Making a valve stem with a double thread

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Mark D
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Location: Sort of between Litchfield and Forest City, MN.

Making a valve stem with a double thread

Postby Mark D » Mon Feb 26, 2007 12:56 am

I made another valve stem today.
This one for a water glass blow down.
Interesting thing about it was that it’s a double thread. Would that be double helix?
Two threads, each of 4 threads per inch, 180 degrees out of phase with each other.
I’d never made a double thread before, and for a while didn’t know how I was going to accomplish this. How would I start the second thread exactly 180 degrees off from the first?
Aha! Eureka! I made the first thread. After the last cut I ran the tool halfway through the travel of the thread and stopped it. Without touching anything else, I loosened the tool post and reset the tool to as exactly between the existing thread cuts as I could. I then touched the tool against the work and finished that cut. Not really surprisingly, it cut right where I wanted it to. So, I went to the start and began cutting a thread just like the first. The big question was whether I’d have it accurate enough to work.
When the thread was finished, I hoped it’d work and finished making the rest of the stem.
When it was done, much later, and cut from the bar, I tried it in the nut. Amazingly it worked better than I could have hoped for. Smooth and easy, but not loose.
Ed, if you’re reading this, yes it’s the one you think it is.
For anyone who’s wondering, I used MP-45. Or, actually, the equivalent.
The T handle that is used to turn this valve stem has a tapered square hole. I wanted to use a spin index fixture and just turn it 90 degrees at a time and mill a tapered flat. But the shaft is .480 dia. I don’t have a way to hold it. Since I was almost done, and running out of time because I have other stuff to do, I just took it to a belt sander and eyeballed it. The handle fits, but not well enough yet.
Mark D.
Mark D. - The bottom of the information curve

Ed Selinsky
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Location: Green Bay WI

Re: Making a valve stem with a double thread

Postby Ed Selinsky » Mon Feb 26, 2007 12:04 pm

Mark,

Thank you for your time and talent in perhaps finally solving the leaky stem issue. This is the valve body that was made new (IIRC) in the rebuild in 1993, but the original stem was used again. I will look forward to a sucessful steam test of it this spring!

Ed Selinsky

Mark D
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Joined: Fri Jul 15, 2005 5:01 pm
Location: Sort of between Litchfield and Forest City, MN.

Re: Making a valve stem with a double thread

Postby Mark D » Mon Feb 26, 2007 2:37 pm

Ed, I don't know about the valve body, but the nut and packing gland both are cast and say "PRIME" "Milwaukee" on them.
I think this is going to take care of the issue, but we won't know for sure 'till we hydro and make sure the new stem seals tight on the seat.
It should, but one never knows for sure 'till it's proved out.
I'm just happy the threads worked out. Unless the weather gets too bad, I'm planning to be at the shop this week and try it out for fit.
If it snows too much, I'll stay out here. I don't like getting all that salt they dump on the highways on my car.
Mark D.
Mark D. - The bottom of the information curve

bsd_mike
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Re: Making a valve stem with a double thread

Postby bsd_mike » Thu Mar 01, 2007 12:29 pm

Mark,
Any chance of a picture?

-Mike

Mark D
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Joined: Fri Jul 15, 2005 5:01 pm
Location: Sort of between Litchfield and Forest City, MN.

Re: Making a valve stem with a double thread

Postby Mark D » Thu Mar 01, 2007 1:58 pm

Hmmm. Maybe. It's all assembled right now, and I'll have to bring my wifes digital camera from home and take the picture, then bring the camera home and upload it from there.
It'll take a while, like maybe Monday before I can do it. But I'll try.
Mark D.
Mark D. - The bottom of the information curve

Brent A
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Location: Twin Cities

Re: Making a valve stem with a double thread

Postby Brent A » Thu Mar 01, 2007 2:24 pm

12:58 pm on a Thursday... No trip to Mpls Jct. Today?

Mark D
Conductor
Posts: 3341
Joined: Fri Jul 15, 2005 5:01 pm
Location: Sort of between Litchfield and Forest City, MN.

Re: Making a valve stem with a double thread

Postby Mark D » Thu Mar 01, 2007 3:21 pm

Nah. It's snowing pretty good in the Cities, as here, and I really don't have a crying need to go to the Cities today, so I decided to not subject my car to all that salt they throw down on the roads in the Cities.
Here I don't see much salt 'cause It's mainly back roads to my house.
I'm going home early. Taking the valve stem with me. Taking pics of it and loading it sometime today. Or tonight. If the power doesn't go out.
First I need to get back up my driveway. Suburban in 4WD had to work pretty hard getting out earlier this morning. It's been snowing the whole time since I left. Should be fun.
Mark D.
Mark D. - The bottom of the information curve

Mark D
Conductor
Posts: 3341
Joined: Fri Jul 15, 2005 5:01 pm
Location: Sort of between Litchfield and Forest City, MN.

Re: Making a valve stem with a double thread

Postby Mark D » Thu Mar 01, 2007 6:01 pm

Here are some not-so-good photo's of the valve stem and a practice piece I made first out of relatively cheap 360 brass to make sure it would work like I thought it should, and a demo piece I made this afternoon just for this thread. The piece in the lower left in the first two, and middle in the last photo has a full thread for the firs thread, and a partial thread running on only the left half of the part for the second thread. This way you can see the first thread only, and the second thread as it's partially formed. If it were carried through to completion, it would look like the one on the lower right, which was my first test piece, or the real thing, on the top.

Image



Image


Image
Mark D. - The bottom of the information curve

Don C.
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Re: Making a valve stem with a double thread

Postby Don C. » Fri Mar 02, 2007 12:10 am

Mark,
Your talents are simply endless. I can't even chew the end off of a freakin' toothpick!

Don C.
"I ain't as good as I once was, but I'm as good once, as I ever was."

bsd_mike
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Joined: Sat Jul 16, 2005 12:56 pm

Re: Making a valve stem with a double thread

Postby bsd_mike » Fri Mar 02, 2007 8:55 am

Looks really good Mark.
I take it you have more than a Taig Lathe at your disposal!
-Mike

Mark D
Conductor
Posts: 3341
Joined: Fri Jul 15, 2005 5:01 pm
Location: Sort of between Litchfield and Forest City, MN.

Re: Making a valve stem with a double thread

Postby Mark D » Fri Mar 02, 2007 12:57 pm

It's an elderly 10" swing Clausing/Colechester. Gear driven, but not the worlds greatest machine.
Main business is automatic machining with single and multi spindle screw machines. Lathe is just something that sometimes comes in handy.
I'm not all that good. It's just that when I have a new challenge, I guess. If I guess right I brag.
In truth, my idea here was just to spread around what I figured out in case someone else runs into a similar problem. There's a lot more than just me making steam locomotive parts. Most of them have already done this a zillion times, but then there's probably someone in my shoes out there too.
Mark D.
Mark D. - The bottom of the information curve


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