Rack and pinion question

[CraigK]

Hi All,

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?

Thanks!

CraigK

 

[Donald Miller]

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.

 

[monochromatic51]

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.

 

[Greg_E]

Maybe buy the rack and the matching pinion gear at the same time?

 

[CraigK]

Thanks all.

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?

 

[Colin Graham]

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.

 

[Curt]

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.

 

[epatsellis]

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...


erie

 

[monochromatic51]

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

 

[CraigK]

Thanks again everyone. So...uh...anyone have any spare rack for a folmer schwing 8x20 laying around? I will give it a good home!!

 

[Curt]

What is needed is a list of the rack and pinion sizes of the old cameras. I know how frustrating it is to find a replacement without having to send it in to a camera repair for replacement or just experimenting by buying and guessing.

 

[barryjyoung]

Having tried to replace just a rack or just a pinion on an old Fluffanduff or six, I heartily recommend that you replace the racks and pinions as complete sets. Here is why.

1. The pinion you replace will have worn the rack that you do not want to replace. Even if you do get the correct pitch and pressure angle (all other dimensions including tooth depth will only affect the spacing between the rack recess and the pinion shaft) the new pinion may not mate with a worn rack worth a hoot, and vice versa if you are replacing a rack.

2. While not always true, it is likely that if the pinion or rack is worn, so is the part it mates with.

3. Your chances of success on this job go up astronomically if you replace all racks and pinions at the same time.

4. If the camera is not worth $100 worth of racks and pinions why are you wasting your time on it?

5. Don't replace racks and keep old pinions you can replace for $8, that is false economy. I would replace an $8 pinion to save a $50 rack but only if I were 100% certain that I knew what I was ordering and that it would fit and that there was no wear somewhere along the rack. If you replace the whole set you have no worries except fitting the new racks and pinions to the old slots and shafts or making new slots and machining the new pinions to fit.

Best of luck

 

[eclarke]

Also, you don't want to use an aluminum rack and a brass pinion, they will gall in a heartbeat. You want the parts to me of the same hardness so one side won't wear unduly..EC

 

[Greg_E]

And steel rusts, so that's why brass may be best, are at least aluminum for all the pieces.

 

[epatsellis]

A good alternative is the nylon rack that stock drive sells, the only downside is 12" lengths, with brass pinions, it's very smooth, and it's very reasonably priced.


erie

 

[Dan Dozer]

Thanks again everyone. So...uh...anyone have any spare rack for a folmer schwing 8x20 laying around? I will give it a good home!!

I just finished building my 8 x 20 and got the gears and gear racks from McMaster Carr. They don't have brass so I got mine made from steel. The cost was about $50 - $60 for two gears and 4' of matching rack.

 

[barryjyoung]

I just finished building my 8 x 20 and got the gears and gear racks from McMaster Carr. They don't have brass so I got mine made from steel.

Hey Dan, I buy racks and pinions from McMaster Carr all the time that are made from brass. Maybe you wanted a different pitch or pressure angle than I use?

 

[Dan Dozer]

Hey Dan, I buy racks and pinions from McMaster Carr all the time that are made from brass. Maybe you wanted a different pitch or pressure angle than I use?

Hi Barry,

I've found out a couple of times before that using the McMaster Carr website, you sometimes don't get all the alternatives to certain parts and pieces. That may have been what happened to me - the only ones I saw were either steel or nylon.

Thanks for the info,

Dan

 

[barryjyoung]

Hi Barry,

I've found out a couple of times before that using the McMaster Carr website, you sometimes don't get all the alternatives to certain parts and pieces. That may have been what happened to me - the only ones I saw were either steel or nylon.

Thanks for the info,

Dan

Hi Dan:

the brass pinions and racks are near the bottom of page 1013.

 

[Curt]

I get my brass rack and pinions at McMaster Carr and they are made by Boston Gear. Very nice, exact, precision set worth every penny.