Tapping strategies on lathes

Steve@Reliance · Apr 10, 2019

So I'm quoting a lathe job, 100,500,1000, 2000, pieces. 1 3/8" 1018 bar and the part is finished at 1.5" long with a 3/4-16 threaded hole through it. Now on the low qty I am happy to drill deep enough to get a 3/4-16 spiral flute tap through the part and face off or part off the extra drilled material. This the way I always did it in the past before we had a lathe with live tooling.Once the the quantity goes up I'm thinking about all the waste and considering thread milling instead. I can't decide if the glass is half empty or full. Just looking for opinions if I should be trying a different approach than" that's how we've always done it".

Booze Daily · Apr 11, 2019

Thread milling would take longer.
I guess you have to weigh the cost of extra cycle time vs. cost of losing the extra matl.

Red James · Apr 11, 2019

How is the 'cut off' end finished? Thread chamfered?

hanermo · Apr 11, 2019

Please add details.
If you are doing the next part from the same bar, why do you need to cut off the pre-drilled section ?

On lathes with live tools spindle-orient is usually standard.
I think.
So you should be able to thread into the same hole, rigid tapping.

Without spindle-orient a floating tap holder should align to the previous threads, just pick the right depth.

Finegrain · Apr 11, 2019

hanermo said:
Please add details.
If you are doing the next part from the same bar, why do you need to cut off the pre-drilled section?

Yes, this. Run the drill through and into the next part. Spiral flute tap has, what, 2 thread pitches of taper? So that's 1/8", which is your parting tool, plus you probably are doing something on the backside, like a 1/2-1 pitch chamfer. I don't see any extra waste.

Regards.

Mike

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Tapping strategies on lathes

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