ID grinding hard chrome.

[eKretz]

Good addendums, guys. And Terry: yes, get the lathe RPM up around 400 and try it out. That will at least get you to a little less than half the wheel width travel per revolution of the part. If you see improvement with that it will be a good indication that you're headed in the right direction. 400 RPM will put you near the high end of work speed at a little over 100FPM - that's getting up there. You really ought to reconsider using the carriage travel if that stroke speed won't go any slower IMO.

For all the suggestions to slow the workpiece RPM: he can't slow the RPM of the part down any further unless he can slow that traverse rate WAY down - which he says he can't do. That suggestion is a non-starter unless he switches to carriage traverse. If that is the lowest possible stroke speed and he doesn't want to switch to carriage traverse he needs to speed the spindle UP. I would say ideally to something like 800 RPM - at 45 ipm traverse that would get him right around ¼ wheel width (actually .056") per rev of the work, but that will be pretty excessive in terms of work speed. Might try 800 RPM rotating with the wheel instead of against.

 

[Terry Keeley]

Do you want a super-polished finish or are the grinding grooves helpful for oil retention, like honing does ?

Looking for a super-polish, thinking the 90 grit AO dry will work but we'll see.

I think the grinder spindle bearings are still suspect. I'd be shocked if the hobby store bearings are really up to the task, from both an intrinsic accuracy and clearance standpoint. They could work, but it would take some luck and swapping/playing with clearances to get right.

I say this because I think I'm hearing high-frequency vibrations that I'm putting down to tiny wheel hops on the work, which don't match the frequency of work rotation, but do wheel rotation.

Might be out of my mind (no comments please), but that's my take. Wheel imbalance could be playing a role too, doing the cup of water on the spindle trick might be worthwhile.

The stock ones were nothing special, I doubt I'd find a "duplex matched pair" in the tiny 1/4 x 3/8. The I/D, O/D shims they use are 0.003 difference in thickness and take up the end play nice. I have some lead tape I might wrap the spindle nose with to help dampen any vibs, my toolmaker buddy mentioned that.

You might give a mandrel-mounted diamond wheel a try.
Diamond Wheels Mandrel Mounted 1/8 3/16 1/4 5/16 3/8 1/2 5/8 3/4 1 Inch Diameter, Internal Grinding

I see a 3/4 dia wheel with a 1/4 shank here... but I don't see the price.

RE:[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.]

As ridged a spindle as you can fudge up is best.

That looks like a re-seller for Diagrind, as mentioned I shud have one of their wheels this week.

 

[Terry Keeley]

Good addendums, guys. And Terry: yes, get the lathe RPM up around 400 and try it out. That will at least get you to a little less than half the wheel width travel per revolution of the part. If you see improvement with that it will be a good indication that you're headed in the right direction. 400 RPM will put you near the high end of work speed at a little over 100FPM - that's getting up there. You really ought to reconsider using the carriage travel if that stroke speed won't go any slower IMO.

Thanks, will try upping the part rpm. I can't use the carriage since I'm grinding a taper, the grinder unit is offset in that cradle.

 

[michiganbuck]

Good to try everything. If upping the spindle RPM does not help, you might tr making slower.
Seems that you have only two variables, part RPM and wheel selection.

 

[eKretz]

Buck, he really can't slow the lathe RPM down. He's already cutting stripes with the full width of the wheel. If he slows it down any further he'll just be cutting coarser "threads." Right now with what he's running that's akin to cross feeding ¾" with a ½" wide wheel on the surface grinder. Slowing the lathe down would be like increasing the cross feed on the surface grinder even further... That will be a definite move in the wrong direction IMO.

Terry, you might need to figure out a way to add the taper at the end... As I recall it's very slight, isn't it? You're in a tough spot if that's as slow as that stroke will go. Maybe you could increase the pressure to the air cylinder to decrease the stuttering and be able to drop the stroke speed a little more? I'd be thinking about that a little. It's a shame they didn't make that part electric.

 

[EmGo]

Buck, he really can't slow the lathe RPM down. He's already cutting stripes with the full width of the wheel.

Here is possibly what's happening ... as you say, wheel is cutting stripes. My first thought is "go to a wider wheel" but that's just a band-aid too. (I'd go wider anyhow, don't like skinny wheels but with that traverse speed it won't help. It's still too much material removal for the setup.)

If he's cutting figure eights in the bore, then the infeed is too high. That would seem to be the case from the sparks on the out-stroke. There shouldn't be any sparks on the backstroke. We're grinding grooves, then infeeding again while there's still too much material in the bore. Now the pressure goes way up, like infeeding too much, and it takes a bite.

Quick and dirty thing to try is, let the wheel traverse a lot more before adding infeed. A lot more. Make it spark out first, then add another tenth.

That'd be like, on a cylindrical, if you're stuck with a ridiculously high traverse rate then you'd just take a fuzz off on each pass, and don't infeed again until it quits sparking.

 

[eKretz]

Yep, and dwelling while that happens is another band-aid. Seems like there are a lot of band-aids on this one; it may soon be dying the death of 1,000 cuts...

It will be difficult to keep that wheel cutting straight doing that though. Cutting the stripe is one thing, at least that's full width. Coming back over it in the other direction is going to be a lot of irregular interrupted cut and uneven wheel wear. Then back the other way and only hitting on part of the former wheelpath, etc. Not so bad when you have a large wheel circumference to part circumference ratio. Not so good when it's the other way around.

 

[EmGo]

It will be difficult to keep that wheel cutting straight doing that though. Cutting the stripe is one thing, at least that's full width. Coming back over it in the other direction is going to be a lot of irregular interrupted cut and uneven wheel wear. Then back the other way and only hitting on part of the former wheelpath, etc. Not so bad when you have a large wheel circumference to part circumference ratio. Not so good when it's the other way around.

Given what he has to work with tho ... short of putting the part into an actual id grinder or converting the stroking mechanism to hydraulic, there's not very many choices. There are generating grinders that take a very light skim cut fast ... I would give it a try just to see.

It's also peculiar that TK said it grinds fine dry. That shouldn't be but sometimes you just have to go with reality ...

 

[eKretz]

Yep. Except it's the dead opposite with the CBN wheel! Sometimes when the band-aids are flying, you never know what will happen. He's probably just going to have to make some tweaks one at a time and fly by the seat of his pants.

 

[Terry Keeley]

Thanks for the input guys, much appreciated.

I tried slowing the wheel way down, speeding it up to about 400 rpm and even running it in the same direction as the wheel, made no difference.

There's something in my process that's making the grinding inconsistent, one time I can get a good result, the next the wheel is grabbing and digging in.

I was able to get a nice finish with the 90 grit white wheel (dry) but when I went to try the 60 grit that worked before it again grabbed.

I'm wondering if my dressing procedure might be at fault. I bolt an arm that holds the dresser in place but it's straight into the wheel (not 15*), I'm going to try a new cluster diamond (meant to be at 0*), if that doesn't work I'll break down and make a new arm.

Oh, and it should work with coolant. I think I either have the wrong stuff or it's mixed too rich causing the wheel to skate.

I'll get it, I always do, lol.

 

[eKretz]

I would steer clear of the cluster diamond with your lack of rigidity. You really need to zip past the wheel pretty good with one of those. They work better on a rigid machine in my experience. And if you don't feed them past the wheel fast enough it will get REALLY closed up. You also can't rotate them to keep them sharp.

This is one of those things that would probably be solved pretty quick in person but is a pain remotely. Lots of machining troubleshooting is that way. It's hard to see, feel or hear (just plain sense) as well through a short video.

Even at 400 RPM your traverse is pretty high, you're still close to half wheel width per rev. Getting to 800 would fix that but that's a pretty outrageous work speed at that point. Out of curiosity, is there a difference in hardness between the 60 and 90 grit wheels? Did you infeed a tenth or two and let it dwell and stroke back and forth until sparkout before trying any more infeed like EG suggested?

I'd like to see a picture of the wheel after some time grinding to see how loaded up it is, then another right after one of those "big bang" grabs to see if it's cleared out. I still think that is what sounds like is happening.

 

[michiganbuck]

Agree the dressing might be poor. A single point at a 15 to 30 angle might be better...and turning the diamond occasionally to a fresh facet.

Anyway you might clamp on a DC motor with an arm to run your travel slower.

 

[Terry Keeley]

Just an update as I'm back to this project.

I made a bunch of changes to tighten up my setup (new cast iron base for grinder mount, tightened lathe spindle bearings and grinder bearings, lapped the grinder mount dovetails) and it's working much, much better.

I'm using a 100 grit CBN resin bond wheel from https://diagrind.com/ to rough with soluble oil at 8:1 as recommended. Also using a "grit dresser" followed with a fine dressing stick to dress and open up the wheel, it cuts pretty good at first but seems to dull quickly (1/2 thou infeed and it wants a dressing).

Would a wheel type dresser work better? What about some moly? Or is that just used on a Vitrified wheel?

I want to end up with a mirror finish so think I'm going to use a 90 grit white AO wheel for the last thou or so, or maybe a 60 grit green Norton "Quantum" wheel. Are these better with synthetic grinding fluid that water soluble oil? I'm using Rustlic G25J and WS5050.

[video]

 

[Milland]

Might be worth a review of some of these links. I use diamond as the grit, but other materials are suggested:

can you grind chrome with a diamond wheel? - Google Search

 

[Terry Keeley]

Might be worth a review of some of these links. I use diamond as the grit, but other materials are suggested:

can you grind chrome with a diamond wheel? - Google Search

You grind hard chrome with diamond?

 

[Milland]

You grind hard chrome with diamond?

No, but I was checking to see what the 'Net wisdom was on the matter, and I found a lot of related comments under that search term, so thought I'd post it.

My understanding is that diamond shouldn't be used for materials that are "carbon thirsty", like irons and steels, but I'm not sure if chrome behaves the same. Since CBN isn't working out ideally, if diamond held up it might be worth the test. Heck, that might have already been tried deeper in the thread, but I'm not reading it all again to check...

 

[michiganbuck]

QT Terry The Op:
(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.

The first thing I would consider would be to improvise the largest wheel arbor to accommodate the high pressure it takes for grinding hard material.
Consider how hard one must push a HSS tool bit to a bench grinder and HSS may be 63 to 68, with chrome perhaps 68 -72.
*Perhaps a special holder need be made for a more robust wheel arbor. Photos of the wheel spindle nose might allow the PM guys to suggest modifications. *A sketch of the wheel holding assembly/holding device including the attachment to the spindle nose might be better.

Wheel deflection causes the wheel to not be able to penetrate the material at first with pushing the wheel or part away. then when enough pressure is made it finally can cut/grind. Often an undetectable chatter occurs at this event to cause additional wheel destruction.

It looks like a nice setup with having the coolant splah box.
I would wiggle-check the machine spindle and the wheel head spindle
for near-zero deflection with a hard one-hand push (that is about 50 lbs). Push on the wheel with 3 fingers (that is about 21 lbs). If the wheel spindle travel has any wiggle I might/would fab-up a pusher device to take out the wiggle. If the wheel has deflection only a more robust arbor will help.

Then I would begin chasing wheels, likely by calling Radac for their input on wheel choices starting with white and pink AO, try a SC wheel ..and after those evaluations even try a diamond wheel.
Wheel price and wheel wear is no consideration because you look for parts per dollar considering time and everything.

OT
How is the lake Ice around Toronto?...I will be off on a fishing trip for likely a week or more so will not be able to reply until I return. You might private message a sketch through PM...or post it in this thread.
Buck

 

[michiganbuck]

On some occasions, a wheel spindle, or a part spindle will have more rigidity in one direction than in the other direction. One might lift pry, and down pry with the same force to find any variance. then the wheel direction is chosen that gives the most righty. Going opposite the part direction with the wheel direction is the most common, but that is not always the best choice.

 

[Terry Keeley]

Thanks Buck for taking the time to reply, I know you have a lot of experience grinding hard materials.

As mentioned I went around the whole setup with a tenths indicator and tightened everything up, it's as rigid as a glorified tool post grinder can be, lol. I'm actually getting decent results now but it's slow going, I rough it in with a 100 grit resin bond CBN wheel plus soluble oil then finish with a white AO 90 grit wheel taking the last few tenths dry, getting a good finish that way. I'm also having some luck with a green Norton 60 grit "Quantum" wheel.



My questions at this point are really about dressing the CBN wheels. For my resin bond wheel I'm using a Norton "grit dresser" (fine diamonds embedded in a matrix) followed by a 220 grit white stick to open it up. Would I get a better dress with a wheel dresser? Stick of Moly?

I also have a Vitrified CBN wheel and there's little if no info around about how to dress/true it, any ideas?

Lastly, the CBN works best with the soluble oil coolant but the jury's out on whether the AO wheels like the oil or synthetic grinding fluid. Any recommendations there?

Looks like there's about 10" on Lake Simcoe an hour north:

https://www.tiktok.com/video/7207602258568072454

Here's some crazy Canucks for ya, have fun!

 

[Milland]

Is there a point where grinding it round, then lapping for size and finish makes sense?