Lathe centers always 60 degrees?

[Bill D]

AFAIK all lathe centers as well as centers for indexers etc are 60 degrees. Why? AFAIK all center drills are also 60 degrees. Countersinks come in 82,90,100 degrees and probably more. In theory the whitworth 55 degree angle is stronger. And it is the oldest unified thread design.
So should centers be 55 degrees shouldn't they. Where they ever. I think the 60 degree angle is just to make the math easier since the sine of 60 is 1/2.
Bill D

 

[4GSR]

Hughes Tool Company always thought that their H-90 connection was the strongest using a 90-degree vee thread design.

 

[Gordon Heaton]

. . .I think the 60 degree angle is just to make the math easier since the sine of 60 is 1/2. . .

Don't know about you, but I've never had an issue with the strength of a center point because of the angle.

 

[michiganbuck]

Going to 45* seems that the forces would push more toward the end, toward the tail and so less toward the parts radial support, and so more stress on the machine.
*and I agree with Bill 60* is just a more simple angle, that has been accepted as a standard.

55 or 60 as the standard would have been fine because one can have a fish gauge at that ankle to turn to grind a center.

 

[MrWhoopee]

Given that there are so many different tapers, spindle noses and threads, I would say that we're lucky that there is only one standard. If you start asking why, someone is going to come up with a reason to use something else. Best we just leave it alone.

 

[Conrad Hoffman]

Just be careful- I've gotten center drills that weren't exactly 60 degrees! Check everything.

 

[sfriedberg]

In theory the whitworth 55 degree angle is stronger.

If you mean stronger against radial or axial thrusts that act on a center, I believe you have it backwards. (Not that the difference between 55 and 60 degrees is going to be significant in this regard). The narrower angle would be easier to deflect and deform.
One might reasonably ask "Well, then, why not 75 degrees? Or 90 degrees?". Only sensible answers are "history" and "the industry needed to pick something".

And it is the oldest unified thread design.

Not sure how that is relevant to choosing a lathe center angle? Right angle shoulders and faced ends are probably the most common angles cut on lathes or mills, but that's not an argument for 90 degree centers.

 

[jims]

AFAIK all lathe centers as well as centers for indexers etc are 60 degrees. Why? AFAIK all center drills are also 60 degrees. Countersinks come in 82,90,100 degrees and probably more. In theory the whitworth 55 degree angle is stronger. And it is the oldest unified thread design.
So should centers be 55 degrees shouldn't they. Where they ever. I think the 60 degree angle is just to make the math easier since the sine of 60 is 1/2.
Bill D

Don’t forget they also make radius center drills. I think mostly for when you offset your tailstock for cutting tapers.
See Keo 10070 R H radius center drill

 

[Milland]

If you mean stronger against radial or axial thrusts that act on a center, I believe you have it backwards. (Not that the difference between 55 and 60 degrees is going to be significant in this regard). The narrower angle would be easier to deflect and deform.

I think the reference might be to strength of the Whitworth fastener system, but if that's the case then I'd point to the designed-in root radius in the male thread as the reason. Much like modern aerospace specs for threads, the controlled radius gives better fatigue life and a greater minor diameter for tensile strength.

Otherwise, I agree - in a lathe center, 55* will be less sectional area than 60* for a given depth, and so less strong. Now, if we're talking equal diameters perhaps the narrower angle is better due to more surface contact, but that's obviously got limits!

 

[eKretz]

I've seen centers from 50° to 75° in very large work.

 

[michiganbuck]

The pressure mentioned was comparing a 45* center to a 60*
but yes, I had it backward, I should have said a 90* point...my bad
55 to 60 would not be anything one could notice..

 

[John Garner]

Can't agree that the Whitworth threadform " . . . Is the oldest unified standard [threadform]".

Certainly the Whitworth is the oldest standard threadform we know about, greatly predating the Unified threadform that was developed after World War II to prevent recurrence of the wartime logistics issues that plagued the Allies' logistics system attributed to the differing national-standard threadforms of Great Britain and the USA.

I speculate that the "all new" threadform -- which was fundamentally derived from the Sellers threadform that was the US national standard threadform during WWII -- was more of a face-saving for the governments and people of Great Britain and Canada than all three countries simply agreeing to accept the Sellers threadform as their national standard threadforms.

It bears noting that the International Standards Organization (ISO) accepted the fundamental geometry of the Unified threadform in their decade-later ISO Metric standard threadform, and then several decades afterward, "badge engineered" the Unified standard into the "USO Inch" standard.

More directly on topic, there are such things as "ball centers", and I recall reading of a long-ago proposal to replace 60 degree center points with a roughly-bell-shaped center point that was derived from a shape that pointed centers took on when severely worn.

 

[Milland]

More directly on topic, there are such things as "ball centers", and I recall reading of a long-ago proposal to replace 60 degree center points with a roughly-bell-shaped center point that was derived from a shape that pointed centers took on when severely worn.

I used to see bell (curved) center drills more often than I do now, but them or actual ball centers are more for turning with an offset tailstock to get shallow angles.

At least, that's my experience...

 

[Bill D]

I just realized bull nose pipe centers tend to be a flatter angle. I think so they can gain a big diameter without so much extra weight a long cone would require. I suppose a sharper angle would also tend to flare out thin pipe as it gets cranked down tight.
Bill D

 

[just Dave]

In maintenance shaft ends see some abuse. I used to feel like a bell center cut a little relief around the mouth of the center and preserving the true center within.

 

[EPAIII]

Two points:

1. A thread profile and a center are two different things and there is no reason to assume they will act the same when analyzed for strength. So just because one angle if better for threads does not, automatically mean it will be better for a lathe center. One is like a hill and the other like a ridge line.

2. The difference between 55 and 60 degrees is rather small. Has anyone actually calculated the strength of either threads or lathe centers with those two angles for a proper comparison? My guess is yes for the threads, but no for the lathe centers.

IMHO, "Much Ado About Nothing".

 

[GregSY]

Not the actual DC armature, but the Niles lathe shown is the actual one...back around 1988 they were putting a big DC double armature in the Niles, the tailstock was in use using a dead center. The machinist lowered the armature, slid the tailstock into place, then relaxed the overhead crane in preparation for moving the steady rest into place. But as soon as he took the load off the crane straps, the dead center smeared like a melted Hershey kiss and the armature landed on the lathe ways. There was no covering up that one. I bet if the angle were 55 degrees...no difference!

 

[Milland]

That could ruin your whole day.

Sounds like either the center wasn't hardened correctly, or somebody didn't calculate the shears stress on the engaged diameter. Oops...

 

[gbent]

Female centers are typically 90 degrees.

 

[MrWhoopee]

Female centers are typically 90 degrees.

Likely to match a typical 45° chamfer.