Difficulty maching mild steel at very small diameters

C

ChristheClockGuy

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Hi Guys this is my first post. I have limited experience with my lathe which is a Sherline 4500, bought on recomendation for its precision and accessories. My passion is clocks and for whatever reason I decided to attempt to machine a balance staff pivot. Now these things are tiny , say 1/4 inch in length and have several critical dimensions. my plan is to first make a scaled up (x4) balance staff from mild steel and then move on to what we call in the UK silver steel (Rod steel I think to my U>S friends).
However all seems to be going well in my endeavors apart from machining the smaller diameters which in the x4 staff are about 0.018 inch. i am using quality brazed carbide cutters upon recommendation and the cutters seem centered as no dimple is left when facing and i aligned the cutters with a filed point.
so question is am I asking too much of this mild steel which is UK EN3B which does tend to shear. Is using this steel the likely cause of the tiny diameters shearing?
In the UK we have EN1A which apparently machines to a better finish??? Also is the use of cutting oil causing shocks....should I be using any at all?

Regards
Chris
 
UK silver steel = drill rod on this side of the pond; the usual variety is a oil hardening steel known as 0-1. I never have tried to turn tiny diameters, so cannot comment on that.
 
I tried my luck googling "turning a balance staff pivot" and a couple of videos came up. Maybe something in one of those would help you? I had to look up what a turning a balance staff pivot was. Now I know.
 
I think that using sharp hand ground HSS toolbits will give you a better results, but most importantly is to use a follower rest. Hand ground sharp HSS toolbits don't need much pressure to cut, while duller carbide bits need much more pressure to cut. The follower rest will keep the part from bending. Don't feel bad, turning thin shafts is not a simple operation. If you don't want to grind your own HSS toolbits, you can buy them pre ground, but for what you want to do it is an important skill.
 
Am I understanding that you are trying to turn a .018 in. diameter and it is 4x the size of the actual part you intend to make? There are watchmaker's lathes for this kind of work and, I'm sure, different techniques and tools for parts this small.


Try these people
forums.watchuseek.com

Watchmaking

Dedicated to discussions about parts and tools and watchmaking in general.
forums.watchuseek.com forums.watchuseek.com
 
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Thanks Guys for your replies. There are traditional ways to machine a staff as on jewelers lathes but remember most factory produced staffs are machine made. Using a Sherline lathe is totally acceptable and proven and as always you get the tradionalist arguments verses the new alternative ideas. leaving that to one side as a given I am investigating possible causes of my failure to machine the very thin pivots. i am minded it is either the metal (mild steel variant prone to shearing) and / or the cutter being everso slightly off center. I plan to try silver steel (drill rod) to see but has anyone any good ideas how to align the cutter to perfect. At the moment I align it under magnification to a filed point in a collet. There has to be a error introduced by the angle of view.
Chris
 
I've had fair luck using music wire for small pins, though not that small. I use HSS tools ground to a razor point and hand feeding, using several cuts to reduce the diameter in steps.
 
That is incredible.
I had no idea you could do that.
What tool holder will hold the triangular bit that way?
 
Hi and welcome! I do mostly micro machining. I would forget Carbide, just use HSS. I would cross reference a staff that is the like or similar and modify if necessary. Your Sherline is a small parts maker. But IMHO not the best at making a staff. And you would need more than just a lathe. You are getting into a VERY big learning curve! Like I said, do the cross reference. Good Luck…Dave

Edit: or just re-pivot the original.
 
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