grub screw issues

[msimpson99]

I finished my second version of my R&P drive reducers and they work great. The only issue I have is that I cant keep the grub screws on the pinions tight. After about 2 hours of breakin they seem to break free.

I have tried locktite 222 (purple)
HF 42 (Blue)
and locktite 242 (blue)

I clean with acetone before each attempt. I then give them a chance to setup.

Here is the catch and I am wondering if this is what is causing the problems. The pinion gears are 3/8" The shaft is 1/4 with flats (D shaft). I machined a 3/8" to 1/4" reducer. It has a hole where the grub screw makes its way through. I am using longer grub screws since they have to get through the reducer.

The grub screws are stainless steel. Could this be causing the problem? I dont want to use locktite red on these as I dont want to start heating things.

[acourtjester]

I don't know if you have the depth but you could try 2 grub screws one on top of the other I have seen this while taking pulleys off shafts. Similar to a jam nut on a bolt (double nut thing).

[msimpson99]

I thought of that. I dont have the depth. When building the reducers it has been a challenge to source the parts. I would have preferred a pinion with a 1/4" bore. This would allow for more byte of the grub or even two grubs.

These are 14-1/2 Pressure Angle to match the racks. I wanted to go with 20 degree pressure angle but I cant get the pinions I want for this. But, I can get some gear rod stock for 20 degree pressure angle. I can get 12" of this for $41. With this I can make my own and move over to 20 degree PA. It runs much smoother in my opinion.

[msimpson99]

Another thought. The excess of the grub screws stick out about 1/4". Can a locktihte a nut onto this?

[WyoGreen]

I think I'd try putting a nut on that excess grub screw length. It should act like a lock nut.

[msimpson99]

The drive reducers are working really well. Its only the X-axis (Non Gantry) drive thats giving me problems.

20161027_003313.jpg

Both the grub screw and the main reduction pulley failed.
I cleaned and re-applied 242 and added a nut shown here:

20161027_003244.jpg

On the pulley I had only 222, so I removed both grubs screws (It has 2) and applied 242.

20161027_003255.jpg

Im getting a little wiggle from the drives, but I think its the tension and the drive mount. I will improve these later. I have the actual no load backlash down to about .001 and repeatability down to abut .001 as well.

[msimpson99]

So far so good, I gave the blue Locktite about 24 hours to set and been working good for about 5 days. I think the problem arises from the fact that the pinion only has about 1/8" of threads. Seems like a bad design for a grub screw to hold something that is obviously goin

[Black Forest]

If you can't get the correct pinion than I would also sleeve the outside of the hub if you have clearance which I think you must if you put a nut there.
That would be structurally much stronger. It would give you more threads to "push" on the shaft and more threads for the Locktite to hold.

[Black Forest]

As a rule of thumb you want to have 1.5 times the diameter of your screw for optimum holding power.