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advice need grinding Rockwell C 60 part

bll230

Hot Rolled
Joined
Jun 14, 2007
Location
Las Vegas
One last item, what should the feed be per pass? Most of the things I have done so far I have gone about .0002 per pass with about a .2 step over, because:

1. I don’t know what I am doing.
2. I haven’t used coolant
3. I try to keep abrasive grit from getting all over the place as my grinder is near my other machines, but at least pointed away.

Is there any issue with cuts that light? Other than time? Once I realized the existing washers were too thin I took 0.0001 off both sides of each with a 150 grit wheel to see how flat they were 80 years on. I thought the higher grit wheel was what I wanted for a smooth finish. It turned out they were still flat.

On the mirror surface, all the washers on the machines are mirror, but is it truly necessary, probably not. All the rotational speeds on a hobber are very low, 10s up to hundred or so for the hob spindle.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
No issue other than the time. That's similar to the way I usually grind softer steel or stuff not prone to movement but with flood coolant: .0005"-.001"ish downfeed and about ¼-⅓ wheel width cross step. Lighter downfeed is good for harder steel if you're going to try to keep the cross high. Without flood coolant I might be more inclined to use a deeper cut but a lot smaller cross step. Something more like a depth of .002" or even much more is easily possible if you drop your cross step down to something like .025" or .050" - the deeper the cut, the more you need to cut the cross step. Play with it on your sample pieces. Be very very careful with those fine grit wheels. One burn mark and your fresh ground part will no longer be flat. Your OEM parts may well have been lapped at the factory. Those old school quality machine makers didn't mess around.
 

rrrgcy

Aluminum
Joined
Jun 5, 2013
Location
South Florida
If paying big money I’d expect clean steel. Scale is from iron oxides, oxidation, de carbing of steel if it isn’t done in a vacuum. Eliminate the atmosphere inside it’s moot. Some seal their piece inside a ss wrap w an included piece of paper to “burn up” and tie down eliminate critical molecules in the atmosphere.

Below image of mickey mouse parallels is after I’ve hard scrubbed and wiped down. Sometimes the scale is a crusty heavier brown dark black, other times light. No idea why. I just grind through the fairly thin finish. That finish may have erratic deposits and can upset your piece’s level on your chuck so you may need to take off more than you intended to flatten your part acceptably on both sides. Gross parts who cares. Pickling chemically gets it off, method changed from sulfuric to hydrochloride acid around ‘64 in the industry, but the “liquor” should still use an inhibitor or else the converted ferric chloride will begin to attack the steel (the solution gets changed out for fresh and carry on). I don’t pickle but there are recipes online w just water (like 25% HCl) and you treat the part for 10 or 30 mins… or something… and don’t hover and breathe. Or like me I just just start w a greater dimension, scrub, wipe, then surface grind it off w more passes to clean steel.

1-FB5-BD3-D-735-D-41-ED-A498-FFE43-B03-AE19.jpg
 

Dan from Oakland

Titanium
Joined
Sep 15, 2005
Location
Oakland, CA
Make a few extra washers while your at it. the HT cost should be the same regardless. All the above is great advice, but you're way overthinking this, grind one side flat and then keep flipping until you get within .005 of size, lap the one side with 400 paper on a surface plate and then test fit your spindles, check your fit. The BC maintenance manual covers how to check clearance by measuring the axial movement of the spindle when its tight in the bearing. You will want to sneak up on your final thicknesses anyway. Good luck!
 

AD Design

Stainless
Joined
Jun 27, 2012
Location
Tennessee USA
Tribolgy International June 2006 comparing O-1 to D2 at same high hardness Rc 60 - “ For relatively low sliding speeds AISI O1 steel performs up to 12 times better than AISI D2 steel in adhesive wear. For higher sliding speeds, however, this order is reversed due to oxidation taking place on the surface of the AISI D2 steel. The wear rate of both tool steels in three-body and two-body abrasion wear is proportional to the applied load.”

-I'd like to accept the findings you've cited and don't wish to dispute what I haven't read but I cannot dismiss what my experience and eyes have seen. I have worked with O-1, A-2, and D-2 in stamping die applications for a few decades. All were hardened by me or by an outside HT. All were hardened above the 55-57 Rc range, many were for relatively low speed applications. The choice of material was usually decided by function of the component.

Simple wipe up/down forms could be considered sliding, lower contact pressure applications used for duty cycles that could be in the millions over the life of the component. D-2 was the preferred material because lower cost material like O-1 simply would not stand up to the abrasion and even A-2 showed greater wear patterns and shorter component life than D-2 in the same application. Those are my real world examples multiplied hundreds of times over 40 odd years.

The steels grouped for tooling purposes were created by people much smarter than I am to purposes clearly spelled out for decades in publications like Machinery's Handbook (among others). I have taken the information and recommendations on faith but I also have eyes that can see the results for comparison. Perhaps the HT of O-1 in my examples wasn't up to snuff but I've seen enough examples from different sources that a range of results is exhibited that is consistent with the published information.

I'd be willing to change my opinion that O-1 holds up to 12x better in abrasion resistance than D-2 but I'd have to see it happen. YMMV with YE.
 

bll230

Hot Rolled
Joined
Jun 14, 2007
Location
Las Vegas
Dan, I have the maintenance manual, that is what is guiding me in all this. My work spindle washer was 3 thousandth too thin, and the hob spindle washer 1 1/2 thousandth too thin.
 
Joined
Apr 14, 2018
Location
Airstrip One, Oceania
You're getting way too carried away. Barber-Colman hobbers are just so-so. It's just a washer, it'll be fine. The thing is never going to be supremely accurate even if you make a $100,000 washer, flat within millionths.
 

bll230

Hot Rolled
Joined
Jun 14, 2007
Location
Las Vegas
You are absolutely right. It is an 80 year old machine. Just trying to do the best I can, and, since I am new to surface grinding, with my 50 year old grinder, I want to learn as much as possible. I have learned a lot from this thread. With all the recommendations about coolant I have decided to get a Kool Mist.


Screen Shot 2022-03-08 at 10.25.40 AM.jpg
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Agree perfect is likely overkill, but if the Op is asking then this is a good practice exercise to make a perfect part.
Dead flat, to a close size, finding a heat treat source, and making a mirror finish.

Good talents to have under one's belt.
 
Joined
Apr 14, 2018
Location
Airstrip One, Oceania
Agree perfect is likely overkill, but if the Op is asking then this is a good practice exercise to make a perfect part.
I was deceived by the name of the site :D

In fact, if one wanted to improve the accuracy of this machine, reworking the bronze tapered bearings would probably help more. All this washer does is set the fit of those, doesn't help with their condition which, after many decades, tends to be less than wonderful.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
I was deceived by the name of the site :D

In fact, if one wanted to improve the accuracy of this machine, reworking the bronze tapered bearings would probably help more. All this washer does is set the fit of those, doesn't help with their condition which, after many decades, tends to be less than wonderful.

I guess both are important if it's going to be reconditioned. Maybe he is already doing both...
 

bll230

Hot Rolled
Joined
Jun 14, 2007
Location
Las Vegas
EG, I don't have the ability to rework the tapers, however,I made new washers to the proper thickness, then properly assembled and checked all the play with a new .0001 indicator, and there is essentially zero runout and play on either spindle. So now I want to get the proper hardened washers. I am absolutely open to suggestions to make my machine better. Email me. I was asking here how to grind the hardened washers, which I have never done. I have made and sold many custom gears out of delrin for RC helicopters, and the delrin was cut very accurately. Now I am working on a steel gear project and I found out that with the additional stresses of cutting steel my machine had an issue, which I found to be the washers. MB and others helped me with a CNC issue in another thread, and now here I have been offered a lot of grinding knowledge.

Always learning.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
One last item, what should the feed be per pass? Most of the things I have done so far I have gone about .0002 per pass with about a .2 step over, because:

1. I don’t know what I am doing.
2. I haven’t used coolant
3. I try to keep abrasive grit from getting all over the place as my grinder is near my other machines, but at least pointed away.

Is there any issue with cuts that light? Other than time? Once I realized the existing washers were too thin I took 0.0001 off both sides of each with a 150 grit wheel to see how flat they were 80 years on. I thought the higher grit wheel was what I wanted for a smooth finish. It turned out they were still flat.

On the mirror surface, all the washers on the machines are mirror, but is it truly necessary, probably not. All the rotational speeds on a hobber are very low, 10s up to hundred or so for the hob spindle.

Let us know how you faired with what wheels and process/if you added coolant/ if you made size and finish.

.0002 and .200 stepover is ok ..and so is .050 stepover..and so is .03 stepover it all depends on the part needs, and the amount of stock taking. the down feed amount...
The follow of the wheel(last area to go over) is often called the finisher area..often with close work one wants to protect the finsher area...and when the follow is lacking a fresh dress may be needed.

Another grinding method is to not step over cross but to full-wheel down-feed while you are off the part and go long travel with down feeds until you get to about +.007 ..and then dress, cool the part, and then finish with crossfeed and step over.

QT: [I try to keep abrasive grit from getting all over the place as my grinder is near my other machines, but at least pointed away.] You might add a catch box in the go direction of the sparks. Most sparks will land to be awept up with a brush.
 

Dan from Oakland

Titanium
Joined
Sep 15, 2005
Location
Oakland, CA
Hey guys- this is a great discussion on grinding and even better that everyone is sharing their knowledge. Half the fun is getting to the finish line in one piece, or nearly so. Carry on!!

bll230- remember on your work spindle, you are going to shift the worm wheel with the new spacer- ever so slightly but it will shift, make sure to blue the contact pattern to check this. The bigger machines require scraping the bore of the worm wheel to shift it if needed - not sure on the small machines. For this reason, always measure from the housing edge to the worm wheel rim before taking things apart, then you can just check the depth on reassembly and be good to go.
 

TheBigLebowski

Aluminum
Joined
Sep 9, 2018
These parts will probably have scale on them from heat treating. It's extremely hard and will load up the wheel quickly, which in turn puts lots of heat into the part.

Given that the parts are small, have excessive stock, are made from an easy to grind material, and you are grinding dry, take a deep cut (~0.002) / shallow stepover on the first pass to get underneath the scale. You get more roughing life out of the wheel between dresses, as only the leading edge breaks down.

If you have a manual grinder, you could really hammer the stock off of these especially since they have a great big hole in the middle of them. The fastest way would be to plunge most of it off as buck suggested. If you have 0.015" to come off and have a good manual grinder.

-shim part as needed so magnet does not deform it
-Plunge rough 0.005" and let cool
-Rough another 0.001" using crossfeed (feed opposite the leading edge of your wheel - it should not break down from plunging)
-flip and repeat for second side
-Redress wheel and let part cool completely
-perform minimum cleanup passes on both sides with little/no magnet
-lap 1 side on surface plate with fine sandpaper to achieve desired finish.
-finish grind to size (probably about ~0.001" more to come off the backside)

ADDED:
Not sure what type of wheel your using, but IMO the Norton 5SG line is the best of the best for doing this kind of work dry. A good sharp diamond is very important. When dressing the wheel you almost want to "thread" it with the diamond to a achieve a nice open dress.
 
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rrrgcy

Aluminum
Joined
Jun 5, 2013
Location
South Florida
Hi AD Design, I’d agree on abrasion resistance D2 better at same hardness. The referenced Tribology report said, “For relatively low sliding speeds AISI O1 steel performs up to 12 times better than AISI D2 steel in adhesive wear.” I’m new to that action. I looked up definitions and as Henry Miller in Tropic of Cancer says, “Well, Fck a duck” - and the heck if I understand a practical difference. D2 would make sense but hardness the same would it matter measurably?

Thrust washer in either material would work fine, and as the Italian tailors at school told me when they measured me for a uniform six ways from Sunday and the end result jacket sucked they’d claim, “Itta’ Fitta’ Fine!!!” You could hear that chorus from all of them as they worked the room to the displeasure of us students. When they should’ve been paying attention to the sartorial their minds were out probably thirsting for… ducks…

* Adhesive wear appears to involve a shear of adhesive bonding between molecules of all things, w transfer film formation where a particle is shed and transferred from one material to the other before it even becomes a wear particle. Wipe your ass after a meal of cream soup and it’s a soft smear on the still intact delicate toilet paper I guess. +1 for O-1 to resist wear

* No guess, Abrasive wear is w similar metals acting on one another having abrasive particles formed during the wear process due to work hardening, phase transformations and third body formation at the interface, with 2- body (only one material plays a role in abrasive process) or 3- body (both play a role, or coming from outside). Wipe your ass after eating hard grain and corn and it’s a hard crusty renegade rash on your now-torn toilet paper which also earlier had been exposed to some grinder abrasive grit, I guess. +1 for D2 to resist wear
 
Joined
Apr 14, 2018
Location
Airstrip One, Oceania
EG, I don't have the ability to rework the tapers, however,I made new washers to the proper thickness, then properly assembled and checked all the play with a new .0001 indicator, and there is essentially zero runout and play on either spindle. So now I want to get the proper hardened washers. I am absolutely open to suggestions to make my machine better.

I have made and sold many custom gears out of delrin for RC helicopters, and the delrin was cut very accurately. Now I am working on a steel gear project and I found out that with the additional stresses of cutting steel my machine had an issue, which I found to be the washers.
There are so many things driving both those spindles that taking all this effort with a couple of thrust washers is not going to get you where you want to be. Backlash in your wormwheel, then in the entire train leading to it. Backlash in the entire train leading to the hob spindle. I'd maybe tend to go too tight on the hob spindle, in a vain attempt to act as a brake on it. There were hobheads that had flywheels for this reason, too.

Simple stuff first, don't even try to climb cut. It's okay with delrin but when you try steel it chatters because the entire geartrain is loose. You can try to adjust it but still, there's a lot of places for vibration to start. You can try oversnugging the bearings but that can be dangerous and never did that much for me, no matter how much I tried. Changing speeds is also worth a shot, but same deal ...

If you snug everything up that you can, and the work fixture is undeniably rigid like the rock of Gibraltar, and you are conventional cutting (maybe drop the feed as low as you dare) and it still shakes and rattles, then either rebuild the whole thing or get a better one.

I know, not a pleasant thing to contemplate but there's too many places in that machine for vibration to develop, one little thrust washer isn't going to solve your problem.

Unfortunately, I have a master's degree in trying to sneak through with shitty setups on bitchy parts, can say with authority that trying to bandaid this problem isn't going to make you happy.

the delrin was cut very accurately.
Oh ? How were you measuring it ? :)
 
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bll230

Hot Rolled
Joined
Jun 14, 2007
Location
Las Vegas
Thanks to MB, Ek, and big L. I'll take the info and try to do good work. I appreciate the other advice, but I was trying to keep on topic. Grinder folks don't necessarily care about nuances of gear production.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
I have run my share of hob grinders but don’t wish to get into machine design. Still, I think a thrust washer/spacer is likened to a bearing. Nobody/few would want a bearing to have 99 .250" balls and one .251" ball. Based on this I think a thrust washer/spacer should be near dead flat.

Heat is one bugger in grinding. Hand sharpening the likes of a lathe tool bit shows how fast a hard part can get super-hot with not much pressure or sparks trail. A surface grinder with rapid hand wheel cranking and a greater spark trail certainly gets a part super-hot quickly. The part surface expanding and quickly cooling builds stresses and perhaps a burn to the point of warping.

One technique fail in grinding is the idea that the smallest overtravel off the part to the right and left is the way to grind. A larger over-travel can give a part some cooling time. A Windex (or the like) bottle of coolant can keep a part cool enough with little mess.

De bugging a part during the grinding process is a very important function for precision grinding. A small rubber blade squeegee can be handy to prep a wet chuck for the next grind.
 








 
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