Sanding Machines The material for this handout has been adapted from Chapter 60 (pages 403-407) of Wood: Technology and Process, by John L. Feirer, Mission Hills, California: Glencoe/Macmillan, 1987 and Unit 16 (pages 173-176) of Carpentry and Building Construction, by John L. Feirer, Gilbert R. Hutchings, and Peter Wilson, Toronto: Copp Clark Pitman, 1982. After studying this chapter, you will be able to: • List safety precautions for sanding machines. • Change a belt on a stationary belt sander. • Describe the basic steps in removing worn abrasive and applying new abrasive to an abrasive disk. LOOK FOR THESE TERMS narrow belt sander-grinder rotary sanding attachments There are sanding machines for every type of cutting and finishing operation. In the school shop, there are four common pieces of sanding equipment.

stationary belt sander stationary disk sander • •

SAFETY •

• •

• • •

•

Be certain the belt or disk is correctly mounted. The belt must track in the center of the drums and platen. Do not operate the disk sander if the abrasive paper is loose. Make sure an adhesive is holding the abrasive disk tightly to the revolving platen. Check the guards and table adjustments to see that they are securely locked. Use the table, fence, and other guides to control the position of the work, whenever possible. The table should be adjusted to 1/16 inch of the belt or disk. Small or irregularly shaped pieces should be held in a hand clamp or special jig or fixture. When sanding the end grain of narrow pieces on the belt sander, always support the work against the table. Sand only on the side of the disk sander that is moving down toward the table. Check the rotation of the disk. Some rotate clockwise, others counterclockwise. Always use a push block when sanding thin pieces on the belt sander.

• •

Do not use power sanders to shape parts when the operations could be better performed on other machines. Sand only clean new wood. Do not sand work that has excess glue or finish on the surface. These materials will load and foul the abrasive. Feed the stock directly against the abrasive belt. Never feed it in from the left or right as it may catch and rip or pull the belt off. Keep the stock in motion when sanding to prevent burning due to friction.

STATIONARY BELT SANDER The stationary belt sander can be used in vertical, horizontal, or slant positions. Fig. S-1. It is set in the desired position by loosening the hand lock and moving the entire unit. The table will tilt 20 degrees toward the belt and 40 degrees away from the belt. A miter gauge can also be used on the machine. With the machine in the horizontal position, a fence can be attached to guide the work for surface sanding. To change a belt, first remove the guards. Then release the tension by turning the belt-tension knob. Remove the old belt and slip on a new one. Apply a slight amount of tension. Then center the belt on the drums by adjusting the idler pulley with the tracking handle. Next, increase the tension and replace the guards. Check the centering adjustment again by moving

the belt by hand. Readjust when necessary. If the sander is to be used in a tilted position, the centering should be done after this adjustment. For surface sanding, place the machine in a horizontal position. The work can be fed freehand across the belt by steadily applying light pressure. However, for more accurate edge sanding, use a fence to guide the work. Fig. S-2. Beveling and angle sanding can be done by tilting the fence and sander. Fig. S-3. Sanding can also be done on the open end of the machine when it is in a horizontal position. Fig. S-4.

For end-grain sanding, the unit should be in a vertical position and the table should be used as guide. Fig. S-5. Bevels and chamfers can also be sanded in this manner by using a miter gauge as a guide.

STATIONARY DISK SANDER The stationary disk sander is used for some types of rough and end-grain sanding. Fig. S-6. It has rather violent action. This makes it effective for fast, rough work.

If the abrasive disk is worn, remove it. If the abrasive disk is attached with glue, soak it in hot water until loose. Then remove it with a putty knife. If rubber cement or stick cement was used, turn on the sander and hold the end of a hardwood stick against it. Move the stick back and forth to loosen the old adhesive. Be sure the metal disk is dry before mounting the new abrasive. To apply the new abrasive, hold the adhesive stick against the metal disk and move it back and forth. Make sure that there is a uniform coat of adhesive on the metal. Then turn off the power and carefully apply the abrasive. Let dry a short time. Clamp on a flat piece of wood to prevent wrinkles. Abrasive disks can be purchased already cut to exact size and with an adhesive coating on the back. All that is needed is to make sure the metal disk is clean. Strip the cover paper off the abrasive and install. Work can be held on the table for endgrain sanding. The table can be used in combination with a miter gauge to sand a chamfer or bevel. Fig. S-7. It can also be used to sand the edge of a circular piece. Fig. S-8. Always sand on the "down" side of the disk. Also, move the stock back and forth on this side. Holding it in one position tends to burn the wood. Most disk sanding is done freehand. Remember that the edge of the disk is moving much faster than the center. Allow for this. To sand circles or arcs, hold the work firmly on the table and revolve it slowly.

NARROW BELT SANDER-GRINDER

ROTARY SANDING ATTACHMENT

The narrow belt sander-grinder is a tabletop machine. It uses a narrow belt that moves around three or four pulleys. Fig. S-9. This machine is excellent for sanding small parts and for getting into hard-to-reach places. Fig. S-10.

Rotary sanding attachments consist of strips of abrasive paper or cloth attached to a metal wheel. Fig. S-11. They can be purchased in several types. Some have rectangular pieces of abrasives. Others have very thin strips of abrasives. They are fastened to a grinder, buffer, or portable electric drill. They are used to sand rounded or intricate surfaces. The brushes force abrasive strips over and around irregular surfaces. It is an excellent tool for sanding wood carvings. Fig. S-12.

•

• • • • • • •

PORTABLE SANDER

INSTALLING THE BELT

SAFETY:

Install the belt so that the arrow on the inside of the belt points in the same direction as the arrow on the side of the sander. When the belt has been placed on the pulleys, it can be made to run straight by adjusting the tracking screw. Fig. S14. The belt should not be allowed to rub against the left side of the machine.

See general safety rules for operation of portable electric tools. a Be sure the abrasive is in good condition and that its grit is correct for the work to be done. Be sure the abrasive belt is installed with the correct tension and is tracking properly. Keep your hands away from abrasive surfaces. Never touch the edge of a belt or disc. Be sure there are no nicks or tears in the edge of a disc or belt. Disconnect the power plug when changing abrasives. Make certain the switch is in the "off" position when plugging in the power cord.

Portable electric sanders are excellent for finish-sanding projects after assembly.

PORTABLE BELT SANDER The portable belt sander operates in a manner similar to the floor-model belt-sanding machine, except that the revolving belt is placed on the work instead of the work against the belt. Fig. S-13. The size of the machine is determined by length and width of belt.

USING A PORTABLE BELT SANDER

FINISHING (OR PAD) SANDER

The proper technique is to put the cord over your right shoulder, hold the machine with both hands, turn the machine on, and lower the back of it slowly onto the wood. Then do the sanding by moving the machine back and forth, and at the same time moving it slowly from one side to the other. Fig. S-15.

There are many kinds of finishing sanders. Parts of a typical one are shown in Fig. S-16. All of these sanders operate on one of the three basic principles shown in Fig. S-17. Those with straight-line action are the least likely to leave cross-grain scratches. The size of this machine is determined by the size of the abrasive sheet used.

Finishing sanders are primarily used for fine finish-sanding after the project is assembled. To replace a sheet of abrasive, first cut a sheet of paper to the required size. The paper is held on the pad at either end and pressure keys are used to lock the paper in place. Release the pressure keys at either end. Fasten the paper in one end and lock the key at that end. Pull the paper tightly over the pad, slip the loose end under the other clamp, and tighten this lock. The exact method of fastening the paper to the pad will vary with different sanders.

USING A FINISHING SANDER The finishing sander should rest evenly on the stock. Apply a moderate amount of pressure and move the sander back and forth, working from one side to the other. Fig. S-18.

OSCILLATING SANDER The oscillating sander can provide both rough and finish sanding. The entire disc rotates slowly in a clockwise direction while at the same time the pad oscillates in small circles. The sandpaper is attached to the pad by Velcro, this makes for quick changing of sandpaper as finer grit sandpaper is needed. Fig. S-19.

S-19 Oscillating Sander.