Thread: Precision ground toolroom stones

I thought the topic had been posted here, but I can't find it....
In June this year, 'Robrenz' published a Youtube video (https://www.youtube.com/watch?v=DVLXsq7pi9Y) that drew my attention.
Not wanting to spend a lot of money but convinced enough that it might work, I bought a couple of sharpening stones from a discount shop ($6 each) and a straight diamond wheel (https://www.ebay.com.au/itm/Diamond-...sAAOSwuxFYtJuP) to fit my surface grinder. It is gong to come in handy for dealing with tungsten carbide projects and tool grinding as well.
I followed the instructions by Robrenz and managed to grind the two stones very nicely flat and parallel and they behave just as he described.
I'm writing this to report that I seem to use them all the time now. I'm amazed at how many tiny dings and burrs I find on my tools now - and remove them without harming the surfaces or anything else.

Thanks Joe,

I am a big fan of Rob's youtube Chanel. He is a master craftsman and everything he does is so well thought out. I also enjoy how he is always thinking about making things better and fast/cheaper to make.

Cheers

Piers

I bought a surface grinder a few days ago and this is going to be one of the first few jobs im going to get into. Dont know if im quite up to the standards required for restoring pratt and whitney levels yet, but surely some oil stones arnt too hard!

Joe
Were the sharpening stones that you used the Robrenz recommended orange India stones? or the more common grey? Does it matter?
Pete

Check out Robrenz instagram page, he post some pretty cool stuff on their too.

Originally Posted by Petip

Joe
Were the sharpening stones that you used the Robrenz recommended orange India stones? or the more common grey? Does it matter?
Pete

Also, which discount shop?

Originally Posted by Petip

Joe
Were the sharpening stones that you used the Robrenz recommended orange India stones? or the more common grey? Does it matter?
Pete

I heard from Rob this morning. This is what he was suggesting in a 6 x 2 x 1 https://www.sharpeningsupplies.com/N...e-P69C126.aspx

Bunnings have Bear brand (which AFAIK is Norton) 8x2x1" stones for $37.
I'm guessing they'd quickly turn into 6x2x1 with a cheap diamond tile cutoff disk in the angle grinder....

Steve

My stones are grey and white combination aluminium oxide stones. Norton 'India Stones' are also aluminium oxide but red....
I suspect that their red colour is to differentiate them from their grey silicon carbide ('Crystolon') stones.
I have no idea if it matters, maybe someone with a scanning electron microscope can tell the differnence.....
Theorizing though, I would say the actual grid is not important, but the bonding might be: when the stones are precision ground with a diamond wheel, we don;t want to grains to be dislodged or shattered - they should be just sheared off flat.
The gaps between the grains should be large enough to allow tiny burrs to fit into them and be sliced off by the sharp edges of the otherwise flat grains. Again, without dislodging or fracturing the grains.
Too fine a stone will have pores or gaps between grains that are too small. My cheap stones were not labelled, but compaing them to my sharpening stones I'm estimating that they are 240 on one side and 400 on the fine side.
The discount shop I bought them from is a shop in the local shopping centre - I can't recall the name but it may the 'Reject shop' or something like it.

I talked to Felix from http://www.mag-pro.com.au/ to ask if he can find stones like that. I remembered that he has worked with and deals with the manufacturer of gauge blocks for Hoffmann Group in Europe. He wrote back tonight that he is trying to source some samples following their recommendations. I'm hoping they don't end up too fine or too expensive for our purpose.

If you happened to see them very cheaply at a discount shop, I'd certainly think it was a good idea to give them a go, but the genuine Norton India stones are available on Amazon for around 20 bucks each as 6 x 2 x 1".

I ground some of these stones the other night, Norton as described above. They are very interesting to use, and seem to work just as Robin describes them. I'll give them a go on some intentional dings to see how they handle a real life situation.

The diamond wheel was a bugger to true. Next time I mount it I'll try to get it as true as possible before dressing. I got a reasonable result by truing with mild steel. It wasn't flat across the wheel, but didn't seem to affect the final result.

I saw some cheap bench stones last night so grabbed them and will grind them when I can to compare with the ones Robin suggested.

Originally Posted by Pete F

The diamond wheel was a bugger to true.

Why not just dress and use a grinding wheel?
I used to dress my syncro seating stones in the valve grinder, this way the angles were the same and valves would
only require a very light lap.
What I am getting at here is that you can dress your wheel in the normal fashion and stone on stone should give you the finish that you want.

cheers, shed

I don't have a grinder, and I watched his video saying you can only 3 way lap square surfaces. I am thinking it might be worth it to buy two stones, cut them up so you have 3 squares, then lap away.

I want a grinder... One day.

Yes it needs to be a diamond wheel. No you can't lap them. Robin specifically made that point in the video.

Flatness is only part of the objective. The diamond wheel actually cuts the abrasive particles in the stone and leaves them with flat tops, that's how these stones function. That's why I said they feel "interesting" to use. Not like a normal stone at all, regardless of how flat the stone is. They feel very different to the touch, quite smooth. Ant sharp protrusions get forced below that top plane and sheared off by the particles below. I was experimenting with them last night both with scrap stock that has been ground and them thrown in the scrap bin and also intensionally centre punching some steel I'd previously ground. Where there was a raised surface the stones took it down to the surrounding surface and then just burnished the surface.