Maximum taper and still hold in lathe chuck jaws

BobM3 · Jun 30, 2021

We have these gear blanks we're trying to optimize strength and weight-wise. The OD of the gear is about 4 inches and the hub (that we clamp on in the lathe) is about 1.5" dia. If I assume a coefficient of friction >= .1 this gives me a maximum taper of 5.7 degrees. Does this number seem reasonable to you guys? I hate to make a new sand pattern for the castings and then have the first part come flying out of the lathe jaws.

rke[pler · Jun 30, 2021

I'm thinking that you're clamping on a "grip" plug on a casting and worrying about the draft on the plug? When I have those I make it a 2 operation and first grip the outside of the part (gear in your case) and turn the plug for it's length. This gives you the grip for the larger end and has the added benefit of making the plug square and perpendicular to the major part of the casting.

HuFlungDung · Jun 30, 2021

You could also consider using serrated carbide grips. These don't permit any adjustment in position once clamped, as the imprinted pattern is permanent. But you could chuck in another location.

Bill D · Jun 30, 2021

Or run a core drill over the spud on a vertical mill. Or a rotary table and a long endmill.
Bill D

BobM3 · Jul 1, 2021

The carbide grips sound like a good idea. I really didn't understand the other ideas. It's a gear blank casting similar to the enclosed. I have some old ones sitting around - I'm going to modify the cast hub and create a 6.5 degree taper and see if it can hold with heavy cuts.

DDoug · Jul 1, 2021

Grippers & Gripper Inserts - Made in the USA | Carr Lane
You could buy some soft jaws, and mount these on them

boslab · Jul 1, 2021

I could lend you one of my chucks, thier all bloody tapered, I’m joking (they are) turn a mandrel to fit and sick a diy drawbar through the headstock, safer than a face full of gear
Mark

CalG · Jul 1, 2021

On difficult to grip work pieces, It is sometimes useful to wrap the surface with copper electrical wire in order to provide some accommodation, and enhance grip.

sfriedberg · Jul 1, 2021

If you are doing enough to tool up for it, an old school technique for dealing with rough and tapered cast shanks would use tilting jaws with serrated grippers. Main part of the chuck jaw is fixed, with a pivot for the part which actually contacts the work. That piece is relieved in the center so it makes contact with the work at two points, axially. Ideally, those points would have independently pivoted serrated grippers, but it was pretty common to have the grippers fixed to the pivoting piece. Short gripper lengths better than long ones in this situation (closer to point contact, which is more stable).

Limy Sami · Jul 2, 2021

BobM3 said:
The carbide grips sound like a good idea. I really didn't understand the other ideas. It's a gear blank casting similar to the enclosed. I have some old ones sitting around - I'm going to modify the cast hub and create a 6.5 degree taper and see if it can hold with heavy cuts.

Silly Q time - why are you creating the 6.5 deg taper.

thermite · Jul 2, 2021

boslab said:
.. turn a mandrel to fit and stick a diy drawbar through the headstock, safer than a face full of gear
Mark

^^^ THIS ^^^

Breakheart Tool - from whom I bought all the sizes they offered - seems to have retired, but their "style" of single-ended expanding mandrel are dead-easy to fab.

His price, "CNC" 'ed as a product was just less than I could be bothered to fab them for meself.

If all a body needs is for one or few sizes? "JFDI" the expander and run it as a collet-style tasking - or even grip the expander in a chuck.

The portion of the gear to be turned is short enuf, hang-out-wise, it won't even need support from a centre.

2CW

TedinNorfolk · Jul 2, 2021

You could dispense with the chucking boss altogether,if that's all it's for. Simply face one side and bore. Then mount on expanding stub mandrel,turn and face other side.

thermite · Jul 2, 2021

TedinNorfolk said:
You could dispense with the chucking boss altogether,if that's all it's for. Simply face one side and bore. Then mount on expanding stub mandrel,turn and face other side.

With appropriate tooling & fixturing, the bore and both sides of the blank could even be prepped as basic two-head progressive drill-press work.

Expending arbor "enters" when time cometh to cut the teeth.

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Maximum taper and still hold in lathe chuck jaws

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