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Unable to get a smooth finish in turning mild steel
- Thread starter compact8
- Start date
- Joined
- Dec 3, 2014
- Messages
- 778
If you insist on carbide inserts and want a fine finish in junk steel like 1018 or A36 your best bet would be a negative rake tool like TNMG or CNMG, crank up the speed to at least double what would be reasonable for high speed steel take a deep enough cut to get thru the mill scale and feed at .003 to .005" for finish cut, maybe twice that for rough cut. Dial it in so your chips are tan to just turning blue, make sure you ready for the flesh melting chips, but with right speed and feed you can easily get a near mirror finish when you get just short of blue chip zone. No oil, and if you use coolant you need to consistently apply it with flood or mist, no periodic spraying as that will cause havoc with the carbide heating and cooling, so either run dry or use lots of mist or flood.
This procedure works for me. The other method that works is to use a vertical shear tool, very light feed, depth of .001" and standard HSS speeds., The shear tool will give acceptable finish but usually will not give you that burnished, almost mirror finish the above negative rake carbide method can.
michael
This procedure works for me. The other method that works is to use a vertical shear tool, very light feed, depth of .001" and standard HSS speeds., The shear tool will give acceptable finish but usually will not give you that burnished, almost mirror finish the above negative rake carbide method can.
michael
That's one works good but like said it just cuts OD work. The one I'm speaking of is like this. You just grind your hss at the end of the blank with a touch of positive rake. I believe theirs a company out of Australia that makes the tool holder but they are easy to make. They come in left and right.
- Joined
- Aug 22, 2012
- Messages
- 4,273
Have a read of this
http://www.conradhoffman.com/advancedsharp.htm
and try out the shear tool.
Thats my goto bit when I cant achieve the finish I want.
- Joined
- Jul 28, 2017
- Messages
- 2,565
If you want to experiment with a vertical shear bit but find the grinding profile(s) a bit challenging, you might want to try a variation as shown in the photos below. I came across this during an online search for shear bits so it is not original to me.
This version only has one ground face, produced on the radius of a grinding wheel. Relief is provided by rotating the tool in the holder, as shown below:
The finish is better, probably could be improved if I had used a slow power feed.
It's my understanding that, due to wear during a cut, there can be some "drift" of the OD when using a shear bit. I bought some cobalt tool blanks to (hopefully) reduce this effect, but have not had a chance to try one to see how it performs in this regard.
This version only has one ground face, produced on the radius of a grinding wheel. Relief is provided by rotating the tool in the holder, as shown below:
The finish is better, probably could be improved if I had used a slow power feed.
It's my understanding that, due to wear during a cut, there can be some "drift" of the OD when using a shear bit. I bought some cobalt tool blanks to (hopefully) reduce this effect, but have not had a chance to try one to see how it performs in this regard.
Socket crews are hard things and difficult sometimes.
Some places look to be cutting and others look like tearing.
Try altering cutter height to see has it changes.
A bit high can cause the edge of the cutter to almost touch and as it lowers it alters the cutting angle.
If you do not already know this trick do this.
Take a picket rule or other small strip of flat steel and hold it verticle between cutter and stock with machine off.
Carefully bring the cutter to touch the work and release the strip.
If the tip of the cutter is exactly on center the strip will be vertical.
Any angle indicates not at center.
Sent from my SAMSUNG-SM-G930A using Tapatalk
Some places look to be cutting and others look like tearing.
Try altering cutter height to see has it changes.
A bit high can cause the edge of the cutter to almost touch and as it lowers it alters the cutting angle.
If you do not already know this trick do this.
Take a picket rule or other small strip of flat steel and hold it verticle between cutter and stock with machine off.
Carefully bring the cutter to touch the work and release the strip.
If the tip of the cutter is exactly on center the strip will be vertical.
Any angle indicates not at center.
Sent from my SAMSUNG-SM-G930A using Tapatalk
- Joined
- Dec 27, 2013
- Messages
- 124
A plan B or whatever letter you are up to would be to finish it out with a file or abrasive. Depending on how scored or "torn up" your surface is, you will need to leave some extra material. A good file properly applied to that work piece might finish it out much better. The strip of emery or a carbide abrasive will also give a good finish if it can be had at all.
- Joined
- Dec 2, 2012
- Messages
- 1,792
Guys since I never heard of Shear Cutting I did google it and came across this.
Seeing is a big help for me to understand how it works.Good for only .001 to .002 but that is all that is needed for a good smooth finish and its also good for SS listening to Tubalcains Youtube.Good subject