John has asked me to give a few pointers about the above operation because it seems that a lot of beginners have so much trouble with it.
I have a bit of a personal opinion about parting off or grooving, both basically the same thing, just that one goes a bit further into the metal than the other.
That is, you either love it, or hate it, find it easy, or struggle endlessly. There is no real ‘in between’.
In industry, parting off is just another everyday turning operation, no different to turning down to size or facing off. But there is a major difference.
Industrial machines are invariably vastly superior with regards to tool rigidity, whereas the smaller sized machines used in the amateur workshop could be classed as being made of rubber compared to the big boys.
So I am going to attempt to show how a few little tricks may be able to help you with this controversial machining operation. Unfortunately, I can’t cover absolutely everything, just the tools and tricks I have been involved with. I am sure there are a lot more people who have different ways about going about things and get good results.
The first thing that baffles people is the vast array of tooling available, and I will make a personal point here. There is no “be all and end all” tool, you use certain tools for certain types of parting off and grooving. This is just a small array of the tooling I have in my arsenal to achieve what I want, and this is no tool boast, I really do use everything shown here to their full effect, and this is growing all the time, as I come across more and more operations that need to be done. I will now try to explain which is used where on the selection I have shown.
I am lucky in that I can machine grind my own small tools, and I use these mainly for grooving fins on cylinders, parting off small diameters and tubes. They are also very handy when you get a little short on material, as the wastage is down to absolute minimum. The small ones at the front are most probably about 0.5mm (0.020”) width, but I have no trouble with breakage, as they impart very little cutting pressure, and so they seem to last forever. These will easily part off up to 12mm diameter brass or aluminium bar.
These are not all my parting tools, I also use brazed tip and larger ground up HSS bits. Just depending what the job calls for, I could go on forever, but would only confuse you more.
These are used in commercial workshops, and easily part off a 75mm (3”) bar of almost any material. I have a pair of these, right handed and left handed, and if bought at full price, a pair would easily cost more than the price of a mini lathe. But you must have a lathe that can take the cutting forces (more on that later). These were purchased off a well known auction site for around £70 for the pair, and I also bought a few spare inserts as well, just in case they go out of fashion and become unavailable.
As I have said, there are all sorts of weird and wonderful types on the market, especially the replaceable tipped variety, and a few definitely look like they are a bit gimmicky in the way they work and hold the tips. I have had varying feedback on the new blade type with the slot in tips, some say they are OK, others that they are just not rigid enough with the tips flying out at inopportune moments.
So these are the sorts of tools that are available, it must be your decision what type you want to use. They all seem to work in their own little way, just that some definitely work a lot better than others.
If it was left to me for just a couple of general purpose ones, the bladed HSS type and the “Q” cut would be on the top of my list. Backed up with hand ground ones.
I use fairly large tool holders, and this shows that with a little care, these small tool bits can be held rigidly and safely.
This is a commercially made tool holder, designed for holding the replaceable blade type. You will notice I have used a couple of extra screws to assist in holding the blades, as sometimes, if they are cutting to larger depths, the blades can move. I find they are good enough up to about 50mm in the softer steels (EN 1A) but do suffer sometimes with the blades snatching down as they are fairly unsupported on the nose.
Now this is one tool that I do thoroughly recommend. These have been available for many years now, but I have only been using one for a couple of years. If I had tried them earlier, with my old lathe, they would definitely have sorted a lot of my problems. Unfortunately they are a little limited in their depth of cut. But for the average user, they are great.
Thank you for this.
I am at the timid end of the spectrum in this subject.
I use a Hobbymat MD65 but the problems I have had are mine and mine alone.
Much food for thought and thank you for it.