sliding part design for dirty environment

[cjccmc]

For sliding steel parts that need to have good resistance to jamming after being "dropped in the dirt" what magnitude of clearances are generally considered better, tighter (.001 -.003") or looser (.015-.020")?
My application would be similar to a rifle design where only so much can be done to shield out debris and "dirt" can be a variety of types and particle sizes. Shapes are pin-in-hole, T-slots, etc. approx .38".

 

[tbuelna]

cjccmc-

This is not an easy question to answer. On one hand, it's obvious that if debris entering the unsealed clearance space between moving parts and causing a jamming/binding condition is a concern, then you'll want to provide as much clearance as possible. On the other hand, with most moving parts there is a limit to how much clearance they can tolerate and still function properly.

The only thing I can suggest is to use seals, wipers, shields, covers, etc. whenever possible. If seals are not an option, then design your sliding interfaces to have localized points of contact with recessed areas between them where debris wiped away from the contact areas can accumulate and not create further damage. For example, if you have a shaft sliding axially in a bore, then machine an enlarged relief in the center portion of the bore and use a close tolerance fit locally at the ends of the bore. This will create a space where debris scraped off of the shaft surface during cycling can accumulate. It is also helpful to use a corrosion resistant coating on the part surfaces. Surface corrosion is typically more of a problem than abrasion damage from dust/debris.

Hope that helps.
Terry

 

[kingnero]

sliding parts of vises that are used in (manual/conventional) milling machines and such typically have about 1/10 of a mm "slop", so no metal shavings can get inbetween them.
that's near the range of your "tighter" tolerances.