Insert for rough turning hard chrome?

[Terry Keeley]

Search turned up empty handed.

Is there an insert (PCD, CBN etc.) that will cut hard chrome plating?

Not looking for a good finish as the parts will be finish ground to size, just want to cut the roughing process down.

Am I dreaming?

 

[john.k]

I know hardchrome can be cut by HSS,as T 99 chrome bores can be rechambered to 30-06 and the muzzles can be counterbored with an ordinary drillbit..........Id suggest you experiment a bit ...the deposit is quite brittle,you may find it fractures down to the underlying steel.

 

[michiganbuck]

I wonder if EDM grinding would work. I used an EDM surface grinder that made good time and close sizes. It used a metallic diamond wheel and salt-based coolant. The wheels held up for a very long time and the surface finish was exceptional.
I never used an EDM boring machine but it looks like they go from 3k to 10k $USD. .
Perhaps the roughing and finishing might be done with one EDM operation.

 

[EmGo]

Am I dreaming?

I think you better just quit while you're ahead

 

[Terry Keeley]

I think you better just quit while you're ahead

Took me about 10 hrs. yesterday to grind out 0.005", it's painful.

 

[michiganbuck]

QT: (Took me about 10 hrs. yesterday to grind out 0.005", it's painful.)
Seems like EDM or a Diamond wheel would beat that.

Are the parts stout enough to solidly resist tooling/grinding pressure? Are the wheel arbor, tool, and machine stout enough?
Would the parts be better-served with a press or light press into or on to a heavy-weight holder of sorts?
Is the wheel arbor, or tool holder as stout as it can be?

For example, I used to clump a wad of childer's modeling clay on a part to resist forces..and that made a world of difference.

 

[EmGo]

Took me about 10 hrs. yesterday to grind out 0.005", it's painful.

On a side or diameter ? I'd usually leave .010" total on about a 2" bore, usually cleaned up okay in about 3 or 4 but with carburizing you never know what it's going to do so not worth the risk ... but by now you should know when your plating cleans and it should be a lot less than that on such a tiny bore ? Then give it an extra half and away ya go ?

If it doesn't clean can always add a bit more ?

That does seem extreme on time. But you got it working now, just need to tune it in

 

[Terry Keeley]

QT: (Took me about 10 hrs. yesterday to grind out 0.005", it's painful.)
Seems like EDM or a Diamond wheel would beat that.

I don't have access to an EDM but do have a diamond wheel coming, although everyone recommends CBN for chrome.

I tried resin bond and metal bond CBN wheels but the Norton 5SG "Quantum" was the best.

My toolmaker buddy thought maybe PCD might work, he used Kennametal KD240 grade inserts to cut bearing races.

 

[EmGo]

My toolmaker buddy thought maybe PCD might work, he used Kennametal KD240 grade inserts to cut bearing races.

Your situation is kind of unique tho, that your holes are so small and tapered The idea trying to run a boring bar through that size hole and take out chrome, just makes me cringe ... IF honing worked, could you run the bores up to a half away from size, then finish grind for the taper ?

If edm works on chrome, that might actually be a good way to go, at least to get close.

 

[Terry Keeley]

On a side or diameter ? I'd usually leave .010" total on about a 2" bore, usually cleaned up okay in about 3 or 4 but with carburizing you never know what it's going to do so not worth the risk ... but by now you should know when your plating cleans and it should be a lot less than that on such a tiny bore ? Then give it an extra half and away ya go ?

If it doesn't clean can always add a bit more ?

That does seem extreme on time. But you got it working now, just need to tune it in

Ya, it's from my other thread, 1" bore.

I asked for about 0.006"/side and got 8, good thing as the last one just cleaned up, the plating ends up thinner at the top and bottom, I even had a few rejects as they didn't plate well at all there.

Trust me I've tried everything (except a diamond wheel).

Your situation is kind of unique tho, that your holes are so small and tapered The idea trying to run a boring bar through that size hole and take out chrome, just makes me cringe ... IF honing worked, could you run the bores up to a half away from size, then finish grind for the taper ?

If edm works on chrome, that might actually be a good way to go, at least to get close.

Honing might work to rough them out, never thought of that. I guess if the straight bore wasn't left exactly concentric to the O/D the grinder would fix that. Hmm...

 

[eKretz]

I forget if I or anyone else already said this in the other thread, but did you ever try one of the seeded gel wheels? Those work pretty good for chrome. Other than that I would expect a good open structure CBN wheel to do the best. That open structure is important. Also very frequent dressing - probably multiple times per part with those itty bitty wheels. One final dress just before finishing, etc.

Edit: just noticed you mentioned 5SG - doh!

And these should not be taking anywhere near 10 hours. You need to find whatever it is that's killing your process and fix it.

 

[triumph406]

Ya, it's from my other thread, 1" bore.

I asked for about 0.006"/side and got 8, good thing as the last one just cleaned up, the plating ends up thinner at the top and bottom, I even had a few rejects as they didn't plate well at all there.

Trust me I've tried everything (except a diamond wheel).



Honing might work to rough them out, never thought of that. I guess if the straight bore wasn't left exactly concentric to the O/D the grinder would fix that. Hmm...

Honing works ok on chrome, that's how Rothwell and nelson finish their cylinders (including taper)

The only downside is with the thin walls of the cylinder (assuming it's an ABC cylinder) your not going to be able to apply a lot of pressure on the stone. Way quicker then 10 hours.

Sunnen 1660 hones can be had cheaply, mandrels and stones aren't expensive new, and can be had cheaply NOS off of ebay.

 

[Terry Keeley]

I forget if I or anyone else already said this in the other thread, but did you ever try one of the seeded gel wheels? Those work pretty good for chrome. Other than that I would expect a good open structure CBN wheel to do the best. That open structure is important. Also very frequent dressing - probably multiple times per part with those itty bitty wheels. One final dress just before finishing, etc.

Edit: just noticed you mentioned 5SG - doh!

And these should not be taking anywhere near 10 hours. You need to find whatever it is that's killing your process and fix it.

I noticed under a loupe the resin bond CBN wheel looked like the "concentration" of grit was fairly low, maybe 25% of the surface, whereas the metal bond wheel looked like maybe 75%, is that what you mean by "open structure"? The metal bond wheel didn't work, just screeched and didn't cut at all. The resin bond wheel was better but not as good as the 5SG ceramic aluminum.

Honing works ok on chrome, that's how Rothwell and nelson finish their cylinders (including taper)

The only downside is with the this walls of the cylinder (assuming it's an ABC cylinder) your not going to be able to apply a lot of pressure on the stone. Way quicker then 10 hours.

Sunnen 1660 hones can be had cheaply, mandrels and stones aren't expensive new, and can be had cheaply NOS off of ebay.

Ya, if I was doing hundreds I'd look into that, or more likely a real ID grinder. Guys using a Sunnen hone to finish a tapered liner need tight control on the chroming process so usually do it in house. As I understand it the taper is put in the brass liner then only a thou or two of chrome can be honed out before the taper starts to straighten out.

 

[triumph406]

Ya, if I was doing hundreds I'd look into that, or more likely a real ID grinder. Guys using a Sunnen hone to finish a tapered liner need tight control on the chroming process so usually do it in house. As I understand it the taper is put in the brass liner then only a thou or two of chrome can be honed out before the taper starts to straighten out.

My understanding is that they started with a straight chromed cylinder and progressively honed more towards the bottom to create the taper. Rothwell aluded to the fact it took a lot of practice to get it right, and that Henry Nelson was the only one who honed the Nelson cylinders presumebly he as the only one who could do it reliably.

See page 2 penultimate post on page by Rothwell

Barton Model Flying Club :: View topic - Cylinder Chroming

Discussion forum covering all the control line types, F2A, F2B, F2C, F2D, F2E together with international contest calendar and photo galleries.

controlline.org.uk

K&B put on a thin layer of chrome, so presumebly they started with a cylinder with the taper either turned/ground prior to plating. And likely took just a couple of passes with the hone to clean up the chrome and obtain the cross hatched finish.

First post on page 3

Barton Model Flying Club :: View topic - Cylinder Chroming

Discussion forum covering all the control line types, F2A, F2B, F2C, F2D, F2E together with international contest calendar and photo galleries.

controlline.org.uk

In the top post the poster said the only person with the magic touch to hone the cylinders was a women. I heard the same thing from the guys who worked at COX. The women there were the best ones at honing taper into cylinders, especially for the Tee-Dee's

 

[john.k]

How are millions of hardchrome gunbarrels made.....I m sure they dont take 12 hrs to finish.........my experience is limited to Jap 7.7 hardcrome barrels,and the chrome is about 1mm-1.5mm thick ,(est )........certainly thicker than the depth of the rifling grooves .....so how as it done ........cant say the plating is only a few microns ,and therefore smooth ..........however ,I suspect your plating is very lumpy and bumpy,which possibly it should not be.

 

[LexD]

Am I dreaming?

The short answer is "yes, you are".
You sort of answered your own question when you mentioned a proper cylindrical grinder because your setup is not rigid enough to apply some cutting pressure on the wheel to get it working properly.

 

[eKretz]

I noticed under a loupe the resin bond CBN wheel looked like the "concentration" of grit was fairly low, maybe 25% of the surface, whereas the metal bond wheel looked like maybe 75%, is that what you mean by "open structure"? The metal bond wheel didn't work, just screeched and didn't cut at all. The resin bond wheel was better but not as good as the 5SG ceramic aluminum.

No, I mean more like a porous appearance to the wheel, lots of open space. So the chrome that gets ground away has somewhere to go besides loading up the wheel.

 

[LexD]

Hard chrome does not actually load up in the wheel, it comes off as a silvery/grey fine slurry, it does however dull the individual abrasive grains of the wheel until they are flat.

 

[john.k]

I dont see any indication of whether this is internal grinding,or external grinding.........I assumed internal from the quoted feed rates .(.0001" per hr)........if its external grinding,then all you need is a decent cylindrical grinder and a silicon carbide wheel ,,,,thats what I use on my Landis ,and can reduce a thick hardchrome plated deposit to the underlying steel in a few minutes,....in general ,the harder and more brittle a material the easier it is to grind to a nice finish and exact size.

 

[eKretz]

Hard chrome does not actually load up in the wheel, it comes off as a silvery/grey fine slurry, it does however dull the individual abrasive grains of the wheel until they are flat.

That powdery swarf also acts as a lubricant and keeps the wheel from cutting. And I have absolutely seen it load up a wheel before. It can still pack in and load up. Open structure helps keep things cooler too. If the heat isn't controlled in the grinding zone the likely result is cracking.