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Home > Product Reviews > A Review of the Diamond Tangential Tool Holder from Eccentric Engineering

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.


  1. After reading these pages, bought a diamond tool holder from eccentric engineering.  Only took a few days to arrive in mail (I live in Australia.) 

    On my little Sieg C3 lathe, the tool overhang was hitting the top slide below the turret tool holder and with the tool pulled hard back against the tool holder, could not rotate the tool holder turret for correct facing angle.  Ended up milling away a small area of the tool underneath to allow the turret to rotate without having to rotate the top slide.  Really easy to flip between cutting and facing angles now by just rotating the tool holder turret.  I don't have a quick change tool holder

    Another small issue was that the size of the tool extending from the tool holder severely reduced the size of bar that could be cut even with the tool pulled back hard against the tool holder.  Not much travel on cross slide on these mini lathes.  I could rotate the top slide at a 45 deg angle to move the tool further back and re-align the tool holder turret back by 45 deg but this took away the ability to use the top slide for cutting angles.

    Discovered that the cross slide had almost an inch of lead screw thread hidden away unused and by some more milling to the lathe carriage to expose all the lead screw thread and a spacer managed to extend the cross slide travel enough to more than make up for the additional size of the tool.

    Tool itself is fantastic, cuts stainless bar like butter, brass looks almost polished and I can finally adjust tool height without having to shim up the tools in the turret with broken hacksaw blades.  First facing operation all the way to the exact centre. Yes!!!

    Made a cam lock for tailstock out of stainless and brass as a first test of the tool today and only area that was a bit difficult was the one shoulder of the stainless steel cam (cutting away from the chuck).  Didn't want to flip the workpiece around and try recentre the cam with it's offset.  Probably should have used another tool to finish off that shoulder but it's all working well and cam is hidden anyway.

    Hope that all makes sense as this is a fairly new hobby for me, just thought I would throw in a mini lathe perspective.



  2. Thanks Simon, I'm glad the tool is working out for you! It's a bummer that you had to modify things to make it work. Did you get the smallest tool they sell?

  3. No I got the second smallest going by the dimension guide on the website, (measured from base of tool holder to lathe centre height.) 

    Smallest one may work better on the Sieg C3 and they do mention Sieg in the text against it but there are different size sieg lathes and I though it best to follow the website selection guide sizes.

    I get more out of my lathe now through some forced mods, a quality tool holder and a bit more comfortable with the lathe's inner workings so a good experience all round



  4.   I have some more experience with tangential bit-holders now, having

    • made a dovetailed version of Richard's design (see my post of 27 December for a list of the various available designs),
    • bought a pre-made tool (their model A8) from Eccentric Engineering, and
    • made a dovetailed clone of the Eccentric version.


      I wouldn't recommend any of the one-part designs (Richard's, Barry's, Jraah's, or Gadgetbuilder's).  At least in my implementation of Richard's design, the screw's grip on the bit is marginal, successful with some screws but not with others [this is consistent with the comment from Eccentric Engineering, quoted in Tyler's post of 21 December].  Also, Richard's design holds the bit so high that there are clearance problems on a small lathe like my C4.


      The Eccentric design is much more satisfactory.  I can't tell any difference in rigidity between my clone (made of 1018 steel) and the hardened 4140 Eccentric version. 


      I found cloning the Eccentric design to be challenging, and it would have been much harder without a model to copy.  There are lots of complex 3-D angles; I found myself using setup strategies (vise-in-a vise, tilted mill head, angle blocks everywhere) that, to say the least, I don't use every day.  Fun.

  5. That's good to know Fenichel, 

    I think a lot of people were convinced that it would be an easy project to make their own. You've seen first hand that it's not as easy as one might think. Thanks for sharing your experience. Any chance of seeing some pictures of your handywork? I'd like to see how the three different designs turned out. 

  6. Tyler said:

    I think a lot of people were convinced that it would be an easy project to make their own. You've seen first hand that it's not as easy as one might think. Thanks for sharing your experience. Any chance of seeing some pictures of your handywork? I'd like to see how the three different designs turned out. 

    It was not easy, but only because it required the patience for lots of setup.  It required no great attention to precision, especially if one ignores the dovetail.  One should not be intimidated by it; no matter how many tangential bit holders you want to have, I'd recommend that you buy at most one.

      Here's a top view of (top to bottom) the Eccentric product, my clone, and my implementation of Richard's design.

    Here they are from their right sides

    and here are the Eccentric product and my clone from their left sides, with their clamping elements separated.

  7. Hey Tyler, Which size toolholder did you get from eccentric for your G0602?

  8. I got the 9.5mm tool. LH and RH. It's the one recommended for 9″ lathes, and since mine is a 10″ it's just about the perfect size. I think the 12mm would be too large.