Thread: How to check if diamond plate is flat?

A straight edge would be fine for that level of accuracy.

Same way you would check a bit of wood. Square or steel ruler should be good enough. Another check is does it wobble on a flat surface. If the metal base is one solid piece I dont think the sun would have distorted it.
Regards
John

A bit over the top but you could try two 150 mm or similar steel rulers and use them as winging sticks

Your diamond plate is steel backed. As steel and aluminium are good conductors of heat and it wouldn't change shape when you leave it in the sun. Put it on a plate of glass to verify it if you want. But I wouldn't be too worried.

Originally Posted by justonething

Your diamond plate is steel backed. As steel and aluminium are good conductors of heat and it wouldn't change shape when you leave it in the sun. Put it on a plate of glass to verify it if you want. But I wouldn't be too worried.

Steel does move with heat,
Search for rail line tracks buckled
It doesn’t take to much heat to move metal!

But with respect to the lapping plate, I think they will be fine,

Cheers Matt.

Originally Posted by justonething

Put it on a plate of glass to verify it if you want.

Put a few drops of coloured liquid on the lapping plate and then place the glass plate on top. The colour should almost disappear if the plate is flat but if the plate is warped there will be differences in the colour strength where the plate is bent.

Originally Posted by Simplicity

Steel does move with heat,
Search for rail line tracks buckled
It doesn’t take to much heat to move metal!

But with respect to the lapping plate, I think they will be fine,

Cheers Matt.

You almost got me. But..... in defence of myself. I thought that steel tracks buckle because they weren't allowed to expand to the extent that the materials need to... It's like embedding the lapping plate in concrete and exposing it to the sun...

Metals have a "coefficient of expansion." In some data base, I'm sure.

My first thought was Bohdan's method (#7) above.
Modern float glass is nearly optically flat as you can see from undistorted reflections.

Many thanks to for all the posts above, some really good stuff in that lot.

This all started when I put my Toledo 300mm ruler as a straight edge on the back of the aluminium plate, and held it up to the light. I could see a sliver of light between the plate and the ruler when checked lengthwise and diagonally. It would appear the ends of the back of the plate were raised slightly. Across the width of the plate it was quite flat.

As recommended above, I tested to see if it was rocking on a granite bench top, but no movement on the corners whatsoever on either face. So no warping detected

I then used my smallest feeler gauge strip (1.5 thou inch) and could not slide that between the ruler and the back of the diamond plate, even though the sliver of light was there if I held it up to the light. Not sure if the ruler is a good straight edge.

Then placed the back of the plate on the granite, and could not slide the feeler strip under it anywhere around the perimeter of the plate. Similar results when I turned the plate over and put the diamond surface on the granite.

Sat the feeler gauge strip on the granite, and placed the plate on top of it. The strip could not slide out. Tried this in several places under the plate, but the plate came with the strip when pulled.

So, I think that if the diamond plate is flat to 0.0015", it should be suitable for flattening my waterstones

Your stone should actually end up flatter than the diamond plate as it is moved over the surface when flattening. I usually put my diamond plate out in the sun to dry off. I use window cleaner as sharpening fluid then rinse off with water. I dont have water stones but have never worried how flat the plate is. My old oil stone does have some dip in it but I still get sharp irons and chisels.
Regards
John