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Thread: Grinding wheel

  1. #1
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    Default Grinding wheel

    I'd be grateful if someone would take the time to tell me if either of the grinding wheel I have are suitable for reshaping a carbide insert I have. I want to repurpose the insert for cutting a custom thread. normally I manually use aldi diamond blocks for sharpening carbide but I need to take quite a lot off this time.
    I collect useful things when I see them and they are cheap and I found I have two wheels I hope are suitable. I believe I want silicon carbide not aluminium oxide which is the common abrasive. According to the sites I read, the first letters on the wheel are the abrasive code. The sites all mention that A is for aluminium Oxide or S for silicon carbide. I tried searching for the codes on these two but couldn't find anything useful. I'm hoping the C stands for carbide

    20170210_191011.jpg

    One says GC 120 J11 VR and the other RC 80 P8 VR.

    Both have their paper washers intact and both have a nice ring to them so I think they are in good condition.

    I also need to make spacers for them. the shaft is a bit under 17mm and the hole in the wheel is a bit over 24mm so about 3.5mm thick spacers. What is best to make those spacers from? I have a plastic rod which has a label on it "wearlon" looks like black polythene to me. or I have aluminium or steel if that's better, or a combination of both? I wondered if the plastic would be a bit soft and allow it to move a bit.

  2. #2
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    Mount them and try them. Your tap test reminded me of something this farm boy learnt many years ago about mounting some old wheel bought at an auction - Stand well back from the direction debris might go when you first start and preferably start from the wall switch whilst keeping your hand near the off in case of load noises. Then let run for some time before use. Probably get a bit of scrap pipe and stand off to the side and grind it a bit and see what happens. I still have a habit of standing off side to the wheel.

  3. #3
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    You need Green grit Silicon Carbide wheels for grinding carbide tools, though diamond or CBN is better. I don't think either of the wheels shown in your picture are suitable.
    The use of plastic for the wheel hub spacer is quite common, but use metal to clamp the wheel to the shaft. When I'm making fittings for grinding wheels I make one of the clamp plates with a bush that fits into the wheel, then I keep that clamp plate with the wheel for future use.

    For "Clamp plate" read "Flange" Thanks Michael.
    Best Regards:
    Baron J.

  4. #4
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    From the Carborundum book I have, the first is a silicon carbide wheel (GC) with 120 grit size, a J bond and a special structure with a vitrified bond.
    The second is also silicon carbide, 80 grit with a harder bond (P), and an open vitrified bond.

    That first wheel has a bore of 1 1/4", roughly 32mm. Sleeving it to get to 17mm may be a bit much. Typically that wheel would be used on a surface grinder as that is the 'standard' bore for smaller SG wheels. The second is the type that is more likely to be found on a bench grinder. The spacer is to keep the wheel centred as the flanges are what holds the wheels and transmits the torque. Plastic is used for them a lot these days.

    (NB - GC = Green Grit according to the book)

    Michael
    Last edited by Michael G; 10th Feb 2017 at 09:52 PM. Reason: more info

  5. #5
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    Thanks for the comments. I guess you are right that there's not too much harm in trying them. However I also agree that everything I read said silicon carbide is green or black and these are both grey which is confusing.

    I've spent some more time searching. If I look up grinding wheel and RC I get hits where RC relates to the hardness of the steel eg RC 55 hardness steel, nothing on the abrasive. GC seems to bring up some hits that mention grinding wheels for sale for extra hard alloys but I couldn't see anything that mentioned abrasive type. I did notice however, the wheels both have the word carborundum on them. I looked up what that was and its another name for silicon carbide. Maybe its just the name of the company though. I did find something that said silicon carbide could be listed as C so maybe its silicon carbide. I just go round in circles so I think I will just try one.

    I came across a thing that said to be very careful with grinding wheels especially on startup and said exactly the same as ybaf, ie stand to the side when starting and as much as possible even when working. It said they are most likely to explode on start up especially when newly fitted. I've got a leather apron and full face mask I'll use especially since the history of these is unknown.

    There's a bit out there on making sure you use the paper washers or make your own, to grip the wheel. If you miss them out that's another thing that can cause them to break up apparently. Anyway, I think because the wheel is gripped from the side on the paper washers, I should be fine to use a plastic spacer.

  6. #6
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    Thanks for the info Michael, that gives me more confidence. I didn't want to burn my way through my insert, which is what I perhaps naively though might happen if it was the wrong abrasive.
    I only measured the centre of the bigger wheel, but I see now what you mean about the centre of the smaller one. I'll fit the big one and give it a go. Odd that they are grey, it seems everything says silicon carbide is green.

  7. #7
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    The words 'Carborundum' on the stones is the company name of the manufacturer, not the material or the purpose. Caborundum inc. is now owned by Saint Gobain, just as is Norton Abrasives.
    I too say "go with trying it" - but you will be much better served with a diamond wheel (not CBN! that's for hard steel). They are now very cheap out of Hongkong. Try a cheap one and you won't go back.
    Cheers, Joe
    retired - less energy, more time to contemplate projects and more shed time....

  8. #8
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    Quote Originally Posted by Michael G View Post
    That first wheel has a bore of 1 1/4", roughly 32mm. Sleeving it to get to 17mm may be a bit much.

    Michael
    G'day Michael, I'm curious as to why you feel that busing may be a bit too much? Not disputing it BTW, just to keep learning and looking for something I may not have thought of.

    Keep your hand on the power switch "in case of unusual noises" if it makes you feel better, but I can assure you it won't do one iota of good if a wheel explodes. I've never personally had a grinding wheel explode, but have other smaller things with less energy let go, and all you hear (if you're lucky) is a bang and that's it. There is nothing left on the arbour so it's not like it's shaking about. If anything I think it's not the best advice as it suggests you may somehow be able to intervene and get a warning, and that could lead to some unsafe practices. In my experience with catastrophic failures there's no warning at all and all you hear is the bang and the feel for remaining body parts/check undies! I pulled a piece from my lathe chuck the other night and it was a reminder how quickly things go pear shaped. I hadn't done that for years, and it was completely my own fault, getting impatient with an interrupted cut where I needed to take off a lot of material. No great harm done other than my pride, and a good reminder not to be so stupid. Again, no warning, just the bang and a glimpse of a part bouncing around the lathe chip pan at high speed. Unlike industry we don't have people looking over our shoulder helping to make sure we don't kill ourselves. I like these types of threads every now and then as a reminder to take care of our own safety. I have a grinder with a guard partially removed and a mental reminder to put the side of it back on. I'll now do that without further delay as there's no good reason to be so lazy with that side of things. As my mum used to say to us as kids, "It's all fun until somebody loses an eye!"

  9. #9
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    Simply because you are going from 17mm to 32mm, so you are adding 7.5mm per side on a 1/4" thick wheel. If the grinder flanges are big enough to clamp on grinding wheel then it should be alright but I can't ever recall seeing a spacer of those proportions supplied commercially. The first safety video I was ever shown was the results of a grinding wheel 'exploding' - it did have an impression because I've always approached the process with a deal of caution since.

    Personally I wouldn't (see previous sentence), but if I absolutely had to use a thin wheel with that size bore on a shaft that size, any spacer I made would be of a stiffish plastic (acetal or similar) rather than something like PE to minimise the possibility of the spacer extruding and going out of round.

    Michael

  10. #10
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    The best thing since sliced bread for touching up carbide inserts is a 3000 grit diamond lap disk.

    Grit 3000 Diamond coated 6" inch Flat Lap wheel Lapidary grinding polishing disc | eBay

    I've purchased direct from THK's website before, but I'd recommend against it at the moment, I get security alerts when I try to access it.

    As far as the wheels you've already got, I've got some of those grey carborundum wheels, I think they came with the grinder originally 30 years ago. I never realised they were Silicon Carbide? Wikipedia tells me that pure SiC is colourless, and the black colour is caused by iron impurities, so I guess that the grey silicon carbide wheels are actually black silicon carbide with a binder that makes it look grey. No idea what causes the colour in green silicon carbide.

  11. #11
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    Ok thanks Michael, I agree I haven't seen anything sold that size commercially, but I'd have to check my bushes as the chances are I probably bush wheels down a reasonable amount as I have various grinders. I normally make my bushes a snug fit to both the wheel and the arbor, use PE and haven't seen an issue, but as you say the flanges would need to contact the paper properly on the wheel.

    It's a shame nobody has caught footage of an actual wheel explosion (at least not that I'm aware of) in real time as I've heard they're rather "spectacular" when they fail, to say the least. I saw one on Youtube that shows them in slow motion but I don't think that conveys just how quickly this all happens. I won't post a link as it's rather graphic. I've spoken to people who have had it happen though and they needed to sit down for a quiet cuppa and pants check for a while after I've seen footage of "blade off" jet engine testing, the forces in high speed rotating parts are quite unbelievable and a testament to engineering that the shrapnel can be contained. I've often wondered if, in the event of a grinder wheel exploding whether things like plastic visors etc would only add to the pieces doing damage.

    Anyway, sorry for the thread drift.

  12. #12
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    Quote Originally Posted by sossity View Post
    Thanks for the comments. I guess you are right that there's not too much harm in trying them. However I also agree that everything I read said silicon carbide is green or black and these are both grey which is confusing.

    I've spent some more time searching. If I look up grinding wheel and RC I get hits where RC relates to the hardness of the steel eg RC 55 hardness steel, nothing on the abrasive. GC seems to bring up some hits that mention grinding wheels for sale for extra hard alloys but I couldn't see anything that mentioned abrasive type. I did notice however, the wheels both have the word carborundum on them. I looked up what that was and its another name for silicon carbide. Maybe its just the name of the company though. I did find something that said silicon carbide could be listed as C so maybe its silicon carbide. I just go round in circles so I think I will just try one.
    There is an ISO standard nomenclature that should be used for grinding wheel. Unfortunately your wheels do not follow it.

    A common wheel number everyone has seen or heard of is 38A. Which is a type of aluminium oxide. Silicon carbide for green the code is 39C and black 37C
    Gold, the colour of choice for the discerning person.

  13. #13
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    I bought these last weekend for 10c a piece.





    Does this help?
    ..Live a Quiet Life & Work with your Hands

  14. #14
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    ..Live a Quiet Life & Work with your Hands

  15. #15
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    ..Live a Quiet Life & Work with your Hands

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