Author Topic: Fabricating a Flywheel  (Read 9435 times)

Offline tinglett

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Re: Fabricating a Flywheel
« Reply #15 on: November 22, 2016, 06:16:05 PM »
The Center Disc

As I mentioned to Jo in my previous post, I didn't make a ton of progress on the flywheel this weekend, but I did manage to make the center disc blank.

I sawed a hunk off a 1/4" by 6" wide bar of CRS.  I was really wishing I had a 5" wide bar as my trusty bandsaw couldn't quite handle that width...so I had to flip it over to finish the cut.  Still, the saw saved tons of elbow grease.  I can't imagine doing this with a hacksaw!



I happened to have on hand a 5/16" mandrel I made for the flywheel for the pottymill horizontal engine so I drilled and reamed a 5/16" hole in the plate for the mandrel.  Reaming was a bit overkill, but I knew the mandrel was slightly undersized so I drilled 1/64th smaller and reamed under for just a bit of a better fit.   I need to re-make the mandrel to a higher quality as it did actually work pretty well.



Here it is with the mandrel installed.



To save a little lathe work I lopped off the corners with my bandsaw like this.  The mandrel was installed and helping to hold it, though the vise really was doing all the work.



Here's the ugly result :).  To save time at the lathe, I really should have setup the bandsaw table and sawed it a little closer to round than this.



Here was my setup.  This was a tough reach for my 7x12 lathe to handle.  In turning it down I was only able to take 10 thousandths cuts, tops, so it went slow.  Once I made progress I would back off the cross slide all the way and rotate the tool a bit more clockwise to try to get it at a better angle for the cuts.  It did cut ok without any real chatter...but it was slow going at 0.010 per pass.   Here you can see it's almost done except for a little flat that remains.



And here's the family shot.  Pretty small family at the moment.  You can see I penciled in the current diameter of 4.239...so it's oversize for now.



I'm thinking next I will cut out the spokes while it is a simple blank like this.  If I screw up there is little lost.  Of course that means I can screw up later as I try to insert this disc into the rim I made the other day.  Opportunities everywhere!

Todd

Offline tinglett

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Re: Fabricating a Flywheel
« Reply #16 on: December 08, 2016, 02:49:46 AM »
Machining The Spokes (part 1)

I finally made progress on this flywheel!  I knew the next step was going to be machining the spokes which will involve work at the rotary table, and this led to a couple side projects.  The net was that I created a plug for centering my RT.  Ok, it isn't a big deal, but it led me on a tangent to create a tailstock adjuster, etc.  I suppose I could post build-logs of those projects. But meanwhile, let's get back to the flywheel.

I centered the flywheel blank from the previous episode onto the RT which was already centered under the mill head.  I'm making a 5-spoke flywheel.  The web design of this one will have 3 holes in each web, which means a single, larger, hole near the hub (3/8") and two outer holes near the outer edge (3/16").  Here I finished drilling the five 3/8" inner holes spaced 72 degrees apart.  Easy work on the RT.



In the next photo you'll see I'm drilling the outer holes.  I used a china pencil to mark the approximate center lines of the spokes.  But from here on the photos will be a bit confusing because I'm going to make curved spokes rather than straight spokes.  I drew these lines mainly so I wouldn't get disoriented myself when I was returning the RT back to 0 again.  The actual curved spoke 1 curves clockwise to the right such that the upper edge of the inner hole that's between spoke 1 and 2 will curve around to the top of the outer hole you see in this picture.

I'm sure this is confusing as it is hard to describe, but hopefully the photos will show where I'm going by the end of this post!



In the next photo I've already gone around and drilled the leftmost hole from each web, and now I've drilled a rightmost hole.  If you look close you'll see this pair of holes defines the left/right sides of spoke 2.   So imagine the pair of inner holes defining the left/right sides of the inner part of the spoke, and the spoke swoops around clockwise to meet this outer pair.   Fun, huh?  And yeah, I was nervous that this was all wrong as I was drilling.  But what the heck...I can always make another blank :).



And now one more drilling step.  Here I'm drilling 1/4" index holes.  These holes are smack inside the web that will be cutout.   I need them for the curved spoke milling that I'm about to perform -- and I need the RT to sweep out that cut.  So I'm resorting to indexing on a fixture plate to position the flywheel for the 5 cuts.



The next photo shows the little fixture plate I created for this flywheel.  Note that I cleverly stamped A, B, C, and D (ok, my stamping skills need work).  Pin A is sized to fit the hub of the flywheel disc, and pin B fits the 1/4" index holes from the previous photo.  This means I can set the flywheel onto these two pins and it will be held in a specific position relative to C, D.  I'll be centering C and D on the RT so I can sweep out these curved cuts.

I need to point out that I stupidly drilled C and D for pins.  I realized after I placed the fixture plate on the RT for the first time that, duh, I really only needed to mark points for centering the plate.  Because these slightly overlap, you'll see that they got off a bit.  That's my drilling skills that need a bit of work, I guess.  So, note to self:  next time I do this I won't drill holes for C and D!



Here I am centering the plate onto position D.  Because I drilled these as holes, I used a 1/4" drill rod as my positioning tool.  If I had simply scribed a point, I could have used a center finder to do this instead.

The RT will be used to make a curved cut, so it doesn't matter what the orientation of the plate is around this center position.  However, I did find I had to experiment to find a good position for clamping.  You'll see that in upcoming photos.  I messed with clamps over the course of a few operations until I found positions that worked ok.



Here's a clear shot.  See where the flywheel is going to get positioned?


Now I'm getting nervous.  Did I get the holes right?  Did I do the math right?  I shifted the RT over in X so I'd get the radius I need to carve out (accounting for the 3/16" end mill I'm using).  It's looking ok so far.


Here's my first test cut.   You'll note it is very light as I was paranoid.   I learned three things.   First, the cut was looking pretty good.   I had backed up X by 10 thousandths so I could do a final pass, so it was expected to not be dead on.  Second, I had a lot of vibration until I remembered to use my Z lock (Doh!  Small mills).  And third, I was really nervous about poor clamping.  I decided one wasn't enough even though two pins are involved.


Sooo...off we go.  I found on my little mill I could do 30 thousandths per pass fairly comfortably.  In a few passes I had the first cut done.  I was only using the RT to swish out a cut, so I really wasn't looking at degrees at all.  It was really obvious where the cut start/stops.  I'd start in the big inner hole and mill to the outer where you can easily feel when you reach the outer hole -- even when it fills with swarf.



Now it was simply a matter of rotating the flywheel for the next cut.  Here you can see I removed clamps from the flywheel disc, I had lifted the flywheel off, rotated, and placed it back on the next index.  I just needed to clamp and make the next cut.


I went round and round, one spoke after the next.  I formed a little procedure.  I was running with 3 clamps.  The one shown in the back was always holding down the fixture.  While the third clamp was still holding the flywheel (this clamp is not shown here), I would move the second clamp from the flywheel to the fixture as you can see here.  Then I'd remove the third flywheel clamp.  Finally, when it was as in this photo, I could rotate the flywheel, put that third clamp back on, and then move that second clamp back onto the flywheel.  That's how I'd get two clamps onto the flywheel for the cuts.


Here's the last rough cut.   You can see how I have two clamps on the flywheel, and that first clamp always holds the fixture plate.  I decided two clamps were enough, so I didn't bother messing with the fixture plate clamp.


Here's a closeup of the final pass.  I should have done these on the first go-around as I had to re-clamp for each one, but I wasn't really sure how it was going to go.  So one thing at a time.  I was a little disappointed with the fit.  I had to extend the radius by about 15 thousandths and yet it was still a little off -- perhaps by close to 20 thousandths on the small hole side as you can see.  I measured the fixture plate with calipers across the pins and found that pin D was about 4 thousandths off in correct distance from the index pin, so I think my drilling of the pin holes C and D screwed it up a bit.  I also may not have gotten the plate centered as well as I should over the RT.  But I'll declare this cut is within filing distance.  Not too bad, and I'm fairly certain my math was right.


And finally, here's the plate with the first cuts all finished.


The next step is obviously to cut the other side of each spoke.  That'll use pin position C and a different radius, but otherwise it's pretty much the same work.  Hopefully it will come out similar in accuracy to this cut.  And then the flywheel disc gets centered on the RT one last time and I'll cut the outer arcs to remove the rest of the webs.

Todd

Offline Kim

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Re: Fabricating a Flywheel
« Reply #17 on: December 08, 2016, 08:02:55 AM »
Very neatly done Todd.  You're flywheel is turning out nicely.
Thanks for sharing all the detail.  Very instructive!
Kim
« Last Edit: December 09, 2016, 07:31:57 AM by Kim »

Offline tinglett

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Re: Fabricating a Flywheel
« Reply #18 on: December 08, 2016, 06:36:51 PM »
Thanks Kim!

As an aside, I did a little more math to cross-check my error.  As an experiment, I did the math if the outer hole were to be 0.150 diameter instead of 0.188 because this is sort-of where the curved cut landed (i.e., slightly inland of the tangent to the hole).  This calculation gave me a new position for pin D which moved 11 thousands in X.  Then I calculated the distance of the original pin D to pin B (the index pin) and also calculated the distance of the new pin D to pin B.  The calculated difference was only 2 thousandths.  When I measured my work, these pins were 4 thousandths off.  Wow...this pin D position error really gets magnified!

I believe this explains why it's off.  Rather than be uber-accurate positioning D, perhaps what I should do is center the mill on D, set the X table to the exact radius, and chuck a scribe (or similar) to check the position.  Then maybe hand-tweak the position until it's right.  The tweaked position should work for all 5 spokes.

Of course these are "just spokes" and accuracy doesn't matter, but eliminating elbow grease needed for hand filing the results sure would matter.  At least to me it would.  I don't mind "bonding" a little to the work, but there are some things in life worth avoiding, and I think filing is one of them if I can avoid it! :)

I'll try to do this when cutting the other side of the spoke from pin C and see how it works.

Todd

Offline Graham G

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Re: Fabricating a Flywheel
« Reply #19 on: December 09, 2016, 12:19:28 AM »
 :praise2: Hi Todd, Your math is way more accurate than mine  :ThumbsUp: But in saying that, how accurate does it have to be as I have worked on full sized flywheels that were cast with a " that's close enough"  theory behind it, they still seem to function ok.
Please don't get me wrong, I am simply saying, a scaled down small tolerance would not affect the final flywheel and what you are making is awesome. 
Cheers
Graham

Offline tinglett

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Re: Fabricating a Flywheel
« Reply #20 on: December 12, 2016, 03:44:38 AM »
Machining the Spokes (part 2 of 2)

It was time to machine the other side of the spokes this weekend.  I started by centering the RT, and centering pin C of my little fixture over the center.



I was concerned about the error from my previous spoke cutting so I was cross checking everything to see what I could do better.   The first thing I found was that my new automatic centering plug for my RT didn't really center it very well.  It was > 30 thou off!  I trued it up directly in the headstock of my lathe, but it still wasn't good enough.  It got me into the ballpark, but I've learned not to trust it.  Need to figure that out another day.  I suspect the head of my mill can't hold it rigid enough to stop the bolts from moving it as I snug it down.

Here's my first cut on the outer side of the spoke.



Even though I had two clamps pretty tight, I found the flywheel was moving.  Dang!  Perhaps my end mill was dulling, but I decided to make an RT (M2 taper) plug with a pin to hold the fixture plate in the center.  I figured it would be better than nothing, and it will still have clamps to help.  That worked really well.

This time I made two cuts before I'd advance to the next spoke (which involves unclamping, etc).  The first was 10 thousandths further away.   That saved a lot of time, and the finish of the last pass was worth doing, I think.  Saves on some filing.  You can see that the spoke cut didn't land on the inner hole perfectly.  I decided to leave this as-is because the spokes seem a little thin already, and I was thinking that spot would be easy to file to fix it.



Here I've got the clamps off and am getting ready for the last spoke curved cut.   I got a little more cavalier about removing clamps because a plug with pin is holding the fixture plate from sliding around.



Here's the flywheel both both sides of the spoke cut.  Now I need to trim along the outer radius to finish removing the web.  Before doing that, I thought for a moment about putting a radius on the spokes.   Unfortunately my small radius end mills have a 1/4" head, so this would have been practical if I had thought ahead about that.  I did test one theory, and that was that the fixture plate can be flipped upside down, and the flywheel placed on it upside down.  You really can trace the same arcs on the other side for stuff like this.  It seemed intuitive, but thought I'd verify it.



Here I'm centering the flywheel on the RT which is already centered under the mill.



Now I can finally trim out the web.  Note that this cut goes right through the index holes that I used to index the fixture plate for the spoke cuts.  This is the point of no return -- once these webs are cut out, I can't put the flywheel on the fixture again.



Despite my clamping, I found the flywheel moving a bit so I solved the problem by inserting my RT plug as I did with the fixture plate.  I had to make a little bushing to match the hole in the flywheel...but it worked really well.  In the end I used 3 clamps instead of the 2 as shown here.



Around and around I went.  Here you can see I was using washers to shim it away from my RT.  I did that between the flywheel and the fixture plate and don't recall if I mentioned it.



And here are some photos of the cut flywheel disc.  It'll need some filing, but all in all it came out pretty good.  Maybe I should have pushed out the inner holes, or made them smaller, in order to have heavier spokes.







Next I'll have to do a bit of filing to clean this up.  Then I plan to fit some kind of hub (press or threads?), and finally fit it to the rim that started this build log.

Todd

Offline Kim

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Re: Fabricating a Flywheel
« Reply #21 on: December 12, 2016, 02:28:27 AM »
Another fascinating post, Todd!

I'm no expert, but those spokes look great to me!  Seems like I've seen curved spoke flywheels with very thin spokes.  You'res don't look too small to me at all. You should be feeling pretty good about this!

Kim

Offline Roger B

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Re: Fabricating a Flywheel
« Reply #22 on: December 12, 2016, 01:33:59 PM »
Nicely done  :ThumbsUp:  :ThumbsUp:
Best regards

Roger

Offline tinglett

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Re: Fabricating a Flywheel
« Reply #23 on: December 20, 2016, 05:15:23 PM »
The Flywheel Gets A Hub


I'm still here and finally have some real time in the shop.  Here the flywheel gets a hub.  I decided early on that I wasn't going to create a ton of swarf out of thick steel, so I'd add the hub later.  Now the question was to make and loctite threads, or to press it together.  I decided that a press fit should do the trick.

But first I thought it best to do the filing and cleanup before things like hubs and rims get in the way.  For the little rough work I had to do, I setup the mill with a little grinding wheel from a dremel.  I used the rim as a support and freehanded it.  Doing this didn't feel like flirting with disaster, but maybe it was.



I noticed the grinding was a bit uneven so I trued up the little grinding wheel like this.  I used Y to align it best I could to center on the wheel, used X to just barely touch it, and used Z to true it up.  I should have setup on the other size of X, though, so it would spew bits toward the wall rather than at me.  Lesson learned...but I barely skimmed anything off.  I found it really did need to be cleaned up.  The wheel had a larger diameter on the bottom than top.



I got creative with a vise and setup to file.  I decided I wouldn't fix every last flaw, but I wanted most of them gone.    It came out pretty good. 



Time for the hub.  This flywheel goes on an engine that calls for a 1/4 inch shaft, so I drilled/reamed the flywheel out to 3/8 inch.  I used a rod to align the flywheel while I clamped it.



I decided the hub would be 5/8 inch, so I turned some 5/8 cold rolled steel down until the flywheel was a tight fit (but would still come off).  I had more length to turn down that would be a press fit.  I realized here that I didn't have enough rod extending from the chuck.  Oh well, I'd have to move it.



Before turning the rod in the previous photo, I had drilled/reamed a bushing to 3/8 inch (matching the flywheel) from the same rod.  Here you can see I'm test fitting that bushing.  I reamed it under so it was a bit tighter.  Here I'm testing that a 1 thousandths trim off the end allows it to fit.  I left the rest at the +1 thousandth size.



I didn't take a photo of turning down the rest of the length.  I tested with a mic to make sure the newly turned section was +1 thousandth over the part I had already turned.  I parted off the rod and pressed it together.  I think in the end it may have been +2 thousands because it was really hard to press.   But it worked!  I don't think it's going anywhere.



Then I faced it off both sides.



I was a little disappointed that this side didn't quite press all the way in.  I didn't post the photo of cleaning up the shoulder of the hub, but perhaps I should have undercut it a little, or cut a bit extra deep to give a place for the pressed metal to go.



Finally, the flywheel moved to the 4-jaw.  I ended up dialing it in on the outer diameter of the flywheel rather than on the new hub I put in.  They were about 5 thousandths off from each other.   I drilled and reamed over for the 1/4 inch shaft it will ride on.



Next up, I need to make some kind of mandrel for truing it up, and I need to fit this inner web into the rim that started this thread.

Todd

Offline Jo

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Re: Fabricating a Flywheel
« Reply #24 on: December 20, 2016, 05:44:24 PM »
Good progress Todd  :ThumbsUp:,

I like the look of using that stone in the mill looks more controlled than in the Dremel. I have a few sanding drums kicking around (since I found that 100s of them can be brought for very little from china  ) that may be a good way of using them too :).

Jo
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Offline Bertie_Bassett

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Re: Fabricating a Flywheel
« Reply #25 on: December 20, 2016, 06:34:13 PM »
that's going to be a fine looking flywheel, thanks for sharing your build progress
one day ill finish a project before starting another!
suffolk - uk

Offline tinglett

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Re: Fabricating a Flywheel
« Reply #26 on: December 21, 2016, 12:43:10 AM »
Fitting the Web Into the Rim
(or, uh ho, Todd ran into trouble :o)


Well, more progress, but not so good progress.  Sigh.

I decided to turn a little recess in the rim to help align the web when I drop it in.  I took off about 15 thousandths and used a dial indicator as a bit of a hack depth gauge so that the rim will drop in approximately centered in the rim.  The rim is a bit oversize in width but I'll turn off the excess when I true it all up at the end.  That clamp goes down to the bottom of the lathe casting.  I need to get one of those magnetic holders for situations like this.



Here's what it looked like.  Hmm...maybe it was more like 20 or 25 thousandths.



Before going further I decided now was a good time to drill/tap for a setscrew.  If I do it later with a rim I'll have to work a tricky angle.  This was tricky enough -- the drill barely reached and I had to work the tap with pliers.  But I got it.



Next I turned up a mandrel in the 4-jaw.  I guess I didn't really need the 4-jaw.  The idea from here on is that I'd turn this mandrel down to 1/4 inch for a very snug fit on the flywheel, I'd thread it and also file a flat for the setscrew, and I'd never remove it from the lathe until all the truing up work is done.  Then for sure everything will be concentric.  The flat hasn't been filed yet in this photo.



Here the flywheel is on and I'm turning it down until about 4 thousandths oversize for the rim recess I just made.  I was measuring with calipers, but readings were coming out consistent so I thought I'd be close.   By the way, I did check it with a dial indicator and the assembly was only off by 2 thousandths.  I was pretty happy about that, but from here on I'm not going to remove the mandrel so I hope it'll stay fairly true.  I was cutting from left to right and the finish was pretty good.



Now I'm getting nervous.  I'm going for a shrink fit so here's my gear for heating up the rim.  I put some spacer blocks inside the rim just in case the little recess didn't work.  I was wishing I had a couple more firebricks as I was just using a regular propane torch to cook it up.  I had some wood blocks handy to drop it on and give it a whack or two if necessary (trying to remember not to do this on the delicate firebricks!).  You'll note I also put a little shaft in the hub of the flywheel and used the setscrew to hold it.  That'll give me a handle.



Even though it was -10F outside, I didn't bother freezing the web.  I figure if I'm going to expand the rim with hundreds of degrees F, the difference of less than 100 by doing this wouldn't change things much.   So I started heating it and kept the flame moving around the rim to try to get it as evenly hot as I could.

At some point the steel started changing color slightly.  It just so happens that I've been browsing a 1912 book "Elements of Machine Work" by Robert H. Smith and I recall reading this.  It goes to a straw color (and it did!) and then starts turning blue and purple.  As the whole rim turned dark straw color and just as it started turning blue I decided now was the time.  Looking it up after the fact, this tells me the rim was more than 430F (221C) and under 630F (332C).

SLUMP!  In it went.  That was SO cool!   It was 4 thousandths over before and there was no way it was going in, but now it did.  I was pumped.



Ah, but my excitement didn't last.  Looking closer, here's what I got.  One side of the web rested nicely on the shelf made by the recess, but the other side still had about 1/4 inch to go.  Drat!  And there was no way it was going to budge.  It's rock solid.



Here's my pathetic flywheel in the lathe.  It looks a little sick.   :facepalm:



Well, maybe I should have heated up to dull red which was my original plan.  Or maybe I should have checked to see if it was really 4 thousandths over.  Or maybe I should have cut the spokes out later so the web would have more bulk and therefore expand a little more slowly.  But there it is.  Wobble city motors.

Ok, but wait!  I realize that the rim is way oversize in width.  I can easily turn away the sides to true it up, though that's going to be a nasty intermittent cut for my little 7x12 lathe.  Still, I'm not going to toss this flywheel without trying.  I'm a little worried how thin the rim will get with I true it up inside and out, but I suppose worst case I could turn the whole dang rim off and try a second time.

Todd
(Thinking positive thoughts, thinking positive, thinking....   Wait, I'd better go turn this thing.)

Offline 10KPete

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Re: Fabricating a Flywheel
« Reply #27 on: December 20, 2016, 10:52:10 PM »
Don't panic!! Just heat the rim again and tap the center down in...

Pete
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Retired, finally!
SB 10K lathe, Benchmaster mill. And stuff.

Offline Jo

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Re: Fabricating a Flywheel
« Reply #28 on: December 21, 2016, 10:55:49 AM »
Todd, As Pete says another heat should sort it - Try putting the whole thing in the kitchen oven at the highest temperature for 20 mins. Then take it out and it should go down on its own or with a little tap.

You may also consider taking the centre fully out before you push it down on its register  ;)

Jo
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Offline Zephyrin

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Re: Fabricating a Flywheel
« Reply #29 on: December 21, 2016, 01:01:34 PM »
You need a piece of tube to push in place the spoked part by its rim and press it with a press or a vice. a good heating would help.
But you may better use this tube to remove first the inner part and start again. good luck ...nothing irreparable up to now !