Cutting Titanium

+1 on slower cutting speeds. The grind for a facing tool for Ti is different than you'd expect. it has to be ground like a trepaning tool because of the increased ductility of the Ti.
 
I can try grinding hss like a trepaning tool before spending money for cobalt, if I knew how to do that... :p . I have been looking at cobalt but as you know it gets a little hard to decide which one for certain metals, all I have seen is for steel and maybe iron. Is there somewhere that will show me how to grind it? Also make sure I turn down the speed... If still a problem I will look for the M42 cobalt. All help is really appreciated,Thanks again.
 
Warren, @Titanium Knurler has experience turning Titanium and can maybe give you first hand knowledge of what will work. I suspect he is using carbide insert tooling. I've never worked with this stuff but if I did, I would experiment with the tip geometry of an M42 cobalt bit to see what worked the best.
 
The muzzle breaks I build are turned Ti alloy. The problem with facing is the pressure put on the cutting edge... I always use HSS for cutting titanium, I'm sure there are grades of carbide especially for Ti, but I haven't explored that much. HSS would work, if ground corrctly. I face after boring, so I don;t see much degrading of the cutting surface. I'm sure @Titanium Knurler will have soem great advice.
 
The problem with machining Ti is that it does not absorb heat much, nor does the chip, all the heat of cutting is concentrated in the tool tip, which leads to rapid dulling. It's not how hard it is, HSS is plenty hard enough, it's the temperature rise, which leads to cobalt and carbide tooling.
 
SO, if you're using carbide on grade 5 Ti, do you still suggest to lower the speed WAY down? I've heard really fast and really slow...how slow are we talking? 400rpm? Slower?
 
On a 1" muzzle break I machine it at 370 RPM
 
Hi everyone, I looked at carbide bits and checked out different grinds for hss bits. I decided to try grinding a hss bit before ordering a carbide tool. I ground a side angle of about 10 degrees, end cut angle of 8 degrees and an end relief of 8 degrees which from what I understand is close to what you might grind a bit for tool steel. I also rounded the tip a bit for a better cut. I lowered the rpm on the lathe to apprx 150 rpm and I was able to make decent cuts on the titanium. If i slowed down my feed I got a pretty smooth cut not perfect but I think very good and the bit isnt getting worn down like the other one. Im thinking if i round the cutting edge a bit more it might be even a smoother cut. Would you agree? Thanks everyone for your help, it looks like I found something that will work satisfactorily. Best forum ever...
 
Warren, I spent a few minutes looking at the machining properties of Titanium and have some ideas on your HSS tool.

Apparently, much of the heat when machining Ti is retained in the tool. This means that the greater the area of contact with the work, the greater the heat generation and retention. Consequently, the larger the nose radius the hotter the tool gets and this leads to edge breakdown. My suggestion, therefore, is to use a small nose radius.

The other thing I learned is that you can transfer more of the heat to the chip instead of the tool by optimizing chip thinning. With HSS tool geometry, the key to chip thinning is back rake. In your post above, you are discussing the side and end edge angles that describe the shape of the tool and you mentioned end relief of 8 degrees but you make no mention of the side relief angle or the rake angles. It might help to show your tool because a tool as described will not cut well.

Based on what I now understand, this is what I would try:
  • Try for a general purpose shape to give you enough mass in the tip to transfer heat.
  • I would use a 12 degree side and end relief. This will give you enough cutting force reduction and edge sharpness to hopefully keep the tool cutting well.
  • I would try 15 degrees of side rake to reduce cutting forces and enhance chip flow to aid in getting the chips out fast.
  • I would use 12 degrees of back rake to thin the chip and aid the side rake in getting the chip, and the heat, out faster.
  • I would keep the nose radius smaller, on the order of 1/64" to limit the area of engagement.
When facing, we normally engage the work with the side cutting edge up near the tip of the tool. The greater the area of engagement, the greater the heat entering the tool. Therefore, I would try to keep the contact area small, keep the speeds on the higher side and keep your depth of cut small. Use coolant and keep the tool moving - do not dwell.

Ti tends to work harden. For a manual lathe guy, this means we cannot slowly enter the work and expect the edge to last. We need to set our depth of cut and enter the work without stalling, pausing or hesitating; doing so will break down the edge faster. Enter the cut at a steady pace and maintain it. This is how I machine stainless and it works well; the tools stay sharp.

Anyway, that's my take on this. Again, I have no first hand experience with Ti but I've done a lot of stainless work and use HSS in preference to carbide. My tools are also based on cutting force reduction and heat dissipation. You might give this a try and modify your tool based on your experience.
 
Thanks Mikey, I probably didnt describe the tool grind very well. But I did cut the titanium with this and it did pretty well, im sure your suggestions could very well improve upon it but it worked pretty well. I didnt use a back rake at all, I can add that and alter the angles a bit. I figured since it worked so well and the tool didnt get worn or change color indicating it got hot I figured I was pretty close anyway. I had no problem cutting with this grind but i will try changing closer to your suggestions and see how it works. Would be interesting to try it and learn by it.
 
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