Press fit Hypodermic Tubing?

What materials are you talking about (tube and thing with hole in)?

The tubes are 316 SS and the holes are 303 SS.

That's like a 3% and a 5% interference. I don't think there's a chance, particularly with SS. I'd vote for bonding.

What is the prospect of warming the holes up, cooling the needles down until they are a sliding fit, positioning them, and then letting the temperature return to ambient?

Hi PWSlack,

I was thinking at the same process which is called shrink fitting. For a 1.00" diameter, the interference should be .001", the smaller part to be inserted is just dipped into liquid nitrogen prior to being positioned, while the receiving part is kept at room temperature.

In this case, I don't think will work due to much smaller diameters, even if the receiving part is warmed.

Swaging the needle into the hole if possible.

What's the best way of swaging the hypodermic tubing? I have tried sanding, but that is not consistent. Do they making swaging tools/machines?

Yes the make machines that swage the tubing into a ferrule.

That's far too much interference for the tube size. Bonding or brazing might be a better bet. If you are doing this in production, you could make the holes precise enough for a press fit, and with the right tooling they could be pressed in. Drilling a larger hole and bushing it with nylon, etc would also be a possibility. I think you could do a .001 press fit in nylon -- but you'd need to experiment.

When faced with a similar situation I experimented to detemine the best sizing for a press fit. Turns out an interference fit of 0.0003 was workable. Any less and the tube could pull out and any more and the tube crushed. I found it easier to modify existing number drills to give me the exact size needed. Since I only had a few thousand holes to do and one modified dril was good for 200 holes it was easier to modify the drill while gauging it with a precision micrometer that read to one tenth of a thousandth.

For a normal production job I would have ordered the special drills sizes in quantity. I did make a fixture to hold the tube while press fitting it into place. The fixture was chucked into a drill press that had been aligned carefully for squareness. Table surface and quill was exactly at 90 degrees to each other.

elnav,

For your next adventure you can try regrinding the drill point of a drill bit. When one is too big and another too small take the smaller and grind one cutting lip a little longer or with less angle; the result is a slightly larger hole than the size of bit.

A reasonable press fit is a .001" interference on a 1" part. So a rule of thumb would be a .000032" interference on a .032" part. I've worked with ultrahigh precision multimillion dollar machines used for making fuel injection nozzles, and even that level of precision would be inadequate for offsetting the point of a .031 drill the correct amount for a consistent press fit, particularly given that the material to be pressed in is a tube, which could crush, if excessive force is required.

Hello Guest,

Pressing is out of the question. Warming the block a little set it on a hot plate but not much hotter. use a cryogenic fluid to super cool the tube and give it a whirl.

A .001" interference is a tall order for the wall thickness of the tube.

I'd put a relief 0.0318" OD x .3125" deep in each end of the holes and stub the tubes into each side by super cooling.

I don't think heating/cooling is workable - got a bit of a thick head today, but:

Take CTE as 20 μm/m - that's 2x10^-5. You're looking for a change ≈ 0.001" in 0.030". Temperature difference would need to be about 1500°C.

Please correct me if I'm wrong.

Another possibility: the tube ends could be precision ground to a long taper, and the holes reamed (or internally ground with a high precision grinder) to match. Each inserted tube would insert to a slightly different depth if they were tapped into place (even if the hammering machine were highly repeatable). However, maybe the insertion depth could be off by a couple thousandths? The advantage of a taper is that you know every part will fit, and assembly is simple. With a straight interference fit, many parts will be too loose or too tight -- unless you are willing to pay for ultrahigh precision machining -- the kind of thing typically done in a clean room.

Let me preface my reply by saying I haven't enough imagination to grasp why you'd want to do such a thing to start with, as syringe needles are usually considered disposable (even the reusable ones) once a few punctures have dulled them.

That said, it sounds as if the hole size is predetermined. If there's valid rationale for trying to press fit them, then try the methodologies previously mentioned, but good luck. Frankly, larger diameter holes and some silver solder or brazing rod will likely be the solution. Much does depend on the end use, however...

First you need to know the wall thickness of the tubes. That is very important.

The best way to press them in is using a horizontal press. This press can be designed with a "push/pull" thumb press bought from Carr-Lane and another "lock-down" press. One press will push the handle over the needle and the press will hold the needle in place. Once again be careful not to dent the tube, thin wall thicknesses can easily be damaged.
The other thing to watch for is the wall thickness of the tube controls the hole DIA on the handle. Thin wall thickness tubes, need very little press force therefore the hole in the handle can be larger then assumed.
The last thing to know, is the type of materialthe handle is made out of, Is it a giving material or very stiff. HDPE, UHMW, DELRIN all of these react different with the tubing.

Good Luck

The last thing to know, is the type of materialthe handle is made out of, Is it a giving material or very stiff. HDPE, UHMW, DELRIN all of these react different with the tubing.

This might better be the first thing to know, because there is a huge difference between pressing a stainless tube into a stainless hole (which is what the original poster intends, per post #2) vs pressing it into a far softer plastic.

Where did handles come into it? Yours seems to be the first post to mention them.