How to route plexiglass?

December 11, 2006 8:21 AM

I've been trying unsuccessfully to figure out how to route a channel in a piece of plexiglass for quite a while and now, having run out of ideas, I turn to the hive mind for help.
I've tried both a Dremel and a full-size router, but since they both spin at high RPMs (even at the Dremel's lowest setting), the plastic winds up melting and burring all over my bits as well as turning opaque due to the heat. My goal is to make the channel as translucent as possible, and I believe that I can put the plexiglass sheet in an oven after routing causing the plastic to smooth out and clear up any opaque areas caused by roughness. Can anyone recommend the proper combination of tool, bit, speed and technique to achieve my goal? Note that I am not wedded to plexiglass; I just need a very translucent material that I can carve channels into.

What this is for: I want to carve a single, continuous channel in the plexiglass, seal it to a glass top with silicone or similar substance such that the gap isn't noticeable. I'll need to get materials with approximately the same index of refraction, I'm sure. Once cured, I want to pump liquid (water, most likely, or perhaps mineral oil) through the path. Translucency is key, and the burring/melting problem I've been experiencing has made progress impossible.

posted by mjbraun to sports, hobbies, & recreation (14 comments total)

There are ways to slow a router down. Most of them involve plugging it into a device which lowers the voltage available to the router. You may be able to slow it down enough this way to keep from burning/melting the plexi.

Channels in plastic are usually cut with something more like a "mill" than a router. Mills are sort of like drill presses where the material is mounted on a table that has x-y adjustability. It's not a drill press exactly but it kind of looks like one. It uses bits that look somewhat like router bits and it functions kind of like one except at slower speeds. They're also used to cut metal. Here is a random example of a milling machine

What material are you actually using? Plain plexiglass? Lexan , which is a brand name for a material like plexiglass (it's what bulletproof "glass" is made of, I think) might be better. It's tougher, clearer, less likely to turn yellow with age. It's also more expensive.
posted by RustyBrooks at 8:31 AM on December 11, 2006

You should be able to do it with a router, just make sure that you take multiple shallow passes and keep the rate of feed high. Allow the bit to cool off between passes and use the biggest bit that you can (smaller bit heats up quicker than a big bit)
posted by zeoslap at 8:35 AM on December 11, 2006

You could also go the route of casting clear resin using something like this
posted by zeoslap at 8:45 AM on December 11, 2006

Do you have a table saw? If you do you probably already know how to cut a channel by lowering the blade and making successive passes or a dadoing blade. It is best to use a blade made for cutting plexiglass, though, and I doubt there are dadoing blades made for plexiglass. Just make a few more passes with the regular blade.
posted by caddis at 8:51 AM on December 11, 2006

It sounds like mjbraun wants a shaped path, which means the table saw is out. Though this method does work great for straight lines.

If you have access to a drill press, it will make your job easier. Like zeoslap says, the key is multiple shallow passes, and appropriate speed. Note though, the speed is going to be a combination of how fast your bit is moving and how fast your piece is moving under the bit. If you can slide the piece under the bit quickly, you can achieve a higher bit RPM. If you have to move slowly, you should slow the bit down as well.

Dremels and routers aren't good at slow speeds. Try a corded hand drill. You can find drill press assemblies for hand drills at the hardware store, which might be easier than finding someone with a real drill press. The corded hand drills usually have excellent torque and infinitely variable speed (down to very slow). At least, better than cordless ones. I have a Dewalt that does this well.
posted by odinsdream at 8:58 AM on December 11, 2006

There are variable-speed Dremels - maybe one of these set on the slowest speed would work for you?
posted by Quietgal at 9:09 AM on December 11, 2006

All,

Thank you for your comments! To respond:

RustyBrooks: I'm just using generic "Home Despot" plexi. Your advice about the yellowing is helpful, and I suspect that once I get my technique down, I'll move on to lexan. Also, from your comments and others, it looks like a milling machine will be my best option, though I'll have to find access to one.

Zeoslap: I actually thought about casting, but given the complexity of the path, it would very difficult to pull off.

OdinsDream: Yeah, the tablesaw angle is out, due to the path being curved and complex. But if I can find a rig for my corded drill, I'll give it a shot.

Quietgal: My Dremel is variable speed, but even at the slowest setting, it's still turning rather rapidly (2k RPM, IIRC) and the result is the same; white gunk everywhere.
posted by mjbraun at 10:32 AM on December 11, 2006

In addition to slow speed and feed, you need a cutter lubricant. I have had good luck with baby oil.

USE EYE PROTECTION. Plex splinters cannot been seen and they cannot be imaged if the get into your eye.
posted by Raybun at 10:54 AM on December 11, 2006

You might have better luck with a softer material like PETG. It's generally more machinable than Plexiglass/acryllic, although it'll still gum up on you. Make sure your bits are sharp.

Can you really smooth out sheet plastic in an oven? You'd have to put it on a perfectly clean pane of glass or it'd get some extra texture. It seems like it'd be really tricky to get the right amount of heat before you melted the corners. Would a heat gun work better? Make sure there's a lot of ventilation.

Do you want you channel translucent or transparent? You can smooth out PETG with files and sandpaper, but you're not going to get it back to transparency.

How big is this overall?
posted by hydrophonic at 11:07 AM on December 11, 2006

I would try engraving it by hand with a burin. Successive passes would get you the depth you want. Labor intensive, but no heat buildup to worry about, and much finer control. Beginning intaglio classes often use plexiglas sheets as engraving plates.
posted by bricoleur at 11:18 AM on December 11, 2006

Try Armor All as a cutting fluid.
posted by hortense at 11:40 AM on December 11, 2006

I used a spary-can of WD-40 or silicone lubricant to act as both coolant for the plastic and as blade lubricant. Lubricated blade means less friction, which means less heat. Additionally, the liquid over the plastic carries away heat.
(Make sure the solvents don't attack the plastic, but I haven't had problems in this regard - plexi should be ok).

In order to remelt it afterwards to turn opaque areas clear, I've used a butane torch at a distance, which allows for quite selective application of heat. However you may also want to get a buffer and buffing compound, as this is the way that plexi is normally smoothed back to transparancy. I stacked a few buffing disks on a powerdrill, and it works. The extra speed of a bench grinder would be more preferrable though.
posted by -harlequin- at 11:47 AM on December 11, 2006

A milling machine would certainly work. As you say, access might be an issue. One other way to address your issue comes to mind. Perhaps you can make a laminate. You are already going to laminate this with glass. Why not form a laminate with the glass on one side, solid plexiglass on the other and in between put pieces of plexiglass that have been cut using a saw? Draw the channels out on a piece of plexiglass that is as thick as you want your channels to be deep and then cut away the material where the channels will go. You could use a bandsaw, jigsaw or even a handheld jigsaw to make the cuts, although a bandsaw with a blade designed to cut plexiglass will likely give you the cleanest cut. Another advantage will be that no sanding and buffing will need to be done on the bottom of the channel as that is just the face of the solid plexiglass sheet. The sides will be exposed and thus easier to sand and buff into a smooth and transparent surface.
posted by caddis at 11:47 AM on December 11, 2006

Plexiglass melts between 265 and 285 deg. F. Since your piece is going to be able to fit into an oven anyway, how about bending the shape of the channel you want into flexible metal piping (such as Cu or Al), heating that in an oven and pressing it into the plexiglass? I'm guessing a coating of mineral oil on the plexiglass would be enough to keep the piping from sticking to the plexi.
posted by jamjam at 12:46 PM on December 11, 2006