Alternative to spring pin

[plangevin]

Hi all,

I am modifying an existing design for an optical encoder. The encoder shaft is coupled to the transmission shaft through spur gears. The gears are locked to the shaft using a spring pin design. This would not be such a pain if we were talking bigger mechanics but we are talking relatively small parts.

Shafts are 1/4 and spring pin are 1/16. No need to explain how the guys like installing the spring pins. The tiny spring pin is something I would like to eliminate but i'm facing some opposition. My colleagues have had bad experience with set screws and clamping hub and decided on spring pin. I cannot put enough emphasis on how it is important for our encoder not to slip and lose position, the logic in our system relies almost strictly on this.

So i'm looking for alternatives to spring pin (clamping hubs and set screws aside) but really can't find none. The shaft is too small to bore a hole large enough to fit a screw unless we go miniature screws, but then we'll have problems fabricating it. Basically another type of pin easier to install would be perfect.

If anybody is aware of a solution to my problem i'd be extremely grateful !

Thanks for your time !

 

[Cockroach]

You can drill a hole on the face of the gear at the interface of Shaft to gear. Pound in a brass pin which acts as a shear key. Basically you have half the pin overlapping the gear and the other half overlapping the shaft. You must drill on assembly after punch marking a spot.

I do this a lot on small parts, they basically never come apart and the pin acts exactly as a shear key so you can do a similar analysis for strengths.

Good luck with it.

Regards,
Cockroach

 

[Tmoose]

How much could you allow the spring pin to extend beyond the hub?
How thick is the hub? [ (Hub OD - 1/4 inch ] /2
I'm thinking of a feature to "start" the pin. Either a counterbore on the hub, just one side if necessary, or a reduced diameter on the pin. Or a pilot with 2 concentric diameters - one that is a slip fit in the hub and shaft, the other that is a slip fit in the spring pin after it is seated in shaft and hub.

 

[MintJulep]

One of the Loctite retaining compounds.

Heat shrink.

Braze or solder.

 

[Compositepro]

What is so difficult about installing spring pins? The pin should have a chamfer on the ends and you can chamfer the entrance to the holes in the shaft and the hub. If you really want to switch you could use a taper pin instead. But it really seems that you haven't developed appropriate assembly procedures and fixtures.

 

[drawoh]

plangevin,

I hate set screws. I don't like the idea of drilling hubs and shafts for pins.

What is wrong with clamping hubs?

--
JHG

 

[cjccmc]

"Basically another type of pin easier to install would be perfect"

Not sure there is such a pin assuming you need zero play in the assembly. I have a spherical linkage design in work now and plan to use spring pins to secure pivot pins to links in holes drilled at assembly. There is considerable history of successful use of spring pins for this type of application. I have a heritage design with no known problems to reference in support of my choice; sounds like you have something that works equally well, may be wise to stick with the devil you know ;-)

 

[MikeHalloran]

If you're asking people to install spring pins with a generic toolbox or their own tools, nobody will be happy.

Get in touch with the spring pin makers and buy some of their tools, with company funds. They have simple tools suitable for field use, and automated ones that can feed, orient, place, and drive the pins into a fixtured part on demand.



Mike Halloran
Pembroke Pines, FL, USA

 

[plangevin]

Getting the right tool is for sure the best solution to our problem. I will definately take some time to dig further into that.

The reason why we don'T like clamp hubs is quite simple. Our equipment is out in the environment and subject to temperature variation. From tests we have done, we found the clamp coupling to slip quite often, even when using appropriate torque and thread locking compound. You have to remember that even with the tiniest slip our ''intelligence'' becomes next to null and we then rely on good old switches. While we make a pretty good use out of these switch, what seperates our product from the competition is the intelligent part which relies on the encoder reading.

Thanks to everyone who offered suggestions, ideas and opinions ! I'll let you know the outcome of it !

 

[DesignerGuy16]

Keys, keyways, and snap rings to trap them are a cheap alternative. If you're not worried about side load, you can use the e-clip type of snap ring that just snaps over the OD, no need to drag it all the way down the shaft.

James Spisich
Design Engineer, CSWP

 

[Artisi]

Spring pin with reduced diameter or taper as a lead seems the best option. Simple and no special tools or fixtures needed for assembly - maybe tweezers to hold the spring pin and position it

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[johnchrc]

You need more taper on the spring pin or entry hole. Also, place in vise and use long dowel for hole alignment if more than one spring pin.

Are you coating the parts and causing the an increase in interference fit?

I find a punch with at least 2x spring pin dia works well. You could make a tool like a punch with a hole that accepts the spring pin face and start pin into hole that way.

What size holes and spring pin are you using + tolerances.

You could also put a very low friction coating on the outer parts making allowance for coating thickness. Xylan, Nedox, Baked on Moly, ans many others.



- CJ