Parting Stainless Steel Hex bar..

Hi All,

I'm new here and i describe myself as a toolalholic, a bikeaholic, an alcoholic (at times:lol:) and love going FAST. I live in the west of Ireland not far from the Wild Atlantic Way. Fantastic biking roads and stunning scenery :)

To support some of these very desirable attributes i have a need to make parts and and bits and pieces.

For the bikes (BSA) im making nuts, bolts, studs, axles etc in Stainless Steel (305) I have a capstan lathe and making the nuts from Stainless hex is a PITA. I keep wearing the parting tool out in one cut, this no matter what speed i use. I tried a double ended carbide tipped toolholder out of desperation.
First try it broke and the tip disappeared into the swarf. second try it bent and the tip shot out into the workshop somewhere. This is on 1/2" Hex bar.

Anybody any pointers on how to overcome this Problem?

Carbide doesn't like interrupted cuts. Have you tried a HSS parting tool? If not, give it a shot.

"Carbide doesn't like interrupted cuts. Have you tried a HSS parting tool? If not, give it a shot."

Yes, it was a HSS parting tool that i was using at first. It did not like interrupted cuts at all. One nut and it was wasted. The HSS parting tool works great on round stock and i was surprised at how fast and clean it can cut Stainless.

Hi Fergie
I think your problem is more one of technique, 1/2" hex should be doddle, I would suspect too high mandrel speed.
I do a lot of s/steel work for my motorcycles and yes it is a difficult material to deal with, especially as I get most of it from scrap yards and not sure of grades etc.
Firstly be bold as it will work harden in an instant if the cut is not maintained or the tool loses its edge.
If you have or can rig up a rear toolpost use that as as it prevents dig in of the tool especially in older machinery, the geometric reasons for doing so are well documented and easy to research, also the swarf drops away instead of curling up in the groove.
I always use a carbide insert tool and have not had any problems with interrupted cuts, I have successfully parted of 2 inch dia using auto feed in my old 9 inch SB lathe so it can be done.
I tend to keep speeds on the low side and let the tool take a decent cut but all lathes behave differently so experiment with what suits yours.
Good luck.
Olderdan

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Originally Posted by olderdan

Hi Fergie
I think your problem is more one of technique, 1/2" hex should be doddle, I would suspect too high mandrel speed.
I do a lot of s/steel work for my motorcycles and yes it is a difficult material to deal with, especially as I get most of it from scrap yards and not sure of grades etc.
Firstly be bold as it will work harden in an instant if the cut is not maintained or the tool loses its edge.
If you have or can rig up a rear toolpost use that as as it prevents dig in of the tool especially in older machinery, the geometric reasons for doing so are well documented and easy to research, also the swarf drops away instead of curling up in the groove.
I always use a carbide insert tool and have not had any problems with interrupted cuts, I have successfully parted of 2 inch dia using auto feed in my old 9 inch SB lathe so it can be done.
I tend to keep speeds on the low side and let the tool take a decent cut but all lathes behave differently so experiment with what suits yours.
Good luck.
Olderdan

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Hi Dan,
Thanks for the feedback. First, i should explain, the lathe is a Spirit Capstan and I have tried different feed rates which is easy to do on this capstan as it has 16 spindle speeds. There is a lever operated parting off slide for the parting tool mounted vertically over the spindle which is very rigid and normally make parting off a dream. I had forgotten the work hardening qualities of SS and i think maybe you're on the right track here. I think I might have been reluctant to feed in fast enough with the 1/2" SS hex as there is quite a bit of noise and vibration as you feed in. Therefore i might have been unknowingly work hardening the material. I shall have another go at it this evening when i get home.

I have a new parting tool with carbide inserts to try and i hope it works better than the last one. Shall comeback with feedback to all.

Try using 303 S steel it has better machining properties.

302, 316, 320 series, I've machined space grade 455 too. S/S is sensitive and obtuse at the same time.
Sensitivity is that RPM and feed rate are developed by feel and observation, in a proper RIGID setup. All friction generates heat. metal needs to be removed at rate in excess of the part acting as the heat-sink.
Olderdan is accurate in his description, and a back post is a great way to address cut-off. Another benefit; freeing tool post of a tool used once per part, figuratively speaking. It is also good for roughing 'left side' of a part awaiting second operations, that is otherwise finished, I rarely employ carbide for short runs, let alone one-off parts

The obtuse side? Reaction S/S has by Work-Hardening; deepening faster than a tool removes material if speed, feed rate, AND temperature are not under control. Work-hardening is just one issue, heat narrows the groove width and binds the tool. You'll find flood coolant, or at least spray atomization, postpones a lot of work-hardening. As he stated, "Be Bold" too.
A good way to gauge the situation is to hand feed, watch and listen. It'll tell you what it likes and refuses to do...

One more process might aid the work. It's the corners that impede steady rigid in-feed, losing advance by intermittent backlash = friction. A change in the part pattern can fix that, such as milling two wrench flats vice a full hexagon.

Stainless Steel is a pain to work with, I feel your pain! I've broken a few lathe tool bits.
I don't have a lot to add, but one thing that comes to mind since your main problem is the parting off. Could you set up a simple cold saw setup where a secondary saw blade driven by an electric motor is used for parting off? Similar to a toolpost grinding setup, but instead of grinding, you'd be sawing. Then the Hex corners wouldn't be a problem, and the lathe could rotate it super slow to get a nice even cut all the way around.

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Originally Posted by tooly

Try using 303 S steel it has better machining properties.

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304, she's a whore;
303, she's for me.

Quote:

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Originally Posted by Fast Fergie

Hi All,

I'm new here and i describe myself as a toolalholic, a bikeaholic, an alcoholic (at times:lol:) and love going FAST. I live in the west of Ireland not far from the Wild Atlantic Way. Fantastic biking roads and stunning scenery :)

To support some of these very desirable attributes i have a need to make parts and and bits and pieces.

For the bikes (BSA) im making nuts, bolts, studs, axles etc in Stainless Steel (305) I have a capstan lathe and making the nuts from Stainless hex is a PITA. I keep wearing the parting tool out in one cut, this no matter what speed i use. I tried a double ended carbide tipped toolholder out of desperation.
First try it broke and the tip disappeared into the swarf. second try it bent and the tip shot out into the workshop somewhere. This is on 1/2" Hex bar.

Anybody any pointers on how to overcome this Problem?

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I feel that some good advice has already been given but am curious as to why you are not keeping your BSA/s original as most fittings on my RGS and Flash are cadmium plated BSF? I do not recall any parts of them made of stainless although for everyday use it may be more decorative. Personally, for boat & mower parts, I use a small angle grinder which can be fitted on a stand and one of those very thin cutting blades and it then takes very little time to face off on my Myford Super 7 at a moderate speed, or slow if using HSS, with a std. 3 grip chuck. Have you checked the tensile strengths of the parts you are making out of 305 compared with the BSA originals as most boat owners will know that SS may fatigue earlier depending on grade, Martensitic or Austenitic, etc.

As you have a capstan lathe you could set up your first cut to the OD diameter with a heavy V shaped tool, then follow up with your parting blade this will get rid of all the interupted cutting giving you a better shot at the job.