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CNC Plastic Material Tips!

(Original thread started on 09-04-13 by Tomislav)

I have a few questions about the materials used to make the panels. First of all, what materials are you using? Is it acrylic? Where do you buy it? And what thickness are the front panels and what thickness are the backer panels? What kind of cutting bits do you use?

 

(Posted by Ron Rollo on 09-04-13)

You can find plastic on line at sites like at "estreet plastic". Everything that we use is Acrylic cast plastic. So you know, there are two basic types of Acrylic plastic. Cast and extruded.

 

CAST means that the plastic is melted and pored into a mold, in our case it is a flat square mold. Depending on how thick they are making the sheets of plastic will depend on how much molten plastic they pore into the mold. Cast has a higher milting point but is not as flexible.

 

EXTRUDED means that the raw plastic is forced through a form or set of rollers. The physical properties of each type of plastic make a huge difference is the way they each react to cutting and or shaping. Extruded has a lower melting point and is much more flexible.

 

In our case, we want CAST. Speaking for myself, I had to learn the hard way. Extruded does not mill well at all. Well, it does at first but because of the low melting point compared to cast, the plastic will end up melting to the hot cutting bit in a matter of seconds. You can imagine that this will make a huge mess and destroy your part, even causing your bit to break!

 

The basic answer to the other question that you have is that the backer panels are .125" thick and the front panels are .25" thick.

 

Here are some additional tips from the school of hard knocks:

It is perfectly normal to melt plastic and break bits in the first few tries unless you have done some serious homework, have an idea of where to start, have the right materiel and bits to use. I melted plastic and broke bits in the beginning as well.

 

I run my CNC at about a 18 to 20 IPM forward feed rate. (CNC's and milling plastic can be ran much faster, like 30 to 60 IPM) Make sure your using CAST plastic. Extruded will melt in a heart beat. Last but not least, you need to be using a double flute end mill bit. Your can use single, triple or even quad flute, but I find that double works best. (flute or flutes are the spiral cuts up the bit that allows the chips to be pulled away from the cut surface. If you do not have flutes, the plastic chips will linger at the point of contact, heat up and melt to the bit. Once it starts, it does not get better and you will do nothing but melt plastic and break bits.

 

When I first purchased my CNC, Recardo gave me five 1/16th inch bits. I thought he was doing me a favor. It turns out they were nothing but trash and they either ended up broken or in the trash.

 

So to recap:

1. You can run you CNC at any speed. The MAX speed depends on how well built your CNC is. If It is a hobby level machine, you will need to slow it down. If it is a high end machine, you can speed up the process and not loose precision.

 

2. Use double flute bits. (I use fishtail double flute bits specifically for plastic.)

 

3. Use CAST plastic, not extruded.

 

Follow those three steps and you will not melt plastic or break bits, at least not as many.

 

Some guys use double sided sticky tape, the kind with a little foam between the two side. I actually use screws to hold down the material around the edges.

 

Diamond tip bits are not going to get you anywhere with this type of cutting. It's not how hard the bit is, it is how sharp and how fast can it get the chips out of the way. That is why you need double flute fish tail end mill bits.

 

Here is an example of a button pack cut out of .5" thick material:

Ron 532

 

Yes, the thickness does play a part in the cutting but the only factor is more time. One other thing that you need to look at is your step down. As an example, if your cutting a .125" thick piece of cast plastic with a 1/8th inch bit, it will take three passes to complete the cut. In other words, the bit will race around the part three times, going a little deeper each time before it breaks loose. As a rule, I never exceed 1/3 the bit diameter. So in this example, my step down for a 1/8th inch bit would be .042". The whole idea here is to NOT bite off more than you can chew. And this is one of the reasons why it takes so long to cut something out. (That button pack pictured above takes a little over an hour to cut out)

 

(Posted by Tomislav Babich on 09-05-13)

Oh and two more question. First do you use clear or white acrylic sheets? And where to buy it in Europe?

 

(Posted by Eric Tomlin on 09-05-13)

We all make our panels out of both white and clear acrylic depending on several factors, etc. As for acrylic in Europe, I'm guessing that Google will give you some good results.

Here's one: http://www.peerless-coatings.co.uk/plastics/acrylic-plastic-sheet/

 

(Posted by Dave Simmons on 10-18-13)

I just checked. Amazon Europe has cast acrylic at a reasonable price. I buy my acrylic here in the USA from Amazon. The Customer Service is first rate and if you join their "Prime" program, shipping is free (3 days) and 2 day shipping is $3.99. At least here in the states.

 

(Posted by Mike learukbuilder on 04-29-14)

I am at the point of buying panels for my bezels (EFIS<EICAS PFD, standby ind) and front panels like the DU,Nav, Engine etc do I look on amazon for Cast Acrylic .25mm in grey or buy it white and spray it grey? I don't know how it works as in, I buy the sheet and does the CNC machine cut and engrave, but how do I get the white engraved text markings for the panels once the panels are cut to shape and size?

 

(Posted by Ron Rollo on 04-29-14)

My best advise to you if your looking to build your panels yourself is to start small. That way when you make the first 10 mistakes, they will be small mistakes and you will not have a lot of material or money wrapped up in the mistakes. Mistakes = learning experiences with the CNC by the way!  A good example to start with is the REV panel on the glare shield.

 

You will want to buy .25" cast white material. Then you will cut it with your CNC machine. From there you will paint it gray. Next you will either engrave it with your CNC, use a laser or just use stickers or dry transfers to complete your artwork. These are no secrets by the way, but time consuming and at times challenging.

 

Just plan on a lot of little bumps along the way but that is how you learn. I hope this helps!