Some comments about Harbor Freight diamond cutting discs and a question

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ericc

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Some time ago I bought a package of Harbor Freight diamond cutting discs for rotary tools. Those are the ones that come in a multi-pack with a 1/8" mandrel intended for use in a rotary tool. I have not seen any comprehensive reviews on the Web for these tools, so maybe this would be of use. In another thread, I proposed these tools as possible candidates for working with carbide tools. After I tried mine, I quickly discovered that they are cutting wheels, and are too flexible for any meaningful grinding, although there is a pretty band of diamonds around the circumference. They cut pretty well *for a short while*. My first wheel stopped cutting suddenly after about 1/2" or so shaping a boring bar by cutting. It didn't even make sparks. I tried it on several lathe tools, and it had become inactive. Closer investigation and comparison with a new disc showed that there were no more diamonds on the edge. The only diamonds remaining were the cosmetic band attached to the faces of the disc. The rim was completely smooth! A new disc has a rough rim, with the diamonds clearly visible, and it cuts well. The diamonds on the face of the disc are primarily cosmetic and are not aggressive. They will work for some light touch up on a brazed tool, so it is not necessary to discard the set. The "dead" disc can also be used for sharpening a TIG tungsten after it has been contaminated. Another use is for polishing junk inserts so they can be brazed into a bar for further use as a Xynudu-style brazed tool. The polishing helps clean them for brazing later. Clean does make a difference. I used a caliper to check what the inactive disc diameter was compared to a new one. The defunct disc is 0.789" in diameter, while the new disc is 0.802". There is really not much meat on these things!

Here is my question. Do you think I'd have a better experience with the Diablo or Dewalt metal wheels that are found in home improvement stores? Some of these are cutting discs and others are grinding discs. I don't really mind, as long as they have a decent amount of diamonds in them. I don't intend to use them for steel, but some of the wheels indicate that they are suitable for use on steel. The Lennox video shows some aggressive use on steel, which is interesting given the warnings about using diamond on ferrous metals. I did a web search and did not find much information on cross-over uses, Thanks,
 
I use the replacement disk for the HF saw blade sharpener. https://www.harborfreight.com/repla...0-volt-circular-saw-blade-sharpener-98862.htm
I have had the same disk on a 1/15hp 3250 rpm motor for perhaps five or six years. I use it for dressing both HSS and carbide tooling. It doesn't cut as aggressively as a new disk but it still cuts. I have a number of the smaller disks for Dremel type tools and they definitely don't last
 
Look for "diamond rotary grinding wheel" instead of cutting wheel. I got a pack of these from HF and have been using them for taking nicks and gouges out of granite, but they should work fine for carbide tools as well. Make sure you spray with water, and don't force them into the work, just touch the work with the grinding wheel. Not sure if these are the ones I bought but they are not dissimilar.

For getting an edge on carbide tools I've been using diamond hones - the credit-card sized ones work great. Can't do a lot of reshaping of course. For that I guess I would use diamond rotary bits, and probably some diamond needle files for cleanup.

As for your question, no I do not think the pricier diamond cutting discs would work better. You want a grinding wheel, not a cutting disc.So maybe 1/4" thick or greater, with the diamonds on the circumference not the perimeter.
 
Hi thinwoodsman. Thanks for the suggestion. I was kind of in a hurry when I bought these. Actually I was doing something more like cutting, since I was repurposing large broken inserts for a small braised boring bar. I was kind of annoyed that the diamonds didn't go down far, but the price was much lower than the real Dremel wheel.

What I was really asking was do the 4-1/2" angle grinder wheels have proportionally more diamonds. I saw a comparison video which suggests that they do. If I try, I'll report back.
 
Thanks, RJ. I was looking at that one. I would need to rig up a slower motor to make use of it.
 
Diamond cutting wheels are not great for steel - carbon is soluble in steel at high temperatures so the diamonds dissolve. They're great for grinding things other than steel, and can be used on steel at low temperatures.
 
I just bought the saw sharpener. That JR got the wheels for. It is cheap enough with a coupon.

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I've used those little HF diamond wheels alot. Mostly for sharpening/ touching up carbide inserts and brazed carbide lathe tools, but I used one to neck down a long read 1/2" carbide end mill the other day. Not by much, a few thou at most, but it worked just fine. I tend to use the face the most. I have a feeling that the thin edge wouldn't work for all that long as there's not a very thick coating of diamond on these.
 
I kludged together a grinder, based on a discarded ceiling fan motor, that uses either the 4" Harbor Freight wheel or a diamond "compound" conical wheel from Amazon/eBay. It turns about 400 RPM and includes a water drip, so no problem grinding on steel. Maybe a bit slow. I'd originally intended it for shaping glass, and it does a bang-up job for that purpose.
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400 RPM? That is giving me some ideas.

I've been getting into refurbing old manual tools this spring (hand-crank drill press, that sort of thing), and one of the items I picked up is a hand-cranked bench-mount grinder. Intended for knives and chisels, can handle up to a 6" wheel (original is 5" I think).

Would be interesting to try a diamond wheel on it, once I turn some true bushings and replace the toolrest. I initially ruled it out as I had read somewhere that diamond wheels have to be run at something like 3K rpm.
 
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