# Tapping Model Pipe Elbows



## Metal Butcher (Feb 27, 2011)

#1 In one of my last posts on my Upshur Farm Engines thread I mentioned that I would need a fitting to re-direct the exhaust pipe to clear the fuel tanks close mounting position. After two days of experimenting I came up with a fixture to drill and tap 1/4" model pipe elbows with a repeatable accuracy. In the past I tried many different methods that yielded inconsistent and unsatisfactory results. This fixture is not my original idea, a very similar fixture was posted by one of our members last year. Unfortunately I couldn't find it, and gave up trying to locate the thread on which it was presented.

Below is a picture of the fixture I made. It consists of two identical halves lined up with dowel pins. I pinned the two 1/2" halves together before milling them to final dimensions. I drilled and reamed both dowel pin holes in one set up. First I reamed .1245" all the way through both halves of the fixture, followed with a .1260" reamer though the top halve at both locations. This allowed the dowel pins to be pressed into one half of the two piece fixture, and a slip fit into the other half.

Two through holes were drilled 5/16" followed by countersinking them with a 3/8" drill for the flanges on the pipe fittings. The countersinking was an eye balled job requiring patience. I would drill in part way and measure with calipers, then drill closer to the target location. I would stop to check the fit, and continue to drill and check. It took quite a bit of time to get the counter sunk steps just right to support the flanges on the pipe fittings. I don't know of any other way to do this since I was dealing with casting variances that could only be eye balled. It worked, and extremely well.







#2 The fixture makes finishing the elbows very quick and simple. In the picture below I lowered the end mill till it touched the top of the fixture and locked the quill. I then zeroed out my quill mounted dial indicator and raised the end mill .002". With one pass I trimmed one end of the elbow, and flipped the fixture over in the vise to trim the other end. It doesn't get any quicker or easier than this.






#3 With one elbow trimmed I went on and did another. You can get a rough idea from the picture of the accuracy a fixture like this provides.






#4 Using the same coordinates of X=.320" and Y=.500" to drill the fixture, the elbows can now be drilled and tapped with accurate results. I set the fixture against a vise work stop since I was planing on finishing more than one elbow. The first step was to center drill, or spot if you prefer, both ends of the elbow.






#5 The next step was to drill with a 7/32" drill at both locations. I drilled .400 deep measuring from the drills tip. I placed a .020" feeler gauge over the center drilled end and lowered the drill till it touched. After locking the quill I zeroed out my dial indicator, unlocked the quill, removed the feeler gauge and drilled till the indicator showed .420", meaning the hole was .400" deep at the tip.






#6 I tapped the holes 1/4"-40 UNS. After locking the tap in the mills chuck I applied downward pressure with one hand on the spider handle and drove the tap in part way by rotating the chuck by hand, to get the tap started strait, and finished up with a small tap wrench. 






#7 I finished up 4 elbows. I only needed one elbow for my project, but I got carried away a little, and made four. You know me, once I start having fun theirs no stopping me. 






#8 Here's a rough sketch of the fixture I made. Feel free to post a proper drawing that anyone could use to make their own fixture. I used the fixture and made four perfectly good elbows, so it's a proven design.






-MB


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## kvom (Feb 27, 2011)

Can I assume that the threads are MTP?

What type of fittings are you using for the piping?


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## SirJohn (Feb 27, 2011)

Excellent post.Thm: The pictures explained it all.


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## 1hand (Feb 27, 2011)

Funny thing, I just came from the PM check out, from ordering parts for my boiler. I got these same castings coming. Thanks for sharing your fixture, It will come in handy in my future.

Matt


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## Metal Butcher (Feb 27, 2011)

kvom  said:
			
		

> Can I assume that the threads are MTP?
> 
> What type of fittings are you using for the piping?



Hi Kvom. The fittings I used were tapped 1/4"-40 UNS strait thread. They will be used to re-direct the 1/4" exhaust pipe on at least one of my Upshur engines. Since there will be virtually no pressure build in the exhaust a tapered pipe thread is not needed.

The 1/4" 90* elbows I used are castings made of bronze, and sold by PM Research.

http://www.pmresearchinc.com/store/product.php?productid=3244&cat=39&page=1

-MB


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## Metal Butcher (Feb 27, 2011)

SirJohn  said:
			
		

> Excellent post.Thm: The pictures explained it all.



Thanks, I'm glad to hear that my attempt to show how the fixture is made and works, is understandable.

-MB


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## Metal Butcher (Feb 27, 2011)

1hand  said:
			
		

> Funny thing, I just came from the PM check out, from ordering parts for my boiler. I got these same castings coming. Thanks for sharing your fixture, It will come in handy in my future.
> 
> Matt



Hi Matt! Glad to hear that my post will be helpful. 

-MB


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## slkride (Feb 27, 2011)

you mite say the jig's up on the pipe fittings now, nice work mb         

                                           slkride


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## Metal Butcher (Feb 27, 2011)

slkride  said:
			
		

> you mite say the jig's up on the pipe fittings now, nice work mb
> 
> slkride



Thanks! That's really funny! Rof}

-MB


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## tel (Feb 28, 2011)

Brilliant! Now where do you get the castings?


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## Dan Rowe (Feb 28, 2011)

tel  said:
			
		

> Brilliant! Now where do you get the castings?



http://www.pmresearchinc.com/store/home.php?cat=39

Nice work MB.

Dan


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## ruralearl (Feb 28, 2011)

Hello, Thank you for posting, it will be useful. I don't know if this is frowned upon (or allowed), but here is a thread about fabricating model pipe elbows on another forum, starts in #579 on page 58: http://bbs.homeshopmachinist.net/showthread.php?t=39202&page=58&highlight=model+pipe
Regards, Earl


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## deverett (Mar 2, 2011)

Metal Butcher  said:
			
		

> #8 Here's a rough sketch of the fixture I made. Feel free to post a proper drawing that anyone could use to make their own fixture. I used the fixture and made four perfectly good elbows, so it's a proven design.
> 
> 
> 
> ...



The jig can be used to tap Tees, Crosses and Unions as well as the elbows. 

Countersink the other two holes. It will mean that the fitting is buried at one end, but after tapping the first end, the fitting can be turned round for the second operation.

Dave
The Emerald Isle


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## Deanofid (Mar 2, 2011)

Shoot, Rick, that's handy as pockets on a shirt. For years, (*many* years) I've done my PMR fittings in the four jaw, and it's never much fun. Done scores of them that way, but no more. I'm makin' one of these jigs!
Thanks!

Dean


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## MikeR C (Mar 6, 2011)

You might consider looking here for the jig:

http://www.homemodelenginemachinist.com/index.php?topic=6959.msg74371#msg74371

Nice job,
MikeR C


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## Kmot (Mar 24, 2011)

Metal Butcher, thanks for posting this. I liked your idea so much I made one for myself, only for the 3/16" size fittings.


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## Metal Butcher (Mar 24, 2011)

Kmot, that looks great!!! :bow:

Now you have a fixture that's solves the set-up problem for good, and should last a lifetime.

-MB


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## tel (Mar 24, 2011)

I've been keen to try this as well, but when I contacted PMR re the sort of postage I would have to pay they were most unhelpful. Don't know why some sites are so coy about postage rates, others seem to be able to put them up OK.


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## Kmot (Mar 24, 2011)

Thanks MB!


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## AlanHaisley (Mar 28, 2011)

MB,

I'm getting "bandwidth exceeded" msg from Photobucket rather than your pictures. ???

Alan


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## Kmot (Mar 28, 2011)

Alan Haisley  said:
			
		

> MB,
> 
> I'm getting "bandwidth exceeded" msg from Photobucket rather than your pictures. ???
> 
> Alan


I just happen to have saved his photos, so I hope Metal Butcher does not mind me posting them for you.


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## Kmot (Mar 28, 2011)

And the rest of them:


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## Reed (Dec 29, 2011)

After reading MikeR C post many moons ago, I remembered the jig when I needed a globe valve for a steam hammer model. I drew a set of diagrams based on this thread and it is posted at:

http://www.homemodelenginemachinist.com/index.php?topic=17069.0

Many thanks to those posting on this thread.

- Reed
Raleigh, NC

P.S. With Marv's suggestion, I have posted links on the original MikeR C's thread also.



			
				MikeR C  said:
			
		

> You might consider looking here for the jig:
> 
> http://www.homemodelenginemachinist.com/index.php?topic=6959.msg74371#msg74371
> 
> ...


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## Brian Rupnow (Mar 20, 2012)

This is probably a really dumb question, but how did you account for the material removed by the slitting saw you used to cut the block apart?---Or did you make two blocks and mill exactly half of each one away?---Or did you start with two seperate blocks clamped together and drill the holes at the split line? I am going to have to make something very close to what you posted to machine the same PM Research 1/4" castings.------and----Can I use a 1/4-28 tap and die on these fittings and pipe? I am not particularly worried about them leaking, as I will probably seal them with Loctite. Its just that if I use only Loctite and don't put any threads on at all, the joints will be fragile when handling the model. I'm not worried about air pressure blowing the joints apart, but the model is quite heavy, and sooner or later some stress is bound to fall on these pipes that will pull a Loctited pipe connection apart and drop the model onto the floor (Or even worse---My foot!!!!)Brian


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## maury (Mar 20, 2012)

Brian, I'm not sure what the original author of the thread did about the gap, bit I too have made similar fixtures. The ones I made were from round stock to be used in the lathe in a 3 jaw chuck. I used a .031 saw, but did not try to account for the gap. The reason is that these are castings, and while they are investment casting quality, there can still be slight dimentional differences. Of course, the gap allows a tight grab on the part 

As far as the thread is concerned, there is no reason you can't use a strait thread instead of a tapered one especially in your case. It would be good to pick one that does not require too much stock being taken off the nipple though. 

The biggest problem I have in making these fittings is the nipples. I bought a collet closer just to do these, but I find I have to really bear down really hard to get it to avoid slipping, especially for the full 11 turns for the pipe thread. I'm making 1/16-27 NPT fittings, and turn down the end of the 5/16 brass tube to .306 before threading.

maury


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## Brian Rupnow (Mar 21, 2012)

I'm off to build one of these fixtures, and to avoid any cutting, I have started with 2 blocks of 1 1/16" square x 1/2" thick plate. I rough cut them on the bandsaw and glued the two "faces" together and squeezed them together in my vice where they will dry for a couple of hours. I will then machine the outside to the appropriate dimensions and drill on the split lines,and add the dowel pins before I break the Loctite bond.


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## Jasonb (Mar 21, 2012)

When I used the fittings on the IHC I went for 40tpi threads 1/8, 3/16 & 1/4 which seemed to work well. 

And I didn't bother with jigs just holding the castings in the corner of the mill vice, did about 20 fittings that way without problems. If you are going to be doing lots of fittings on a regular basis then it may be worth spending the time on jigs but I didn't see the need.

As Maury says the castings do vary so the gap makes sure you get a good grip, I found quite a few are slightly squashed and not cast as perfectly round and there is also some mould shift which makes the dowel pins redundant as teh two halves of the jig need to move to accomodate the misalignment.

J


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## Brian Rupnow (Mar 21, 2012)

Well!!! That went amazingly well!!! I followed the rough sketch, although the only REAL important dimensions are the 0.320" offset from face of block to center of hole and the 5/16" and 3/8" drill diameters. I found that I had to use my Dremel tool to remove a very small bit of material from both "halves" of the jig on the inside corner, as my elbow castings don't have really "clean" inside corners, but other than that it seems to work fine the way I did it. Thank you for the neat "how to" post and the drawing.---Brian


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## rkepler (Mar 21, 2012)

When I made a jig for pipe fittings I made it from round stock so I could do all the operations in the lathe. I recall that I copied someone else's jig design from Live Steam.






The advantage is that you can put a stop behind it and then run the sequential operations - face, spot drill, depth drill, tap. If you have a turret you can run a face in a few seconds, without it's a still less than a minute if you have enough chucks. I went crazy and made a bunch of fittings, still came close to running out of 5/16-27 elbows.


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## Brian Rupnow (Mar 22, 2012)

Here is my first succesfully machined and tapped elbow. I used a 7/32" dia drill and only drilled .33" deep from where the tip first contacted the flat machined face of the elbow, then tapped with a 1/4"-28 tap. I found that when using MetalButchers original drill depth of 0.4" that the tip of the drill broke through the far side of the elbow. Even at a drill depth of 3.3" there is still plenty of open passage for air flow, and using a standard tap (not a bottoming tap) seems to get a sufficient depth of threads into the elbow.


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## Jasonb (Mar 22, 2012)

Hope that was 0.33" not 3.3" 

J


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## Blogwitch (Mar 22, 2012)

The thing is Jason, most of my sets of these fittings that came from PM are really badly cast as well. :wall: :rant:

Maybe they only send out good ones to our American cousins and us the garbage, as they most probably already know we in the UK can make silk purses out of pigs ears, or in this case, good out of crap. ;D ;D

 :fan:


John


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