Metrology of carrier shaft tapers

[JHOLLAND1]

From Cutting Tool Engineering-current issue. Interesting method of taper check. I suspect
Forrest had the last word on this when at the shipyard
Quote
"The propulsion drive shafts of Navy submarines, ships and aircraft carriers require maintenance about every 2 years.
That involves dry docking the ship or submarine at a Navy shipyard, removing the shaft, inspecting it for wear, filling
in any worn areas using additive techniques and then removing excess material on a lathe and with a hand-held grinder.
The shafts measure up to 30" in diameter and 60' or more in length. The current method for inspecting a shaft taper,
which has been the accepted practice for 50 years, utilizes a bluing fit. Resnick noted that there are a total
of five ring gages used by the U.S. shipyard community for inspecting such large shafts. Each gage weighs 500 to 600 lbs.
and is positioned onto a shaft using a sledge hammer with a specific weight and a prescribed number of hammer blows.
Then the gage, which has a bluing die applied to its contact surface, is removed and a group of inspectors collectively determine the percentage of bluing transferred from the gage to the shaft, with a good shaft having at least 80 percent of
the die. “If the shaft needs additional machining, it’s reinstalled on the machine tool and the process is reiterated,” Resnick
said. “It’s very time-consuming and very archaic.” The inspection process takes about 72 man-hours. “The standard rule of
thumb on what are called hotel services, or write-up expenses while in dry dock, is that they cost $250,000 a day minimum,” said Sean Krieger, project engineer with a specialty in repair technology at the Applied Research Laboratory at
Penn State. “So the clock is ticking the minute that submarine or ship arrives in the dry dock for refurbishment work.”
The Pearl Harbor Navy Shipyard asked ARL to help improve its metrology processes, including shaft taper inspection.
Before that initial project ended, ARL recommended using a Laser Tracker from laser measurement system provider
Faro Technologies Inc.,"
end quote

http://www.scribd.com/doc/22394302/c...g-October-2009
http://www.ctemag.com/


jh

[CalG]

I have been inspecting tapers with a sledge hammer for years.

It's the approved method.

Now, where did I leave that dark corner?.....

CalG

[A_Pmech]

I'm more interested in hearing how they break the taper without disturbing the blue. I suspect that's the fun part. One wrong movement and SMEAR!

[The real Leigh]

Originally Posted by JHOLLAND1

From Cutting Tool Engineering-current issue.

Is that copyrighted material (if it's a quote from the article the answer is yes).

If so, please remove it and provide a link to the online article from the magazine website.

Thanks.

- Leigh

[JHOLLAND1]

Leigh

I found no copyright restrictions or proclamations of copyright by either author or publisher anywhere in the 88 page pdf.
I cited source and have now enclosed in quotation marks.
I have not altered document other than segmental extraction. I am not trying to make money off this.
The real proof that publisher allows broad reproduction privledges is permitting a full download and upload to my document website. No embeded blocking kernels which are common in copyright pdf files which block reproduction.

Download the pdf from my site and judge for yourself. If you need more I will attempt to contact publisher for clarification.

jh

[Forrest Addy]

This post is right up my alley. I worked for 31 years in a machine shop at Puget Sound Naval Shipyard. The citation is BS in part but there is some truth to it.

First of all the underwater overhaul interval of a Naval vessel isn't two years. It used to be five years but since the 70's or so it's been seven.

Next is while the ship is drydocked a lot of other activity is going on. The exterior hull is blasted to bare metal, corrosion repaired, and a new paint system is applied and boy is the Navy ever fussy about how this phase of the underwater work is performed. The propellers, shafting, rudders and rudder stock are removed for inspection and testing for flaws and cracks, repaired etc. The water lubricated bearings are re-staved to suit the any re-cuts required by shaft sleeve re-cuts, replacement etc. The entire salt water plumbing system, (main and aux condenser, fire and flushing, ballasting etc) is overhauled and those sections suffering corrosion and damage replaced. So you don't drydock a ship just to inspect the shafting. While it's in drydock a whole slew of work items and systems are addressed taking six to nine months. Running Navy is not cheap.

I've tested shaft tapers of all sizes including carrier shafting and fitted them to propellers. Yeah the specs say 80% bearing with the gage and later with the propeller to be fitted to it. Everytime I ever fitted a taper gage on a prop shaft we did it right on the lathe. We hung the gage from a single pendant with a chain hoist to fine possition it vertically, We backed the crane away a few feet and lunged the gage on the taper. Naturally it sticks. Feelers merely tell you if one end is big. To get the full fit information you go over it with a lead hammer tapping while listening to the sound and so locate the parts solidly seating and those parts not bearing. We chalked this info on the gage for later reference. Back the crane away from plumb a few inches, give the gage a solid smack from a 16 lb lead hammer and the gage would pop clear of the taper with very little smear.

Yes, lots of prussian blue was used to slobber up the gage and enough had to be applied to get a reliable reading but not enough to smear or spread. If you could see the texture of the gage metal through the blue that was about right.

I don't know about other shipyards but we never used sledge hammers on gages even real big gages.

It didn't take 20 guys to sign off the taper fit. When the time came we called the engineers who sent down a tech to eyeball the fit and co-sign the A sketch. The A skecth is a document that certifies the work item (Ship, Job Order, Plan#, Pc# etc was performed per standard such and such, and the criteria was met, inspected, and approved by the undersigned on the date etc.

When it came time to check the shaft in the prop the prop was laid thrust side down, the bore cleaned and stoned, the shaft hoisted up vertically (up to 45 tons! up to 60 feet!) and the taper blued. Then we lowered the shaft into the prop bore, lined up the keys, and let the shaft settle the last few inches as fast as the hook could drop. This made a soft thud you could feel through your feet for some distance. Chances are the shaft would stick in the taper. When that happened the crane would take a strain and the riggers and local strongmen would whale away on the big end of the prop hub with big lead hammers until it unstuck. Usually the shaft would bounce up a half inch or so. Wild ride for the crane operator.

Then the engr tech and the shop rep would look at the bearing and again sign off the papers. Not a big deal. Just hard fussy work on a large scale. There were never any histrionics if there was a do-over. The engineer had the call and usually stood right there and often shared in the work as the bore was touched up with a big air buffer. If there was a problem it usually took less than an hour to fix.

The Navy has far more than 4 or 5 gages. A set was usually made for every unique shaft design. Two sets it there was a muff coupling. I've seen as many as eight gage pairs at a time lined up along the columns back when. The Navy keeps these gages until the last ship of the class has been scrapped and the spare shafting removed from the Federal Stock inventory nad delivered into the hands of the scrap meerchants.

[number 2]

Forrest Addy, out of curiosity how heavy was the lead hammer? ive never seen one. Are they still in use or has copper taken over. Sounds very usefull.

[The real Leigh]

Originally Posted by JHOLLAND1

I found no copyright restrictions or proclamations of copyright by either author or publisher anywhere in the 88 page pdf.

Under federal law, exclusive copyright vests in the publisher at the time the work is created.

No copyright notice is required in any form.

The only exception to this is that an author can retain copyright to a work published as part of an aggregate work like a magazine if a notice to that effect is included.

Kindly provide permission from the publisher or remove the text.

Copyright law info can be found on the Copyright Office website www.copyright.gov

- Leigh

[Forrest Addy]

Number, we called them "lead hammers" but actually they were made of scrap Babbitt. We had a Babbitt room (actually a sort of foundry) where we poured Babbitt bearings. The Babbitt metal makes an excellent soft hammer because it's considerably harder than lead but a bit softer than annealed copper. It wouldn't mar even softer bronze alloys but if struck with enough vigor would bend or deform more delicate parts. Since the lead content was small it posed a lower health hazard but these days I don't know if Babbitt hammers are still allowed. Also it was simply and almost infinitely recyclable.

Babbitt hammers were use in every shop in a 10,000 man shipyard. Hundreds were swapped at the tooroom every day. Renewing the heads formed a large part of the Babbitt room workload in slack times. It was a good job for the apprentices that rotated through it.

Babbitt hammers are readily made in the home shop if one were to make a mold, secure some scrap babbitt, and whip up some suitable pipe handles.

[number 2]

Cheers for that. I come from a recreational fishing family and we have been making out own sinkers for years, so we have scrap lead around. Ive not ever seen babbit. Lead as a health risk seems to get glossed over around here.

[JHOLLAND1]

Leigh
This am I had a 15 minute conversation with Mr Alan Richter, editor of Cutting Tool Engineering. He agreed to review posts in this forum and related links. You are correct- his publication is covered by copyright as noted in small print bottom of page 82. I missed this. He may choose to respond as a forum participant or may reply to me only in email. Hope to have response later today.

jh

[bryan_machine]

Forrest - of course the way you describe it makes perfect sense.

And it's not hard to see why using a laser tracker could help.

But having never been in a shipyard, I'm confused by a few things...

1. The gage only tells you about the end of the shaft, right? So it only tells you that the taper at the very end that is fitted to the prop is correct?

The rest of the shaft is just measured with mics? Such shafts are cylinderical, no?


2. So you have a very long very heavy shaft, suspended vertically with a crane, how do you hang onto the shaft safely? This would seem to be a really nasty accident waiting to happen.

[JHOLLAND1]

Hello Jackson,

I reviewed your subformum on metrology and have no problem with you posting the few paragraphs of the “Tech Swap” article about making military parts from Cutting Tool Engineering’s October 2009 issue because you noted where the information initially appeared and provided links to CTE’s Web site as well as the entire issue on the Scribd site. As I mentioned in our phone conversation, I consider your posting of those paragraphs to be a fair, noncommercial use of the information. There’s a mention of Resnick, and you might want to note that he is Ralph Resnick, chief technology offers for the National Center for Defense Manufacturing and Machining in Latrobe, Pa. I have a bit of an issue with Forrest Addy’s post though. The information in the article and what you posted is based on what people in that particular project conveyed to me when I interviewed them and they agreed the information was correct prior to publication. However, it appears some of what they said doesn’t follow actual practices, at least at the Puget Sound Naval Shipyard. Please note: that section of the article had nothing to do with or any reason to provide insight into the other activities conducted while a ship or submarine is dry docked. It was only intended to focus on propulsion drive shaft inspection. I suppose it adds to a free-rambling online exchange, but it’s off topic. Also, I have no idea where the “It didn’t take 20 guys to sign off on the taper fit” reference comes from.

Hope this replies helps clarify things.

Cordially,

Alan Richter

Editor

Cutting Tool Engineering



my note
In the interest of fairness and education I will contact Mr Resnick for input in shaft metrology.

jh

explicit approval requested and received to post Alan Richter's email.

thanks

[The real Leigh]

Originally Posted by JHOLLAND1

explicit approval requested and received to post Alan Richter's email.

Thank you very much.

Just trying to keep everything legal (unemployed attorneys are a good thing )

- Leigh

[JHOLLAND1]

Leigh
you are managing this correctly. I learned a bit and perhaps main stream manufacturing media folks will look at this forum favorably. certainly Alan Richter was just super in his response to these concerns

jh