Scribbler: gear slips on motor shaft

Iamretired

What glue would be good to tighten gear on shaft?
Loctite is very expensive.

erco

Loctite (AKA cyanoacrylate, AKA superglue) is VERY cheap. 20 years ago it was expensive, like $100 a bottle in machine shop usage. Wiki "cyanoacrylate" for its interesting medical history:

CA glue was in veterinary use for mending bone, hide, and tortoise shell by at least the early 1970s.[citation needed] The inventor of cyanoacrylates, Harry Coover, said in 1966 that a CA spray was used in the Vietnam War to retard bleeding in wounded soldiers until they could be brought to a hospital. Butyl cyanoacrylate has been used medically since the 1970s outside the US, but due to its potential to irritate the skin, the U.S. Food and Drug Administration did not approve its use as a medical adhesive until 1998 with Dermabond.[3] Research has demonstrated the use of cyanoacrylate in wound closure as being safer and more functional than traditional suturing.[4] The adhesive has demonstrated superior performance in the time required to close a wound, incidence of infection (suture canals through the skin's epidermal, dermal, and subcutaneous fat layers introduce extra routes of contamination),[4] and final cosmetic appearance.[5][6]

But I digress. Are you saying that your small white nylon pinion came off of your motor shaft, inside the white nylon motor module? If so, it probably split somewhere and can't be glued reliably. If it didn't split, you could try some gap-filling superglue and accelerator, but it may be be a short-lived fix. Those pinions split regularly, they are a press fit on the motor shaft, and they are hard to source.

Worst case, you may have to replace your whole motor module. You can get them at Solarbotics or Pololu. http://www.pololu.com/catalog/product/187

Ken Gracey

Iamretired, I haven't heard of this particular Scribbler problem before.

I've got some spare Scribbler guts in the office. Contact me offline at kgracey@parallax.com and I'll get you the parts you need. Be specific in your request so I can do the right surgery on a Scribbler or two.

Thanks, Ken Gracey

PJAllen

JBWeld ! !

W9GFO

erco wrote: »

Loctite (AKA cyanoacrylate, AKA superglue) is VERY cheap.

Loctite is a brand that makes many different things. They are commonly known for thread locker such as Loctite 243 which is not a cyanoacrylate.

Loctite may make Super Glue but Loctite is not "also known as" Super Glue or cyanoacrylate.

Rich H

RobotWorkshop

If it is the small pinon gear on the motor shaft I would carefully inspect it to see if there is a split between one of the teeth. If so then the gear needs to be replaced. Even if you could glue it the teeth won't line up properly and it will bind whenever it comes to the teeth with the split.

I've never heard of one breaking on the Scribbler robots but I have seen this MANY times in the past and it is a problem on many devices that use a press fit plastic pinon gear on the motor. I recall the old Radio Shack small 4 pen plotter had that issue and I've seen it occur on just about all of the OWI (MOVIT) robot kits. After a while all of those end up splitting.

There is a cure! On all the OWI robots I replaced the pinon gears with brass ones (used a small arbor press) and they will never split again. If it ever happens to my scribbler it will get the same treatment.

Robert

Phil Pilgrim (PhiPi)

I'll second PJ's JB Weld recommendation. That stuff is amazing! It's basically a metal-filled epoxy. I used it once to repair a cast iron sprocket that snapped apart on a paint dipping machine that a friend of mine uses in his fishing tackle company. (Well, okay, I broke it using a cheap gear puller to remove it from the motor shaft.) It was meant to be an emergency repair until a new sprocket could be obtained. Instead, the repaired sprocket got used for years thereafter. I've also used it for cementing heatsink fins on the backs of DIPs. The embedded metal particles help to promote the heat transfer.

-Phil

Iamretired

Thank all of you for responding. I think I will give JBWELD a try.
John