stepper shaft to threaded rod - HELP!

[jamwaffles]

hi. im building my own cnc machine and i cant work out how to simply mount a piece of M10 or M8 threaded rod onto a 6mm stepper shaft. any help would be great.

james waples, 14

[LeeWay]

Couplers can be as simple or as elaborate as you want to make them. Read dirt cheap to expensive.

You could of course, buy couplings to fit, but without reducing the end on your threaded rod, you are limited.
You could get an extension nut. These are long nuts used for joining two lengths of threaded rod. Use a set screw or lock tight in it then use a bushing on the motor coupler.

Rubber hose also works fairly well with hose clamps.

If you use M10 rod, you could even drill a 6MM hole in the end and directly couple the motor into the rod using a set screw or two.

[M250cnc]

Hi James

Are you sure you are cut out for building your own cnc machine

Anyway reduce the diameter of the threaded rods to the same diameter as the stepper shaft

The stepper shaft should have a flat on it copy that onto the shaft

Make a sleeve to fit both together the screw fixing will locate on each flat.

Phil_H

[HankMcSpank]

An old thread (I found it via google!).....

A thing that's nagging me...eveyone says backlash is the evil of homemade cnc (& I can see why)...but how on earth can coupling a motor to the leadscrew, threaded rod etc with a hose & clips *not* be more of a problem...surely there's a bit of rotational 'play' with the relatively soft hose as the motor goes from turning one way, to the opposite direction?

[ger21]

Originally Posted by HankMcSpank ...but how on earth can coupling a motor to the leadscrew, threaded rod etc with a hose & clips *not* be more of a problem...

Supposedly hose couplers actually work OK. And if you're only willing to spend $1 on your couplers, what can you expect??

[HankMcSpank]

Originally Posted by ger21 Supposedly hose couplers actually work OK. And if you're only willing to spend $1 on your couplers, what can you expect??

They must, because everyone seems to recommend using them! But if I get a piece of hosepipe & hold it in each hand, I reckon I can turn it (might be an illusion!)...I'm thinking that same movement must play havoc when the stepper motor chages direction!

[ger21]

Originally Posted by HankMcSpank They must, because everyone seems to recommend using them! But if I get a piece of hosepipe & hold it in each hand, I reckon I can turn it (might be an illusion!)...

But when you hold it in your hand, you're not holding it nearly as tightly as if clamped to two shafts. Imagine if the two shafts were 1/4" (6mm) apart, with a hose clamp on each shaft, it'd be far more rigid than when holding it in your hand.

And while it's popular on the very cheap machines, you don't see too many here using that method anymore. Not when you can buy real couplers for $5.

[irving2008]

Originally Posted by jamwaffles hi. im building my own cnc machine and i cant work out how to simply mount a piece of M10 or M8 threaded rod onto a 6mm stepper shaft. any help would be great. james waples, 14

James,

Have a look at these couplers by way of example. Ideally, as suggested, you need to machine the end of the rod down to 8mm so it can pass through an 8mm ball race for support and then into the coupler for the motor. At the far end it also ideally needs to be machined down to 8mm to pass through a ball race and then threaded 8mm for a nut to control the backlash. For a low-end/low-speed machine however its possible to get away with no supports and a bit of hose with 2 jubilee clips, but don't expect great accuracy/repeatability if you spin the screw fast as the hose tends to 'wind-up'. Like many things, the 'correct' answer depends what you aim to do with the machine.

Why don't you come and join the UK CNC community on www.mycncuk.com as well as here...

[HankMcSpank]

Originally Posted by irving2008 James, At the far end it also ideally needs to be machined down to 8mm to pass through a ball race and then threaded 8mm for a nut to control the backlash. Why don't you come and join the UK CNC community on www.mycncuk.com as well as here...

Surely that's whip you're trying to control *not* backlash (ie where the linear screw is unsupported and moves around at the opposite end to the stepper motor?

[ger21]

No, he's using the bearing as a thrust bearing to keep the screw from moving axially, which would be backlash.

[LeeWay]

I mentioned the hose because nothing needs to be turned down to get the motor to drive a screw. Cheap and easy. That is what the original poster was looking for I thought.
It is not without some give if you put some torque on it. The spider couplings shown in the link also have give with enough force.
I think a rubber hose may have done better in my case rather than the little spiders I initially used. They aren't zero backlash and usually aren't advertised as such.
It all boils down to how much work you want to put into it and how much money as well.

Some of the little machines I have seen could probably be run with duct tape couplings.

[blackbeard52]

Hank
What you dont seem to realize is most who would use that rubber hose setup are just building a cnc for the first time and want to get their feet wet. It does work to the accuracy that a moderate woodworker would be pleased with. That being said not most but all will soon upgrade to a better coupler. Reguardless and amazingly, it does work to acceptable beginner accuracy.

Bob

Bob