Can't get a good finish with HSS

[Wedg1e]

I was on a job in an Aerospace factory about ten years ago and asked one of the machinists if I could blag a Fanta bottle of neat soluble oil: he collared me as we were packing up and slipped a half-full 25L drum of the stuff into the van
I think I've used 2L of it between the lathes and mill... mix it too 'strong' and it leaves the machine sticky to touch.

 

[Maker]

Turn it as a single job, inside/outside, face, part.

That way (as long as you don't move it in the chuck) it'll all be perfectly concentric.

Oh well, at least I'll get some 4 jaw practice.

I had a little play with the carbide tool taking heavier cuts, all left a very nice surface finish but the swarf was definitely much nicer taking a heavier cut.


That's the horrible stringy crap I was getting with a 30 thou cut at 8 thou per rev.


That's 40 thou at the same feed rate, better but not perfect.


50 thou was even better, but I don't think the spindle motor was happy with it, it's 1.5 Kw but running at 20 Hz so suitably downrated. This was also very smokey, the last two were smoking a little but not as bad.

60 thousandths depth feeding at 4 thou per rev was the best of them, no smoke, no unhappy noises from the motor, just tight coils running parallel to the tool before falling down into the tray at the front. 0.07" and 0.08" were the same but with the coils breaking off no longer than an inch long. They were however starting to get a bit smokey and I ran out of material before I could try much more (There's a big hole through the bar).




I did also try 100 thou at 2 thou per rev which left this:



I broke the coolant nozzle I got with the lathe so I'm using a piece of aquarium hose tie wrapped to the tool.


I don't think I'll use it very often, it makes a hell of a mess.

 

[RichardM]

I don't think I'll use it very often, it makes a hell of a mess.

It's the reason I leave the chuck guards on my lathe usually with an apron taped to the end when I had the suds on

Need to make a suds tank and sort a pump for the new one, but it's not high priority. I bought 5 litres of cutting fluid from Silkolene when they had the site in Belper and still have just under half left

 

[Richard.]

Hi @Maker
As none of these lazy s0ds have actually gone to the effort to show you there hss tool profiles to help you out I thought I'd take the liberty to show you the particular one I use. It's my "go to" tool for sizing down before a final skim with an insert. Now I could be doing things completely wrong but as the pros ain't showing you there's it's better than nothing. It took me a good 1/3 of that bar before I got it to a standard I was ok with. Not perfect like the mirror finish I can get with an insert but not too shabby for someone that dabbles. As you can see I keep a little hobby collection of both types.

 

[I'm getting on a bit]

Richard that tool look's like a screwcutting tool you are holding.

But if it works good for you.

Can you explain your reasoning why you rough with hss and finish with an insert tool

 

[Maker]

You've got to top or side rake Richard? How heavy a cut can you take with that?

 

[addjunkie]

http://www.bbssystem.com/manuals/Lathe-Tutorial.pdf

Have a read here

 

[Richard.]

Richard that tool look's like a screwcutting tool you are holding.

But if it works good for you.

Can you explain your reasoning why you rough with hss and finish with an insert tool

Because I'm tight and my lathe gets used for hobby use so time isn't an issue for me. If I was to take all my sizing cuts with carbide inserts I'd go through them much quickly and at 3-5 quid a pop I'd rather use hss bar and dress it when I reck it. I can't get a mirror finish with hss so I finish it with carbide.
Ref the tool shape I'm just a beginner and if it looks incorrect it probably is. It's just the best shape I've managed to find so far to get a reasonable finish on my work. If you can show me a better one I'll be up for trying it as I'm always keen to improve.

 

[Richard.]

You've got to top or side rake Richard? How heavy a cut can you take with that?

That's a piece of case harden able aviation steel
It is quite hard but Machines lovely.
That tool doesn't have any rake your right, I usually put a bit of positive rake on it then file a 2mm rad on the nose. My lathe is tiny. It doesn't do big cuts no matter what tool I'm using or it's not happy it's metric so I would say the biggest I let it cut is 0.25 (1/2mm) off the diameter. I'm never in a rush though and usually happy taking little cuts

 

[I'm getting on a bit]

Because I'm tight and my lathe gets used for hobby use so time isn't an issue for me. If I was to take all my sizing cuts with carbide inserts I'd go through them much quickly and at 3-5 quid a pop I'd rather use hss bar and dress it when I reck it. I can't get a mirror finish with hss so I finish it with carbide.
Ref the tool shape I'm just a beginner and if it looks incorrect it probably is. It's just the best shape I've managed to find so far to get a reasonable finish on my work. If you can show me a better one I'll be up for trying it as I'm always keen to improve.

Yeah I thought it was because you are thrifty.

What size lathe do you have ?

If you could use TPUN inserts you get thirty edges per ten so way cheaper than your paying.

I don't use hss unless I'm cutting grooves for circlips etc

The only thing wrong with the shape you showed would be the amount of grinding involved

 

[Richard.]

What size lathe do you have

It's a little myford ml10. Tiny little thing but I love it.

 

[I'm getting on a bit]

Regarding the TPUN inserts they are designed for turning with only very light facing cuts.

Message to maker and his springy looking swarf, when I was an apprentice we used to have competitions to see who could get them the longest.

But if you want to get then shorter then while you are taking a diameter cut quickly backing off the compound slide Will break the swarf shorter

 

[Maker]

The only thing wrong with the shape you showed would be the amount of grinding involved

When I grind a new tool I start off with a cut off disk in the angle grinder to save time time grinding.

 

[ukracer]

Well they are not going to scream quality at 5 quid a piece with a handful of inserts.

But strangely enough they do work... Lol

 

[ukracer]

I tested my lathe out today for a laugh...
I will post pics later, but I used old shock absorber rod and an insert but whilst I did not mess with setting I was not impressed with the initial finish...

 

[Richard.]

I tested my lathe out today for a laugh...
I will post pics later, but I used old shock absorber rod and an insert but whilst I did not mess with setting I was not impressed with the initial finish...

If there is one thing I've learnt in the short space of time I've had mine and that is any number of things can effect the finish.
Tool tip, tool stick out, tool angle, tool height, tool type, feed speed, rpm, cut depth, material type, material roundness, vibration, lathe wear, and probably more.
I wouldn't worry about it till you start dialing it in for a nice finish.

 

[MattF]

As Richard says, multiple things can affect finish. I have some rod here which I've never managed to get a good finish on without resorting to files or abrasives, for example.

 

[Hood]

First thing I would say is it looks like the insert is knackered, was it new when you tried or was it like that?

Second is how deep did you go? it looks as if you were trying to cut less than the nose Rad of the carbide insert, if so that rarely gets a good finish unless it has a sharp positive edge.

 

[Richard.]

First thing I would say is it looks like the insert is knackered, was it new

I thought that but if you zoom in on it it's not looking too bad actually, just a little discoloured

 

[Hood]

The more I zoom in the more I would say it is knackered
It actually looks like an old style insert/chip breaker as well, often they were very material specific.