Thread: DMTs & does anyone have a micrometer?

My DMT plates are all perfectly flat as indicated by my machinist straight edge. You can easily see the effect of honing a razor with tape. Just set the bevel with tape on the razor then color the bevel with a permanent marker. If you take the tape off and hone the razor you will find that it will take a significant amount of work to remove the marker all the way to the edge unless you torque the edge into the stone/plate.

Well, I build pipes in my spare time, so I just happened to have a digital micrometer laying about...a piece of electrical tape that I use for...well...electrical stuff comes in at 0.0065 of an inch (measured in three places, all came out the same). Just thought I'd confirm the 3M data.

Mark

That does not sound like much of a variance on the DMT. I would not be concerned.
The one I used made really bad grooves in the hone, not little ones but really big, wide ones.
I am sure it was a fluke. Many people here are using them and none have reported a problem.

I just checked the DMT website and indeed, I was correct on the flatness claims:

Here's a quote regarding the D8 series (8 x 3)

"The precision-engineered surface flatness to + / -0.001” will remain flat forever, offering the sharpest edges with no maintenance."

and in reference to the coarsest stone:

"With a surface flatness to +/- 0.001" Double-X is perfect for flattening water stones, Arkansas stones, and synthetic stones."


Now, considering that +/- 0.001" over 8 inches is pretty much the standard for basic machinists squares, it will have no discernible impact on razors or flattening hones. There is of course always the chance that a defective hone might get out and if so I would expect DMT to make it right. Personally, I think the D8 series is one heck of a bargain.

Regards

Christian

Another difference is that the tape affects the angle of the razor in a consistent way, while a slight variance in the hone will probably be gradual enough that the razor can adjust to it as you hone. A good X pattern stroke should compensate for some slight unevenness. My Belgian blue hone is way off flat when checked against a straight edge, but it works fine with razors of all sizes and shapes.

Josh

Well, if the consensus then is that .001" variance has no effect on adversely affecting a razors edge during honing, I'll live with that and chalk up my tribulations to my inexperience rather than being able to blame my lackluster results on the plates and hones

SRP member Sticky had mentioned in an recent post that the average thickness of a pencil mark is four billionths of an inch. With that in mind, aside from seeing where a hone is "out of the box", I see no need whatsoever to go through the trouble of ever doing a pencil grid for re-lapping a hone after the initial lapping. Why even bother taking the time to remove 4 billionths of an inch if a .001 variance has no ill effect? I ask this rhetorical question because I've used the pencil grid when re-lapping hones in the past. I'll do nothing more than some brief refresher passes on the diamond plates to clean the surfaces of my Norton 4000/8000 more than anything else and call it plenty good enough.

Originally Posted by Chrisl

SRP member Sticky had mentioned in an recent post that the average thickness of a pencil mark is four billionths of an inch. With that in mind, aside from seeing where a hone is "out of the box", I see no need whatsoever to go through the trouble of ever doing a pencil grid for re-lapping a hone after the initial lapping. Why even bother taking the time to remove 4 billionths of an inch if a .001 variance has no ill effect? I ask this rhetorical question because I've used the pencil grid when re-lapping hones in the past. I'll do nothing more than some brief refresher passes on the diamond plates to clean the surfaces of my Norton 4000/8000 more than anything else and call it plenty good enough.

The pencil mark was somewhere between 4 to 17 billionths as measured electronically with a Wheatstone Bridge. Geometric analysis agreed with the Bridge.

The rational behind drawing a second grid and re-lapping is because the first lapping will introduce errors (much larger than 4 billionths), from the operator, the initial unevenness of the hone, and the DMT plate. The worse your hone is at first, the bigger the introduced errors. If your hone starts out pretty flat, then the errors will likely be small. Many times small enough to be fine for razor use (depending on the operator's skill at lapping).

I only re-mark and lap twice under 3 conditions:

• This is the first time I am lapping this particular hone. OR-
• Using a 6" machinists rule, before beginning to lap (new or previously lapped-by-me): I see more than about 0.006" or 0.007" of daylight, at any point, between the rule and hone.
• I have the slightest suspicion/feeling that I might need to...

The only way a lapping job could be w/in 4-17 billionths of an inch is if all of your grid marks disappeared equally and at the same time. This will be impossible on a DMT plate because the DMT is not that accurate. All of us operators are even worse...

I think the pencil grid is just for reference to the flatness of the hone you'e lapping. If the pencil wears away only on the edges with a few laps, then you know the stone was way off from being flat. I heard someone (probably Josh) also say that once they have lapped completely flat the first time, they re-do the grid and give a couple laps. That's all it should take to erase the pencil and you will know it is flat.

Also, I know nothing about micrometers, but isn't it possible that with ANY machined product, even digital, there could be a variance in its measurement? i.e. 0 to a micrometer that may be off could really be 0.0001 or something so that over a large measure, the number will be slightly off, if only by maybe .001"?

Originally Posted by heavydutysg135

My DMT plates are all perfectly flat as indicated by my machinist straight edge.

Nothing is perfectly flat. I am reasonably sure that your DMTs have more than 0.00000000001 " error to them.