Rack and pinion question
I am in the process of restoring an 8x20. I need to order some more rack for it (I've built an extension). My problem is I do not know how to measure the rack so that I can order the right kind. I suppose you buy it in lengths of a few feet and need to specify the thickness of the stock, but what about the number of teeth? (are they teeth?) what is pitch? and how do I measure it? I've found a few websites that seem to have lots of gear rack for sale in various sizes, but how do I figure out which one is for me? The camera is an old Folmer Schwing.
Also, if the right rack is not available in brass, can I use other metals like steal or aluminium even if the pinions are brass?
Last edited by CraigK; 01-30-2007 at 07:26 PM. Click to view previous post history.
The rack that I have seen (Small Parts) is specified in teeth per inch. The measurement would be taken from the number of gear peaks over a linear inch. While pitch may be involved in certain gear applications, the most important parameter in your application would be teeth per inch...if the rack matches the pinion, the assembly should work with no problem.
The rack has 5 dimensitions of intrest overall length width height TPI teeth per inch the last dimensition is depth of tooth other dimensitions which are crest radius which is the radius on the peek of the tooth there is also a radius on the flanks of the tooth.
Maybe buy the rack and the matching pinion gear at the same time?
What a wealth of knowledge!
Thanks for the tip Greg, I thought about that but I already have the pinions and some rack. I just need more of the same or some that is close enough for jazz.
So do you guys figure it would do no harm if I got steal or other non-brass rack even though the pinions I have are brass?
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Another consideration is pressure angle. Alot of steel gears are 14.5 degrees while most brass are 20 degrees... Needless to say they dont work together.
Hi, I noticed that no one gave you an exact answer. To measure the existing rack you would need a tool, thread measuring tool, they get expensive. The cost of the ones for bolts aren't bad but rack measuring tools are more common to a machine shop and not the home shop. That said If you are matching a rack to an existing pinion or gear you have to be; exact.
I found that my Seneca wood cameras have the same racks as a camera I built many years ago. It was from Small Parts Inc. Brass Rack 48 pitch 20d PA. My Kodak 2D has a different set all together.
I'm building a 5x7 and have ordered the racks and pinions and have them ready. Two 24 inch racks that are 32 pitch 3/16 inch face, and 20 degree pressure angle (PA). The pinions are called spur gears and have a 32 pitch 16 teeth, .5 pitch dia.
The racks were $56.44 for two. The gears were $34.92 for four.
It's expensive but I will have close to two feet of extension and since I have a new Canham bellows and two fine planks of old Mahogany it's worth it compared to what a Canham 5x7 costs.
Back to your question about what rack to get. You need to take it to a machine shop or you can order some gears that match the gears on the camera then you will know which rack will mesh with it. Give Small Parts a call and talk to their tech. rep. or call Boston Gear. The racks and gears I bought were actually made by Boston Gear. A machinist can tell you right away what it is though and would be a good way to go.
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Just for the record, and to answer the question, gears are specified in diametrical pitch, e.g. a 1" 20 dp gear has 20 teeth, the teeth per inch on a rack is irrelevent, as at some point the rack has to have a round gear engaged. (ref. http://www.sdp-si.com/D190/PDF/D190T25.pdf)
If you are going to be using gears, Stock drive products has a set of excellent catalogs, with extensive tech info on gears, and various drive systems. Worth far more than the $0 they charge for them...
In reply to an earler post the materials that the rack and gear are made out of is not important pitch, flank angle, and depth of tooth are the important parts of rack and pinion gears
Last edited by monochromatic51; 01-31-2007 at 06:36 PM. Click to view previous post history.
Thanks again everyone. So...uh...anyone have any spare rack for a folmer schwing 8x20 laying around? I will give it a good home!!