Machinists Level

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John Hasler
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Re: Machinists Level

Post by John Hasler » Mon Feb 19, 2018 2:33 pm

RMinMN wrote:
Mon Feb 19, 2018 7:27 am
If you require a certain level of precision, you buy that and pay the price. If your lathe has never been leveled, the precision of this level is better than any guess. You decide if the price for this level matches its presumed level of precision.
A lathe needs to be flat, not level. Leveling is just one way to get there.

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SteveM
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Re: Machinists Level

Post by SteveM » Mon Feb 19, 2018 4:05 pm

wlw-19958 wrote:
Mon Feb 19, 2018 1:47 pm
The picture is not a 12" model. It is either 6" or 8"
model.
6" 98's go for about the same on ebay.
wlw-19958 wrote:
Mon Feb 19, 2018 1:47 pm
I cannot tell if this is the 97 model or the 98 from the
pictures provided.
That will make a difference. The OP will have to let us know.

Steve

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mklotz
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Re: Machinists Level

Post by mklotz » Mon Feb 19, 2018 4:28 pm

How does one determine the amount of bed twist that is tolerable given a description of the accuracy required?

I read about people using levels with incredible accuracy claims to untwist a lathe bed and it makes me suspicious that such accuracy is not really required for typical home shop work. However, it's a only a suspicion; hence the question above. The answer I would like to see goes something like this...

The worst error due to bed twist is ... and an error of ... occurs for every ... arc second of twist.

Given an answer like that, it should be straightforward to determine how sensitive a level the user requires. Nevertheless, I've never seen it expressed in this way.
Regards, Marv

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Russ Hanscom
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Re: Machinists Level

Post by Russ Hanscom » Mon Feb 19, 2018 6:21 pm

I would have to go with Marv; without knowing the twist/error relationship, the rest is just an exercise. Might turn a part with a measured twist, straighten the lathe, and cut a new part and compare the error.

Leveling the bed is really just a convenience; the lathe could be mounted at a 90 sticking out from the wall - obviously not level but capable of a good part if the bed is true. Note that a lot of fancy CNC machined have inclined beds.

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SteveM
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Re: Machinists Level

Post by SteveM » Tue Feb 20, 2018 7:05 am

Russ Hanscom wrote:
Mon Feb 19, 2018 6:21 pm
Leveling the bed is really just a convenience;
Level is just the most convenient substitute for ensuring that both ends of the bed are in the same plane. I've looked at a lathe, put the level on, took a reading and then checked that the off-level reading was the same at the other end.
Russ Hanscom wrote:
Mon Feb 19, 2018 6:21 pm
the lathe could be mounted at a 90 sticking out from the wall - obviously not level but capable of a good part if the bed is true.
Would be really hard to operate, and there's no way I'm going to be on the "downhill" side from that!

Steve

John Hasler
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Re: Machinists Level

Post by John Hasler » Tue Feb 20, 2018 8:51 am

Steve writes:
> Level is just the most convenient substitute for ensuring that both ends of the bed are in the same plane.
> I've looked at a lathe, put the level on, took a reading and then checked that the off-level reading was the
> same at the other end.

A level is a nulling instrument. Due to symmetry you can more accurately judge that the bubble is centered on zero than that it is exactly as far off on one reading as it was on a previous one.

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SteveM
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Re: Machinists Level

Post by SteveM » Tue Feb 20, 2018 9:40 am

John Hasler wrote:
Tue Feb 20, 2018 8:51 am
A level is a nulling instrument. Due to symmetry you can more accurately judge that the bubble is centered on zero than that it is exactly as far off on one reading as it was on a previous one.
Yes, but there are lines on the tube, and the bubble on a line means the same angle at one end of the bed as the other. I didn't have the ability to level the lathe I was checking, but the check at each end told me that we were at least close on the bed not having a twist in it. Not perfect, but useful. If it had shown the bed wildly off, then I would have known that any measurements I took would have been suspect.

The second set of lines on a carpenters level refers to a slope of 1/8" per foot, which is used for things like the slope on gutters, so you can use the lines for measurements.

Steve

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wlw-19958
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Re: Machinists Level

Post by wlw-19958 » Tue Feb 20, 2018 10:54 am

Hi There,

Just to be clear, the model 97 level has two lines which
are for centering the bubble. The 98 has a series of lines
on either side of the bubble. A 97 can be converted to a
model 98 by replacing the vial but this probably isn't an
economical solution.

Good Luck!
-Blue Chips-
Webb

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SteveM
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Re: Machinists Level

Post by SteveM » Tue Feb 20, 2018 11:28 am

wlw-19958 wrote:
Tue Feb 20, 2018 10:54 am
Just to be clear, the model 97 level has two lines which
are for centering the bubble. The 98 has a series of lines
on either side of the bubble.
Thanks for that info.

Here is a 97:
Starrett97.jpg
Starrett97.jpg (17.91 KiB) Viewed 1945 times
And here is a 98:
Starrett98.jpg
Starrett98.jpg (7.49 KiB) Viewed 1945 times
Steve

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wlw-19958
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Re: Machinists Level

Post by wlw-19958 » Tue Feb 20, 2018 1:15 pm

Hi There,

QED

Good Luck!
-Blue Chips-
Webb

jpfalt
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Re: Machinists Level

Post by jpfalt » Sat Mar 31, 2018 11:04 pm

Having recently priced the vial, that alone is worth the $60. Levelling the base and readjusting the vial is pretty trivial. I'd say go for it.

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