# Mounting parts on lathe problem!



## Grimm (Oct 5, 2009)

I purchased some gears for my project and they had some fairly large hubs on them. I wanted to turn and face them down on the lathe to loose some weight and make them look more scale. The problem I wanted to make sure of was to not damage the teeth on the gears as they are gripped in the 3-jaw chuck. I cut a strip of thin plastic off and wrapped it around the gear and put them in the chuck. This appeared to work but I couldn't get the gear flat in the chuck, and every time I tried to adjust it, the other side would get out of kilter. Very frustrating!!







So I had a thought and cut off a short section of a wood dowel that was just a bit bigger in diameter then the gear. I slipped the dowel in far enough to give enough room for the gear. I then wrapped the gear in the plastic and put it in the chuck so that it was firmly against the dowel and I clamped the chuck down so the jaws embedded themselves in the dowel and held the gear without marring the teeth. This worked and when I checked it with a gauge it was only off by .0001 inches. I started off by facing the gear hub and everything was going good, until disaster struck.







The gear came out of the chuck and was cut and marred so much so I'm going to have to get another one. I think what happened was that as I was cutting the gear heated up and the plastic melted and released the gear. Does anyone know of a better way to mount gears that will keep them in place and not mar the teeth? My other gear is larger and I think I might be able to mount it on a faceplate but that sounds difficult to get it lined up. Any ideas? Thanks,

Frustrated Jason


----------



## John J (Dec 29, 2007)

What about mounting the gear on a shaft. the inserting the shaft in the chuck. These are plastic gears? Maybe turn at a slower speed? Reduce the thickness of the the material that you are taking off


----------



## plewitzke (Jan 2, 2008)

Can you mount soft jaws to your chuck and bore them to the diameter of the gears? They would be less likely to damage the gear teeth and would provide a good grip, not to mention running true. Good luck with your project. 
Pete


----------



## Dwight Ennis (Jan 2, 2008)

If you only want to turn down/face off the hubs, you could turn a fixture with a slight protrusion that would fit into the gear's center hole to align/center it, and a ring attachment that would clamp the gear into the fixture from the front via three or four screws around the outside leaving the hub exposed. Little chance of screwing the teeth that way.


----------



## Grimm (Oct 5, 2009)

Thanks John - That's a good idea, I'm just not too sure how I would attach the gear to the shaft, maybe solder it? The gears are brass, I just used the plastic to protect the teeth of the gears. 
Pete - another good idea, do you know where I could pick some up? I looked around for some soft jaws but I couldn't find any for my small 3" chuck. 


Dwight - Yet another good idea.  I think I understand how it would work, but wouldn't it also not allow me to face the hub because the ring attachment would be in the way? 

Jason


----------



## Les (Feb 11, 2008)

Jerry,

Dwight is almost there. Chuck your gear up with an indicator and some copper scrap under the jaws so that the outside face (the one you can get to) is running true. Now check your hub hole to see if it's bored true, or better, see below. Face off the hub hole now, so it's parallel to the indicated face of the gear. Be better, or best to skip down and make sure the hub hole and face are good as described below. Problem is, sometimes the gear is so sloppily made (by machinist's standards, that compromise is necessary). You make a 'fixture' by turning a piece so the gear hub hole slips onto it with no--or as little--play as your skills permit. You thread this thing and put a nut and washer on it, and clamp it into the chuck. Better, don't remove it from the chuck in the first place. Just turn it to fit, using crocus cloth to get the final dim, and slip your gear on there. Try all your gears for fit, manufacturer's tolerances might not be so good as yours. I want to come back to this point in a minute. You then slip your gears onto this 'fixture' (threaded shaft) with a spacer washer for flatness against the nut (remember, threads have pitch and the nut might have a slightly different one, if so, face off nut first). Run an indicator across the outside face of your gear to make sure the hub has been bored at a true normal (right angle) to the face of the gear. If it hasn't, rebore it. Reamers are good for this kind of thing, just take it slowly. I think I got most of it. If not, post.

Some misc, out-of-order thoughts on what you're doing.

1. Arg. Don't ever, if possible, clamp onto small gear teeth. If you must, do it lightly. And forget using plastic, the teeth bite in here but not there, and etc. Use soft copper shims on the jaws between the teeth. Soft brass shim stock is okay too.

2. Never, ever assume the item you've just paid a nice sum for is anywhere near accurately made. Assume ALL faces and normals are off and check 'em out to see what you've got. Especially if it's cast or stamped. Especially if it's cast.

3. After doing all the indicating you can think of: is it round, even, around the face of the teeth? Check every 90 deg and see if the tooth depth is the same. There are instances of deep and shallow teeth out there. Are the face of the teeth parallel to the hub hole? Are they normal (at right angles) to the face of the gear?

4. A machined gear is likely to be okay, but you never know. The gear machine might've been having a bad day when yours came through. Or the machine operator. Or a bad batch of gear stock (it happens).

5. Obviously, with a gear the first thing you want is a 'true' hub hole. To find that out, you need to know if the major diameter of the gear is round. Use a micrometer. and check at least every 90 deg around the gear. Then mount the gear with shim stock and indicate the hub hole. But, you say, my tell-tale indicator won't fit into that tiny hole! Turn a press-fit length of stock and indicate that. 

6. Is your hub hole normal to the gear face? Turn a tight-fitting axle and put the gear on and indicate the face of the gear, as above. If it is not, within acceptable limits, check to see if the axis of the hole is parallel across the face of the gears, major diameter, to the axis of the hub hole. If it is, forget the face unless there's a major problem. 

7. Are all gear holes the same diameter? (Supposing you've bought more than one.)

I know a lot of this is out of order and repetitive, but I'm not doing so hot today. Read it through, post if questions.

Les


----------



## xo18thfa (Jan 2, 2008)

Well, let me be the t**d in the punch bowl. Would not the "best" way be to clamp it on a face plate? Oh boy, a real set-up deal there.


----------



## Dwight Ennis (Jan 2, 2008)

I think I understand how it would work, but wouldn't it also not allow me to face the hub because the ring attachment would be in the way?The reason it's a ring and not a disc is that the ring clamps to the backing plate around the outside of the gear, keeping the hub exposed.


----------



## Les (Feb 11, 2008)

Dwight,

Not sure what you have in mind. 

The one thing I didn't say was, to face off the hub, you'd need to mount it in the chuck, with brass/copper stock under the jaws. Unless it's spoked or has holes. Then a faceplate would be good. Wasn't my greatest day, yesterday, probably shouldn't have even tried. But if you want to mount it on the chuck, you need to know if the gear is truly round, and that the plane of the gear is uniform. Cast gears, which is what I had in mind, plus wanting to give more info. While you're checking that, it's easy to take a look at the symmetry of the tooth depth. And so on.

Les


----------



## Dwight Ennis (Jan 2, 2008)

Les,
The original question was... I purchased some gears for my project and they had some fairly large hubs on them. I wanted to turn and face them down on the lathe to loose some weight and make them look more scale.I took the question at face value and answered it with the idea of how I'd approach a similar problem. Since he said he tried chucking them by the teeth (I wouldn't have done that) and it didn't work, my thought was to turn a fixture that would chuck in the lathe and support the gear body by its sides - i.e. clamp the gear body between the fixture's backing plate and the ring, leaving the hub exposed for facing. How true the gear has to be depends upon it's use - functional or merely decorative (i.e. a piece of scenery). As he didn't specify, and was willing to live with any inaccuracies induced by chucking it by the teeth, I assumed accuracy wasn't all that relevant, as the gear is probably destined for a scenic use of some sort.









You make a good point though. If the gear is to be functional, he'll have to exercise greater caution in setup and perhaps my idea won't work - or maybe it will if the gear is already true. My suggestion won't affect the shaft bore or its perpendicularity as the bore is already there - only the hub length will change (which is what he said he wanted). A shorter hub will provide less support, and the gear may wobble on the shaft. However, I go back to the original question, which was to turn down/face off the hub length.









Nice to see your type btw. Haven't seen you around for a while. Hope all is well.


----------



## Grimm (Oct 5, 2009)

Hi Guys,

Thank you all for your help, I have a much better idea on how to handle these things now. I should have posted some pictures of the gears so there wouldn't be so much confusion. The gears are brass and the teeth are .130" wide. The large one is ~1" in diameter and the small one is ~1/2" in diameter. The hubs are very large and push the thickness of each gear out to about .372". The hub on the large gear is so big it must almost double the weight of the gear. The gears are machined not cast and I do wish to use them as functional gears. When I did finally get the small gear chucked up and ran the dial gauge on the hub is was pretty true, only about .0001" off. I wasn't planning of modifying the hub bore or the teeth at all, only to reduce the size of the hubs. Here are the pictures, I did a little facing on the large gear as it was so easy to chuck up the large hub. 




















Thanks again for everyone's help.

Jason


----------



## Les (Feb 11, 2008)

Dwight,

Had some family problems, but put it down for now. Thanks.









Had Jason posted those pixes I'dve saved myself some typing. The thing I tried--and I think failed at--was to bring home to him the issues of concentricity, parallelism and normalicy, that is, one axis being at a true right angle to the others. The opposite faces of the gear, for instance, ought to be parallel, and the whole OD of the gear ought to be round. And that roundness of the OD should be concentric to the bore of the axle hole. Now that I've seen a pic, he's home free almost no matter how he attacks it, those are good, machined (not cast) gears, and I'll bet there's no worthwhile error in them. For some reason, my mind fixed on cast gears, not machined.

While I'm thinking on it, Jason, if you gouged a gear tooth, some judicious filing will bring you back to rights, since at those sizes there's no heavy load on them.

Dwight, building a fixture like you suggested is certainly feasible and a good approach. I never used a faceplate much, preferring my own lashups. Er, fixtures.







But always to remember, there's more than one way to skin a cat.

I simply must get my lathe going, so I can join the fun. 

Les


----------



## Semper Vaporo (Jan 2, 2008)

I think you were right to point out the need to maintain concentricity, parallelism and normalicy. The axle and gear teeth must be concentric or the gear may either slip one part of each revolution and/or bind at 180 degrees from the slip point. Parallel faces should not be a mechanical problem unless the faces are used as bearing surfaces, but visually it may look bad if one face is not normal to the axle... Would look like it is wobbling, poor workmanship.

If'n it was me... and I will not sully the term Machinist by associating me with the profession... and I wanted to reduce the bulk of the gear, I think I'd reduce the thickness of the hub portion using a grinder. Unless that face really needed to be parallel to the opposite face of the gear or normal to the axis of rotation, but even then a good fixture to hold the gear normal to the grinder would improve the result and the fixture would not have to grip the gear teeth as tightly as would be necessary on a lathe.

To reduce the diameter of the hub it would be best to chuck the gear in an arbor (a shaft through the hole in the middle with a nut to clamp down on the gear to grip it while spinning (or a bolt through the hole into a larger shaft being held in the chuck). The only difficulty is the overall diameter of the nut or bolt head would need to be smaller than the size you want to make the hub... tho', I suppose with a narrow enough tool you could cut behind it. Should also attempt to maintain the fillet at the juncture of the hub and gear disk. (Oh, and you will lose those stamped numbers!)


----------



## Grimm (Oct 5, 2009)

No worries Les, I got your message and a really appreciate the help.  I would have liked to keep the gear but, alas, the damage is worse then what you can see in the pictures. 

C.T. - I'm thinking I might try something similar. I have some tool steel rod I just bought for axles that I was going to use to make a arbor but instead of having a bolt I was going to just solder the gear onto it. If I'm careful with the solder and cut the arbor on the mill, I'm hoping that I can keep everything in line and square. I will test on the small gear, nothing to loose that way.  

Jason


----------



## Dwight Ennis (Jan 2, 2008)

Had some family problems, but put it down for now. Thanks. Glad everything settled down for you Les, and glad to see you back!


----------



## Michael Glavin (Jan 2, 2009)

Machining an arbor with minimal interference between the arbor and gear hub bore together with a step or shoulder to seat the gear against utilizing a bolt and washer to fix the gear in place for machining as noted previously sounds like the best approach IMO. If it were me I’d machine the hub to the diameter desired at least partially no sense machining the area that will be discarded and then use a parting tool to separate the unwanted hub stack height from the gear. I’ve done this successfully on similar pieces. Subsequent to parting the unwanted hub material the gear will still be fixed on the disposable arbor which should allow you to machine a new bevel on the new gear hub face providing the clearance or interference to gear bore is minimal as noted this with heat cycling would get the job done. 

Michael Glavin


----------



## Les (Feb 11, 2008)

Posted By Grimm on 06 Dec 2009 04:19 AM 
No worries Les, I got your message and a really appreciate the help.  I would have liked to keep the gear but, alas, the damage is worse then what you can see in the pictures. 

C.T. - I'm thinking I might try something similar. I have some tool steel rod I just bought for axles that I was going to use to make a arbor but instead of having a bolt I was going to just solder the gear onto it. If I'm careful with the solder and cut the arbor on the mill, I'm hoping that I can keep everything in line and square. I will test on the small gear, nothing to loose that way.  

Jason 

Jason,

That post wasn't one of my more sterling efforts. I screwed up by not just answering your question, instead, knowing your interest in machining, I tried to make it a 'teachable moment'.

I can't see any reason why you cannot use a strip of brass shim stock between the teeth of your gear and your chuck jaws, then you could take that face down any way that suited you. I'd even suggest you try a strip out of a coke can, that aluminum is fairly soft. I've never tried it, but I'm not above doing so if I can remember. Old habits die hard. By inserting a press-fit piece of round stock in the hub hole, you can indicate off that. It just needs to be thumb-pressure, and can even be tapered to assist starting. (Be careful how far up you taper). Nowhere is it written you have to chuck up a part with a dying strain on the chuck wrench. Just snug enough to hold, and use a smaller-ground tool and take lighter cuts, and you're home free.

Les


----------



## Les (Feb 11, 2008)

C.T. wrote: "The axle and gear teeth must be concentric or the gear may either slip one part of each revolution and/or bind at 180 degrees from the slip point."'

I have wondered on occasion where people describe binding in the motor block, just whether the gears have 'cold-flowed' with age, and are egg-shaped. Plastic gears can do that, particularly where an unfriendly lube is applied.

You're also on the money about finishing the sides of a gear: you just want good work, and once in a blue moon you'll uncover a warped gear.


----------



## Grimm (Oct 5, 2009)

Hi Les,

I took your advice and wrapped the in a strip of copper. It worked!







There was no damage to the teeth, at least that I could see. I faced off the dowel again and used it to back the gear so it would be aligned correctly. Now I'm going to try the large gear and see if I can align it without having a dowel backing it. Here are the results, I think you can see the difference from the previous pictures.











Thanks again for everyone's help,

Jason


----------



## therbert (Sep 18, 2008)

Another option, if you have a four-jaw chuck, would be to use a piece of shafting tha fits accurately in the hole of the hub of the gear, and soft-solder the gear to the shaft, with about .250" or a little more of the shaft sticking out beyond the gear face yo want to machine. Then center the shaft in the four-jaw, indicating on the stub of the shaft protruding past the gear. 

You could then proceed to face and turn down the hub, not worrying about the stub of the shaft, you could just face it off. When the gear hub is down to size, remove it from the lathe and heat to remove from the shaft. Old-time machinists also used to use shellac for mounting parts to be machined.

Granted, the soldering part only works on metals with higher melting points. If it was pot metal, you could use the shellac idea, but plastic would require either some type of mechanical fastener, or a machineable collet.

Good luck on your project!

Tom


----------



## Grimm (Oct 5, 2009)

Thanks Tom, 

A four-jaw chuck is definitely on my "must get" list. I may just do that with the large gear, it seems easier that way and I'm not worried about getting solder on the gear, as long as I don't get any on the teeth that is. 

Jason


----------



## Les (Feb 11, 2008)

Jason,

Well, if you're happy, I'm happy.









I see some ripples in the hub, probably immensely magnified by the camera. Are you setting an infeed depth, then running the tool in towards the hub? Or are you starting at various places with different settings on the infeed?

Want a secret? To take those ripples out, use a 6" mill ******* file. Follow up with crocus cloth. (A type of aluminum oxide 'sandpaper' for smoothing off metal finishes).

Keep up the good work, you're on your way!

Les


----------

