Remember that o-ring groove in that piston?

Since you haven't thrown the drill press away yet, why not take it on as a challenge? Tram it in like a vertical mill. If it doesn't, take action. I know that you won't do that again anyway, since you already owned up to it here. Since you already had it in the lathe, that would be the best place to drill the hole. I assume by saying "too small", you mean "too short"?

One of the worst things that happens to me since the kids grew up and left home many years ago is that when something goes wrong in the shop, or if something is lost, I have no one to blame it on but me! Pretty tough to take sometimes.

Actually, your post is a good wake up call for me, as I have never trammed my own drill press. Worse than that, I have an X-Y table bolted to the table 99% of the time, and, on top of that, I have another table, made of wood, that is T-shaped so it can be quickly clmaped in the vise mounted to the X-Y table. The leg of the "T" is a piece of 2X4. How perpendicular can all that be?

Do inquiring (sp?) minds want to know?

Pete Stanaitis

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Bob La L> Well, I tried to assemble the hole thing and the push rod threaded into

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.

Long before I found a mill I fixed my cheap drill press by making the head slide down the column so I didn't need the table, only the squarer base. It can also be clamped to a large beam or plate to drill it.

jsw

Bore it out oversized and concentric, tap it, and either use a larger rod, or an internal/external threaded bushing.

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.

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

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

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

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

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)

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.

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.

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.

tend to drill larger

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.