Taunton, MA · Used Gages 508-343-1219
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Used granite surface plate: what you can check yourself

A used granite plate can be a good buy or a heavy paperweight. Most of the answer shows up before anyone puts an indicator on it: the size, the tag, the edges, the working area, and what it sits on. This guide covers the checks a buyer or seller can do with a phone camera and a few minutes. It doesn't replace a flatness check by a qualified lab, and it won't tell you a plate is in spec.

Ask about a plate: 508-343-1219 Open the full gage checklist

1. Size and thickness

  • Measure length, width and thickness with a tape and put the tape in the photo.
  • Note which face is the working face (usually the top, with or without ledges).
  • Thickness and size drive weight, and weight drives moving cost. Ask how it'll be lifted and loaded before you agree on anything. Moving heavy shop equipment? See the rigging checklist.

2. Grade stamp or tag

  • Look for a maker's label, a grade stamp, a serial number, or an old inspection sticker on the edge or side.
  • Photograph it close up. If there's a date on an old sticker, write it down. It tells you when someone last looked, not what the plate reads today.
  • No tag? That doesn't make it a bad plate. It means the grade is unknown, so price and plan as unknown.

3. Chips, cracks and edge damage

  • Chips on the outside edges and corners are common on old plates. They're mostly cosmetic if they stay off the working area, but ask for a close-up of each one.
  • Chips or gouges inside the working area matter more. Anything that sits on that spot won't sit flat, so you lose that part of the plate.
  • Look hard for cracks, especially ones that run across the top or down a side. A crack is a reason to stop and ask questions, not a thing to shrug off.
  • Check the bottom and the support points too, if you can see them. Damage where it rests on the stand can be worse than a chipped corner.

4. Stains and cleanliness

  • Dark spots, rust marks and oil stains are common. A stain by itself doesn't tell you the plate is worn, but it does tell you how it was treated.
  • Ask the seller to wipe the top clean before taking photos. Dirt hides chips and wear.
  • Look for a shiny or worn-looking patch where people did most of their work. That's the spot most likely to be worn low, so point your repeat-reading check there.
  • Ask what was used to clean it. Plain surface plate cleaner or mild soap and water is what you want to hear.

5. The stand

  • A good plate on a bad stand is a problem. Check the stand for rust, bent legs, cracked welds and missing leveling feet.
  • Ask whether the stand was made for this plate. A plate that hangs past its supports or sits on random blocks may not have been supported the way the maker intended.
  • Photograph the stand from the side and the corners so you can see how the plate sits on it.
  • No stand? Plan for one, and plan for how the plate gets onto it.

6. A simple repeat-reading check (a screen, not a flatness check)

This is a quick screen to spot an obvious problem. It is not a flatness check and it does not tell you the plate's grade or whether it's in spec.

  • Clean the top. Set a dial or test indicator on a small stand with a flat, clean base.
  • Touch the indicator to the plate, set it to zero, then slowly slide the stand across the plate and watch the needle.
  • Come back to the starting spot and see if it returns to zero. If it does, try the worn-looking patch and the corners.
  • A needle that stays calm is a good sign. A needle that jumps around or won't come back to zero is a reason to ask more questions or bring in a qualified lab.
  • Sellers: a short video of this, with the plate clean, helps a buyer more than a long description.
Re-lapping is a question to ask, not a number to quote. If a plate is worn, the usual fix is re-lapping by a surface plate service. Before you buy a worn plate, ask whether re-lapping plus moving it would cost more than a new plate of the same size. Get a quote from a local service for your exact plate before you count on it. We don't quote lapping costs here.

The six photos to ask for (or send)

  1. The whole plate on its stand, from a corner.
  2. The top, wiped clean, with a tape across it.
  3. A side view with a tape showing thickness.
  4. The label, grade stamp or tag, close up.
  5. Every chip, crack or stain, close up.
  6. The stand: legs, feet and where the plate rests.

Buy, negotiate or walk

Buy

Clean working area, edges chipped only outside it, a readable tag, a solid stand, and a calm repeat-reading screen.

Negotiate

No tag, heavy stains, a worn-looking patch, a rough stand, or a hard move. Each one is a fair reason to talk about price or plan for re-lapping.

Walk

Cracks, chips in the working area, a seller who won't send close-ups, or a screen where the needle won't settle.

Used surface plate questions

Is a used granite surface plate worth buying?

It can be, if the working area is clean and undamaged, the stand is solid, and the move is manageable. If it needs re-lapping, ask what that costs before you decide.

How can I tell if a used surface plate is still flat?

You can't prove it from photos or a quick indicator sweep. The repeat-reading screen on this page can catch an obvious problem, but only a qualified lab can tell you the plate is in spec.

Do chips on the edge ruin a surface plate?

Usually not, if they stay off the working area. Chips inside the working area, or cracks anywhere, are a bigger deal.

This guide is about what you can see and check yourself. It is not a calibration, a flatness report or a grade rating. We don't rate plates.

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