Could a bad finish be caused by bad steel?

[Maker]

I was turning a bar down earlier and I couldn't for the life of me get a nice finish. Using a tool* that had worked nicely before left a rough finish, no matter the speed of the chuck or the feed. The bar was cut off of a car wheel spanner. Could it be that it was just cheap, crappy steel or is there something I'm missing?

*I resharpened it with no noticeable effect so I tried polishing it slightly on a wet stone for woodworking chisels and it was ever so slightly better but still unacceptable.

 

[MattF]

Some stuff just flat out refuses to take a nice finish. I have some old iron rod here which is the same. Love the stuff, but it gives a finish like cack. Files and emery cloth are your friends, in this scenario.

 

[roofman]

some types of steel turn really nasty no matter what combo you use...old bed iron type stuff is horrible and often used in bolts ect

 

[MattH]

Sometimes it can be the material but other times you can get a better finish by taking a much heavier cut. Often you think you should speed up and take lighter cuts but a heavy strong chip can give a clean finish.

 

[Hitch]

Plain black steel bar isn't very good for turning.

 

[roofman]

on the other side of the coin usually ally bar of any describtion is a dream to turn (except for the cutting curlys) but i have about 10 Kilo of round stock which is like turning warm toffy...going to scrap it out as its useless

 

[Maker]

I'll chuck it out then. I only used it as I needed 13 mm diameter so I had the choice between this, some rebar or some 1 1/4" bar.

Has anyone turned rebar before? I did a couple of days ago and once all the ribs were gone, it machined quite nicely.

Sometimes it can be the material but other times you can get a better finish by taking a much heavier cut. Often you think you should speed up and take lighter cuts but a heavy strong chip can give a clean finish.

What is considered a heavy cut? I had usually taken no more than 0.01" (off the radius) on steel but I was playing yesterday with this tool on good steel and was able to comfortably get 0.025" (I think it was 0.004" per rev feedrate) which I thought was very impressive.

 

[Spark plug]

on the other side of the coin usually ally bar of any describtion is a dream to turn (except for the cutting curlys) but i have about 10 Kilo of round stock which is like turning warm toffy...going to scrap it out as its useless

I find with aluminium like that you need a razor sharp tool a heavy cut and fast feed

 

[roofman]

I find with aluminium like that you need a razor sharp tool a heavy cut and fast feed

ive tried it every way mate..i think it must have a high magnesium content or summit or come from Rowntree

 

[Bladevane]

All non-abrasive cutting of steel is done by plastically deforming the material. As carbon content increases so ductility decreases and hence the ability of the material to deform under load. As the material was a spanner it has a higher carbon content than mild steel so takes more energy to deform. Your (presumably) HSS cutter can only be run at fairly low loads unlike carbide tips which can absorb the much higher energy input needed.

 

[Bladevane]

Roofman - a problem with aluminium alloys is they are so soft they appear to weld to the tool. Try using paraffin during cutting.

 

[MattH]

On your lathe I'd call heavy at least 25thou, probably around 40 per side.
0.001 is nothing, not even a finish pass. It's relatively hard to hold a single thou so better to aim for more on a finish pass, maybe 5thou.
Feed will be down to horsepower. Remember, use speed to control the colour of your chip on steel and speed to control the chip formation.

 

[MattH]

Sorry, just re read 10thou.

 

[MattH]

Also get yourself some carbide insert tooling if you are messing around with unknown bits of steel.

 

[Maker]

I'll go out later and have a play with heavier cuts (on a better piece of steel). I also need to sort out the tailstock as it's out of line at the moment.

Also get yourself some carbide insert tooling if you are messing around with unknown bits of steel.

I've got some inserts I was given, but still not bought a holder for them. It didn't work to simply hold the inserts straight in the tool holder.

 

[Tinbasherdan]

I have some crap black steel ive acquired in the past and no matter what I do, it ends up looking like its been threaded!

 

[roofman]

Roofman - a problem with aluminium alloys is they are so soft they appear to weld to the tool. Try using paraffin during cutting.

cheers bud i do use WD40 which helps a lot but you are correct about the welding to the tool,sometimes i have to stop and scrape the tool edge of kind of melted alloy turning this stuff i have

 

[Maker]

cheers bud i do use WD40 which helps a lot but you are correct about the welding to the tool,sometimes i have to stop and scrape the tool edge of kind of melted alloy turning this stuff i have

Parting ali on the lathes at school always welded the chip to the blade, I'm sure WD40 would have helped but "WD40 isn't cutting oil".

 

[roofman]

Parting ali on the lathes at school always welded the chip to the blade, I'm sure WD40 would have helped but "WD40 isn't cutting oil".

LOL yea i know that but it is a lubricant and coolant when your backs against the wall...Its not a ant flame thrower too

 

[MattH]

You need a much higher rake with Ali cutting tools, a high polish helps as well.