Bob La Londe wrote:
"Tim Wescott" wrote in message
...
Bob La Londe wrote:
"Tim Wescott" wrote in message
...
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?
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com