Using a hand grinder for repair broken china and glass

1 The hand grinder is probably the most needed tool in the repair and restoration of china and glass. Restoration work cannot be done without its use. It is a precision instrument but it is not expensive, and it can be used for many purposes other than china mending. With this standard type of hand grinder, which operates at a speed of approximately 20,000 revolutions per minute, and diamond-charged No. 2 wheels, a straight groove 1/8" deep can be ground into a piece of hard china 1/8" thick in a fraction of a minute. A novice can learn how to use it in a very short time.

2 Repair substances will not hold in place, due to expansion, contraction, and vibration, unless some means is provided to anchor the substance. To anchor means to provide retention, to lock in the substance so it cannot come out or pull away from the damaged area. The anchor is something for the substance to hold fast to. Just as a dentist must grind a tooth to provide an anchor for the filling that will be pressed into the cavity, so must an anchor be provided to hold the repair substance securely in place.

Anchors are provided by the grinding of grooves or slots, in or on the damaged area. The method of grinding these grooves varies, depending on the type and nature of the damage. Each one of the specific techniques for the five classifications of damages will specify the size, shape, angle, etc., of these grooves to effect a good anchor. So be sure to study these techniques in detail before starting to grind, and plan the procedures accordingly.

3 The grinder is made for intermittent use only. Operating at a speed of 20,000 revolutions per minute, it generates heat very fast.
After a few minutes' use, it will become too hot to hold in the hand. Before this happens, shut the motor off and set the grinder aside until it cools off, which should be in another few minutes. Never leave the motor running when the grinder is not in use as the motor windings would burn out in a short time.

4 When grinding, hold the grinder in one hand and the article to be ground in the other. Keep both arms tight against the body as a means of support and to steady the grinding operation. There is no control over the grinding unless such a position is maintained during the process. Both the article and the grinder must be held absolutely steady if the desired results are to be obtained.

A good grinding requires control. Without it, the grinding could cause more damage to repair. A foot control can be supplied with the grinder and it can be extremely helpful. It is a combination of a start and stop switch and a rheostat type of speed control device. It is operated by pressure applied by the foot. Light pressure starts the grinder at low speed, and progressively heavier pressure increases the speed until the maximum is reached. Taking the foot off the pedal automatically stops the grinder. When using this control, put the grinder switch in the ON position and leave it there. This control operates in the same manner as the speed control on a portable home sewing machine.

5 For greater control, hold the grinder in the palm of the hand with the four fingers. The thumb is extended and pressed against the article or the body. The article to be ground is held in the other hand, and is pressed against the body to keep it steady. When both are held in this manner, a slight wrist action, like a hinge, places the wheel in the proper position and angle to grind the groove, and also permits withdrawing the wheel in the same arc. This or a similar control method will prevent any twisting or turning of the grinder while the grinding is being done. It can easily be understood that if a groove has been partly ground, any twisting or turning of the grinder at this point could result in breaking the thin grinding wheel or a piece out of the article itself.

6 The extended thumb method to support and steady the hand holding the grinder can be applied in many other ways than pressing against the article or body. In some cases, the size, shape, and position of the article to be ground is such that pressing the thumb against the article or body is either impossible or impracticable. In these cases, the thumb can be pressed against any convenient surface, such as a wall, workbench, etc. In cases where the other hand is not needed to hold the article to be ground, this hand can be held against some solid surface with the thumb extended.

The two extended thumbs are then pressed together to provide the desired support for grinding purposes. Always keep in mind that some means must be found to support both the article and the grinder to prevent any shaking while the grinding is being done. Even normal breathing can disturb the delicate balance so hold your breath during the time the wheel is in motion. This type of careful grinding will result in a clean, sharp, straight, and perfect cut, and also permit ease in control and depth of the cut, without damage to the wheel or article.

7 In grinding, keep the wheel contact point always in view. Grind in such a way that you can see what you are doing. Keep the motor below the item and the wheel up, wherever possible. Grind slowly and with the utmost care. Let the speed of the wheel do the work, exerting only enough pressure to make contact with the china. In grinding, the wheel actually chips out small specks of china. On very thin china, apply scarcely any pressure; otherwise the wheel may break out a piece of the article and spoil the repair. On very fine china it is a good idea to provide some support near the grinding area, using the fingers, as the grinding is being done, to prevent any breaking out of a piece. Either hold the thin china between the thumb and index finger or press a finger against the china as a back-up support. Hold as close to the grinding point as possible, but watch your fingers. (Glass articles should be heated at a temperature not exceeding 125 degrees before any grinding is done. This prevents chipping or cracking the glass. )

8 In grinding a hole in glass or china articles to make into a lamp, use the small wide grinding wheel that measures 1/2" in diameter and 3/16" wide. First cut a groove with the side of the wheel, about 1/16" deep, about the length of the size of the hole to be ground. Another groove is cut the same length and depth as the first cut, across the first cut, which will form a figure like a plus sign. Then insert the edge of the wheel at the point where the two grooves cross each other and start to grind, turning the article as you grind. The two grooves will keep the wheel centred. Keep on grinding and turning until the hole extends completely through the article. ( The side of the wheel must be used because the screw which holds the wheel in place prevents grinding from the end)

9 A guard is mounted on the grinder to protect the fingers from the revolving collet. This is a good safety feature, especially for the housewife. In addition to knowing how to use the grinder, it is necessary to know what some of the parts of the grinder are called, and how the different accessories are mounted. They are:

  • The round knurled part that holds the grinders and cutters in the grinder is called the collet.
  • The small round part in the box, about 7/8" long, that is split part way into four sections, is called the collet sleeve. There are two of these sleeves, one in the box with the accessories and the other in the collet on the motor. Each sleeve is for a different size shank of a tool. It will be noted that the large grinding wheels are mounted on a larger diameter shank than the steel cutters. The larger diameter shank is 1/8" in diameter, and the smaller 3/32" in diameter. In using a grinder or cutter, the proper size sleeve must be put in the collet.
    This is done by loosening the end knurled section of the collet, which has a squared end for a wrench to fit. Turning counter clockwise will loosen and remove this knurled section from the collet. If this end section is tight, insert a nail that fits snugly into the hole in the bottom knurled section, which is next to the motor.
    This nail will contact the guard on the motor and keep the motor shaft from turning when loosening the collet. Use a pair of pliers or an end wrench to loosen the end section ( turning counter clockwise ). After loosening, the section can be turned and removed with the fingers. Just keep turning until the section comes off. The collet sleeve will now be exposed. Remove it by simply pulling it out of the collet.
  • After inserting the other sleeve ( it will go in only one way), reverse the above procedure. Screw on the end section with the fingers, turning in a clockwise direction, until it is hand-tight. Then insert the shank of the tool to be used into the hole in the sleeve. The shank should be set in about 3/4" into the sleeve. Tighten the end section firmly with a pair of pliers or an end wrench. ( The nail in the bottom section will keep the motor shaft from turning. ) Just be sure the collet is tight, otherwise the shank of the tool will slip in the sleeve and cause wear when it is being used to grind or cut.
    If it is not tightened securely, the tool could also slide out of the collet or wobble and possibly spoil the grinding job. After the nail is removed from the bottom section, the grinder is ready for use.
  • The plain shank, without any grinding wheel attached, that measures about 1 3/4" long and has a screw and a lock washer on one end, is called the mandrel. This mandrel is the tool on which the No. 2 grinding wheels and the hard carbide rubber wheels are mounted when they are to be used. The small grinder, for grinding holes in glass and china, and the thin wheels, having only one side coated with grinding compound, are also mounted on this mandrel.
    The screw and lock washer on the one end of the mandrel are removed. ( The washer is always kept against the head of the screw.) The screw is inserted in the hole in the centre of the grinding wheel, and the screw replaced in the end of the mandrel and tightened lightly with a small screwdriver. Do not make the screw too tight or it may break the thin wheel in half. The screw is long enough to allow several No. 2 wheels to be mounted together. The mandrel comes with both the 1/8" and 3/32" diameter shanks. The one supplied with the grinder is 3/32" in diameter, which is suitable for the average grinding. For heavy-duty grinding on china over 1/4" thick where large diameter grinding wheels over 1" in diameter are used, the 1/8" diameter shank mandrel should be used as the larger shank makes the mandrel more rigid. ( The heavier shank mandrel can be obtained from the Klein Company.) In inserting the mandrel in the proper size collet sleeve, set it in about 3/4" and tighten the collet securely.
  • The diamond-charged thin grinding wheels, which are about 1/64" thick and 1" in diameter, are the No. 2 grinding wheels. They can be used singly or in multiples up to about four, all mounted together on the mandrel. For multiple use the diameters of the wheels should be approximately the same size.

Safety rules in using the grinder

10 Always be sure the switch is in the OFF position before plugging the grinder into an electric outlet. This is important, not only for personal safety reasons, but also to prevent any damage to an article by having the grinding wheel revolve unexpectedly when plugging it in. A painful injury can result if a revolving wheel touches any part of the body. When the white dot is visible in the switch, the motor switch is on.

11 Use a shield, goggles, or safety glasses when operating the grinder. Flying particles of china or the grinding wheel itself could strike the eyes and cause serious injury. Regular eyeglasses could also be pitted and ruined. Be safe, take precautions. Also, it is a good idea to grind in a well-ventilated area as the grinding dust is likely to permeate the atmosphere.

12 Never put the grinder down with the motor running. It could cause personal injury or damage anything that came in contact with the revolving wheel. Also, the heat generated while the motor is running will make the grinder so hot after about fifteen minutes that it cannot be handled. If this practice is followed often enough, the heat will also damage and eventually burn out the motor windings. Where a foot control device is being used, the motor will be shut off automatically as soon as the foot is removed from the pedal.

Maintenance of the grinder

13 Keep the grinder clean of the dust and powder created by its use. Occasionally blow through the motor openings to get the dust and powder out of the motor housing. Air pressure from any source will be suitable, such as from a vacuum cleaner, paint spray compressor, etc. Be sure to have on some form of eye protection when blowing out the motor.

14 Every once in awhile, depending on its use, apply a drop of oil to the bearings in the end bells. Wipe off any excess oil immediately. Do not oil too often or too much, as too much oil is just as injurious to a motor as too little.

15 Provide a safe place out of the way to put or hang the grinder when not in use or during cooling-off periods. This will prevent any damage that might occur if it is pushed about on the work table where it might be knocked to the floor. It will also prevent breaking the thin grinding wheel by accidentally striking it with some object. Given proper care and use, the grinder will last indefinitely. ( The manufacturer of the Thor grinder gives a one-year guarantee against any defects not caused by careless handling or use. )

Grinder accessoiries and their use

The names and uses of the accessories are:

  • The three fibre brushes are called jewellery brushes and are used to clean jewellery.
  • The wire brush is used to clean and burnish brass and other metals, but not for polishing.
  • The four grinding wheels are used to enlarge holes in pottery, grind the edges of glass, and for similar purposes.
  • The steel cutters are used as rotary files on metal.
  • The hard carbide rubber wheel is used to polish metal and other surfaces, to smooth off nicks on the rims of china or glass, and to level off pewter repairs.
  • The small 1/2" diameter by 3/16" wheel is used for grinding holes in glass, china, and pottery.
  • The thin wheel, having only one side coated with the grinding compound, is for grinding between fingers of a figurine. With this type of wheel with one safe side, it is possible to grind on one finger without damaging the others.

17 In addition to the accessories supplied with the grinder, there are hundreds of different wheels, points, and cutters available.

Restoring china