes. If a pepper mill is made from cast acrylic, and lots are, it
will eventually form cracks just from the oil in the pepper. So maybe
it gets in and acts like a wedge. If your part gets oily it can be
cleaned. But it would be a good idea to buff the area with plastic
polish, like Meguire's, after cleaning. Be careful about polishing.
Some compounds have oil in them.
My 14 inch Delta bandsaw arrived yesterday, and I think it will work out
nicely. I still have some reservations about buying it over the Rigid,
but not enough to jump through the additional hoops or to inconvenience
friends over it. I have to choose between fixing up a distressed older
Ford Ranger, or buying a distressed older full size truck and fixing
that up. I'm too cheap to buy a new one :)
As is typical, the instructions with the saw were less than perfect. My
favorite part is that they say to install the guards with the stand
assembly, then mount the saw (which would be greatly complicated by the
presense of the guards), then remove the guards to install the belt.
It is slightly annoying that the open stand model does not have step
pulleys. Do any of you have experience changing the pulleys? At least
in theory, that and a couple of small tweaks to the upper guard would
allow easy speed changes.
The tilting table is nice, but it is a little weak on locking at
horizontal. It would be difficult to make a fair comparison to the
Rigid based on a floor model, especially one where the table is not
installed properly. My "loyalty" to Rigid is based on their table saw,
which is great.
After some test cuts with wood, I threw the acrylic slab on some roller
stands and roughed the next part - almost. The blade did not track
terribly well, but backing out and retrying with some more tension did
the job; it's time to read the Bandsaw Book. As I had hoped (and
remembered), the chips cleared the cut and there was no problem with
melting. The only irritation was that after removing the paper backing,
I found cracks near the surface. I think that was shipping damage (it
was on the outer edge). I am hesitant to cut a replacement because it
would go on the mill in no time, and that's work that should wait until
next week. It would also be a lot more fun than today's agenda:
assembling shelves and generally moving junk around the house to make
room for more junk :)
Happy New Year!
I would seriously consider adding a set of step pulleys to get more
I have also found that cutting acrylic with the worng type of blade or
at too fast/slow of speeds can actualy induce edge cracks. Maybe not
right away, but it can happen hours or days later just setting there.
This may or may not be from the saw blade itself and it may be part
and parcel of the quality of the acrylic material itself. I have cut
aquarium tops out of mixed brands and types of acrylics and on some I
will get minute cracks extending from the edge inwards, but on others
they come out fine without any cracks....same blades, same cutting
speeds only differences is in the actual material itself..being the
brands and type FF, GP etc.
I also found out that the longer a band saw blade is the better in
regards to running cooler. It only a small difference perhaps but it
can make the difference in running in the cut warmer or cooler and
inducing cracks, but since blade length is not changeable it hinges
mainly on the blade used and the FPM used. I did find that most all
wood working blades gave me more headaches than metal cutting blades,
and that constant pitch blades worked better than varipitch blades,
and blades with a set worked substantially better than the typically
finer toothed blades using wavy set. And what I really found that was
amazing wa if I take a blade that I intend to use use only for
acrylics, and install it on my bandsaw, and make a distinctly colored
line across the blade, say like at the weld joint with a red majic
marker etc, turn it on at low speed and take a fine smooth file and
just barely touch the edge of the kerf on the blade on both sides,
just one complete round of the blade (usiing marked line for
reference) my edges of the acrylic is a lot smoother and any wiggling
of the material when feeding it in does not produce such pronounced
cut marks....In other words I reduce the kerf width on a set type
blade slightly and sort of get rid of the points but it still leaves
a sharp cutting edge with somewhat reduced kerf and cutting area.
Have a few questions in regards to your Ridgid Tablesaw....I am
contemplating on buying a new TS myself.....one to dedicate strictly
to wood or acrylics, and use my older TS for the opposite of what the
new saw would be used for...Is the Ridgid belt driven or direct drive,
and does it lend itself to an easy non propreitary motor change if
need be? I hate propreitary anything if I can get by without
it......Are the tables cast alum or iron, and how good is the rip
fence? ANy comparason between it and the 10" Ryobi that HD carries.
OUr HD used to carry Ridgid now its nothing but Ryobi stuff. Not even
Delta bench top tools are in that store. Are there side extension
tables on the Ridgid and if so are they stamped steel or cast
Any concerns that the motor, frame, etc. on the open stand model are not
made for it in some way? I admit is seems unlikely, but better to ask
It is belt driven. I suspect you could mount another motor on it. Is
there anything in particular that would tell you what you need to know?
> and how good is the rip
Very good IMHO. I had to deviate from their stated alignment procedures
on the splitter and fence height, but "doing it correctly", I had no
troubles. The fence glides when you want, and locks when you want.
Someone with more joinery experience than I have might take a different
> ANy comparason between it and the 10" Ryobi that HD carries.
I am not sure which saw you mean, but I have seen nothing from Ryobi
that can compare with the Rigid TS. That is not to impugn Ryobi; they
provide reasonable products for the casual user. I have a Ryobi drill
press that is ok (and then some) for small stuff.
Scary. My local Lowe's has taken down their Hitachi and Jet [*] ts
display models, leaving a piece of semi-portable Delta made junk
(seriously!!) that almost sent me packing w/o the bandsaw until I looked
at the latter. I was willing to do that because I had read good things
about the saw.
[*] it now takes a natural disaster to get me to even consider Jet
products, but I hear enough good about them that despite my bad
experiences, I think Lowe's should display it. They should display at
least one contractors' saw.
> Not even
The extensions are cast iron. It is a great machine IMHO. If nothing
else, look carefully at it before buying something else.
The saw is quite heavy, but the caster system is very nice, so for
moving around my garage and back out of the way, the weight is not a
factor. I am convinced the setups benefit from the extra metal.
Negatives about the Rigid: the motor might be a little lean for some
jobs. Hitachi offered a much higher power rating, but I noted that the
Jet used the same specs as the Rigid. I no longer consider "Jet does it
too" to be any kind of reassurance [**], but I did at the time. The
bottom line was that I was suspicious of the Hitachi numbers. Also, the
Rigid is more solid than the Hitachi. I will admit that I did not fully
appreciate that when I made the call, hence my claims that my purchase
was part homework and part luck.
The arbor on the Rigid could be a little longer. Put a very wide dado
stack on it, and the shipped washers won't fit. I plan to get some flat
grade 8 washers for that situation.
The biggest concern I had with the saw was again with the arbor. I had
trouble with the early blade changes, and it almost felt like it was
trying to cross thread, but in the middle where that should not be a
factor. I now suspect that the threads varied in height a little, and
that some wear corrected it. There are bare spots on the outer margins
of the threads right where things got tight, and the nut moves smoothly now.
It is probably universal, but find another wrench to use on the arbor
nut. One of the delivered flat wrenches works great to hold the arbor
itself, but you can do better to turn the nut.
Have I mentioned that I like the saw? :)
[**] Sorry for the Jet bashing, but I can't be fair to you w/o
mentioning Jet, as they were part of the process. A lot has happened
since then, and I am very unlikely to buy from them again.
Thanks for the run down on the Ridgid Table saw. Now all I have to do
is find one to put my eyeballs on and check it out.....
I am like you ...no more JET anything. I got burned big time on a
GHB1340 lathe by both JET and their dealer (BLue Ridge MAchinery) and
afater some serious arguing with JET they finally did agree to do what
they could do to make things right with the machine I got.......but
hindsight is 20/20 and I should really have had it sent back and went
shopping elsewhere......Was nice BRM was suire quick to graab the sale
and the money, but after a call or two with all the problems the
"person" that handled JET line end of the sales or any warranty stuff
was never ever around anymore...........Then Jet tried to make me go
through BRM, for problems, but finally they worked with me one on one
without BRM being involved at all, that is until the problem with the
chipped and multi colored white/yellow/cream/tan/grey/and lots of
other mix matched colors that was used to patch up or so called touch
up the lathe and all the deep dings and nicks in the 1/8" thick paint
job that was nothing but cracks and craze marks, decided to send the
money to pay for refinishing to BRM and they sent me an invoice with a
credit for that amount trying to make me purchase that credit amount n
materials of any kind from them....That did not cut it, and more
fighting ensued, and finally JET sent me a gal of their paint and a
gal of their primer, and a check for labor for all the work I had to
do....on a brand new in the crate machine.
I don;t remember the count on the individual items that had to be
replaced on that lathe, but I wound up with 2 or 3 6" 3 jaw chucks, a
couple of faceplates, 2 sets of tumbler gear changers and pyramid
gears, a box full of tail stock quills, and feed screws, a compound
slide, 2 motors, a new lead screw and a bunch of other odds and ends.
Most times replacemenmt parts were as bad as or worse than original
lathe parts......PITYFUL stuff.
Sorry about my rant and hijacking your thread......
Most of that sounds cosmetic to me. Were they covering genuine metal
defects, or was it just a lousy coat of paint? Not that the paint
should be lousy, but I figure the non-precision surfaces are pretty much
negotiable as long as they are painted or oily.
My concerns with Jet are at the design level. There is a difference
between disagreeing with a customer and (vacantly) arguing with them.
Jet did the latter when I pointed out things like a cheesey sheet metal
contact that is not long enough to reach the switch it is intended to
throw. Further, that said cheesey metal contact is supported at only
one point, so that it would likely to rotate out of position even if it
were long enough to do its job, etc. Their tenoning jig isn't much
better, though it is not actively dangerous (other than the blade
spinning inches from the user's hands, but that goes with the territory).
Your financial struggle sounds similar to mine. However, I was not
seeking a full refund because I frankly didn't deserve it. I _should_
have told the salesman to answer all of my questions or find a
convenvient place to stick the saw. I failed to do that for various
reasons. After some haggling with Jet and the retailer, the retailer
finally dropped the price to more or less their cost, so I ended up with
un ungainly but efficient stand in for a metal chop saw for not a whole
lot of money. The real payload on that order was the mill, and that
turned out very well.
Back to your lathe. The above does _not_ sound cosmetic.
That's ok, I was pretty much done with it anyay :)
Cutting acrylic is no big deal any freshly shapened blade will munch the
stuff. Use course teeth. I have cut acres of the stuff and if you want
really smooth edges without saw marks there is a simple way. se circular
or table saw or router (multiple passes)
Ehen you get thru te stuff don't use any solvents or try to flame polish
Break out a nice fresh pair of scissors. 99cent store is good enough
If you hod one of the blades at just the right angle you can use this as
a scraper and shave away all those swirls with just a few strokes.
Polish it finer with some 400 grit wet/dry paper. Finish up with some
polishing compound either in a bench buffer or just by hand.
Don't get alcohol near it.
You can drink while you do this. It might actually help, but keep the
spirits away from the polished edge.
I flame polish virtually 99% of any edges of acrylic I cut. It has to
be finished almost to perfection and without any scratches or it will
make a crack later on, but if done properly acrylic certainly can be
flame polished very nicely.
Scraping is also my preferred way of knocking it down over sanding as
well. I made tools for scraping it out of carbide and HSS blanks. A
Noki type deburing tool also is good for knocking off the edge if
On Sun, 1 Jan 2006 10:46:27 -0800, firstname.lastname@example.org (daniel
Yes Flame polishing works well and I have done it many time. I worked in
the sign industry as a screenprinter for almost 30 years and the surest
way to get crazed edges was to fire polish the stuff and print on it
with solvent based inks that really bite the surface It only shows on
clear acrylic obviously
I bought a printer's saw with a sliding table a while back, mostly for
sawing small pieces out of larger plastic sheet stock and ran some
experiments with 3 different carbide-tipped saw blades, two of which are
marketed for plastic or non-ferrous stock. A short discussion and sample
cuts can be seen here:
Pretty good results were obtained from each with no melting and very little
chipping. I was presently surprised to find that the saw cuts could be held
parallel to within 0.002" or better. It will be interesting to see how well
it works on aluminum.
Part of the secret is to have a saw that is sharp enough & powerful
enough to cut fairly agressively. It needs to get the material out of
the way so the heat doesn't build up & start melting. If your are timid
while you cut, you'll get heat build up, melting & the problems it
Part of the problem is that there is a positive feedback issue. Once the
stuff starts getting hot, it will soften & expand into the cut, where it
will get hotter, expand more, and so on until you either get a mess or
the thing seizes up.
Another problem I've run into on the bandsaw is that you can get a soft
melted "burr" that will suddenly stop things when it gets to the edge of
the little slotted insert disk in the table.
While I hesitate to blame machines for things that might be my fault, in
the case of the dreaded Craftsman saw, it's the saw that's timid; it has
trouble with wood too :( If I see another $15 Wal-Mart junker like the
one I keep at work, I will buy two of them!
Yup. That's pretty much what happened. The first part is almost done,
and so I will probably try the circular saw next.
If all goes well, the bandsaw will arrive on Saturday. I had planned to
buy a Rigid (their table saw is _really_ nice!), but a Delta was more
readily available. Having already put this off a while over stupid
logistic problems, I decided to stop waiting.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.