When we say we have "loose" screws, we don't meean that the screws have rotated loose. Mostly, the screws do not rotate after tightening....it is the contact surface between the screw and the shaft that wears loose. Therefore, Loctite does not solve this wear problem - it just makes you think the screw is still tight when you test it with an allen key.

A pair of good quality, fine thread pitch screws tightened (and re-tightened) onto a proper flat spot on the shaft, creating a good contact surface, are the keys to getting it right. Loctite is just for peace of mind really :)

Exactly what I'm trying to say.
When the set screw bites well into the shaft, the gear will not come "loose" as it "nails" themselves tightly. & if set screw stay firmly "biting-on" the shaft, it will not get loosen due to the locknut-ish effect. Its a vicious cycle...

I cheated!
On one machine, I just TIG welded the Pinion to the shaft. It hasn't moved since that time that I know of! :)

I must have been lucky. When I did my machine I heard that 20 tooth pinions will give better performance. Well, 20 tooth in Metric has a very small shaft area. I turned a bush to strengthen the shaft area where I put my grub screw in. In 4 years NO - MOVEMENT... yet. Must have done it right from the beginning as I believe I took the pinion off a few times during the construction, therby getting the screw to BITE into the shaft.

Kobus, we have a slight advantage over the Americans, our typical grubscrew has a finer thread pitch and it tightens better.

Sean, I like your style! SALUTE!!!:cool:
I always cheat but not to the extend of welding a motor shaft! :D

Well,
To be honest, it was for that 48" extended z-slide and the motor had plenty of enough holding torque with the cable balancer - but the induced load on the shaft during rapid up/down moves, it would constantly work loose - so I welded it!

Not a problem after that!

I have a constant thing with the grub screws/pinions working lose.This Saturday morning will consist of tightening it again.How do I know it a circle is not a circle anymore. Sean I like that welding idea.

Hennie,
Did you grind the second flat on the motor shaft 90 deg off for a second grub screw? I am wondering how many people who have had this problem have actually done the second screw fix.

Jip, did that.

Get a longer screw, drill a hole threw the extra, tighten with a reasonable loctite and run a wire threw the hole and twist it secure like they do on airplanes.

Jas

Attachment 13218


this might work

Jason,
Maybe, but the issue isn't the screw backing out...its the registration between the point of the fastener and the shaft. Some "grub" screws have a flat bullet point, others sharp, others knurled. The issue is getting a flat to flat connection on a round shaft - thus the reason why so many have ground an additional flat side to the motor shaft for 2 points of contact with the pinion.

A flat mill file or a carefully handled grinder does the trick quickly!

Fix the problem with a spring pin. I and someone else on this forum mentioned that already but some seem to think that this would make changing a motor or pinion in the future harder to do. I have been using this method for many years now and I have never really found it that hard to change something later. Just remove the pin and redrill. Also this is extremely precise and stays that way. I just finished engraving 4000 1'' square lamacoid plastic tags with consecutive numbers from 1 to 4000 with not a hitch. Now that is a lot of lines of code.

Just my 2 cents worth.:D

Ok,so if the grub screw is tightened and it still shows marks on the project when cutting where does one look.The one thing I never thought to look at is the shaft that comes out of the gearbox.One of my gearboxes are F... How I found out?I had power on the motors and wiggled the pinion gear and the whole shaft moved there is a lot of backlash.It was the one x-axis motor.Moral of the whole story don`t let the spring pull the motor through the rack.I will take the gearbox apart and see what it looks like inside.Will get new pinions for my Motion king motors and fit them.

Sorry for post to old thread. But has anyone tried doing keyed shaft and spur gear? This way the set/grub screw is just to hold from falling off, not from keeping registration with the shaft.

Jack, there really isn't much "meat" on the 20 or 24 teeth spur gear left for a key way. Hence, grub screw.
you might have more space in 34 or larger spur gear.
But than again, grub screw is a good hack.

Instead of using a grub screw, then use a pin. It will not come loose and it will not fall out. On the 24 tooth pinion it works great.

I'm too lazy to drill precision pin holes... Grub screw suits lazy me very well.