Insert for rough turning hard chrome?

[Terry Keeley]

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.

I think you're right. I forgot I had a sample that got chromed in a place I could test my KD240 PCD insert and a little came off in a powdery form but the edge was quickly destroyed. Forces were quit high as well and I'd be worried about ruining my parts if they spun in the fixture etc.

Here's my setup (home shop alert), it lacks the rigidity of a real ID grinder but I'm getting good results, just painfully slow.

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.

I never tried a silicone carbide wheel, got any specs for what's used on chrome?

 

[Big Buck]

We alway's ground hard chrome as it would easily chip from the original surface. I think we used a plnk Cincinaiti milicron 60 grit wheel and used quite a bit of wheel pressure to rough in the dia. close to size & alway's using coolant to keep part cool , the wheel from loading up and breathing chrome dust.

 

[michiganbuck]

Likely not an issue here but always worth a try is the direction of the wheel and the part.
With so much difference between the wheel RPM and the part RPM going one way or the other is acceptable and the interaction is not as important as what direction leads to increased rigidity.
Grinding pressure is often much more than people think..and the harder the material the more pressure is needed. One might have to exert 50 pounds of pressure to make proper abrasive pressure to have the abrasive particles penetrate the part
So the machine, wheel and wheel arbor, part, and wheel and part holding device, all need to withstand that pressure.
Grinding hard chrome I would like the biggest diameter wheel arbor that would fit the part bore and mounted so it could not shift on the mount, sometimes good grinding can only be accomplished with a point-mounted wheel with a 1/2" + shank.
Pushing on the wheel, part, and machine areas with a 3-finger push can tell how stout a set-up is in various directions... that is about 20-25 pounds of pressure in most cases.

 

[Terry Keeley]

Likely not an issue here but always worth a try is the direction of the wheel and the part.
With so much difference between the wheel RPM and the part RPM going one way or the other is acceptable and the interaction is not as important as what direction leads to increased rigidity.
Grinding pressure is often much more than people think..and the harder the material the more pressure is needed. One might have to exert 50 pounds of pressure to make proper abrasive pressure to have the abrasive particles penetrate the part
So the machine, wheel and wheel arbor, part, and wheel and part holding device, all need to withstand that pressure.
Grinding hard chrome I would like the biggest diameter wheel arbor that would fit the part bore and mounted so ut could not shift on the mount, sometimes good grinding can only be accomplished with a point-mounted wheel with a 1/2" + shank.

Yup, my equipment is lacking for sure with the dinky 1/4" arbor wheels.

The Ukrainians/Russians are big into model engines, here's a clip grinding a liner on a real machine:

 

[triumph406]

This is how the late Wayne Trvin chromed his cylinders , on page 2 he mentions that the cylinders were finished on the hone

Chroming

www.nclra.org

 

[Terry Keeley]

This is how the late Wayne Trvin chromed his cylinders , on page 2 he mentions that the cylinders were finished on the hone

Chroming

www.nclra.org

Kinda getting off topic a bit but thanks for that, I did my own plating 25 years ago and it was a lot easier to grind, my setup was no where as good as it is now. I think the plate I got is much harder.

That fixture with it's "thiefs" is a common setup in the model engine world, attached is the one the late Jim Allen designed, he worked with Nelson quite a bit.

My commercial plater just uses lead tape (he let me do the masking & fixturing), I did get some extra buildup around the ports and some "dingleberries" at the top and bottom tho.

 

[LexD]

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.

That's a new one on me, I have never had the "swarf" load up the wheel and stop it from cutting.

 

[EmGo]

Yup, my equipment is lacking for sure with the dinky 1/4" arbor wheels.

Would be the same situation with Heald or Bryant, wheel size is determined by the hole size, no way around it ... I do keep meaning to draw up a new quill for you though, that could be improved a little.

That's a new one on me, I have never had the "swarf" load up the wheel and stop it from cutting.

Swarf is the normal term for grinding chips, at least in north america. People will say the wheel is 'glazed' when it fills up with swarf and can't cut anymore, too. Pretty common.

 

[LexD]

I realise that, but what I am saying is that I have never had chrome swarf build up on a grinding wheel, it doesn't do that, hard chrome does however dull the grit to a point that it will not cut and needs to be dressed to expose fresh grit.

 

[eKretz]

Have a look in Terry's thread here, in particular post #104

ID grinding hard chrome.

Is there a point where grinding it round, then lapping for size and finish makes sense? It's got a very slight taper.

www.practicalmachinist.com

and you'll see a very loaded wheel from grinding chrome. And yeah most of the time the wheel dulls and gets a redress long before it's heavily loaded. Or at least should be. It's also somewhat dependent on the wheel structure and the bond type. If running vitrified aluminum oxide wheels and a fairly soft bond, the wheel probably wouldn't have a very large chance of loading much. The grit would pull out and self clean the wheel before it ever became any kind of problem. I'm from a job shop background. Sometimes we had to "run what we brung." Wasn't always optimal.

 

[Terry Keeley]

Would be the same situation with Heald or Bryant, wheel size is determined by the hole size, no way around it ... I do keep meaning to draw up a new quill for you though, that could be improved a little.



Swarf is the normal term for grinding chips, at least in north america. People will say the wheel is 'glazed' when it fills up with swarf and can't cut anymore, too. Pretty common.

I think the 13mm diameter long nose on my spindle plus the fact the bearings in the front of it are only 3/8" x 1/4" aren't helping. They have other spindles that attach to my air motor but they are all close to the ID of my sleeves, I might be able to turn down the OD of one slightly to give a little more room.

I have the AMH-301 but maybe the 303, 311 or the 601 would be better:

0.897" (22.8mm) Diameter - ARTCO - American Rotary Tools Company

NSK MA series spindles are designed to operate smoothly at high speeds for long hours of continuous cutting and grinding when coupled with an appropriately adjusted air line kit (filter/regulator/micro-mist oiler). We highly recommend using the manufactur

www.artcotools.com

edit: found a 303 reasonable, incoming...

 

[BT Fabrication]

for hard chrome, ceramic inserts would cut it, about 0.050" per pass depth max. If wondering check out the guy over on youtube Cutting edge engineering, he turns down hard chrome on hydraulic cylinders daily it seems like.

 

[john.k]

Hydraulic cylinder do not have hardchrome...the rods are hardchromed ,and Ive done lots of rods.........cut with a bandsaw ,alls needed is to grind a groove around to remove the chrome on the sawcut.........the chrome grinds easily with a SiC angle grinder wheel.......at some stage about 20 years ago ,hexavalent Cr salts were banned ,and the industry had to do with chlorides and sulfates ,whereas previouly hardchrome was done with Chromic acid ...which use to bubble foul brown gases like a witches cauldron..........a friend of mine used to do hardchrome in a trailer in his backyard at home........he died of some horrible bone cancer ,so I dont recommend it.

 

[john.k]

Its also possible to get a sensitization to chrome,which can kill,and doctors dont know anything about it,its so rare......Something as common as a leather /chrome tanned watchband can sensitize to chrome.

 

[Terry Keeley]

for hard chrome, ceramic inserts would cut it, about 0.050" per pass depth max. If wondering check out the guy over on youtube Cutting edge engineering, he turns down hard chrome on hydraulic cylinders daily it seems like.

Ceramic insert? Got a link? I looked through his vids and couldn't find anything.

https://www.youtube.com/@CuttingEdgeEngineering/videos

edit: Iscar says their PCBN can be used for heavy interrupted cuts in materials to 70Rc but ceramic is no good:

https://www.iscar.com/Catalogs/publication-2018/CBN_2018.pdf

 

[michiganbuck]

QT: Op;(Ceramic insert? Got a link?)
Back in the 70 and 80s NTK was making what I thought were the best ceramic inserts.. they were good for hardened steel with light cuts and high surface speed, high RPM turning..a Japanese outfit then now world wide.

NTK Cuttingtools - Home

Sam Beto was that USA rep. Likely he is now retired.

NTK Cuttingtools - Products

and PDC

NTK Cuttingtools - PCD

 

[eKretz]

I ran across a wheel that seems to be made just for hard chrome, not sure if they have it in a size amenable to you. Noritake CXE. Don't see any on google, you might have to contact a distributor. It may just be the same as a 5SG too, not sure.

I'll post a pdf in your grinding thread.

 

[Terry Keeley]

Found this old post, seems to suggest (as does Iscar) that high CBN content inserts will work, another guys says SECO TH1000 carbide also is good:

turning chrome plating

i regularly turn chrome plating on 2 inch up to 3.5 inch diameter shafts. the plating thickness is about .070" per side. i use a sumitomo diamond tipped insert right now. it is working right now, however it takes a while. just wondering if anyone regularly turns chrome plating and what kind...

www.practicalmachinist.com

 

[LexD]

Have a look in Terry's thread here, in particular post #104

ID grinding hard chrome.

Is there a point where grinding it round, then lapping for size and finish makes sense? It's got a very slight taper.

www.practicalmachinist.com

and you'll see a very loaded wheel from grinding chrome. And yeah most of the time the wheel dulls and gets a redress long before it's heavily loaded. Or at least should be. It's also somewhat dependent on the wheel structure and the bond type. If running vitrified aluminum oxide wheels and a fairly soft bond, the wheel probably wouldn't have a very large chance of loading much. The grit would pull out and self clean the wheel before it ever became any kind of problem. I'm from a job shop background. Sometimes we had to "run what we brung." Wasn't always optimal.

Yes, it does look very badly loaded, I wonder what type of wheel it is because I have never had that problem grinding hard chrome.

 

[john.k]

IMHO,swarf loaded grit equals no or insufficient coolant .....I have never done internal without flood coolant ,because the small wheel will heat and load very quickly......a lot of people say ,too much splash around ...these are the ones with problems.