A topic for Glenn or Harold re: metrics

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Harold_V
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Re: A topic for Glenn or Harold re: metrics

Post by Harold_V »

The thread dial functions only for imperial. For metric, it's easy enough on the Graziano to simply reverse the machine, which is done by electromagnetic clutch, not by reversing the motor. It's instantaneous, and does no harm to the machine.

H
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liveaboard
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Re: A topic for Glenn or Harold re: metrics

Post by liveaboard »

I've not yet needed such an accurate thread. When I do, I'll have to figure it out.
I don't have a 127 / 120 gear set, but (for instance) a 1mm thread calculates at 0.99888mm with the change gear set I have.
(42/89, 40/80)
I'm sure my worn out lead screw has more error than that.

I've always used reverse, it's how I learned to cut threads. Unless the thread is really long, it takes just a few seconds. If the thread is really long, I speed up the motor for backing up.
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Harold_V
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Re: A topic for Glenn or Harold re: metrics

Post by Harold_V »

Thanks for the response.
I suspect that for the work you do, that's probably adequate (not trying to be rude). The almost four tenths thou error per thread would add up to a woeful amount of error for long engagements, which was my point. In such a case, one would simply cut the pitch diameter somewhat undersized, but the error in lead isn't ideal, as the loading on the thread is at one point, so if the load is extreme, there's a failure of the thread due to limited support.

I recall, many years ago, when I was employed by United Precision, a now defunct machine shop in Utah, that a small repair job came in that was given to me to solve. It required a metric thread, but none of the machines in the shop were capable. I did exactly what you do and achieved acceptable results, primarily because the length of engagement was relatively short. One does what one must do to get the job done.

H
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tornitore45
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Re: A topic for Glenn or Harold re: metrics

Post by tornitore45 »

No doubt Harold knows about the 120/127

The thread dial will not work. On the other hand, even threading metric with a metric lead screw present problems with the thread dial.
SAE threads are TPI, one single gear on the thread dial covers all the thread pitches even the 1/2 pitch
Metric threads are not always commensurable to the lead screw pitch therefore several gears are available to be fitted on a metric thread dial.

For example, M4-0.7 with a 5mm lead screw. The threads are in step every 35 mm so the thread dial gear must have a multiple of 7 teeth
But M10-1.25 requires a thread dial gear with multiple of 4 teeth
This is because there is no concept of rational-number of threads per mm

I have seen documentations of technique allowing the disengagement of the 1/2 nut but sound a bit "Micky Mouse" to me.
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Bill Shields
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Re: A topic for Glenn or Harold re: metrics

Post by Bill Shields »

And for those of us with belt drive imperial machines....we stick with imperial threading to avoid headaches
Too many things going on to bother listing them.
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tornitore45
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Re: A topic for Glenn or Harold re: metrics

Post by tornitore45 »

How does the belt drive affect the threading? Anything that spin the spindle should work but there must be some side effect?
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Bill Shields
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Re: A topic for Glenn or Harold re: metrics

Post by Bill Shields »

belt drive = old clunker that does not have INCH / METRIC conversion gearbox built in.
Too many things going on to bother listing them.
atunguyd
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Re: A topic for Glenn or Harold re: metrics

Post by atunguyd »


Harold_V wrote: That's when the light came on. Instructions were for 1 kg (220 pounds). A 55 pound bag is ¼ kg.
Oh dear Harold I think you just proved your own point about not being able to transition to metric.

1kg is 0.22 pounds, not 220) and a 0.55 lbs bag is a ¼ kg

I know everything is bigger over there on the US but you just made the metric system 1000 times bigger [emoji23]


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Harold_V
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Re: A topic for Glenn or Harold re: metrics

Post by Harold_V »

atunguyd wrote: Wed Dec 01, 2021 11:53 pm
Harold_V wrote: That's when the light came on. Instructions were for 1 kg (220 pounds). A 55 pound bag is ¼ kg.
Oh dear Harold I think you just proved your own point about not being able to transition to metric.

1kg is 0.22 pounds, not 220) and a 0.55 lbs bag is a ¼ kg

I know everything is bigger over there on the US but you just made the metric system 1000 times bigger [emoji23]


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Chuckle!

See what I mean?

Ok, my apology folks. I meant to say 100 kg, which is what the printed instructions discuss. Just goes to show that we old folks struggle with new things.

H
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pete
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Re: A topic for Glenn or Harold re: metrics

Post by pete »

Well actually 1 kg is 2.2 lbs for general round numbers, or more exactly it's 2.20462 lbs per kg. :-)
atunguyd
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Re: A topic for Glenn or Harold re: metrics

Post by atunguyd »

pete wrote:Well actually 1 kg is 2.2 lbs for general round numbers, or more exactly it's 2.20462 lbs per kg. :-)
There always has to be one wise guy [emoji12]

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pete
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Re: A topic for Glenn or Harold re: metrics

Post by pete »

Lol, I was thinking to myself exactly the same when I made that post. :-)

But this sort of proves it's better to stick with the measurement system your most familiar with since it reduces the chances of simple mistakes. NASA even learned that with trying to land one of there expensive probes inside a planet instead of onto it.
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