Stone Files and Whetstones
Stones are commercially available either as sintered or as sawed stones;
depending on their geometry they are called "stone file" or "whetstone".
These stones are used to remove burrs, to bevel edges and to sharpen cutting edges.
They are, however, usually unsuited for use on ground steel surfaces because they
contact the steel with only a few points and would thus scratch the surface.
Inspection Stones and Flattening Stones:
Practice in the workshop requires that plane surfaces, before mating, be checked for (usually locally limited) planeness flaws. The sliding friction should indicate whether the surface is perfectly plane or whether it shows burrs, upsetting deformations (after an impact or after incidences of scoring) or soiling.
Also, it is necessary to remove such elevations with a flattening stone without damaging the surrounding plane surface.
Thus, the working surface of such a stone must have plane parts in order not to scratch the plane surface of the workpiece as well as cutting edges and recesses (pores) to receive the removed material.
In order to meet these specifications a stone must undergo appropriate treatment. In this process the surface must, however, not become completely smooth, but should have an appearance as shown below:
Typical Profile of an Inspection and Flattening Stone:
Part of the surface is plane and can be used to check for planeness because it does not scratch the surface. The recesses nevertheless permit to remove minor burrs and upsettings.
Typical Profile of an Inspection Stone:
A large part of the surface is plane and in order to maintain the quality of its surface this stone should be used predominantly to check for planeness.
A smooth and plane stone without recesses is not well suited for the purposes described above because it does not allow for space to receive removed chips and only the outer edges are available to cut away material.
Guidelines for the Use and Treatment of Stones:
- Always choose a type of stone that is appropriate for the job. Do not use a smooth stone, such as an inspection stone, for a location where seizure / scoring has occured or for working down a 0.03mm burr. The stone would take harm.
- If you detect a bump by means of the inspection stone, you have to choose an appropriate tool to remove the raised part. Burrs in unhardened materials are best removed by means of a scraper or a HSS file; for burrs in hardened materials a stone file is usually more suitable. Only with bumps in the middle of a surface there is no other possibility than to use a flattening stone. Here, the guiding principle is:
Give the stone time to remove the bump!
This means, patiently move the flattening stone back and forth over the bump and exert only gentle pressure until the stone has removed the bump and is in full contact with the surface. Using too much pressure is wrong because this could damage the stone and also the workpiece.
If the circumstances permit, it is better to work away the bump from one side. Move the stone back and forth from the plane part of the surface in such away that only the outer part of the bump and the edge of the stone contact each other. This causes less wear on the surface of the stone. However, this method too requires some patience.
- Stones used to remove material as described above collect the removed material in their pores and recesses. Therefore, one has to clean them from time to time. This can be done by washing them with kerosene and using a stiff brush (often, an old toothbrush will do).
In many cases, major metal chips cannot be released from the recesses by this method. However, they have to be removed because, otherwise, the chips would protrude from the surface of the stone and make it uneven. The chips have to be taken out one by one using a scribing iron or other pointed tool. You can feel protruding chips most easily by sliding the stone gently across a ground cylindrical or conical surface.
- In this context, it is worth mentioning that an inspection stone is very well suited to check the quality of a plane, ground surface. For this purpose move the stone across the surface exerting slight pressure. All bumps and recesses will show immediately; these may be caused by a slightly eccentric grinding wheel even if the runout is only one tenth of a micrometer.
After years of careful use a flattening stone becomes continually smoother; it turns into an inspection stone.
We at Blaha Company manufacture such inspection stones that meet appropriate quality standards. Provided the geometry is suitable, we can improve your stones to meet these standards as well.