Grinding stones for air grinder - do the different colours mean anything?

[twr7cx]

In regards to grinding stones for an air grinder, do the different colours mean anything e.g. more course or fine etc? Or is it just a case of pick the shape that suits the job at hand and the colour is the colour?

https://www.aulro.com/afvb/images/imported/2018/06/110.jpg

[workingonit]

In regards to grinding stones for an air grinder, do the different colours mean anything e.g. more course or fine etc? Or is it just a case of pick the shape that suits the job at hand and the colour is the colour?

On bench grinders dark grey is often silicon carbide. Pure white an aluminium oxide. Grey with white flex a mix. Different colours for different metals, alloys, or carbides.

Not sure what the colours represent in air grinders - all I can say is I rarely use the airstones, preferring the tungsten carbide bur die grinders for steels and aluminium - fast material removal, long lasting - maybe stones for more sensitive rates of removal?

Die Grinder Bits | eBay (https://www.ebay.com/bhp/die-grinder-bits)

[Toxic_Avenger]

For grinding or cutting wheels, there is a spec printed on each disc that will give info on what makes up the disc, and where its strengths may lie (ie large agressive grit, and bond strength holding it all together)

https://www.aulro.com/afvb/images/imported/2018/06/111.jpg

For vitrified mounted points like you've pictured, there is a standard, but for the sort of stones you get with a dremel or other tool, it's probably pot luck.
Color may signify various grits for some manufacturers, but your mileage may vary. Is there any spec written on it? To be blunt, if it was for a job that mattered,you wouldn't be using the cheap ones that came in the box in any case.

If you were to buy some of those 'vitrified mounted points', there are a few options available from St Gobain (Flexovit), and they have a classification system to make a bit more sense of it all.

https://www.aulro.com/afvb/images/imported/2018/06/112.jpg
Using the convention in the top pic, their spec shows AlOx grit, various grits (36, 46, 60) and PV signifying Pointed vitrified.

If you have the money and the inclination, get some carbide bits and watch the metal chips fly.

[twr7cx]

I've just got a bit of aluminium that i want to clean up (it's the replacement for the EGR piece prior to the inlet manifold on my TD5 - it's a 60mm pipe but the opening at the mounting flange was only 56mm so I wanted to open it up by removing the lip). I used a metal lathe to take out the bulk of the material but it wouldn't mount dead straight so I stopped short to finish it by hand rather and thought the air grinder might be the easiest for the job. It just needs less than a mm removed from 1/2 of it now. The flange is about 15mm thick.

[trout1105]

I have no idea about the stone colours But it looks like a very handy bit of kit, Nice[thumbsupbig]

[workingonit]

I've just got a bit of aluminium that i want to clean up (it's the replacement for the EGR piece prior to the inlet manifold on my TD5 - it's a 60mm pipe but the opening at the mounting flange was only 56mm so I wanted to open it up by removing the lip). I used a metal lathe to take out the bulk of the material but it wouldn't mount dead straight so I stopped short to finish it by hand rather and thought the air grinder might be the easiest for the job. It just needs less than a mm removed from 1/2 of it now. The flange is about 15mm thick.

Mounting in a four jaw or face plate on the lathe might give you the centering needed. or onto a mill with an indexable cutter.

I find pure aluminium tends to clog the grindstone face, in the worst case running the grindstone on some brick material to freshen the grindstone. Zinc alloy grinds more like steel. One of your coarse stones should do for a small one off job. Have a look at the die grinders though - a good set in the tool shops are around $100 for five shapes - a well known hardware chain sells similar sets for twice the price - even cheaper on the net. I think I would do bulk removal with the die grinder and then refine the surface with one of your stones.

[Bigbjorn]

On bench grinders dark grey is often silicon carbide. Pure white an aluminium oxide. Grey with white flex a mix. Different colours for different metals, alloys, or carbides.

Not sure what the colours represent in air grinders - all I can say is I rarely use the airstones, preferring the tungsten carbide bur die grinders for steels and aluminium - fast material removal, long lasting - maybe stones for more sensitive rates of removal?

Die Grinder Bits | eBay (https://www.ebay.com/bhp/die-grinder-bits)

Silicon carbide wheels are always green in my experience. They are used for grinding tungsten carbide cutting tools such as lathe tools. Use tungsten carbide rotary burrs for metal removal and those stones for final finishing.

If buying rotary burrs make sure you get the solid carbide ones. Cheapies are commonly a TC cutter silver soldered or brazed to a steel shank. If you use them hard then the solder can soften and the cutter head falls off.

[workingonit]

Silicon carbide wheels are always green in my experience. They are used for grinding tungsten carbide cutting tools such as lathe tools. Use tungsten carbide rotary burrs for metal removal and those stones for final finishing.

If buying rotary burrs make sure you get the solid carbide ones. Cheapies are commonly a TC cutter silver soldered or brazed to a steel shank. If you use them hard then the solder can soften and the cutter head falls off.

Agree with the comment about getting solids. And I was surprised at how long they last. I expected all the teeth to be ripped off after an hour of work, but after about 15 hours accumulated work still good as new. In fact they're outlasting the cheap air tools!

Wiki has carbide as yellow to green to bluish black. One of my fine carbide wheels has a light green tint. The coarse ones are more black than anything. My loose lapidary grit is grey black. So neither of us has seen yellow? [biggrin]

I've one bench grinder reserved for tool sharpening, writing on the machine to remind me - silicon side for tungsten carbide, and the aluminium side for HSS and Crobalt.

[Bigbjorn]

Agree with the comment about getting solids. And I was surprised at how long they last. I expected all the teeth to be ripped off after an hour of work, but after about 15 hours accumulated work still good as new. In fact they're outlasting the cheap air tools!

Wiki has carbide as yellow to green to bluish black. One of my fine carbide wheels has a light green tint. The coarse ones are more black than anything. My loose lapidary grit is grey black. So neither of us has seen yellow? [biggrin]

I've one bench grinder reserved for tool sharpening, writing on the machine to remind me - silicon side for tungsten carbide, and the aluminium side for HSS and Crobalt.

I once upon a time was a fitter and turner-machinist first class. I have trade papers and advanced trade certificate saying so[bigsmile]. In my machine shop days I never saw a silicon carbide wheel in anything but green. In fact, they were always called "green wheels", "use the green wheel for that". We had, and I still do, grinding wheels in grey, white and green.

[workingonit]

I once upon a time was a fitter and turner-machinist first class. I have trade papers and advanced trade certificate saying so[bigsmile]. In my machine shop days I never saw a silicon carbide wheel in anything but green. In fact, they were always called "green wheels", "use the green wheel for that". We had, and I still do, grinding wheels in grey, white and green.

Afraid I'm only Wiki qualified.[bigsad] Green and yellow are the purist, being formed closest to the heat source. I can only guess that would mean sharper grains and better grinding characteristics for tougher tooling.

I'm guessing you're retired - do you keep up your skills in any hobby way? When I was 50'ish I asked the TAFE if I could do a machining trade course to better understand my machines and methods and was told only if I had an apprenticeship...

[twr7cx]

When I was 50'ish I asked the TAFE if I could do a machining trade course to better understand my machines and methods and was told only if I had an apprenticeship...

I tried approaching TasTafe regarding a few courses I wanted to do out of interest for hobby. Sadly I had the same response as I don't have a trade certificate it was a no. It's sad and disappointing that there is little opportunity for adult education in skills.

[Bigbjorn]

Afraid I'm only Wiki qualified.[bigsad] Green and yellow are the purist, being formed closest to the heat source. I can only guess that would mean sharper grains and better grinding characteristics for tougher tooling.

I'm guessing you're retired - do you keep up your skills in any hobby way? When I was 50'ish I asked the TAFE if I could do a machining trade course to better understand my machines and methods and was told only if I had an apprenticeship...

I most certainly am retired. I am 77. I still have a full complement of fitter's, repairer.s and restorer's tools, a lathe and drill press, three bench grinders, a tool post grinder, stick and mig welders.

I can't speak for the NT TAFE system. Qld barely has one these days as far as trade skills go. TAFE's got closed down and shrunk willy nilly in the 1990's and the management were told to go commercial and offer courses people would pay well for. Before then most colleges offered hobby machining courses. Some guys had been doing these for 20+ years. Cheaper than owning your own machine tools and tooling. Also offered were courses in Foundry and in Blacksmithing. They also offered four level courses in Machining for people working or planning to work in the field and could get some training. Otherwise you did an apprenticeship. The four level course and a good bit of hands on experience might have got you a Tradesman's Rights Certificate. Most shops regarded these with a good degree of suspicion and thought of the holders as glorified TA's.

[workingonit]

I tried approaching TasTafe regarding a few courses I wanted to do out of interest for hobby. Sadly I had the same response as I don't have a trade certificate it was a no. It's sad and disappointing that there is little opportunity for adult education in skills.

Interesting to hear someone else had the same response. I find it ironic that I'm a baby boomer educated by second hand old tech books that no one wants now, and by forums and youtube. Sympathy for Bigbjorn, as I've met a few fitters and turners, the common theme was that they could turn their hand to anything, whereas these days its certificates for one application only and otherwise hopeless outside the box.

[workingonit]

glorified TA's.

I used to go bush camping on weekends with a well paid TA at Jabiru mines. His job was to pass the tradesman the required tool, and put up with it being thrown back at him if it wasn't the right one[bigrolf] Sort of like a golf caddie...

[twr7cx]

I find pure aluminium tends to clog the grindstone face

Yep, you were right about that:

https://www.aulro.com/afvb/images/imported/2018/06/141.jpg

I found the white ball stone to be the most effective although the curve on the sides has been flattened out from use and it's started to take on more of a cylindrical shape now.

Anyways, managed to achieve what I needed with them. I had had the kit for years sitting in a drawer unused so it was just a bonus.

https://www.aulro.com/afvb/images/imported/2018/06/142.jpg
https://www.aulro.com/afvb/images/imported/2018/06/143.jpg

Previously the ID of the hole through the mounting flange was 3mm smaller than the pipe which meant there was a lip possibly disrupting/restricting airflow a bit. The inlet manifold opening hole was also bigger than 60mm, so no reason to be smaller. Now it's been opened up to match although from the photo looking into the inlet manifold it seems there's a lip on the left side of it's inlet (possibly the EGR replacement is not exactly built straight?), but I can live with that as it's better than it was.

[Bigbjorn]

Yep, you were right about that:

https://www.aulro.com/afvb/images/imported/2018/06/141.jpg

I found the white ball stone to be the most effective although the curve on the sides has been flattened out from use and it's started to take on more of a cylindrical shape now.

Anyways, managed to achieve what I needed with them. I had had the kit for years sitting in a drawer unused so it was just a bonus.

https://www.aulro.com/afvb/images/imported/2018/06/142.jpg
https://www.aulro.com/afvb/images/imported/2018/06/143.jpg

Previously the ID of the hole through the mounting flange was 3mm smaller than the pipe which meant there was a lip possibly disrupting/restricting airflow a bit. The inlet manifold opening hole was also bigger than 60mm, so no reason to be smaller. Now it's been opened up to match although from the photo looking into the inlet manifold it seems there's a lip on the left side of it's inlet (possibly the EGR replacement is not exactly built straight?), but I can live with that as it's better than it was.

Aluminium will clog normal double cut TC burrs. For ally work you need aluminium cut burrs which are much coarser with plenty of space for chips in the teeth. TC burrs need to be run flat out. I see hobbyists unfamiliar with their use seemingly afraid to open the throttle. For fine detail and fine finishing use diamond coated points. Slow but favoured by die makers for finishing.

Those air die grinders need a high capacity compressor. They use lots of air to get the cutting speed up where it should be. Using them on the normal 240 v. home workshop compressor means spending a lot of time waiting for the tank to fill again.