This article first appeared in Practical Engineering 1940 Vol1 No3. The article is accurate as of 1940. The article describes machinery that was brought to the Engineering market at the time.
One of the most recent introductions of the firm of Jones and Shipman, Ltd., of East Park Road, Leicester, is the hydraulic horizontal spindle surface-grinding machine illustrated on this page. Although it was placed on the market only quite recently, it has met with such an excellent reception by the trade that the makers have been inundated with orders and deliveries cannot be given under approximately nine months.
There are two models—the Model SP618, which has a capacity of 6in, x 18in., and the Model SP1,027, with a capacity of l0in. x 27in. Both machines are basically similar in general design, though, of course, the larger-capacity model is of heavier construction.
The work for which these machines have been expressly designed is the rapid and accurate grinding of flat surfaces within the capacities stated. Careful consideration has been given to the question of design, with the object of enabling exceptionally high quality finishes to be produced, and with this object in view, the controls have been made especially sensitive. The wheel-head elevating and table cross screws are produced with a limit of .0005in. in 12in. and the handwheel graduations register within .0003in. per .05in. To ensure perfect balance, individual points are all tested by a Societe Genevoise vibration instrument.
This objective—the elimination of vibration—has also influenced the design of the bed and wheelhead column, which are cast integrally and precisely ribbed to ensure complete rigidity under the most strenuous working conditions. A stiffening bar is fitted under the cross saddle to avoid distortion of the work table when loaded. The entire bed and vertical column casting is of heavily ribbed box section, and forms a solid structure upon which the wheelhead table and wheelhead controls are built. The main machine bed also houses the electrical apparatus and the oil supply tank, which has a separate compartment for the hydraulic pump. The long vertical slides on the column carry the wheelhead assembly, which is counterbalanced to ensure accurate and sensitive movements.
The grinding wheel is carried on a cartridge-type spindle of heavy alloy steel, mounted on plain journal and thrust bearings, with provision for adjustment. If desired, a precision pre-loaded ball-bearing spindle can be supplied to special order. The spindle is lubricated by the self -contained oiling system.
In the case of the Model SP618, the grinding wheel supplied is 8in. x 1/2in. x 2in. bore, while the larger model has a wheel 10in. x 1in. x 2in. bore. Wider wheels up to 2in. can be supplied to order. Adjustable balance weights are incorporated in the wheel flange plates.
The motive power for the grinding wheel is a 3 h.p. dynamically balanced electric motor which runs at 1,440 r.p.m., and the drive is taken to the wheelhead by means of vee-belts and pulleys. Three changes of speed are obtainable by means of cone pulleys, and the driving belt is totally enclosed by covers which can be easily swung open for inspection.
The worktable is driven hydraulically and travels longitudinally on vee-flat slides. Its rate of travel is infinitely variable up to a maximum of 80ft. per minute, and it can be traversed by the hand or hydraulic mechanism at will. The length of travel is controlled by adjustable stop dogs, and the slideways are automatically lubricated by the hydraulic system. For clamping down work or fixtures, there are three tee-slots in the top of the table, and these will accommodate 1in. tee-bolts.
The complete worktable unit is carried on the cross saddle, traversing laterally on fiat slideways. Cross guiding is accomplished by vertical slideways, centrally disposed around and adjacent to the cross-feed screw, thus eliminating any tendency towards side-binding. Here again, the hydraulic system attends to the lubrication of the slideways automatically.
The hydraulically operated automatic cross feed can be applied in either direction, and has a rate of .008in. to .lin. per stroke. A trip motion is provided which automatically cuts out the cross traverse and stops the traversing table in the loading position at the completion of the range of cross traverse, set by the trip dogs. For wheel-truing purposes there is a continuous slow cross feed.
The pump which supplies the hydraulic system is of the helical gear type, and has only two rotating parts. The driving motor is built inside the bed of the machine, where it is protected from the ingress of dust or water. The valve gear has been designed to give shockless reverse at high speeds. As already mentioned, the hydraulic system attends to the lubrication of the cross-traverse, table-traverse slideways and carriage mechanisms, the oil being filtered before being returned to the tank for re-circulation.
As will be seen, all controls are readily accessible at the front of the machine, and all important controls are fitted with sensitive micrometer adjustments. The electric control gear is incorporated in a panel at the front, and is of the push-button operated type. The table traverse and wheel-head are controlled separately, while the suds pump and dust extractor (when fitted) are arranged to start and stop with the wheelhead. Both of these last-named items are obtainable as extra equipment.
Other items of equipment which have been specially designed for use with these machines, and are available as extras, are the built-in wheel-truing device, a universal swivelling vice, 4-3/4in. index centres, radius and angular wheel-truing attachment, and a high speed grinding attachment.
The swivelling vice has been specially designed for holding work to any desired compound angle, and has three separate swivelling movements which are fully graduated and can be locked in any position. The high-speed grinding attachment consists of a small-diameter wheel driven by an endless belt from a pulley which is attached to the wheel spindle in place of the normal grinding wheel. This enables speeds up to 20,000 r.p.m. to be obtained for grinding narrow slots, small radii, etc.