Correct Way To Chuck A Machine Gear?

Sorry for the dumb question.

If I wanted to bore/expand the ID of a hubless machine gear such as those common on a lathe,
what would be the best way to mount one in a 4-jaw independent chuck. Clearly, the chuck jaws may
land in-between some teeth or on the edge of teeth. Is this a simple matter of using a piece of brass
or hard plastic between the chuck jaw and the gear OD? Is there a better method, or am I making a
mountain out of a molehill?
Thanks in advance.
(I did search forums first)

PMc

View attachment 300778 View attachment 300779 View attachment 300784

mcload said:

Sorry for the dumb question.

If I wanted to bore/expand the ID of a hubless machine gear such as those common on a lathe,
what would be the best way to mount one in a 4-jaw independent chuck. Clearly, the chuck jaws may
land in-between some teeth or on the edge of teeth. Is this a simple matter of using a piece of brass
or hard plastic between the chuck jaw and the gear OD? Is there a better method, or am I making a
mountain out of a molehill?
Thanks in advance.
(I did search forums first)

PMc

View attachment 300778 View attachment 300779 View attachment 300784

Click to expand...

If you reverse the jaws you'll have a lot more purchase. I will stay tuned to see if anyone recommends brass sheet in between. It couldn't hurt. I've been using hide leather to hold things that I got from the drive belt maker but not sure if that is the best idea in a part like a gear.

If you don't have a good leather on hand this guy is awesome to work with and his box of "Remnants" is very useful and affordable.

Custom Leather Drive Belts-Single-ply (11/64''), up to 4'' wide

The o.d. isn't necessarily concentric with the teeth, so if you want to do it right you have to put wires in tooth spaces, then indicate over the wires. That doesn't give you too much grip, so take light light cuts.

If you've got a lot to take out, rough them first, then indicate over wires for the finish cut.

Really depends on the gears application and allowable run-out (is is ground to spec or just hobbed?), but most of the gears I've bored have been low rpm with some acceptable back-lash in the gear train, so I tend to bore soft jaws in a 3 jaw chuck to hold them. The soft jaws tend to grab across more teeth than your typical hard jaws and aren't as aggressive on the lands of the teeth. If more accuracy is required, as stated above it's best to grab and center the gear off of the actual face of the teeth along the pitch diameter. The tool room lathe you have pictured could go either way. If it's something simple like a South bend or Logan, the soft jaw approach will work fine for their gear train requirements.

EmanuelGoldstein said:

The o.d. isn't necessarily concentric with the teeth, so if you want to do it right you have to put wires in tooth spaces, then indicate over the wires. That doesn't give you too much grip, so take light light cuts.

If you've got a lot to take out, rough them first, then indicate over wires for the finish cut.

Click to expand...

+1

Formula for calculating correct wire/pin size for given spur gear DP is available in Machinery's Handbook. Look for 'Checking Gear Size Measurement over Wires or Pins' I used this method to accurately center for boring spur gear without hub. Hope this helps.

Best Regards,
Bob

M.B. Naegle said:

... most of the gears I've bored have been low rpm with some acceptable back-lash in the gear train, so I tend to bore soft jaws in a 3 jaw chuck to hold them.

Click to expand...

Me, too. But he asked 'what is the correct way'

Just mount in your four jaw and indicate on the present bore. That's the beauty of a 4-jaw, being able to compensate for any irregularities in the mounted part. The gear is most likely cast iron, so I don't see the chuck doing any major damage (if any) at all. It also can't hurt to use copper pieces as a buffer, but it makes for a more delicate setup.

Like said above, take light cuts on the bore to keep your setup in good stead.

Rather than messing with wires and worrying about pitch dia vs outer dia, why not put the gear in the chuck with the jaws reversed and then indicate off the bore to center it. That's of course assuming that the person who made it in the first place had the pitch diameter concentric with the bore--which seems to be a safe assumption.

This is a classic of making it harder to do at every turn,

if, the object is to enlarge the bore, simply protecting the gear teeth, with a soft material, dialing it in, taking easy cuts, might work

Last suggestion works unless the reason for boring is because the bore is all wallered out.

Oops Next to last suggestion.

donie said:

This is a classic of making it harder to do at every turn,

if, the object is to enlarge the bore, simply protecting the gear teeth, with a soft material, dialing it in, taking easy cuts, might work 1

Click to expand...

I agree with this, providing the bore is accessible and not damaged. Considering this was obvious, I assumed there was some reason that the bore could not be used to center the work.

Best Regards,
Bob

Because he asked what's the best way to do it, not the easiest. No, you can not depend on the bore being concentric with the teeth. Lots of times it doesn't matter so much but if you want gears to run smoothly, minimum runout is important.

Agreed, most likely there's no need in this case but if someone, some day wants to know the correct way, it's over wires.

Dobermann said:

Rather than messing with wires and worrying about pitch dia vs outer dia, why not put the gear in the chuck with the jaws reversed and then indicate off the bore to center it. That's of course assuming that the person who made it in the first place had the pitch diameter concentric with the bore--which seems to be a safe assumption.

Click to expand...

Aye. Prolly run a wrap of Copper flashing around it and do just that in the 6-jaw, quick check and good enuf.

Its for a SB, not a PT6.

Wire size = 1.728 / DP

So if the gear was 14 DP, the wire would be 1.728 / 14 = .12342

Having such means you can now measure gear and refer to tables like this published by Van Keuren - a measuring wire maker

(differing table for odd numbers of teeth)

Thank you all for the great info; I'll have to study the wire business in greater depth.

Before I started this thread, I was thinking of using a piece of Delrin round stock
to create a clamping ring of sorts. Cut off a 1" puck and square both sides. Then bore
out the OD of the gear plus 10K. Then cut an eighth-inch horizontal slit in the ring.

The ring then becomes a clamping surface with firm holding while protecting the teeth.
Yes, you would be right in saying the gear can possibly slip in the ring.
Just a thought.

PMc

mcload said:

Thank you all for the great info; I'll have to study the wire business in greater depth.

Before I started this thread, I was thinking of using a piece of Delrin round stock
to create a clamping ring of sorts. Cut off a 1" puck and square both sides. Then bore
out the OD of the gear plus 10K. Then cut an eighth-inch horizontal slit in the ring.

The ring then becomes a clamping surface with firm holding while protecting the teeth.
Yes, you would be right in saying the gear can possibly slip in the ring.
Just a thought.

PMc

Click to expand...

Been done. Often. Works fine. Also other plastics, plumbing and conduit included. Scrap Copper or aluminium flashing. Copper tubing ("DWV" is faily hefty diameter), PVC, CPVC, ABS, Pipe and tubing fittings as well as tube drops and scraps. Old kitchen cutting boards plastic, wood, or bamboo. I do this and that with nice quality Oak. Where to get it? One high-grade stair tread lasts for ages.



Generally no need of the overbore, just a chamfer so yah get an easy start into the fixture. Once sliced, flex works BOTH ways, so is enough to open it up.

IOW - use whatever is to-hand to do onesies and fewsies. Taking it easy, it need not spin atall.

Mass production? Throughput matters, labour and time need to come down?

THEN you go for more durable bespoke fixturing with "built-in" time-savers as to centering reliabily, holding well for item after item.

Meanwhile, don't put a thousand bucks worth of time and labour into fixturing for a ten dollar item, one-only.

"Run what yah got!" gently and alertly.

Skill comes with time and it saves-back the time it took a'learning.

Thanks...I'm making mountains out of molehills as usual.
But some interesting techniques in the replies for sure.!

PMc

mcload said:

Thanks...I'm making mountains out of molehills as usual.
But some interesting techniques in the replies for sure.!

PMc

Click to expand...

Manual lathes and mills are sore simple-minded critters. All the cleverness YOU have to furnish.

Workholding, jigs and fixtures can be the "fun" part of that, and soon grow to where workholding and tooling as a class FAR outweigh the investment in the core machine.

4-Jaw is "core". "If you can only have the ONE", etc.

3-J I'm proud to not even OWN!

But I DO have 2-jaw, 6-jaw, magnetic, "many" collet systems, including Hardinge step and pot to 5 inches of the 7 inches they made them for and more than one type of internal expanders and mandrels.

Also plenty of faceplates with all manner of clamping goods - most of those shared with mill, shaper, and slotter.


"Techniques?" Even the ancients nested odd shapes amongst dowel rods, set them in plaster or low-Eutectic metals for removal after the work was done.

Or affixed them with melted stick shellac. Think diamonds and how they are faceted. Brown shellac, heat worked, alcohol clean-up, still beats most miracle adhesives that are not as easily released, let-alone re-used.

Keep yer eyes open, mind hungry, find it has all "been done before", and more than just the one time.

Goldstein, is that you that is saying the only way "to do it right is over wires"?

And what tolerances are you talking about with wires and rings, worrying that mess in a 4 jaw chuck?
I have the most accurate four jaw chucks, on the most accurate lathes possible, I reject your directive, and the troll jumps in and says.

by the way you SB fans HGR has been listing SB Skinner 4 jaw chucks, pretty cheeap.

donie said:

Goldstein, is that you that is saying the only way "to do it right is over wires"?

Click to expand...

It's not the only way, I've seen chucks and fixtures that locate off the teeth, but they are a bunch more expensive.

Fact is, thread title is "what is the correct way to bore gears" ... the "correct" way is not to locate on the od. OD is not necesarily concentric with the teeth.

For a South Bend yeah, who cares.

Well, some people do. You can hear runout. It goes rrrr-rrrrr-rrrr instead of whooooo. There are threads here complaining about that. I think it's silly but ... if you really care about that stuff, have to locate off the teeth themselves.

btw, 1.728 over the dp gives a good size for the wires but for something like this, they don't have to be that size. Just all three the same and big enough to extend beyond the o.d. will work.

And what tolerances are you talking about with wires and rings, worrying that mess in a 4 jaw chuck?

Click to expand...

For grinding, I'd habitually indicate to under a half thou runout over the wires. Try for two tenths but to be honest, lots of times after heat treat the parts aren't that round. And parts that aren't heat treated aren't always as great as they'd lead you to believe, either. Sometimes can't get under a thou and you'll move the gear around two or three times to get the best spot. Stuff distorts. Then when you touch off on the bore, you see how the three-jaw that originally held the blank shows up in the part later on. The wheel almost always makes a triangle before it makes a circle. Keyways distort parts badly, too.

Just for shits and giggles ... for expensive parts we'd take forgings, rough them. Stress relieve. Finish turn. Cut teeth. Carburize. Quench on plugs. (Spiral beevils even have special quenching presses to control distortion during quench.) Grind the bores while holding over wires. Last, grind the teeth off the .0002" fit on a mandrel with ground centers. Check on a redliner for concentricity and an involute tester for tooth shape and a lead tester for straightness.

Was working at a place that said "Oh bullshit, we don't need to do all that" so they made 1,000 scrap parts. Made me snicker. When OP said "correct", well .... there is only one "correct". The better question is, "how good does it have to be ?"

I have the most accurate four jaw chucks, on the most accurate lathes possible, I reject your directive, and the troll jumps in and says.

Click to expand...

Reject away, didn't mean to tell you you had to do anything But if you really want concentric teeth on your gears, can't trust the o.d. Places like Boston make blanks as cheap as possible then throw them on a mandrel to cut teeth. Can easily have several thou runout between i.d. and o.d. and on top of that the teeth can be way off from both, if the hob has runout or the mandrel centers aren't so good.

Teeth is what counts. The o.d. fits air.