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HSS Tool Bit Size

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Blue Heeler26/06/2019 05:46:44
189 forum posts

G'day all,

If you have a 9x20, 10x22, Myford etc sized lathe what size HSS toolbit do you prefer to use?

I do like 1/4" tool size because its a lot quicker to grind and I get a good finish, my QCTP and lathe take up to 1/2" tool size.

To increase my knowledge...its dumb question time thinking

Does the size of the radius (smaller on a smaller tool bit & larger on a larger toolbit) play a part in the final finish ie is there a difference using different sized tool bits?

Cheers all,


Thor26/06/2019 06:23:14
1120 forum posts
31 photos

Hi Jim,

For my small lathe I use 5mm or 6mm square section HSS toolbits, I have a few 8mm for my larger lathe. As you say it is quicker to grind a smaller section toolbit to shape, I only have a small benchgrinder so large section toolbits takes far to long to grind. On my small lathe I even have a tangential toolholder that takes 1/8" toolbits that I use for small jobs.

Nose radius does play a part in the finish you get, I use a diamond hone to round the corner of the cutting edge. A couple of links you may find useful:




JasonB26/06/2019 07:06:26
16288 forum posts
1723 photos
1 articles

Bigger tool will be more rigid particularly if you need to have it sticking out a long way so things like roughing tools are better in a larger cross section but if it's just a small form tool for a special job as you say easier to grind a smaller section tool.

Bigger the corner radius the smoother the finish should be but there comes a point where you can get a wider cut and chatter can become an issue more so on a smaller tool.

larry phelan 126/06/2019 09:47:44
509 forum posts
11 photos

Hi Blue Heeler,

There is no such thing as Dumb question time. As was pointed out to me by Neil, "No question is stupid if you don't know the answer " How true, so ask away, someone here has the answer.

If you think your question is dumb, you should hear some of the ones I have asked !, but the other Members were kind to me and set me right.

My machine is a 6" centre hight and I use 3/8" or 1/2" sq tool bits mostly but sometimes 3/16 1/4" sq. Depends on the job. And yes, rounding the tip does seem to improve the finish but others will give you far more details about this.

Don't be afraid to ask and to have a go, no better way to learn.

Blue Heeler27/06/2019 00:58:27
189 forum posts

Thank you Thor, Jason and Larry much appreciated the posts.

Hopper27/06/2019 02:01:53
3715 forum posts
73 photos

I've gone from using the standard 3/8" square to using 1/4" square on the Myford. Still cuts .100" deep without complaint. As you say, much easier to sharpen, and cheaper to buy.

thaiguzzi27/06/2019 04:32:47
575 forum posts
131 photos

On my Boxford ('Mercan 9 x22" i like bigger is better (and cooler). Minimum 3/8", preferably 1/2" sq HSS.

Pain in the ar#e grinding the initial shape, but once there it's only ever a quick touch up or hone.

And i don't get on with the no name Chinesium stuff - better NOS - S/H Brit/Euro/US brand names.

Clive B27/06/2019 08:23:48
24 forum posts
20 photos


You might also want to consider the following type of holder which uses 3/16" square toolbits:

hss bit holders.jpg

These are very economical with HSS, you can use both ends of a 30mm length, and the 3/16 HSS can be ground very quickly to shape. I tend to use them for small form tools and other odd shaped cutters that don't get a lot of use; the toolbit seems to be held very firmly in the holder - I was a bit sceptical at first. The shank is 1/2" square.

They are available from Chronos, who also do a version for 1/8" sq HSS.


Mick B127/06/2019 09:11:48
1191 forum posts
66 photos

I've got one 1/4" square HSS that I've ground to a full radius (ie. 1/8" - or thereabouts). It'll cut a full radius with no chatter in alli, brass, phosphor bronze or titanium so long as I keep it sharp and the the speed low - don't think I've ever tried it on steel.

For parallel turning, I tend to use a small radius of 15 to 30 thou (-ish). If you want a smooth finish, the radius needs to be a few times the feed rate per rev, or you'll get a miniature furrowed effect. Sometimes that's aesthetically attractive and functionally acceptable, sometimes not.

IanT27/06/2019 09:37:25
1326 forum posts
136 photos


Quite a few replies already here but my few pennies worth for what they are worth.

I've tried to standardise on 3/16th HSS for most turning operations on both my lathes, as people have stated - they are much easier to initially shape and to then keep sharp. I've made various 'sub' toolholders so they fit into my other tool holding devices (e.g. QCTH & Lammas blocks). I've made these adaptors to fit my hand shaper too btw.

I do use larger HSS sections - especially where more tool extension/support is needed - parting or finish turning into crankshafts for instance. Generally, these bits can be kept just for these purposes, so re-sharpening isn't such a problem. I also have a good selection of larger HSS bits for my Atlas shaper - where I use larger sections directly or in traditional angled toolholders. I usual I'm afraid.

With respect to rounding the tool end, it does two things. The first is to help protect the cutting edge - a sharp tip will break more easily and the second is to potentially give a smoother finish. Essentially you want a tip slightly wider than the distance the tool will travel in a single revolution - assuming a fine feed of course. This is also true for shaper tools. Obviously, if you are taking roughing cuts, this latter aspect doesn't apply - but the stronger (rounded) tip still will...

Best way to find out is to experiment a little and see what works for you (and what doesn't) - all part of the fun!



Ian S C27/06/2019 12:23:55
7447 forum posts
230 photos

I normally use 1/4" square HSS for general work, but often use other sizes up to 5/8 as I have some that I got at a very low price, 3/8", 1/2" and 5/8". My first thread cutting tool was made from a bit of a 3/8" square file, it was qyite adequate for steel, the first thread cut was in cast iron(all that I had at the time) 1/2" UNC.

Ian S C

Howard Lewis28/06/2019 23:04:26
2341 forum posts
2 photos

I have used home made Tangential Turning tools with 1/8, and 5/16 HSS toolbits. The commercial Diamond turning tools use 1/4 toolbits. They all work well, in my experience, as long as they are kept sharp.

There have been at least two designs published to use 1/8 HSS bits. My 5/16 one was just a magnified version.

For turning or facing, I use almost nothing else. Will remove metal at almost unbelieveably small cuts.

Sharpening is dead simple, only one face to grind! The holder produces the clearance angles.

The only use of carbide tips is now roughing (100 degree corners of CCMT0604 ) boring, (80 degree corner of CCMT 0604 ) or radius turning (rare ) with 55 degree carbide tip. I suppose that atrainguler, 60 degree tip, or a 55 degree tip can be used for screwcutting. But on the rare occasions, for external Metric threads, I have used a metric thread cutting tip.

Tangential tools get my vote! (Easy to grind HSS so not prone to chipping, and inexpensive )


Blue Heeler28/06/2019 23:29:24
189 forum posts

Howard I've been tempted to buy a Tangential Turning tool for years to try one out.

duncan webster29/06/2019 00:35:13
2234 forum posts
32 photos
Posted by Blue Heeler on 28/06/2019 23:29:24:

Howard I've been tempted to buy a Tangential Turning tool for years to try one out.

Buy one (or make one) you won't regret it

Anthony Knights29/06/2019 06:16:17
272 forum posts
87 photos

I made left and right handed versions of a tangential tool design by Mike Cox and use them for most of my turning operations. HSS bits and dead easy to grind once you have made the jig to hold them. The flat step on top of the RH tool is at centre height for my machine . Makes setting really easy.

rh tool.jpg

old mart30/06/2019 12:07:38
600 forum posts
54 photos

Surely, it depends on the difference in height between the bottom of the toolpost and the centre height. The same goes with a qctp with the holders at their lowest position. The largest shank size that will fit adds to the stiffness.

The 9 X 20 which I use has all of its tools milled down to 17.53mm so as not to need shims, but using this size is rather rare.

Edited By old mart on 30/06/2019 12:08:46

Nicholas Wheeler 130/06/2019 13:57:46
275 forum posts
16 photos
Posted by Anthony Knights on 29/06/2019 06:16:17:

I made left and right handed versions of a tangential tool design by Mike Cox and use them for most of my turning operations. HSS bits and dead easy to grind once you have made the jig to hold them. The flat step on top of the RH tool is at centre height for my machine . Makes setting really easy.

rh tool.jpg

I do a lot of work with just those tools on my 10x22. It will happily make a depth of cut just smaller than the 3mm tool bit, used in a Dixon QCTP. I also use carbide tools(8mm tool holders) and can take at least 4mm DOC in steel without any problems.

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