Centroid Community CNC Support Forum

rk9268vc wrote: ↑Thu Sep 16, 2021 11:24 pm Just slap it in-between the motor and the ballscrew

Here is picture

Thanks for all your replies. Very helpful information. Just after posting, I stumbled upon another forum where someone converted the same PM-833TV and used the gas strut show below. He reported excellent results. I really like the idea of unloading the Z-axis as it improves the Z-axis movement and solves the braking problem.

Sean, you mentioned using what sounds like an adjustable pneumatic cylinder. Do you have a source or any information on these. I like the idea of being able to adjust the force.

Thanks.... Richard

Gas struts loose their charge over time and have variable force throughout the stroke since the volume of nitrogen is fixed. Air cylinders are a better choice since the pressure/force remains constant over the full length of the stroke and can be adjusted to exactly match the weight of the moving parts.

Air cylinders can be purchased at any pneumatic supply house or online from Amazon and eBay. While a little more expensive, I like McMaster because of the depth and breadth of products they carry as well as they also have 3D models of most items.

https://www.mcmaster.com/air-cylinders/

Along with the air cylinder, you will also need a pressure regulator. Be sure to get one that is a "relieving" type. This means that if the downstream pressure increases above the setpoint, the regulator will bleed off the excess.

https://www.mcmaster.com/air-pressure-regulators/

You probably also want a filter and oiler in the system as well. You can buy these separately and plumb them in, or you can buy a combined unit called, appropriately, a FRL (Filter/Regulator/Lubricator).

https://www.mcmaster.com/frls/

RJS100 wrote: ↑Sun Sep 19, 2021 11:52 pm Thanks for all your replies. Very helpful information. Just after posting, I stumbled upon another forum where someone converted the same PM-833TV and used the gas strut show below. He reported excellent results. I really like the idea of unloading the Z-axis as it improves the Z-axis movement and solves the braking problem.

Sean, you mentioned using what sounds like an adjustable pneumatic cylinder. Do you have a source or any information on these. I like the idea of being able to adjust the force.

Thanks.... Richard

Exactly as Tom posted. McMaster is a great place for many items you might need but they can also be found just about anywhere online. My machine does have a relieving type regulator for the Z axis and a pressure gauge. The incoming airline to the machine also goes through a FRL on the front of the machine. I can monitor the pressure coming in and keep an eye out on the lubricating oil level in the FRL. For the record, the machine came this way from the factory.

Thanks... I will have to research these a bit. I like the ability to adjust the pressure.

Regards... Richard

Most of the "adjustable" gas springs can only reduce the spring force by letting the pressurised gas out - a one time event.

I was pretty sure I'd seen some with Schraeder valve couplings on them so you could recharge them but I can't see anything like that when I look. The gas seems to be nitrogen, so they probably don't recommend recharging with compressed air, hence perhaps why they aren't sold.

Perhaps someone has spotted an air spring with a gas coupling? The alternative which I have seen is to make your own air spring (length of plastic pipe with piston and seal) and use your compressed air supply with an adjustable regulator.

The only problem I see here is that the cost of these options is more than just buying a bigger stepper or servo.

You'd also need a bigger power supply and driver for the larger stepper/servo. You'd then need to tune your drives for the larger upward force, probably sacrificing top speed and acceleration in exchange.

rk9268vc wrote: ↑Tue Sep 21, 2021 11:18 pm The only problem I see here is that the cost of these options is more than just buying a bigger stepper or servo.

oh if it were only that simple.