Wobbly Wheels

[Smifffy]

Having now fitted both of my leading wheels to the crank axle with loctite, I stuck the how lot in the frames but noticed a distinct wobble (flange effectively moving into and away from the fame as the wheel turns) to the wheels.

A quick check with the dial guage showed 0.5 mm on one wheel and 0.4 on the other - very very dissapointing. When applying the dial guage to the wheel treads, there is a slight variation (0.2-0.3mm) but this may be due to the dial guage point moving up and down the taper on the tread as the wheel wobbles.

As I have used 'cotton reels' on the axle shoulders, which are a snug fit, it's unlikely (?) that the wheels are not sitting true on the axles. I can therefore assume the error is coming from either the axle hole in the wheel being off true or the shoulders on the axles not being 'in line' with the axle diameters.

I struggle to think that the axle holes are likely to be off true, as they were bored in the Mill and the wheel treads and outer faces turned in a purpose made jig in the lathe.

I turned the axle shoulders in the 4 jaw set up with the dial gauge.

Once I've identified the error, it won't be a big deal to turn a couple more axles for the driving and rear coupled wheels if required, but the crank axle will be a pain.

Any thoughts from anyone in terms of where/what I should check to pinpoint the cause ? Also, any suggestions on how to fix for the crank axle - is fitting a bush between the axle and the wheel a big "no no!" for wheels on a 5" gauge ?

Mark

[welshy]

If you find the axle holes are square in the wheels you could make some new axles but use a straight journal which is a press/push fit as opposed to the cotton reel profile, Use Loctite 638 (on both surfaces) ensuring the surfaces are absolutely clean. Loctite 638 does not need any clearance and works even with a press fit. If it is the wheel holes that are running out you are better off clocking the wheels up on a faceplate and re-boring the holes slightly oversize, you can always take a light skim over the wheel rim.
If you cannot determine where the error is you could do both of the above.
Hope this helps.
Mike

[Smifffy]

My strongest suspicion is the shoulder on the axles - as they are made from 3/4 Silver Steel, I can stick one in a collet in the lathe and see how true the shoulder runs - I'm not sure that my centres are 100% centre, otherwise I would stick them all between centres to check.

[havoc]

That would be far fetched. If you turned the axles, then the shoulder must be perpendicular on the step you turned at the same time. You could get something conical in the lathe, but not out-of-perpendicular if you machined 2 surfaces at the same time.

[Smifffy]

Hi Havoc,

My thinking is, that the axle was not square in the 4 jaw. So although the shoulder will be sqaure (its face to the smaller diameter) it's possible (?) that the it is not in alignment with the axle ?

I'm about to dive into the workshop now for a few hours, so I will drop one of the fixed wheels off its axle and see how true the axle is in the lathe. Failing that, then I guess it's got to be the hole in the wheels - but I did these over a year ago now and I'm trying to remember exactly how I held the wheel on the mill table when I bored it.

[weldsol]

Hi Mark
As a thought if the cotton reel landings were tight you may have raised a burr which you have trapped between the shoulder face and the wheel ?

As a thought 2 did you under cut the corner on the shoulder or countersink the wheel hole as this may be holding the wheel off slightly ?

Paul

[engineernut]

Jan 2, 2010 14:42:23 GMT Smifffy said:

Failing that, then I guess it's got to be the hole in the wheels - but I did these over a year ago now and I'm trying to remember exactly how I held the wheel on the mill table when I bored it.

On all Flywheels/ Wheels that I machine I always turn the edges, faces, and bore the hole for the axle all whilst the Flywheel/Wheel is held in/on chuck/faceplate or whatever.
In that way the bore will be perfectly square through the Flywheel/Wheel. Everything else will also be concentric. ;D
The Flywheel/Wheel is then turned over to machine the reverse side.
Dave

[baggo]

Jan 2, 2010 14:42:23 GMT Smifffy said:

I'm trying to remember exactly how I held the wheel on the mill table when I bored it.

Hi Mark,

Does that mean you bored them in the mill rather than in the lathe? If so, is it possible the milling spindle is/was not exactly perpendicular to the table? Just a thought.

John

[Smifffy]

I had to check my Fotopic website to see how I did the axle holes in the wheels, and I did them in that lathe, not the mill:



Sometimes, I struggle to remember what I did last week, no wonder I can't remember from over a year ago :-) I'm sure it's only going to get worse, and I'm only 45 :-(

So, I removed one of the wheels from one of the plain axles, and after cleaning it up stuck it in the 4 jaw (extended more than I normally would) and set it true. Referring to Fig 1 below, the red text is roughly the point at which I used the dial gauge to position it. I then moved the dial gauge along and checked the run out as shown. There are two sets of figures, one for one end of the axle and the one for the other end.

Not good!

Going one step further, I stuck a 'fresh' length of 3/4" Silver Steel in the 4 jaw and set it with the dial gauge close to the jaws. Then again (Fig 2), checked the run out further along its length - again not good :-(



So, what now ? My first check will be to drop the 4 jaw off its back plate and see how that alone runs in the lathe. If that is true, I'll have to assume that the 4 jaw is worn and useless (I acquired it with a previous lathe 2nd hand). If it's not true, I can face it off and try again.

Otherwise, I guess I can turn two new axles between centres. That's not something I've done before (but that applies to all of this :-) ), however I'll give it a go. I am concerned though, about drilling the centres true in the axle ends. The crank axle, I will have to do between centres (some more head scratching to come) and fit bushes in the wheel holes (I'll centre the wheels on the back plate and open up the holes a bit).

Any thoughts/suggestions ?

Cheers

Mark

[brozier]

Hi Smiffy,

Make sure everything is spotlessly clean - the odd bit of swarf won't help. A bottle brush is great for cleaning chuck threads. then a blast of WD40 to get rid of the awkward bits.

I'd be inclined to give the back plate a skim - it may not have been machined on your lathe.

If you still have issues then the jaws may be worn. If you have a dremel type hand grinder you should be able to lash this to the tool post and use it as a tool post grinder to true up the jaws.

For accuracy/repeatability you might consider a collet chuck.

I recently bought a Shoba through hole ER25 collet chuck from Chronos and invested in a full set of imperial collets from Hong Kong (ebay) and they have less than 0.0005" TIR which is plenty accurate enough for me. All for the cost of about £65 which is what you'd pay for a couple of Myford collets!


cheers
Bryan

[Smifffy]

Hi Bryan,

I do normally keep all threads and jaw surfaces clean and I did check today,so I'm pretty sure that's not the issue.

Good point on skimming the surface of the backplate, I will do that anyway and see if it trues things up.

I can fit collets directly into my Boxford (I only realised this just recently) and do have a 3/4" MT3 Collet, but with the length of my axles, there's just far too much length out of the collet to work on the end. I suppose that I can still run a centre at the work end ?

Regards

Mark

[chris vine]

Hi Mark,

Before you go off skimming back plates etc,

It seems to me that the wobble on the wheels must be more than any error on the chuck. You could easily see the wheels wobble and I think you would have noticed it if the chuck was that far out.

Can you put the wheels back on the axles without locktite and see what you can work out. IE do they now run true (perhaps with the axles between centres and spun by hand.

Or, if you hold the axle still, do the wheels rotating on their seats run true?

A bit of deduction will help you loads in this tricky situation I think.

Chris.

[Deleted]

Mark. Going back to the chuck, I've never ever heard of a four jaw chuck wearing out any of the slides, screws or jaw points: they just don't get the same use as a three jaw. Unless yours was constantly making square posts in a previous life, I would suspect mounting problems.
Have you clocked the face of the chuck? There should be no detectable run out, and if there is, I would, as previously suggested, look for swarf trapped somewhere. If that doesn't fix you may have to true up the backplate.
JB

[havoc]

What you measured doesn't have any bearing on the problem you see. Think about it, if the axles did have that runout before you turned the step, then after you turned the step, it would have been 0 and the step and flange would be perpendicular.

Have you put a piece of silver steel (that you didn't machined) in the bore of the wheel and checked that?

[Smifffy]

Hi Chris, JB,

I've had my doubts about the 4 jaw for a while now, I've just (somewhat lazily or stupidly - more than likely both) not acted on my doubts. Having stuck a peice of silver steel protruding a good length out of the chuck, the variation is visible to the naked eye. I have already tried rotating one of the unfixed wheels on an axle whilst it (the axle) was in the frames and yes, the variation is there. However, Chris, I will follow up on your suggested checks tomorrow (to bloody cold now!).

JB, there are a couple of things I want to check with the chuck - I did run the dial gauge against the outside diameter of the chuck and there was an approx 0.1 variation. However, the surface is far from clean and has many dings and scratches. I don't think I can run the dial gauge against the face due to the jaw ways. I will drop it off its backing plate and see how true that is. I've also noticed that the backplate doesn't screw right back on to the lathe mandrel as I would expect, so again there may be something there.

A few things to do whilst I wait for some more 3/4" Silver Steel anyway.

The shame for me, was my target for the Christmas break was to have the wheels fixed on the axles and into the frames by the time I was back at work - that obviously won't happen now, but it's all part of the fun, ......I think, ........maybe..... :-)

Mark

[baggo]

Mark,

looking through your photos of the wheel machining I notice that after you had faced off the backs of the wheels in the 4 jaw you bolted the wheels to a faceplate? and then bored the axle holes. Are you sure that faceplate runs true? If it is running slightly 'wobbly' that could well be the cause of the problem.

What I do, although it's not much help to you now, is to face off the backs of the wheels and bore the axle holes at the same set up. That way the bore is guaranteed to be square to the back of the wheel.

John

[Smifffy]

Good point John. I'll check out the faceplate tomorrow.

Once I've got my 4 jaw sorted and can turn down a couple of new axles, I will do so with a push fit and see how perpendicular they are to the wheel backs.

Cheers

Mark

[Deleted]

Picking up on John's point, if the backplate is fouled or running out it will affect the the faceplate AND the 4jaw. Checking OD run out will do little good: If you haven't got a 'pear' type dti Put a tool up against one quadrant face and put a feeler guage between the two. Check each quadrant in turn and establish errors. Easy!
JB

[Smifffy]

I'm going to be busy looking into this tomorrow :-)

Havoc, I'm sorry, but I'm struggling to follow your thoughts here. If the shoulder is not true to the axle, which is held by its original o/d in the axle boxes, then surely that would result in a wobble ? If the shoulder is turned true, then its o/d will be concentric to the axle itself, but from my measurements it isn't. If you lived nearby, I would pop around for a chat :-)

Mark

[Deleted]

Hi Mark
This must be very frustrating for you, chasing a time target can make things worse. It may help to take a step back from trying to get the wheels done by a certain time, and take a bit of time to check the lathe over and analyse the problem.

Just a few points that may help:-

If you rotate the wheel on a stationary axle and it wobbles, then the problem is the wheel, I would guess that your faceplate is out of true as John suggested. We are talking a wobble on the face of the plate, not a radial run out. Faceplates can and do warp. Also as John said I would have bored the hole at the same time as facing the back of the wheel. You need to check that the faceplate seats properly on the spindle, and if it still wobbles then give the face a skim.

If the wheel rotates true on a stationary axle then the problem is the axle. I'm not sure that you could turn the wheel seat with a wobble, I think it would either be eccentric and/or tapered.

Try rotating the axle in the axleboxes and check for eccentricity

Check whether the wheel rocks on the axle, the wheel seat could be tapered, or the hole in the wheel could be tapered.

You could have a combination of minor faults in the wheel and axle that add up to a bigger problem.

You should be able to clock the face of the 4 jaw, if you take the jaws out, just lift the dti plunger over the jaw slot as you rotate the chuck by hand. If the face runs out check that it is seated properly on the spindle. If still no good remove the chuck from the backplate and check that, it may well need a skim.
The important thing to check is the axial wobble, a little bit of eccentricity won't matter on a 4 jaw chuck.

It is possible for the chuck jaws to become bell mouthed, through wear or abuse, this is common on 3 jaw chucks, but could well happen on a 4 jaw. Try chucking a length of silver steel with a long overhang. Clock it up true, check near the chuck and then further away. Then try pushing the end of the bar to one side and reclock. If the reading is different try pushing it again with chuck in a different position. If this changes the reading again, then you are effectively wobbling the bar in the jaws. If this is the case the jaws are probably bell mouthed, they can probably be trued up by grinding.

You may be best to turn the axles either between centres or use your collet with support from either a fixed steady or a tailstock centre. You said your not sure about you centres, so you need to check these and the alignment of the tailstock. Also don't assume the collet is true, check it.

Depending on the amount of run out you have:

Perfection whilst the aim is not absolutely necessary, I was reading some info on wheel standards and 1 thou per inch of diameter was considered exceptable, so bear this in mind.

It may be worth considering mounting the complete wheelset between centres and skimming the wheels to true them up.

I hope some of this helps and you get to the bottom of the problem.

One other thing which I hope you will take as a constructive comment and not a critisism of you work, is that your axles look a tiny bit short. in full size practice I believe the axles are flush with the face of the wheel or may even stick out slightly. If you are making new ones it may be worth bearing this in mind. I hope you accept this helpful, I don't wish to offend particularly as things are not going to well for you at the moment.

Best of luck with getting it sorted, please keep us updated, so that others can learn what can and does go wrong and what to look out for.

Trevor