Attaching focusing rack to rails?

[Curtis Nelson]

OK, I'm stuck.

I'm building an 8x10 camera, and I'm using a brass rack & pinions to serve as the focusing mechanism. The problem is, I'm not quite sure how to attach the rack to the focusing rails. The rack is 1/8" wide & high. I'm thinking my options are:

1. Drill VERY tiny holes (<= 1/16") in the rack and attach it to the focusing rails with really tiny pins.

2. Gorilla glue.

3. rout a 1/8" channel down the middle of the focusing rail (as opposed to the edge) and let friction do the rest.

Am I in the ballpark on this, or is the a better way?

Thanks for all your help.

Curtis

 

[r0l4nd]

I have tried all three methods.

1. Didnt work. Either the pins were too small to hold the rack on securely or they were too big and interfered with the spur gear.

2. Worked fine for about a month. Then I started to get play in the rack.

3. Worked fine for about a week. Then the rack moved without moving the rails.

In the end I went for a combination of 2 and 3. A routed channel with glue to hold the rack in place (I used araldite impact adhesive). Worked perfectly. You just have to watch that you get the channel perfectly level. I couldn't do this with my hand router and ended up milling it out on the lathe with a small routing cutter.

PS Where did you get the rack and pinions from?
After seeing the prices everyone seems to want for them I made my own.
Next time I will DEFINATELY buy them!

 

[Curtis Nelson]

r0l4nd,

Thanks for the feedback.

I bought my rack and gears from McMaster-Carr (www.mcmaster.com). I paid $25 for a 2' brass rack and $7 each for the pinion gears.