Angle grinder questions

I previously posted a question about a Harbor Freight 4.5" angle grinder I got which is this model:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber1309
regardless of the quality of Harbor Freight tools, and since I bought it just to work on a small part of a project I did not want to spend too much on it.
I wanted to use it to cut some concrete blocks and it came with a depressed center metal cut off disc, so I went and got a 4.5" diamond blade (which turns out to be about the same price as the grinder itself!) I ran into difficulty installing the diamond blade because with the center not depressed there is no room to put in the locking nut.
Here is a picture of the ginder:
http://i173.photobucket.com/albums/w67/143house/temp/P1010674.jpg
You can see there is a "backing flange" and the locking nut removed.
Closer view of the body showing brand/model:
http://i173.photobucket.com/albums/w67/143house/temp/P1010676.jpg
Now I put back in the backing flange, you can see it is quite deep and almost the same depth:
http://i173.photobucket.com/albums/w67/143house/temp/P1010677.jpg
Now I put on the locking nut:
http://i173.photobucket.com/albums/w67/143house/temp/P1010678.jpg
Some of you suggested that I flip the locking nut around. This will not work, because the tool that tightens the nut needs to be applied to that side with the four small holes.
I then went to HD and looked at their grinders and I do not see a backing flange like the big one I have. I did find this:
http://i173.photobucket.com/albums/w67/143house/temp/P1010679.jpg
a special backing flange.
So it seems like I could use this flange and the diamond blade instead of the original backing flange?
Question #2: why are some blades "continuous" and some are segmented? What are the pros and cons?
Thanks,
MC
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That particular sort of large backing flange is intended only for use with depressed center grinding discs. It's not appropriate for a flat diamond wheel, because it won't grip it in the center
(By the way, this looks exactly like what Makita used to include with their 4.5 inch grinders maybe 5 or more years ago. Makita has now switched to a smaller flange and larger nut, both about 45 mm in diameter, and that's what new grinders come with.)

This is closer, but may not be appropriate for your grinder. The flange is cut in some way to ensure that it doesn't rotate on the grinder shaft, but the method isn't standardized. For example, that DeWalt flange won't work properly on my Makita grinder. So you need something that fits properly on *your* grinder's shaft. I can't tell from the photos what exactly your grinder does to key the flange to the shaft. Makita and Hitachi use two flats on the shaft and a slot in the flange.
Since your HF grinder's flange and nut looks like old Makita gear, they may be a copy of Makita right down to the dimensions. If that's true, a new Makita flange and nut set ought to fit it.
Here's a photo of Makita flanges. You want something like the leftmost one for flat discs like your diamond wheel: http://www.makita.com/menu.php?pg cessory_tbl&tagc_grinder_flanges&cat_tag6&tbl=1&f You also want a larger nut, one that's the same diameter as your new (smaller) flange - not the small original one in your photos. Here are some Makita ones; looks like the leftmost nut probably matches the flange in the previous paragraph: http://www.makita.com/menu.php?pg cessory_tbl&tagc_grinder_lock_nuts&cat_tag7&tbl=2&f To find something that will work, go to a real tool store, one that carries spare parts for name-brand grinders, and find a flange+nut pair that fits your grinder that holds a thin cutoff disc properly.
(Or just buy another grinder with the correct hardware. I have a cheap "Superior" brand 4.5 inch grinder that cost all of $20, and it comes with the correct flange and nut for thin discs. The Makita flange+nut would cost me $10 or more, so a second grinder for $20 isn't a bad deal.)
    Dave
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The HF grinder quality is fine, I say its as good as mine Craftsman or even mine Bosch. The only thing is the Bosh looks much nicer but I couldn't say it works better - from a serious homeowner/handyman perspective ( I use mine 14" wet gas saw for cutting), not a pro.

The depressed cup is used for grinding not cutting, so don't use it for the diamond cutting blade.
I have 7 grinders from various companies, including HF, and all thin cutting blades fit right out of the box without anything more to buy. Don't use the depressed cup for this. There might be a big thick flat washer for the backer plate used for the cutting blades or maybe already build into the grinder. From the picture, looks like the blade could fits in without the depressed cup or you're missing a backing plate. I would guess you're missing a backer plate from HF. The DeWalt backer plate you show will not work.
BTW, three 4" diamond blades for $10 at HF: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?ItemnumberF152

Continuous for wet and segmented for dry cutting.
Pros and cons: The wet cutting blade last longer but its messy either wet or dry with any cutting blades. You could get a nice adjustable speed grinder with a water kit for wet cutting and wet polishing, but HF doesn't have it. I try to use wet cutting whenever possible to save my 14" Hilti blades which cost $125 a pop. Forget about wet cutting when you're cutting tile on the roof. Dry cutting is convenient and no water to fool around with but do ware dust protection.
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MiamiCuse wrote:

cutoff wheels which will fit it almost anyplace that sells power tools.
That's what I use.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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