花崗岩は、極めて高い強度、密度、耐久性、耐腐食性を持つ火成岩の一種です。しかし、花崗岩は非常に汎用性が高く、正方形や長方形の形状だけに使われるものではありません。実際、当社では、あらゆる形状、角度、曲線を持つ花崗岩部品を日常的に取り扱い、優れた成果を上げています。
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:
■ 機械加工可能
■ 切断および仕上げ時に正確に平坦になります
■錆びにくい
■耐久性
■長持ちする
花崗岩製の部品は、お手入れも簡単です。特注デザインを作成する際は、その優れた利点を考慮して、ぜひ花崗岩をお選びください。

規格／高摩耗用途
ZHHIMGが標準表面プレート製品に使用している花崗岩は、石英含有量が高く、耐摩耗性と耐損傷性に優れています。スーペリアブラックカラーは吸水率が低く、プレート上に置いた精密ゲージの錆びを防ぎます。ZHHIMGの花崗岩は、光の反射を抑えることで、プレートを使用する際の目の疲れを軽減します。また、熱膨張を最小限に抑えるため、花崗岩の種類は熱膨張を考慮して選定しています。

CUSTOM APPLICATIONS
用途に応じて、カスタム形状、ねじ込みインサート、スロット、その他の加工を施したプレートが必要な場合は、ブラック・ジナン・ブラックのような素材を選択することをお勧めします。この天然素材は、優れた剛性、優れた振動減衰性、そして向上した加工性を備えています。

石の色だけでは、その物理的特性を示すものではないことに注意することが重要です。一般的に、花崗岩の色は鉱物の有無に直接関係しており、これは表面プレート材料として優れた特性とは無関係である可能性があります。表面プレートに最適なピンク、グレー、黒の花崗岩もあれば、精密用途には全く不向きな黒、グレー、ピンクの花崗岩もあります。表面プレート材料としての花崗岩の重要な特性は、色とは全く関係がなく、以下のとおりです。
■剛性（荷重下でのたわみ - 弾性係数で表される）
■硬度
■密度
■耐摩耗性
■安定性
■ 多孔性

私たちは数多くの花崗岩素材をテストし、比較検討してきました。その結果、済南産黒花崗岩がこれまでで最高の素材であるという結論に至りました。インド産黒花崗岩と南アフリカ産花崗岩は済南産黒花崗岩に似ていますが、物理的特性は済南産黒花崗岩に劣ります。ZHHIMGは今後も世界中の花崗岩素材を探し続け、その物理的特性を比較検討していきます。

お客様のプロジェクトに最適な花崗岩について詳しくご相談されたい場合は、当社までご連絡ください。info@zhhimg.com.

メーカーによって使用する規格は異なります。世界には多くの規格が存在します。
仕様の基礎として、DIN規格、ASME B89.3.7-2013、連邦規格GGG-P-463c（花崗岩表面板）などを採用している。

お客様のご要望に応じて、花崗岩製の精密検査板を製造いたします。より詳しい規格情報や詳細については、お気軽にお問い合わせください。

平面度とは、表面上のすべての点が、底面と上面という2つの平行な平面内に収まっている状態を指します。これらの平面間の距離を測定することで、表面全体の平面度が算出されます。この平面度測定値には通常、許容誤差が設けられ、等級が示される場合もあります。

例えば、3つの標準等級の平面度許容差は、連邦規格において以下の式で定義されています。
■ 実験室グレード AA = (40 + 対角線の二乗/25) x 0.000001インチ (片側)
■ 検査等級A = 実験室等級AA × 2
■ 工具室グレードB = 実験室グレードAA × 4。

標準サイズの表面板については、この仕様の要件を超える平面度公差を保証します。平面度に加えて、ASME B89.3.7-2013および連邦規格GGG-P-463cでは、繰り返し測定精度、表面板花崗岩の材料特性、表面仕上げ、支持点位置、剛性、許容される検査方法、ねじ込みインサートの取り付けなどについても規定しています。

ZHHIMG社製の花崗岩製定盤および花崗岩製検査板は、本仕様書に定められたすべての要件を満たしているか、またはそれを上回っています。現時点では、花崗岩製アングルプレート、平行定規、またはマスタースクエアに関する明確な仕様は存在しません。

他の規格の式は以下に記載されています。ダウンロード.

まず、プレートを清潔に保つことが重要です。空気中の研磨粉塵は、ワークピースやゲージの接触面に付着しやすく、プレートの摩耗の最大の原因となります。次に、プレートをカバーして粉塵や損傷から保護してください。プレートを使用しないときはカバーをかけ、定期的に回転させて特定の箇所に過度の負荷がかからないようにし、ゲージの鋼製接触パッドを超硬パッドに交換することで、プレートの寿命を延ばすことができます。また、プレートの上に食べ物や清涼飲料水を置かないようにしてください。多くの清涼飲料水には炭酸またはリン酸が含まれており、これらは軟質の鉱物を溶かして表面に小さな穴を残す可能性があることに注意してください。

これは、お皿の使い方によって異なります。可能であれば、一日の始め（または勤務シフトの開始時）と終わりに、お皿を洗浄することをお勧めします。お皿が汚れた場合、特に油っぽい液体や粘り気のある液体で汚れた場合は、すぐに洗浄してください。

プレートは、液体またはZHHIMG無水表面プレートクリーナーで定期的に洗浄してください。洗浄液の選択は重要です。揮発性溶剤（アセトン、ラッカーシンナー、アルコールなど）を使用すると、蒸発によって表面が冷え、変形する可能性があります。この場合、使用前にプレートを平らにしておく必要があります。そうしないと、測定誤差が発生します。

プレートが正常化するまでの時間は、プレートのサイズと冷却量によって異なります。小型のプレートであれば1時間で十分でしょう。大型のプレートの場合は2時間かかる場合があります。水性洗浄剤を使用する場合は、蒸発冷却も伴います。

プレートは水分を保持するため、表面に接触する金属部品が錆びる可能性があります。また、一部の洗浄剤は乾燥後に粘着性の残留物を残すため、空気中の埃を引き寄せ、摩耗を軽減するどころか、かえって摩耗を増加させてしまう可能性があります。

これはプレートの使用状況と環境によって異なります。新しいプレートまたは精密花崗岩製アクセサリーは、購入後1年以内に完全な再校正を受けることをお勧めします。花崗岩製定盤を頻繁に使用する場合は、この間隔を6か月に短縮することをお勧めします。電子水準器または同様の機器を使用して、繰り返し測定誤差を毎月検査することで、摩耗箇所を特定でき、作業はわずか数分で完了します。最初の再校正の結果が確定したら、社内品質システムで許可または要求される範囲で、校正間隔を延長または短縮することができます。

弊社では、お客様の花崗岩製定盤の点検および校正に関するサービスを提供しております。

校正結果にばらつきが生じる原因としては、いくつかの可能性が考えられます。

• 校正前に表面を温水または冷水で洗浄したが、正規化するのに十分な時間が与えられなかった。
• プレートの支持が不適切です
• 温度変化
• 草稿
• プレート表面に直射日光やその他の放射熱が当たらないようにしてください。また、天井照明が表面を加熱していないことを確認してください。
• 冬と夏の間の垂直温度勾配の変化（可能であれば、校正実施時の垂直温度勾配を把握してください。）
• 出荷後、プレートが正常化するのに十分な時間が与えられていない
• 検査機器の不適切な使用、または校正されていない機器の使用
• 摩耗による表面変化

精密花崗岩には何種類の穴がありますか？

精密花崗岩部品の溝

多くの工場、検査室、研究所において、精密な花崗岩製定盤は正確な測定の基準として欠かせない存在です。あらゆる直線測定は、最終寸法を算出するための正確な基準面を必要とするため、定盤は加工前の作業検査やレイアウトにおいて最適な基準面となります。また、高さ測定やゲージ面の測定にも理想的なベースとなります。さらに、高い平面度、安定性、総合的な品質、そして優れた仕上がりにより、高度な機械式、電子式、光学式ゲージシステムの取り付けにも最適です。これらの測定プロセスにおいては、定盤の校正を常に最新の状態に保つことが不可欠です。

Repeat Measurements and Flatness

平面度と繰り返し測定は、精密な表面を実現するために不可欠です。平面度とは、表面上のすべての点が、ベース面とルーフ面という2つの平行な平面内に収まっている状態を指します。これらの平面間の距離を測定することで、表面全体の平面度を算出します。この平面度測定値には通常、許容誤差が設けられ、等級が示される場合もあります。

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

DIN規格、GB規格、ASME規格、JJS規格…国によって異なる規格…

規格に関する詳細情報。

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.

定盤が平面度と繰り返し測定の両方の仕様を満たすことを保証するため、花崗岩定盤の製造業者は、仕様の基準として連邦規格GGG-P-463cを使用する必要があります。この規格は、繰り返し測定精度、定盤花崗岩の材料特性、表面仕上げ、支持点の位置、剛性、許容される検査方法、およびねじ込みインサートの取り付け方法について規定しています。

Checking Plate Accuracy

いくつかの簡単なガイドラインに従えば、花崗岩製定盤への投資は長年にわたって有効に活用できるはずです。定盤の使用頻度、作業環境、および要求される精度によって、定盤の精度チェックの頻度は異なります。一般的な目安としては、新品の定盤は購入後1年以内に完全な再校正を受けることが推奨されます。定盤を頻繁に使用する場合は、この間隔を6ヶ月に短縮することをお勧めします。

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

場合によっては、定盤校正値にばらつきが生じることがあります。摩耗による表面変化、検査機器の不適切な使用、校正されていない機器の使用などが、こうしたばらつきの原因となることがあります。しかし、最も一般的な要因は温度と支持条件です。

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

いくつかのガイドラインに従うことで、花崗岩製定盤の摩耗を軽減し、最終的には寿命を延ばすことができます。

まず、プレートを清潔に保つことが重要です。空気中の研磨粉塵は、ワークピースやゲージの接触面に付着しやすいため、プレートの摩耗の最大の原因となります。

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.

プレートを定期的に回転させ、特定の箇所に過度の負荷がかからないようにしてください。また、ゲージングに使用するスチール製の接触パッドを超硬パッドに交換することをお勧めします。

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

花崗岩製定盤の表面研磨が必要になった場合、現場で研磨するか、校正施設で行うかを検討してください。工場または専用施設で研磨するのが常に望ましいです。ただし、定盤の摩耗がそれほどひどくなく、一般的に許容誤差から0.001インチ以内であれば、現場で研磨することも可能です。定盤の摩耗が許容誤差から0.001インチ以上ずれている場合、または表面にひどい凹みや傷がある場合は、研磨前に工場に送って研削する必要があります。

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

現場での校正および表面処理技術者の選定には細心の注意を払う必要があります。認定資格の有無を確認し、技術者が使用する機器の校正がトレーサブルであることを確認してください。また、経験も重要な要素です。精密な花崗岩の研磨を正しく行うには、長年の経験を積む必要があるからです。

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. 校正前に表面を温水または冷水で洗浄したが、正常化するのに十分な時間が与えられなかった。

2. プレートの支持が不適切です。

3．温度変化。

4. 草稿。

5. プレートの表面に直射日光やその他の放射熱が当たらないようにしてください。天井照明が表面を加熱していないことを確認してください。

6．冬と夏の間の垂直温度勾配の変化。可能であれば、校正実施時の垂直温度勾配を把握してください。

7. 出荷後、プレートが正常化するのに十分な時間が与えられなかった。

8. 検査機器の不適切な使用、または校正されていない機器の使用。

9. 摩耗による表面変化。

Tech Tips

• すべての直線測定は、最終寸法が測定される正確な基準面に依存するため、定盤は機械加工前の作業検査とレイアウトに最適な基準面を提供する。
• Controlling local area flatness to a tighter tolerance than overall flatness guarantees a gradual change in surface flatness profile, thereby minimizing local errors.
• 効果的な検査プログラムには、オートコリメータを用いた定期的な検査を含めるべきであり、国家検査機関にトレーサブルな全体的な平面度の実際の校正を行う必要がある。

花崗岩を構成する鉱物粒子のうち、90%以上は長石と石英で、その中でも長石が最も多い。長石は白、灰色、肉色を呈することが多く、石英は主に無色または灰白色で、これらが花崗岩の基本的な色を構成している。長石と石英は硬い鉱物であり、鋼のナイフでも動かすのは難しい。花崗岩中の黒色の斑点は主に黒雲母だが、他にもいくつかの鉱物が含まれている。黒雲母は比較的柔らかいが、応力に対する抵抗力は弱くなく、同時に花崗岩中の含有量は少なく、10%未満であることが多い。これが花崗岩が特に強い物質条件である。

花崗岩が強いもう一つの理由は、その鉱物粒子が互いにしっかりと結合し、埋め込まれていることです。孔隙は岩石全体の体積の1%未満であることが多く、そのため花崗岩は強い圧力に耐えることができ、水分が浸透しにくいのです。

花崗岩部品は、錆びない石でできており、耐酸性、耐アルカリ性、耐摩耗性に優れ、長寿命で、特別なメンテナンスは不要です。花崗岩精密部品は、主に機械産業の工具に使用されます。そのため、花崗岩精密部品または花崗岩部品と呼ばれます。花崗岩精密部品の特性は、基本的に花崗岩プラットフォームの特性と同じです。花崗岩精密部品の工具と測定の紹介: 精密加工とマイクロ加工技術は、機械製造産業の重要な発展方向であり、ハイテクレベルを測定するための重要な指標となっています。最先端技術と防衛産業の発展は、精密加工とマイクロ加工技術と切り離すことはできません。花崗岩部品は、測定中にスムーズにスライドし、停滞しません。作業面の測定では、一般的な傷は測定精度に影響しません。花崗岩部品は、需要側の要件に従って設計および製造する必要があります。

応用分野：

周知のとおり、ますます多くの機械や設備が精密な花崗岩部品を採用するようになっています。

花崗岩製の部品は、動的動作、リニアモーター、CMM、CNC、レーザー加工機などに使用されます。

詳しい情報については、お気軽にお問い合わせください。

花崗岩製の測定装置および機械部品は、高品質の済南黒花崗岩で作られています。高精度、長寿命、優れた安定性、耐腐食性を備えているため、現代産業の製品検査や、機械・航空宇宙、科学研究などの分野でますます広く使用されています。

利点

鋳鉄の2倍の硬度；

寸法のわずかな変化は温度変化によるものです。

絞る必要がないので、作業が中断されることはありません。

微細な結晶構造とわずかな粘着性により、バリや突起がなく、長期間にわたって高い平面度を維持し、他の部品や器具に損傷を与えることもありません。

磁性材料との使用において、トラブルのない動作を実現します。

長寿命で錆びないため、メンテナンスコストが低く抑えられます。

精密花崗岩製定盤は、高精度を実現するために高水準の平面度まで精密研磨されており、高度な機械式、電子式、光学式計測システムを取り付けるためのベースとして使用されます。

花崗岩製定盤のユニークな特徴の一部：

硬度の均一性。

負荷条件下でも正確。

振動吸収材

お手入れが簡単。

巻き付きに強い。

低多孔性；

非研磨性。

非磁性

花崗岩製定盤の利点

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.