花岗岩是一种火成岩，因其极高的强度、密度、耐久性和抗腐蚀性而被广泛开采。但花岗岩的用途也非常广泛——它并非只能用于制作方形和矩形！事实上，我们经常使用各种形状、角度和曲线的花岗岩构件，并取得了卓越的成果。
Through our state of the art processing, cut surfaces can be exceptionally flat. These qualities make granite the ideal material to create custom-size and custom-design machine bases and metrology components. Granite is:
■ 可加工
■ 切割和加工后非常平整
■ 防锈
■ 耐用
■ 持久耐用
花岗岩构件也易于清洁。在设计定制方案时，务必选择花岗岩，因为它具有诸多优越优势。

标准/高磨损应用
ZHHIMG标准平板产品所用的花岗岩石英含量高，因此具有更强的耐磨性和抗损性。我们的高级黑色花岗岩吸水率低，可最大限度地降低精密量具放置于平板上时生锈的可能性。ZHHIMG提供的花岗岩颜色可减少眩光，从而减轻使用者的眼部疲劳。我们在选择花岗岩类型时充分考虑了热膨胀系数，力求将热膨胀的影响降至最低。

CUSTOM APPLICATIONS
当您的应用需要带有特殊形状、螺纹嵌件、槽或其他加工结构的板材时，您可以选择像济南黑铁这样的材料。这种天然材料具有优异的刚度、出色的减振性能和更佳的加工性能。

需要注意的是，颜色本身并不能反映石材的物理特性。一般来说，花岗岩的颜色与其所含矿物质的多少直接相关，而矿物质的多少可能与它作为精密加工板材的特性无关。有些粉色、灰色和黑色花岗岩非常适合用作精密加工板材，而有些黑色、灰色和粉色花岗岩则完全不适用于精密加工。花岗岩作为精密加工板材的关键特性与颜色无关，具体如下：
■ 刚度（负载下的挠度 - 由弹性模量表示）
■ 硬度
■ 密度
■ 耐磨性
■ 稳定性
■ 孔隙率

我们测试并比较了多种花岗岩材料，最终得出结论：济南黑花岗岩是我们迄今为止所知的最佳材料。印度黑花岗岩和南非花岗岩与济南黑花岗岩相似，但它们的物理性能略逊于济南黑花岗岩。ZHHIMG将继续在全球范围内寻找更多花岗岩材料，并比较它们的物理性能。

如需进一步探讨适合您项目的花岗岩，请联系我们。info@zhhimg.com.

不同的制造商采用不同的标准。世界上有很多种标准。
DIN 标准、ASME B89.3.7-2013 或联邦规范 GGG-P-463c（花岗岩表面板）等作为其规范的基础。

我们可以根据您的要求生产花岗岩精密检测板。如果您想了解更多标准信息，欢迎联系我们。

平整度可以理解为表面上所有点都包含在两个平行平面内，即底面和顶面。这两个平面之间的距离即为表面的整体平整度。这种平整度测量通常带有公差，并且可能包含等级标识。

例如，联邦规范中定义了三种标准等级的平面度公差，其计算公式如下：
■ 实验室级 AA = (40 + 对角线平方/25) x .000001" (单边)
■ 检验等级 A = 实验室等级 AA x 2
■ 工具室 B 级 = 实验室 AA 级 x 4。

对于标准尺寸的平板，我们保证其平面度公差超过本规范的要求。除平面度外，ASME B89.3.7-2013 和联邦规范 GGG-P-463c 还涵盖以下主题：重复测量精度、平板花岗岩的材料特性、表面光洁度、支撑点位置、刚度、可接受的检验方法、螺纹嵌件的安装等。

ZHHIMG生产的花岗岩平板和花岗岩检验板符合或超过本规范中规定的所有要求。目前，尚无针对花岗岩角板、平行板或标准方尺的明确规范。

你可以在以下位置找到其他标准的公式：下载.

首先，保持平板清洁至关重要。空气中的磨料粉尘通常是平板磨损的主要原因，因为它容易嵌入工件和量规的接触面上。其次，用东西盖住平板，防止灰尘和损坏。不使用时盖住平板、定期旋转平板以避免单一区域过度磨损，以及将量规上的钢制接触垫更换为硬质合金接触垫，都可以延长平板的使用寿命。此外，避免在平板上放置食物或软饮料。请注意，许多软饮料含有碳酸或磷酸，这些物质会溶解平板上较软的矿物质，并在表面留下细小的凹坑。

这取决于餐盘的使用方式。如果可以，我们建议在一天（或一个工作班次）开始和结束时分别清洗餐盘。如果餐盘沾染了污渍，特别是油性或粘性液体，则应立即清洗。

定期使用液体或ZHHIMG免水表面清洗剂清洁印版。清洗剂的选择至关重要。如果使用挥发性溶剂（例如丙酮、稀释剂、酒精等），溶剂挥发会导致印版表面冷却变形。在这种情况下，必须先让印版恢复到正常温度后再使用，否则会导致测量误差。

盘子达到正常温度所需的时间取决于盘子的大小和冷却程度。较小的盘子通常需要一小时，较大的盘子可能需要两小时。如果使用水基清洁剂，还会伴有一些蒸发冷却作用。

盘子还会残留水分，这可能会导致与盘子表面接触的金属部件生锈。有些清洁剂干燥后会留下粘性残留物，这些残留物会吸附空气中的灰尘，实际上会加剧磨损，而不是减少磨损。

这取决于平板的使用情况和环境。我们建议新平板或精密花岗岩配件在购买后一年内进行全面重新校准。如果花岗岩平板使用频繁，建议将此间隔缩短至六个月。每月使用电子水平仪或类似设备检查重复测量误差，即可发现任何磨损点，且只需几分钟即可完成。首次重新校准结果确定后，可根据贵公司内部质量体系的允许或要求延长或缩短校准间隔。

我们可以提供花岗岩台面检测和校准服务。

校准结果出现差异可能有以下几个原因：

• 校准前，表面用热水或冷水清洗，且未给予足够的归一化时间。
• 盘子支撑不当。
• 温度变化
• 草稿
• 避免阳光直射或其他辐射热照射到盘子表面。确保头顶照明不会加热盘子表面。
• 冬季和夏季垂直温度梯度的变化（如果可能，请了解校准时的垂直温度梯度。）
• 装运后，板材未获得足够的归一化时间。
• 不当使用检测设备或使用未经校准的设备
• 磨损引起的表面变化

精密花岗岩上有多少种孔？

精密花岗岩组件上的槽

对于许多工厂、检验室和实验室而言，精密花岗岩平板是进行精确测量的基础。由于所有线性测量都依赖于精确的参考面来获取最终尺寸，因此平板为加工前的工件检验和布局提供了最佳的参考平面。它们也是进行高度测量和表面测量的理想基底。此外，其高度的平整度、稳定性、整体质量和工艺使其成为安装复杂机械、电子和光学测量系统的理想选择。对于所有这些测量过程，保持平板的校准至关重要。

Repeat Measurements and Flatness

平面度和重复测量对于确保表面精度至关重要。平面度可以理解为表面上所有点都包含在两个平行平面（底面和顶面）内。测量这两个平面之间的距离即可得出表面的整体平面度。平面度测量通常带有公差，并且可能包含等级标识。

The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:

DIN标准、GB标准、ASME标准、JJS标准……不同国家有不同的标准……

更多关于标准的信息。

In addition to flatness, repeatability must be ensured. A repeat measurement is a measurement of local flatness areas. It is a measurement taken anywhere on the surface of a plate that will repeat within the stated tolerance. Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.

为确保台面满足平整度和重复测量精度要求，花岗岩台面制造商应以联邦规范 GGG-P-463c 为基础制定其规格。该标准涵盖重复测量精度、花岗岩台面材料特性、表面光洁度、支撑点位置、刚度、可接受的检验方法以及螺纹嵌件的安装。

Checking Plate Accuracy

遵循一些简单的指导原则，花岗岩平板的使用寿命可以长达数年。平板的精度检查频率取决于其使用情况、车间环境和所需精度。一般而言，新平板应在购买后一年内进行全面校准。如果平板使用频繁，建议将校准周期缩短至六个月。

Before a surface plate has worn beyond specification for overall flatness, it will show worn or wavy posts. Monthly inspection for repeat measurement errors using a repeat reading gage will identify wear spots. A repeat reading gage is a high-precision instrument that detects local error and can be displayed on a high magnification electronic amplifier.

An effective inspection program should include regular checks with an autocollimator, providing actual calibration of overall flatness traceable to National Institute of Standards and Technology (NIST). Comprehensive calibration by the manufacturer or an independent company is necessary from time to time.

Variations Between Calibrations

在某些情况下，表面板校准结果会存在差异。有时，表面磨损导致的表面变化、检测设备使用不当或使用未经校准的设备等因素都可能导致这些差异。然而，最常见的两个因素是温度和支撑条件。

One of the most important variables is temperature. For instance, the surface might have been washed with a hot or cold solution prior to calibration and not allowed sufficient time to normalize. Other causes of temperature change include drafts of cold or hot air, direct sunlight, overhead lighting or other sources of radiant heat on the surface of the plate.

There also can be variations in the vertical temperature gradient between winter and summer. In some cases, the plate is not allowed sufficient time to normalize after shipment. It is a good idea to record the vertical gradient temperature at the time the calibration is performed.

Another common cause for calibration variation is a plate that is improperly supported. A surface plate should be supported at three points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered.

Only three points can rest solidly on anything but a precision surface. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same three points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. Consider using steel stands with support beams designed to line up with the proper support points. Stands for this purpose are generally available from the surface plate manufacturer.

If the plate is properly supported, precise leveling is only necessary if an application specifies it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

Extend Plate Life

遵循一些指导原则可以减少花岗岩台面的磨损，最终延长其使用寿命。

首先，保持量规清洁至关重要。空气中的磨蚀性粉尘通常是造成量规磨损的最大原因，因为它容易嵌入工件和量规的接触面上。

It also is important to cover plates to protect it from dust and damage. Wear life can be extended by covering the plate when not in use.

定期旋转测量盘，避免单个区域过度使用。此外，建议将测量盘上的钢制接触垫更换为硬质合金接触垫。

Avoid setting food or soft drinks on the plate. Many soft drinks contain either carbonic or phosphoric acid, which can dissolve the softer minerals and leave small pits in the surface.

Where to Relap

当花岗岩平板需要重新研磨时，应考虑是在现场还是在校准中心进行。最好是在工厂或专用设施进行研磨。但是，如果平板磨损不太严重，通常在所需公差的 0.001 英寸以内，则可以在现场进行研磨。如果平板磨损严重，超出公差 0.001 英寸以上，或者表面有严重的凹坑或缺口，则应先送回工厂进行研磨，然后再进行研磨。

A calibration facility has the equipment and factory setting providing the optimum conditions for proper plate calibration and rework if necessary.

选择现场校准和表面修复技术人员时务必格外谨慎。务必索取其资质认证，并确认技术人员使用的设备具有可追溯的校准记录。经验也是重要因素，因为要掌握如何正确研磨精密花岗岩需要多年的学习。

Critical measurements start with a precision granite surface plate as a baseline. By ensuring a reliable reference by using a properly calibrated surface plate, manufacturers have one of the essential tools for reliable measurements and better quality parts.Q

Checklist for Calibration Variations

1. 在校准之前，用热溶液或冷溶液清洗表面，并且没有给予足够的时间来使其归一化。

2. 板材支撑不当。

3. 温度变化。

4. 草稿。

5. 避免阳光直射或其他辐射热源照射到盘子表面。务必确保上方照明不会加热盘子表面。

6. 冬季和夏季垂直温度梯度的变化。如果可能，请了解校准时的垂直温度梯度。

7. 装运后，板材未给予足够的稳定时间。

8. 检验设备使用不当或使用未经校准的设备。

9. 磨损引起的表面变化。

Tech Tips

• 由于每一项线性测量都依赖于一个精确的参考面来获取最终尺寸，因此平板为加工前的工件检查和布局提供了最佳的参考平面。
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• 有效的检验程序应包括使用自动准直仪进行定期检查，提供可追溯至国家检验机构的整体平面度实际校准。

花岗岩的矿物颗粒中，90%以上是长石和石英，其中长石含量最高。长石通常呈白色、灰色或肉红色，石英大多为无色或灰白色，它们共同构成了花岗岩的基本颜色。长石和石英都是硬质矿物，用钢刀都很难切割。至于花岗岩中的暗斑，主要是黑云母，但也含有一些其他矿物。黑云母虽然质地相对较软，但其抗压能力并不弱，而且在花岗岩中的含量很少，通常低于10%。这正是花岗岩特别坚固的物质状态。

花岗岩坚固的另一个原因是其矿物颗粒紧密结合、相互嵌合。孔隙率通常不到岩石总体积的1%。这使得花岗岩能够承受巨大的压力，并且不易被水分渗透。

花岗岩部件由石材制成，不生锈，耐酸碱，耐磨性好，使用寿命长，无需特殊维护。花岗岩精密部件主要用于机械行业的刀具制造，因此被称为花岗岩精密部件或花岗岩部件。花岗岩精密部件的特性与花岗岩平台基本相同。花岗岩精密部件的刀具制造及测量简介：精密加工和微加工技术是机械制造业的重要发展方向，也是衡量高新技术水平的重要指标。尖端技术和国防工业的发展离不开精密加工和微加工技术。花岗岩部件在测量过程中滑动顺畅，不会出现卡顿。工作表面测量时，一般划痕不会影响测量精度。花岗岩部件需要根据需求方的要求进行设计和生产。

应用领域：

众所周知，越来越多的机器和设备选择精密花岗岩部件。

花岗岩部件用于动态运动、直线电机、三坐标测量机、数控机床、激光加工机……

欢迎联系我们了解更多信息。

花岗岩测量设备和花岗岩机械部件均采用优质济南黑花岗岩制造。由于其精度高、使用寿命长、稳定性好、耐腐蚀性强，已被越来越多地应用于现代工业的产品检测以及机械航空航天、科学研究等领域。

优势

硬度是铸铁的两倍；

----尺寸的微小变化是由于温度变化引起的；

----无需拧干，因此不会中断工作；

----由于晶粒结构细密、粘性小，无毛刺或凸起，保证了较长使用寿命内的高度平整度，且不会对其他零件或仪器造成损坏；

----与磁性材料配合使用，运行无故障；

使用寿命长，不生锈，因此维护成本低。

精密花岗岩表面板经过精密研磨，达到很高的平整度标准，以保证精度，并用作安装精密机械、电子和光学测量系统的底座。

花岗岩表面板的一些独特特征：

硬度均匀性；

负载条件下精度高；

减振剂；

易于清洁;

耐缠绕；

低孔隙率；

不具磨蚀性；

非磁性

花岗岩表面板的优点

First, the rock after a long period of natural aging, uniform structure, coefficient minimum, the internal stress completely disappear, not deformed, so the precision is high.

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Precision Granite Base Can Improve Machine Tool Performances

Requirements are constantly increasing in mechanical engineering in general and in machine tool construction in particular. Achieving maximum precision and performance values without increasing costs are constant challenges to being competitive. The machine tool bed is a decisive factor here. Therefore, more and more machine tool manufacturers are relying on granite. Due to its physical parameters, it offers clear advantages that cannot be achieved with steel or polymer concrete.

Granite is a so-called volcanic deep rock and has a very dense and homogeneous structure with an extremely low coefficient of expansion, low thermal conductivity and high vibration damping.

Below you will discover why the common opinion that granite is mainly only suitable as machine base for high-end coordinate measuring machines is long outdated and why this natural material as a machine tool base is a very advantageous alternative to steel or cast iron even for high-precision machine tools.

We can manufacture granite components for dynamic motion, granite components for linear motors, granite components for ndt, granite components for xray, granite components for cmm, granite components for cnc, granite precision for laser, granite components for aerospace, granite components for precision stages...

High Added Value Without Additional Costs
The increasing use of granite in mechanical engineering is not so much due to the massive increase in the price of steel. Rather, it is because the added value for the machine tool achieved with a machine bed made of granite is possible at very little or no extra cost. This is proven by cost comparisons of well-known machine tool manufacturers in Germany and Europe.

The considerable gain in thermodynamic stability, vibration damping and long-term precision made possible by granite cannot be achieved with a cast iron or steel bed, or only at relatively high cost. For example, thermal errors can account for up to 75% of the total error of a machine, with compensation often attempted for by software – with moderate success. Due to its low thermal conductivity, granite is the better foundation for long-term precision.

With a tolerance of 1 μm, granite easily meets the flatness requirements according to DIN 876 for the degree of accuracy 00. With a value of 6 on the hardness scale 1 to 10, it is extremely hard, and with its specific weight of 2.8g/cm³ it almost reaches the value of aluminium. This also results in additional advantages such as higher feed rates, higher axis accelerations and an extension of the tool life for cutting machine tools. Thus, the change from a cast bed to a granite machine bed moves the machine tool in question into the high-end class in terms of precision and performance – at no extra cost.

Granite’s Improved Ecological Footprint
In contrast to materials such as steel or cast iron, natural stone does not have to be produced with a great deal of energy and using additives. Only relatively small amounts of energy are required for quarrying and surface treatment. This results in a superior ecological footprint, which even at the end of a machine’s life surpasses that of steel as a material. The granite bed can be the basis for a new machine or be used for completely different purposes such as shredding for road construction.

Nor are there any shortages of resources for granite. It is a deep rock formed from magma within the earth’s crust. It has ‘matured’ for millions of years and is available in very large quantities as a natural resource on almost all continents, including all of Europe.

Conclusion: The numerous demonstrable advantages of granite compared to steel or cast iron justify the increasing willingness of mechanical engineers to use this natural material as a foundation for high-precision, high-performance machine tools. Detailed information about granite properties, which are advantageous for machine tools and mechanical engineering, can be found in this further article.

A repeat measurement is a measurement of local flatness areas. The Repeat Measurement specification states that a measurement taken anywhere on the surface of a plate will repeat within the stated tolerance. Controlling local area flatness tighter than overall flatness guarantees a gradual change in surface flatness profile thereby minimizing local errors.

Most manufacturers, including imported brands, adhere to the Federal Specification of overall flatness tolerances but many overlook the repeat measurements. Many of the low value or budget plates available in the market today will not guarantee repeat measurements. A manufacturer who does not guarantee repeat measurements is NOT producing plates that meet the requirements of ASME B89.3.7-2013 or Federal Specification GGG-P-463c, or DIN 876, GB, JJS...

Both are critical to ensure a precision surface for accurate measurements. Flatness specification alone is not sufficient to guarantee measurement accuracy. Take as an example, a 36 X 48 Inspection Grade A surface plate, which meets ONLY the flatness specification of .000300". If the piece being checked bridges several peaks, and the gage being used is in a low spot, the measurement error could be the full tolerance in one area, 000300"! Actually, it can be much higher if the gage is resting on the slope of an incline.

Errors of .000600"-.000800" are possible, depending upon the severity of the slope, and the arm length of the gage being used. If this plate had a Repeat Measurement specification of .000050"F.I.R. then the measurement error would be less than .000050" regardless of where the measurement is taken on the plate. Another problem, which usually arises when an untrained technician attempts to resurface a plate on-site, is the use of Repeat Measurements alone to certify a plate.

The instruments that are used to verify repeatability are NOT designed to check overall flatness. When set to zero on a perfectly curved surface, they will continue to read zero, whether that surface is perfectly flat or perfectly concave or convex 1/2"! They simply verify the uniformity of the surface, not the flatness. Only a plate that meets both the flatness specification AND the repeat measurement specification truly meets the requirements of ASME B89.3.7-2013  or Federal Specification GGG-P-463c.

Ask us about or flatness specification and repeat measurement promise by calling +86 19969991659 or emailing INFO@ZHHIMG.COM

Yes, but they can only be guaranteed for a specific vertical temperature gradient. The effects of thermal expansion on the plate could easily cause a change in accuracy greater than the tolerance if there is a change in the gradient. In some cases, if the tolerance is tight enough, the heat absorbed from overhead lighting can cause enough of a gradient change over several hours.

Granite has a coefficient of thermal expansion of approximately .0000035 inches per inch per 1°F. As an example: A 36" x 48" x 8" surface plate has an accuracy of .000075" (1/2 of Grade AA) at a gradient of 0°F, the top and bottom are the same temperature. If the top of the plate warms up to the point where it is 1°F warmer than the bottom, the accuracy would change to .000275" convex ! Therefore, ordering a plate with a tolerance tighter than Laboratory Grade AA should only be considered if there is adequate climate control.

A surface plate should be supported at 3 points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered. Only 3 points can rest solidly on anything but a precision surface.

The plate should be supported at these points during production, and it should be supported only at these three points while in use. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same 3 points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. All zhhimg steel stands have support beams designed to line up with the proper support points.

If the plate is properly supported, precise leveling is only necessary if your application calls for it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

Why Choose Granite for Machine Bases and Metrology Components?

The answer is 'yes' for almost every application. The advantages of granite include: No rust or corrosion, almost immune to warping, no compensating hump when nicked, longer wear life, smoother action, greater precision, virtually non-magnetic, low co-efficient of thermal expansion, and low maintenance cost.

Granite is a type of igneous rock quarried for its extreme strength, density, durability, and resistance to corrosion. But granite is also very versatile– it’s not just for squares and rectangles! In fact, Starrett Tru-Stone confidently works with granite components engineered in shapes, angles, and curves of all variations on a regular basis—with excellent outcomes.

Through our state of the art processing, cut surfaces can be exceptionally flat. These qualities make granite the ideal material to create custom-size and custom-design machine bases and metrology components. Granite is:

machineable
precisely flat when cut and finished
rust resistant
durable
long lasting
Granite components are also easy to clean. When creating custom designs, be sure to choose granite for its superior benefits.

STANDARDS / HIGH WEAR APPLICATIONS
The granite utilized by ZhongHui for our standard surface plate products has high quartz content, which provides greater resistance to wear and damage. Our Superior Black and Crystal Pink colors have low water absorption rates, minimizing the possibility of your precision gages rusting while setting on the plates. The colors of granite offered by ZhongHui result in less glare, which means less eyestrain for individuals using the plates. We have chosen our granite types while considering thermal expansion in an effort to keep this aspect minimal.

CUSTOM APPLICATIONS
When your application calls for a plate with custom shapes, threaded inserts, slots or other machining, you’ll want to select a material like Black Diabase. This natural material offers superior stiffness, excellent vibration dampening, and improved machinability.

Yes, if they are not too badly worn. Our factory setting and equipment allow the optimum conditions for proper plate calibration and rework if necessary. Generally, if a plate is within .001" of the required tolerance, it can be resurfaced on-site. If a plate is worn to the point where it is more than .001" out of tolerance, or if it is badly pitted or nicked, then it will need to be sent to the factory for grinding prior to relapping.

Great care should be exercised in selecting an on-site calibration and resurfacing technician. We urge you to use caution in selecting your calibration service. Ask for accreditation and verify the equipment that the technician will use has a National Inspection Institution traceable calibration. It takes many years to learn how to properly lap precision granite.

ZhongHui provides quick turn-around on calibrations performed in our factory. Send your plates in for calibration if possible. Your quality and reputation depend on the accuracy of your measurement instruments including surface plates!

Our black surface plates have a significantly higher density and are up to three times as stiff. Therefore, a plate made of the black does not need to be as thick as a granite plate of the same size to have equal or greater resistance to deflection. Reduced thickness means less weight and lower shipping costs.

Beware of others who use lower quality black granite in the same thickness. As stated above, properties of granite, like wood or metal, vary by material and color, and is not an accurate predictor of stiffness, hardness, or wear resistance. In fact, many types of black granite and diabase are very soft and not suitable for surface plate applications.

No. The specialized equipment and training necessary to rework these items requires that they be returned to the factory for calibration and rework.

Yes. Ceramic and granite have similar characteristics, and the methods used to calibrate and lap granite can be used with ceramic items as well. Ceramics are more difficult to lap than granite resulting in a higher cost.

Yes, provided that the inserts are recessed below the surface. If steel inserts are flush with, or above the surface plane, they must be spot-faced down before the plate can be lapped. If required, we can provide that service.

Yes. Steel inserts with the desired thread (English or metric) can be epoxy bonded into the plate at the desired locations. ZhongHui uses CNC machines to provide the tightest insert locations within +/- 0.005”. For less critical inserts, our locational tolerance for threaded inserts is ±.060". Other options include steel T-Bars and dovetail slots machined directly into the granite.

Inserts that are properly bonded using high strength epoxy and good workmanship will withstand a great deal of torsional and shear force. In a recent test, using 3/8"-16 threaded inserts, an independent testing laboratory measured the force required to pull an epoxy-bonded insert from a surface plate. Ten plates were tested. Out of these ten, in nine cases, the granite fractured first. The average load at the point of failure was 10,020 lbs. for gray granite and 12,310 lbs. for black. In the single case where an insert pulled free of the plate, the load at the point of failure was 12,990 lbs.! If a work piece forms a bridge across the insert and extreme torque is applied, it is possible to generate enough force to fracture the granite. Partially for this reason, ZhongHui gives guidelines for the maximum safe torque that can be applied the epoxy bonded inserts: https://www.zhhimg.com/standard-thread-inserts-product/

Yes, but only at our factory. At our plant, we can restore almost any plate to 'like-new' condition, usually for less than half the cost of replacing it. Damaged edges can be cosmetically patched, deep grooves, nicks, and pits can be ground out, and the attached supports can be replaced. In addition, we can modify your plate to increase its versatility by adding solid or threaded steel inserts and cutting slots or clamping lips, per your specifications.

Why Choose Granite?
Granite is a type of igneous rock formed in the Earth millions of years ago. The composition of igneous rock contained many minerals such as quartz that is extremely hard and wear-resistant. In addition to hardness and wear resistance granite has approximately half the coefficient of expansion as cast iron. As its volumetric weight is approximately one third that of cast iron, granite is easier to manoeuvre.

For machine bases and metrology components, black granite is the colour most used. Black granite has a higher percentage of quartz than other colours and is, therefore, the hardest wearing.

Granite is cost-effective, and cut surfaces can be exceptionally flat. Not only can it be hand lapped to achieve extremes of accuracy, but re-conditioning can be performed without moving the plate or table off-site. It is entirely a hand lapping operation and generally costs much less than re-conditioning a cast iron alternative.

These qualities make granite the ideal material to create custom-size and custom-design machine bases and metrology components such as the granite surface plate.

ZhongHui produces bespoke granite products that are created to support specific measurement requirements. These bespoke items vary from straight edges to tri squares. Due to the versatile nature of granite, the components can be produced to any size required; they are hard wearing and long-lasting.

Advantages of Granite Surface Plates
The importance of measuring on an even surface was established by British inventor Henry Maudsley in the 1800s. As a machine tool innovator, he determined that consistent production of parts required a solid surface for reliable measurements.

The industrial revolution created a demand for measuring surfaces, so engineering company Crown Windley created manufacturing standards. The standards for surface plates were first set by Crown in 1904 using metal. As the demand and cost for metal increased, alternative materials for the measuring surface were investigated.

In America, monument creator Wallace Herman established that black granite was an excellent surface plate material alternative to metal. As granite is non-magnetic and doesn’t rust, it soon became the preferred measuring surface.

A granite surface plate is an essential investment for laboratories and test facilities. A granite surface plate of 600 x 600 mm can be mounted on a support stand. The stands provide a working height of 34” (0.86m) with five adjustable points for levelling.

For reliable and consistent measurement results, a granite surface plate is crucial. As the surface is a smooth and stable plane, it enables instruments to be carefully manipulated.

The main advantages of granite surface plates are:

• Non-reflective
• Resistant to chemicals and corrosion
• Low coefficient of expansion compared with cart iron so less affected by temperature change
• Naturally rigid and hard-wearing
• The plane of the surface is unaffected if scratched
• Will not rust
• Non-magnetic
• Easy to clean and maintain
• Calibration and resurfacing can be done onsite
• Suitable for drilling for threaded support inserts
• High vibration damping

For many shops, inspection rooms and laboratories, precision granite surface plates are relied on as the basis for accurate measurement. Because every linear measurement depends on an accurate reference surface from which final dimensions are taken, surface plates provide the best reference plane for work inspection and layout prior to machining. They also are ideal bases for making height measurements and gaging surfaces. Further, a high degree of flatness, stability, overall quality and workmanship make them a good choice for mounting sophisticated mechanical, electronic and optical gaging systems. For any of these measurement processes, it is imperative to keep surface plates calibrated.

Repeat Measurements and Flatness
Both flatness and repeat measurements are critical to ensure a precision surface. Flatness can be considered as all points on the surface being contained within two parallel planes, the base plane and the roof plane. The measurement of distance between the planes is the overall flatness of the surface. This flatness measurement commonly carries a tolerance and may include a grade designation.

The flatness tolerances for three standard grades are defined in the federal specification as determined by the following formula:
Laboratory Grade AA = (40 + diagonal² / 25) x 0.000001 inch (unilateral)
Inspection Grade A = Laboratory Grade AA x 2
Tool Room Grade B = Laboratory Grade AA x 4

In addition to flatness, repeatability must be ensured. A repeat measurement is a measurement of local flatness areas. It is a measurement taken anywhere on the surface of a plate that will repeat within the stated tolerance. Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.

To ensure a surface plate meets both the flatness and repeat measurement specifications, manufacturers of granite surface plates should use Federal Specification GGG-P-463c as a basis for their specifications. This standard addresses repeat measurement accuracy, material properties of surface plate granites, surface finish, support point location, stiffness, acceptable methods of inspection and installation of threaded inserts.

Before a surface plate has worn beyond specification for overall flatness, it will show worn or wavy posts. Monthly inspection for repeat measurement errors using a repeat reading gage will identify wear spots. A repeat reading gage is a high-precision instrument that detects local error and can be displayed on a high magnification electronic amplifier.

Checking Plate Accuracy
By following a few simple guidelines, an investment in a granite surface plate should last for many years. Depending on plate usage, shop environment and required accuracy, frequency of checking the surface plate accuracy varies. A general rule of thumb is for a new plate to receive a full recalibration within one year of purchase. If the plate is used frequently, it is advisable to shorten this interval to six months.

Before a surface plate has worn beyond specification for overall flatness, it will show worn or wavy posts. Monthly inspection for repeat measurement errors using a repeat reading gage will identify wear spots. A repeat reading gage is a high-precision instrument that detects local error and can be displayed on a high magnification electronic amplifier.

An effective inspection program should include regular checks with an autocollimator, providing actual calibration of overall flatness traceable to National Institute of Standards and Technology (NIST). Comprehensive calibration by the manufacturer or an independent company is necessary from time to time.

Variations Between Calibrations
In some cases, there are variations between surface plate calibrations. Sometimes factors such as surface change resulting from wear, incorrect use of inspection equipment or use of noncalibrated equipment can account for these variations. The two most common factors, however, are temperature and support.

One of the most important variables is temperature. For instance, the surface might have been washed with a hot or cold solution prior to calibration and not allowed sufficient time to normalize. Other causes of temperature change include drafts of cold or hot air, direct sunlight, overhead lighting or other sources of radiant heat on the surface of the plate.

There also can be variations in the vertical temperature gradient between winter and summer. In some cases, the plate is not allowed sufficient time to normalize after shipment. It is a good idea to record the vertical gradient temperature at the time the calibration is performed.

Another common cause for calibration variation is a plate that is improperly supported. A surface plate should be supported at three points, ideally located 20% of the length in from the ends of the plate. Two supports should be located 20% of the width in from the long sides, and the remaining support should be centered.

Only three points can rest solidly on anything but a precision surface. Attempting to support the plate at more than three points will cause the plate to receive its support from various combinations of three points, which will not be the same three points on which it was supported during production. This will introduce errors as the plate deflects to conform to the new support arrangement. Consider using steel stands with support beams designed to line up with the proper support points. Stands for this purpose are generally available from the surface plate manufacturer.

If the plate is properly supported, precise leveling is only necessary if an application specifies it. Leveling is not necessary to maintain the accuracy of a properly supported plate.

It is important to keep the plate clean. Airborne abrasive dust is usually the greatest source of wear and tear on a plate, as it tends to embed in workpieces and the contact surfaces of gages. Cover plates to protect them from dust and damage. Wear life can be extended by covering the plate when not in use.

Extend Plate Life
Following a few guidelines will reduce wear on a granite surface plate and ultimately, extend its life.

First, it is important to keep the plate clean. Airborne abrasive dust is usually the greatest source of wear and tear on a plate, as it tends to embed in workpieces and the contact surfaces of gages.

It also is important to cover plates to protect it from dust and damage. Wear life can be extended by covering the plate when not in use.

Rotate the plate periodically so that a single area does not receive excessive use. Also, it is recommended to replace steel contact pads on gaging with carbide pads.

Avoid setting food or soft drinks on the plate. Many soft drinks contain either carbonic or phosphoric acid, which can dissolve the softer minerals and leave small pits in the surface.

Where to Relap
When a granite surface plate needs re-surfacing, consider whether to have this service performed on-site or at the calibration facility. It is always preferable to have the plate relapped at the factory or a dedicated facility. If, however, the plate is not too badly worn, generally within 0.001 inch of the required tolerance, it can be resurfaced on-site. If a plate is worn to the point where it is more than 0.001 inch out of tolerance, or if it is badly pitted or nicked, then it should be sent to the factory for grinding prior to relapping.

A calibration facility has the equipment and factory setting providing the optimum conditions for proper plate calibration and rework if necessary.

Great care should be exercised in selecting an on-site calibration and resurfacing technician. Ask for accreditation and verify the equipment that the technician will use has a NIST-traceable calibration. Experience also is an important factor, as it takes many years to learn how to correctly lap precision granite.

Critical measurements start with a precision granite surface plate as a baseline. By ensuring a reliable reference by using a properly calibrated surface plate, manufacturers have one of the essential tools for reliable measurements and better quality parts.

Checklist for Calibration Variations

1. The surface was washed with a hot or cold solution prior to calibration and was not allowed sufficient time to normalize.
2. The plate is improperly supported.
3. Temperature change.
4. Drafts.
5. Direct sunlight or other radiant heat on the surface of the plate. Be sure that overhead lighting is not heating the surface.
6. Variations in the vertical temperature gradient between winter and summer. If at all possible, know the vertical gradient temperature at the time the calibration is performed.
7. Plate not allowed sufficient time to normalize after shipment.
8. Improper use of inspection equipment or use of noncalibrated equipment.
9. Surface change resulting from wear.

Tech Tips
Because every linear measurement depends on an accurate reference surface from which final dimensions are taken, surface plates provide the best reference plane for work inspection and layout prior to machining.

Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.