Drilling 3/8" hole in an Arca-Swiss rail base?

[r.e.]

I have a 50cm Arca-Swiss rail base with telescopic rail. Does anyone know what is involved in drilling a hole in the base to accommodate a 3/8" tripod screw?

I'm thinking of doing this in order to bypass the Arca-Swiss quick release plate that I have. The idea is to be able to screw the base directly (a) to the crown of a Gitzo 1325 tripod, and (b) to a head on a Ries tripod. The physicists here can correct me if I'm wrong, but my thinking is that the greater surface contact between the rail base, on one hand, and the Gitzo crown or Ries head, on the other, will give me a more stable set-up.

I also have an 8cm Arca-Swiss base, same base but shorter, that came with a 3/8" hole, so it can be done. I just don't know what is involved.

Thanks.

[John Kasaian]

A box of Krispy Kremes for the local High School metal shop teacher?

[r.e.]

A box of Krispy Kremes for the local High School metal shop teacher?

Is it that easy? The 8cm base that I have has a 3/8" threaded insert in a drilled hole. Can't tell what keeps the insert in the hole, but it has tiny teeth all around the outside like gears. Is that because the hole for the insert also has teeth? And what holds it in? Glue of some kind?

[winterclock]

Without seeing it the threaded insert sounds like a PEMS insert, they require a specifically sized hole and are pressed in. A high school shop with a vertical mill should be able to do this. If the area where the hole is going to be is solid it might be easier to just drill and tap for a 3/8" keensert.

[r.e.]

Hi James,

The base for the rail is hollow in the middle. The insert goes from the bottom through about 1/8" of metal, protruding into the hollow space by about another 1/8". On the bottom of the base, the insert has tiny teeth around its outside. Looking through the hollow, the part of the insert that protrudes is smooth all way round. It also looks like the part of the insert that I can see in the hollow might be slightly larger in diameter than the diameter of the insert at the bottom of the base. I may be wrong about this, but it looks like the insert may be inserted from the hollow of the base through to the bottom, rather than from the bottom into the hollow. But it is hard to tell, and probably very difficult to make a photograph of it. The hollow, from the bottom of the base to the top where the rail fits, is all of 1/2".

I need to look up what a PEMS insert is.

I hope that this doesn't sound too confusing.

[Leigh]

The standard tripod thread in that size is 3/8"-16, the '-16' meaning 15 threads per inch.

If you want to actually cut the treads in the rail, you drill a 5/16" hole, then use a T-handle to drive the 3/8-16 tap into the hole, thus cutting the threads.

Unless you have a proper drill press and a vise or similar device to hold the rail in position while it's being drilled, I would suggest having it done by a professional machinist or shop teacher. It's a five minute job for someone with the right tools.

- Leigh

[r.e.]

Leigh,

Thanks. I appreciate the diplomacy with which you suggest that I not do this myself, not that it is necessary, given that I have neither the tools nor the skills. I mean, here I am asking how it's done :)

[Leigh]

I need to look up what a PEMS insert is.
PEM (Pennsylvania Engineering and Manufacturing) makes a broad range of captive fasteners, commonly called PEM nuts or by the trademarked name of PEMserts.

These fasteners work very well, and are widely used in commercial products.

They would not be an appropriate solution in this case because they require special tooling including an arbor press for proper application. The amount of force used is quite critical to proper insertion and retention of the insert.

- Leigh

[winterclock]

I replied a PEM based on the OP's description of their other rail, merely drilling and tapping the rail would result in less than 1/8" of thread; certainly not enough to rely on. Another option more in keeping with the high school metal shop approach would be an internal nut plate located by flat head screws.

[r.e.]

merely drilling and tapping the rail would result in less than 1/8" of thread

It looks to me like there is at least 3/8" of insert and thread. Unfortunately, I can only make a visual estimate because I can see it but not get at the part of the insert that is in the hollow to measure. But I'm definitely not far off.

[David Lindquist]

The standard tripod thread in that size is 3/8"-16, the '-16' meaning 15 threads per inch.

If you want to actually cut the treads in the rail, you drill a 5/16" hole, then use a T-handle to drive the 3/8-16 tap into the hole, thus cutting the threads.

Unless you have a proper drill press and a vise or similar device to hold the rail in position while it's being drilled, I would suggest having it done by a professional machinist or shop teacher. It's a five minute job for someone with the right tools.

- Leigh

Hi Leigh, Is it too late for you to edit this to "... -the '16' meaning 16 threads per inch."

I always appreciate your skilled and informative posts here and on PM.
David

[Leigh]

Hi David,

Yeah, typo. That's what I get for not proof-reading the post, as I usually do. :o

Thanks,

- Leigh

[winterclock]

From your description it is definitely a PEM nut, it gives the tripod screw some meat to hold onto. If the thickness of the rail metal is only about 1/8" that will not be enough threaded thickness for the screw. The PEM nut has ridges that when pressed or pulled into the aluminum of the rail, actually form grooves to hold it in place and keep it from spinning. They require a carefully sized hole which is why I recommend someone with a vertical mill cuts the hole. It will need to be pulled into place if you only want one hole in the rail. This can be done with a bolt, nut, and a couple of washers

[Steve Smith]

Something else to consider if this is a heavy camera. See if you can find out what thread the screw in the tripod is. It could be British Standard Whitworth or UNC.


Steve.

[John Koehrer]

There are inserts available from Menards and others(Pem nuts?)
inserted with something that looks like a POP rivet tool but the arbor rotates and squeezes the nut onto the metal the nut is inserted to.

I'd agree that 1/8" isn't enough to tap without risk of the insert just pulling out and damaging the rail.

Regarding Steve's comment re the technical size of the screw, I've never had a problem with the local Hdw Store having the inserts or T-nuts. They're likely to be UNC though.

[Steve Smith]

Regarding Steve's comment re the technical size of the screw, I've never had a problem with the local Hdw Store having the inserts or T-nuts. They're likely to be UNC though.

Traditionally, tripod threads were 1/4" and 3/8" Whitworth but now they are just as likely to be UNC. There is a five degree difference in the cutting angle of these threads so with a tripod screw with one thread in a camera with the other, the faces of the threads will not be in contact over the whole area. With a light camera it probably won't make much difference but with a heavy camera, matching threads will give a more secure fitting.


Steve.

[r.e.]

Thanks for all the input. Very helpful.

[Jeffrey Sipress]

Probably not a Pemnut, but rather a Keensert. Not really necessary unless you plan to thread something into it repeatedly. To create a tapped hole in your rail, just find a local machine shop. Forget about the high school! Get it done right.

[Frank Petronio]

Besides all the US High School shop classes have been closed because of lawsuits and the lack of a manufacturing industry.

[dsphotog]

Is this what you need?
http://www.bhphotovideo.com/c/product/554344-REG/manfrotto_120

[r.e.]

Is this what you need?
http://www.bhphotovideo.com/c/product/554344-REG/manfrotto_120

Thanks, but no. I want to be able to mount the base for an Arca-Swiss rail directly to a 3/8" screw instead of to an Arca-Swiss quick release clamp: http://www.bhphotovideo.com/c/product/342302-REG/Arca_Swiss_802010_Quick_Release_with_Flip_lock.html

The Arca-Swiss base does not currently have any hole for a screw, neither 3/8" nor 1/4". It can only be mounted to an Arca-Swiss clamp like the one above.

[John Koehrer]

If you really want to go directly into the rail, use an aluminum bar small enough to fit widthwise and 1/4" thick ~6" long, tap this for 3/8", drill a 3/8" hole in the rail. Slide the bar into the rail, align the holes and you're done. The length and thickness of the insert will give you the rigidity you want.
If you like use as large as will fit into the rail and run it the entire length.

[r.e.]

If you really want to go directly into the rail, use an aluminum bar small enough to fit widthwise and 1/4" thick ~6" long, tap this for 3/8", drill a 3/8" hole in the rail. Slide the bar into the rail, align the holes and you're done. The length and thickness of the insert will give you the rigidity you want.
If you like use as large as will fit into the rail and run it the entire length.


Hi John,

I'm having trouble visualizing your suggestion.

There is a picture of the component that I am talking about in the .pdf at the following URL: http://www.rodklukas.com/resources/arca.pdf

Page 1.5 of the .pdf is headed "The Optical Bench". The photograph at the top of that page is of what Arca-Swiss calls a "telescopic monorail". It consists of three parts. The bottom part is the base (in my case it is 50cm long). On top of that, there are two rails. Each of these rails is 25cm long and each fits into, and slides along, the base. The two levers that you see on the base lock the two rails wherever one wants them. The result is that the rail for the camera is a minimum of 50cm long and, when when the two rails are telescoped, up to 75mm long (Arca-Swiss, for stability reasons, recommends that the two rails not be telescoped beyond the base for more than half their length).

The base is the right width and shape to fit into an Arca-Swiss clamp. It is hollow in the middle and about 1/8" thick on each of the bottom, two sides and top.

If you could, I'd appreciate it if you could expand a little on your suggestion so that I can understand it better.

Thanks.

[Leigh]

The insert idea is by far the best, but there are potential problems.

How much clearance exists between the bottom of the telescoping rails and the inside of the base? How wide (side to side) is this clear area?

This will determine the maximum thickness of any insert you might use. I expect the space is small, since there's no advantage to Arca to make it larger.

The basic idea is to take a metal plate, as wide as will fit in the assembly and perhaps 150mm long, with a hole in the middle tapped 3/8"-16.
For adequate strength and thread engagement the plate should be at least 1/4" (~6.5mm) thick.

Then you drill a hole in the bottom of the base 3/8" (~9.5mm) in diameter for the screw to pass through from the tripod head to the metal plate.

One problem is the length of the screw in the tripod head. These are intentionally short, so they don't damage the camera.
If the base is too thick the screw won't engage the threaded plate far enough to hold the camera securely.

Although this solution works in theory, I'm concerned that it would not be strong enough to hold the camera securely.

- Leigh

[r.e.]

Leigh,

Each of the four sides of the base is 1/8" thick and the hollow in the middle, with the caveat below, is 15/16" wide and 7/16" high.

If I understand this, a plate would be placed in the hollow at the centre of the base.

There are a couple of issues.

First, three of the four corners of the hollow are at 90º but the fourth is 45º. One corner is 45º for reasons having to do with affixing the base to an Arca-Swiss quick release clamp (dovetails). This means that something would have to hold the plate securely in the hollow other than just the four sides of the hollow.

The second is that each of the two levers that are used to lock the rails above the base have a mechanism inside the hollow. When the lever is tightened, it pushes the head of a flat screw on the top of the base against one of the rails and locks it via friction. One of these mechanisms would have to be taken apart in order to get the plate to the centre of the base, although I suppose that that is not a big deal.

Re your last point, I just checked the screw on the crown of a 1325 Gitzo tripod and the screw on the top of a Ries Double Tilt Head, and they both protrude about 1/4". However, the screw on a Manfrotto 410 quick release plate protrudes somewhat less (the screws for this particular quick release plate, both 1/4" and 3/8", are actually kind of skimpy, with not much thread above the plate, but maybe that is the norm).

[Leigh]

I've never seen the camera with which you're working. I'm simply attempting an engineering analysis based on available information.

From the catalog illustrations it appears that the base has a U-shaped cross-section, which would allow the plate to be dropped in place from above rather than being slid in from the end. There may be internal obstructions of which I'm unaware that would prevent this.

The tripod screws are not long enough to provide adequate thread engagement. The minimum free length based on the dimensions given previously would be 3/8", with 1/2" being more desirable.

I''m not recommending this approach; just presenting the pros and cons.

- Leigh

[r.e.]

Hi Leigh,

I greatly appreciate your comments.

The base, looking at it from either end, is basically a 50cm long, rectangular tube (hollow centre) with dovetails at the bottom of the tube where it is slotted into an Arca-Swiss quick release clamp, and guides on the top of the tube into which one slides the two rails. In other words, the two rails are not dropped into the base, they are slid into guides at the top of the base.

Intuitively (I'm not an engineer :)), I agree that tripod screws are not long enough to make it sensible to fit a plate into the hollow.

I think that Arca-Swiss had it right in using an insert to accommodate 3/8" screws in shorter versions of the base. As mentioned above, I have an 8cm version of this base that can take a 3/8" screw. For whatever reason, Arca-Swiss seems not to offer that option with its longer telescopic bases. These have to be mounted on an Arca-Swiss quick release clamp.

Anyway, I appreciate everyone's comments.

As for those who have suggested that I should take this job to a bona fide machinist's shop, that is precisely what I intend to do :)

[r.e.]

The people who responded who appear to know something about machining might enjoy this: http://boingboing.net/2011/11/27/worlds-smallest-v-12-engine.html

Thanks.