# HDPE as the body of a 3-D Printer?

I've been working on my own DIY 3-D printer recently, and I've been trying to experiment a little with different materials for the body. Someone suggested using HDPE (high-density polyethylene), since it works well on a CNC machine, which would make creating a number of prototypes easy. I know HDPE can also be used for filament, but I've never tried it before. Does anybody have any input on HDPE, or other potential materials for the body? I'm trying to avoid using wood, as I've had some poor experiences with it.

• Really hard to beat aluminum extrusion frames. Are you particularly wanting a cut-sheet construction printer? – Ryan Carlyle Jun 4 '16 at 5:49
• Not necessarily, but I have a lot of experience with CAD/CAM programs, so I'm trying to use this as an oppurtunity to stretch my design muscles a little. – ArkCaptainNoah Jun 7 '16 at 3:06

I've used what is commonly described as UHMW-PE, aka, Ultra-high Molecular Weight Polyethylene for various projects. You may know this material is often used in cutting boards, as it cleans easily and doesn't cut easily.

it does machine in a manner similar to aluminum, although the tool should be cooled/lubricated to prevent a build-up of melted plastic on the cutting edges. You can get away without coolant or lubricant if cutting speeds are slow and the swarf is cleared away from the cutter.

I'd not considered such a material for constructing a 3d printer, as it's expensive, but I've also not compared the prices to equivalent sizes of aluminum.

I'd consider that the use in a 3d printer would be a good substitute for lexan, as one can tighten the bolts without fear of cracking. For bolts subject to rotation or vibration, self-locking nuts are a good idea. If you have use of a broach, cutting out a pocket for the nuts would be easily accomplished.

I have downloaded the plans for the open-source 3d printer known as DICE, which calls for aluminum, but the pricing I've found was excessive for the right quantities. I think I'll explore the same bill of materials in HDPE or UHMW-PE (which may be different names for the same substance).

Equally useful to know is that the material is very slippery, effectively self-lubricating under the right conditions. Unfortunately, for a 3d printer application, I don't believe the self-lubricating part would work for carriages but might be fun to try with linear slides.

It is not as stiff as aluminum, so where stiffness is needed and not provided by the architecture, a thicker piece may be indicated. I can just barely bend with my fingers a piece of 3 mm (1/8") a small amount, but cannot do so for aluminum.

Here's the result of a quick search for UHMWPE: https://www.interstateplastics.com/Uhmw-Natural-Virgin-Sheet-UHMNV~~SH.php?thickness=0.125&dim2=12&dim3=24 which gives a price for 1/8" white sheet 24 x 12" as US\$26.06 while the black version is available only as thin as 1/4" for about US$ 28.00

The equivalent size in aluminum 6061T6 at onlinemetals.com is about US\$3.00 more expensive. That is lower than I expected, skewing the idea farther away from UHMWPE than one might hope. The equivalent for 1/4" is almost US\$ 60, quite a bit higher.

It would appear that if you need the thicker stuff, the price is better for plastic, not so good for the aluminum.

• My biggest problem currently is trying to determine how thick I want/need the sheets to be in order to create a solid object, that's capable of handling the constant vibrations of a 3-D printer, without causing any problems, so until I have a better idea of the exact dimensions, I probably won't be purchasing any materials. Either way, I appreciate the info! – ArkCaptainNoah Jun 7 '16 at 3:30
• I'm happy to have helped. If you want to perform some inexpensive tests, purchase cutting boards from the local big box store. I'm able to get quite thick material of some size locally at less than ten dollars per board. If you believe my answer qualifies, please click the check box icon. Thanks – fred_dot_u Jun 7 '16 at 9:55

The main consideration when building the body/frame of a 3D printer is the stiffness. The stiffer the material, the less the frame will deform under load, and the more accurate and repeatable your results will be.

UHMW has a Tensile Modulus of Elasticity around 120,000 psi (http://www.polytechindustrial.com/products/plastic-stock-shapes/uhmw-polyethylene)

Aluminium has a Modulus of Elasticity around 10,000,000 psi (Mott, Applied Strength of Materials, 5th Edition, depends on the specific alloy)

Aluminium is around 100 times stiffer than UHMW.

• I'd be curious to know how the figures compare for lexan sheet at 3 or 6 mm thickness, considering how many 3d printers use it for construction. – fred_dot_u Jun 16 '16 at 19:44
• Lexan (Polycarbonate) has a modulus around 340,000 psi (sabic-ip.com/resins/DataSheet/Internet/PDF/…) – BlackSquareTaco Jun 17 '16 at 4:31
• Loving the 'Lets apply science' answer. – creuzerm Jun 17 '16 at 14:18
• One piece of the science I'd like to see applied is what happens to the stiffness of acrylic when the bolts are tightened enough to keep the geometry of the frame from changing. I would expect that the cracks will propagate into the frame and destroy the stiffness. I'd also suggest that one can crank down pretty heavily on bolts in UHMW-PE without cracking. – fred_dot_u Jun 17 '16 at 14:41

I've tried this material (8 mm thickness) for a Prusa i3 clone of my own design but needed to abandon using it as it doesn't allow to be cut by laser easily on my friends laser cutting machine (not a hobby laser cutting machine, it is his business).

HDPE requires lower speed than cutting Plexiglas or Acrylic resulting in more heat input and a small top cut and a large bottom cut width leaving the edges far from being straight.