Machining titanium

[deverett]

I am considering - read dreaming - about making a hot air engine. Jerry Howell recommends titanium for the hot cap.

So, I look on eBay for some titanium and after coughing at the price, continue dreaming.

However, I contacted the vendor about machineability, asking about using HSS tools in a Myford lathe for cutting titanium and the very helpful reply I got back was:

" Hi Dave.

The main reason we use carbide tools is for the higher cutting speed snd tool life.

You can turn titanium fairly easy provide you * Use low cutting speeds. * Maintain high feed rates. * Use copious amounts of cutting fluid. * Use sharp tools and replace them at the first sign of wear. Tool failure occurs quickly after a small initial amount of wear. * Never stop feeding while tool and work are in moving contact. Allowing a tool to dwell in moving contact causes work hardening and promotes smearing, seizing and tool breakdown. In summary we use a small Myford lathe for small detail parts with no problems. If you need any further techincal help please feel free to contact us at any time. Best of luck "

Perhaps the above may be of interest to others contemplating the use of titanium.

Dave
The Emerald Isle

 

[CrewCab]

How big a piece do you want Dave

CC

 

[CrewCab]

As for machining it I've read up a little and found there seems to be two schools of thought ......

1) As you said above and
2) High speed, High feed rates but shallow cuts, less metal removal but provides a better finish

Here's a useful link which discusses the alternative methods of machining and the problems in machining due to titanium's superior physical properties (light weight, more elastic than steel and doesn't conduct heat etc) ........... I found it interesting anyway :

I picked up a few round offcuts on eBlag a while back and have just played with them, what I've found is ..........

1) COOLANT IS A MUST, ............ LOTS OF ............. Titanium is similar to magnesium (though not quite as fierce) and the chips/offcuts will catch fire quite easily without lots of coolant, hard to extinguish too ............ there has been a recent thread on here recently........... Click Here

2) It responds better to turning than milling (somewhere on the web there's an "exotic" reason, but I can't recall it)
3) Machines with a larger mass (ie Bl**dy Heavy) :big: ........... produce better results

hth,

anyway, as I said I ended up with a few bits .............. so ask away, I can go have a root :big:

CC

 

[deverett]

More useful info on Titanium machining. Certainly much food for thought in the two links. Don't know why, but I didn't read Seanol's thread on machining titanium.

While out here in the Perishin' Gulf I have lots of time to dream and when the internet is working, lots of time for research. Pity that all the research never seems to be converted into action.

CC, many thanks for the offer of a piece of Titanium. I was considering building Jerry Howell's hot air fan, but without drawings I would guess the hot cap would be about 2" dia x about 3" long. Much as I would like to take you up on your offer, I believe it would languish in a dark hole in my workshop for a very long time before being put to use - that is if the dream ever became reality.

Dave
The Emerald Isle

 

[CrewCab]

Biggest I have is 21/2" dia x 7/8" long ........... I suppose if you wanted to build a smaller version :

CC

 

[ariz]

well, what I'm saying below is to be considered as my humble opinion, absolutely IMHO

I can find titanium easily in Germany: I buy it on ebay (I live in Italy) and sometimes I can get a bargain and pay few money for great pieces

so I work with it often, even more than what would be right: it isn't a material that is right for everything... in the past days I have made 2 cylinders and 2 pistons of titanium, because I cannot find cast iron! I'm almost sure that the engine will not run properly and I will have to remake these parts of cast iron, when I will get it

however, this is my opinion: I always work it (turning) with high speed, high feed rate and deep cuts. in this manner I can work without coolant. I use coolant only for cutoff. Obviously, I use carbide inserts and not HSS (sometimes I can see the insert that becomes red in the part of contact with the piece: it is time to change it).
titanium catch fire when you go with shallow cuts, and chips are like fine hair of wool: in this condition temperatures rise and the fine chips catch fire immediately.
turning titanium in this way (high, high, deep) let you to obtain fine finish, like a mirror, but it is difficult to reach the exact measure, because of the deep cuts.
it is easy to turn titanium in this way.

on the other hand, milling is very difficult, I don't know why.
boring is more difficult yet: on small holes, it is very easy to break the drill rod. here lot of cutting fluid is necessary.
threading is still more difficult. the only way to go, is to forget the rules and make a hole that is near the thread to be done.
if you have to thread a M4 screw (4 mm), do make a hole of 3,5/3,6 sometimes 3,7 mm with titanium
every attempt below 3,5 will result with a broken tap.
but also with a hole of 3,7 the resulting thread is strong enough. I don't know why, but this is my experience.

I repeat, I'm not an expert and these are only my observations about working with titanium. take them with caution, and anyway take on hand something to extinguish fire!