Good Shaft couplers

[klick0]

This may seem like a dumb question, but i'm gonna ask it anyway eheh.

I have some pretty cheap shaft couplers to join 1/4" to 1/4" shafts, and on my Z axis it keeps disconnecting (well it's done it twice..) I have 1/4" shaft DC servo motors and 1/4" shaft lead screw. Does anyone do anything like put a cotter pin in there, or something, mine just have one small screw set thing, and obviously I twisted as hard as I could but it still fell out during machining, and then the Z axis dropped into the table at 100IPM hehe, not good.

I recently switching from a very slow stepper system to a pretty fast servo system (same table). I was doing 3d foam engraving so I was running hte machine at 120IPM, but more likely it was moving at about 90-100... obviously a lot of up and down action.

I guess i'm just wondering if people use shaft couplers with like 4 set screws for each side (total 8) or something, or if you drill into the shafts and put something directly threw that? I dunno, i'm about to just drill a hole into my servo and shaft and tap it or something, put a bolt through there, that definatly wouldn't go anywhere.

Thanks,
Ross

[2muchstuff]

Do your shafts have flat spots on them where the set screws touch, if not they should. One set screw per shaft is not enough, for maximum holding power there should be 2 set 90 degrees apart from each other. When installing new screws use Loctite on them. The blue stuff will allow you remove them at a later date if needed, the red stuff, you will need a torch to heat them up to get them out.

[klick0]

Loctite, i'll get some of that immediatly, thanks for your response.

The motor is keyed like you say, but the lead screw is not, since i just cut it to size with a cutoff tool. I could probably grind a keyway into it.

I'll probably buy new couplers that have 2 set screws per each shaft (4 total) and the loctite stuff, that should do the trick it sounds like it.

Thanks and happy new year,
Ross

[wizard]

Originally Posted by klick0 This may seem like a dumb question, but i'm gonna ask it anyway eheh.

The dumb questions are the ones that never get asked!

I have some pretty cheap shaft couplers to join 1/4" to 1/4" shafts, and on my Z axis it keeps disconnecting (well it's done it twice..) I have 1/4" shaft DC servo motors and 1/4" shaft lead screw.

Those are small shaft sizes which can be a pain when you expect to drive osscilating torque through them.

Does anyone do anything like put a cotter pin in there, or something, mine just have one small screw set thing, and obviously I twisted as hard as I could but it still fell out during machining, and then the Z axis dropped into the table at 100IPM hehe, not good.

DO NOT attempt to pin such small shafts you will eventually twist the shaft off. Even a key way will reduce the shaft strength significantly but should be better than a through pin.

The thing with set screws is the the need for high quality units with the right points. Ideally the couplers will have two set screw holes aligned 120 degrees apart. As to the lossening set screws make sure the threads are proper, sloppy fits are not help here.

You may eventually find that set screws with or without a key way are not enough. I'd suggest that you look inoto the various taper locking arraingements for the coupler. Just about all of the industrial servo systems that I see exposed to this sort of start stop action have some sort of taper lock or splined shaft.

I recently switching from a very slow stepper system to a pretty fast servo system (same table). I was doing 3d foam engraving so I was running hte machine at 120IPM, but more likely it was moving at about 90-100... obviously a lot of up and down action.

Yep this is the sign that you need to complete the upgrade by selecting better components for the dirve train.

I guess i'm just wondering if people use shaft couplers with like 4 set screws for each side (total 8) or something, or if you drill into the shafts and put something directly threw that? I dunno, i'm about to just drill a hole into my servo and shaft and tap it or something, put a bolt through there, that definatly wouldn't go anywhere.

Don't be to sure about that bolt you arel very likely to shear it off. As fo multiple set screws as mentioned above you need no more that two sets 120 degrees apart. I say sets because it is concieveable that you could have two at each station. I do wonder what size set screw you may be using, it often pays to upgrade to a heavier set screw. It also might pay to go with a a square drive set screw instead of an Allen style. I would imagine that the set screws for a coupleing on a 1/4" shaft are small, thus you are not likely to ever get a reasonable amount of torque on them.

Thanks, Ross

Thanks
Dave

[Karl_T]

FWIW,

I went down this exact path on my CNC when I switched from step to servo. Some investiation in machinery handbook showed the best torque holding without losing shaft torque was a woodruff key. I keyed the shafts and have no trouble.

Karl

[erase42]

there are couplers available with a very nice clamp mechanism, basically the end of the unit is split and there is a small screw on each side so the coupler clamps on the whole shaft not just the tip of a set screw. one thing to watch for is some have a very hard rubber coupler in the center if you use that kind, make sure you have some sort of solid thrust bearing on your leadscrew. if you dont that rubber softens with the repeated compression and decompression from switching directions. the one on my foamcutter developed .14 " in play before i figured that it was the cause of the flats on any radius that i cut. Lack of a solid thrust bearing my be your prob now if its a home made machine.
ED