Milling Plexiglas

[Kristy]

Hi,

I was wondering if anyone could offer some advise for milling Plexiglas. Specifically, what are the best cutters to use and the proper feed rates? I imagine if the feed rate is to high the Plexiglas will melt and if it's to low it will splinter and crack. I will be cutting material up to one inch thick. Not sure if it make a difference or not but I have a NSK Astro-E 250 spindle. (2000-25,000min-1)

Thank you in advance for any assistance.

[1000IPM]

Hello Kristy

We mill plexi and acrylic faces with a 1/4 shank 3/16 cutter. Onsrud makes them. They are single flute upspiral 65-018. As far as feed rates - you can tell by cutting your material. If you are going too slow - you'll get extremely fine chips - too fast - fills the cut gap and the chips re-adhere themselves gluing your channel shut. We'll take 1/2" passes with this bit.

[project5k]

i would think that if the feed rate is too high would be where you would run into cracking, and too slow would be where you would see the melting.. just my theory tho as i've never tried it...

[1000IPM]

project5k - I can only tell you what I see on a daily basis - as far as cracking acrylic - if your bits are sharp - no problems - go too quick - the plastic stays in the path you cut - doesn't clear fast enough and closes the gap - sticks in the channel and welds back together.

[stevespo]

I'd love to hear some actual feed rates and RPM examples. I've been cutting Lexan with decent results, but I always get some fusing of the chips as I make the cut.

I'm using a 1/4" upcut 2 flute carbide bit, in a PC router spinning at 10K RPM with feed rates of 60-90 IPM. Depth of cut varies, but generally 1/8-1/4" for slotting.

If I raise the RPM or slow the feed rate too much, I get major melting. So, for me a slower RPM and faster feedrate seems to work best. I would like to try a single flute upcut and even faster feedrates. That might be the ticket. If I could use a misting system, that would also help a lot - but I have an MDF worktable, so no misting/coolant - other than compressed air.

Steve

[Geof]

Originally Posted by stevespo ...If I raise the RPM or slow the feed rate too much, I get major melting.... If I could use a misting system, that would also help a lot - but I have an MDF worktable, so no misting/coolant - other than compressed air. Steve

When machining plastics without coolant I used beeswax, regular paraffin wax and soap as a lubricant. Just rub it along the line of the cut or along the edge; it just not need a great amount to make quite a difference.

[Kristy]

Hi,

Thanks so much for all the info. I think I am just about ready to cut some test pieces. I have attached some info on spot cooling if anyone is interested. This information came from another on-line forum. Hope you find it useful.

A little device called a Vortex Gun will help a lot in this area. For more info check out the following

Mini Cooler
Cool small parts and tools with clean, cold air.
Prevent burning, melting or breakage.
http://www.exair.com/spotcooling_products/mc_page.htm

What is the Mini Cooler?
A proven way to reduce downtime and increase productivity on a variety of operations involving small parts where heat is the problem. EXAIR's Mini Cooler produces a stream of 20°F (-7°C) cold air to prevent heat build-up. The Mini Cooler is particularly effective on high speed operations to prevent burning, melting and breakage. Operation is quiet (76 dBA) and there are no moving parts to wear out.

Adjustable Spot Cooler
Cold air to -30°F (-34°C) from your compressed air supply for spot cooling!
http://www.exair.com/spotcooling_products/asc_page.htm

What is the Adjustable Spot Cooler?
A low cost, reliable, maintenance free solution to a variety of industrial spot cooling problems. With the turn of a knob, you can select the temperature best suited to your application. The Adjustable Spot Cooler provides a precise temperature setting from -30°F (-34°C) to room temperature.

The Adjustable Spot Cooler incorporates a vortex tube that converts an ordinary supply of compressed air into cold air. The Adjustable Spot Cooler can produce:

Temperatures from -30° to +70°F (-34°C to 21°C)

Parts included for flow rates from 15 to 30 SCFM (425 to 850 SLPM)
25 SCFM (708 SLPM) generator factory installed

Refrigeration up to 2000 Btu/hr. (504 Kcal/hr.)

Flexible tubing that holds its position directs the cold air. A swivel magnetic base provides easy mounting and portability. No moving parts or CFC's assures maintenance free operation.

Why Use The Adjustable Spot Cooler?
The Adjustable Spot Cooler is quiet (less than 75 dBA), easily set with a thermometer and holds the temperature setting. It's ideal for applications where mist or liquid cooling cannot be used due to part contamination or cost. Tolerances, product finish and production rates can improve dramatically.

The Adjustable Spot Cooler is available with either a single point or dual point hose kit. The single point system (Model 3825) is recommended for cooling a small surface like solder joints, hot melts or drilled plastics. The dual point system (Model 3925) is recommended when heat is generated over a larger surface area.

Vortex Tubes for spot cooling
Cooling with Compressed Air
http://www.newmantools.com/vortex.htm
order go to www.kbctools.com

[Geof]

Originally Posted by Kristy Hi, Thanks so much for all the info. I think I am just about ready to cut some test pieces. I have attached some info on spot cooling if anyone is interested. This information came from another on-line forum. Hope you find it useful. A little device called a Vortex Gun... ....Parts included for flow rates from 15 to 30 SCFM (425 to 850 SLPM) 25 SCFM (708 SLPM) generator factory installed

The Vortex Gun may be a little device but do you know how big and expensive a 30CFM compressor is?

[Kristy]

Originally Posted by Geof The Vortex Gun may be a little device but do you know how big and expensive a 30CFM compressor is?

lol..I thought the same thing! You never know what someone will find useful so I posted it anyway. Some people have way more tools then I ever will.

[low_48]

Use an Onsrud o flute dry. Go to the Onsrud site and it will give you feed and speed for all plastic cutting.

http://www.plasticrouting.com/BitSea...?Page=Material

[Stepper Monkey]

Just thought I'd point out that in regards to the coolant comments, you need to run dry or use straight water. Almost all standard coolants will usually invisibly damage the material! If anyone knows of one that doesn't I'm all ears.
Problem is you don't see it right away and it looks perfect, but it does something to the material surface and a few months or a year later the stuff will cloud, craze, or flake really bad. Not great for customer satisfaction....
Thought it might be helpful to not have to re-discover that one first-hand!

[MichaelHenry]

I've been using Hangsterfer S-500 at about 4-5% on acrylic with good luck and nice surface finish. No cracking so far and it's been around 6 months on the oldest part.

My latest project used a 1/8" carbide 4-flute end mill at 4000 rpm and 16 ipm feed rate.

Mike