Machine Tool Foundations

Machine Tool Foundations

Machine Tool Foundations - In general, many machine tools can be erected on the concrete floor if this is sufficiently strong. Otherwise the machine must be placed on a concrete or brickwork foundation arranged according to the Foundation Plan in order to ensure smooth running and a high degree of accuracy. On the prepared foundation the machine is placed with suspended bolts and supported by iron wedges.

Machine tools such as lathes, which induce very little dynamic force, way be bolted directly to the floor without special foundations.

Lathes may also be kept directly over felt pads or strips. Felt strips approximately 10 cm x 10 cm sizes are kept under the supporting points of the lathe and glued. Leveling may be done by altering the thickness of the felt strip.

For machine tools, where vibrations occur, a concrete foundation must be prepared. For machine tools of normal accuracy and of upto 30 tons in weight, the foundations are generally made of concrete and, rarely, of rubble concrete or brick. In some cases, foundations may be reinforced with a steel supporting net.

The thickness of concrete foundations within a range of 0.6-1.4 m is used or radial drill presses, shapers, slotters and vertical broaching machines; for precision machine tools this thickness is increased by 20%.

For machine tools weighing over 12 tons and also those subject to high dynamic loads (such as slotters, shapers, etc.), foundations are made of concrete reinforced with a steel net which is laid under the upper surface of the foundation at a depth of 20 to 30 mm. The net is fabricated from round steel bars of 6 to 8 mm in diamoter with a cell size of ISO by 150 mm.

For light weight machines under 4 tons, such as millers, gear cutters, and drilling machines, a 0.25 m thick concretefoundation is used. For these machines at least 0.5 m thick brick foundation may be laid in dry around instead of concrete foundation.

The installation directly on a concrete hop floor is permitted for machine tools weighing upto IS tons with beds of medium and high rigidity, excluder machine tools operating. under dynamic loads (e.g., shapers, slotters, etc and also machine tools sensitive to vibrations, such as jig borers. Most machine tools can be instated on shop concrete floors.

The thickness of a concrete foundation block is calculated' from the condition of its strength and is taken as not less than 150 mm. The main material used for making foundations for machine tools is concrete of grade 75 and stronger (usually 90 and: for critical dimensions 110).

The number designating the grade of concrete indicates the compression strength in kgf per sq. cm after having set for 28 days. For heavier machine tools, as described earlier, concrete foundations reinforced with steel network made of round bars are to bet, employed.

The Concrete for a reinforced foundation should be of grade 100 or stronger. Sometimes, at a load exceeding 0'5 kgf per sq. cm, the concrete floor of the shop is also reinforced with a. network.  

Besides concrete, other possible materials for foundations can be cheap local stone of any kind with strength of atleast ­100 kgf per sq-cm, and well baked brick. Brick foundations; may be water-proofed (by asphalting the surfaces) to protect, against damage by ground water if necessary.

For some of the precision machine toots, it may be necessity protect the machine foundation against external vibrations such 81 those caused by hammers, presses etc. The foundation in such cases should be mounted on suitable isolating layers in order to, limit the amplitude of motion caused by the vibration of floor itself.