anti galling tips..on ss to ss press fit

[JAYDEE23]

I am looking for some help. Here are the conditions.

I start with sa-182 (sometimes 479) 304ss or 316ss bar.
-drill and ream a 1/4" hole through.
-insert precision ground rod into hole with 0.0000" to 0.0001" total clearance. requires moderate hammer hits to insert.
-finish machine surface perpendicular to rod/hole
-remove pin in direction away from machined surface with slide hammer

When rod is removed I am looking to achieve a burr free very sharp hole edge in addition to no galling on the way in or out. Ive used 304 to 304 and graphite powder and had slight to moderate gallin on the i.d. of the hole and rod.

-Suggestion for rod material that i can use to both avoid galling under this condition yet maintain like machinability so i have a burr free..very sharp hole left when i pull the rod out.

-lubrication suggestion for this condition?

I appreciate any help..thank you..

 

[JAYDEE23]

HERE IS A SKETCH

 

[EdStainless]

The pin should not be SS. Use a heat treated steel pin with a lube. The greater the hardness difference between the materials the better your chances of avoiding galling.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[unclesyd]

When we make such a hole we will push a plug type broach through the hole then insert a teardrop plug hole into the hole with a small tip sticking out and the either Blanchard Grind the piece or use a conventional lap to take the tip off. The final step is to diamond lap the part for edge retention. Our requirements are a little tighter than yours and with no edge visible at 100X.
On some of the tougher alloys we will plate the broach with a flash coat of Copper, a mono- molecular layer for lubrication.

Another approach we will use at times is use a diamond or helical hone on the bore. Either one will true the hole and not leave a burr.

http://www.helicallap.com/

http://www.engis.com/products/honing/

 

[JAYDEE23]

Edstainless...first thank you for your response....

-non stainless hard material is an easy fix to avoid galling but then my concern is the metal machining differently disturbing the overal sharpness of the hole edge once the pin is pulled.

Unclesyd
-I am not sure i understand your teardrop approach. Could you explain this further? As for surface finish i am just looking for 8 microinch or so.

Looking for rod / lube combo to achieve no galling vs. like machinability balance.

 

[unclesyd]

The type broach I was referring to is a tear drop shape ground on the end of an undersize push pin. It only makes line contact such as a ball would make. This is essentially Ballizing on a stick. The plug is straight with a rounded nose and has "0" clearance with the bore for a snug fit. This holds the shape of bore while grinding or abrasive lapping. It is removed prior to diamond lapping. Diamond lapping will will remove any edge left by any previous operation. As posted we inspect for an edge at 100X.
We use the flash Copper on the broach as a lubricant, 2-3 broaching operations without and 40-50 holes with the Copper plate.
I still think the Helical lap will give you your hole.

 

[bruv]

Have you tried Molykote D-321R? It comes in a spray can, is easily applied, and we use it quite a lot in applications where there is potential for galling.

 

[JAYDEE23]

no i have not...ive used graphite powder so far...

 

[JAYDEE23]

I am thinking of ordering some 303 ss rod...sulfur help improve galling characteristics...machinability should be plenty similar to 304 to leave me with a quality hole...perhaps some moly lube....??

 

[MikeMet]

Try ion nitriding the pins. The nitrided surface will typically not gall with on stainless steel. I have used this to prevent galling in different application where stainless on stainless is required. Do a batch with as many pins as they can fit in the oven to reduce costs.

 

[btrueblood]

FWIW, silver plating is what Swagelok uses on the mating threads of their stainless parts.

 

[tripleZ]

Swagelok will also coat some of their smaller packing bolts in the valve assemblies with a material called Everlube. It's a teflon based coating. Coating is always focused on the threaded areas, I believe to help with the prevalence of galling in 316ss.

 

[CcanDo]

Heat Part-Chill Part ??

 

[israelkk]

What kind of reamer will give you 0.0000" to 0.0001" total clearance. It seams unrealistic. What are the pin dimensions and tolerances?

 

[JAYDEE23]

I am not a machinist so i depend on my guys and they inform me the +/- 0.0001 is achieveable...the checks with 0.0001 step pins seem to confirm this.

pin is +0/-0.0002

 

[israelkk]

I do not understand. If the pin is +0/-0.0002" then even if the reamed hole is +/-0.00000 then the interference will be +0/-0.0002"? Therefore, how you claim +0/-0.0001"?

How deep is the reamed hole?