ID grinding hard chrome.

[Terry Keeley]

I'm trying to grind some 1" ID brass sleeves, about 2" long that are chrome plated.

The chrome varies quite a bit in thickness (couple thou) so I'm looking for a wheel to rough them in fairly quickly. So far I've tried AO 19A46-K5VG (46 grit) and 32A60-KVBE (60 grit) Norton wheels but they cut only about 1/2 thou and want a re-dress.

Did some searching and see guys recommending Norton Norton SGB 60 J, also CBN. Is diamond any good for chrome? Any other recommendations?

The only small Norton SGB I found were these:

13 x 13 mm Norton SGB 60 J VS3 Grinding Wheel

Ideally I'd like a straight type 1 wheel to fit my arbor, 3/4 x 1/4 x 1/4 hole would be perfect, like these:

Type B1A1 Tools (CBN on the Periphery) | Store

Was thinking to use a 90 grit white AO wheel for finishing.

I'm just using an NSK grinder on a lathe so not the most rigid setup:

 

[gbent]

Try narrowing up the cutting length of the wheel, a lot.

 

[Terry Keeley]

Tried that, thanks.

I learned my plater is using a Fluoride process that gives super hard chrome (up to 70Rc) and all my AO wheels are having a tough time. I had a light blue ceramic mounted point that cut well so I'm going to p/u a Norton 5SG46-JVS wheel to cut up.

 

[Milland]

I think it would be worthwhile to try a CBN pin. Maybe 1/2" OD x 1/4" wide? 70Rc could be right in CBN's wheelhouse, but check with Norton or someone on use with chrome.

 

[Terry Keeley]

I think it would be worthwhile to try a CBN pin. Maybe 1/2" OD x 1/4" wide? 70Rc could be right in CBN's wheelhouse, but check with Norton or someone on use with chrome.

Ya, as mentioned I found these:

Type B1A1 Tools (CBN on the Periphery) | Store

My spindle will only take 1/8" shank mounted points or it has a 5mm arbor that I've made 1/4" flanges to fit.

If these ceramic alumina wheels work that'd be great, easy to dress and I can get a bunch of them out of an 8" wheel!

 

[EmGo]

I learned my plater is using a Fluoride process that gives super hard chrome (up to 70Rc) and all my AO wheels are having a tough time.

Hardness was never a problem in a Heald ... I bet part of your problem is that the wheelhead is too slow, it makes the wheel act really soft.. How fast does that thing spin ?

Borazon worked well for me/us at certain jobs where wheel wear would have been a problem, but it wasn't chrome. Pink wheels worked okay on chrome but again, that was larger holes and also faster wheel speed (I bet, since don't know yours but ours was 35,000 I think. And bigger holes. 1" is gonna be a bitch, probably want over 50,000 rpm.)

 

[Terry Keeley]

Hardness was never a problem in a Heald ... I bet part of your problem is that the wheelhead is too slow, it makes the wheel act really soft.. How fast does that thing spin ?

Borazon worked well for me/us at certain jobs where wheel wear would have been a problem, but it wasn't chrome. Pink wheels worked okay on chrome but again, that was larger holes and also faster wheel speed (I bet, since don't know yours but ours was 35,000 I think. And bigger holes. 1" is gonna be a bitch, probably want over 50,000 rpm.)

This NSK airmotor spins at 30K but my setup isn't anywhere near as rigid as a real ID grinder. It is pretty accurate tho, with the carriage and cross slide locked down I can infeed 1/2 a tenth with that little cradle setup. With a little frigging around I can get the fixture running dead nuts true.

 

[EmGo]

This NSK airmotor spins at 30K but my setup isn't anywhere near as rigid as a real ID grinder.

Should be okay on rigid, you're not taking pounds of material an hour but the low speed makes the wheel act soft, which sounds like a part of your problem. That, and it's chrome. Ugh

Just have to fight it until you get a combination that will work.

One thing about your setup tho, I'd always flood the hole with coolant, which is going to be nasty with your setup. Not sure what you can do about that but grinding really likes coolant.

 

[eKretz]

So far I've heard that the wheels "want a re-dress" and "have a tough time" but no specifics. Without those it's hard to say what is actually going on. Are you losing wheel material and getting taper? is the wheel loading up and burning the part? And yeah, coolant is really helpful any time you can use it. Lots of benefits including keeping the wheel clean.

 

[Terry Keeley]

Man, I'm getting near my wits end with this.

No matter what I do it seems the wheel doesn't want to cut well at all, then it grabs and digs in.

I'm only feeding a tenth or less at a time, I let it stroke 4 or 5 times until it sounds like it's not grinding much anymore before I feed again. I'm using Rustlick Ultracut Pro CF at 10%, I even tried some full strength, that didn't work at all.

For wheels I've tried: 19A46-K5VG, 32A60-KVBE, a white 90 grit wheel from Dumore, a 60 grit pink ID wheel, an 5SG46-JVS ceramic cut from a surface grinding wheel, I even tried a SiC 46 grit (didn't work at all) and a 170 grit CBN that may be OK for finishing as it did seem to cut a bit.

I got a new single point Norton diamond dresser and am aggressively dressing the wheels, they feel very sharp.

I tried thinning the width down to 1/8" or so and thinking it might be catching in the interrupted cut I rounded the corners of the wheel.

I tightened the gib right up on the grinder mount, that just helped prevent the wheel pulling into the part somewhat. As mentioned the carriage and cross slide on the lathe are locked down.

Here's a pic of the part and a short video of what's happening:

What the heck am I doing wrong???

 

[eKretz]

For one thing I'd slow that traverse/stroke rate WAY down. That looks like it's going way too fast. Try to set that so your wheel is moving something like an absolute max of 1/4 of its width per revolution of the part. For another, how fast are you spinning the part? I'd probably start that at about 40-50 FPM and see how it goes from there.

 

[EmGo]

I'm kinda with Ed here on both those items except maybe not quite that slow on traverse. But your workhead speed is making the chrome harder, and it's already hard enough. Also, not real enamoured with the way I see sparks on the reverse ? How are you infeeding ? In a heald, you normally infeed at the beginning of the in stroke, no feed on the return. That way the front edge of the wheel takes all the wear, and it kind of gives a spring pass on the way back out.

It does seem like you are grinding tho, from your description it was just rubbing the poor thing to death. You my still need a different wheel but slow everything (except wheel speed) down and give it another try. And cut your infeed, I think. Normally in just carburized steel I'd be taking a tenth per side per pass in a much beefier setup.

A coarser, more open grit might help too.

You'll get there, eventually. Looks better than your description sounded, to be honest.

 

[eKretz]

I was being a little conservative since the sparks seem to be showing that his setup is lacking rigidity - very inconsistent. Sometimes with the sparking and sometimes not. Kinda' weird. Unless you're onto something and he is infeeding on the return?

 

[Milland]

To me, part of the problem may be arc of engagement - I think the wheel shown in the video is too large, so too much surface area in contact. With the nose diameter of the grinder it looks like the wheel size is required unless you abandon it and go with a 1/2" or so pin, so the grinder itself never enters.

Is the grinder spindle stiff enough to handle further distance to the bearings? You'll be helped by the lower engagement force. And yes, try a coarser CBN grit for roughing.

I'd also bet the lathe spindle is "relatively" loose and with bearing errors becoming a source of random light/heavy engagement.

Frankly, I'd look to see if I could make my own hone (or buy if the right geometry is affordable) with strip CBN grit, maaaybe using cut diamond lapping sheets if CBN solid lengths are too expensive. For experimenting you could use the current grinder as the stroke mechanism and just use the lathe spindle for rotation.

[Not a grinding expert, just my views on things]

 

[triumph406]

Here's a pic of the part and a short video of what's happening:

What engine is that for?

I presume your grinding taper into the bore.

There's a few websites where people discuss making model engines, The ones who make ABC and AAC liners would likly know the answer to your wheel dilemma.

 

[Mechanola]

Time to try three-stones honing. Way better rigidity, load evenly distributed

 

[Milland]

Here's an option for cheap experimenting: SUNNEN K12 600G CBN HONING STONE (K12NM005)1195904 NEW OLD STOCK | eBay

Similar may be available from Ebay: https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=CBN+honing+stone&_sacat=0

Sunnen info: https://www.sunnen.com/userfiles/resources/sunnen-catalog-precisionhoningsupplies.pdf

If you search for diamond lapping film (or sheet), be certain that the results shown are for diamond grit, many will be for Alox or Si carbide.

 

[EmGo]

Stone size is fine, it's normal to run 2/3 to 3/4 of the bore size with the wheel, no difference in contact area due to wheel size anyhow, it's all line contact. Lathe bearings are fine too, dedicated i.d. grinders are just simple bearing setups like a lathe, belt drive so maybe a tiny bit smoother but not a world-stopper and he wants a taper so honing is out ...

What I don't lke is the way it seems to be consistently grinding on the outstroke ? but no description of how we're feeding, Mr Keeley. And while I'm thinking of it, you can try dressing faster. A coarser dress will give you a bit more open wheel.

Everything looks reasonably good but seems like your grains aren't sharp. Process is okay, just needs development.

 

[eKretz]

It will be a little tricky to get the taper he's looking for with a hone. The wheel is a little on the larger side, but he mentioned narrowing it which would reduce surface area in contact. I did hear the spindle slowing down quite a bit though. Wouldn't hurt to use a bit smaller diameter wheel. 60%-80% of bore size is generally recommended range IIRC. Don't want to be too small or you run into other issues.

 

[triumph406]

See post #124 of this thread

.90 cu in, 30,000 RPM, 7.2 HP custom built nitro engine

from the post

I make the stones, which are mounted on tapered mandrels of different lengths, from scrape surface grinding wheels. For example, the ID of the engine's cylinder is 1.125". I drill a 1/4" hole & cut with a band saw, 1/2" or 3/4" wide, 100 grit aluminum oxide wheels which are dressed round after mounting. The size of the dressed wheels are approximately 1.000" to 1.100

I use a sulfur based grinding oil, Sunnen #MB 30-5, which has been used to previously grind chrome.Never use new grinding oil to finish grind hard industrial chrome.

No dressing of the stone will be necessary to finish many pieces

from post #132

No special tools are required to make small size grinding wheels. Any high speed steel drill will make many holes in any type of aluminum oxide wheel. Regrind the cutting flutes when they become to dull. Of course the drill will eventually become garbage. The wheels are rough cut using a course tooth band saw blade. Again, many pieces can be cut & the band saw blade will become garbage. You can make or purchase heavy paper pieces to glue, with rubber cement, on to both sides of the wheels. Clamp the stones to the mandrels shaft with machined steel washers, but never directly on the stone's surface!