Material selection for ACME "nut" in a small scissor jack

[dubc4]

Hi all,

I'm working on a small scissor jack lifting device, similar to a motorcycle/ATV jack. It uses this threaded rod:

https://www.mcmaster.com/93410a615

The "follower nut" that will travel up and down the rod to lift/lower the scissor is currently designed as a one piece construction component. It is a turned component with the ACME female thread through the center (see attached picture... picture only shows the rod partially threaded, ignore that... needed to eliminate some detail in the model for my slow computer). As you can see it also supports the wheels that would bear a portion of the weight from the jack.

Based on the rod material, what would be a suitable material for this female threaded component? The whole thing would be hand powered, so not a high speed application. The scissor jack itself is only going to lift ~500lbs at most so nothing on the extreme end of load bearing either. I'm just concerned that choosing the wrong material could lead to the screw/nut binding together? What is the best practice for choosing a mating material for these moving screw/nut combinations?

Any guidance would be appreciated.

Thank you,

 

[DAVIDSTECKER]

It looks like the mating lead screw nuts from McMaster-Carr are made from 932 Bearing Bronze.
It say's there are used in hand powered devices.

 

[SnTMan]

Other materials per McMaster: "Cast iron nuts have good machinability and high strength. 360 brass nuts have excellent machinability and good corrosion resistance. 932 bearing bronze and 673 bronze nuts are wear resistant. They have good machinability and fair corrosion resistance. PET plastic nuts are lightweight and corrosion resistant."

What'd be wrong with plain old carbon steel?

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[3DDave]

Since the rod-nut is in bending you need to figure out what the applied load is. This will be many times the load that is being lifted due to the leverage. Most any steel and some lubricant will be a decent start to prevent galling, which is often a problem if both parts are the same stainless steel alloy at the same material condition/hardness.

 

[dubc4]

Thank you for the replies. I also looked at the materials of the lead screws and nuts available on McMaster Carr... bronze seemed to be the obvious choice for a lead screw nut for motion, but since the part is somewhat large and a single piece (and multipurpose) I figured bronze would increase cost.

I was hoping someone would suggest carbon steel but was worried about galling... 1018 and 1045 seem to be much less hard than the alloy steel listed for that rod... so maybe galling won't be an issue with some grease.

 

[cdill21]

Galling is going to be much less likely with carbon steel than with stainless. Since this screw is in the open, be sure the environment it is in is clean, otherwise that grease is going to gather all kinds of dust and dirt.

If bronze is strong enough, I would use that. Find the right sized nut and make it an insert into your blue part.

https://www.mcmaster.com/bronze-nuts.

If your concern is cost, and not time and effort, you can find these much cheaper than on McMaster.

Good Luck!
Chris

 

[Jboggs]

Do not use carbon steel, for two reasons. One - galling WILL be an issue. Two - corrosion potential. That's why almost all the lifting jacks I have seen, even extremely heavy duty ones, use bronze or some similar material for the nut. Check Nook Industries, Joyce-Dayton, Duff-Norton. They have made these things for decades, so they know what they're doing.

 

[DAVIDSTECKER]

I'd probably go with a 80-55-06 ductile iron to run against the steel screw.
It's high in Graphite.