Easy to machine materials?

[cnczoner]

Compared to aluminum, I know that machinable wax is much easier on the machine (with "easier" meaning that there's less stress on the cutting tool, so it can be cut faster). But what about other easy-to-acquire materials such as acrylic? Are there any low-cost plastics that machine easier?

Purpose btw is making quick prototypes so I can easier visualize it and see how it fits in with other components, but these are not "mechanical" parts.

Cheers,
-Neil.

[Caprirs]

Some plastics are tricky to machine because the plastic can melt to the tool bit and quickly gum everything up. Cutting acrylic and polycarbonate the chips can stick to the tool and make a big molten wad of goo in seconds.

Delrin and nylon are less likely to melt to the tool. However, depending on the geometry being machined, the piece can warp a lot after machining and creep over time. For example, if you start with a 6" long by 1" thick plate of delrin and machine .030" off one face, when released from the vise, it may warp or bow .010". Put that part on the shelf for a month and it will warp or bow even more.

[edmunds]

Hi Neil!

Have You tried plywood?
The ones from hardwoods (birch, beech etc) seem to be nice. The ones from spruce are slightly softer.

Maybe MDF...They are in different densities.. I haven`t tried those..

[Dave Stallon]

I specialise in plastics and it is merely an engineering problem...just because it can be easy to machine does not mean you do not have to give it some respect.. Get the speeds and feeds right and you will solve most of it as far as clogging is concerned but you must have cutters that are designed for the job and an air blast will help... Parraffin is still a good coolant for home use.
Distortion is usually a different issue but still an engineering problem, it is a stress relieving issue especially with the cheaper materials..
If the material has been produced too quickly in order to keep the price down then cooling will have been forced, expansion rates on "plastics" are high so forced cooling on the outside means that the inside will dragging itself all over the place trying to cool down and will remain under stress..just as with steel..so...when you put a cutter through it the stress is relieved..The solution is to heat treat it and remove the stress in the first place..If you plough into it with a blunt cutter you will simply create more stress and more problems...I have made products that are highly accurate and have remained so for years after production..
A low cost plastic would be Polyethelene..HDPE...surprisingly stable in small sizes but keep away from heat and long flat sections.. easy to machine and very forgiving...don't go mad on spindle speed, that is the usual error, this stuff prefers a fast feed..
Sorry about the lecture, I am trying to be helpful..PM me if you have specific questions and I will help all I can.
Dave@plastics-machining.com www.plastics-machining.com

[Torque1st]

Dave- Forgive me for asking but how do you apply paraffins as a coolant?

In one of the shops I knew they used liquid nitrogen to help machine some plastics and foams.

[VWSatOz]

Just try MDF and see how you go. It may do all you need.

[Dave Stallon]

Hi Eric...I have to go careful my English and yours often mean different things..so...just to make sure we are talking about the same thing..Parraffin to me is a very light oil used in old lamps and heaters...That being the case I use a container like a hand held garden bug spray ..I guess even a water pistol would do the job...any simple system for delivering liquid...It works well on most plastics especially nylon ..as with all oils avoid drinking the damn stuff...Liquid nitrogen is great for the really soft plastics like polyurethane but difficult to use at home... I have used the "Freezer Spray" cans in the past as used in electronics fault finding and plumbing repairs..
Dave

[Torque1st]

Thanks Dave, I just noticed the UK location. Over here that would be Kerosene. I have used kerosene/paraffin for a cutting fluid on aluminum but never on plastics. I will give it a try!

Now I have to go back to work under the hood on my truck, -excuse me, -I think that may mean the bonnet on my lorry for you.

[Dave Stallon]

Two great nations seperated by a common language..

[Jim E]

Hi Neil.

If you're looking to machine acrylic, only use cast acrylic, which tends to give you chips rather than weld up. In any case, a small jet of air from a compressor, right at the cutting edge, will keep it cool.

But. You might like to try Foamex. It is a closed cell structure pvc foam, seems stable, takes no machining, won't weld up easily. Only available in about 24mm thick max though. Try a local signmaker for a piece.

The best material is a dense urethane foam though. Exactly what you need, but $$$$. You may find someone with small offcuts if your requirements are small.

Jim

[wihusker]

as a pattern maker, I use many types of materials for patterns and rapid prototyping. A good source for tooling boards is Freeman Manufacturing. For a product that machines well, and is stable their RenShape 5179 is a good choice. It is a urethane tooling board. They have a sample kit they will sell you that has many varieties of materials. www.freemansupply.net

[classTools]

Try cutting Corian or similar. I have cut 1/2" Corian very smoothly with a 1/2" carbide end mill, 3500 rpm, 35 ipm, 1/4" DOC. It's solid plastic, doesn't seem to melt, and cuts like aluminum with very nice chips. There is no stone in it.

The only problem is expense. A friendly kitchen countertop shop can help you there, they always have large bins of offcuts.