Rack & PInion

[FDS2008]

I am looking into a rack & pinion drive system for a parking lot security gate and wanted to know if anyone has any experience with the max. allowable displacement (from vibration) between the two. I selected a gear with DP=5, PA=20° and a pinion of 2.4" pitch dia. with 12 teeth. The overall rack addendum is 0.20". Our gate may rock laterally as the drive moves it linearly (possibly up to 1/16"=0.0625").

I realixe that backlash is normally designed so that the gear system does not jam, so I am assuming if the pinion moves towards the rack (what I am calling lateral movement), there is a risk of jamming. My questions are:

1 - Can we install the pinion further away from the rack (say by 1/16") so that we reduce the potential for the system jamming? Will this have an effect on the limear motion (less contact, etc.)?

2 - What would be the maximum amount the pinion could move away from the rack? Is there any rule of thumb estimate?

3 - Does anyone have any expereince with aluminum racks?

Thanks

 

[drawoh]

FDS2008,

If you make custom gears, the fabrictor can do all sorts of weird things for you. I was told they would cut the gears so that action would be optimized when my gears were pressed together in a zero backlash configuration. In your case, they should be able to optimize your gears for increased clearance.

How accurate will your gears be when they are covered in ice or mud, or when somebody dents the gate?

JHG

 

[MikeHalloran]

When you get the quote for the rack, you'll take another look at roller chain.



Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

A parking lot gate is not exactly a precise platform. There are reasons why chains are usually chosen as the drive transfer mechanism, since they are extraordinarily forgiving on alignment and tension.

If no one ever bumps it, blocks it, or crashes into it, a rack and pinion might survive, but what are the odds of those things never happening?

And, if someone does something silly to the gate/rack, how quickly can you get it back into operation, compared to replacing a chain?

TTFN

FAQ731-376

 

[berkshire]

If you are hell bent on installing a rack and pinion. Install it with the teeth facing down and use a spring loaded pinion.
B.E.

 

[FDS2008]

Thanks everyone, it appears to be unanimous, except for drawoh, however, I have never tested the actual movement vibration and it could even be worse than I am assuming. It's interesting that they can change the gear profile to eliminate jamming, I am assuming there would be a reduction in time of contact per tooth.

I had my reservations for using a rack & pinion after speaking to different suppliers and seeing what type of clerances we were working with. I discussed this with teh client and he does nto want to take the risk of jamming either, so we are back on the chain drive option.

For my own information, is the aluminum rack not very common. Have any of you ever seen one in action, and if so, at what linear forces? I was interested in knowing how much wear it has since it is not as hard as steel.

 

[IRstuff]

It's also not just a question of jamming. If the clearance is uncontrolled, you could have too loose an engagement, which would cause increased wear and potential breakage of the gears.

I can't swear that I've ever seen a rack and pinion on a gate; if I noticed, it appeared to always be a chain. I could imagine that a gate in a more controlled environment would work well with rack and pinion. In fact, my current garage door uses a toothed belt and drive gear instead of a chain. The main rationales appear to be weight of the chain, and some degree of flexibility in the belt. I'm not necessarily convinced, but it's a brand new system, so it'll be a while before anything definitive develops.

TTFN

FAQ731-376