Discussion in 'Article Discussion' started by Tim S, 14 Mar 2008.
woah....what happened to using a dremel???
dremel works fine for most of it provided you use the right bits, but its mostly good for wood/aluminum/steel
the article is fantastic as a beginners guide.
from personal experience, one of the things to watch if CNC milling acryl/plexi or similar is to check what coolant they use. Certain coolants will stain the acryl/plexi permanently, sometimes soaking in a good way. the coolants used to mill aerospace parts are particularly guilty of this.
however, the coolants that do not stain are your best friends, as because the flow is high volume, you can mill almost any type of acryl/plexi with a very high degree of precision. the easiest way to find someone who will do CNC milling work is to pull out the phonebook, or look for local part manufacturing shops.
Its not acetone, but close. IPS Weld-On, the stuff you use to bond acrylic (usually #4, #3, or #16) is the best. If you are in a bind, and want to make your own, its actually MEK. If you blend about 50/50 by volume of acrylic scrap and MEK... you have a grade of weld-on somewhere between #3 and #4 (#3 sets faster, #4 gives you more set time). Recently, Weld-On has changed its formulations though... so what the new formulas are now are anyone's guess. The old stuff was better though, thats what I hear from the fabricators, so Ive stocked up on the old #4 and #3.
As for saws, the problem with those fine tooth 'panel' blades is that on any sheet that is thicker than the height of the teeth, the sheet melts to the blade. So even though having a blade with more teeth is preferred, if those teeth are short, chances are you will end up burning the acrylic. This can end up blackening the edges, or be more subtle... sealing the surface of the acrylic so it cant be bonded with regular solvents (like abrasion resistant acrylics). The trick with acrylic and any saw is you have to cut fast enough that it wont melt and bind, but slow enough that you dont end up chipping. With those panel blades (like the one shown in the article), this 'sweet spot' or middle ground is overlapped, or it doesnt exist... you are going to get one or the other it seems... IME.
The best blades I have used (besides just buying an acrylic blade) are the finer tooth carbides. The tips of the blade are wider than the main disk of the blade, so friction is minimized. If you rub a little blade wax on, it will cut the acrylic like butter. Still, even with a belt drive table saw (direct drives arent very good for acrylic) and a sweet fence ( I use a powermatic table saw, one of the best made), you still get some chipping and want to polish up the edges. So I tend to do all 'show' cuts with first a saw, and then finish them up on the router lift. Once again, you want to go fast enough not to chip, bit slow enough not to chip... 18,000 rpm is the speed you want on the router as well, and just a straight 1/2" cutting bit works well.
I suggested the DIY forums otherwise at Reef Central. There are guys there who know EVERYTHING about acrylic, because its their business to.
Oh, and as far as extruded vs. cast... unless you are doing heat shaping/bends, I bet for most of your projects extruded will be just fine. For the aquariums, cast is a must because it holds up to pressure better, and bonds better. Of course, like I said, it depends... as its not just 'CAST' vs. 'EXTRUDED', but Continuous Cast, Extruded, and Cell Cast. Also, I suppose I need to include for the EU guys... the grade of acrylic made in the US vs. China vs. EU is very different. The EU extruded is much higher quality than the US (more expensive too), so good its used in many applications that would warrant cast if in the US. The 'cast' coming out of China is also dangerous to work with, as its actually recycled and mixed with some nasty plasticizers in the process which release when the acrylic is heated. Using a drill bit or dremel even can release black smoke and fumes like you woulnt believe... I had to run out of the basement when I did it myself it was so potent. The good stuff should almost smell sweet when you cut it... not like a toxic dump. If you work with something that smells like that, work outdoors with it. Its bad juju. And forget using an oven for heat forming... I doubt it wouldnt burst into flames before it hits 250. The chinese acrylic is poured like a resin into the specific shapes desired, like casting a glass jar almost, because they wouldnt want to have to machine it later.
Interesting read, some good tips to try out next time!
My way of opening cans like that, (5 gallon cans of Kilz go off like bombs too,) Is to tap the edge facing away from you with a sharp nail. to hold the nail in place, your hand has to be covering the lid. When it goes POP the contents paint the inside of your hand.D Loaded statement!) I had one fly off never to be seen again, so I learned to be cautious.
-I think the lids are the real reason channel lock pliers were invented. -In particular for the ones on PVC glue. You want the lid on pretty tight anyway. I didn't get the lid on my Tap solvent right one time, and I started to hear a hissing from the cap. It was the sound of my 'spensive glue going away!
@undertheradar - I think cc3d was talking about a trick to make gel glue using shavings, acetone, and MEK, (from the Mod The Nation Forums?)
-I do love the smell of good plexi. It is kinda sweet, now that you mention it. The cheap stuff smells like something you put on your yard to kill bugs.
@wywywywy - For me: tile saw I'm not sure I'd try it on a table saw. It would chip like crazy. Do you want a bondable edge? If you're going for just a decorative bevel, then I'd try a router or just file it down.
-Seth has a valid point. One of the best ways to cut extruded plexi is with a dremel. Everything else gums up.
Ah, tile saws. And yes I want a bondable edge.
I've never used one of these though.
So just a case of rotating the table top 45deg, then cut?
And if I am to buy one, I would guess 600w is more than enough?
I'm not sure if the table top versions will tilt, but they are the cheapest type of wetsaw you can get. (I was kind of joking when I said that.) They also have the ability to cut whole sheets or just tiny parts. My big tile saw is the type with the arm that hangs over the work. The arm and cutting table only have 14" of clearance. My handsaw type wetsaw is what I use for bevels, and it's great for cutting up big sheets. The problem is it cannot cut small pieces that a guide cannot be clamped to. If you buy a tile saw, make sure it can do what you want.
-Also- The duller the blade, the smoother the cut will be, (and slower.) I'd drag a brick ot the sides of the blade to break it in a bit. I have a blade that is so dull the edge is rounded off. It leaves a nearly glassy edge. A new blade will look like it was done with 80 grit sandpaper.
Power isn't important. The saws with big motors are for cutting up granite counters. You only want to cut plexi.
-does not chip
-safer (won't kick back like a regular tablesaw, and you can get your fingers close to the blade.)
-cost $ and can't be used for much
I hope I helped. (join us! JOIIIINNNN UUUSSSS!)
Far easier when you have acess to a laser cutter
I was rather annoyed how you kept saying "No material, and I mean NO material can ----- like acrylic." That's just false. Polycarbonate as well as other plastics can be bent and fused and look great.
Have you ever tried fusing polycarbonate before? Pain in the butt.
There are problems with a laser cutter though. I prefer my CNC router. A Laser cutter is a bit like flame polishing your edges before bonding... the surface isnt as flat any more, and its surface capilaries are sealed, so bonding doesnt always take too well. You have to go back and sand the edges before bonding with the laser cut stuff.
Ya, know undertheradar YOU should write an article on acrylic since you've worked with it the most and seem quite knowledgable of it. After reading most of these posts about this particular subject, I am seeing that working with acrylic seems to be more of preference of how and what to use for this material to manipulate it specially from those who've worked with it but not necessarily are proficient of this subject. Preferably, I like to use my cnc machine to work with this material, the cuts are always precise and repeatable and with a speed control such as:
will prevent any melting of any 1/4 inch thick plexi or acrylic (although I found a better priced speed control on ebay with shipping I payed $20 USD, can't go wrong, also this helps with knowing what feeds and speeds to use:
I have a Neiko brand found on ebay for $14.00 USD (this includes shipping, and the But IT Now)
it works on a laser with reflective tape method and man these investments are worth it, specially for thoise who contest their PC cases.
I am a machinist by trade, schooled in mechanical engineering but learning about acrylic comes from reading the project log here on bit-tech.net, they are loaded with info, more than anyone thinks, the subject may not be in depth but it is hands on by the modder that speaks more than just the subject, and if their way doesn't help you, then you're better off leaving it be. At 18,000 rpm the acrylic will melt because of the saw being used, I've used extruded and cell cast and for some reason, I got the same results, as far as melting goes, there were varying differences between the two but the melting at the same speeds was...welll, the same, hence the speed control, when purchasing the speed control be sure the item description says that torque in one way or the other is not lost. As for CNC, in the time it takes anyone on here to build and finish a Case, including it's electronic innards, you could've built your own cnc machine(specially for those who know how to CAD there designs.) Look into cnczone.com look up hossmachine and see the total cost for putting toghether a home brewed cnc machine (under $2000 USD) laser cutting is also very good.
I am a noob to acrylic and I am going to use your tips to make a Gigabyte Galaxy cpu block top. Thankyou for the article and for the tips to get me started.
Is there any way to tell cast from extruded acrylic by looking at it?
Itll usually say on the covering. Most sheet acrylic is cast. On extruded tubing, itll have waves and other minor defects that will stand out. Cast tubing will be totally clear and cost more. Tap Plastics is a good place to get small orders from, and their website has everything clearly marked.
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