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Posted by Terry on May 3, 2006, 4:10 am
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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.
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Posted by =?ISO-8859-1?Q?Nick_M=FCller?= on May 3, 2006, 4:18 am
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> 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>
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Posted by R. Zimmerman on May 3, 2006, 5:41 am
Please log in for more thread options 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
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.
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Posted by Terry on May 3, 2006, 12:33 pm
Please log in for more thread options 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.
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Posted by =?ISO-8859-1?Q?Nick_M=FCller?= on May 3, 2006, 2:15 pm
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> 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>
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> appreciated.