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A Review of the Diamond Tangential Tool Holder from Eccentric Engineering

I was a skeptic. As were two of my friends who have over 50 years of machining experience between them. But now I’m a believer. As for my friends? Read on …

A few months ago I contacted Gary Sneesby from Eccentric Engineering to see if I could write a review of their Diamond Tool Holder. I had heard great things about tangential tool holders, but I was still a bit skeptical and didn’t know quite what to expect.

The tool took about 10 days to arrive, which I thought was fast considering it came all the way from Australia to Seattle. You can also buy the Diamond tool holder from a local UK or US distributor (see the Eccentric Engineering website for details). Either way the tool is about the same price, but you might get it quicker and pay a bit less for shipping if you order from your local distributer.

The tool comes with a the tool holder, an allen key, a quality HSS tool bit (8% Cobalt), the grinding jig, and full color instructions with pictures to hang by your grinder.

So, how well does it work? Exceptionally well!

Using the Diamond Tool Holder with a round HSS tool bit

Here’s why I think this tool is great for the beginner:

  1. It’s very easy to grind using the included jig.
  2. It produces an exceptional finish. I consistently get as good (or better) a finish using the diamond tool holder than I get using a properly ground HSS tool bit.
  3. It’s very rigid allowing for deeper cuts. I can take cuts of about .015-.025 deep on my small lathe using a conventional HSS tool bit, but I can remove nearly twice as much with the diamond tool holder (.030 to .050) depending on the material I’m cutting – without chatter!
  4. The grinding jig can be used to easily grind 55 and 60 degree threading tools for use with the diamond tool holder.

Eccentric Engineering has a promotional video that they put together that shows all the features of their diamond tool holder. The video seems a little dated, but it’s well done and worth watching.

They show the tool being used on a larger lathe where they take very deep cuts (as much as .100 at a time). I wasn’t able to achieve cuts that aggressive, but I have a much smaller, less rigid lathe in my home shop than what they used in their video. And since many of you have a lathe similar in size to my 10×22, I thought I’d make my own video showing the results I was able to achieve, and therefor the results you should be able to expect with a similar sized lathe.

My video is a bit long (sorry) so if you get impatient just make sure you watch the last 2 or 3 minutes where I show how well the tool cuts cast iron.

My overall impression is a positive one. The tool is well made and of excellent quality. I really do get exceptional results with it. As to the grinding jig, my first impression was that it was a bit wonky with its use of a cap screw to adjust the angle for grinding a threading tool. But after using it I realized that it’s not wonky at all. But rather a simple and elegant solution.

Using the grinding jig is as advertised – extremely simple to do. And the bit seems to hold an edge longer than my hand ground HSS tool bits do. In fact, I’ve been using the original bit for a few months now on Steel, aluminum, brass, bronze, and cast iron and I haven’t needed to re-grind it yet (although I have touched it up occasionally with a diamond hone). Initially I was concerned that the one-size-fits-all approach with the 12 degree rake and relief angles would be very effective on some meals, but less effective on others. After all, a HSS tool bit properly ground for steel has slightly different rake and relief angles than one ground for aluminum or brass. Right? But it turns out that 12 degrees is a very good compromise across all the metals I’ve tried so far.

I don’t have anything negative to say about the diamond tool holder from Eccentric Engineering. It performs as advertised and has exceeded my expectations. In fact, I am planning on purchasing a second one so that I’ll have one tool holder for a square bit and one for a round bit. I tend to switch back and fourth between a round and square bit a lot depending on the job, so it would be nice to have a dedicated quick change tool holder for each pre-set to centerline.

As for my two friends with over 50 years of machining experience? They were impressed too. They haven’t bought their own yet, but then again they get a kick out of grinding their own HSS tool bits and drills. They were convinced that a properly ground HSS bit would give better results than the diamond tool holder.

So I challenged one of them to grind a fresh HSS bit for steel and put their grinding skills to the test. The result? The finish was comparable but the chips coming off of the diamond tool holder were smaller and took more of the heat with them (turning a darker blue) than the chips from the hand ground HSS bit. The lathe (a restored Atlas) also seemed to labor less using the diamond tool holder, and deeper cuts were possible without chatter. I should give credit here to my friend Barry, his HSS bit did produce a similar finish. But he still spent a few minutes grinding it to shape. At least twice as long as it takes to grind one using the diamond tool holder jig.

So if you’re one of those guys that thinks he can grind a drill bit just as good by hand as someone using a professional drill sharpening machine (and I’m not talking Drill Doctor results, I’m talking DAREx) than stick with grinding your HSS tool bits by hand. But for everyone else, I’d highly recommend the diamond tool holder from Eccentric Engineering! You won’t regret it.

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About Tyler

Tyler is a hobby machinist and 3D printing aficionado. He teaches computer programming and web development at Highline College near Seattle. Tyler founded Projects In Metal in 2008 because he was frustrated by the lack of free plans available for hobby machinists.