Thread: Cylindrical square theory

Originally Posted by Graziano

I have to reverse the spindle to dress the wheel properly as the Makino diamond dresser points upwards into the wheel. I did find that a fresh dressed wheel without any glaze seems to heat a lot less which I do for the final pass of 0.01mm and then feed across the shaft very very slowly. I can't stick the tongue out at the side as the coolant is a bit rank at the moment .

Hi Graziano,

I've been battling wheel dressing for the last few days... I've just about given up trying to understand what's going on, I'm grinding M2 at 64 RC with a Norton 5SG46 wheel, I'm getting mirror finish with some patterns that seem to come and go at random, I can hear a slight difference in sound when I get the problem... I'll eventually suss it out.. but it is related to dressing somehow...

You shouldn't be stopping the wheel after it's dressed, just starting and stopping will cause problems at the level you're trying to achieve, I'm of the opinion that having a slow ramp on the VFD avoids the slippage problems. I've got a 30 second ramp on power up and down.... and of course make sure the coolant is off when the wheel is stopped.. If it's a cup wheel, you might want to check the balance, some seem to have good dynamic balance, some seem to balance statically but not spin up properly...

Sometimes I think there's more of the "dark arts" involved in grinding than you might otherwise think...

Oh, and don't forget the sacrifice the chickens while facing the rising sun ...

Regards
Ray

Hi Ray, I have been getting the same chicken wire faint pattern, I have noticed that the more glazed the wheel gets, the shinier the grinding finish. I dress the wheel before the last 0.05mm or so.

To properly avoid it (so I was told) you apparently need to "Sharpen" the wheel after dressing with one of those wheels made of washers side by side that gives a texture to the wheel surface, so it's a two step process: dress to flatten the rounding of the edge, then sharpen or texture the wheel surface.

The Makino wheel hubs are all right hand threads with a tabbed washer under the nut driven by a keyway, I have it as tight as I'm comfortable with, seems to work ok.

Originally Posted by Stustoys

Hi Graziano,

The wheel dresser sounds strange, got a picture?
Do you have another wheel dresser you could use for the last dressing?

Not sure that the very very slow feed is such a good idea. Many faster passes might work better.

Stuart

It's a cast iron thing that came with about a half carat diamond rod stick in it and is angled upwards at 45 degrees with a T bolt in the base to fit to the table slot. It came with the Makino and is painted the same colour and looks a bit like the one that came with the Cincinatti T&C. As far as the feed goes, I was removing about 2 hundredths of a mm at a time, the slower sideways feed along the shaft axis prevents burning discolouration of the shaft visible under the coolant flood.


This is the basic setup for grinding my spindle shafts from 32mm 12L14 steel down to 20.002mm for the bearing fits up against the shoulders, then a reduction down to 19.97mm dia for the rest of the shaft with about 0.001mm taper over the length. I use the larger diameter area 150mm long to align the shaft to the table to minimise taper to about 0.001mm over about 130mm of it. No sign of the dresser in the pic.




The thicker part of the spindle shaft gets ground then the end to end taper is measured with the Mitutoyo mic and then half the difference is applied to the shaft using the digital indicator. Then I grind it and do it all over again until I'm happy with the taper.

There is a marked difference between "truing" a grinding wheel with a diamond tool and "dressing" the wheel to expose new sharp grit on its surface.
Truing the wheel with the diamond is not the same as dressing.The diamond neatly cuts the wheel to shape but dulls all the grit at the same time. After truing it is best to dress the wheel with a dressing stick which is like the same material as grindstones.The old fashioned grey dressing stick.
I had the same problem with grinding HSS knives for woodwork and it was the truing that was making everything grind hot and slow. Better to give the wheel a dressing freehand after truing to expose fresh grit.
Certainly solved my problems and ended up with a much better job.

Originally Posted by localele

There is a marked difference between "truing" a grinding wheel with a diamond tool and "dressing" the wheel to expose new sharp grit on its surface.
Truing the wheel with the diamond is not the same as dressing.The diamond neatly cuts the wheel to shape but dulls all the grit at the same time. After truing it is best to dress the wheel with a dressing stick which is like the same material as grindstones.The old fashioned grey dressing stick.
I had the same problem with grinding HSS knives for woodwork and it was the truing that was making everything grind hot and slow. Better to give the wheel a dressing freehand after truing to expose fresh grit.
Certainly solved my problems and ended up with a much better job.

So it's truing and then dressing the wheel, it's good to know there's a straightforward way to dress as I haven't been doing it at all. I certainly need to brush up on my grinding terminology.

I took a pic today of the Makino's diamond dresser for Stu: it's more like 5 degrees rather than the 45 degrees, I mentioned earlier.

Originally Posted by localele

There is a marked difference between "truing" a grinding wheel with a diamond tool and "dressing" the wheel to expose new sharp grit on its surface.
Truing the wheel with the diamond is not the same as dressing.The diamond neatly cuts the wheel to shape but dulls all the grit at the same time. After truing it is best to dress the wheel with a dressing stick which is like the same material as grindstones.The old fashioned grey dressing stick.
I had the same problem with grinding HSS knives for woodwork and it was the truing that was making everything grind hot and slow. Better to give the wheel a dressing freehand after truing to expose fresh grit.
Certainly solved my problems and ended up with a much better job.

Hi Michael,

Interesting.... I've only come across that truing/dressing process with respect to resin bonded CBN or diamond wheels. Where the diamond or cbn particles are buried after the truing process and then they need to be exposed to get fresh cutting particles by dressing....

I think there might be a significant difference between single point diamond dressing and Brake Truing...

I've got a Norton Brake Truing Device, and dressing sticks, but I've never considered using it on alox wheels. The binder on the 5SG wheels is pretty soft, and I've no idea how you would use a dressing stick by hand on the surface grinder without getting it out of true..

What sort of grinder where you using to grind the knife blades?

Regards
Ray

You know amongst the Makino grinder accessories was a lump of dressing stick that was hard to recognise due to the black layer of greasy crud on it. I expect you'd need a steady hand to manually dress a T&C grinder wheel correctly. I was under the impression it used one of those dressers that look like they were made from star washers grouped together.

Hi Ray, The info. came from my mate Paul Williams who's business was Academy Saws in Sydney. Spent his life making and grinding saws and blades. I have a jig I built on my milling machine to grind my jointer and thicknesser knives and was having trouble.While I realise you guys are talking about superfine tolerances I think the info. still hold true.
I use a Norton seeded gel wheel mounted on an arbour to do the grinding.After a slow truing pass with a mounted diamond dresser the wheels didn't cut very well at all.On Paul's advice I dressed the wheel by hand to expose some fresh grit and also slowed the wheel speed down and get a much better result.The amount of out of round would be hard to measure from a dressing but certainly it worked in my situation.
It all sounds opposite to surface grinding where you have higher speeds for both the wheel and feed.

Hi Micheal,

I just notice I misspelt your name earlier, sorry...

What you say all makes sense, and I understand the point, I'm thinking I'll try giving the wheel a light touch with a dressing stick, Just to see what happens... the problem I'm chasing is a light pattern that only become visible when you get close to mirror finish, and it's faint lines that run at right angles to the wheel axis, as if the wheel had a tiny flat spot, ( or high spot) It's not wheel balance, as the pattern comes and goes, seemingly at random.. also I've been pretty carefull with the balancing, I suspect it might be something peculiar with this wheel... could be a bit of grinding dust getting embedded in the wheel I guess...

Anyway, that's my problem, chasing mirror finish... Gerbilsquasher's chasing microns... I know what I'd rather be chasing...

Regards
Ray

The Blohm surface grinder I've borrowed has a fairly coarse silicon carbide wheel that has a porous structure kind of like bubbles or small voids in the wheel, the manufacturer must have something that burns out completely when the wheel gets fired leaving the voids, to give what I imagine is a pre dressed wheel once you true it up. I used it to grind some very old Ebay Rex MM which I understand is M2 steel, it worked well enough for me to skim the rough forged 5/8" square bars.

Originally Posted by RayG

the problem I'm chasing is a light pattern that only become visible when you get close to mirror finish, and it's faint lines that run at right angles to the wheel axis, as if the wheel had a tiny flat spot, ( or high spot) It's not wheel balance, as the pattern comes and goes, seemingly at random..
Regards
Ray

That sounds a bit like a harmonic balance more than a dynamic problem Ray, but then, I know jack about surface grinders.

I think I know what you mean Ray. It is like a bit of fine netting thrown over it.
I think that with the higher RPM of surface grinders that dressing won't make it out of round or balance enough to cause a problem .
When chasing the mirror finish do you actually polish it as well?

I get that too, I was referring to it as the "Chicken wire pattern" but mosquito net would be more accurate. I know for a fact I get harmonics as the shaft will get an audio tone of about 1000 Hertz if I advance the grinder wheel into the shaft for the next grinding pass too fast as the steel "rings" . Ray, I wonder if you could dampen the harmonics with a lump of steel or carbide glued to the M2 you are grinding?.

The ringing noise is reduced by dressing the stone.I think it is the impacted swarf in the stone and as soon as you dress it out and get fresh sharp grit the ringing will go.This is the same on a bench grinder for that matter.It is how I know when to dress my stones as the noise changes.

Originally Posted by localele

The ringing noise is reduced by dressing the stone.I think it is the impacted swarf in the stone and as soon as you dress it out and get fresh sharp grit the ringing will go.This is the same on a bench grinder for that matter.It is how I know when to dress my stones as the noise changes.

I am using a harder white aluminium oxide wheel when this happens (trued but not dressed). The much softer blue silicon carbide wheel doesn't do it at all. I prefer the silicon carbide wheel but it's so soft I have to true it at least twice as much. The finish never gets that bright shiny finish of the partially glazed aluminium oxide wheel though as I suspect the surface particles wear off before it can glaze too much. If Ray is using a soft friable wheel then he may never get that chrome like finish of the glazed wheel.

I think a large part of my ringing problem is the fact that it's a shaft that can ring, in a steel that can ring too, 12L14 even though it's leaded is still a stronger steel than your average soft dead mild steel (1018?).