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[What are typical grinding lubricants?]

#11

Knife Sharpening / Re: SG-250 - Oil Better Suited...

Last post by RichColvin - May 19, 2026, 11:27:06 PM

I remember using oils for keeping cutting tools cool and working efficiently (e.g., on drills, milling machines, and metal lathes).  I could not remember using oils for this purpose, so I asked Claude.ai.  Whilst AIs are not always right, Claude does seem quite good.  

Question:  What are typical grinding lubricants?

There was a long iteration of options provided, based on, 

• Material being ground (steel, carbide, ceramic, aluminum)
• Wheel type (CBN, diamond, aluminum oxide)
• Precision requirements
• Environmental/health regulations

But it was summarized as:

For most general-purpose surface or cylindrical grinding, water-soluble synthetic or semi-synthetic fluids are the go-to choice due to their cooling efficiency and cleanliness.

I followed this up with the question:
What is most commonly used for aluminum oxide grinding wheels?

For aluminum oxide grinding wheels specifically, the choice depends on the application, but here's the breakdown:

Most Common: Water-Based Synthetics & Semi-Synthetics
These are the dominant choice for aluminum oxide wheels because:

• Aluminum oxide generates significant heat — water-based fluids excel at cooling
• They keep the wheel from "loading up" (pores clogging with swarf)
• Good for ferrous metals, which are the typical workpiece material paired with Al₂O₃ wheels
• Easy to maintain and cost-effective

By Application
General surface/cylindrical grinding (most common use case)

• Synthetic or semi-synthetic water-based fluids are standard
• Concentration typically 3–8% in water

Precision grinding (tool & cutter, OD grinding)

• Semi-synthetic fluids for the balance of cooling + lubrication
• Sometimes light sulfurized mineral oil for very fine finishes on steel

Heavy stock removal

• Soluble oil emulsions — the oil content helps with lubrication under higher loads

Light/bench grinding

• Often run dry, or with a wax stick touched to the wheel periodically

What to Avoid with Al₂O₃ Wheels

• Straight heavy oils — poor cooling, can cause thermal cracking in the wheel bond
• Alkaline fluids with high pH — can degrade certain wheel bonds over time

So, I think we are good with water.

#12

General Tormek Questions / Re: Angle Master Degree Differ...

Last post by Ken S - May 19, 2026, 11:22:02 PM

The Anglemaster, being a Tormek product, is calibrated to the standard 250mm Tormek grinding wheels. If the oversize difference with CBN wheels bothers you, take a millimeter reading of their diameter and make a fine sharpie line. Your guess will be close enough.

Ken

[Primary Facets]

#13

Drill Bit Sharpening / SPAs on Twist Drills

Last post by RichColvin - May 19, 2026, 10:56:27 PM

Dan Heil contacted me by eMail and noted,

You can grind a SPA by setting the (DBS-22 clearance angle) to 90 degrees.

I tried it and that indeed worked ... exceptionally well!  Here is the resulting grind on a ½" drill bit.

This is a really big find by Dan as SPAs are really good on larger drill bits, and as noted on GadgetBuilder,

Secondary Point Angles ... extend drill life, improve hole finish and minimize the exit burr on through-drilled holes.

You can also see that the secondary facets are quite a bit rougher than the primary facets. This is due to using a different grinding wheel, making this a faster process

Primary Facets	Started with DC-250 diamond course grinding wheel (drill was in bad shape) Finished with DF-250 diamond fine grinding wheel
Secondary Facets	Used DC-250 diamond course grinding wheel
SPAs	Used DF-250 diamond fine grinding wheel

#14

General Tormek Questions / Angle Master Degree Difference

Last post by Rossy66 - May 19, 2026, 10:25:52 PM

I apologize if this is a stupid question but, I was wondering if anyone knows the degree difference on the angle master setting of 250mm to the middle scale of 10"?

I ask because I use 10" CBN wheels with my T8 and I am wondering if the difference between both numbers makes much of a difference in degrees also, why does the adjustable guide not point to the 10" mark?

Thanks

#15

Knife Sharpening / Re: SG-250 - Oil Better Suited...

Last post by John Hancock Sr - May 19, 2026, 03:12:24 AM

Still, from a physics standpoint, in a situation where a solid moves in relationship to another, the friction coefficient is the ratio of the tangential force to the normal force. If there is no friction, there is no tangential force applied to the material being cut, so no work being done and obviously no matter being removed.

The work being done can be measured by the material being removed (bonds being broken within the steel) and the generation of heat. You need to maximise the first and minimise the second. We want as little heat as possible and as much material removal as possible for maximum efficiency. This is achieved by ensuring that the relative MOHs hardness of the abrasive is higher than the steel, the abrasive keeps as sharp as possible (friability helps with this) and the surfaces slide past one another as smoothly as possible, which is done by lubrication. The lubricant also assists in removing any heat that may be generated by friction. Water and oil have both been traditionally used on sharpening stones.

#16

Knife Sharpening / Re: SG-250 - Oil Better Suited...

Last post by John Hancock Sr - May 19, 2026, 03:01:22 AM

Eventually found that my trusted ceramic stones just couldn't handle the harder steels, loads of work, glazing on the stones,

There are different ceramic compounds and they have differing harnesses. It really depends on the MOHs hardness of the ceramic in the stone.

#17

Knife Sharpening / Re: SG-250 - Oil Better Suited...

Last post by John Hancock Sr - May 19, 2026, 02:57:45 AM

Friction is nothing more than generating heat.

Indeed, the water actually acts as a lubricant as states by Tormek.

#18

Knife Sharpening / Re: SG-250 - Oil Better Suited...

Last post by Sir Amwell - May 19, 2026, 01:22:16 AM

Maybe you are asking too much of your SG250 stone?
And looking for an alternative like oil to run it through is not going to get more performance out of it?
The SG250 works just fine, through water with occasional regrading,for most everyday day steels, with correct honing gives good results.
But for harder steels?
It just won't cut it.
I spent a long time on bench stones, hand sharpening.
Eventually found that my trusted ceramic stones just couldn't handle the harder steels, loads of work, glazing on the stones, nagura stones, re flattening etc etc.
Oil addition didn't help either.
Diamond or CBN did though.....
Just my two pennorth.....

#19

Knife Sharpening / Re: SG-250 - Oil Better Suited...

Last post by Ken S - May 18, 2026, 10:50:32 PM

I have seen difficulties which reoccur occasionally, such as frozen EZYlocks and noisy water troughs on T8s. These are frustrating, but can be handled. I don't recall ever reading a previous post recommending oil instead of water with the SG. I am not saying that oil would not work. I am just puzzled that in fifty years of product innovation, Tormek does not recommend using an oillike coolant instead of water. My guess would be that Tormek has good reasons for staying with water. They do recommend ACC as an alternative which offers more rust prevention.

Ken

#20

Knife Sharpening / Re: SG-250 - Oil Better Suited...

Last post by tgbto - May 18, 2026, 04:35:03 PM

This is patently false and a myth that needs to die. Friction is nothing more than generating heat.

Thank you for your kind, nuanced words.

Still, from a physics standpoint, in a situation where a solid moves in relationship to another, the friction coefficient is the ratio of the tangential force to the normal force. If there is no friction, there is no tangential force applied to the material being cut, so no work being done and obviously no matter being removed.

In the same fashion, a frictionless action of a knife blade on a tomato will press down on the tomato but not cut it. Our job as sharpeners is to make sure friction happens over such a tiny surface that the cells are instantly sheared in two by the focused tangential force without the tomato being deformed by the normal force.

Heat is a byproduct of friction, heat reduces cutting of abrasives, and increases wear ; hence the need to use a coolant in many situations where friction generates a lot of heat, or to reduce friction using a lubricant where the unlubricated action would generate more heat than the tool (drill/belt/wheel) or piece would be able to withstand locally. Cutting fluids act as both.