-
Welcome back Guest! Did you know you can mentor other members here at H-M? If not, please check out our Relaunch of Hobby Machinist Mentoring Program!
Lathe Tool Holders
- Thread starter redvan22
- Start date
- Joined
- Dec 18, 2022
- Messages
- 2,584
Yes, yes they were.... is why I paid the price, I am not certain anyone else makes inserts for this particular parting blade...
- Joined
- Dec 18, 2022
- Messages
- 2,584
If you have bad equipment then I am not certain what to tell you, if your referring to mine I paid almost 6000 for it before adding any tooling. I am not sold on the idea that HSS is the answer for everything, I get it, some folks like HSS, I use it for some applications but not everything. As far as tool pressure goes, you can reduce it by taking lighter cuts and slowing down your machine feed. I know 2 guys who bought a Harbor Freight 8x16 lathe and they are running the standard tool post (not a QCTP) with 1/4" tool holders using carbide inserts turning bushings and they have no issues with it.Putting a $100 tool with inserts on a $300 lathe will get you no-where .
Last edited:
- Joined
- Sep 1, 2023
- Messages
- 997
( @Huub Buis , just quoting your post to provide context, not specifically replying to you
)I think there's an important point hidden in those insert specs, that I've highlighted, that I reckon is worth talking about.
Nobody has specifically focused on nose radius yet, so given my limited recent experience on my little 7x14, I thought I'd mention it.
From what I gather (and have experienced myself, more of which in a bit), getting decent results out of mini lathes is all about tool pressure. As in, we want as little tool pressure as we can, whilst still removing the necessary material as efficiently as we can get away with (time being the one thing we can't buy more of!).
One important factor in tool pressure is the nose radius of the tool. For carbide inserts, the ISO specification has 12 values. Of these 12 possible radii, us mini lathe users (unless maybe we've made notable rigidity/torque modifications to our mini lathes) should probably be using the smallest three: up to 04 (although, in my limited searching, I've not come across 01 and 02 radius inserts for sale; having rambled on in this post about it, I'm going to have a more thorough search now, though. EDIT: Oh, apparently there are tons on offer; I must have been temporarily blind!)
The good thing about an HSS tool is that the nose radius of the tool is limited only by what one wants it to be and one's skills with a stone (no way am I going to be able to get a reliable and repeatable nose radius on my bench grinder with my grinding skills as they are!). The pre-ground HSS tool sets that I've seen also tend to have very minimal if any nose radii.
With inserts, as a beginner, it's very easy to accidentally buy the wrong insert, since, there are 9 ways of getting it wrong as opposed to 3 ways of getting it right!
A few weeks ago, I decided to try out some inserts (DCGT) that I had on some brass. I can easily manage 0.050" DOC with a sensible manual feed at 800 RPM-odd on my 7x14 using HSS, when turning brass, so I figured I'd start off with 0.025" to see what was what.
It was chatter city. I then looked at the spec of these inserts and I then noticed I'd picked up the wrong box. I'd picked up a box with 08 radius I'd ordered by accident, instead of the correct 04 radius box I intended to use. That's twice the radius; meaning...um, well, I don't precisely know (twice the tool pressure? Some power of the tool pressure? I expect someone will tell me) but it's more than was good!
Switched inserts and happily managed the 0.050" DOC.
Mind you, I immediately switched back to my HSS tool, simply because I love using tools I created, even one as simple as a RH turning tool: it definitely compounds the gratification.
(Also, HSS tools are less likely to chip when used by a clumsy eejit like me, so that's another benefit
)
Last edited:
- Joined
- May 16, 2016
- Messages
- 1,703
Be aware that insert tooling can sometimes cause more poblems than it solves, especialy on a min lathe. The problem is that most mini lathes lack the rigidity aand the HP that is required to use insert tooling. This can be partly overcome by careful selection of the inserts. AS has been suggeswted get a copy of D Bests book on the subject, but also learn how to correctly sharpen HSS tools. They are your best friend.
- Joined
- Jan 31, 2016
- Messages
- 12,794
Iscar makes the best cutoff tools I've ever used . They are aggressive tools which are not suited for smallerish lathes . ( not meaning yours ) If the Iscars don't work when properly used , there is another issue somewhere in the chain . I've seen people rip their compounds off the machine and blame the cutter for instance . FWIW , I own nothing but Iscar , and quite a few of them at that . As far as the inserts , I always use Iscars also .
- Joined
- Sep 1, 2023
- Messages
- 997
To be fair, David's book, whilst a brilliant primer and completely worth the price, is aimed at people who own slightly larger lathes than the mini lathes (10"-14" swing, if I remember correctly; hopefully someone will correct any failure of my memory). These lathes tend to have a bit more rigidity and oomph.
OP should still get the book and read it of course (it really is great), but they'll need to mentally accommodate the more modest capabilities of mini lathes whilst reading it.
- Joined
- Dec 18, 2022
- Messages
- 2,584
I very much like the Iscar parting blade I have, it is very thin .060 so I am always careful to make certain it is perpendicular to my work piece and it cuts smooth as butter (actually makes me feel good when I use it). I am currently setting up a holder for a HSS blade which I want to use as a wide grooving tool where I can control the shape better, for o-rings you want a small radius in the bottom corners.
A larger tool nose radius will make a longer (twice the radius equals = twice the cutting edge length) cutting edge. That longer cutting edge will increase radial and axial cutting forces especially on steel (less on aluminum). Once you cut deeper than the nose radius, radial cutting forces don't increase any more and the stock will not deflect more when you take a deeper cut what makes getting to a tight dimension easier. The stock can absorb axial cutting forces (stock is a pillar) easy (easier) so that is a lesser problem. This is why generally you should cut deeper than the tool nose radius.
To reduce the cutting forces (axial and radial) you can reduce the feed rate. The advantage of deeper cuts is that chip breaking improves. For tool life it makes "no" difference cutting twice shallow and fast or once deep and slow. As long as the feed/rev is enough to prevent rubbing, you can reduce the feed rate to increase cutting depth.
If you have small diameter stock, than you have to reduce depth of cut way down the tool nose radius or the part will flex. On a non rigid mini lathe you quickly reach the cutting depth limit.
On my mini lathe I generally use the 04 (0.4 mm) type inserts because the 02 (0.2 mm) type inserts are often quit expensive. I use DCGT and CCGT 02 inserts for cutting steel when all other options fail. Also in my not so rigid boring head (mill), I use these G 02 type inserts.