# Bit Speed on Plexiglass????



## garycurtis (Sep 17, 2007)

I'm planning to make a few jigs using plexiglass. The bit can be any modest straight bit. My first few attempts ended with the plastic shattering. Even with relatively shallow cuts.

What am I doing wrong?

Gary Curtis
Northern California


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## bobj3 (Jan 17, 2006)

Hi Gary

It maybe the bit you are trying to use, most straight bits are Not made to plunge in... they have a blank spot right in the center of the bit .

Try one like below
http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_plung.html
Or
http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_solid.html

Note.. the picture below, this is the one you should use in a router (upcut) down cut in a plunge router.. 


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garycurtis said:


> I'm planning to make a few jigs using plexiglass. The bit can be any modest straight bit. My first few attempts ended with the plastic shattering. Even with relatively shallow cuts.
> 
> What am I doing wrong?
> 
> ...


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## fibertech (May 7, 2005)

Bob, Where can you get Plexiglass? I am hoping to make a couple of router bases and want clear. Thanks in advance. -Derek


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## bobj3 (Jan 17, 2006)

Hi Derek

I'm not a big fan of Plexiglass ,it's great if you need to replace some glass but for jigs I don't like it ,, it's almost always under size and it is almost always comes with clear or blue film on it that's are to draw on...and like the name it will flex easy..HD/Lowes/Ace has it on hand.

But I do like acrylic ,it almost always comes with a paper cover that I can draw on and it comes in a true size, if you ask for 1/4" it will be 1/4" thick unlike Plexiglass ,if you ask for 1/4" you will get 9/32" thick the norm...

I sometimes get the acrylic from HD or Ace but you must look hard for it..
and take a your ruler with you...

When I have the time I also get some from the plastic companys in town out of the cut off box,,they just about all have one...some great deals, 50 to 75 cents ea....the stuff I like best is the scratch resistance to a point ,it's a flim that they put on the plastic,I think ....... 


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fibertech said:


> Bob, Where can you get Plexiglass? I am hoping to make a couple of router bases and want clear. Thanks in advance. -Derek


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## RustyW (Dec 28, 2005)

Plexiglas is acrylic. It's just one of many brand names for an acrylic sheet product. The reason the stuff at home centers is undersized and with plastic rather than paper masked, is because they get the cheapest available product. I prefer polycarbonate (Lexan,Hyzoid are common brands) which can be worked like wood with common woodworking tools. Acrylic I treat more like mdf, if you drill it eventually it will crack out from the hole. Luckily for me, I work at a glass shop near lots of gravel plants. At least once a week I cut and install scratch resistant polycarbonate windshields in their equipment. So I have tons of cut offs and scraps.


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## fibertech (May 7, 2005)

Thanks guys. I have a couple of Tap Plastics in the Seattle area that I can check. We are currently trying to sell our house and move further north. That would put me 25 miles from the Grizzly headquarters. My shop will be more than twice what it is now. I want to devote much more time to this hobby. -Derek


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## kp91 (Sep 10, 2004)

Rusty,

If you're having trouble drilling plexi, you can try a trick that works about 85% of the time for me. Deliberately dull the drill at the point where the grind angle transitions to the outside diameter of the bit. By dulling these 'ears', it will prevent the bit from catching as you drill.

You can also pilot drill your holes with a propane torch and a nail.


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## Lee Brubaker (Jan 30, 2006)

For jigs I prefer polycarbonate. It wont shatter & stands up to hard use. As BJ says, take your ruler with you because often in plastics the thickness's are in mm's instead of inches.

Lee


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## cbsjoez1935 (Mar 14, 2007)

Gary

I noticed that you did not respond to the suggestions on bit speed for plexiglass. I am not sure what problem you are having. If it is using the bit as a drill bit, you are going to need the plunge cut type, as suggested by BobJ. If you are attempting to use a staraight cutting bit as a "planing bit" on the edges that is something else. Could you please clarify your usage? Too high a speed with too low a feed speed could cause melting.

Joe Z.


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## garycurtis (Sep 17, 2007)

I am the OP on this thread. I'll be making jigs, so there will be a few holes bored straight in, but the breakage has been primarily on cutting and shaping edges.

I got all of my Plexiglass and Polycarbonate (known as Lexan) from Hastings Plastic in Santa Monica, Calif. Behind their store, they have several dumpsters. A treasure trove.

Again my question. What speeds do I use for drilling (I have end mills) and for edge shaping?

Gary Curtis


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## Mike (Nov 22, 2004)

Gary, end mills are not designed for router use. Buy yourself a 1/4" up-cut spiral solid carbide bit and use it at full speed. You may get a bit of melting on the edge but it will usually snap off cleanly when it cools.


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## garycurtis (Sep 17, 2007)

Mike, I called the bits end mills, but in fact they are router bits made for end drilling, including both up-cut and down-cut spirals.

Still, nobody has answered the question about edge shaping on Plexiglass and lexan.

Gary


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## bobj3 (Jan 17, 2006)

Hi Gary

I not sure if this will help,,, They make saw blades to cut plexiglass most have 80 teeth or more and they make router bits just for doing the same job..

They have many flutes, I have two that I got from Grizzly but I can find the part number for them on the net or in the book from Grizzly..

If you hit plexiglass on the edge it will break the same thing is true if you use a standard router bit it's hitting the edge with a very small hammer in a way it maybe spinning at 20,000 rpm but it's still flat so to speak...  most router bits have only two cutting flutes some have 3 but the plastic cutting router bits have as many as 15 or 20 flutes and they just take a very small bit at that..so you could say that it's always on the plastic like a soild rod...almost at 20,000 rpm's 


If you want to see it just ask and I will post a snapshot of one...

Here's one that only has 3 flutes but made for plastic but it's small.
http://www.precisebits.com/products...n=ALL&txtFromSearch=fromSearch&I1.x=8&I1.y=12

Here's one more,Fish tail point eliminates backside breakout and splinterin.
http://www.precisebits.com/products...=ALL&txtFromSearch=fromSearch&I1.x=10&I1.y=10
http://www.precisebits.com/products...=ALL&txtFromSearch=fromSearch&I1.x=15&I1.y=13

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## waif69 (Feb 29, 2008)

Mike said:


> Gary, end mills are not designed for router use. Buy yourself a 1/4" up-cut spiral solid carbide bit and use it at full speed. You may get a bit of melting on the edge but it will usually snap off cleanly when it cools.


Gary, I see that Mike indicated the speed to be full, I am guessing that to mean that you want the router to run at it's top speed. If I am wrong, Mike, please correct me.


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## caliban (Apr 30, 2008)

Delvies Plastics Has various sizes and thicknesses of acrylic sheet at decent prices. _e.g_., 

3/8" Crystal Clear Cell Cast Acrylic 12"x12"

Price: $8.50


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## Mike (Nov 22, 2004)

Caliban, you need to remember the forum is worldwide. Pricing information on a product should include a location, IE.. Here in Detroit, MI a 4x8 sheet of 1/4" thick Masonite (brand name) or tempered hardboard runs about $13.00. This is one of the better choices for making templates since it is inexpensive, easy to work with and reasonably durable.

Gary, Full speed or 20K RPM should work. Sharp cutting tools are critical for success.


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## caliban (Apr 30, 2008)

Delvies Plastics is a web/mail order company located in Salt Lake City, Ut. According to the website, they ship worldwide.

All my templates are hardboard, but the question Fibertech asked was: "Bob, Where can you get Plexiglass?"


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## garycurtis (Sep 17, 2007)

Somebody on an Enlish WWing website just offered a suggestion. They advised to sandwich plexiglass or Lexan between two sheets of 1/4 ply bore drilling or edge boring. For milling or shaping an edge. 

I tried the technique this morning and it performed beautifully with a rabbeting bit. It should do even better with a spiral. 

Thanks all,

Gary Curtis


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## Dave_Willemain (May 4, 2008)

*Hardboard as well!*



garycurtis said:


> Somebody on an Enlish WWing website just offered a suggestion. They advised to sandwich plexiglass or Lexan between two sheets of 1/4 ply bore drilling or edge boring. For milling or shaping an edge.
> 
> I tried the technique this morning and it performed beautifully with a rabbeting bit. It should do even better with a spiral.
> 
> ...


I have used this technique with hard board in the past. Cheap 1/8" works fine!


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## waif69 (Feb 29, 2008)

That is a great tip, I wish I knew that before I made my router plate. I received a bit of tear out on a few of the edges.


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## F3RR3T (Jun 16, 2008)

i find it helps when making your cut to go slow, because the plastic really sucks up the heat and can warp if your not on a flat surface


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## Tale Gunner (Sep 24, 2004)

According to all I have done with Plexiglass or Acrylic glass it has to be cut with very low speeds allowing time to cool after each cut.


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## TWheels (May 26, 2006)

I know this response does not answer the question, but I am very interested in the answer for both lexan (polycarbonate) which has very good mechanical strength but does not have good chemical resistance against organic solvents, and acrylic (plexiglass), which has good chemical resistance. 

Do the O-flute router bits live up to their advertising as the best for cutting lexan and acrylics?


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## TWheels (May 26, 2006)

I have been checking out various web sites for router bits for cutting polycarbonate and acrylic. The most informative seems to be Onsrud. They sell a variety of bits but they all recommend high speeds for cutting. As my budget allows, I will be exploring and reporting. Today I am going to try two O-flute bits from Amana on lexan from Lee Valley. The Delvie's Plastic web site does indeed have very good prices for acrylic sheets.


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