New fastening method?

Yeah, I think I see the same problem. Neat idea anyway.

Ingenius, but perhaps not practical in this form, esp. since I am no whiz at threading, and esp. esp. not on short-short #4 set screws!

But how bout this, a kind of inverse of your idea: Tap top and bottom together with the fine thread, but only go in a thread or two in the bottom, for use as a starter/alignment thread. Then, in the bottom plate, tap the course thread. Now, the same effect will occur with a fine-thread set screw.

The only problem with this is that this effect would probably best realized by closer increment of pitch than what typically occurs between coarse and fine threads. ie, if using 4-48, probably the bottom plate should be tapped at 4-47, 4-46, or 4-45. This would require having taps custom ground, unless these oddball threads just happen to exist in some specialty industry. For example, Singer made all kinds of odd threads on standard diameters in their commercial sewing machines.

Still, a do-able strategy without undo machining pyrotechnics. Great lead!

"Proctologically Violated©®" wrote in message news:qXDLh.423$ snipped-for-privacy@newsfe12.lga...

"Proctologically Violated©®" wrote in message news:qXDLh.423$ snipped-for-privacy@newsfe12.lga...

Suppose (this may not be the case) that the material was slightly elastic (compressible). If you could compress it even a few percent and clamp it in that configuration while drilling and tapping, you could totally eliminate the gaps and play. It would require - probably - that you also embed the screws in some sort of setting filler to obviate any slop in the threads.

But I guess I don't see why there's "not much room for screw heads". If you're using 4-40 hardware, a 1/4" thick sheet is a mile thick by comparison. Flat-head socket screws would do the trick, and make for the clamping action you're after.

I do it all the time, in both thicker and thinner materials. I make up pressing moulds for pyrotechnic composition. The "cavity plate" is always a non-standard thickness, determined by the compressability of the composition, the final pressure, moisture content, etc. Almost always I'm forced to laminate two or more sheets of stock to a final "over ideal" thickness, then to face mill the plate to final thickness before boring the cavities. In order to avoid material's squishing into the gaps between laminations, I fill the interface with a glue of some sort (from PVC cement to Loc-Tite, depending).

LLoyd

Let's think about this. We have two plates connected with a screw. Because of slop in the threads we can put a .010 shim between them. Just. If we put a .012 shim between them it must be forced. So maybe using a .008 shim would work when tapping the plates when there is .010 slop in the threads. I can't think, I slept poorly last night. ERS

If you just want to do it different, you could drill angled holes through both pieces (while clamped together) and use roll pins/spring pins, and have the holes face different ways so the pieces won't pull apart until you remove the pins.

Dave

Well, I guess by not the idea of just running screws directly into two holes in series has been dismissed as ineffective.

The two-pitched screw idea was cute, albeit impossible. It would become theoretically possible if the pitches were opposite - i.e., one left hand and one right hand with an allen socket. A little tough, perhaps, positioning the screw between the plates and reaching through with the allen key, but theoretically possible. The screws would have to be threaded by rolling, I expect. I doubt they exist.

I'm thinking something like a wall anchor. Suppose you drilled the hole through the two plates, then threaded them with a tapered tap (like a pipe thread on a small scale). Now insert a tapered screw, and bottom it out on the threads. I'm not sure that would be any better than straight threads, but I expect it would be.

Why don't you pop-rivet them?

If you drill a three-diameter hole (well really a two-diameter in the bottom plate and a shallow counterrbore in the top one) you can allow for the rivet to expand in the bottom plate and the head to be sunk in the top plate; use aluminium rivets and you can just drill them out when you have to take it apart.

Would be nice and tight...

Well, nothing here is nearly elaborate enough so...

Take a threaded rod. Cut in half. Drill+Thread inside of one with RH threads Drill+Thread inside of one with LH threads Thread half of a rod with RH threads (fits into previous rod threaded RH internal) Thread half of the same rod with LH threads (fits into rod threaded LH internal)

Thread rod sections together to form a turnbuckle, leave some of the internal rod visible. You did drill all the way through on at least one of the outer rods, and you did slot that end of the inner rod, right?

Thread that disaster into a threaded hole all the way through the 2 plates, then turn the inner turnbuckle rod to tighten the plates together.

Or, the outer rods can have blind ends on both ends, and the rod in the middle also has RH threads, but the threads are coarser (larger pitch).

Screw the outer rods onto the inner rod, leaving a space in the middle. Thread the whole thing in place, making sure the 2 outer rods turn the same amount while threading it in. (slot on each end, screwdriver on each side)

Once in place, hold 1 outer rod in place and tighten the other. Plates will be drawn together.

Dave

Two pitch screws are very easy to do BUT you use two different sizes for the different threads. That way you have clearance to install them. Larger hole to the outside.

How about an old standby. Hot rivets? Drill and countersink both sides. Then heat the rivet and peen it in place. Let it cool and mill both sides flat. Want to take it apart? Drill them out.

Or if you need a blind hole on one side you could use an inverted taper in the bottom hole and drive the rivet from the top.

Solder 'em?

John

"Proctologically Violated©®" wrote in message news:qXDLh.423$ snipped-for-privacy@newsfe12.lga...

Some interesting ideas posted here. I can't tel what your requirements are, but if the two plates are only loaded in shear then a simple solution would be to simply pin them toghether with press fit pins. Both, one, or neither hole in each plate could be blind, depending on what you need. By controlling the amount of press you could put them apart by hand or never get them apart. I would recommend that the pin diameter be no less than 75% of the plate thickness and no more than the plate thickness. If you make the pins yourself don't forget to include a lead in chanfer on each end of the pins.

Let us know how it turns out.

Maybe you could rivet the plates together:

______ ____________ ____________ \ / \ Rivet / | | | | Top plate | | | | | |

---------| |--------------- | | | | | | | | Bottom plate | | / \ / \ ~~~~~~ ~~~~~~~~~~~~ ~~~~~~~~~~~~

S.

Off the wall but might work:

Chill one plate with dry ice or liquid N2 and tap it cold. It will expand as it returns to room temp, making the pitch slightly coarser than nominal. When your setscrew enters the slightly steeper threads the slight differential in pitch might draw the plates together, and the slight mismatch to the set screw thread will make a tight fit.

I don't really know if this would work, but a quick experiment would tell the tale. It'd work best in ally because of the higher coefficient of thermal expansion.

Another related idea if you could find a 4-39 or 4-47 tap (yeah, right!) or a pair of metric and SAE taps that have very similar diameters and slightly different pitches. Then I'd tap one side nominal and the other side slightly-coarser-than-nominal. Let's say you might get 1/6 of a turn out of sync (about 17%) in fairly loose threads before it binds up. The difference in progress per turn in

47tpi vs 48 tpi is .000443 in per turn and 47 pitch is .02127 per turn or .003546" in 1/6 turn so you'd get about 8 turns or .170" of penetration before bindup. Might wanna shim the plates a teense to start the setscrews, then pull the shims and tighten the screws. Idea here is to make the shims so the screws get tight in tension just before they bind due to thread mismatch so you get max penetration and engaged threadlength.

I'd just weld the f****rs. I assume that you've rejected rosette welds, right?

That could be better than rivetting (or perhaps some of the other suggested methods as well).

For removal, drill and thread the pins, and make a puller.

Or you can just buy pull pins.

97352A110 at even has grooves for air to pass through.

Later,

Charlie

--Sounds to me what you need to do is build yourself an oversied Cleco tool and make a bunch of Clecos. Would that fill the bill?

If you find some .002" minus shims, we could use them under the counter spindle of one of our machines, ha.