Thread loss on linear slide

[wildcat]

I hope that someone can provide some advice on the following. I have a slide that rides in aluminum chanel. The slide is moved with a small moter attached to a threaded rod which then is threaded through an aluminum plate (1/2 in. thick). Please see the attached image as it will make this a lot clearer. The aluminum is 6061T6 and the rod is commonly available 1/4-20 threaded rod (ReadyBolt). The threaded rod is not lubricated. The plate is threaded only on one side for 1/2in with a guide hole in the over side. This setup has been working well for approximately a month and has had a total linear movement of ~2520 ft. (the rod is approximately 24in. long). The plate moves at a rate of 1in./40sec with this setup. Today I found that the thread in the plate has been stripped out with fine aluminum powder around. There is very little resistance to the plate moving when not on the rod so I don't think that the plate bound up. What was done wrong here? Lubrication would have helped but failured seems to have occured very quickly. Should aluminum and steel not be used together like this? How would you have changed this? The plate only has to support a couple of pounds. Thank you.

[Ken_Shea]

Wildcat,
While steel and aluminum do not make for good partners this rapid failure is likely due to the fact that the threaded is quite rough, actually grinding the aluminum, creating that aluminum residue which in turn speeds up the wear process.

If you have to use that combination polish the threaded rod smooth, lubricate with dry lubricant and wipe frequently after use. or better yet fabricate screw nut from delrin.

Ken

[2muchstuff]

Aluminum is much softer than steel and that threaded rod ate right into the aluminum plate. If you must use a threaded rod, run a die several times back and forth along the rod. This will help remove some of the rough edges. Anytime you have 2 surfaces running against each other, they should be lubricated.

[erase42]

an easy easy harware store fix for this would be to drill out your threaded plate just large enough to hammer in a threaded rod connector (long nut) then tap a hole in from the top or bottom for a set screw to hold the nut in place. then as soon as possible id make a derlin nut to fit in that hole to replace the steel nut. not pretty, but only about 25 cents.

[wildcat]

Thank you for the replies and I would like to fully understand them as this is the first apparatus like this I have built.

Would lubrication prevented failure or only slightly delayed it?

While impractical due to weight, if steel plate would have been used would failure been prevented?

If Delrin is used is lubrication required? Is Delrin more resistant to abrasion than aluminum?

Could something other threaded rod been used? I considered ACME screw but one this long was costly. The 1/4 threaded rod has the disadvantage of being very wobbly over this length.

Thanks again for all the help.

[erase42]

in my opinion, lubrication would delay, not prevent this failure. yes with a steel plate you would still be fine, but some sort of lube would still be needed. thats why i mention to put a steel nut in there. the weight wouldnt really change, but the durability will improve. i think with durlin you would want to go with some sort of graphite or a light white grease maybe. and yes durlin is many many times more durable than aluminum when it comes to friction wear. Id say that its the best possible way to go, its light, durable and very easy to tap, drill or machine and its pretty cheap too. ive seen chunks of it for sale on ebay from time to time.

[Ken_Shea]

Another point that may offer better life for the assembly is to get stainless threaded rod or un-plated rod since it will be much smoother then the usually zinc plated rod found in hardware stores.

As alluded to, there is no need to replace the plate jut add a screw nut to the back side of it, this will require offsetting the threaded rod, threaded rod end support and motor.

Ken

[Geof]

A few posts have mentioned tapping a steel plate or using a steel nut. If you do this be paranoid about very good lubrication; steel running continuously on steel can gall and seize. In these types of application it is much better to use two different materials such as brass or Delrin and steel. Aluminum is a different material so you would expect it would work but unfortunately it can gall up with steel, or just about any other metal, because it is not strong the galled section just tears away until you get what you observed.