I don't recall you saying. Is the coupler steel or some other metal? How many threads (approximately) in the coupler for the set screw to grab. The risk, of course, is that you may strip those threads if you rely on pressure alone. That is one reason I suggested a cup or flat in the shaft.

As for red vs. blue Loctite, there is a big difference between a 1/4" bolt and a 4-40 or 6-32 size set screw. For small fasteners, I use red routinely, like on wheel collars for models. It holds, and I have never had a problem removing the set screws.

John

 

Does the set screw protrude? Maybe an additional lock nut if possible?

 

That is what these are.


Actually just look at them again . They are mode flat. Where do I get the ones with the point? How would I know what size to use?

What are they actually called?

The couplers I use that are mounted on a shaft with no flat etc, have a double set screw at 90°, you could always drill and tap another, yours coming from China they are most likely to be metric.
The name depends where you buy them from, set screws in N.A. Grub screws in UK.
I received the pointed ones in the couplers I purchased.
BTW, a nice hardware source for CNC hardware is Misumi, they send a huge catalogue when you register that has useful engineering info in it.
What type of coupler, bellows type?
Max.

 

The only way to loosen a bolt that's been locked with red loctite is to heat the part with a small torch.
I like using the type used for cooking desserts, like creme bruilé

I assume you mean the red type?

I hope I can get the blue one loose. Though I only put it on the shaft end and not the motor end of the coupler.

 

Does the set screw protrude? Maybe an additional lock nut if possible?

No it is tiny. No way to get anything on there.

 

I have two types of couplers. One type has two pairs of set screws. Each pair is at right angles to one another.
One pair for the motor. The other pair for the shaft. This was the one with the loose set screw. I added some locktite and am waiting to see how that goes.


The second type has a split in the coupler. There are two of these. There is a larger screw that closes the gap in the coupler split and a smaller set screw to take up the slop. In my investigation, I noticed that this type wobbles a bit when the motor is off of the machine. I was able to clean up the wobble by resetting all of the screws but it still wobbles a tiny bit. Should they wobble at all?

Maybe I should just replace those couplers?

 

No it is tiny. No way to get anything on there.

How big is "tiny". For someone working on ships, that might be 1/4-28. For me, that might be a 000-120 thread.

John

 

Maybe I should just replace those couplers?

With what? Welded splines? Think about it. Such couplings are not difficult to solve.

John

 

Are they backing off, or slipping? If slipping maybe you can put a flat spot on the shaft.

 

Are they backing off, or slipping? If slipping maybe you can put a flat spot on the shaft.

I think that suggestion is already on the floor.

John

 

Even within the Loctite "colors" there are different strengths. The purple is for screw in the "number" range, like 10-32 and under. Here is the "color" chart with the different numbers and what they are for http://us.henkel-adhesives-blog.com...ween-Red-Blue-Green-and-Purple-Threadlockers/

Most of the auto parts places sell the little single use tubes of Loctite and if you have an ACE hardware near by, they have a row of bins with metric and imperial/inch screws.

 

Are they backing off, or slipping? If slipping maybe you can put a flat spot on the shaft.

Backing off. Then the whole coupler slips

 

Even within the Loctite "colors" there are different strengths. The purple is for screw in the "number" range, like 10-32 and under. Here is the "color" chart with the different numbers and what they are for http://us.henkel-adhesives-blog.com...ween-Red-Blue-Green-and-Purple-Threadlockers/

Most of the auto parts places sell the little single use tubes of Loctite and if you have an ACE hardware near by, they have a row of bins with metric and imperial/inch screws.

I picked up blue. I think the lightest they had. Rated as "medium" strength.

 

I have also been known to replace set screws with hardened bolts. I suspect the set screws that came with the kit are not hardened properly, I've had that problem before too. It all depends if you have room. It also allows for more torque on the screws.

 

Are they bellows type or spider couplers? or? If bellows, are they aluminum?
Max.

 

Cup set screws will walk out if the thread or shaft tolerances are too loose and the shaft is driven in both directions. A point set screw will reduce this tendency but doesn't address the underlying problem. Consider replacing the couplings with well-made ones that fit the shaft better or shimming the interface.

 

I know you guys keep bringing up the "pointed" set screws, but, the problem with them is, unless there is enough thickness in the hub, they limit the number of threads engaged. In my ~50 years as a tool maker - machinist - fabricator, almost no place have pointed set screws been used. The most common set screw in industry use is the, knurled cup point type. The knurl and the cup both bite into the shaft and secure better, and allow almost full length thread engagement.

As far as a flat being put on the shaft, that isn't done much either. The usual thing is to secure the position with one screw and then take the other screw out and drill a spot in the shaft using a tap drill size drill through the screw hole. The drill depth only needs to be the depth of the drill point. The place the knurled cup point in the drilled spot. Just a flat on the shaft can still allow the coupler pulley or what ever move. When the screw point goes into the drilled spot there is no way for it to move.
A picture/link to knurled cup point set screws - http://www.allfasteners.com.au/sock...thread-14.9-high-tensile-plain-unplated-black

 

For shafts that have no flat etc, I have found the split collar/compression types the better for grip, rather than the screw on to the shaft type.

Max.

 

I know you guys keep bringing up the "pointed" set screws, but, the problem with them is, unless there is enough thickness in the hub, they limit the number of threads engaged. In my ~50 years as a tool maker - machinist - fabricator, almost no place have pointed set screws been used. The most common set screw in industry use is the, knurled cup point type. The knurl and the cup both bite into the shaft and secure better, and allow almost full length thread engagement.

As far as a flat being put on the shaft, that isn't done much either. The usual thing is to secure the position with one screw and then take the other screw out and drill a spot in the shaft using a tap drill size drill through the screw hole. The drill depth only needs to be the depth of the drill point. The place the knurled cup point in the drilled spot. Just a flat on the shaft can still allow the coupler pulley or what ever move. When the screw point goes into the drilled spot there is no way for it to move.
A picture/link to knurled cup point set screws - http://www.allfasteners.com.au/sock...thread-14.9-high-tensile-plain-unplated-black

I'm surprised that no one's mentioned brass-tipped set screws in this thread. They have the advantage of not marring the shaft they're pressed against.

 

We use lots of sets screws and must adjust them regularly as part of calibration procedures.

The important ones that we don't want working loose between PM's are secured by a second set screw, torqued down against the top of the first one.

IT WORKS GREAT. If you have a deep enough threaded hole