Help! Trying to grind large spherical radius on small part.. Maybe need CNC grinder..

PANTERA79 · Nov 7, 2021

Hey guys, my problem, need to grind a 35" radius on the end face of a 7/8 diameter part. So far I have tried dressing the radius on the wheel, using my std. old Crystal Lake OD grinder. No luck.. wheel breaks down very fast. This is a production job, so I need a better method than a one-sey type fixture.. Here are my thoughts, and please correct me if I'm wrong. Thinking maybe I should try a universal type OD grinder, where the work head can be moved off center, (swivel) and use a cup wheel. But then I'm thinking that would generate a taper, not a true radius?? Than I thought maybe a tool grinder like a Yuasa GX, or similar, like to sharpen ball end mills, but the radius on those I know can't go that large.. Unless I'm missing something, don't know much about tool grinders.. Lastly, a 2-axis cnc cylindrical.. I know even less about these, but if it programs like a lathe with a G03, I could program a radius move? If both axis permit circular interpolation? But I would rather do on some sort of manual grinder if possible. Oh and no, actual automotive tappet grinders like a sunnen or old Tobin-arp leave horrendous finishes, and really don't grind a true spherical radius, already been down that road.. Lol. Thanks guys for any help offered!

CalG · Nov 7, 2021

cup wheel, tilted head, work mounted on a rotary table.

Generate the radius. (look up the term)

Common method for lens making.

Dan from Oakland · Nov 7, 2021

You can search "generating a sphere" here on PM using the search tool.

Here is a link to an article that describes the process in pretty simple terms. Rather than a flycutter on a boring head used to machine the part, you would mount a diamond dresser point in a boring head at a given radius and angle and use that to dress your grinding wheel. Of course you could make a simple disc with a stem and with the diamond mounted at a given radius for your job. The math is pretty simple- here is the article:

Generating spherical surfaces | Cutting Tool Engineering

This is the same process used to dress large radi into the face of a grinding wheel for grinding the face of automotive camshaft lifter/followers. On mine, the dressing diamond rotates on about a 1" radius and is kicked off centerliine by a few degrees to generate anywhere between an 80" to 130" radius.

PANTERA79 · Nov 7, 2021

CalG said:
cup wheel, tilted head, work mounted on a rotary table.

Generate the radius. (look up the term)

Common method for lens making.

ok, please excuse my ignorance, just trying to wrap my head around the set up. Cup wheel I got, work mounted on rotary table, like on a tool-cutter grinder like a Cinici-monoset or similar, (not a universal OD grinder with swivel workhead?) And you say tilt the head? How would that be accomplished? Thanks, sorry I'm not familiar with the process of grinding large radius.

michiganbuck · Nov 7, 2021

How close Does it have to be?
Easy to get .005 making a gauge drawing it on a sheet of mylar, and hand dressing the wheel to the gauge.

I would drill a hole in a 2x4, to make a diamond pocket in its end. then carefully drill a swing hole 35" away, to likely get better than .002.

Yes, Swing this at a 3/4, 1", whatever wheel.

A production job, then you leave this dresser on the machine table and set a length gauge to one of your table stops so get the swing arm exactly in the same place (long travel) at the nest wheel dressing.

Likely a 40x2 x 1/2 steel bar stock bolted to the table. A 40" x 1 x 1/2 for the Swingarm.

likely take an hour to fab the dressing fixture in house.

Being fancy, surface grind a key slot in the bar for square locating.

Weld a couple of swing stop tabs so as not to go off the swing.
Have a raised ride on near the dressing end so not riding on the whole length of the bar.

Yes, this is for dressing the OD of an OD grinder .. for dressing the wheel side face just make an offset to the table and swing in the long travel direction.

No reason you could not get the radius to .001.

PANTERA79 · Nov 7, 2021

Ok, so let me ask you this, I actually made a dresser for my current set up, for dressing the radius on the side of the wheel, machining a slot my vmc,on a piece of plate I bolt to the grinder table, at the 35" radius and made a post for the diamond to swing thru the 35" radius slot. So my part, chucked up in the work head, and coming in and facing down with the grinder, as if I'm parting off on the lathe, the finish has not been good, plus the wheel is breaking down very fast. Like I said, I know little about the operations of running a grinder.. Do you think I should be using a cup wheel and plunging with the x axis? Or feeding down with a larger wider stone with Z axis? Or maybe I would be better going to a larger grinding machine with bigger wheels and more rigidity? Sorry for the most basic dumb questions..

michiganbuck · Nov 7, 2021

QT: [Sorry for the most basic dumb questions.. no question is dumb.

Having a straight side cup wheel you can angle a wheel to get a male radius to a part. Angled the other way to get a female (concave radius) I'm not sure if a perfect radius.

A straight-sided cup wheel keeps the same radius as it wears away/ a flared cup wheel changes size.

The side of a wheel is the poor way to use a wheel and using the OD of a wheel is much better. Plus the grit and gride of the wheel play a big part in how it performs.

I am not seeing your setup, is the part pointing up out of a work head and spinning?
The wheel mounted to a vertical spindle with a type one wheel having a radius dressed to its side face?.

Most often a radius-dressed grinding wheel will not put a radius on a square nose (any shape part) part with not rapidly breaking down where the take-away is greatly different along the part. This is a common problem using the side or the OD of the wheel. grinding an even amount and a wheel shape holds up for a long time.

For a quick check take a bowel and turn it at an angle until you see the radius you are seeking at the edge, this may help you think about a setup.

You may choose a concave ball nose cutter to rough in the part form.

I have to head out so will get back to this with your posting more information.
Buck.

CarbideBob · Nov 7, 2021

The cup wheel is dressed straight.
The setup is fancy.
CNC if end open is just rad cut like on a lathe.

Bob

PANTERA79 · Nov 7, 2021

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gappmast · Nov 7, 2021

PANTERA79 said:
Hey guys, my problem, need to grind a 35" radius on the end face of a 7/8 diameter part. So far I have tried dressing the radius on the wheel, using my std. old Crystal Lake OD grinder. No luck.. wheel breaks down very fast. This is a production job, so I need a better method than a one-sey type fixture.. Here are my thoughts, and please correct me if I'm wrong. Thinking maybe I should try a universal type OD grinder, where the work head can be moved off center, (swivel) and use a cup wheel. But then I'm thinking that would generate a taper, not a true radius?? Than I thought maybe a tool grinder like a Yuasa GX, or similar, like to sharpen ball end mills, but the radius on those I know can't go that large.. Unless I'm missing something, don't know much about tool grinders.. Lastly, a 2-axis cnc cylindrical.. I know even less about these, but if it programs like a lathe with a G03, I could program a radius move? If both axis permit circular interpolation? But I would rather do on some sort of manual grinder if possible. Oh and no, actual automotive tappet grinders like a sunnen or old Tobin-arp leave horrendous finishes, and really don't grind a true spherical radius, already been down that road.. Lol. Thanks guys for any help offered!

The Sunnen and Tobin Arp machines DO grind a spherical. I have seen traces of lifters ground on a Sunnen and they were given a thumbs up by TRW engineers. You will get a good finish if you have the correct stone, coolant and dress on the wheel.

CalG · Nov 7, 2021

Search string

Rogers & Clark lens generator at DuckDuckGo

Look at the layout of a Rogers and Clark. Loh makes them also (or did)

Workpiece length will be a significant factor in tooling. Lenses are mounted in plaster or waxed on.

CarbideBob · Nov 7, 2021

Big problem here verses the B-port method to generate a sphere or radius is that the wheel or cutter size is fixed and can not be changed.
Dressing in a 35 inch rad a bit of a challenge without cnc or a profile dresser.
One option is a plated CBN wheel for finish work. Likely 300-600 dollars.
Not a whole lot of rise and fall here at this part size so it's a bit fussy. Sub tenths will count.
Then we get into can you check a 25 inch against a 45 inch rad on this part? It is only 7/8.

Glass and lens grinders do this sort of stuff and did not need cnc but so complicated.
Want to invest the time and effort to go down this deep rabbit hole? One can spend a long time of sleepless nights, dreams and nightmares.

My hope is that with all the brain power here a easy and simple answer to do what is needed given the machines in use.
Bob

michiganbuck · Nov 7, 2021

Patera, with that Od grinder you can fab up the swing arm dresser I described and dress the 35 " radius into the OD of a type 1 wheel(simple straight wheel)..turn your work head 90* and feed straight in.

On the swing grinder you can extend the table to place your work head back and so the part nose end is 35" back from the swing pivot center and swing the part to the Od of a straight flat dressed wheel. yes, you would swing it very little to cross over a small part.

You can also use the swing arm dresser on the swing machine.. but not using the machine's swing ..just plunge the part straight onto the wheel that has the radius dressed into the OD of a type 1 wheel.

You can place a 6" straight cup wheel on the swing-machine and turn the wheel head to the angle where arc of the wheel shows a 35" radius to the part.

*No matter how you grind it, best would be to tool/cutter/turn that radius on the part before heat-treat so leaving about .005 left to grind.

Do you have Lathe, or a machine to rough in the radius?

The wheel arc method does not need rough-in.. but rough-in would save time and wheel.

Making a simple crush dresser and using a creusable aluminum oxide wheel is another good option.

likely take perhaps 20 seconds to grind .005 to a very nice finish radius.

OPS... I don't know if your Od grinder has a swing work head or a turn-able wheel head.

May need to put your swing grinder work head on the OD grinder for this part.

PANTERA79 · Nov 7, 2021

michiganbuck said:
Patera, with that Od grinder you can fab up the swing arm dresser I described and dress the 35 " radius into the OD of a type 1 wheel(simple straight wheel)..turn your work head 90* and feed straight in.

On the swing grinder you can extend the table to place your work head back and so the part nose end is 35" back from the swing pivot center and swing the part to the Od of a straight flat dressed wheel. yes, you would swing it very little to cross over a small part.

You can also use the swing arm dresser on the swing machine.. but not using the machine's swing ..just plunge the part straight onto the wheel that has the radius dressed into the OD of a type 1 wheel.

You can place a 6" straight cup wheel on the swing-machine and turn the wheel head to the angle where arc of the wheel shows a 35" radius to the part.

*No matter how you grind it, best would be to tool/cutter/turn that radius on the part before heat-treat so leaving about .005 left to grind.

Do you have Lathe, or a machine to rough in the radius?

The wheel arc method does not need rough-in.. but rough-in would save time and wheel.

Making a simple crush dresser and using a creusable aluminum oxide wheel is another good option.

likely take perhaps 20 seconds to grind .005 to a very nice finish radius.

OPS... I don't know if your Od grinder has a swing work head or a turn-able wheel head.

May need to put your swing grinder work head on the OD grinder for this part.

Buck, I do not currently have a CNC lathe anymore since starting this shop. Only automatic screw machines, an a couple Hardinge AHC's that are making the blank. I did however think about picking up a CNC Hardinge to rough the radius detail in before HT than grind and finish after HT which is 62-64c But... I was thinking maybe rough turning the radius is a wasted effort, since really at 35" on the 7/8 diameter we are only talking I believe .005/.006 from the od to the center being removed. So your best advice if you were going to tackle this job would be an nice shape OD grinder with a type 1 straight wheel, plunge with the work head being at 90 deg. Or.. modify a tool grinder, like the old P&W, Cincinnati Monoset style? But swinging the cut on a cup wheel I just don't know if there is provisions on the cutter grinder to swing such a large radius. I didn't think so, but I'm not familiar with cutter grinder set up at all. Maybe it can?

michiganbuck · Nov 7, 2021

OT; (Buck, I do not currently have a CNC lathe anymore0
Your right .oo5/.006 is not worth the roughing.
Did you try the eyeball trick turning a 6" cereal bowl to see if the needed radius might be made from the arc of the wheel set at a little angle? with the part at wheel center height and spinning to/at the wheel.

Just guessing it would take about 8 to 10 degrees turning the straight-sided cup wheel, likely a 60 H white AO..the part end going straight toward the edge arc of the wheel.

looking for .020 .002 0r .0002?

PANTERA79 · Nov 7, 2021

I see what your saying! I really appreciate all the help on a Sunday. I feel you have really opened my eyes to some of the issues I'm having. I'm ready to get to the shop in the morning and try to work this out! I'm thinking tipping the wheel just may work. My biggest issue I see was working with the side of the wheel. I'm going to look at a grinder in the morning that the workhead can swivel 90-deg. Thanks again for all your help, and thanks to all that have posted thus far! Great place, with great minds. The only thing that's conclusive is even thou I been in the machining field all my life (I'm 49) The more I learn the more I realize how much I still don't know still about this great industry.

ballen · Nov 8, 2021

Not sure if this is on-topic or off-topic, but shows one simple way to machine a spherical surface:

Making a ballshape on the milling machine - YouTube

michiganbuck · Nov 8, 2021

looking for a better finish with cup wheels I would dress the od and ID angles of the cup wheel to run smooth. Yes, the angles/features of the wheel that I am not using, using a Nobiid stick, a carborundum stick, an old carbide tool of sorts, a slug of a broken diamond wheel or an abrasive roller dresser.

Cups run/grind best at the face edge opposite the mounting face...any other use and you need to be careful to not overfeed and so beak the wheel

Always consider the RPM whenever using a wheel not common to your use.

michiganbuck · Nov 8, 2021

Turning a copy ball with a manual lathe
Copy A Ball on the Lathe! - YouTube

I had a friend who became an expert at copy work using a moll and a rotary table. He would eyeball a part with bringing a ball nose probe to the original part to cut/machine the on to be done.
He was so good that when he retired from a shop they gave him a mill so he might run a few parts in his spare hours at home.

I just used a yardstick to draw a 35" radius on a piece of copy paper, then turning a 6" bowl looked over to the edge to see what looks like less than 5*

I could feel that with my protractor to be more exact to see how much to turn a 6" wheel, to use the onside edge for grinding..

JohnMartin · Nov 8, 2021

PANTERA79 said:
But... I was thinking maybe rough turning the radius is a wasted effort, since really at 35" on the 7/8 diameter we are only talking I believe .005/.006 from the od to the center being removed. ?

If you do the math correctly, you’ll find it’s actually less than half that much. No roughing necessary, I think.

Help! Trying to grind large spherical radius on small part.. Maybe need CNC grinder..

Aluminum

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