Stepper to Lead Screw Coupler Help

[FixitMike]

Note that a spring pin will hold just as accurately as a dowel, and it does not require a reamed hole.

http://www.mcmaster.com/#roll-pins/=10q0wyo

[Longknife]

Thanks for the advice.

I will talk to some machinist friends to source a good drill bit. As I say, the big box store bits I have now barely make a dent in either material.

[CosmosK]

imho, roll pins are a pain. Reamer a hole is easy. The reamer will follow the pilot hole, easy as can be.

To ream: drill undersize by a few thou. So, for an 1/8" dowel, get a .120" drill, then ream .1245".

You'll need:
#30 drill $0.98 http://www.mcmaster.com/mv1453013190/#30585a43
.1245" reamer $12.48 http://www.mcmaster.com/#8803a21
1/8" dowel pin $8.12 http://www.mcmaster.com/#97395a451 (or similar)

You might get the entrance of your holes started with the part disassembled. Center punch would help too. As mentioned, press not tap as the motor and ballnut are sensitive to shock.

You might try another coupling to fit in it's place. Clamp style will be a step up from set screw: http://www.mcmaster.com/#standard-shaft ... s/=10qhv6k

good luck

[CosmosK]

Thanks for the advice.

I will talk to some machinist friends to source a good drill bit. As I say, the big box store bits I have now barely make a dent in either material.

Right, they sell so-so quality stuff. Not for drilling into anything but wood or drywall.

Mcmaster is my favorite. They have a great web page layout. There's also MSC direct. HSS bits will get through most steel.

[weber765]

I think you are asking for trouble down the road with either dowel pins or set screws, The dowel pin or spring pin weakens the shaft and can cause the shaft to break and they sometimes will wallow the hole out. I do not like set screws on a flat either they also can start to chew up the shaft and cause problems. I have made a lot of repairs over the years for both. Again I would suggest a coupling with a split hub that will not slip such as these; Helical flexible shaft couplings

http://www.mcmaster.com/#flexible-shaft ... s/=10qrpgw

Glenn

[CosmosK]

I think you are asking for trouble down the road with either dowel pins or set screws, The dowel pin or spring pin weakens the shaft and can cause the shaft to break and they sometimes will wallow the hole out. I do not like set screws on a flat either they also can start to chew up the shaft and cause problems. I have made a lot of repairs over the years for both. Again I would suggest a coupling with a split hub that will not slip such as these; Helical flexible shaft couplings

http://www.mcmaster.com/#flexible-shaft ... s/=10qrpgw

Glenn

I agree, crossdrilling the shaft is not ideal, but we're talking about a situation where options are limited. Strength is not an issue. That little stepper doesn't have to power to shear a 1/8" dowel or the ballscrew shaft with a hole in it.

What does this mean? "wallow the hole out"

[weber765]

Wallow the hole out means that the hole size becomes a bit larger because when the shaft changes direction if there is any movement it can cause the hole to start to over size (wallow ) . You may have no problem at all. But with the inertia from your head movement rapidly changing directions it could be an consideration. Hand drilled and reamed holes are sometimes not as round as people think they are, and hammering a dowel pin in with out a press causes shock, and removing a pin that sheared and then rotated in the coupling is a real bugger, it also can ruin the shaft.
A very cheap coupling that my dad used for years was a piece of rubber hose and several hose clamps. It may be a option ( I never careed for it but it is still on the machine after 6 years ) and he has never had a problem with it.

Glenn

[CosmosK]

Yes, you have to be careful, but reamed and pressed pin should be rock solid imho. I'd take that over a piece of hose, but each to their own!

[weber765]

I would not use a hose either and if I used a pin I would use a tapered pin but it requires a special reamer. Anyways hope it works well for you.

Glenn

[Longknife]

My machine's been sitting idle and I finally decided to deal with my coupler issue.

Unfortunately there doesn't appear to be any Lovejoy type couplers that will accommodate the 1.5" gap I have in between shaft ends. I would need to put a coupler on either shaft end and then connect them with a small length of 8mm shaft. I may try that route eventually and use couplers that don't allow axial movement.

For now, I've drilled a détente in the shafts for the set screws (now allen type cap screws). I'm hoping ti holds up moderately well.

Thanks