Processes

Cutting plastics

Circular Saw Troubleshooting

PROBLEM: Melting or Gummed Edges.
Suggested Solutions:
1. Increase blade tooth size.
2. Increase saw speed.
3. Provide better clamping and/or support for material.
4. Reduce feed rate.
5. Check blade and arbour for wobble.
6. Inspect blade for sharpness.

PROBLEM: Chipping.
Suggested Solutions:
1. Decrease blade tooth size.
2. Reduce saw speed.
3. Increase feed rate.
4. Use air to cool blade.
5. Inspect blade for sharpness.
6. Check blade fence alignment.

Band saws
Band saws are useful for trimming formed parts or irregular shapes. Band saws should be run at 2,000 ft. per minute and have between 3 - 15 teeth per inch. Coarser (larger tooth) blades perform better with thicker gauge plastic. Because vibration can induce cracking of some sheet plastics, proper support of the part to be trimmed is important. If the cut edge is not smooth, cracks will propagate from rough or notched edges.

Band Saw Troubleshooting

PROBLEM: Melting or Gummed Edges
Suggested Solutions:
1. Increase tooth size.
2. Reduce saw speed.
3. Use air to cool blade.
4. Check blade sharpness.

PROBLEM: Chipping
Suggested Solutions:
1. Decrease tooth size.
2. Slow down stock feed rate.
3. Provide better clamping and/or support to eliminate vibration.
4. Check blade sharpness.

Routing
Routing produces a smooth edge on most plastics and can be employed to cut curved or irregular shapes. Routers with a speed of 20,000 to 25,000 rpm are preferred. Use straight fluted carbide-tipped or high-speed steel router bits. Bits should be 10 to 13 mm diameter for best results. Portable routers, over-arm routers, or under-the-table routers are all useful. Use a router with at least a 1 h.p. motor. Special care must be used when routing.
USE PROPER GUARDING AND EYE PROTECTION.
Material feed rates need to be monitored. Feeding the material at fast rates can result in shattering. It is important to feed the sheet against the rotation of the router bit and to provide a fence for sizing, Router bits must be kept sharp. Cooling the bit with compressed air during operation will aid chip removal and prolong sharpness.

Shearing, Blanking, Punching
Other methods for cutting some types of plastic sheet include: shearing, blanking and punching, Shears produce straight-edged cuts, while blanking dies and punches can produce a wide variety of shapes. It is important to adjust the blade clearance in relationship to the bed knife. A clearance of .001" is desirable to avoid a rough edge cut. Material thicker than 3.0-mm gauge should be saw cut. Stack shearing is not recommended. Blanking and punching may be utilised for some plastics up to 3.0 mm. Other fabrication techniques such as sawing, drilling and routing should be used for thicker gauges.

Laser cutting
Laser beams can be used to cut most plastic sheet. Laser power and travel speed must be optimised in order to minimise whitening while cutting.

Die cutting
Some plastic sheet in gauges up to 3.0 mm can be die cut using steel rule or matched metal dies are the most common types and double bevel blades provide adequate edges for most applications. If improved edge finish is required, try the flush type of blade. Under normal conditions, 3 point (.042") thick blades work well. Keep the backup pad in good condition. It is important to have parallel alignment of the die and platen.

Drilling
Drills specifically designed for plastics are recommended, although standard twist drills for metal or wood can also be used, if sharpened for plastic. Most plastics are easily drilled using zero-degree rake angle bits with dubbed off cutting edges. Regulate pressure and speed until a continuous spiralling chip is observed. Back out drill regularly to free chips. This is particularly important when drilling deep holes. Use air or water as a coolant, if required. Do not use cutting oils. Be sure drilled holes are smooth with no evidence of cracks or roughness, which can cause weak areas in fastening. Always hold or clamp securely to prevent cracking or slipping and to ensure operator safety.

Milling
Most plastic sheet can be machined with standard high-speed milling cutters for metal, provided the cutters have sharp edges and adequate clearance at the heel. Favourable results can be achieved using a 15-mm diameter bit at 500 rpm with a travel of 125 mm per minute.