Tapping Model Pipe Elbows
- Thread starter Metal Butcher
- Start date
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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.
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:
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
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
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
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.
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
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
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
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.
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.
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.
Hope that was 0.33" not 3.3" 
J
J
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
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
