Holding a Workpiece in a Lathe

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Further to my thread about excessive belt-belt spacing between a pair of crankshaft pulleys, just over 3mm wider than the twin alternator pulley.
Pulley-3580881_zpschsqeab6.png~original


I made the boss to fit each side of the pulley: one with a groove, one with a ridge. This clamps in my lathe chuck, and the pulley bolts onto the respective face.

So, if you are bolting this to an ally bung, or using a bolt and washer through the middle, how do you propose to machine both faces accurately to each other? At some point you will need to remove the bolts, find another clamping method and perform a second operation.

Having reduced the outer part of mating outer faces by a total of about 3mm, I'm in the position suggested above.

I planned to do one of these:
(1) glue it to the boss with cyanoacrylate glue. I'm sure I've read this works, but worried about release.
(2) countersink the bolt holes and use countersunk M8 screws.
(3) make a smaller boss that just covers the hole and hold it with the tailstock, or a center screw. Remove ridge by hand.

Thoughts?
 
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Further to my thread about excessive belt-belt spacing between a pair of crankshaft pulleys, just over 3mm wider than the twin alternator pulley.
Pulley-3580881_zpschsqeab6.png~original


I made the boss to fit each side of the pulley: one with a groove, one with a ridge. This clamps in my lathe chuck, and the pulley bolts onto the respective face.



Having reduced the outer part of mating outer faces by a total of about 3mm, I'm in the position suggested above.

I planned to do one of these:
(1) glue it to the boss with cyanoacrylate glue. I'm sure I've read this works, but worried about release.
(2) countersink the bolt holes and use countersunk M8 screws.
(3) make a smaller boss that just covers the hole and hold it with the tailstock, or a center screw. Remove ridge by hand.

Thoughts?

Yes that's as complicated as hell I hav'nt got the foggiest idea what you are going on about. What exactly is it that you are trying to do?
 

DownWest

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My four jaw would hold it on the outer edge, leaving the face clear to machine out to the jaws. Rather than risk touching the jaws, I would leave a tiny ridge to file off by hand.
 

prof pat pending

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How's the bore in the middle of the pulley?

if it's reasonable, here's what you do :)


Get a large countersink bolt. As large as you can find, as long as the head is smaller than your bore.
Turn a boss on your lump of ally that is a snug fit in the bore.
Drill, tap and countersink the boss to suit the countersink bolt.
without removing the ally from you chuck, hacksaw two slots through the middle of the boss at 90 degrees to each other.
Place the pulley on the boss, fit the bolt and do it up.
Your pulley is now clamped on the bore and you can machine all of the faces together.

Remember that you might need to machine the ring to match the depth of the groove ;)

hope this helps :)
 
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Machine a boss that's an interference fit in the pulley hole, then freeze the boss and heat the pulley up, fit boss to pulley and allow to cool.
 

PuffTheMagicDragon

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I'm not sure that I understand what it is that you are trying to do but can't you just invert the jaws and grip the pulley halves from the bore?
 

DinghyMan

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My four jaw would hold it on the outer edge, leaving the face clear to machine out to the jaws. Rather than risk touching the jaws, I would leave a tiny ridge to file off by hand.

Just mount the workpiece further forward gripping on the outer edge and machine in one go.

If you are not used to mounting workpieces this way just use an adjustable spider behind it. See http://bbs.homeshopmachinist.net/threads/24007-Chuck-spider-(pic)

If your lathe isn't big enough, either buy a bigger one or get some soft jaws and make some jaw extensions.

Super glue works very well for holding items on a lathe, do a search for clock makers and you will see it used a good bit, just add a bit of heat to break the bond but do the heat bit outside as the fumes are poisonous. Clickspring on Youtube uses it in quite a few of his projects
 

Daydreamer

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This really should be a straightforward lathe task but it does need a little bit of planning.
So, two questions:
do you not have reverse jaws for your chuck and if not, do you have a faceplate?
 

rogerthebodger

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This is how I have done similar jobs in the past.

If I could not hold the pulley with the internal jaws of my chuck I would make and internal collet by machining a spigot to be a close fit on the internal dia with a face to square up the pulley. I would the drill and tap a BSP hole in the center size about 1/2 the spigot dia. I would the cut 2 slots in and X too allow the spigot to open up and tighten onto the inside dia of the pulley. This is done by screwing a tapered plug into the BSP tapped hole. then machine the face. If you machine onto the spigot no problem as its a once off tool.
 

Heckler

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This really should be a straightforward lathe task but it does need a little bit of planning.
So, two questions:
do you not have reverse jaws for your chuck and if not, do you have a faceplate?
All the lathes I have used, you could reverse the jaws.
S
 
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