[rceebuilder]

I was using 8 mm metric screw to drive the axis of my small router The speed was not so disturbing for a small distance The max jog speed was about 6 mm per sec .Then I built a new router with a 1 meter long X axis but now I have a new problem :low jogging speed. I checked the cost of ball screw , rack pinion and belt drive but all of them require usd 100 per axis. So I decided to try steel wire drive method .I have tensioned a 0.2mm steel wire and wound it on a 8 mm steel shaft at 3 turns. With this way the motion transmission is perfect and there is no backlash at all.The only problem is linear motion of the drive shaft .When the shaft is turned it is forced to move axialy too .it is because of the wound effect of the wire. I hope I could describe what I mean . May be this picture help. The shaft will be directly driven with a step motor. Do you have any idea to compansate the linear motion of the shaft?

Murat..

[chuckknigh]

Yes -- the screw is moving 1 thread laterally, per rotation. If you mount the screw on a nut, and then allow the whole thing to move laterally, the entry and exit points for the wire will remain constant.

A similar idea cropped up on DIY-CNC a while back. You might check the Yahoo archives.

-- Chuck Knight

[davesaudio]

solid wire?
Has anyone determined the wire life span?
D

[rceebuilder]

it works on some photocopy machines more than 10 years.

[zoltan]

Rceebuilder,

You made me curios. I do not understand very well your system. Could you, please, get in more details? Eventually a sketch will be helpful.

Thank you,

Zoltan

[rceebuilder]

Zoltan , Here is the 2 type of wire driven gantry project. Of course the wire will be plied type. The only problem is how to compansate drive shaft's lateral movement.

[Charlye]

rceebuilder,

If you are going to directly drive the 8mm shaft with a 1.8 degree/fullstep motor then you'll get 0.1256mm (0.0049 inch) of linear motion per step. With micro stepping it gets slightly better. 8mm rod with 0.2 m wire you can drive 600mm of linear motion with only 24 full rotations.. so that's only 5mm of lateral motion. Is that fatal?

I'm looking seriously at using the looping wire system on my first machine, which will be a simple 2d plotter and foam hotwire cutter.

Of course going with a small diameter drive rod gets better resolution, but more wear and tear on the wire and even more lateral movement.

Playing around with numbers I found that using a 1/4 inch drive rod results in a ~0.1mm step (0.0997mm but who's counting). Using English parts to get metric motion, a bit funny.

Ideas for the lateral movement.. I like Mr Knight's idea of using the nut and threads. If your steel wire 'threads per inch' matched that of available nut/screws you'd be all set. Changing the gauge of the wire can help get you there.

Charlye

[geoff p]

How about setting the drive shaft at an angle to the wire: you know the diameter of the wire and that of the shaft, so calculate the angle, and squint the beast a bit. I used to do this on a home-made machine of very limited travel. It might work for you!
Or set two small ball-races, one each side of the shaft, to force the wire to enter-and-exit the helix where you want.

[Netjams]

How about setting the drive shaft at an angle to the wire: you know the diameter of the wire and that of the shaft, so calculate the angle, and squint the beast a bit. I used to do this on a home-made machine of very limited travel. It might work for you!
Or set two small ball-races, one each side of the shaft, to force the wire to enter-and-exit the helix where you want.

That will work

[rceebuilder]

I applied it to my 40" x 20" router in x and y axis . The result is awesome . Particularly I liked gantry speed. Precision is enough for me. I will send some pictures soon.

Murat..

[dkowalcz]

You could use allthread, no? A 3 foot piece of 1/2" dia is about $5 USD, and add 35 cents for a nut. Not the greatest setup, but I think it'd be more reliable.

[dkowalcz]

It occurred to me that my other post could be construed as rude, so I'll add that MIT used wire drives in some of their experimental robots.

The idea was to get force transfer from a small shaft (eg, the motor) to a larger shaft (eg, an arm joint) with no backlash, and cheaply. Very clever design.

[rceebuilder]

Here are the photos of my cnc .

[esmiller]

Here are the photos of my cnc .

Interesting.. took me a minute to realize that te Y axis motor is mounted ON the Z axis carriage.. very nice.. any pics of your X axis system?

Eddie

[digital_life]

100u$ per axis isnt too much, i wonder. anyway please consider that time is money too. and when testing things out like this, mitakes are common, so if you make a mistake, you are trowhing money out. (been there, done that)
i live in argentina, when a ballscrew set for a 60x60x10xms router is almost 1500u$.

[zoltan]

Hi,

Are you satisfied with the accuracy and backlash of this solution? Did you verify what force can you transmit through this system? How did you solve the issue with moving the wire along of shaft? What do you think about using steel tape, like those from tape meter or what name they have in English - they are use for measurements? I was playing today with the idea...even I was thinking about few radial electromagnets inside of pulley of let's say 20 mm diameter, powered from 24 V at 1 A through two isolated rings to improve the adherence coefficient which is w/o around 0.18..?

Zoltan

[rceebuilder]

I have tried to mill some PCB . As you know PCB milling requires high accuracy . Also I tried to drill same 10 holes 20 times . It never missed a hole . I think accuracy is about +/ - 0,1- 0,15 mm . So in my opinion with this system wood working can be done succesfully. But works like pcb milling may not be satisfy . In my trials no backlash setting applied. It worth to try

[vid1900]

The cable drive is actually a good system. This is a close-up (the best pic I could take) of a 1.25" bronze "gear" driving a 1/16" 7x7 stainless steel cable. This drive system is the GOTO drive for a 200lb telescope. It has to be very accurate to track the sky at 1000x .

I got this scope before I moved to New York from

www.webstertelescopes.com

They use this drive system even when the scopes weigh 600lbs or more. The cable makes 2 wraps around the gear. The gear is driven by a Pitman servo motor with a 2000 tic encoder.

If you lift a spring held lever, it releases the cable just enough to let the scope freewheel. This may be another feature one could use for CNC.

If you need better pics let me know.

vid

[digital_life]

right now i cant, but i makes me want to build some sort of trying device for this system..seems pretty good.

[LeeWay]

Basically its the same system that we used on Shrimp Boats when I was younger to haul 1000's of pounds of fish out of the Gulf and onto the boat deck with. The rope wrapped around a smooth wench head and the hoister could let it free wheel idle in the air just by pulling or easing the tension on the other end of the rope.
So with this concept, you can get as much torque and strength as would be needed.
It may be that some of the accuracy was in the settings. Perhaps some minute settings in the size of the pully or shaft could be toyed with to acheive better accuracy.

Another concept that might be fun to try is chain drive. At least with a chain (like bicycle) you would have the same backlash over the length of the chain. This could be dealt with and accounted for in the software.
I was thinking a straight run of tensioned chain. Then a sprocket attached to the motor. You would need a skid plate to keep the chain in the srocket, but thats asy enough.
Probably could be done from parts in the garage or on the curb at your neighbors house.
Anyone toyed with chain?