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Extending spring back?

 
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Cybertrash



Joined: 05 Nov 2012
Posts: 8
Location: Stockholm, Sweden

PostPosted: Fri Nov 30, 2012 3:00 pm    Post subject: Extending spring back? Reply with quote

Hi!

I own a Pacemaker Speed Graphic with a Spring ("Graphic"?) back, and I am interested in using instant film with it. After looking at the available options I've decided that 3.25x4.25 pack film seems to be the best option (in terms of availability and price) and a local shop sells some Fuji 100C and 3000B for a reasonable price.

As I understand the holders for these films (Fuji PA-145 or Polaroid 405) would normally require a Graflok back as they are too thick to fit in front of the Ground Glass on a Graphic back. I have tried looking for a Graflok back that I could fit onto my camera (replacing the Graphic back) on eBay and other sources, to no avail.

I did however come across an article or forum post somewhere that suggested that it would be possible to simply extend the screws on the Graphic back (using spacers, or wingnuts which you would loosen for pack film, and tighten for normal holders). I was wondering if you were familiar with this method, and does it seem feasable at all? If such is the case, what materials would one require?
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45PSS



Joined: 28 Sep 2001
Posts: 3196
Location: Mid Peninsula, Ca.

PostPosted: Fri Nov 30, 2012 9:29 pm    Post subject: Reply with quote

The stock screws that hold the springs for the focus frame to the camera back are #4-40 5/16 inch long.

A longer screw, a flat washer and a piece of 1/8 brass tubing is all that is needed.

A piece of all thread also called thread rod and wing nut can be substituted for the longer screw.
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Cybertrash



Joined: 05 Nov 2012
Posts: 8
Location: Stockholm, Sweden

PostPosted: Mon Dec 03, 2012 12:22 pm    Post subject: Reply with quote

Alright, that's great news!

Now, I must admit that I am fairly ignorant when it comes to screw measurements and hardware in general. I take it the #4-40 refers to thread size? Do you know if that's an international measurement? As for the brass tubing, the 1/8 refers to inches?

I take it I would have to measure the difference between a normal film holder and a PA-145 pack film holder, and simply get a screw that is <difference> longer than the stock screw? Then where does the brass tubing fit in, and would this kind of modification still work with the normal film holders?

I am sorry if these questions come off as daft, I fear that I might not be terribly intelligent.
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Henry



Joined: 09 May 2001
Posts: 1439
Location: Allentown, Pennsylvania

PostPosted: Mon Dec 03, 2012 3:03 pm    Post subject: Reply with quote

The 4 in 4-40 refers to the stock diameter; the 40 is the number of threads per inch. Offhand I don't know the size of a no. 4, but it's surely not a metric. Here in the USA you can find these items in a hardware store. Likewise, the 1/8 inch brass tubing (don't know if that's inner or outer diameter, probably the latter) may be found in hobby shops that cater to model railroad trade.
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45PSS



Joined: 28 Sep 2001
Posts: 3196
Location: Mid Peninsula, Ca.

PostPosted: Mon Dec 03, 2012 8:11 pm    Post subject: Reply with quote

All measurements are the inch system. Graflex used engineers ruler to lay out many parts of their cameras so the exact measurement will be in tenths of an inch. Tubing and pipe are referred to by its Inside Diameter, rods or solid stock are referred to by their Outside Diameter.

Small screws and drill bits not an exact fraction were assigned a number. The first number is the screw diameter followed by the number of threads per inch. Metric screws are listed by diameter in millimeters first then by the number of millimeters per thread.

A #4 screw has a major thread diameter of .1120 inch and a close fit body hole is .1160 inch. 1/8 inch = .1250 inch. Multiply by 25.4 to get the metric equivalent.
.1120*25.4=2.8448
.1160*25.4=2.9464
.1250*25.4=3.175

Check hobby shops that cater to model railroading or remote controlled vehicles or aircraft as they may have the U.S. sizes. There may be some online sources as well in your area.

A 2.5mm screw will be too small and a 3mm screw will be too big but a 3mm ID tube will probably work, aluminum tubing will be too soft, brass will be best.
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