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Rolland-Christians
09-02-2010, 07:12 PM
Hi-I was asked yesterday if I could rifle drill a .875" hole lengthwise through the center of a 4.5" shaft that is 110" long, and keep an accurate center. I have been thinking about this, and am not sure. I have a lathe with a stretch bed, and can get about 160"+ between centers, and have a couple good steady rests, but am not sure about the procedure. Using a small gun tap with air or oil to start, then going up in size would be theoretically possible. The finish doesn't have to be perfect because it only carrys air, but the center would have to be pretty precise. Has anyone else tried to do this? This job may not materialize because of the expense, but now I would like to know if this is possible-Thanks, Rolland Christians (Oh, by the way, I just joined this group yesterday-I have a small machine shop in North Florida, and take on some pretty strange projects for people. Used to be a machinist for Ford in Mn. a long time ago)

Evan
09-02-2010, 08:03 PM
Seems to me that if it only carries air and not bullets or similar then the requirement for accurate centering applies only to the ends. Not so?

MrDan
09-02-2010, 08:19 PM
I have a small machine shop in North Florida, and take on some pretty strange projects for people.

North Florida = ...strange people for projects. (I was born in Ocala.) :)

Welcome, this is a great group here.

Black_Moons
09-02-2010, 08:25 PM
If it only carrys air, why are you not just buying premade hose/tube that can handle the pressure/tempature required?

J Tiers
09-02-2010, 08:37 PM
Hi-I was asked yesterday if I could rifle drill a .875" hole lengthwise through the center of a 4.5" shaft that is 110" long, and keep an accurate center. .................................................. Used to be a machinist for Ford in Mn. a long time ago)

Sounds like a tall order without a real gun-drilling setup. It can be done, it was done by the hundreds per day in WW2.

A machinist in MN? Would that be the Highland plant? Down by the "Ford bridge" in St Paul? Used to go by there all the time. Even had a tour of it ages ago.

Rich Carlstedt
09-02-2010, 10:26 PM
Thats a perfect job for a gundriller
To them its a piece of cake and a two hour job
Rich

Mcgyver
09-02-2010, 10:34 PM
Welcome Rolland

gun drill schmun drill. If you look at post 19 in this thread, it went by without fanfar but in it I explained a technique that is almost foolproof using standard drills and reamers....the original story came with the claim of holding a thou over 3 or 4' with a 3/4" hole. Having used it, I believe it just might be that good (i haven't drilled 4') so depending on your view of 'accurate' this will probably work.

http://bbs.homeshopmachinist.net/showthread.php?t=43014

Rolland-Christians
09-02-2010, 11:02 PM
Thanks, it only carries air, but also is the main driveshaft and turns a large fan using a 1200HP cat engine-The air is for the air clutch. It should be concentric to maintain balance of the shaft. I bought my bridgeport and Ajax lathes from a machine shop that went out of business a couple years ago in Ocala Fl-The plant in Mn was at Eveleth, worked in the Fairlane and Thunderbird plants (Taconite processing plants, worked as a field millwright, plant millwright, and machinist-Untill they laid me off for the last time in 1981, so I moved to Florida)Worked for McGraw Edison as a machinist in Ft Lauderdale for awhile in the early eighties, and then someone bought the shop and broke it up, sold the land, and told us to go find another job-Did a lot of portable boring for them, under all the drawbridges in Fort Lauderdale, re-bored and re bushed the machinery underneath, one side at a time, and they would open the other side to let the boats through.

J Tiers
09-02-2010, 11:16 PM
Welcome Rolland

gun drill schmun drill. If you look at post 19 in this thread, it went by without fanfar but in it I explained a technique that is almost foolproof using standard drills and reamers....the original story came with the claim of holding a thou over 3 or 4' with a 3/4" hole. Having used it, I believe it just might be that good (i haven't drilled 4') so depending on your view of 'accurate' this will probably work.


Well, since you are in a "metric country, you wouldn't know this (;) ), but that hole he wants is apparently 9 feet and 2" long.....or about 2.8 m.

much of the problem is getting a machine to swing that length of shafting, while manipulating a drill of some sort which is the same length plus a bit.

If you have to pull out the bit for any reason, it's gonna be a pain. Oil out the drill tip would take care of the chip issue.

That 160" bed is going to result in only about 40" or a bit more of clear space, so some sort of clamp holder that a long drill slides through, or a slide bearing arrangement and an external frame to steady the drill rod and guide it down the center may be necessary.

or a gun drilling setup, which is about that to begin with. You will "make" a gun drill setup to do the job, essentially.

Evan
09-02-2010, 11:31 PM
Seems to me that thick wall pipe would serve just as well.

Tony Ennis
09-02-2010, 11:35 PM
Seems to me that thick wall pipe would serve just as well.

Or at least be a good place to start.

Evan
09-02-2010, 11:47 PM
I did a quick calculation of the bending strength of a solid bar that size vs a pipe with 0.5 inch wall thickness.

The solid bar with simple supports at each end and with a 2000 lb distributed load located evenly starting 20 inches from each end will produce a static deflection of 0.111" at the centre.

The 1/2 inch wall pipe with the same loading deflects an additional 0.075".

All that is required is a couple of end caps and a few spiders tacked to a suitable piece of air pipe that runs down the centre of the main shaft pipe. Seamless DOM should suffice for the shaft just fine.

It will also weigh half as much which will make the stiffness to mass ratio higher.

J Tiers
09-03-2010, 12:12 AM
Unless I am unable to read today, the part is a SHAFT, which probably needs little in bending, and plenty in torque capability.

However, the issue is not the design, he apparently has been told that, and much more how that hole is getting down it.

That having been said, a 1200 HP Cat diesel, and a large fan..... I don't think that is a good place to have a rough, and particularly not a "scored" inside diameter. Torque-wise vibrations might cause those scores to become stress raisers, and lead to a fracture. With a 1200HP fan, that is probably not a good idea, it makes a spun-off chuck in the shop seem like a dropped nail paring.......

So half-way methods are not the very best here..... Someone with a 25' bed machine could deal with it in short order, especially if they have an oil-fed drill. Not all jobs that darken the door are ones you want. or that you should do.

Evan
09-03-2010, 12:32 AM
Unless I am unable to read today, the part is a SHAFT, which probably needs little in bending, and plenty in torque capability.


No kidding? The point is to show how little the core contributes to the strength. The torque capability will be directly proportional to the bending strength, which is what I have a program to calculate.

lwalker
09-03-2010, 08:27 AM
I'm confused, are you saying Ford made their own steel up there?


<snip>...The plant in Mn was at Eveleth, worked in the Fairlane and Thunderbird plants (Taconite processing plants, ...

becksmachine
09-03-2010, 08:27 AM
Yes, it is very doable.

As for doing it in an engine lathe, it would be a long haul to go that deep with a gun drill. Other considerations aside, you really couldn't feed it manually with the tailstock, consistent and continuous chip formation is key to getting the chip to eject itself so you don't need to peck, even with the high pressure coolant.

Oh and a coolant pump that would supply about 5-20 gpm at 500-1500 psi and the means to contain this flow when it is squirting out of the hole.

Rich has it right, a piece of cake for the people that are set up for it, but somewhat involved for a one of.

Dave

Peter S
09-03-2010, 08:28 AM
Just for anyones interest....I have a book by Joseph Serafin (ex-Ford Motor Co.) which explains how he made accurate deep holes, I found it interesting anyway.

See post # 13 on this thread:

http://bbs.homeshopmachinist.net/showthread.php?t=22874

J Tiers
09-03-2010, 08:31 AM
No kidding? The point is to show how little the core contributes to the strength. The torque capability will be directly proportional to the bending strength, which is what I have a program to calculate.

The core contributes NOTHING to torsional strength or stiffness at zero radius, and contribution increases as you go outwards.

However, I was not arguing about the loss of strength, Evan, that is irrelevant, the design is set, and the task is to MAKE the part.

I was more addressing the issue of someone's comment that the finish wasn't important. While the core contributes little strength even at that radius, it IS stressed all the way in to that bore, and a stress riser in there may have bad effects.

Especially when a "flywheel" is coupled to a nearly megawatt piston engine. And when the "flywheel" is a device which inherently has periodic vibrations from airflow, obstructions etc.... i.e. a big fan. It is similar to a large aircraft engine application.

So make-shift methods of boring the hole may give a worse finish than an actually suitable way of doing the job, and those finish issues might actually affect the operation negatively.

Evan
09-03-2010, 08:59 AM
However, I was not arguing about the loss of strength, Evan, that is irrelevant, the design is set, and the task is to MAKE the part.


Perhaps, perhaps not. Not many driveshafts in that sort of application are made from bar stock. Have a look on a large hiway tractor. Same application but much more demanding. The drive shafts are tubes.

J Tiers
09-03-2010, 10:23 PM
Perhaps, perhaps not. Not many driveshafts in that sort of application are made from bar stock. Have a look on a large hiway tractor. Same application but much more demanding. The drive shafts are tubes.

Ho-hum..... Also on lots of trucks, cars, etc. Old, old old OLD news.

Demanding? In what way? At what power level? What if it breaks?

How is the application LIKE a truck driveshaft? How is it UNLIKE a truck driveshaft?

What is the peak torque? What is the torque "ripple"?

Answer those questions, and the problem begins to shape itself.

Evan
09-03-2010, 11:33 PM
You already know the answers to those questions Jerry. You also know that driveshafts are tubular, not bar stock. For a simple quick calculation of the required torque transmission capability calculate the area of a 4.5 inch shaft with a 3.5 inch ID. Then take the shear strength of that amount of material and compare to the probable torque rating of a 1200 hp diesel at 2000 rpm.

By a basic rule of thumb you can count on ductile steels to have a shear strength at least half the ultimate tensile strength. For mild steel that is around 30ksi. You can do the rest of the math. A half inch wall is grossly overrated even allowing for a ten times safety margin.

Rolland-Christians
09-03-2010, 11:48 PM
Seems to me that thick wall pipe would serve just as well.
Hi Evan-That was my original suggestion too, but the engineers are afraid it will take too long for the air to reach full pressure on the clutch with the extra volume-Now they are looking at moving the air clutch to the fan shaft, and then I won't have to bore the driving shaft, it can be solid or mechanical tubing-Each solution brings up another problem-but if it were easy, anyone could do it! Thanks, Rolland

Rolland-Christians
09-03-2010, 11:53 PM
I'm confused, are you saying Ford made their own steel up there?
Ford owns taconite mines and processing facilities on the Iron Range-They make taconite pellets and sell them to the highest bidder, not sure how much of their own steel they get back-Rolland

Evan
09-04-2010, 02:07 AM
Hi Evan-That was my original suggestion too, but the engineers are afraid it will take too long for the air to reach full pressure on the clutch with the extra volume

That is why you stick a length of pipe down the center with occasional disks welded to it to prevent whipping. Caps or plugs at each end with the pipe fitted through the caps and the volume problem is solved.

J Tiers
09-04-2010, 10:33 AM
You already know the answers to those questions Jerry. You also know that driveshafts are tubular, not bar stock. For a simple quick calculation of the required torque transmission capability calculate the area of a 4.5 inch shaft with a 3.5 inch ID. Then take the shear strength of that amount of material and compare to the probable torque rating of a 1200 hp diesel at 2000 rpm.

By a basic rule of thumb you can count on ductile steels to have a shear strength at least half the ultimate tensile strength. For mild steel that is around 30ksi. You can do the rest of the math. A half inch wall is grossly overrated even allowing for a ten times safety margin.

Very silly....... that straw man was not the point.........

The point was that:

1) the equipment mentioned was obviously not suitable for a proper job of boring the hole.

2) make-shift boring means might likely produce stress-risers in the form of gross irregularities in the bore, which is not a good thing when dealing with a shaft at this power level, especially one with the very good possibility of reversing stresses. AND pressure in the bore besides.

3) Not all jobs are worth taking on...... there are specialists for a reason.

The exact likelihood of a problem is less important than the obvious fact that it's a PITA to do, might have a bad result, and can be easily and suitably done by a company with the proper tools.

Rolland-Christians
09-04-2010, 10:57 AM
I want to thank all of you for your input-Gives me a lot more information when dealing with the engineers on this job. My primary hesitation on bidding this part of the job (fabricating and boring a shaft) is of course liability, I am too small a company to be able to afford mistakes. The best I can do is to point these people in the proper direction, my job really starts on assembly, I am responsible for all the alignment, placement of the machinery, and proper base materials, etc. This is also a government owned facility, and there is a lot of red tape and many people to go through for each change. I will advise what the final solution is when it is made. (The other thing about mechanical tubing is the keyways that have to be cut on the outside, so am still not sure what the final material will be.) Again, I thank all of you for your input, it has been very helpful. Rolland