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Posted by RoyJ on May 3, 2006, 9:36 am
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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.
>
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Posted by Bob Engelhardt on May 3, 2006, 2:31 pm
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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
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Posted by Bob Engelhardt on May 3, 2006, 10:54 pm
Please log in for more thread options Bob Engelhardt wrote:
> ... drill holes around the circumference .. Maybe 8 (every 22 1/2 deg).
> ...
Oops, that would be every *45* deg.
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Posted by Bob Engelhardt on May 5, 2006, 7:30 pm
Please log in for more thread options 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
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Posted by Terry on May 5, 2006, 9:35 pm
Please log in for more thread options 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.
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> 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.
>