Graflex.org

[45PSS]

How To Make A Super Speed Graphic Cam From Scratch

Materials Needed: 1 piece of metal .032 thick and at least 1.5 inches long by ¾ inches high.Portable test target that you can see thru the lens at 100 feet and has distinct lines to focus on. Focusing loupe.
Tools needed: (Digital) Caliper; small straight edge; protractor; machinist scribe; mill bastard file. Dremel with cutoff wheels and small (narrow) grinding stone.


Part A: Determine lens focusing characteristics.
Mount camera on a tripod and aim at an infinity target al least 5000 feet away. Run rails in fully then out .040 plus or minus .010. 1mm=.0394 inches. If you have another lens and have an infinity point established for the rails to be at, then use it. Mount the lens that a cam is need for on the camera. Move the front standard out until the lens is at infinity focus on the ground glass with the front standard square to the rails and locked. Set infinity stops now if desired.<br>
Move the rails out 1.082 inches, this is the closest focus distance that the rangefinder will track. Find a point on the bed that you can reference the rail movement to that will be accessible from infinity to the close focus point that you can easily measure with the caliper without moving anything. The front standard interferes with using the end of the rails to the end of the bed for long lens. Once you have determined your reference point return the rails to the infinity starting point.<br>
Set up the test target and position it 100 feet from the camera's film plane. Using the focusing loupe focus the lens on the test target by moving the rails forward, lock rails when test target is in sharp focus. Using the caliper measure and record the distance from infinity that the rails have moved. Move target to 50 feet from film plane. Focus as before and record the rail movement from the Infinity position. Next set target to 25 feet and focus and measure travel of rails from infinity and record. Next set target to 15 feet and focus and measure rail travel and record. Next set target to 10 feet, focus and record rail travel from infinity. Follow this procedure for 8, 7, 6, 5, 4, and 3.5 feet or until the travel limit of the rangefinder actuator is reached.

Part B: Fabricate the cam blank.
Use an existing cam or download a copy and print to exact scale and use as a template for the bottom and sides, or using the caliper, straight edge, protractor, and machinist scribe draw a trapezoid with a base of 1.5 inches long with the sides tilting 7 degrees inward. The right top should be .703 inches from the base and the left should be .6 inches minimum up from the base, some lens may require it to be higher. Leave the bottom flat and the left edge sharp if copying from an existing cam or pattern.Cut out the cam blank using the Dremel with a cutoff wheel and dress smooth with the file. A mill smooth file can be used but will require more filing to dress an edge. This blank should now fit into the cam slot on the camera and slide up to the stop pin. Dress with the file if needed until it will just fit if desired.<br>
The cam moves 1.058 times as much as the bed moves. Take all the measurements from the lens focusing step and multiply each of them by 1.058 listing the results by each distance that they were measured at. Example: the rails moves .015 inches from infinity to 100 feet focused. 1.058 x .015 = .01587 round to .0159 @ 100ft.<br>
Taking the cam blank, measure 1.356 inches from the lower left corner and mark the base at this point. Staying perpendicular to the base at the 1.356 inch mark go up .695 inches and mark. This is the cam infinity point. Next subtract the 100ft. movement factor from the infinity base start point measurement and mark that point on the base. Example: 1.356 - .0159 = 1.297. Now measure 1.297 from the lower left corner and mark the 100ft. start point on the base of the cam blank. Now go up perpendicular to the base the cam height distance for 100ft. and mark this point. Do the same for the rest of the distance measurements for this lens. Now you will have the cam height points marked for each distance along the top edge of the cam. Use the Dremel with the grinding stone to remove the excess material or use a file. Test the cam for accuracy in the camera with the lens and ground glass. Round the right lower corner and notch the bottom if desired. Notch in bottom is .035 up and in 1/4 inch from each end of the base of the cam.

Cam height at measured distances:
Infinity - .695
100 feet - .685
50 feet - .680
25 feet - .674
15 feet - .664
10 feet - .647
8 feet - .638
7 feet - .634
6 feet - .618
5 feet - .602
4 feet - .589
3.5 feet- .566

All measurements are from a point perpendicular to the base of the cam/rangefinder housing to the cam follower arm.

Draw you cam out on paper first as your lens may not go to a distance where the left edge will be lower than .6 inches in which case you should make your blank with the left edge a few thousands higher than the lowest cam height you will use at the left edge.

Option B: Take all the measurements to a machinist and have them cut it for you.

Update:
I have discovered that a USP #NP15 connector plate (nail plate, 1 7/8 inch wide, 5 inches long, galvanized, .037 thick) will make four cams and cost $.49 at the local hardware store.

[Rick from OZ]

Charles,

Well done - I'm impressed with the effort and time, but even more that you are sharing this with the community in this day and age.

Thanks, too, to RichS for designing the test target and maintaining his dowloadable super cam database.

It's great to see.

. Rick

[RichS]

Yes, thanks for all this effort, and sharing it. I just hope that soon I'll be able to use it

[45PSS]

How I did it:
I took the rangefinder out of my parts body, put a cam into position even though there was no tube in place. The cam will sit under the rangefinder arm and against the bottom rail which is actually formed into the housing.
Taking one of my working cameras I observed the position of the cam when the camera was set to the infinity position. Transfering the cam position to the spare RF housing, I measured the infinity heigth with a Preformance Tools 6 inch digital caliper.
Taking the working camera and turning it up side down I placed a straight edge against the cam base and the follower arm and scribed the cam at the infinity position, then moved the rails out the travel of the actuator and scribed the cam again. I then took the cam out of the camera and measured the distance between the two scribes. This is the cam travel distance. Then I marked the rails to the bed at the infinity and full actuator distance and measured it. This is the rail travel. Dividing the Cam movement length by the Rail movement length gives the Cam movement factor.

Taking a 18 x 24 inch artist canvas painted white with an L bracket glued to the back so that the canvas is in a verticle position, I placed copies of Norman Koren's Lens Test Chart printed on plain paper @ 1400dpi and some copies of 1951 USAF Test pattern.
Having attached the canvas to an economy light stand I used a tape measure to set the target up 100 feet from the camera film plane. The camera was on a tripod with a quick release palte. I focused the camera at 100 feet on the target. With the rails locked I removed the camera, turned it upside down and scribed the 100 foot position on the cam the same way I had done at the infinity and full travel positions. Next I measured 50 feet from the film plane and moved the test target to that position, focused and scribed the cam and continued this procedure until all marked distances on the camera scale had been scribed onto the cam.

Now I took the sctribed cam and put it into the loose RF housing. Using the straight edge against the edge of the follower arm and base rail I moved the cam to the 100 foot scribe line on the cam then measured the distance between the base rail and the follower arm edge where it touches the cam. I did this for the rest of the distance scribe points. The scribe line is two or three thousands to the left of the actual touch point. These are the cam height at a given distance.
NOW Taking a Top Rangefinder Crown or Speed whose rangefinder is set up to factory specs a simular procedure can be applied to create a Top Rangefinder Graphic Cam Fabrication procedure. A Crown would be the easiest to create the procedure with because when it comes to measureing the cam height at given distances it will be easier to remove the bellows and front standard from the camera body as the Top RF Graphic rangefinder is not seperatable from the camera body and retain its operational state.
The factory service manual states that the cam height at infinity is to be .437 inches.
Anyone undertaking this and needing help feel free to contact me.
Charles

[macandal]

[45PSS]

1. the measurements you make focusing the lens you have are the ones you take to the machinist.
2. This procedure and cam heights will not work for Pacemaker Crown and Speed top rangefinders.
_________________
The best camera ever made is the one that YOU enjoy using and produces the image quality that satifies YOU.

[macandal]

[richydicky]

I downloaded the cam designer program from Southbristolviews and although it produces a printed page of the cam shapes I don't have the resources, skills or time to hack away at a piece of brass to make a cam. If the program could optionally create a file of measurements that could be used by a laser or cnc cutter I could get that done.

I tried to contact Rich at southbristol but don't know if the messages get through as I can only access his site through a VPN for some reason. So if Rich S is reading this would be grateful if you could respond.

Many Thanks
Richard Dickson

[Rick from OZ]

@45PSS wrote: