centering pin question

Zip · Jan 4, 2021

I'm looking to ensure that two pieces of aluminum stock return to their original position after being shifted (right/left about 1/8") (handgun site base).

Is there a tool bit (and screw) that will accomplish what I have in my rough drawing. Looking for an alignment rod hole in the 0.138-0.164 range.

Thanks

View attachment baseLOCK.BMP

Pathogen · Jan 4, 2021

Zip said:
I'm looking to ensure that two pieces of aluminum stock return to their original position after being shifted (right/left about 1/8") (handgun site base).

Is there a tool bit (and screw) that will accomplish what I have in my rough drawing. Looking for an alignment rod hole in the 0.138-0.164 range.

Thanks

View attachment 309524

McMaster-Carr

BoxcarPete · Jan 4, 2021

Pathogen said:
McMaster-Carr

Not quite, I don't think.

What you're looking for is called a dog point, and McMaster has a very limited selection:

McMaster-Carr

You might need to custom make it to get what you want, most dog points I'm finding are set-screw type.

Zip · Jan 4, 2021

BoxcarPete said:
Not quite, I don't think.

What you're looking for is called a dog point, and McMaster has a very limited selection:

McMaster-Carr

You might need to custom make it to get what you want, most dog points I'm finding are set-screw type.

That's closer to what I need.. guess I need one with a "longer un-threaded <dog point>?" so both the top and bottom pieces use the same inserted dowel rod <dog point> for more precise alignment. Doesn't require any clamping pressure - strictly alignment. Other anchor points will take care of the clamping requirement.

Just to make my point, I could use a piece of smooth drill bit dropped in the hole to align the top/bottom then just thread in a cap screw (maybe with coil spring) to prevent the drill bit from falling out. Might need a small hole on the bottom in case the drill bit won't come out when needed ..then I could use a wire to push it out.

Scottl · Jan 4, 2021

If you can accommodate a greater difference in diameter between the smooth and threaded parts why not drill a slightly undersize hole in the end of a screw and press in a piece of drill blank?

Zip · Jan 4, 2021

Scottl said:
If you can accommodate a greater difference in diameter between the smooth and threaded parts why not drill a slightly undersize hole in the end of a screw and press in a piece of drill blank?

I need to allow the drill blank removal so the top and bottom pieces can slide apart via a pivot point..(like a pair of scissors) Something like attached is where I'm going. But with less thread and more alignment rod.

jccaclimber · Jan 4, 2021

Does it need to come apart often? Would something like a NAAMS pull dowel work, maybe with a different screw threaded in to the top of it?

What is the quantity? Last time I needed a dozen screws like this I just made a fixture (aka rod with a hole in the center) and knocked them out on a lathe in 15 minutes, but I didn't have a tight OD requirement.

Can you go from the opposite direction and use a shoulder bolt?

Zip · Jan 4, 2021

jccaclimber said:
Does it need to come apart often? Would something like a NAAMS pull dowel work, maybe with a different screw threaded in to the top of it?

What is the quantity? Last time I needed a dozen screws like this I just made a fixture (aka rod with a hole in the center) and knocked them out on a lathe in 15 minutes, but I didn't have a tight OD requirement.

Can you go from the opposite direction and use a shoulder bolt?

I think the pull dowel idea will work if I can locate one in the 0.138-0.164 range preferably.

jccaclimber · Jan 4, 2021

Zip said:
I think the pull dowel idea will work if I can locate one in the 0.138-0.164 range preferably.

No experience with this source, but it might fit the bill. That’s a bit smaller than the usual threaded pull dowel sizes.

4mm x 20mm Steel Pull Dowel Pin || Bolts Plus Inc.
Note, lists as not in stock online, but it does exist. Probably a very small thread in it though.

Zip · Jan 4, 2021

Thanks to everyone...I'm in a better position understanding what's out there. My options have been expanded!

dian · Jan 5, 2021

pull dowels are quite expensive.

Scottl · Jan 5, 2021

Zip said:
I need to allow the drill blank removal so the top and bottom pieces can slide apart via a pivot point..(like a pair of scissors) Something like attached is where I'm going. But with less thread and more alignment rod.

View attachment 309557 View attachment 309559

And if you press the pin into a drilled screw and ream the pin holes the pin will come out with the screw. The reason I suggest this is because turning the ends of screws into smooth, precise pins is not just a simple turning job. Often the screw material leads to uneven surface finish. I know, because I have made dog point screws from commercial hardware, Including stainless ones to solve an automotive corrosion issue and no matter how carefully they are turned there are often spots where minor tear out occurs. Not an issue for most applications but rough as a corn cob compared to a smoothly ground pin.

jccaclimber · Jan 5, 2021

I wasn't going to go into this more, but a countersink, a thread, and a slip fit diameter all needing to be very concentric (and the same on the mating fastener) could be an issue with a long pin. I'm assuming it's not a looser fit, or the OP could consider just using the fastener OD.

Zip · Jan 5, 2021

dian said:
pull dowels are quite expensive.

Thanks to all posts...couldn't locate the 4M-20M pull dowels suggested by jccaclimber...but did locate a set of 5M X 20M on ebay (10 pieces for $8.09 free ship)

Pull Out Dowel Pin M5 X 10-M20 X 150 Tight Tolerance 10PK | eBay

Also found some some smaller stainless pins..$7.72 and free shipping I'll work with them also,

https://www.walmart.com/ip/Unique-B...ss-Steel-Dowel-Pins-Fasten-Elements/179116482

Again..thanks all...I have plenty of ideas to work with.

magneticanomaly · Jan 5, 2021

Ball plunger, plus extra words to make post long enough

Zip · Feb 4, 2021

UPDATE..I located these M3x20 stainless dowel pins which will work nicely. Will be aligning (2) pieces of layered flat bar 6061 T6511 aluminum. (One 1/4" the other 3/8")

What is the correct procedure to ensure the proper (snug) fitment of the pins into and through the aluminum. i.e. make several step up drill holes, what speed, cutting oil?, what size drill should I make the final cut with etc

Really want the pin to be precise as it is pushed through both flat bars.

Thanks!

BoxcarPete · Feb 4, 2021

Need a tight slip fit on both? + reamer.

Need a light friction fit on one and slip on the other? + reamer and - reamer.

For that size, you'd want to be removing 0.1~0.2mm (0.004~.008) with the reamer, so that'd be a #33 drill.

Zip · Feb 4, 2021

BoxcarPete said:
Need a tight slip fit on both? + reamer.

Need a light friction fit on one and slip on the other? + reamer and - reamer.

For that size, you'd want to be removing 0.1~0.2mm (0.004~.008) with the reamer, so that'd be a #33 drill.

Yes...it's a handgun sight base...so I want it tight on both. It will primarily used to align both, the dowel pin will then remain inserted.. Both pieces will be further secured with screws once centered.

EPAIII · Feb 4, 2021

I think what you are trying to remember is a shoulder screw.

McMaster-Carr

It puts the threaded area at the tip of the screw instead of just under the head.

But I do not think it is ideal for this. Any screw or pin with a cylindrical section to use for alignment must have a certain amount of clearance in both holes. That gives you TWICE that clearance as a wiggle factor because it is just a bit loose in BOTH holes.

A tapered pin is a much better idea. If properly fitted, they will seat down to a zero clearance. You can still have threads on the tip to hold it in the holes.

BoxcarPete said:
Not quite, I don't think.

What you're looking for is called a dog point, and McMaster has a very limited selection:

McMaster-Carr

You might need to custom make it to get what you want, most dog points I'm finding are set-screw type.

John Garner · Feb 4, 2021

Use your favorite search engine to look up "expanding pin", "expanding dowel"; and "expanding bolt". Then take a look at S B Whistler's "Metaligner". I suspect those searches will point you toward a solution for your quest.

I'll mention that many years ago, my employer used a tweaked variant of the AN386 taper pin (external threaded shank on both the big and little ends of the tapered portion) for a somewhat similar application.

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