Do you have access to a lathe?

I would turn the smaller rod down a hair then drill out the center of the lager diameter 1" to accept the smaller...

 

you could take an inch or so thick piece of aluminum or some other semi soft material. pop it in the drill press. Drill it about halfway with the bigger size bit. Then use a center punch of the right diam and punch the bottom (which should already have an indent from the drill bit) then drill out the rest with the smaller bit. You could then cut the top 1/4 of the material off with a bandsaw or angle grinder which would let you nest the 2 rods together and hold them while allowing for a window to tack. The problem is once you final weld the 2 together the whole thing is going to warp.

using a piece of angle iron with the right size shim stock on the smaller rod is probably the easiest way, then you can clamp it down to help fight warping.

 

See below. This would be just to hold them centered while you make 3 tack welds.

 

I'm guessing you don't have a lathe. Do you have a drill press? Try taking a thick piece of scrap. Clamp the scrap to the table. Drill completely through with the smaller size, then drill halfway through with the larger size without unclamping the workpiece. Then cut the piece in half across the hole.
You can then lay the two rods in this half-circle jig and their centers will be lined up.

You might even get away using just a hand drill. The larger drill should follow the hole of the smaller drill if you're careful.

 

Hello cromwell, I have included an image which would utilize a length of angle iron and some shims. If you were using 1/2"round and centering it on 1" you would need for the shims to be 1/4" thick, if you were using 3/4" round and centering it on 1" you would need to use 1/8" thick shims. I believe you get the idea. The view that is shown in the image would be looking down from the top. Good luck and best regards, Allan

EDIT:Have an additional image to give some orientation and also possibly show some access holes to help with tacking while the rods are being held. The shims, as they appear, would be on the inside of the angel and not as they look in the image.

 

Hello cromwell, I have included an image which would utilize a length of angle iron and some shims. If you were using 1/2"round and centering it on 1" you would need for the shims to be 1/4" thick, if you were using 3/4" round and centering it on 1" you would need to use 1/8" thick shims. I believe you get the idea. The view that is shown in the image would be looking down from the top. Good luck and best regards, Allan

+1. i had the same idea

 

Just like aevald said. Get piece of angle, lay the 3/4'' rod in angle, take a 1/8'' 6010 welding rod and cut in half, knock off coating, bend into a close 90 and lay in angle , take chisel and tap welding rod into bottom of angle, lay 1/2'' rod on top. You can then tack 1/8'' rod to angle to keep it from shifting. For the 1'' try 1/4'' rod.

 

Not mentioned, but probably assumed by Allen and the others, is that you also need to shim the rest of the bar material at some point, so it stays straight. If not that angle iron will tip up the connection and while it may be "centered" at the joint, it won't be centered and straight.

If you simply support the 1/2" with a length of 3/16" angle and the 3/4" with a piece of 1/4" angle, and make sure they line up ( the real trick), you kill 2 birds with one stone.

 

Very good point DSW, the longer you can make the angle and the shims the better the accuracy of the centering. Regards, Allan

EDIT: couldn't edit my other post again so I'll try to include an updated image here. This might better explain what Doug was referring to and I was agreeing with.

 

Hi all, I had a similar job some time back, had to join a drill bit to a longer shank to make an extension drill....it had to run true.

I have two cast iron vee blocks that I use for all welding situations working with round stock.

The secret is not to lay the blocks down on the welding table as you normally would but to clamp them against an angle plate.

Now the vees are in line when clamped sideways on but not in line looking along the bottom.....you don't want them in line on the bottom, they have to be at different heights to one another to allow for the different diams.

So I clamped the one Vee block tightly against the angle plate and down on a 1" thick packer, then I clamped the second vee block to the angle plate with another 1" block beneath it....this will allow you to butt weld bars of the same diam in line in two planes.

For material with different diams, just put a packer of half the thickness of the biggest rod beneath one of the vee blocks.....the two rods will be in line in two planes.

If this was a job that was a regular occurance, I would have the vee blocks with a hole through the side so that they could be bolted to the angle plate and just move one block up or down for half the diam difference.

The vee blocks can be made from angle iron welded to a base block....quicker to make than describe.

This job can also be done in the lathe....hold one piece in the chuck and the shorter piece in the tailstock with a hollow adaptor or a drill chuck......then cover the bed and Tig weld two good tacks to hold the rods and finally remove and weld fully on the bench.
Ian.

 

I use the angle iron method with shims under the small bar. Use a caliper to check size, then tack. Roll bar on surface to check alignment, persuade w BFH, tack again and weld. Works for me.

 

Yup.

Put the whole stupid thing on a piece of angle (angle long enough to support 2 pieces).

Tack some shims onto the legs of the angle iron to center the smaller dia piece, make sure you don't go to the center of the angle bend as this will throw you off. Place a few sets of shims to fully support the smaller dia piece.

Clamp it.

Tack it.

Weld it.

 

i got one for you.

take the threaded rod and spin two nuts on the very end of the rod.

jamb the nuts tight

take the threaded rod with the nuts on the end to the belt sander.

chuck the rod up in a drill and run the nuts across the belt sander with the drill spinning the rod.

this will "turn down the nuts"

when the nuts are roughly the same size as the outside as the 3/4" pipe use it as a bushing and weld the entire thing to the pipe, nut, threaded rod an all.

As long as the nut and pipe are the same size, and are flush, you will be very close to center.

Red Neck machine shop!

 

Just need a well-controlled big lathe....


From: http://mme.uwaterloo.ca/~camj/pdf/W...ral Evolution Model of Direct-Drive Friction Welding of Plain Carbon Steel,.pdf
​

I. INTRODUCTION
DIRECT-DRIVE friction welding is a well-established
solid-state joining process, which can be used to join a wide
range of conventional steel alloys, as well as more metallurgically
challenging systems such as dissimilar metal combinations
and superalloys. Figure 1 illustrates the four basic
stages in direct-drive friction welding. In the start-up stage,
one work piece is clamped in a spindle and a variable speed
DC motor is used to rotate it at a predetermined speed relative
to a stationary work piece. To begin the heat-up stage,
the two parts are brought together and an axial compressive
force, F1, is applied. Initially, heat is generated by
friction at the faying surfaces. This raises the temperature
of the metal at the weld interface and causes a decrease in
the flow stress of the metal. When the flow stress of the
heated metal at the weld interface becomes less than the
applied axial compressive stress, the metal begins to plastically
deform at a high strain rate. This plastic deformation
now generates the heat at the interface. At the same
time, the plastically deforming metal at the interface flows
radially outward to create the flash, carrying with it any
oxides and contaminants at the faying surfaces. This plastic
flow of metal and formation of the flash occurs during
the burn-off stage and results in axial displacement of both
work pieces toward each other and shortening of the overall
weldment. Finally, the welding process is completed during
the forging stage by stopping all rotation and applying
a high compressive force, F3.
Friction welding has several advantages over conventional
fusion welding processes. Since friction welding is a solidstate
joining process, all defects associated with melting and
solidification in a typical fusion weld are absent in a friction
weld. During friction welding, the heat is highly concentrated
at the weld interface. As a result, a friction weld
has a very narrow heat-affected zone (HAZ), which limits
the variations in mechanical properties of the base metal to
a small region. Friction welding has the additional advantages
that filler metal, flux, and shielding gas are not required
and the cycle time of the process is very short; small parts
take only a few seconds to weld. Finally, once a suitable
welding procedure has been established, the resultant weld
dimensions and high weld quality are very consistent and
reproducible.

​

More technical information which is interesting, if not usable by us:

http://www.twi.co.uk/technical-know...ed-papers/aero-engine-improvements-through-linear-friction-welding-august-2005/​

How's your head now?? ​

 

Thanks to all for the great ideas!

I ended up trying aevald's idea of a couple pieces of long angle. The 1/2" rod was supported the for about 1 foot with shims.

I did a light tack and then spun it to check if it was centered.


I am surprised how accurate and straight it turned out.

I like jdbuckshot idea of the 'nut' solution also...will have to try that.

Definitely need a Bridgeport mill for production work. Still saving for that.

Excellent feedback ...:drinkup:

 

You could use extruded aluminum angle since it has sharp 90 degree corners and will nest, unlike steel angle iron. Shim the smaller side with another angle/other shims and you're good.

 

Aevald:

I agree with your solution.
I have a piece of 2 inch angle mounted on the edge of my welding bench for just such a jig. I simply lay in shims and tack them as needed.
Works like a dream.:drinkup::drinkup:

Cheers.
Glenn.

 

Get a nice, square cut on the larger rod, debur, then use a small, adjustable square to scribe a small square onto the surface of the fresh cut. Start with 1/8" protrusion on the ruler, and adjust as necessary, depending on your marking apparatus. Once you've got the small square's ID sized exactly to the OD of your small rod, you're set.
-Aaron