Re: Threading and Compound
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Is the tool advanced with the compound?or the cross feed?
John Lindo was the first that I know going straight? in. He is using his RLS with automated Z and X. He threw his compound?away.
Ralph
On Sat, Mar 2, 2024 at 1:35?PM Charles Kinzer < ckinzer@...> wrote:
This is a topic that has been discussed repeatedly on this list.? I guess it won't hurt to cover the same ground again.
In the hobby world, typically making small threads, at low speeds, often in friendly materials like brass or aluminum, there may be little to no difference what method is used.
In production, and with larger threads, and harder materials like steel or stainless steel, and at production speeds, there is a significant difference. And the difference is all about how the chip is produced.? This is what the 29.5 (or 29) degree angle is all about.? (Note:? You will find some production work that does go "straight in" however as there are times when that is still possible.)
When you go straight in, you are producing two equal size chips from the left and right cutting edges.? The chip from the left edge goes up and to the right.? The chip from the right edge goes up and to the left.? That means they collide in the air space above nose of the tool.? This causes a tearing effect and also puts more stress on the cutting tool tip.? The result can be poor surface finish, wasted power (time) dissipated in the two chips mashing together, more heat, and even a broken tool tip.? A poor surface finish would be the most likely risk in a mini lathe in my opinion.
The purpose of the angled compound movement is to have almost all cutting on the left edge.? By having the compound at 29.5 (or 29) degrees there will be a very slight skim cut on the right edge.? This ensures a clean surface on that side of the thread and also helps cause tool contact for heat transfer on the right edge.? This eliminates that chip collision problem.
Sometimes on this list I have seen people say it makes a "stair step" thread.? This technique, used properly, does NOT do that.? If somebody is getting that result, it is due to a simple geometry error that can be one or all of these things:? Compound not really at the correct angle (the protractor markings on mini lathes are notoriously inaccurate - measure with a machinist's protractor), the tool bit is not ground to the correct angle (double check with a "thread gauge" a.k.a. "Fish Tail"), and/or the tool bit is not perpendicular to the work piece.
Charles E. "Chuck" Kinzer
On Saturday, March 2, 2024 at 09:58:47 AM PST, davesmith1800 < davesmith1@...> wrote:
Here photo from How to Run a LatheIt shows two ways of threading.?? I have used both to me they work same.
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