I need a suggestion. I need to telescope a length of 3.5" x.120 steel
tube inside a piece of 3 1/2" sched 40 welded pipe 24" long. I have
.05" of clearance which is just right for my purposes EXCEPT for the
weld bead on the pipe. I could go get a stick of seamless but that
would defeat the principle of using up my drop and add even more. I
only need to take off about .02" to get a nice slip fit.
My first thought was to dress an old grinding wheel down to 3.5",
mounting it on a long arbor and driving it through with my heavy 5/8"
drill but I can invision the possibility of a broken arm should the
Can anyone suggest a safer or easier method?
A hole saw might do the job. You would have to grind the first half inch of
the weld down to start it but that would be easy with a Dremel or similar
tool. Do it in a drill press
(or lathe) - kep the speed way down and pressure moderate and lots of lube.
Hole saw or other edged cutter with a pilot pin that has a groove in it for
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Works evevery time it is tried!
I did the same thing only the size was a piece of 2.5" sched40 that I
wanted to slip a piece of 2" into for a grinder stand.
I tried sanding cones in a die grinder with drill rod modified to reach
down the pipe about 18" or so, the halfway point. If would have taken
forever to get this done, and very quickly got too sloppy, couldn't
control the sanding cone and keep it on the burr.
So, like you, I thought, why not make a cutter that can be turned with a
handdrill, and cut the burr out (this was all before I had a lathe,
drill press, or mill). So I borrowed my dad's lathe and made a round
plug, the same diameter as the I.D. of the pipe, tapped the center
.5-13NC, hacksawed a 1/4 wide groove to accept HSS bit, and added some
screws to retain the cutter. I ground the bit to be similar to a lathe
bit. It worked, but I would suggest using a large drive shank than 1/2
all-thread. The cut is interrupted, so it shocks the shank and drill
every time it hits the burr and tends to bind the plug up in the pipe
as it gets twisted off axis. I couldn't slow the drill down because it
didn't have the torque needed to drive thru the cut. Because I was
manually feeding the drill, the cut was way to deep too. So this all
made for a very choppy, brutal method. This method doesn't really
provide you with a way to incrementally cut the burr, you need a way to
control the depth of cut and a way to keep the drive shank center in the
To do it again, I would build a more rigid drive shank, and probably
figure out how to do it in the drill press, or the lathe with the pipe
mounted on the cross-slide.
Come to think of it, I used a stone that I took off of its short arbor
and put it on some all-thread and drove it carefully with a air die
grinder at probably 3-6000 rpm. Used wood blocks to take some of the
whip out of the all-thread. This was mostly to clean of the rough
spots, not to cut all the burr.
Glenn Ashmore wrote:
Use the dressed grinding wheel, but make a key slotted eccentric disc to
follow the bead down the pipe ahead of the wheel.
The disc keeps the grinding wheel positioned along the bead and the bead
makes a temporary key that you remove as you go.
Something like an 1/4" disc turned to 3.5" diameter with a center pivot hole
for a pilot on the grinding arbor offset 1/8" from center. Dress your
grinding wheel to 3.25 in. and as an added benefit the rest of the id will
be protected. Cut a slot clocked to the offset axis to fit the weld bead
and off you go. Might need to install a cheap bronze bushing int the disc
for the pilot to turn in.
There will be a slight undercut to get a flush surfacec with a 3 1/4 "
wheel, but probably a lot less than what you would get just tossing a 3 1/2"
wheel through it with no guide.
Haven't tried this yet, but I have the same issue with some welded stainless
tubing that would be near perfect except the bead. My original thought was
a custom set of push broaches but that seems like it would be too much
effort to save...very little.
Ok, here's an idea. What about making a large D-bit just the size of your
desired ID of the pipe? Grind away just the first 1/2" or so with a die
grinder, then put your pipe in a stout vise and run your D-bit in from the
end. Since a D-bit has over half of a cylindrical shape it will follow straight
down the pipe, and just (ideally) nip away a bit of the weld on each rotation.
If you have a lathe with a big spindle bore you could mount your pipe in a
chuck and feed the D-bit in using the apron.
Sort of like a big homemade gun drill.
It has to rotate. This is going to be the pedestal for my "dream"
rotating, adjustable height, lighted, dust collecting 5 position
sharpening/grinding/polishing/buffing station with lazy susan wheel and
Right now I have all that equipment crammed in a corner of the shop
generating grit, lint and dust. It takes longer to find, clean and set
up than it does to do the job. I want to be able to select the wheels
and compounds I need, mount them all and move immediately from one to
the other. I don't have enough room is my shop to spread it out so a
rotating pedestal is the logical solution.
Jim Roberts wrote:
Ah. Why not redesign with clearance, and use a surplus Timken tapered roller
bearing at the top? Whenever I think "telescoping" I think of 1/4" of clearance
with 1/4" bushings welded where they need to be. This is how the boom on my
old boom truck worked, and it worked really well. I'd suggest forgetting the
idea of removing the internal weld bead.
Glenn Ashmore wrote:
Agree on bushings. Everytime I ever used a nice good slip fit of an
entire length just a small amount of rust made it a bi%@* to get to
telescope again. Now I is smarter, I use bushings, not as much contact
area to give me grief, and if I have some that fits, I usually use
brass or bronze or even nylon etc.
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A bit hard to describe but you can also scrape it out. The inside
diameter is 3.505" so get a piece of bar stock, weld a bar on one
end at a slight angle, a cutter on the other end, total length
about 3.600. Drill a series of holes near the cutter end to allow
adjustment, and pull it though. If it is real hard to keep it
from binding, exhange the cutter end for a half round file thta
is wedged in place.
But the real way to do it is to put bushings on one end of the
outer, one end of the inner. Cut a grove in the inner tube
bushing to accomdate the weld seam.
Glenn Ashmore wrote:
You've got some pretty good suggestions on this, and I'm going to add
my suggestion, not because I think it's a particularly good one. I
just took it personally that I had to come up with a suggestion. You
could take a hand held air driven cutoff wheel and cut all the way
through the pipe lengthwise along the weld joint. That will remove
the weld bead at the expense of leaving a burr that can probably be
cleaned up just by running your tubing down it a few times. If the
slot weakens the pipe too much, you can weld it at the ends where you
can easily clean up the inside with a die grinder.