Attaching a Stepper

[andy_ck87028]

Hi,

I have seen from numerous pictures from this wonderful website that the 'normal' technique is to have a stepper directly connected to the ball screw. I am also aware that often the ball screw would have been machined down to create a spindle. Given that Steppers will have their own spindle, what is the normal method of attachment between the ball screw spindle and the stepper motor spindle?

Also, although I am starting to appreciate that stepper size is critical and gearing does not necessarily provide increased torque, I am inclined (unless convinced otherwise) to utilise a geared attachment between stepper spindle and ball screw spindle. If I were to do that, how should I respond to issues of backlash? Would a timing pulley assembly be sufficient for example?

Any opinions will be read with immense interest.

Andy

(Merry Xmas from currently very warm Australia)

[Al_The_Man]

Andy, If you use a geared attachment, I would recommend a low backlash compact planetary gearbox such as Bayside etc, but if you only need a small reduction, say 2 or 3 to one, a timing belt/pulley arrangement can offer a very low backlash setup, it is not quite so compact as the planetary set-up, but is cheaper.
Al

[berin]

Yes I'd reccomend COGS and pullys, They are a LOW tooth count but ofer very low resistance. Not to mention they are designed to CLAMP to the threaded rod and the motor.
Heck I even have some to offer but I only have 2/3's of what you need. I have the LARGE cog to connect to the threaded rod. and I have the matching pullys which is about 5-8" pulled tight flat. But I dont have the clamping cog for the stepper motor.
The pully method is nice because you do not HAVE to have the stepper or servo motor perficly alined. Where as a direct connection or GEARED connection must be VERY accurate. Other wise you create a lot of resistance and unwanted ware.
And you dont have any PLAY when using the pully system where as a geared system can have a little bit of +/- play. Not much but depending on the setup can be a few 32'nds down to a few 64ths or less. Could even be nothing at all but thats subject to change depending on usage and wear. AND gear material for example PLASTIC.

http://www.globalspec.com/FeaturedPr...xhibitID=13198
In the picture the image on the far left looks like what I'm missing or the one next to it on the right side.

[andy_ck87028]

Thanks Guys

I've just re-read Berin's reply and realised that you were tabling an offer. Thanks for that thought. As I need to build for x,y,z axis, I'll need repeatable assemblies. The x and y need to be carbon copies otherwise I can foresee calibration complexities when I start to operate. At this stage, I'll probably mock up an assembly using local parts (I'm planning to pick up some trashed photocopiers which I reckon could be good sources for steppers, timing pulleys, etc). Once I have assembled one axis, I'll play.

If I do choose to go down the gearing path, secondhand meccano is a very cheap and durable option. Also, introduced wear should be a minor concern because of the standard and regular construction.

One very cheap option suggested by a friend was a pulley and cord arrangement. He gave me the tip to buy cord with a fibreglass core. My concern with that arrangement would be slippage but I then saw that timing belts also have a fibreglass or metal band. On that basis, timing belts would have to be better option.

Andy

[berin]

calibration complexityes, LOL not really, the software compinsates for that regardless. All you have to do is give MAX step rates and the precision of the axis. That is it nothing more nothing less. The software takes up the part of differings in gearing and step rate. Your slowest part sets your max speed of step rate.

If you would like I could post a picture of the kind of belt drive I'm talking about, on second thought I think I will just because I can. Though I cant till I get home. (jingle bells, jingle bells, What on earth is this,) christmass eve tonight merry christmas every one.
If your intrested in cnc parts let me know because I can get you almost any thing your looking for OTHER THEN lead screws for really cheep!!!