I am building a new hub for a 8" rim I use on my mini chopper. I
turned down a tube to about 3/16" thick, and bored each end to fit a
new bearing. I then CNC machined 2 mounts out of 1/8" thick steel, one
for my rim and one for a disc brake. They each have four mounting
holes on them.

I then attempted to weld the two mounts onto the tube. The mounts fit
very snug on the tube so I was able to get them perfectly square before
I started welding. Though for the hub to work properly, I can only
weld on one side of each mount becuase the other side needs to sit
flush against the rim and the disc brake. This is how the original hub
was designed.

I began by making small tacks 180 deg from eachother. Then I stitch
welded small portion 90 deg apart until I had a bead all around the
tube. But both mounts ended up warping up towards the welded side. So
now my mounts are not perfectly square to the tube, and I have about
..030" run out on my disc brake and rim when spinning on the axle.

So basically I have to start all over again, but I really don't know
how to avoid this warpage while welding on one side of a part. I
could use less heat, but I really want to make sure I penetrate the
1/8" steel. This is a wheel hub which has a lot of weight on it, 100's
of pounds.

Any suggestions in preventing this type of warpage would be greatly
appreciated.

Thanks.

Bevel prep the inside bore of the mount so that you have a 45 degree bevel
3/32 nds deep. Make up a dummy flange/disc to mimic the wheel and the disc.
Bolt them to the mounts in order to hold the mounts flat during welding.
With the preparation you only need to put in enough weld to come out a
sixteenth of an inch maximum beyond the mount surface. You will have almost
full penetration with the bevel prep. The more weld you locate further
away from the centreline of the mount the more distortion you will have.
I am guessing the mounts are just small flanges with bolt holes. Can
you modify your CNC program to create several ribs on the open face of the
mount. It would add fancy detail and create a more rigid disc mount.
Randy

"Terry" wrote in message
oups.com...
I am building a new hub for a 8" rim I use on my mini chopper. I
turned down a tube to about 3/16" thick, and bored each end to fit a
new bearing. I then CNC machined 2 mounts out of 1/8" thick steel, one
for my rim and one for a disc brake. They each have four mounting
holes on them.

I then attempted to weld the two mounts onto the tube. The mounts fit
very snug on the tube so I was able to get them perfectly square before
I started welding. Though for the hub to work properly, I can only
weld on one side of each mount becuase the other side needs to sit
flush against the rim and the disc brake. This is how the original hub
was designed.

I began by making small tacks 180 deg from eachother. Then I stitch
welded small portion 90 deg apart until I had a bead all around the
tube. But both mounts ended up warping up towards the welded side. So
now my mounts are not perfectly square to the tube, and I have about
..030" run out on my disc brake and rim when spinning on the axle.

So basically I have to start all over again, but I really don't know
how to avoid this warpage while welding on one side of a part. I
could use less heat, but I really want to make sure I penetrate the
1/8" steel. This is a wheel hub which has a lot of weight on it, 100's
of pounds.

Any suggestions in preventing this type of warpage would be greatly
appreciated.

Thanks.

Thanks for the information. Yes, the mounts are small flanges with 4
bolt holes. I will bevel the inside bore of my flanges, and build a
mount to keep the flanges from bending. Some 1/4" steel should work
pretty well. I'll probably step down the current one notch and take a
little more time in between each weld to minimize the heat.

Do you think that even if I sucesfully weld the flanges on the tube
without warpage (while mounted to some sort of support piece), that
when I remove the support piece from the flange, it will have some sort
of memory and warp anyway? It would probably be best to let the piece
completely cool down before I pull anything apart.

I could add some ribs to the flange, but I would have to start out with
a thicker piece and take off a lot of material. How tall and how many
ribs would you recommend for an 1/8" thick flange. It is about 4"
diameter with a 1 1/8 center bore.

I don't have the option to weld first and then machine. My mill does
not have the Z travel to accomodate my hub.

Before I begin machining a new hub I will try the old hammer and dial
indicator trick to see if I can true up my flanges. Maybe I'll get
lucky this time! Thanks.

Terry wrote:

Do you think that even if I sucesfully weld the flanges on the tube
without warpage (while mounted to some sort of support piece), that
when I remove the support piece from the flange, it will have some sort
of memory and warp anyway?

It will.


It would probably be best to let the piece
completely cool down before I pull anything apart.

Doesn't help that much.

I would (if you insist on machining then welding) weld it in a different
way that makes less warpage.

Drill holes into the flanges (diameter 6..7mm) and countersink them (on
the outer side). The holes have to match the center of the tube's wall.
Weld into those holes with a MAG (quite high current). These welds tend
to pull the flange flush to the tube. Of course you have to clamp your
work while welding.
Trick is to make the welds in a short time with high current that
assures that you melt the tube. You won't have succes with stick welding
and less success with TIGing.
Make some trial welds to get the trick. It is not very difficult.
There are even special gas nozzles (for MIG/MAG) for that job, but you
don't need them. I have one but never use it.
Holes can even be bigger -to some amount- than the tube's wall thickness

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO // Eigenbau-Digitalanzeige
http://www.yadro.de

I would try something like an extra one eighth rib on the outside rim. It
is only four inches in diameter so that should do it. It will locate your
weld closer to the neutral axis of the disc.
I agree with one comment about overwelding. Can you shrink the assembly
on and just put a couple of locating tacks in???
I worked for a company that build wheels for ore trucks. Their original
design called for simply shrinking the rim onto the steel centerpiece. No
weld was required at all. Later designs had just a little bead to locate
the rim on the centerpiece. These were big wheels handling hundreds of tons
payload.
Your solution will end up being the combination of all the contributions
here.
Yes you are right about letting your assembly cool after welding. Warm to
the touch is OK.
Randy


"Terry" wrote in message
ups.com...
snip
I could add some ribs to the flange, but I would have to start out with
a thicker piece and take off a lot of material. How tall and how many
ribs would you recommend for an 1/8" thick flange. It is about 4"
diameter with a 1 1/8 center bore.

I don't have the option to weld first and then machine. My mill does
not have the Z travel to accomodate my hub.

Before I begin machining a new hub I will try the old hammer and dial
indicator trick to see if I can true up my flanges. Maybe I'll get
lucky this time! Thanks.

I like the idea of shrinking the flange onto the tube. I can easily
machine the flange I.D. to be a couple of thousands smaller than the
tube O.D. Then I could use a hotplate to heat up the flange then slip
it into place and let cool. I could then put some very small tack
welds in place.

How much undersized would you recommend making the flange I.D. compared
to the tube O.D. for a permanent fit with no chance of slippage?

If I can't true up my existing assembly, I will go this route on the
next one. Thanks.

For steel the coefficient of linear expansion is about 12 x 10e-6 per
degree C. Figure the max temp difference you can achieve while
assembling the worst case fit (oversized shaft tolerance with undersized
hub tolerance. If you put a 1" shaft in some liquid nitogen at -196C and
heat the hub to the max your home oven will go (say 270C) you will get
..0055" of total expansion/shrinkage. The max interferance fit you can
get in practice has a lot to do with how accurate your machining is plus
how well you can assemble the parts before they start normalizing their
temps.

We did one aluminum prototype in two pieces that was supposed to have
..002" clearance with the temps we were using. We wound up using a press
to assemble since the aluminum conducted the heat so fast. But the parts
were bonded together1

Cheers.


Terry wrote:
I like the idea of shrinking the flange onto the tube. I can easily
machine the flange I.D. to be a couple of thousands smaller than the
tube O.D. Then I could use a hotplate to heat up the flange then slip
it into place and let cool. I could then put some very small tack
welds in place.

How much undersized would you recommend making the flange I.D. compared
to the tube O.D. for a permanent fit with no chance of slippage?

If I can't true up my existing assembly, I will go this route on the
next one. Thanks.

idea:

cut slight taper on part to be inserted (less than a morse taper, like a
degree, or maybe even half a degree), with matching taper in the axle
end. freeze spindles, heat outer tube, slam together "pronto-like" (wood
block, vice, huge hammer). bonded forever, no welding, no add'l fasteners.

reamers -might- be available in sizes correct for the outer tube, to
simplify things...

Using a taper will work but makes it very tough to get the longitudinal
position correct.

dave wrote:
idea:

cut slight taper on part to be inserted (less than a morse taper, like a
degree, or maybe even half a degree), with matching taper in the axle
end. freeze spindles, heat outer tube, slam together "pronto-like" (wood
block, vice, huge hammer). bonded forever, no welding, no add'l fasteners.

reamers -might- be available in sizes correct for the outer tube, to
simplify things...

Terry wrote:

Any suggestions in preventing this type of warpage would be greatly
appreciated.

Change the sequence of operations. First weld, then machine (the holes
for the bearings).

Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO // Eigenbau-Digitalanzeige
http://www.yadro.de

With welding you can reduce but never eliminate the warpage. If it's
critical, weld first, machine second. Sounds like you need tolerances in
the .001" to .003" range, no choice but to weld first. In fact, you
would be well advised to stress relieve the part after welding and
before machining. If you don't, the vibration from use will stress
relive it for you, your mounting flanges will drift.

Terry wrote:

I am building a new hub for a 8" rim I use on my mini chopper. I
turned down a tube to about 3/16" thick, and bored each end to fit a
new bearing. I then CNC machined 2 mounts out of 1/8" thick steel, one
for my rim and one for a disc brake. They each have four mounting
holes on them.

I then attempted to weld the two mounts onto the tube. The mounts fit
very snug on the tube so I was able to get them perfectly square before
I started welding. Though for the hub to work properly, I can only
weld on one side of each mount becuase the other side needs to sit
flush against the rim and the disc brake. This is how the original hub
was designed.

I began by making small tacks 180 deg from eachother. Then I stitch
welded small portion 90 deg apart until I had a bead all around the
tube. But both mounts ended up warping up towards the welded side. So
now my mounts are not perfectly square to the tube, and I have about
.030" run out on my disc brake and rim when spinning on the axle.

So basically I have to start all over again, but I really don't know
how to avoid this warpage while welding on one side of a part. I
could use less heat, but I really want to make sure I penetrate the
1/8" steel. This is a wheel hub which has a lot of weight on it, 100's
of pounds.

Any suggestions in preventing this type of warpage would be greatly
appreciated.

Thanks.

First, I doubt that the mount has to be welded all the way around. They
seldom do in HSM projects.

*Assuming* that they do not, here is what I would do (it's what you
might call a vertical plug weld): on your mount, before you cut out the
hole for the tube, drill holes (3/8 diam +-) around the circumference of
the hole, centered on the circumference. Maybe 8 (every 22 1/2 deg).
When you then cut the hole for the tube, it will have semicircular
notches around it. Fit the mount to the tube and fill in the notches
with weld.

Let us know if you try this and how it works,
Bob

Bob Engelhardt wrote:
... drill holes around the circumference .. Maybe 8 (every 22 1/2 deg).
...

Oops, that would be every *45* deg.

Bob Engelhardt wrote:
... here is what I would do ...
Fit the mount to the tube and fill in the notches with weld.

I was so taken with this idea that I had to try it. View from the
outside (front):
http://home.comcast.net/~bobengelhardt/weldfront.jpg
and from the inside (back):
http://home.comcast.net/~bobengelhardt/weldback.jpg

The shaft is 1" diam, the notch was drilled with a 5/16" bit. A 3/8"
notch would have made it easier to get weld deposited in the back/inside.

I know, the weld is cold. But that was the welder's fault, not the
technique's.

Bob

Looks good. I'll have to machine some new flanges. I will modify my
program to add the notches. So the idea is if I do a quick weld to
fill in each notch 180 deg apart I should minimize the heat and the
warpage on the part.

I might give this a try.

Thanks for the demo.