Honden L 560B lathe

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mbelfer
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Re: Honden L 560B lathe

Post by mbelfer »

Thanks, some of which is supposition but none of which helps me be sure of the initial size to bore the hole before starting the thread. i have a nose copy i made a long time ago but cant remember how i calculated the minor diameter on the first backplate i made. the only way i am sure will give me correct minor diameter is the three wire method, but even for that you need a known nominal diameter. you cant just put a mike or caliper across a thread to get the diameter - it depends on too many factors

i must keep the thinking cap on a bit longer.
mbelfer
Posts: 9
Joined: Thu May 19, 2016 10:38 pm
Location: Melbourne Australia

Re: Honden L 560B lathe

Post by mbelfer »

Hit send too early: pls disregard prior post. I still need to be reasonably sure of the initial size to bore the hole before starting the thread. i have a nose copy i made a long time ago but cant remember how i calculated the minor diameter on the first backplate i made. (it was 35 years ago) the only way i am sure will give me correct nose thread diameter is the three wire method, but even for that you need a known nominal diameter. the only thing i am sure is that it is NOT the 2" printed in the manual, as the register is at least 70 thou over that, even the threads are over the 2", but probably not enough to be 2-1/8 (which would be weird anyway).

Certainly 10ths are not worth chasing, but i do need a reasonable starting bore size or it will be so sloppy as to be useless once the thread can do up.(dont ask how I know!!)
its a bit of a catch 22 situation
i must keep the thinking cap on a bit longer.
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Harold_V
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Re: Honden L 560B lathe

Post by Harold_V »

mbelfer wrote: Sun Feb 14, 2021 10:32 pm Now you cant bore an exact internal thread without starting from the correct minor diameter,
I'd like to invite you to rethink that statement. Knowing the minor diameter plays little (no) role in achieving the proper pitch diameter. There are far too many variables that make that simply unreliable.

If you hope to achieve the proper pitch diameter, you are best served by making a plug gauge. Even then, unless the form of both threads is correct, the gauge may or may not serve the intended purpose, so spend the necessary time it takes to get the threading tool ground properly. It should match the form of the thread on the spindle.

My advice to you is to measure the major diameter of the thread on the spindle (using wires), then to duplicate that diameter on the plug gauge you should make. Ensure that the threading tool has the correct form, and, having premeasured the spindle with wires, duplicate that fit on the plug gauge. That way your endeavor should yield success.

It is important that you understand that you SHOULD NOT create threads by working from either the major or minor diameters. Too many chances for poor results in doing so.

H

Edit:
you cant just put a mike or caliper across a thread to get the diameter
Ahhh! But you can! There is no good reason why you can not. I would not trust a caliper, be it vernier, dial or digital, but I'd certainly trust a micrometer. And, if the thread is too wide to permit the anvil and spindle of the mic to work, simply place a shim between one of them and the thread. Subtract the thickness of the shim from the resulting reading and that should (reliably) indicate the major diameter. Regardless of the pitch, you can always make contact with the major diameter with either the spindle or anvil.

I couldn't help but notice that you mentioned that the register is larger than 2". The register diameter should not have a relationship with the thread, although it must be of equal size, or larger, than the major diameter. It could well be that the register is metric, but the thread is not. Only you can make that determination.

If the major diameter measures greater than 2.000", then you are correct in thinking that it is not Imperial, even if the pitch is. They would NOT send out a bastard thread, as the spindle must accommodate commonly available accessories.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
mbelfer
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Re: Honden L 560B lathe

Post by mbelfer »

OK you sound like you speak with authority, so I am rethinking As s I said, I do have a duplicate spindle nose (it has a register so it is more than just a plug gauge). So I have rethought, and viewed many videos, and read whatever I can find about internal threading. so please help me understand why starting hole diameter is not only important but critical?

I have to start from a bored hole. If that hole is too small, the plug gauge will never enter no matter how perfectly formed the thread is. If it is too large then engagement will be reduced and the backplate wont be held securely. In the extreme, with a very large starting hole it will be a clearance fit and just slide in. The starting bore must be in between, and that determines percentage depth.

The spindle measures 1.983 over the crests - what hole size would you bore? (You have cut an internal thread before, I suppose?)
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Steggy
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Re: Honden L 560B lathe

Post by Steggy »

Just for reference, the spindle on my JET 1236PS is 2-1/4" × 8 TPI. The register diameter is exactly 2.250", measured with a 3" mike.
mbelfer wrote:OK you sound like you speak with authority...
Harold knows his stuff. I recommend you carefully "listen" to him. :D

BTW, the thread form on your lathe's spindle might not be 60 degrees. I seem to dimly recall there were lathes produced with spindles having the Whitworth thread form, which is 55 degrees with radiused crests—USS and ISO (metric) use flattened crests.
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Music isn’t at all difficult.  All you gotta do is play the right notes at the right time!  :D
mbelfer
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Joined: Thu May 19, 2016 10:38 pm
Location: Melbourne Australia

Re: Honden L 560B lathe

Post by mbelfer »

60 degree 8TPI thread gauge fits very closely. (gauge set by SPI)
M
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Harold_V
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Re: Honden L 560B lathe

Post by Harold_V »

mbelfer wrote: Mon Feb 15, 2021 1:56 pm so please help me understand why starting hole diameter is not only important but critical?
The minor diameter of threads should NEVER make contact with the major diameter of the fitting thread. That is not true of tapered pipe threads, which have a sharp V form.

The major and minor diameters of threads, be they A or B threads, are important, as they establish the parameters within which the threads, which bear on the ****pitch diameter****, are formed. That said, a properly profiled thread will bear on the opposing thread flank, but it is measured at the theoretical pitch diameter. For that reason the form should be correct, so the thread will bear correctly, and the measurement at the pitch diameter is reliable.
I have to start from a bored hole. If that hole is too small, the plug gauge will never enter no matter how perfectly formed the thread is. If it is too large then engagement will be reduced and the backplate wont be held securely.
Yes, that is correct as far as the mating thread entering the generated thread, as an undersized hole (minor diameter too small) will prevent the mating part from entering, but it is NOT true that an oversized bore will yield a sloppy thread, as the minor diameter is not a diameter that should be used to determine the pitch diameter, nor does it bear on the opposing thread. It provides the necessary clearance for the mating thread's minor diameter. It does nothing else. It should ***not*** be used as a guide to create the pitch diameter. That's what I tried to convey in my previous message.
In the extreme, with a very large starting hole it will be a clearance fit and just slide in. The starting bore must be in between, and that determines percentage depth.
Correct. But it does NOT determine pitch diameter, and that's why you should NEVER use either the minor or major diameter of a thread to determine pitch diameter. Depending on the thread in question, the amount of tolerance allowed for the flat, plus error in thread form, plus error in the minor (or major) pitch diameter, the chance of hitting the proper *pitch diameter* is left to chance. It's akin to measuring the size of a gas tank to determine how much gas it contains. There is no relationship. Get it? Measuring the tank will give you a theoretical content, but that does not reflect the amount it contains, only the amount it can contain. Same deal with working from major/minor dimensions. Theory tells you that you should be a given depth, but that's true ONLY when every parameter is correct. Any variations and your formula is valueless. The flat of the tool, alone, allows a great enough variation that you can hit the proper *pitch* diameter ONLY by chance.

Threads are not gauged by their major and minor diameters. They are gauged by their pitch diameters, taking in to consideration that the major and minor must fall within given parameters. Threads can be rejected (may not function) if all parameters are not held within those parameters. They are all important, as you can see.
The spindle measures 1.983 over the crests
That is within the boundaries of a 2"-8 class 2A thread (1.9978"/1-9828"). It is out of range for a class 3A thread (2.000"/1.9848").
- what hole size would you bore?
For a class 2B thread, I'd bore 1.8647"/1.8797". For class 3B, I'd bore 1.8647"/1.8795".

Pitch diameter for a class 2B thread is 1.9188"/1.9292" For a class 3B thread pitch diameter is 1.9188"/1.9261"

Take note that the tolerance of the minor diameter is greater by almost twice the tolerance of the pitch diameter. That does not take in to account that the flat of the threading tool, too, has a broad tolerance. Get the idea?
(You have cut an internal thread before, I suppose?)
Somewhere in the deep, dark corners of my memory, I seem to recall having cut an internal thread at some time in my years in the shop. I started in the trade in 1957. My background is almost exclusively in the aero-space and defense industry. I ran my own commercial shop for 16 years. Yes, it's safe to say I've stepped in that puddle of oil before.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
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