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Re: ER Collet nut

m. allan noah
 

Maybe we miscommunicate, Ray, or maybe one of us is wrong. I would like to clear it up, just so that later readers of this thread don't get the wrong idea and scrap a part. So, let me try from scratch.

The thread dial is measuring two things concurrently: the rotation of the leadscrew, and also the linear distance the carriage has traveled. On many smallish lathes, if the leadscrew is not turning, one dial rotation is 4 inches of carriage travel. Nearly any imperial thread you could cut on a small lathe works with such a dial because the thread pitch repeats at least once in 4 inches. So, at a minimum, you can engage on the same mark on the dial anywhere along the bed, and be in time with your previous passes.

This is not the case for metric threads (or module or DP worms) on an imperial lathe with an imperial thread dial. If you move the carriage such that the thread dial has made one or more whole rotations, you have covered some imperial distance. This distance will not be an even multiple of your metric thread pitch. For example, if you move one full dial rotation right on a 9" or 10L, you just covered 4 inches, or 101.6mm. I cannot come up with a metric thread that repeats evenly in that distance. Interestingly, if the dial went around 3 times (304.8mm), you could cut the seldom-used .6mm pitch using the half-nuts in the 'imperial' way.

Now, the technique DJ mentioned is the one I use. In that case, we are reversing the lathe spindle as well, not just winding the carriage to the right and taking another pass. That ensures that the relationship between the carriage, work, and leadscrew is maintained. It is unfortunately slower, however.

Please feel free to point out any errors in my understanding or explanation, I certainly might have missed something.

allan


""


On Wed, Feb 15, 2023 at 7:48 PM Ray De Jong via <dejongray=[email protected]> wrote:
But it does work as that is how I have been threading Metric since making the 4 stud gears I needed. Its important to note that when reaching the end of the thread on each pass you STOP the lathe, then dissengage the half nutsand return to the beginning of the next cut, now note; ?just return the carriage slowly untill you can re-engage the half nuts to the marked position from your first cut. And then repeat this procedure untill completing to your desired fit.
?I must impress though, that you should select a spindle speed that allows the spindle to stop fairly quickly or. having a VFD with breaking set light(as I have) allows a fairly quick stop without threat of losing the chuck ;) BTW I have 1947 9A and a 1986 10K underdrive - with a Hitachi VFD

On Wednesday, February 15, 2023 at 09:18:51 AM PST, m. allan noah <kitno455@...> wrote:


Too bad it isn't true.

allan

On Wed, Feb 15, 2023 at 11:53 AM Andrei <calciu1@...> wrote:
Yes, that is the plan, anyway. ?
From: [email protected] <[email protected]> on behalf of Rick <vwrick@...>
Sent: Wednesday, February 15, 2023 11:49 AM
To: [email protected] <[email protected]>
Subject: Re: [SouthBendLathe] ER Collet nut
?

Are you saying you can just disengage the half nut, hand crank the carriage back, and restart on the same number?



On Wed, Feb 15, 2023 at 10:58 AM, Andrei wrote:

The only difference between metric and imperial on using threading dial is that with metric you have to start ON THE SAME mark, every time.?
?
From: [email protected] <[email protected]> on behalf of William Nelson <wnnelson@...>
Sent: Wednesday, February 15, 2023 10:55 AM
To: [email protected] <[email protected]>
Subject: Re: [SouthBendLathe] ER Collet nut
?
I had that idea a while ago as I had some parts to make that would have been easier to leave in the chuck and go back and forth to the lathe and mill. I considered using carbide tooling to thread a commercial hex block as there was sufficient wall thickness for the threads. I never got around to it but it is still in the back of my mind. If I had a surface grinder making one would be much easier. I have a 10k and have used the printed gears from Ebay with great success making metric threads. I believe I saw a way to use the threading dial on you tube but never tried it. Something about using the same mark on the dial I believe but don't hold me to it.
--
Bill From Socal



--
"well, I stand up next to a mountain- and I chop it down with the edge of my hand"



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"well, I stand up next to a mountain- and I chop it down with the edge of my hand"
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