Thread: DMTs & does anyone have a micrometer?

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"?

On a new hone I would always lap twice. On a hone that I have used for several razors then I would lap twice, maybe.
I always lightly lap my hones on 1000 grit before each honing session so the amount of wear on my hones is never very much.

"Sticky" has a very relevant work backround and consequent insight to the subject of flatness and how it is, and is not, obtained. I will be paying close attention to his comments.

For those of you who believe that 0.001" is too much, I just hopped over to the Shapton site and checked the specs on the two Diamond Reference Plates they offer.

The Diamond Glass reference plate is accurate to 5 micron or 0.0001968498" and sells for a quite reasonable $289.00. But, you say... you want MORE... err LESS.... Ok, enter the big gun in Diamond Reference plates, the two sided, cast iron model which is accurate to an incredible 3.5 microns... that's 0.0001377949" for you non-metric types and it goes for a paltry $489.00. The two sides, one for lapping stones and the other for lapping bevels on plane irons and chisels etc. and would not be suitable for razors based on it's pattern with rather large holes to swallow up swarf etc.

So in a sense, you would have to spend at least $234.00 more to gain approximately 0.0008" in accuracy across an 8" length over a DMT.

Many of us have been quite happy using nothing more than wet/dry paper on a floor tile or a piece of reasonable (we're assuming now) flat glass. I doubt they approch anything near the 0.001" that DMT specs for their diamond plates. Lets not forget that 50 years ago, when straight shaving was more the norm... few if any gents went to these lengths to get their hones flat... I recall my dads hones ( he was a barber and was quite skilled with the straight), they were all clearly hollowed in the center from years and years of use... I suspect they all matched up more or less as he didn't seem to have any problems getting business in his shop for shaves nor haircuts.

I'm all for these kinds of discussions but sometimes we need to do a reality check to keep us in the real world. Well... at least I need to... I'm usually the first one to buy something new and improved only to find out that the old stuff worked just as well.

Regards

Christian

Originally Posted by kaptain_zero

For those of you who believe that 0.001" is too much, I just hopped over to the Shapton site and checked the specs on the two Diamond Reference Plates they offer.

The Diamond Glass reference plate is accurate to 5 micron or 0.0001968498" and sells for a quite reasonable $289.00. But, you say... you want MORE... err LESS.... Ok, enter the big gun in Diamond Reference plates, the two sided, cast iron model which is accurate to an incredible 3.5 microns... that's 0.0001377949" for you non-metric types and it goes for a paltry $489.00. The two sides, one for lapping stones and the other for lapping bevels on plane irons and chisels etc. and would not be suitable for razors based on it's pattern with rather large holes to swallow up swarf etc.

So in a sense, you would have to spend at least $234.00 more to gain approximately 0.0008" in accuracy across an 8" length over a DMT.

Many of us have been quite happy using nothing more than wet/dry paper on a floor tile or a piece of reasonable (we're assuming now) flat glass. I doubt they approch anything near the 0.001" that DMT specs for their diamond plates. Lets not forget that 50 years ago, when straight shaving was more the norm... few if any gents went to these lengths to get their hones flat... I recall my dads hones ( he was a barber and was quite skilled with the straight), they were all clearly hollowed in the center from years and years of use... I suspect they all matched up more or less as he didn't seem to have any problems getting business in his shop for shaves nor haircuts.

I'm all for these kinds of discussions but sometimes we need to do a reality check to keep us in the real world. Well... at least I need to... I'm usually the first one to buy something new and improved only to find out that the old stuff worked just as well.

Regards

Christian

Excellent comments. I have long suspected that back in the day, hones were seldom or never flattened and yet they worked just fine. Barber hones are hard enough that I can't imagine anyone would be able to flatten them without the benefit of 21st century equipment. Out of the box they aren't really flat, and unless you have an extra extra coarse diamond hone, those hones are a real beast to lap.

Glad to get some confirmation on my theory.

And I agree that we can go waaaaaaay overboard here. I think the unavoidable variations in the operator's stroke--human error--play a much bigger role than the hone's flatness to within a few thousandths of an inch.

Josh