Machinist

[Lawrence London <lfljvenaura@gmail.com>]

---------- Forwarded message ----------
From: Avant Geared <avantgeard@gmail.com>
Date: Thu, Jan 25, 2018 at 8:43 PM
Subject: Precision-ground flat stones for deburing, ROBRENZ video, diamond grinding wheels
To: smallmachineshop@groups.facebook.com

If you're going to make your own ROBRENZ-type precision deburring flat stones you can make good use of the following information.

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PRECISION GROUND TOOLROOM STONES
I describe/show where and how to use precision ground flat stones. Why these are an absolute must for working with high precision tooling. What makes them work and how to make your own your own set.
PRECISION GROUND TOOLROOM STONES - YouTube

Precision Flat Stones for deburring - more info from Robin Renzetti - 2016 FB comments

Robin Renzetti

You want it to feel a bit dull so the stone will only remove the burrs or raised metal. As soon as it engages the full surface after removing the

burrs it will not cut any further which is exactly what you want. Think of it as a large gage block stone, only capable of removing a burr not

changing the size of the block. These stones are for use on very precise ground or lapped tools and parts and you dont want a stone that will

scratch/cut a lapped tool surface you just want to remove the minute burrs. You need a pair because proper technique is to first rub the two

against each other to make sure nothing is on the stones surface before you stone something. I plan on doing an extensive video on making and

using precision ground flat stones.

Robin Renzetti

I have used all the other methods mentioned and diamond plates and they are great for a general flat stone that is more aggressive for heavier

burrs on lower precision items. But IMO they are not flat enough and dull enough to use on high precision tooling like Herman Schmidt tools or

precision levels etc.

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This looks like a good source for stones to grind; these are Norton:
Norton Combination India Stone
Norton Combination India Stone
Item # NCMBN
Size 6" x 2" x 1" - $19.99

Norton combination, India (aluminum oxide) and Crystolon (carborundum).
two each of the 3/4 X 1.5 X 4 and 1X2X6.

Conversation with RobRenz about precision grinding these stones:

ROBRENZ:
Thanks Steve you are going to love them. Make sure you get a good finish on the stones or they will behave more aggressively than what you saw in the video.
SRMS:
Hi Robin, Would you recommend using the 3 to 6 micron diamond slurry you mentioned in one of the comments below to smooth the stone surface, or will they be okay with a proper grind?
ROBRENZ:
They will do fine just ground as long as you have a balanced, trued, and dressed diamond wheel and use a slow final cross traverse 

Here it all is again in one place plus a new reference:

The point made in Rob's video is that the precision stones have their abrasives smoothed out so they only polish, not cut and they are especially flat. If you are using them to maintain your metrology instruments this is the only thing you want. I doubt this can be achieved through manual processing of the inexpensive combo stones.

Here is a 2007 PM thread on diamond wheels that has a lot of useful basic information, i.e. wheel ID, dressing and conditioning
Diamond surface grinding wheel
Diamond surface grinding wheel

http://www.practicalmachinist.com/vb/general/diamond-surface-grinding-wheel-139034/

Conversation:

What leads you to believe it's a diamond wheel? What are you trying to grind on the wheel?

Post the letters and numbers. Superabrasive wheels are not usually a solid wheel. They're bonded to the edge of metal, or otherwise have a thin layer of abrasive with a large core of nonabrasive material.

Wheels with a normal abrasive should take the following form:
Prefix - Abrasive - Grit - Grade - Structure - Bond - Suffix
example:
R - A - 40 - G - 10 - V - 843

R is a letter the manufacturer decided to use. A is the abrasive type, which stands for Aluminum Oxide (C is silicon carbide). 40 is the grit size of the abrasive (Higher number is finer grit). G is the grade, or how strong the bonding agent is and how readily it will decompose (A is soft, Z is hard). 10 is the structure, or porosity of the wheel (1 is dense, higher numbers are more porous). V is the bond type, or the kind of material used to bond the abrasive (V is a vitrified bond, the most common kind).

For superabrasive wheels (Diamond and CBN) the formula differs slightly:
</font>

• Prefix - Abrasive (B or D)</font>
• Grit</font>
• Grade</font>
• Abrasive concentration - Usually from 25 to 100. Low numbers means low concentration of abrasives.</font>
• Bond</font>
• Bond modification - Sometimes the bond is modified to work better in a specific superabrasive application. This is manufacturer dependent.</font>
• Abrasive depth - Thickness of the wheel's abrasive layer. Specified in fractional inches or mm.</font>

More information:

Try Nortons N 5468779 89A 1206 4A V2 for dressing and cleaning the crud out of diamond wheels. 1"x 1" x 6"

We used molybdenum blocks to dress diamond. If you need to do a lot of dressing, a brake dresser works very well. If the wheel hasn't been damaged and just needs cleaned up, the Norton sticks, as Arnie3 mentioned, do a good job.

Especially this:

"Fixing" a diamond wheel is a 2 step process. Dressing and conditioning. Dressing is getting the wheel to run true and round. Conditioning is getting the resin bond back far enough to let some diamond particles stick out far enough to do some grinding. On a surface grinder a brake dresser is quick and easy,the moly blocks joeby mentioned in his post work too. I use a lot of diamond and CBN wheels on Heald ID grinders to grind plasma spray on overhauled gas turbine parts. They range from 1/2" to 3" dia and when they get worn on the "front" blind bores get small in the bottom. Flipping them over sometimes works but usually I grind them straight. Mount the wheel in a good whirlygig on a surface grinder or between centers on a arbor in an OD grinder and with a 60 grit green wheel grind it straight. For blind bores I usually put some taper in them(.001 an inch),wet is best but dry will work. Carefully wrap one layer of masking tape tightly around the outside of the wheel and indicate it in w/n .0005. The tape will save your indicator points. Condition with a soft alum oxide stick or a peice of white wheel,just hold it against the wheel for a second or two while it is running. The less you "condition" the better the finish but the wheel is much less aggressive.

And:

If it (the diamond wheel) is running reasonably round you will be ok just forcing an abrasive stick or old grinding wheel into it free hand. You are flood cooling I assume ? Look at it with a magnifying glass. The diamonds should have a little tail of bond behind them. Good luck.

Rob supplied this sourcing info for the stones he uses:

6 x 2 x 1 india combination MSC# AT05108568 15.99 sale
8 x 2 x 1 india combination MSC# AT05108584 19.09 sale

And to repeat his comments in the video site, setup and procedure is all important:

ROBRENZ:
Thanks Steve you are going to love them. Make sure you get a good finish on the stones or they will behave more aggressively than what you saw in the video.
SRMS:
Hi Robin, Would you recommend using the 3 to 6 micron diamond slurry you mentioned in one of the comments below to smooth the stone surface, or will they be okay with a proper grind?
ROBRENZ:
They will do fine just ground as long as you have a balanced, trued, and dressed diamond wheel and use a slow final cross traverse

--

Avant Geared

avantgeard@gmail.com
https://sites.google.com/site/avantgeared
Avant: culturally or stylistically advanced  Geared: one outfitted with proper gear

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Lawrence F. London, Jr.
lfljvenaura@gmail.com

https://sites.google.com/site/avantgeared