Cutting acrylic

Hello all,
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?
Thanks!
Bill
[*] that means more than five sets of them ;)
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"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.
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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:

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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.
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Roy wrote:

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 plastic =:0
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.
Bill
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wrote:

Bill, 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. ERS
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Eric,

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 better.
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

:( Thanks for the heads up!
Bill
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Eric,

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 the slots.
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!
Bill
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wrote:

Bill, 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. ERS
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Hello all,
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!
Bill
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I would seriously consider adding a set of step pulleys to get more control.
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 alum/iron?
Regards
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Roy,

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 up front.

[snip]
Thanks!
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?

Cast iron.
> 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 view.
> 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? :)
Bill
[**] 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.
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wrote: snip

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......
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Roy,

Happy hunting. I think you'll like what you see.

[snip]
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 :)
Bill
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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 it. 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.
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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 need be.
On Sun, 1 Jan 2006 10:46:27 -0800, snipped-for-privacy@webtv.net (daniel peterman) wrote:

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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
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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:
http://member.newsguy.com/~mphenry/hammond_saw_blades.htm
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.
Mike
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Keywords:

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 brings.
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.
Doug White
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Doug,

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.
Bill
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