# Do your bits wobble?



## Bogstandard (Dec 3, 2007)

Now I have your attention, I am talking about flywheels, not body parts.

I was reading Chucks great post about his making of an open column twin, and Hilmar's comment about wobbly flywheels.
There are lots of ways of mounting flywheels, from keyed shafts, the way Chuck has done it with tapers (there are a few tapered methods) but the most general one, and the easiest to do is the humble grub screw stuck in from the side. But it is this grub screw method that causes the worst of the shakes.
If you can get the flywheel hole to be a 'wringing' fit on the shaft, there is usually no problems with runout, but with just a couple of thou clearance (like I usually get) the problem rears its ugly head as soon as we tighten up.
I have done one of my crappy sketches to show you what happens.







I have exaggerated it to show what happens when you use one grub screw from the side, it basically doubles the error on the fit of shaft to hole and 'kicks' the flywheel over to one side and gives you a pronounced side to side wobble.
The cure for this is fairly simple, stick another grub screw in the other side, as in the pic. You will still get wobble, but only up and down, which is much less noticeable and easily dressed up true, unlike with one grub screw, which can be dressed true, but move the grub screw and retighten and you will find the wobble comes back due to the unstable mounting contact points.
This is of course assuming your axle hole is concentric with the rest of the flywheel.

John


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## cfellows (Dec 3, 2007)

Here's another method of attaching a flywheel to a shaft, similar to the tapered split bushing, but without the taper. The bushing is turned to a relatively tight, pressed fit into the flywheel hub. The center hole of the bushing should be a close sliding fit on the crankshaft. The bushing is split radially, next to the flange, halfway through the bushing. Then, the flange is split axially, through to the center hole and the first split. A tangential hole is drilled through the flange, crossing the axial split. The hole is widened on one side to accomodate the tightening screw head. The other side is threaded for the tightening screw.

The bushing is then pressed into the flywheel. The assembly is then slid onto the shaft and the screw is tightened which draws the flange end securely onto the shaft.

This method has the advantage that the flywheel is easily removed when the screw is loosened. I've also found that this method produces no detectable wobble.


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## Bogstandard (Dec 3, 2007)

Chuck, this one you suggest is a good method, I have used a very similar one but it was all machined on the flywheel boss rather than being separate, but does rely on a close tolerance fit to get wobble free running.

Has anyone else got any good methods for mounting up wobbly bits without the wobble.

John


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## compound driver (Dec 3, 2007)

HI
Cutting a key way and making a decent key requires a bit of thought.
If your machining a cast iron flywheel its important to remember that the dust from machining the cast will stick to the bore and give a false feel to the fit of teh shaft. I always blow the bore out with the airline before measuring of trieal fitting.
Nine times out of ten thats the reason for a wobble on mounting the flywheel. The key should have about a half degree taper its full length and be as long as the hub

Grub screws just dont work well and will always tend to push the wheel off axis or off center if two screws are used. 

Cheers kevin


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## cfellows (Dec 3, 2007)

I've also found that I am more likely to get a true running flywheel if I am able to cut the bore with a single point boring tool in the lathe. Using drill bits and reamers seem less likely to give me a true running flywheel. Must be doing something wrong!

Chuck


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## Bogstandard (Dec 3, 2007)

Please remember lads, we are working with little engines here and a lot of the beginners usually only have or know how to use a drill bit for boring a hole thru a flywheel and also 1/4" diameter is a fairly large hole, often smaller.
But your tips are definitely worth considering on something a little larger, and by the builders with a lot more experience.

John


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## Bogstandard (Dec 3, 2007)

That is what my sketch is all about, if you can't get a nice 'wringing' fit (that means you have to twist it to get it on and off the shaft), rather than having to go thru the process of making a new flywheel, or plugging the hole and remachining, by using two grubs you can at least get an acceptable, almost straight running flywheel that is fairly easily trued up.
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In an ideal world there would be no need for tips like this, but we are human and as such, not everyone can make a perfect fit every time. It is not a crime to have a few less than perfect bits. 

Hands up all those who have never made an off centre piece, or a hole too large, and if you put your hand up, can you please tell us your name, because it must be some sort of religious one.

What should we do, leave these poor unfortunate souls to a life of ridicule by the so called 'experts' because of their wobbly bits?, or help them to overcome their disgrace in the eyes of the experienced with just a little bit of help? (and an extra grub screw).

When these outcasts with the wobbles become more experienced and start to get onto the straight and true, they will again repeat these lessons that they have learnt to the new less fortunates, and so the circle carries on.



Sermon over



Wobbly John


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## compound driver (Dec 4, 2007)

Hi
99% of the reamed holes I see on engines both large and small 
have had the bore reamed way to fast and have had much too much metal removed with 
the reamer!
Guys reamers are not jobbers drills an H7 reamer is what it says
and is designed to ream an H7 hole and to do that it must only be asked to remove a few thou 5 at most. 
Use the slowest speed you can or hand ream the hole if you can.Take it in one cut trying not to remove the reamer before its gone through. On cast iron an air blast can help keep the dust out of the bore and help to generate a true hole.
Once the holes reamed make the shaft to fit and not the other way around. If you can see tooling marks in a reamed hole its buggered!

Come to that if your really worried about wobble take a look at a full size traction engine many of them have some degree of wobble in the flywheel and more in the wheels.

Cheers kevin


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## Cedge (Dec 4, 2007)

John
Maybe it's just the shade tree mechanic coming out in me, but if I have the wobble bits problem, I either bush the hole and re-shoot the hole or I break out my hand dandy knurl and run a light pattern over the spot on the shaft where the flywheel is going to sit. It expands the metal a wee bit and is very easy to polish back for a nice snug fit.... but then I'm just ignorant enough not to know any better....LOL All I know is there is only one wobbly flywheel here and that one is due to a bent flywheel spokes. 

Cutting tapered key ways is great if you have broaching skills and something to do it with... but some of us have neither. Kevin... it's all about how many ways are there for skinning cats. There simply is no one right way when the cat is fighting being skinned.

Steve 
Who proudly wobbles his OEM bits due to well worn balls.


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## compound driver (Dec 5, 2007)

HI Cedge

The key way does not carry the taper the key does that. If you want to cut a keyway in a 1/4 inch bore it can be done easily using the saddle of the lathe and a tool ground to plane the metal out of the bore. Broaching is the best way but there are certainly plenty of other ways to do it.
If that fails soft solder a plug of teh parent metal into the bore and drill down the wall of the bore this should if done well give you a half the key way hole in the plug and half in the flywheel. Once thats done melt the plug out and either make a round key or use a needle file to make the keyway square.

If you thinking its not possible on small shafts say bellow 1/4 inch it certainly is. I have keyed 5/32" shafts on models and on one occasion a 1/8" shaft. The 1/8" was pushing it a bit but still looked good and worked ok.

On the point of right ways there certainly is a right way to do things and as engineers thats what we all strive for. That does not meen there is only ever one way to do a job lol

Cheers kevin


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## Bogstandard (Dec 5, 2007)

I must now intervene on this post.

What are we doing here?

Is it a site where help is readily available to hopefully assist people make things a little better, or a site where you are told that if you don't do it this way or that way your legs will fall off. 

What a load of utter bullshit. Please excuse the language, but this is now starting to happen with greater frequency, AND IT WILL STOP.

Are you honestly trying to tell me that a complete newbie is going to attempt to produce a keyed shaft and hub, or is he going to do as the drawing he is using says, and that is use a grub screw. He doesn't have a squillion years experience from making anything from steam engines to space shuttles, all he knows is that when he tightens up the grub screw his flywheel wobbles. So my original post is to get this newbie to do a small mod that will make it look a lot better than his original effort, and explain why it happens that way. 
No rocket science, no multi thousand pound machinery, no specialist tooling other than a drill, tap and a grub screw. The machinery, tooling and experience all come later, at this point in time all he is interested in is getting his little treasure of an engine he has just made running and looking its best.


No please's anymore, LOOK AT THE ORIGINAL POST, AND HELP rather than bickering amongst ourselves trying to outdo each other on how things should be done, rather than helping to keep this site what it should be, a haven where newbies and oldies alike can share a bit of knowledge and get things made. No TELLINGS just SUGGESTIONS.

If you want to show and tell how to get the holes to size and true running then DO A POST ABOUT IT, don't go around hijacking posts and turning them into battlefields, and see just how it feels to have a simple post like this turned into a free for all, that if not stopped now will get out of hand.

Any adverse comments or arguments on this subject will be seriously edited.

Only constructive bits to be added.


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## Cedge (Dec 5, 2007)

Kevin
After 25 years of dealing with engineers and correcting their "right way" out in the field, I understand things a bit more, now that you've explained the problem...LOL. I've saved the bacon of many a young pup engineer and I've allowed just as many pompous old experts to hoist themselves by their on petard. It all depended on their attitude. Yup...I know a bit about engineers and experts. I have a friend who is an engineer and I even respect a few.

Lighten up dude...LOL This stuff is supposed to be fun. We're not all engineers and neither accepted industry practice nor national standards dictate our efforts. No one has to sign off on my little projects, so I'm allowed to fudge a bit if my shop capabilities fall a bit short. As long as safety is not compromised we get to do things the best way we can. . You're possibly right... there probably is an accepted "right way" but I'm a hobbyist and I'm not actually required to live by it. Me?... I'll go on skinning cats in the most expedient fashion, using whatever is close at hand.

It's called being flexible, adaptive, practical, creative, pragmatic, imaginative, ingenious .... you choose your favorite. Try it... you might actually like it.... (huge hairy evil grin). 

Steve 
Who can't imagine an Engineer having fun and sex at the same time.


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## compound driver (Dec 5, 2007)

Cedge
read what i put at the end of my post will ya. and John do what you want I really couldnt give a monkeys anymore all my posts on this subject put forward useable ways to mount a flywheel with out wobble.

You say you want to help new model engineers well showing how to cut a key way and fit a flywheel with a key in my books does just that .

Any one with a lathe drill press and a couple of hand files can fit a key to a flywhel and shaft.

Lets see if this gets edited lol

No need to edit this, but do read the PM I sent to you. That should explain all.


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## mklotz (Dec 5, 2007)

If you're going to use setscrews, a close fit between drive shaft and flywheel is essential for wobble free operation.

Amateurs should think about buying a set of "over and under" reamers* in addition to their regular assortment of reamers. They're not terribly expensive and are useful for far more than flywheel fitting. Measure your crankshaft diameter accurately (i.e., use a micrometer) and then use the "over" or "under" reamer that comes closest to matching that size. Be sure the hole in the flywheel is drilled and reamed on the same chucking that produces the final wheel circumference so that the hole is concentric to the circumference.

Also, if the flywheel is sufficiently meaty, rather than tapping the flywheel hub for the setscrew consider drilling radially through the middle of the flywheel width, which centralizes the setscrew location and doesn't produce the canting John showed in his first sketch. Doing this, you may end up with a hole too long to tap to full depth. If so, tap only the top part of the hole for the setscrew and drop a short length of brass rod into the hole before inserting the setscrew. (I call this a pusher rod.)

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* Over and under reamer sets consist of a pair of reamers - one 0.001" larger and one 0.001" smaller than the most common sizes (my set runs from 1/8" to 1/2" by sixteenths).
Thus the set contains a 0.124" and a 0.126" reamer (though no 0.125"), a 0.186" and a 0.188", etc. up to 0.499" and 0.501".


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## Bogstandard (Dec 5, 2007)

There is a lot of useful information in this post, and can easily get lost because of the beginner type post this is meant to be.
Maybe if some of the more technical stuff in here could be repeated under its own heading ie. 'getting holes the right size and concentric' or 'alternative ways of fixing a flywheel', preferably with an accompanying sketch or picture. This will then ensure that the information becomes a good, easily referenced archive for everyone.

John


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## tattoomike68 (Dec 5, 2007)

Bogstandard  said:
			
		

> There is a lot of useful information in this post, and can easily get lost because of the beginner type post this is meant to be.
> Maybe if some of the more technical stuff in here could be repeated under its own heading ie. 'getting holes the right size and concentric' or 'alternative ways of fixing a flywheel', preferably with an accompanying sketch or picture. This will then ensure that the information becomes a good, easily referenced archive for everyone.
> 
> John



You can rename the whole thread, like "Flywheel runout and mounting methods" it would then be named more about what the topic is about.

On my little engines I threaded the crankshaft and tapped the flywheel and used a jam nut to lock it down.

On some larger thing I have machined like the huge woodchipper rotors and large suction fans they had a tapped hole in the end of the drive shaft to hold the rotors in place up against a shoulder machined into the shaft.

On the big woodchippers like you see at a saw mill the rotor would be on a taper with a strait key and then 2 jam nuts and the spider type lock washer with a tang in the keyway and tangs you can bent into slots in the nut to lock them in place (like you see on machine spindles).


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## Powder keg (Dec 5, 2007)

The final result here is what were after. I'm a Foreman/Machinist in a machine shop. Over the last few years I've noticed a few things. You give ten machinists the same job, and they will all do it a different way!? How can that be? I was talking to an older gentleman about that and he said "There is more than one way to skin a cat, But as long as we can keep the skin when where done, All is good:O)" I keep this in mind when I see a machinist doing a job totally backwards. As long as the plane flies when we get done, all is good:O)

Now Kevin, If you have time, Please give us a tutorial on keying or broaching holes on the lathe. I had to explain how to put some grease groves in a bushing the other day to a guy we are training. It's done the same way. I would be especially interested in the smaller ones. Are they done the same as the bigger ones? How do you grind the tool? What is the standard size key for an 1/8" shaft?:O) Where did you get an endmill that small? If you don't have pictures, Sketches would be great! It really helps get your point across. Its good to see the different ways to do stuff. That's why I love these forums so much. 

John, I like what you are doing here. Keep up the good work:O)

Everyone else, Pay attention, There's a Quiz at the end:O)


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## AlanHaisley (Mar 27, 2008)

Bogstandard  said:
			
		

> I have exaggerated it to show what happens when you use one grub screw from the side, it basically doubles the error on the fit of shaft to hole and 'kicks' the flywheel over to one side and gives you a pronounced side to side wobble.
> The cure for this is fairly simple, stick another grub screw in the other side, as in the pic. You will still get wobble, but only up and down, which is much less noticeable and easily dressed up true, unlike with one grub screw, which can be dressed true, but move the grub screw and retighten and you will find the wobble comes back due to the unstable mounting contact points.
> This is of course assuming your axle hole is concentric with the rest of the flywheel.
> John


John,

Wouldn't it be better with 3 setscrews, installed 120 degrees apart? If done carefully the gap could be spread evenly and the flywheel set at right angles to the shaft. (If it were me, I'd then fill the gap as much as possible with gap filling CA. Once set up it would provide a bearing surface better than three little screw points. No good on something big but I'm only doing little model engines.)

If I do a larger wheel sometime, I'll probably try for a tapered split hub. As a beginner, I suspect that that is one of the easier methods to get really good results.

By the way, I'm a rank beginner with metalwork. Untill about a year ago I had done nothing beyond use tinsnips and a drill on anything metallic. But when I read about methods that are beyond me, I just file them away in my memory. Some day many of them will be useful for something.

Alan


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