advice need grinding Rockwell C 60 part

[eKretz]

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.

 

[Dan from Oakland]

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]

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]

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.

 

[EmGo]

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]

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.

 

[michiganbuck]

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.

 

[EmGo]

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

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]

I was deceived by the name of the site

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]

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]

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]

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]

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.

 

[EmGo]

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 ?

 

[bll230]

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]

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.

 

[eKretz]

I'm sort of a glutton for knowledge and I know that EG knows his stuff about gear cutting. I soak up everything, so I don't mind a little related OT but I also feel like the OP should be allowed to steer his thread where he would like it to go. At any rate, I hope that the thrust washers at least make some improvement, let us know how it goes.

 

[EmGo]

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.

That isn't how these work tho. Depending on how old the machine is, on one side of the hob spindle there is a cone-shaped bronze bushing and a steel cone that runs in it. On older ones, same deal on the outside end, on newer ones just a straight sleeve. Some of the very very last ones have roller bearings.

So the thrust washer really doesn't do much. It sets the fit between the bronze cup and steel cone, but that's not very critical and even if it was way less than flat, as long as it kept those two parts at about the right distance, things'd be fine. Heck, a wavy one might get lube in there better.

If he's lucky, tightening up that fit will help with the chatter but ... let's hope so, but the drive train on those things changes directions about fourteen times, everywhere you look are bevel gears spur gears bushings and a worm gear; so many places for things to get loose and sloppy. It's real unlikely that getting a mirror finish and perfect flatness on this thrust washer is going to solve the problem.

 

[bll230]

Alright, to explain what EG is describing, my hob spindle washer was about 0.002 (that is a lot) too thin. So when I adjusted the spindle to no play with the lockrings I was setting to the taper, so to speak, and the thrust washer was not contacting. Then in use, the hob spindle could move left-right that 0.002 (which is really a lot of play on the hob) but the real significance of this situation is the two thousandth motion into the taper was the same as pushing a morse taper into its socket another two thousandths, which on a Morse locks the taper. The taper is similar to a Morse or B&S. So in use my hob spindle, in addition to allowing the hob an unacceptable amount of left-right play, was attempting to taper lock every time it pushed toward the taper.

The work spindle was doing the same thing to the tune of 0.003. The oil film strength was sufficient for delrin and brass gears, but for the steel gears the tapers were moving and psuedo locking.

EG may be right that my 80 year old machine may still make sucky steel gears, but getting rid of the taper locking and eliminating the left-right play has got to be a good start at improvement.

 

[bll230]

The washers ready to go to heat treat. I made an extra large one as a practice piece. Ground with the same 46H wheel I used on my chuck. I will be getting the recommended Norton 5SG-46H for grinding the hardened washers.