Machining and Moulding
Plastics sheets show many of the characteristics of composite wood-based boards. Most woodworking tools can be used, providing they are kept sharp. The biggest problem is frictional heat, which causes the plastic material, especially swarf, to melt. The HIPS (yoghurt and charcoal) sheets are particularly susceptible to melting. The general rule is, ‘fast speed, slow feed’, and if necessary use water based cutting fluids. Plastics materials expand when they are heated and contract on cooling. For all except the Yoghurt and Charcoal this can be as much as 2mm per m over a 10 degree temperature change.
Smile Plastics sheets will scratch if handled roughly, so care should be taken when they are being moved and stacked, especially when they are laid flat on the floor or a worksurface. They will also bend if stacked badly, but stacking ‘in the other direction’ will normally return bent sheets to their original shape. The Polyethylene range bend more than the HIPS ones. Metal clamps should have a softer buffer to avoid indentation of the sheet surface.
Holes up to 25 mm diameter can be made with standard tools, trepanning tools should be used for larger holes. Drills should be kept sharp, and the drill regularly withdrawn to ensure that melting is not taking place at the point – the ‘woodpecker’ method. A point angle of at least 100° should be used. Special drills for plastics are available with fast helices and polished flutes. Cooling should be by air blast as a minimum, water or emulsions are preferable, oil based coolants should be avoided. Liquids should be washed off with water after machining.
Milling and Routing
Milling machines and woodworking routers can be successfully used on the panels. Sharp tools and a relatively slow feed rate give the best results. To prevent chatter, care should be taken to ensure that work is securely clamped using broad, soft faced jaws.
Our panels can be CNC machined and water cut. They cannot however be laser cut.
Most saws can be used to cut Smile Plastics board, and fine teeth are preferred. A wavy set or skip tooth saw is recommended to ensure that the friction from the face of the blade is kept to a minimum and that swarf is rapidly removed. Reciprocating blade saws (e.g. jig saws) can generate heat and attention should be given to swarf removal and blade cooling, especially with HIPS. For circular saws, TCT blades are preferred, the kerf width should be greater than the blade, with deep gullets, all helping to reduce friction and remove swarf speedily.
Feed rates should be slow enough to give a good cut, but fast enough to avoid frictional rubbing at the cutting edge. It is difficult, however, to achieve fine finishes with sawing and finishing is often recommended.
Rail saws are effective at cutting clean straight lines through the material.
Sharp edges can be routed. We’d also recommend using a deburring tool (like the one shown) to cleanly remove the sharp edges.
Most types of physical fastenings can be used including screws, clips, rivets and bolts, especially those recommended for MDF boards. Smile Plastics boards also offer other fastening possibilities. The sheets can be edge welded using plastics heat welding methods. This involves a hot air gun and a ‘welding’ rod made from the same material. Secondly, the flexibility of the hdpe material can be exploited by incorporating snap fit fastenings, thereby avoiding the waste of the essential resources of time, materials, energy and money.
Because of their surface properties, HDPE boards are difficult to glue using conventional spreading adhesives. However lap joints and small areas can be successfully glued using primers and cyanoacrylate adhesives. Most adhesive manufacturers offer products for polystyrene which are suitable for the HIPS range.
If you want to glue the edges some ‘solvent glues/gels’ will work such as Tensol (gels will fill some voids and, if you want, an oil or powder pigment could be added to make sure you get a perfect seam.
Epoxy and other resins may suitable for use with HIPS and Bottle, but check your specific product first. If you do use solvent glues do not let the glue sit on the finished surface it can damage and melt the surface of the material.
Mitred joints can provide a strong and seamless join as illustrated here.
On heating, Smile Plastics boards will soften, allowing forming, normally between the two halves of a matched mould. Sheets up to 12 mm can be formed this way with drawing down to about 3 mm possible. Thin material up to 6 mm can be vacuum formed using conventional techniques. Yoghurt and Charcoal are soft and easily bendable at 140°C.
You can heat and form the material using basic sheet moulding processes.
Smile Plastics boards are supplied with a semi-gloss press finish and should require no finishing. Scratches can be carefully sanded out with a fine grade of sand paper or scotch brite pads (fine scotch brite pads are particularly effective). The HIPS range will take quite a good shine with conventional car polishes. When the surface of Yogurt is sanded , the material appears much whiter.
Random orbital sanders are strongly recommended; belt sanders can melt the surface
Smile Plastics recycled plastics sheets require little maintenance. Surface dirt can be easily removed using a mild detergent and warm water. However, the material is relatively soft so abrasive cleaners should be used with caution. The HIPS panels are sensitive to organic solvents, especially nail varnish remover, paint stripper, etc. Yogurt may tend to yellow slightly in strong sunlight but this surface effect can be easily removed with conventional bathroom cleaners or light sanding. Scratches can be sanded out using appropriate grades of paper.
If you are using the sheets for tables or work surfaces, ensure that they have a sufficient supporting structure to ensure that the material does not buckle or warp over time. This is particularly important when using 5 or 12mm sheets, or the Dapple or Snowflake HDPE material. We would recommend 20mm sheets for any table top or work surface.
Smile Plastics sheets must not be exposed to excessive heat as this will melt and eventually burn the material. They will withstand hot water, but prolonged application of boiling water will soften the sheet and cause it to lose rigidity. On a supported horizontal surface this may not be important but a structural element will exhibit a rapid decrease of physical properties between 95°C and 200°C.
Organic solvents may cause the HDPE to swell and should be used with caution. Organic solvents must NOT be used with the HIPS and other ranges.
Sunlight will affect the sheets in two ways. Firstly the colours may fade, the bottle grades are sensitive to this, and, secondly, the material itself will eventually become degraded and will start to lose physical properties. Yogurt will tend to yellow on exposure to sunlight. For outdoor applications we suggest that you discuss the project with us first.