Author Topic: FLYWHEEL WOBBLE  (Read 3819 times)

Offline Davis2x1

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FLYWHEEL WOBBLE
« on: September 09, 2015, 07:39:41 PM »
Finished my "coke bottle" engine but I have a little flywheel wobble. I would like to true up the OD but I need a suggestion for making a mandrel to hold it. 5/16 ID.

Thanks, Dave
Dave
Sherline Mill and Lathe

Offline Bearcar1

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Re: FLYWHEEL WOBBLE
« Reply #1 on: September 09, 2015, 10:24:32 PM »
Hello Dave, glad to hear that you completed your engine, which I assume is the PM Research set of castings? Anyway, can you determine if it is the rim that is out of true or that the central hole has been drilled 'not straight'. The reason that I say this is that if the rime appears to be of equal thickness in the rim all around and the hub is the same, then that would indicate to me that the hole is not straight. If it is not, and you merely turn the diameter and sides square to the hole, sure, it will eliminate the wobble but it will not look right when standing stationary. If the central hole is the culprit, then may I suggest that it be plugged and the flywheel be remounted and carefully centered in the lathes jaws and the hole be redrilled/bored. Use a center drill first and then use a series of smaller drills to open out the hole and use a reamer to take it to final size. To answer your original question, a bit of steel bar gripped in the lathe chuck can be used by turning down a spigot that is an exact fit to the hole in your flywheel. A hole that has been drilled and tapped in the end of the spigot, using a suitable fastener and a small flat washer can be utilized to hold the flywheel on the spigot while very light cuts are made. MAy I suggest that you drill and tap that hole BEFORE you turn down the spigot and do so with the fastener screwed in. This will lessen the chance that doing so after the fact will distort and or increase the OD that was achieved to fit into the flywheel. I hope that this makes some sense and I will be more than happy to clarify with a CoC drawing if need be. But first, you need to make sure which part of the part is the cause of the runout, The hole, or the rim.


Best of luck,
regards
BC1
Jim

Offline mklotz

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Re: FLYWHEEL WOBBLE
« Reply #2 on: September 09, 2015, 11:28:21 PM »
I have to agree with Jim.  Your first job is to determine the cause of the wobble.

Tell us how the flywhel is attached to the crankshaft.  If setscrews are used, they, in concert with a less than perfect match of flywheel hole to crank OD, can be a source of wobble.  There's a reason why the experts mount flywheels with draw-in collets.

A bit more informaton will really help to elicit some good advice.
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Offline b.lindsey

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Re: FLYWHEEL WOBBLE
« Reply #3 on: September 09, 2015, 11:59:47 PM »
All good advice Dave and most of us have had to deal with wobble at some point. Only thing I would add is that a mandrel of only 5/16" diameter can give rise to some chatter when machining things square. As Jim said, light cuts are in order if the rims are the culprit. Don't make things worse by adding chatter marks.

Bill

Offline rmw

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Re: FLYWHEEL WOBBLE
« Reply #4 on: September 10, 2015, 02:50:27 PM »
I  am certainly no expert, but I stopped having that trouble when I started using a boring bar to bring the hole to reamer size.  It seems drills don't find their way dead straight, but proper boring does.
Greg

Offline GWRdriver

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Re: FLYWHEEL WOBBLE
« Reply #5 on: September 10, 2015, 05:32:53 PM »
Dave,
I probably don't now need to tell you this but drilling and boring are two different operations with two different outcomes.  There are times in model engineering when drilling just won't do.  For disks, like flywheels, drilling is little more than a roughing operation.  You NEVER drill a flywheel bore as a final operation - it will never run true, except by the pure luck.  As said by Marv, even if it's bored if the bore is too loose a fit to the crankshaft, and affixing device (ie, setscrews, keys, etc) will pull the wheel off center.  When turning a flywheel you bore it (on a faceplate perhaps) to a very close fit to the crankshaft.  What "close" is depends upon the crankshaft diameter.  For a 1/2" diam crankshaft I would shoot for diameter+.0005" fit.  Hopefully your crankshaft OD is straight, you should check that it doesn't have a taper.

If I have found myself in the position where the remedy is actually a salvage operation.  I would mount the F'wheel on a faceplace, indicate the rim true (concentric) and bore out the hub by not more than 1/16" on the ID (1/8" total.)  Bearcar1 refers to sleeving in his post.  I would then turn a steel sleeve to a press or Loctite fit this bore.  Once that's done remount the wheel and rebore the sleeve to fit your crankshaft.  Face the sleeve off and it will virtually disappear.

The thing is, problems like this (wobble) are usually due to accumulated error and every time you say "that'll do" or "that's good enough" you may be adding to the accumulated error.  If you say drilling is "quicker and should do OK", then you're toast right there.  Often to correct the problem you have to go back a few steps and "correct a problem to correct a problem."
« Last Edit: September 10, 2015, 05:40:04 PM by GWRdriver »
Cheers,
Harry

Offline Davis2x1

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Re: FLYWHEEL WOBBLE
« Reply #6 on: September 10, 2015, 07:36:41 PM »
Jim: I was thinking about making an arbor (spigot) to true up the OD. But after indicating the OD +- .001" and the bore +- .010" I decided to go the way of plugging and re-boring as the problem is with the bore.

Marv: You indicated using a draw-in collet. Is this the same as a "taper lock" hub. If so I tried, but can not find one small enough, i.e. 5/16 OD shaft. Make my own??

I appreciate the other comments and have learned my lesson on drilling, reaming(don't have any) and boring. When I first worked on the bore I did drill it out 1/8" dia. The problem was that rather than going step by step, I tried to bore out the hole with an 5/16" end mill. There was chatter and the mill tried to climb to one side creating an off center, oblong hole. Subsequent bores were made by stepping up a little at a time. As I stated in the engine showcase, this was my first attempt at model building.

I did find a small boring bar in with the tool bits and it worked fine to clean-up and center the hole. Now on to the bushing.

Thanks for the help, Dave
Dave
Sherline Mill and Lathe

Offline mklotz

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Re: FLYWHEEL WOBBLE
« Reply #7 on: September 10, 2015, 09:03:20 PM »
Marv: You indicated using a draw-in collet. Is this the same as a "taper lock" hub. If so I tried, but can not find one small enough, i.e. 5/16 OD shaft. Make my own??

Yes, they're the same thing, at least in my muddled mind.  Most of us make our own.

As I advised the Zeester in the dim past, scratch this litany on the inside of your safety glasses lens...

Drills are bulk stock removal tools.
Bore to make the hole straight.
Ream to bring the hole to size.
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Offline fumopuc

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Re: FLYWHEEL WOBBLE
« Reply #8 on: September 11, 2015, 06:03:21 AM »
Hi Dave, I know that this is an European source, but may be there is something similar available on your side of the pound also.
http://www.conrad.de/ce/de/product/1000866/SIT-LOCK-CAL-3-Spannsatz-CAL3-815-Innen-Durchmesser-8-mm-Aussen-Durchmesser-15-mm?queryFromSuggest=true
Kind Regards
Achim

Offline Robert Hornby

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Re: FLYWHEEL WOBBLE
« Reply #9 on: September 11, 2015, 08:27:34 AM »
Merv,
Why is reaming preferred over boring?
Age and treachery will always overcome youth and skill

Offline Dan Rowe

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Re: FLYWHEEL WOBBLE
« Reply #10 on: September 11, 2015, 12:33:55 PM »
Reaming is quicker and gives a very nice finish, a good way to go if you have reamers on hand...we never had fancy tooling on the ships I worked.

Cheers Dan
ShaylocoDan

Offline Roger B

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Re: FLYWHEEL WOBBLE
« Reply #11 on: September 21, 2015, 11:57:33 AM »
This thread shows how I made a taper collet for a 125mm flywheel on a 12mm shaft. I used a similar technique for a 50mm flywheel on an 8mm shaft but only used 4 holes instead of 6.

http://www.modelenginemaker.com/index.php/topic,2821.15.html

Best regards

Roger

Offline Davis2x1

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Re: FLYWHEEL WOBBLE
« Reply #12 on: September 24, 2015, 09:57:21 PM »
Roger,

Thank for the link for the taper hubs. I'll try to make one as a trial unit.

BTW I plugged my flywheel and did a re-bore with a small boring tool I cut down. It worked out well and I now have a concentric bore.

Thanks for your help.  Dave
Dave
Sherline Mill and Lathe