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Old 02-06-2013, 03:41 PM   #1
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Default Good method for turning flywheel?

I recently read a thread on one of the machining websites about a method for turning a flywheel that I am unsure about. it just doesn't seem to be a safe way of doing it, so I would like some input on whether or not it is a legitimate method.

The machinest said he cuts a square piece of aluminum plate (his was 2 inches square) and then he center punches it. He then puts gaffers tape on the chuck jaws and adjusts them in to make them close together. He then presses the piece of plate between the jaws and the tailstock with a live center in it. The plate is held only by the pressure of the live center in the center punch hole pressing against the chuck.

Is this a safe way to hold the piece for machining? It seems to me that a square piece of plate banging against the tool as it spins would put a LOT of pressure on the piece and would knock it out of the pinched-in position. I would cut the ends off the square piece first to make it closer to the rounded disk it will become so there wouldn't be so much pounding on the tool, but I still am nervous about this method of holding the stock for turning.

Is this pinched-in process a legitimate way to do this? Thoughts?

Jeff



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Old 02-06-2013, 04:28 PM   #2
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As you described it sounds like an accident waiting to happen. Of course it depends on size and material for starters, cast vs cut surface, but not a solid method in my opinion.

If that was the kind of thing you wanted to do, I'd drill a center hole on each side of the hub, and place a center in the spindle or chuck and another in the TS, make up a bolt to drive with the chuck and away you go.

On an 8" CI flywheel with spokes, I grabbed it with outside jaws and shimmed the runout both axially and radially to 1/2 of the measured amount, and cut the face and OD to clean. Then with a concentric OD recenter so as the hub can be made round, then remachine the OD to be concentric with the hub.

Since there was a greater amount of stock that could be removed from the OD vs the hub, it makes sense to center to the hub, then the OD in this case.



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Old 02-06-2013, 05:43 PM   #3
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If that was the kind of thing you wanted to do, I'd drill a center hole on each side of the hub, and place a center in the spindle or chuck and another in the TS, make up a bolt to drive with the chuck and away you go.

How would you make up a bolt to drive with the chuck? I get what you are saying about having a center in both the chuck and TS, but how do you get the bolt setup to drive the piece?

Jeff

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Old 02-06-2013, 05:51 PM   #4
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That's Bogstandard's method, and it works well. Cuts have to be light on the perimeter until you get fairly close to round, as the interrupted cuts can tear it lose.
If you prefer, you can take the corners off with the saw, to get closer to round, but even that isn't necessary.

I have used this method several times. No problems at all.

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Old 02-06-2013, 06:08 PM   #5
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Originally Posted by rleete View Post
That's Bogstandard's method, and it works well. Cuts have to be light on the perimeter until you get fairly close to round, as the interrupted cuts can tear it lose.
If you prefer, you can take the corners off with the saw, to get closer to round, but even that isn't necessary.

I have used this method several times. No problems at all.
>
Thank you for that response! It just seemed to me that not much would be holding the piece when turning it. Do you tighten up the tailstock as tight as you can get it? Also, is it better to center drill the piece for the live center, or just punch it? If center drilled it would at least offer some addtional depth for the live center. Can you tell I'm a bit nervous?
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Old 02-06-2013, 06:15 PM   #6
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Quote:
Is this a safe way to hold the piece for machining? It seems to me that a square piece of plate banging against the tool as it spins would put a LOT of pressure on the piece and would knock it out of the pinched-in position. I would cut the ends off the square piece first to make it closer to the rounded disk it will become so there wouldn't be so much pounding on the tool, but I still am nervous about this method of holding the stock for turning.

Is this pinched-in process a legitimate way to do this? Thoughts?

I have used this method and it works fine . Do not remember when or where i learned it but had to be in a USAF shop may have figured it out on my own not sure. I do agree I would not start with a square on the lathe either. I rough cut the circle on the band saw first leave the layout line line . or as you say start with a hexagon not a square.
You need to take light cuts . position the hand wheel on the tail stock at 1 or two o'clock looking from the tail stock end of the lathe this will keep the TS tight. Do not over tighten this will put unneeded force on the main bearings and LS bearings.
I have had the tool dig in and the part spin when using this method just remount the part if you used tape. I often just have a piece of rubber glued to a temp plate held in the chuck. no need to be nervous . I have used this method at least a half dozen times and never had apart fly off the lathe.

I have said before do not try a setup you are not sure of so you are right to ask my friend.
As far as center drill vs center punch I have done both. Do not remember a huge difference. but if doing a flywheel and needing to drill for a shaft hole later anyway go for the center drill.


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Old 02-06-2013, 06:24 PM   #7
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Likely it was my post you saw. There are a couple of ways to go about it. I generally make very light cuts like .005" and have no issues. Center drill method would give you a little more "margin" for error. Also possible to drill under sized like .125" and put some round rod in the chuck but leave enough room for the live center to not hit it. I have cut away the corners on the bandsaw before but not everyone has one in the shop and my post was intended for a minimal shop. Do it the way you are most comfortable with for safety.

Always good to ask when you are not sure.

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Old 02-06-2013, 06:25 PM   #8
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Once again you folks have been great! Thank you everyone for the help! I'm desperately trying not to hurt myself and everyone's input is VERY much appreciated!

Jeff

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Old 02-06-2013, 06:36 PM   #9
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have no issues. Center drill method would give you a little more "margin" for error. Also possible to drill under sized like .125" and put some round rod in the chuck but leave enough room for the live center to not hit it. I have cut

I like the idea of using a rod in the chuck to help make sure it doesn't let loose on me. So you are saying I could drill a short way into the back side of the piece and then mount that over a short rod in the chuck and I would be OK as long as the center drill from the other side didn't go through to the rod. It esssentially would then be almost the same as truing between centers.

Just BTW, if you handle is an indication that you own a vette, I'm part of that club too!

Jeff

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Old 02-06-2013, 09:07 PM   #10
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Quote:
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I like the idea of using a rod in the chuck to help make sure it doesn't let loose on me. So you are saying I could drill a short way into the back side of the piece and then mount that over a short rod in the chuck and I would be OK as long as the center drill from the other side didn't go through to the rod. It esssentially would then be almost the same as truing between centers.

Just BTW, if you handle is an indication that you own a vette, I'm part of that club too!

Jeff
You can drill all the way through the flywheel. Just keep the rod from going all the way through.

Yes, my username is accurate. I have a Black 1985 Vette. It is what got me started with learning to do machine work. Took a machine shop class so I could make some modified brake mounts to put some heavy duty brakes up front. Then I discovered that small steam engines were a perfect way to improve my skills. Fairly low cost, not too large, and require some reasonable accuracy.


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