How straight is the side of a diamond plate?

[MikeAllen]

I have atoma 400 that I’m using for lapping my stone. I saw a video of someone using a straight edge and flashlight to see if stone is flat and need lapping.

I don’t have a straight edge but I turned my atoma 400 on its side and used the flashlight of my cell phone. Light did peel through at the center. I spend a minute of so lapping, and retested and did not see light.


How straight do you think the stone plate is. Am I wasting my time with this?

 

[life2short1971]

I'd say its pretty flat. If you draw a grid on the top of your stone with a pencil and it is lapped away quickly and completely your stone is now flat.

 

[Wid]

I’ve been doing this for years with a DMT. It’s been flat enough for me.

 

[MikeAllen]

Awesome thanks guys

 

[JPO]

I also use the side of my dmt plate to check if my stones are flat. I am not sure how accurate it is, but it is definitely more accurate then just using pencil grids.
I don't have any razors that are straight enough for this to matter.

 

[Tanuki]

My opinion, you are wasting your time using the Atoma's side as a straight edge. They did not make it with that level of flatness in mind, plus you (or at least I) probably don't treat it as carefully as a machinist's straight edge or square should be treated.

I use the base of an inexpensive machinist's square to roughly check levels.

If your Atoma is quickly erasing your grid, your hone is flat enough. That is the surface of the Atoma that was machined flat.

My reference for flat moved from my Atoma 400 to a DMT Dia-flat 95. I can't tell the difference in my edges, but the 10x4 size is easy to use without running the hone off the late edges. Also, the heft of the steel vs aluminum alloy helps me keep hone and plate in solid contact.

 

[JPO]

I just checked the sides of both my atoma and dmt plates against a sertified straight edge. No visible tolerance difference was seen.

I think how you use the lapping plate play a bigger role in the results you get. There is a reason why the lapping plates wear more in the middle. They are not removing the same amount of material evenly if you just go back and forth.

 

[Gamma]

A pencil grid can come off completely long before a stone is flat. That doesn't mean it will come off early, just means that it can happen. Softer stones, softer pencils more swarf, etc - all can factor in here.
I"ll use a grid to start off, get an idea, but for finished results I use certified straight edge to confirm flatness.

I have a bunch of Atoma plates in rotation now, my oldest is a 400x with a 140x pad on the back. One edge is dead flat, the other edge is not flat. I have a newer 140x plate where both edges are not flat but both are flatter than the 'out' edge on the older plate.

 

[Empire straights]

I have a couple cheap Chinese plates and my straight edge says their edges are straight.

 

[Tanuki]

I just checked the sides of both my atoma and dmt plates against a sertified straight edge. No visible tolerance difference was seen.

I think how you use the lapping plate play a bigger role in the results you get. There is a reason why the lapping plates wear more in the middle. They are not removing the same amount of material evenly if you just go back and forth.

A pencil grid can come off completely long before a stone is flat. That doesn't mean it will come off early, just means that it can happen. Softer stones, softer pencils more swarf, etc - all can factor in here.
I"ll use a grid to start off, get an idea, but for finished results I use certified straight edge to confirm flatness.

I have a bunch of Atoma plates in rotation now, my oldest is a 400x with a 140x pad on the back. One edge is dead flat, the other edge is not flat. I have a newer 140x plate where both edges are not flat but both are flatter than the 'out' edge on the older plate.

I have a couple cheap Chinese plates and my straight edge says their edges are straight.

I was about to grab my high lumen flashlight and go check my various Atoma, DMT, Eze Lap and Ultra Sharp plates against my ~1μ granite reference plate.

Instead I'm going with YMMV on diamond plate edge flatness. I'm getting an urge to own a 12" machinist's straightedge, but I think I'll fight it...

OK, lost the fight. It will be a lot easier to play with than the granite, and only about 12x less flat at .0005" claimed tolerance.

 

[natto]

My 200mm straigt edge was about 20$. Great tool, no more guesswork, I love it.

 

[Mr Kooby Shemayrew]

but I think I'll fight it...

OK, lost the fight.

On behalf of everyone here, I just wanted to let you know, we are all proud of you.

 

[Empire straights]

I was about to grab my high lumen flashlight and go check my various Atoma, DMT, Eze Lap and Ultra Sharp plates against my ~1μ granite reference plate.

Instead I'm going with YMMV on diamond plate edge flatness. I'm getting an urge to own a 12" machinist's straightedge, but I think I'll fight it...

OK, lost the fight. It will be a lot easier to play with than the granite, and only about 12x less flat at .0005" claimed tolerance.

Your stones don't need to be machinist flat, and you'll get real good a reading blade if you hone in hand on wonky stones but I suggest start with knives for this.

 

[Gamma]

It will be a lot easier to play with than the granite, and only about 12x less flat at .0005" claimed tolerance.

it would be difficult to judge flatness of a lapped stone on a reference plate, especially if the lapped stone is wet/damp. It's much easier with the a thinner side of a straightedge.

I bought a machinists straight edge so I know for sure the starting reference point is straight. Most rules in my home have been used for cutting stuff and are now most definitely not straight. Even my most unused draftsman's rule, which was what I was using originally, is not all that straight.

 

[Tanuki]

Your stones don't need to be machinist flat, and you'll get real good a reading blade if you hone in hand on wonky stones but I suggest start with knives for this.

Agreed on the over-valued flatness. Some days it's simply about shaving in the den, other days it's a science fair project down in my basement.

I'm not partial to honing in hand. I have enough opportunities to drop stones and razors without that. Plus, I like my fingertips attached. I use my balsa strops in hand, but they are light, dry, grippy, two inches deep, and the strokes are spine leading. No bloodletting or busted blades ... yet.

it would be difficult to judge flatness of a lapped stone on a reference plate, especially if the lapped stone is wet/damp. It's much easier with the a thinner side of a straightedge.

Absolutely right. I could have easily checked the flatness of the diamond plate edges on the granite. Hone and balsa strop faces, not so much.

At 12"/300mm a straightedge will be twice as long as any of my inexpensive machinist squares, which see a lot of use in woodworking territory, far from the SR/honing play pen.

 

[Loner16]

I'm quite sure the edge of your Atoma plate is more than straight enough... Sometimes we're just chasing shadows!
I was Tool & Die Maker, so I have enough truly straight edges to choose from. That said, I wouldn't go out of my way to get one when something else is just straight enough.
That said... to each his own...