counter-weights

[georgebarr]

I would like to know if there is any way to make the z-axis lighter so as not to put too much load on a small stepper motor? Some people have suggested a gas-charged cylinder (which has constant force), springs with a cable inside (cable used to limit the amount of stretch so as not to break the spring), weights attached to a pulley using cables, and etc. Are there any other easy methods to make the z-axis lighter in weight? Amoung these methods, which offers the best performance versus ease of construction ratio? My z-axis will travel about 2 feet (my first cnc machine).

Thanks,

[chuckknigh]

I don't know if it'll work, but here's an idea I got at Lowes.

I was taking a close look at their plywood panel saw, and wondered how they negated the weight of the saw/carriage. So, I asked.

He showed me the back -- it's a BRICK, tied to a string, and run over a pulley. Low tech, but functional...a counterweight is a counterweight.

Surely something similar could be run over the *side* of your machine...a pulley at the top of the Z axis, another at the one side of the Y axis, and a brick...

-- Chuck Knight

[buscht]

George, I found out that the gas spring is not a constant force. The force increases as the spring is compressed. Just like a regular spring.

The way to minimize this is to have alot longer spring than you need. If a 24" long spring increases 20% in force, a 48" long spring would only gain 10% over 24".

I would think that a gas spring would be impractical over this distance.

A counterweight in a PVC tube might be the best.

How about copying the counterweight from a garage door. I've seen several types, not just the big spring.

[High Seas]

BUNGIE! Its good for other than Jumping! Increase its effective length by using a couple of blocks (pulleys) and weave the cord up and down in between the linear rails/drive rod/shaft. As the effective length is longer, you'd get more uniform spring tension until you get it stretcccched to the limit. Would take some fiddling to get it all set and balanced - but the investment is not to great.
Jim

[HuFlungDung]

How about a large helium filled balloon tied to it You can have it floating above the roof of your garage if need be The neighbours would be wondering why it is going up and down all the time.

[aghobby]

Maybe this will help you, some of the big machine that i repair have air cylinder to counter balance the weight of the z axis. The air pressure on the cylinder is adjust to get a "0" weight to the axis ballscrew drive. So the weight of the big 8 motor tools mounted like a revolver seems to be invisible to the drive system.

You only have to done somes basic arithmetics to get the proper cylinder size and the correct air pressure for your application, air cylinder are cheap and easy to find at ebay.

Hope this help,

Alex

[biomed_eng]

Most if not all gas cylinders are NOT constant force.

You need to get a "constant force" spring. This is in my opinion the best solution...it has near zero mass unlike a mass counterbalance.

Obviously you can search http://search.yahoo.com/search?p=%22...t&cop=mss&tab=

[Urgundiz]

georgebarr,

I think the best way of having a ligth Z axis is to not putting weigth on it

Not a joke, I mean do not put a router but put a flex shaft to a router hanging out of the axis. If you use an enclosure with noise dampening stuff (do not forget force air to the motor to avoid overheat) maybe you got two benefits..

only my 2c (of euro )

/U

[georgebarr]

Urgundiz,
Where can I find a good heavy duty fex shaft? The Dremel type fex shaft is not strong enough.

Thanks,

[georgebarr]

I found some "constant force" springs at https://sdp-si.com/eStore/Group.ASP?GroupID=65
Are these the correct ones to use?

[Urgundiz]

Originally posted by georgebarr Urgundiz, Where can I find a good heavy duty fex shaft? The Dremel type fex shaft is not strong enough. Thanks,

Well, i think a standard drill flex shaft could be useful. I know the wolfcraft ones:

http://www.wolfcraft.de/en/produkte/...astera41a.html

- 8 and 6mm chuck
- 2 or 3 ball bearings

Sure the 8mm chuck, 3 ball bearings, heavy duty will have a chance.

If I remember well, prices moves between 30 and 45 Euro, so it will be about 35 to 50 US$

Questions:
- Drill flex shafts will support the rpm of a router motor?
- These are for heavy duty, but what about lateral forces in routing?

hope it helps..
/U

[Urgundiz]

You can see USA catalog showing same item at

http://www.wolfcraft.com/pdf/drillout.pdf

/U