Wheel dressing

ballen · May 27, 2019

Below is a photo of a 46 K AO grinding wheel on my cylindrical grinder. It's 25mm (1") wide.

I ground about 0.2mm (0.008") off the diameter of a good-sized piece of 4140 PH and after a light dress the wheel looks like this:

You can see that there's a lot of bits embedded in the wheel. My question: do I need to dress more off the wheel, to get rid of the steel that's embedded there? I have the impression that the finish I am getting now is not as good as normally, and am wondering if that's why.

Milland · May 27, 2019

Yes, dress it to clean abrasive.

michiganbuck · May 27, 2019

Loss of needed surface finish, increase amps usage, lowering of RPM, and part heating are/can be be good reason to dress.
But the loading/dulling is what causes self dresses of the wheel with break down. An abrasive edge gets loaded or dull and so is self released to expose another sharp grit. In production grinding the dress frequency is important to cost savings. In a production job one might try an H or I wheel to see if the number of dressing might go down.

Having an overhead dresser or a quick set-up a quick dress is little loss of time and wheel so is often a good solution a problem.

Still with that said QT Milland : [Yes, dress it to clean abrasive.]

A hand gauge can be used with closing ones eyes and feeling a finish with a ball point pen
https://www.mscdirect.com/product/details/06558167

This was common use at the big shop.
https://www.amazon.com/Taylor-Hobso...+profilometer&qid=1558959581&s=gateway&sr=8-6

ballen · May 28, 2019

Milland, Buck, thanks for the advice.

Milland -- OK. Unfortunately that will mean taking at least 1mm (0.040") off the radius. Normally I thought that dressing is only supposed to remove a very small amount, say 0.02mm (0.001"). Does that mean that the way I was grinding the piece was wrong because I clogged up the wheel like this?

Buck -- this is not production, I use my grinder only for one-offs. I don't have an overhead dresser but it's not hard to put the dresser on and take a pass. But to get the wheel clean is going to require removing a lot of depth. I think you are agreeing with what Milland wrote but am not 100% sure. Is that right?

I'll try the ball point pen trick. But it's easy enough to judge the surface finish by eye and I can compare it to other things I have ground.

Milland · May 28, 2019

How are you dressing the wheel? I'd think that a sharp diamond passing over the face should take only ~250/500µ to clean the surface - is your diamond now dull?

As to why the wheel clogged, I'd guess the PH steel isn't that hard (~35RC?). and just acted "soft" for your wheel composition. A wheel designed for softer materials might have fared better.

Were you grinding dry, or with coolant? From seeing your comment here: (Surface grinder coolant needed?) I'd think you are, could the concentration be low?.

Richard King · May 28, 2019

Ballen I spoke of this during the class. You can also call the brothers and ask them as they were super in their knowledge in grinding. I always say to check the diamond to be sure it is sharp and dress course to the wheel doesn't dull. Another mistake people make is the dress to little off and traverse back and forth to many times and the wheels gets burnished and loads up. Be sure to have more coolant then you think you need too, as it cools and cleans the wheel. I found these 2 manuals over on Keith Ruckers Vintage Machinery site. I also donate $100.00 a year for his site is free but he asks for donations. There are other re-prints you can search for too. The one is for a surface grinder, but dressing the wheel principal is the same. Note the 2nd paragraph on page 15 in the Do-All one. Norton - http://vintagemachinery.org/pubs/1834/6637.pdf Do-all -http://vintagemachinery.org/pubs/257/18421.pdf

michiganbuck · May 28, 2019

Being sure I am on a facet edge/corner I touch wheel and take about .003 off the wheel with down feeds of .0005 to .001 per cross pass pass for truing and cleaning a wheel. Yes more if needed to flatten the whole bottom.
(Yes for the odd wheel like a super fine very hard wheel I might only take .0002 per cross much going by the sound)
For resizing I take much more per pass then finish with a few .0005 to .001 depending on the wheel, with traveling not crazy fast but not slow-poke. I guess about like a lathe chuck at about 100 RPM. (some day I will clock that.)

Some times looks are deceiving and a smoother finish will/may look to not be smoother. It is the result of light refection with the rougher finish not reflecting light as well so seeming smoother, the smoother reflects so well that imperfection is better seen.

ballen · May 28, 2019

Milland, the dress (wet!) is with a conventional single point diamond. It's in a Studer stock holder fastened to the swivel table.

Normally I get a better finish so I don't think the diamond is responsible. The problem is that I did not go deep enough. But I'll try rotating my diamond or changing it for a sharper one.

You're right about the steel, it's typically 28-34 hardness. I'll see if I have a harder wheel the next time.

Yes, I'm grinding and dressing wet. The coolant is about 4% concentration which is "in the zone". I actually thought that lower was better provided that nothing rusts (it doesn't).

Richard, thanks for the references, I read a few pages about this. Yeah, it's probably what's wrong. I am not used to having a wheel clog like this but I think the steel was too soft for the wheel. I'll also make sure that the coolant is really running hard next time.

Buck, thanks for the tips.I'm good with dressing off 0.003", but think that I will need to take of 10 times that amount here. Do you think the problem is that the steel was too soft for the wheel? Or that the wheel was dull BEFORE I started grinding and that's the cause for all the embedded bit in the wheel?

tdmidget · May 28, 2019

The coolant may not be getting to the right place. It's messier, but it should directed with a fairly strong stream to the grinding interface, the place where the wheel meets the work.One of the major benefits of coolant is the flushing of chips and abrasive grains from the grinding interface. This improves finish and maximizes cooling. It also creates a lot of mist which is why it is not popular. Some production systems run as much as 1000 psi but this is a totally enclosed machine. Make sure that the stream is a wide as the wheel and directed at the point where the wheel contacts the work. If this doesn't help then a wheel change may be necessary.
In one off and repair type operations a good grinder hand can usually make most wheels work. As my apprenticeship instructor used to say, " If you spend more time changing wheels than grinding, you won't be there long".

ballen · Jun 3, 2019

TD, Buck, Richard, Milland,

Thanks a lot for the advice. I did almost everything that was suggested:

- Put in a brand-new really sharp diamond
- Dressed the wheel clean (had to remove 1.5mm of depth!)
- Turned up the coolant flow to max (I use a plastic nozzle that jets it right into the interface)

The one thing I did not do was change the wheel for a harder one, partly based on the remark that it should be possible to get decent results even with a non-ideal choice of grinding wheel.

One other thing that helped the finish was to slow down the left/right feed, apparently I had it too fast. I was happy with the result:

To the best of my ability to measure this is round and parallel to within a micron (40 millionths of an inch).

pianoman8t8 · Jun 6, 2019

Dress to clean-looking abrasive??? Sounds excessive... We run production cylindrical grinding here (CNC Studer grinders, and a couple other CNC's), and we don't dress back to clean abrasive. If we did, we'd be consuming wheels to no end. The discoloration you're seeing is normal. I wouldn't sweat it. An average part for us is removing .006" on diameter on roughly 4" diameter, on maybe 4-5 diameters ranging from 1" wide to 4" wide. In 4340 forged and induction hardened (in certain spots) steel. I'll dress the 20" dia, 2" wide OD wheel 2-3 times per part, taking about .0008" radial depth per dress at about .004ipr on the dress. And I have zero issues holding size and finish. Granted, we're not shooting for anything tighter than +/-0.00015" and 15uin finish.

CarbideBob · Jun 6, 2019

pianoman8t8 said:
Dress to clean-looking abrasive??? Sounds excessive...

Yeah that would be rather silly and won't help.
Dressing a wheel is about putting the correct structure into it for the job.
Sort of cutting threads into you wheel. This is why a lot of passes at zero depth makes for a loaded wheel. Not flatted or burnished grains, just too smooth and too many in contact at a given time.
It's all about unit grain pressure, too many grains in contact, not enough pressure on each and they won't cut. Too few, the wheel size goes away and the finish is rough.
One can move a wheel from hard to soft or vice-versa with differing dresses.
Bob

michiganbuck · Jun 7, 2019

ballen said:
TD, Buck, Richard, Milland,

Thanks a lot for the advice. I did almost everything that was suggested:

- Put in a brand-new really sharp diamond
- Dressed the wheel clean (had to remove 1.5mm of depth!)
- Turned up the coolant flow to max (I use a plastic nozzle that jets it right into the interface)

The one thing I did not do was change the wheel for a harder one, partly based on the remark that it should be possible to get decent results even with a non-ideal choice of grinding wheel.

One other thing that helped the finish was to slow down the left/right feed, apparently I had it too fast. I was happy with the result:

To the best of my ability to measure this is round and parallel to within a micron (40 millionths of an inch).

Nice work.. but you should/could have posted a photo of your set-up
Buck

ballen · Jun 7, 2019

Hi Buck,

michiganbuck said:
Nice work.. but you should/could have posted a photo of your set-up

Fair enough, I owe a lot more than that to you and the others here. But I didn't take any photos of that grinding.

However I do have a few photos from a couple of weeks back. Project here was modifying a MT5 center by (a) turning an extraction thread and (b) turning/grinding it to a short MT5 to fit the workstock. Here's a few shots from that. Similar setup to what I used on the tailstock quill.

This next shot shows how the center is running on the left side. Chucked in a 12mm collet is a short bit of steel rod that I've faced in a lathe and then drilled a center hole into. That plus a blob of moly grease worked well.

ballen · Jun 10, 2019

Here's a photo of the diamond dressers I have collected for my cylindrical grinder. If anyone would like to comment on which would be best suited for particular tasks, I would be interested to hear. I've identified them with letters to make it easy to identify any particular one.

Kees · Jun 11, 2019

I would prefer B, maybe also C . I think D an E are for a Diaform attachment. G and H for removing a lot of your stone, not for good grinding results.I never use that type.

But judging from your photos I think you already achieve pretty good results.Looks fine to me!

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