Machining Stainless Steel R/ Bar On End

Ozwelder

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I have a job to machine a recess in the end of the 303 stainless round bar.

The diameter is 42mm and will require a groove in the end of the diameter - 31mm OD 13.71 - ID and 4.35 mm deep.

I have faced off the end with a carbide tool and achieved a finish that reflects the tooling, so that was ok.

Owning only a right hand carbide tool I had to to use a HSS tool to make the cut. I chose a 1/4" sq HSS blank and left it square, save for relief of about 10 degrees on front and side faces. also radiused the corners and I used sulphur bearing cutting oil.

The resulting cut chattered badly despite precautions of locking the saddle and minimising overhang on tool holder and the compound slide.
I used much lower RPMs than the carbide facing cut.

Should I grind right and left HSS tools and try those,or was the square cut HSS correct for the application or perhaps keeps reducing the RPM?

Practical advice will be appreciated.

Thanks
Ozwelder
 
Try slower & holding a tool on top of your cutting tool with your hand to take vibration out. I've done this to take the harmonics out. Spindle speed is only about 90 RPM. It sounds like you may have a small lathe using small tools so it wouldn't even be that fast.
 
Cutting to much at a time is my guess. You can grind a V notch in the center of the tool, or start with a pointed tool and finish the outer edges with the square tool. I usually go with the latter. Also the sides of the tool need to be ground for the dia/radious like a trepanning tool. What you're doing is trepanning. If I understand you right.
 
Thanks for your reply
Lathe is 12 x36 generic from that big country to the left of Taiwan.
The speed for the HSS was 360 rpm. The toll holder is a bit of 5/8" square with a 1/4" slot milled in it.
In turn that fits in the 5/8" slot of a QCTP
I went and had another look at the overhang from the tool holder-there was about 1/2" poking out of the tool holder..I'll shorten that up and drop the RPM's back to 90.
 
Cutting to much at a time is my guess. You can grind a V notch in the center of the tool, or start with a pointed tool and finish the outer edges with the square tool. I usually go with the latter. Also the sides of the tool need to be ground for the dia/radious like a trepanning tool. What you're doing is trepanning. If I understand you right.

No, its not quite, about half way through of the thickness of 8.mm.I have trepaned before but only o carbon steel and understand the need for clearance. I'll grind the radiu and give that a try along with the other things.The feed was minimal like .010" a pass.The chips came off like tiny needles.

The job is actually a part of a lathe which originally was die cast metal but was broken.It is the spacer between the gross slide dial and the cross slide which I'll make in three parts and tack together.
The bit I am machining is the round bit with the zero mark that butts up to the graduated cross slide dial. The hollow side meets the dial.
 
Oh. I thought you meant you was using a 1/4 tool.

The part is probably work hardened now so if you are able to get the carbide back in there for a skim cut might make it easier. Is probably made that part out of aluminum.
 
If you left the HSS tool square,does that mean you had a broad,flat cutting surface? If so,to avoid chattering,make the cutting tip very small,and feed across slowly. A wide tip will chatter in just about everything.

Not that this would work here,but I have smoothed up cuts made with a form cutting tool,which is necessarily wide. I turn off the lathe and rotate the chuck by hand while hand feeding the form tool in a few thou.. Get the speed slow enough,and just about any chattering can be cured.

This trick I use most often on brass,when making fancy moldings on things like parts for mechanical antiques,brass cannon models,etc..
 
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Narrow your tool. You can take what amounts to facing cuts to get the width to final size. Wide tools tend to chatter far more than narrow tools.
 
If this is going to have s through hole in it I would drill that first. Then grind a tool to bore the rest of it.
 
I tool the advice and ground back the width of the cutter and dropped the rpms to 100.
Taking only a skim at a time the chatter went away. Until that is, the knob on the fixed steady came loose because the pin the secures fell out of the plastic knob.<GRRR!>
Thankfully that happened at the end and I was able to part off and clean up the work. A new job now emerges in making knobs that will not fall of the fixed steady.
Thanks for all your help gents

ozwelder
 
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