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Thread: Angle Grinder Abrasive Discs
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8th Jul 2019, 10:35 AM #16Member: Blue and white apron brigade
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The Josco ceramic flap discs can have the worn outer edges of the flaps and plastic backing disc pared back to expose fresh flap edges. I wonder if a 115 mm disc could be pared back enough to fit on a 100 mm grinder although there might be a spindle mounting difference?
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8th Jul 2019, 01:08 PM #17Member
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8th Jul 2019, 05:59 PM #18Diamond Member
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+1 for Smith and Arrow. Ben at Smith and Arrow was offering a discount to forum members, not sure if this is still the case, but within the last year, he came to the party for me and our Mens Shed when I sent in an order. I had good and friendly service and would happily recommend them to anyone. They also have ceramic flap discs in limited grits, at least they did at the time, not certain what the situation is now.
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8th Jul 2019, 06:25 PM #19
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8th Jul 2019, 06:28 PM #20Senior Member
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Smith and Arrow are the ones I use to deal with.
Its been a couple of years since I last bought anything from them but they seem to have expanded their product range.
Tony
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8th Jul 2019, 07:02 PM #21Best Regards:
Baron J.
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8th Jul 2019, 07:22 PM #22
...although the 115mm (4.5") discs have a 22mm centre hole, whereas the 100mm 4" have a 16mm. Did you find that the nut and back plate on the spindle were the same?
My 5" grinders have a M14 spindle, whereas the 4" are M10 or thereabouts.
That being said, I've never owned a dedicated 115mm (4.5") grinder. 4's or 5's for me.
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9th Jul 2019, 06:11 AM #23
Hi,
I was going to reply earlier, but decided to check and make sure first. I have to confess that all the discs that I have, flap, grinding and thin cutting ones of both 100 mm and 115 mm size, all have 22.32 mm spindle holes. Only the 100 mm steel diamond coated edge ones, for the tile cutting machine have a smaller spindle hole.
I've recently bought some 180 mm abrasive discs and they have the same size hole in them as well !Best Regards:
Baron J.
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9th Jul 2019, 08:13 AM #24
What brand discs, particularly the 100mm ones, did you look at? I am almost certain that 100mm has the 16mm hole, 115 and up (excluding the larger abrasive cutoff saw wheels 350mm+ dia) run the 22mm centre.
Fitting the 7" on a 5" grinder is an old trick. AKA the widowmaker. So is running 9" wheels down to 5" then wearing them out on a smaller grinder. Issue being the wheel max RPM at the cutting edge is not respected, and they can potentially fly apart... I'm told. I wouldn't like to find out.
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9th Jul 2019, 09:06 AM #25Member: Blue and white apron brigade
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Provided the same grinding wheel materials are used, as well as optimal cutting speeds, the specced max RPMs for wheels are related to the forces involved required to hold the wheel together.
The specced RPMs are for the maximum forces which is when the wheel is at its max size ie before it starts to wear.
When the radius of a wheel is reduced, at the same RPM, the force applied to the outer edge of the wheel is also reduced so these wheels can safely run at a higher RPMs and not fall apart.
It even makes sense to spin smaller wheels faster because then they run at their optimal linear speed for grinding and cutting. If they are not spun faster the material won't be removed as quickly and so the tendency is to push them harder which makes the wheel wear quicker as well as increasing the chances of breakage.
Here is a graph of manufacturer specced cutting wheel RPMs versus wheel diameter (blue triangles and LHS axis). As wheel size is reduced the speeds increase dramatically but they almost all end up having the same linear speed (red squares RHS axis) of 80 m/s second. The odd one out is a special Dremel wheel.
prmVdiam.jpg
Same applies to grinding wheels, as they wear they can be spun faster which (as long as you know what you are doing) is another good reason to have variable speed on a grinder. The old Atkins pedestal grinder I had, had its motor in the base and had pulleys and belt fitted up to another set of pulleys on its spindle so the speeds could be changed.
My home made thin kerf cutting wheel mini table saw uses 125mm discs and is mounted on a grinding wheel on a VFD so when the wheel gets smaller I can spin it faster.
guard2.jpg
Probably the main reason this is not available as standard on grinders is the average ningnong would just abuse the speeds and destroy the wheel and possibly themselves.
It's interesting that motor vehicles are not governed for speed to anywhere near the same degree.
Same with wood lathes where inexperienced wood turners load up a large irregular lump of wood and then spin it too fast and wear the lump in the side of their head.
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9th Jul 2019, 10:51 AM #26
A couple of my 5 inch grinders have variable speed, there usually sold for polishing sanding grinding.
Never had a problem using quality worn 9 inch grinding wheels in a 5inch many years ago.
My mate worked at a tank fabrication place where they beveled up to 20mm plate for the auto welder and would bring boxes home for me. The boss had no problem with it as to them there now rubbish.Using Tapatalk
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