Tapping Model Pipe Elbows

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Metal Butcher

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#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.

P1050275.jpg


#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.

P1050276.jpg


#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.

P1050294.jpg


#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.

P1050297.jpg


#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.

P1050299.jpg


#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.

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#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.

P1050311.jpg


#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.

P1050313.jpg


-MB

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

slkride
 
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
 
Brilliant! Now where do you get the castings?
 
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.
P1050313.jpg


-MB

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

res491.jpg


res496.jpg
 
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
 
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.
 
MB,

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

Alan
 
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