Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Old May 14th 10, 05:58 PM posted to rec.crafts.metalworking
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Default Remember that o-ring groove in that piston?

"Tim Wescott" wrote in message
...
Bob La Londe wrote:
"Tim Wescott" wrote in message
...
Bob La Londe wrote:
"Tim Wescott" wrote in message
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Bob La Londe wrote:
Well, I tried to assemble the hole thing and the push rod threaded
into my piston crooked... How is that possible I wondered. I did
everything on the lathe. Oh, ****. No I didn't. My mini lathe was
too small so I only center drilled the piston on the lathe. I
drilled it on the drill press. I really need to throw this damn
thing away. The table was tilted side to side. I straightened that
today, but found the table is also slightly tilted front to back.
GACK!!! Its not horrible for punching holes in sheet, but I guess I
need to add a mill drill to my wish list for anything else.

Next time, rough drill it undersized in the press, then bore the hole
to size, with a boring bar in the lathe.

I'm not sure about "too small", though -- unless the tailstock chuck
won't take the drill, you should be able to keep loads light by
feeding slowly.

Actually it has an amazing amount of power for a cheap tiny lathe. HF
calls it a 7 X 10, but I think its really a 7 x 8. Several people
on-line have commented that when they swap out to the 14" bed from The
Little Machine Shop they gain about 6 inches of working length rather
than the 4 you would expect. As soon as they are back in stock I plan
to order the longer bed for it, and turn the old bed into a tail stock
parking rest. I still want a bigger lathe but this little one is handy
sometimes.

Now to save that piston... I am thinking I might bore it out further,
hammer in a plug, and re drill it concentrically. Then either drive in
a couple wedge pins or just slap a couple weld tacks on it.

(a) Press in a plug -- even doing this in a vise is going to be more
accurate than hammering it in.


Well, the little 12 ton air over press would have probably been my tool
of choice too, but I might not have thought of it until too late

(b) How much force on the piston, and which way?


Not all that much. (maybe 20 or 30 if there is a plug up) If the guide
rod is straight it's will have a few pounds of vacuum in one direction as
it draws in material and a few more of pressure as it pushed out
material. Right now its hand operated, but the dimensions are planned for
it to be able to drop into an electric caulking gun. (different piston
entirely when I do that conversion)

If the piston isn't going to be pulling hard on the rod, a press fit or
shrink fit may be plenty strong enough. Or a light press fit with one
of the more insanely strong Loctites, or epoxy. Or just fill the hole
with epoxy & call it a plug (hmm).



I'll have to thank about that. Epoxy would work for strength, but this
is an aluminum hand injector that may be handling liquid media upto about
400 degrees... Ideally the media should never run above about 350, but
my thermal remote tells me its hitting 400 occasionally. You know I
bought that thermal remote for checking the preheat on welding thicker
aluminum plate, and since then I have used it for all kinds of things.



(c) Press, weld (not if it's epoxy, though), _then_ bore out the hole --
and check the outside for concentricity and warps, too.


A few thousandths wouldn't hurt a thing. There is a lot of clearance on
this piston. The o-rings fill the gap. The degree of accuracy for the
push rod to be perpendicular to the piston o-rings is important though.
I already have a rod guide, but can't use it the way it is. If it
doesn't go in and out straight the piston will lose suction or pressure
out the back.


In that case, were it me and had I a welder handy that would work on the
material, I'd bore it out to some (over) size, press a plug, weld, then do
it right.

Which is starting to sound like it's as much work as just making another
piston, if it's fairly simple. Maybe you should put the current one into
the trophy case as a reminder, and just make another one?


I've been thinking that. LOL, but I'm stubborn and I hate to waste any of
my aluminum stock if I can help it. In order to get a decent price on
aluminum I have to order from Discount Steel in Texas or for quantity from
Metals to Go on the east coast. As a result I have to save to make a metal
order and then try and guess what projects I am going to be playing with 6
months from now. LOL. I have enough aluminum rod right now to make plenty,
but like I said I hate to waste it. I actually have an idea right now for
converting this piston for the caulking gun application so maybe its time
for me to step it up a notch and skip the hand operation entirely. Its
just that I wanted to approach this in a stepwise fashion and not get in a
hurry to do too much innovation all at once and wind up with a molten PVC
explosion in my shop.




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Old May 14th 10, 06:40 PM posted to rec.crafts.metalworking
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Default Remember that o-ring groove in that piston?

"Robert Swinney" wrote in message
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Seems to me a drill press out of tram, even with a tilted table, would
only tend to drill larger
holes - not holes at the angle of tilt.


Run out will result in a larger hole... don't get me started on runout.
LOL. A drill bit tends to drill in the direction it is pointed.




Bob Swinney
"Bob La Londe" wrote in message
...
Well, I tried to assemble the hole thing and the push rod threaded into my
piston crooked... How is that possible I wondered. I did everything on
the
lathe. Oh, ****. No I didn't. My mini lathe was too small so I only
center drilled the piston on the lathe. I drilled it on the drill press.
I
really need to throw this damn thing away. The table was tilted side to
side. I straightened that today, but found the table is also slightly
tilted front to back. GACK!!! Its not horrible for punching holes in
sheet, but I guess I need to add a mill drill to my wish list for anything
else.



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Old May 15th 10, 02:40 AM posted to rec.crafts.metalworking
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First recorded activity by DIYBanter: Jul 2006
Posts: 2,600
Default Remember that o-ring groove in that piston?

On 2010-05-14, Robert Swinney wrote:
Seems to me a drill press out of tram, even with a tilted table, would only tend to drill larger
holes - not holes at the angle of tilt.


Huh?

Perhaps if the workpiece was being rotated (such as in a lathe
chuck) instead of the bit.

However, if the bit is rotating (as is normal on a drill press)
I can't see how it would enlarge the hole (other than making it slightly
elliptical based on the angle, thus making a very slightly larger major
axis on the surface of the workpiece.) The diameter of the hole along
the axis of the bit will still be circular and as accurate as the bit
can drill anyway. :-)

But the *real* problem often with inexpensive drill presses is
that the force of the drill bit (especially with the usual chisel-point
bits) causes the arm supporting the table to deflect a bit, thus taking
a table which is in tram before you start drilling and forcing it out of
tram while drilling -- and then letting it return to tram when you
release the force. There just is not enough cast iron in the arm, and
not a long enough bearing surface on the column to prevent the
deflection. You can reduce it a bit by using a split-point drill bit,
which reduces the force needed to drive the bit into the workpiece.

Enjoy,
DoN.

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