Can't get the hang of HSS!

For what it's worth Jeremy ...

... Back in’t toolroom in the 50s and adopted frequently during the building of my skeleton clock (and other projects), I used this technique for fine finishing. The result is not unlike JasonB produces. Oh! and for brass in particular, no top rake.

The (HSS) tool tip is modified in line with a technique called diamond turning*. The flat, stoned parallel with the saddle traverse, spans a little more than the pitch of the feed.

Cheers,

Sam

*I haven’t been able to find any reference to 'diamond turning' as applied in this context, but it has nothing to do with diamond as a material, but the faceting.

It may be that folk are confusing using the Diamond Turning Tool (A tangential turning tool ) from Eccentric Engineering, with diamond turning..

It is called the Diamond Tool, because the ground face of the toolbit is diamond shaped.

Quite a few people have made their own tangential turning tools (At least two designs have been published in MEW )

Howard

For clarification, my recollection of ‘diamond turning’ takes me back to either ONC or HNC Mech. Eng.

I can’t be sure if the tool tip was an actual faceted diamond.

The particular facet was set to be parallel with the traverse using a microscope, while the width of the facet spanned the feed pitch.

I seem to recall it was used mainly for aluminium in the aircraft industry, but not sure.

Have fun,

Sam

To me Diamond turning uses a pointed tool that and fairly high feed rate and is mostly used on facing cuts where the combination of feed & speed creates a "thread" which catches the light

I'm a newbie lathe turner and had similar problems trying to get smooth turning, mainly ali and some steel. I've given up on HSS tools for modifying pre-manufactured steel parts because I'm never sure what grade steel is used or its hardness and now use a TCT tipped tool and keep the HSS tools for softer metals. For me, the biggest difference in turned finish came from micro adjusting the WM280V rpm to slower and using a low feed rate until I could achieve a smooth continuous ribbon peel. One continuous ribbon from 30mm dia. ali was 1.5M long.

I had to solve a problem with the Warco lathe first: I noticed there was 'chatter at the tool tip turning some steel. Checks are easier if you have a DRO on both axis of the cross slide table, but mine had bad 'slop'. You can confirm by giving the cross slide a hard push in each direction. If you get a clunk or it moves, you have work to do on the compound gibs and leadscrew to reduce it. If the crossslide has backlash as you turn, you will get a poor finish with very visible tooling marks, because you are relying too much on your hand pressure on the wheel to keep the tool steady as it cuts.

Once you get the compound slop and backlash minimised you can further improve finish by using a lubricant and keeping the work piece cool or letting it cool between breaks.

I'm sure the lathe experts will tell me where I'm going wrong, even though I've had to work things out from first principles.

Often the case Jim, you learn a lot more by trying things out for yourself and finding what works best for your own combination of tools and meterials. There can be so many combinations of factors that affect a job and sometimes the standard rules just don't apply. But still remember that many of these 'rules' have been created by many good engineers over many, many years so are grounded in the real world and apply to the vast majority of tasks..

Not at all, seems sensible to me!

Long ribbons of swarf are debatable though. Pros prefer chips to ribbons because ribbons make swarf control difficult when it's produced in quantity. H&S issues too: I've been smacked the face hard enough to draw blood by a ball of swarf that was catapulted at me the chuck, and avoid sweeping it by hand because it may be razor sharp. I have a WM280 too, and although it's powerful enough to make chips I dislike being showered by smoking hot metal fragments. Ribbons are often a good sign the finish will be acceptable, so I normally go for ribbons.

Carbide is a good choice for unknown metal. Manufactured items are often ground rather than turned or milled, and downright awkward to machine at home. Carbide's extra hardness is a virtue, but don't dismiss HSS which sometimes works better. In some workshops it's always the best bet. Given machinable metal, I find HSS is more tolerant than carbide because the latter is fussier about speed, depth of cut and feed-rate for best results. However, I only use HSS when carbide struggles to get good finish or I need to sneak up to an accurate dimension by taking very fine cuts.

Dave

There is so much good information here - I'm going to put some stock in the lathe and work through everyone's advice and ideas . Dave's comment about the lead screw is interesting - although I haven't managed to crash the saddle yet, the travel has always had a few very slight stalling points. Haven't had the time to work out if it is the travel itself or related to the hand wheel. Turning by hand has always been tricky to do smoothly, have put it down to a lack of practice so far...

Jerry.

I'm afraid first principles have led into a cul-de-sac. My lathe has 15 thou or more backlash on the cross slide, but I still get good finishes; a few microns Ra. Likewise I get good finishes on my repetition lathe, and that doesn't even have leadscrews, just levers. So on the push test backlash is several inches!

Carbide is probably less forgiving than HSS. Often, but not always, carbide requires high surface speeds to get a good finish. Similarly it is possible to take fine depths of cut with carbide and still get a good finish, but it is dependent on material. I run carbide dry, but mostly use flood coolant with HSS. Coolant can improve finish, but conversely it can make things worse, especially with carbide.

Like SoD says ribbons are bad. With carbide tooling it's a myth than small chips lead to a poor finish. Much time and money has been spent designing inserts to break the swarf as it comes off the work. In other words the cut is continuous, leading to a good finish, but the swarf ribbon is broken after leaving the work. That might give the impression of non-continuous cutting. Of course some materials, such as brass and cast iron, are inherently short chipping.

Peruse this: Turning Trials

Andrew

My beginners results taught me that whatever tool type or tool shape you put in the tool holder and expect it to do, each lathe can be different and taking some time to clock what the compound slide is doing, might show errors which can be improved? I know I lack is experience and human operating skills which might allow me to produce good finishes, even when the lathe has some wear or could be better adjusted. I think the results from a Chinese lathe can be better after taking time to do measurements and adjustments on it. Whether it will stay that way is debatable.

One of the first things that we were taught as Apprentices was how to use both hands to turn a handwheel smoothly, to produce a steady feed. It will be worth spending some time time learning the skill.

Even if your lathe has power cross feed, there will be times when a steady handfeed has to be used, usually with the Tposlide offset to turn a short taper, Such as when trimming up a soft centre )..

Then we were taught how to grind HSS tools.

Howard