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.