IBM IBM/Simplex impulse clock contact cleaning suggestions?

[pianoman]

I haven't seen a thread that directly addressed this topic, forgive me if I missed something obvious in the search terms...

I have a Simplex impulse movement clock, which uses the same impulse movement as the old IBM/ITR systems with the "A" and "B" circuits. However, I've noticed that occasionally my clock stops advancing. I suspect this is because the contacts on the normally open and normally closed contacts may be a bit corroded, and I doubt the solenoid in the clock draws enough current to overcome the additional resistance.

In my other hobby, electromechanical traffic signal controllers, I have resolved this problem with some fine grit sandpaper folded in half. I simply sand the contacts a bit, which generally removes the dirt and not the actual metal contact surface. I then spray some electrical contact cleaner in there to clear out the grit.

That being said, I didn't know if there was perhaps a better method for these clocks. When I bench-tested this clock I did try adjusting the contacts a bit closer to the common terminal, but apparently that only worked for so long (about two days!). Just wanted to check in with the group to see what the pros do!

 

[Toughtool]

For cleaning contacts, I would recommend you use a strip of bond paper, saturated with 90% alcohol, pulling it through the closed contact. The bond paper is abrasive enough to loosen the dirt and the alcohol is to dissolve the oils. Using sand paper is too rough and will remove some of the metal, however small.

The contacts in the impulse secondary are designed to be switched, meaning opened or closed, without current. Some may even be plated with a conductive metal like silver and sanding will remove these coatings. Make sure the current is not applied when the contacts are transferred. The contacts should actually be polished to make then as smooth as possible, by burnishing them. If you observe the operation of an ITR and IBM secondary, you will see the armature rotate, then release (current dropped), then the hands move forward as the armature rotates back to the resting position, and if the time is right, opening or closing the contacts. The Simplex impulse movement should work the same way.

For contacts that open and close under a load (current applied) There will be pitting and metal deposits from the arcing. There will always be arcing when a contact makes or breaks under a current load. Just a matter of how severe. These should be first dressed with an abrasive, like sandpaper, or a file to remove the deposited metal , then burnished, or better yet, replaced. .

This as a supporting reference, from: Buy Martindale BURNXRB21, Dia-mond D Contact Burnishing Tool, Blades Only

Martindale, BURNXRB21, 3/16" x .007" x 1-1/2" Dia-mond D Contact Burnishing Tool, Blades Only
These exceptional tools are designed to burnish and polish all types of contacts - without removing virtually any precious metal. They leave no grit, no filings, no dust and no film that would start new carbon build-up. Diamond D Contact Burnishers perform superbly on all types of metal, including silver, gold, platinum, molybdenum and tungsten. We have designed them with just enough stiffness to apply the proper pressure to the contact face. Our contact burnishers are available either with plastic handles or in our handy PocketPen Holder. Proven by years and years of faithful field service, these tools have greatly extended the lives of millions of contacts.

If you want to know about contacts, here is a very technical reference: the Electrical Contact Design Manual . A great resource.

https://www.deringerney.com/publications/ney_electrical_contact_manual/

Their main website here:
https://www.deringerney.com/product...ctrical-contact-manufacturing/contact-rivets/

On Edit: Sorry, when I first found this site they did not require filling out a form with your name and other information to download the PDFs. Joe

 

[pianoman]

Thanks for the suggestions. I ordered some burnishing blades and picked up some alcohol; unfortunately due to the current craziness the best I could find was 70% concentration so that will have to do. I'll pull the clock down this weekend and give the alcohol treatment a try first and see what comes off, then go from there.

 

[Toughtool]

OK. Another thing you may want to do is check the contact adjustment. Since you did not post a photo, I don't know what model type your movement resembles. For educational purposes, here is a clip from the November 15, 1937, ITR Service Instructions # 201 to show how this contact is adjusted.

1.The text says make sure the A and B contact does not bridge, meaning A is opened before B is made.
2.There is contact movement after the contact is made. Here the image on the right shows us that the contact "should lift off brass support when made". The brass support is used to position the contact closer or farther away from the "Switch Operating Lever" , also called the operating strap. This adjustment assures the contact is under tension and that there is a small amount of wiping as it is lifted away from the brass support.

 

[pianoman]

OK. Another thing you may want to do is check the contact adjustment. Since you did not post a photo, I don't know what model type your movement resembles. For educational purposes, here is a clip from the November 15, 1937, ITR Service Instructions # 201 to show how this contact is adjusted.

1.The text says make sure the A and B contact does not bridge, meaning A is opened before B is made.
2.There is contact movement after the contact is made. Here the image on the right shows us that the contact "should lift off brass support when made". The brass support is used to position the contact closer or farther away from the "Switch Operating Lever" , also called the operating strap. This adjustment assures the contact is under tension and that there is a small amount of wiping as it is lifted away from the brass support.

View attachment 625428

The movement in my Simplex clock is very similar to what you posted here, and I think the same general principles apply. I will definitely check the contact adjustment, the clock was knocked around in shipping as the seller wedged it diagonally into a rectangular box, so there's a good chance it's not properly adjusted. I actually had to adjust the solenoid when it first arrived because the armature couldn't travel far enough to advance the clock 1 minute.

 

[Toughtool]

OK, Here is one of my 561-2s, showing where to look for the drive pawl and check pawl. In the de-energized photo, look through the hole in the plate and you will see the pawl tip in the gear tooth. This is at rest. In the energized photo the check pawl is trapped by the pin on the drive hub so it will not disengage and it locks the minute hand from moving. Remember the hand advances and the contacts will transfer after the current is removed. Also the movement must be "12 o'clock", up position, because the pawls are gravity operated.