RAMS
Member
A gunsmith tells me MIM parts can't be polished. Can that be true?
Polishing MIM parts
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scooter123
Member
I don't buy it. While I'm not certain that they are MIM, I suspect that the thumb piece for the cylinder release on the new stainless revolvers are MIM. It's a small part that could easily be produced with the MIM process at what would be a fairly easy cost savings.
I've polished these parts on my 610 and 620 and the result is they look chrome plated. However, I did find that the surface would take on a "marbled" look when I tried to refine the finish by simply using a polishing compound. What I did to get a good and level high polish was to wet sand from 800-1500 grit, then further refining with a Diamond Lapping Paste, and finally do the final polish with a high grade polishing compound. Point is, IMO it can be polished, however the approach used has to follow the traditional steps for polishing without any shortcuts.
I'll also note that I wouldn't think about or suggest polishing internal MIM parts. I don't know the hardness or material specifics for the rebound slides in my MIM revolvers but do know they are very hard. In addition, fully polishing a "working" surface is NOT good practice, lubricant's don't "wet out" well on fully polished surfaces and you actually want some scratches to retain lubricants. I've been designing and building industrial machinery for a lot of years and if you have gibs and ways that have become fully polished by use they will then start to gall rather quickly unless you change to a lubricant with a high degree of "wetting" agents and that's only a short term "crutch". The best long term fix is to grind or "shape" the running surfaces to provide those essential scratches to retain and spread your lube.
I've polished these parts on my 610 and 620 and the result is they look chrome plated. However, I did find that the surface would take on a "marbled" look when I tried to refine the finish by simply using a polishing compound. What I did to get a good and level high polish was to wet sand from 800-1500 grit, then further refining with a Diamond Lapping Paste, and finally do the final polish with a high grade polishing compound. Point is, IMO it can be polished, however the approach used has to follow the traditional steps for polishing without any shortcuts.
I'll also note that I wouldn't think about or suggest polishing internal MIM parts. I don't know the hardness or material specifics for the rebound slides in my MIM revolvers but do know they are very hard. In addition, fully polishing a "working" surface is NOT good practice, lubricant's don't "wet out" well on fully polished surfaces and you actually want some scratches to retain lubricants. I've been designing and building industrial machinery for a lot of years and if you have gibs and ways that have become fully polished by use they will then start to gall rather quickly unless you change to a lubricant with a high degree of "wetting" agents and that's only a short term "crutch". The best long term fix is to grind or "shape" the running surfaces to provide those essential scratches to retain and spread your lube.
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From my experience doing trigger jobs on newer S&W revolvers most of the MIM parts have a pretty good to excellent finish except for some occasional mold parting lines or molding flash. It is easily polished off with a stone with no detrimental effects that I have noticed.
diamonback68
US Veteran
Look at the hammer and trigger guys, it's dark gray metal. If you polish it, it will still just be somewhat shiny dark gray metal. What's to gain? Am I missing the point on what parts you want to polish?
They can be polished, but since they're not as dense as forged parts they won't polish AS WELL, or with the same result.
This is assuming you're talking about engagement surfaces on hammers & triggers, not trying to make shiny jewelry out of a MIM part.
Denis
This is assuming you're talking about engagement surfaces on hammers & triggers, not trying to make shiny jewelry out of a MIM part.
Denis
"This is assuming you're talking about engagement surfaces on hammers & triggers, not trying to make shiny jewelry out of a MIM part."
You assume correctly, Denis. I am asking about engagement surfaces that come into play for action/trigger jobs.
Thanks, guys. All of you in one way or another have confirmed what the gunsmith told me.
"I've been designing and building industrial machinery for a lot of years and if you have gibs and ways that have become fully polished by use they will then start to gall rather quickly..."
scooter, you must mean a type of steel other than pre-MIM traditional steel for internal engagement surfaces, right?
You assume correctly, Denis. I am asking about engagement surfaces that come into play for action/trigger jobs.
Thanks, guys. All of you in one way or another have confirmed what the gunsmith told me.
"I've been designing and building industrial machinery for a lot of years and if you have gibs and ways that have become fully polished by use they will then start to gall rather quickly..."
scooter, you must mean a type of steel other than pre-MIM traditional steel for internal engagement surfaces, right?
I've been told by the Performance Center that the MIMs don't polish up as well, and by my local S&W certified longtime gunsmith that the results are not the same.
As far as polishing engagement surfaces goes, honing & stoning have been done on those in Smiths & other guns for decades.
It's part of what constitutes a true "action job", as opposed to merely swapping into lighter springs.
Keep 'em at least very lightly oiled & there should be no problems with galling, especially in non-stainless surfaces.
Deliberately introducing lube-retaining scratches on mated working surfaces is a new one on me.
It was never brought up at the brief S&W armorer's school I went to years ago.
Denis
As far as polishing engagement surfaces goes, honing & stoning have been done on those in Smiths & other guns for decades.
It's part of what constitutes a true "action job", as opposed to merely swapping into lighter springs.
Keep 'em at least very lightly oiled & there should be no problems with galling, especially in non-stainless surfaces.
Deliberately introducing lube-retaining scratches on mated working surfaces is a new one on me.
It was never brought up at the brief S&W armorer's school I went to years ago.
Denis
I have a 66-5 3.25" and the hammer and trigger were both jeweled, like a rifle bolt, and have a mirror-bright polish. Were these items not MIM?
No idea.
Look at the back of the trigger, is it hollow?
Polishing, to the naked eye, is not a good way to judge the degree of polish involved.
Under magnification the surface that looks bright & shiny to your eyeball will look markedly less smooth.
Denis
Look at the back of the trigger, is it hollow?
Polishing, to the naked eye, is not a good way to judge the degree of polish involved.
Under magnification the surface that looks bright & shiny to your eyeball will look markedly less smooth.
Denis
Yes, back of trigger is 'hollow.' The sides of both trigger/hammer are 'burled' as in jeweling.
(Brown tint is reflection)
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I figured such.
The ability to be polished is what I questioned re: other posts re: same.
(Looks like someone did a nice job anyway
)
Bullseye Smith
Member
Look at this hammer, it is MIM and you can polish it as just as bright as the gun if you want.
Bullseye Smith
Member
Plus on the trigger job, There has been alot of bull hockey said about it, the forged parts only has a .004 -.006 thickest of hardness (case harden) where the MIM is just as hard in the center as the out side is. I can take MIM and polish the contact points to where you can see yourself in them and have no problems with it. Light oil is all I ever use except on a new guns first range vist I use grease (White) to help the surfaces out some. I did polish one of my guns to a mirrow finish and put over 5000 rounds down the tube with no sign of wear to the hammer or trigger, some of the mirrow finish was a little dull but not bad at all. That gun is in the safe for retirement 
.
.Again- VISUAL brightness is not the indicator. Not talking about polishing to match a frame, or to look at your gorgeous face in.
Yes, you can polish MIM parts BRIGHTLY. You can polish through the external colors.
What your eye sees isn't the same as what the mating surfaces feel though.
MIMs are more microscopically porous than forged parts.
MIMs don't polish down as slick as forged parts, despite what your eyes see.
You spend an equal amount of time & effort in polishing the engagement surfaces on a MIM and a forged part, stick them under magnification, and you'll see a difference.
Whether you feel it in the trigger pull or not is another matter.
Denis
Yes, you can polish MIM parts BRIGHTLY. You can polish through the external colors.
What your eye sees isn't the same as what the mating surfaces feel though.
MIMs are more microscopically porous than forged parts.
MIMs don't polish down as slick as forged parts, despite what your eyes see.
You spend an equal amount of time & effort in polishing the engagement surfaces on a MIM and a forged part, stick them under magnification, and you'll see a difference.
Whether you feel it in the trigger pull or not is another matter.
Denis
Bullseye Smith
Member
Again- VISUAL brightness is not the indicator. Not talking about polishing to match a frame, or to look at your gorgeous face in.
Yes, you can polish MIM parts BRIGHTLY. You can polish through the external colors.
What your eye sees isn't the same as what the mating surfaces feel though.
MIMs are more microscopically porous than forged parts.
MIMs don't polish down as slick as forged parts, despite what your eyes see.
You spend an equal amount of time & effort in polishing the engagement surfaces on a MIM and a forged part, stick them under magnification, and you'll see a difference.
Whether you feel it in the trigger pull or not is another matter.
Denis
I only have my eye and feel along with the end results, a MIM system can give a smother and slicker action than you can get with the forged any day of the week. For a action job the MIM is "KING", Looks and collection the forged system is "KING". Two different systems to pick from to your likeness.
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