Need a way to turn a 30 tpi screw.

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earlgo
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Re: Need a way to turn a 30 tpi screw.

Post by earlgo » Thu Mar 15, 2018 9:08 am

Harold, I am not a fan of Dulite black oxide finishes as taught by the CST. I have done rust blueing, heat blueing, and Brownell's Oxpho Blue. Dulite takes too much room and equipment to be useful to the hobbyist.
Re the maroon color: We were taught that the temp in the Dulite bath was wrong if that happened. At Denver's elevation of 5000 ft, boiling water was not at 212° and it was sometimes difficult to get the Dulite tanks hot enough. Different story down here at 1000 ft. Mauser bolt release springs always came out maroon, however. I have a Lafever Single Barrel Trap Gun with a cast receiver that I Dulite blued at the CST and it came out a beautiful black color. A few years later it had turned a lovely purple maroon, so one can't tell right away. I also have a commercial Dan Wesson Revolver with an investment cast frame that over the years has taken on a decided purple hue. Funny stuff, blueing. However no S&W or Colt or Ruger I ever saw even hinted at maroon.
Lefever SB trap  circa 1930.JPG
DWMod15-2 frame.jpg
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

spro
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Re: Need a way to turn a 30 tpi screw.

Post by spro » Thu Mar 15, 2018 9:52 am

Hey Almost too pretty to work!
There are many to say more about the beautiful workmanship .

JackF
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Re: Need a way to turn a 30 tpi screw.

Post by JackF » Thu Mar 15, 2018 10:06 am

Thanks Earl, needless to say there is no rush. :wink: I would prefer to blue or blacken it if your test on 41L40 doesn't work out.

Thanks Harold for your input. :)

Jack.

John Hasler
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Re: Need a way to turn a 30 tpi screw.

Post by John Hasler » Thu Mar 15, 2018 10:50 am

Pickling in strong sodium hydroxide should remove the lead from the surface.

earlgo
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Re: Need a way to turn a 30 tpi screw.

Post by earlgo » Thu Mar 15, 2018 4:10 pm

The answer is yes it will blue. Here are examples left to right: 44-40 cold blue at room temp, Oxphlo Blue at 200°F, Heat blue at somewhere near 600° and not blued.
Blue results.jpg
I have never liked the 44-40 cold blue as it seems to rub away a lot quicker than the Oxphlo Blue. Surfaces cleaned with brake cleaner and post treated with silicon spray. For the heat blue, I set the lead pot at 700° set a pan of brass chips on the surface and set the slug on top of the brass chips. Took about 40 minutes, but the color is nice in my opinion.
The material cuts very nicely, by the way.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

earlgo
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Re: Need a way to turn a 30 tpi screw.

Post by earlgo » Mon Mar 19, 2018 10:10 am

This should maybe be in the gunsmith section but it is also relevant here.
Wisner's is a company that makes obsolete gun parts on modern machinery and is located in Washington state.http://www.wisnersinc.com/about-us/. They list a takedown screw for the Favorite.
Years ago I purchased from Brownell's a large 3 ring binder full of obsolete gun part drawings, and in the intervening years Wisner's apparently opened a shop to make those parts.
From what I found out cruising the I-net, the Model 1885 up to M1915 used the ring head takedown screw and the slotted screw came on the M1915 and later.
Just a FYI
Reverse threading.jpg
Setup
This is setup for "reverse" threading away from the headstock.
I expect a safety lecture from everyone, so let 'er rip. OSHA would have me jailed forever if this were a commercial shop. But it only takes one sleeve catch to remember. It is sort of like forgetting to remove the chuck key. The big bolt is for a counterbalance so the lathe doesn't walk away. I should have bolted on a chunk of steel instead of the projecting bolt, so this is a cautionary picture.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

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GlennW
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Re: Need a way to turn a 30 tpi screw.

Post by GlennW » Mon Mar 19, 2018 10:17 am

Not that you are doing it wrong, but for simplification, why not just use a chuck?

Grab the stock, turn it to size, and thread it.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

John Hasler
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Re: Need a way to turn a 30 tpi screw.

Post by John Hasler » Mon Mar 19, 2018 1:19 pm

With the dog already there to bite I don't see that the bolts make things significantly worse. I agree with Glenn, though. Why not just use the 4-jaw?

Harold_V
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Re: Need a way to turn a 30 tpi screw.

Post by Harold_V » Mon Mar 19, 2018 3:43 pm

I've machined a huge number of long, slender threads in my years in the shop. While I don't know the reason for the centers setup, one thing I do know is that it's the way to machine threads if you hope to have then straight. Small diameter threads taper readily when the end isn't supported properly, and it doesn't take a very long thread length to detect taper. As much as I detest machining between centers, it's entirely possible you'd find me with a similar setup.

While we all (I assume) do it, running a center with a chucked item isn't considered good practice. The reason is obvious if you analyze what happens when parts are run between centers as opposed to being chucked, with a center supporting the outer end. Chucked pieces can't self correct for movement due to stresses being relieved. End result, the machined piece isn't always straight. When working between centers, that's not true.

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

John Hasler
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Re: Need a way to turn a 30 tpi screw.

Post by John Hasler » Mon Mar 19, 2018 4:06 pm

Harlod writes:
> Chucked pieces can't self correct for movement due to stresses being relieved.
> End result, the machined piece isn't always straight. When working between
> centers, that's not true.

Hadn't thought of that. Thanks.

Seems like you could still have a problem when threading since you aren't correcting the OD as you cut. I guess you could start with an oversize piece and bring the tops of the threads into spec with a finish pass.

I don't think I want to try to make anything where that would matter on my old Logan.

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GlennW
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Re: Need a way to turn a 30 tpi screw.

Post by GlennW » Mon Mar 19, 2018 4:30 pm

Harold_V wrote:
Mon Mar 19, 2018 3:43 pm
I've machined a huge number of long, slender threads in my years in the shop. While I don't know the reason for the centers setup, one thing I do know is that it's the way to machine threads if you hope to have then straight.
While I don't disagree, looking at the part in question, and it's use, I didn't really consider a 5/16-30 thread that is about 3/8" in length to be long and slender and troublesome to cut. Especially using leaded stock.

But then again, I'm looking at it from making it with my machine (which doesn't have 30 tpi as a selection) and tooling and knowing the results I get, and "earlgo" is making it on his machine and tooling, which I know nothing about.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

Harold_V
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Re: Need a way to turn a 30 tpi screw.

Post by Harold_V » Tue Mar 20, 2018 1:09 am

I agree, Glenn. A 30 pitch thread that short isn't likely to deflect. Just thought I'd toss in my thoughts, as some folks don't realize how challenging chasing a thread is, thanks to the relatively large amount of tool in contact with the part.

John, while the OD could be of concern, unless there is considerable movement of the part, the OD isn't likely to be troublesome, as in theory, it never contacts the mating part, so slight mislocation would be acceptable. However, assuming it would be critical, and assuming there was significant displacement of the major diameter, one could take a finish cut on the major diameter after the pitch diameter was achieved. The amount of effort dedicated would be in keeping with stringent requirements, however, and in many cases it would simply be ignored. Note that for class 2A threads, there's typically an allowance (clearance, or undersize) of the major diameter, and a tap is made oversized on the major, to ensure that major diameters do not contact one another.

If you'd like to see how things turn out when chucking and supporting with a center, before removing the piece from the chuck, but after it is fully machined, release the center and place an indicator on the end of the piece, where it's been machined. You're likely to discover it does not run true. And, assuming it doesn't, and you used a center, you're likely to discover that not only does the machined surface not run true in a free state, but it is also not concentric with the center hole. When a stiff piece is machined, any changes will manifest themselves as side pressure, causing the tailstock to oscillate, so two problems are created, not just one. That condition is especially true on old, small sized machines, which often have a loose quill and are not all that rigid.

If you hope to end up with a straight, round and concentric long item that is machined, working between centers, as obnoxious as it is, is one sure way to achieve your goal.

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

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