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crank it!
- Thread starter joegamma1
- Start date
I don't have any real measurements yet, the question has just been rattling around in my head.
I would probably have to stay slightly larger than my dead/live centers radially as well as shorter than each horizontally, if my thinking is in the ballpark.
I would probably have to stay slightly larger than my dead/live centers radially as well as shorter than each horizontally, if my thinking is in the ballpark.
- Joined
- Jul 29, 2011
- Messages
- 207
Put one end in your 4 jaw chuck the other in the tailstock. Offset the tailstock and the four jaw by the amount of the crank offset. Make sure the crank is oriented as desired (so it's not turning elliptically) and turn at a slow speed as everything is out of balance.
To put it in perspective imagine turning a one piece crank for an 8 cylinder engine And please take pics of the process for others.
Good luck it's not impossible just a bit difficult. Take your time with the setup as well as turning it.
Maybe someone else can give more detailed instructions ??
To put it in perspective imagine turning a one piece crank for an 8 cylinder engine And please take pics of the process for others.
Good luck it's not impossible just a bit difficult. Take your time with the setup as well as turning it.
Maybe someone else can give more detailed instructions ??
- Joined
- Jan 22, 2011
- Messages
- 8,016
Offsetting the ts will not yield a crank, but a taper.
Make sure your bar stock is large enough to accommodate the part. Turn the journals on both ends, true with each other. Leave a center section large enough to take care of the throw. Now make some tooling. Take a piece of round stock and bore a close fitting hole to slip up on your end journals. Bore this hole offset by the throw you want. You'll want to true up the od and faces. Make it long enough to saw in two, one for each end. Drill and tap some set screw holes to clamp on the end journals. They should be oversized by .100 or so for finishing, btw. Before you saw it in half, mill a flat along the side to give yourself something to indicate on to make sure your timing is right between the two pieces. One of the pieces should have a center drilled hole true the OD. If the throw versus the journal diameter gives an interference problem, make the journal hole shallow enough to leave drilling stock on one end of your tooling. These are called "catheads" in some circles.
Now when you have these two pieces clamped onto the journals, in time with each other, simply chuck and tailstock the fixture and the "lump" you left in the middle when you turned the journals will be running out by the throw amount. Turn this away and you have the crank journal. Go back and finish the end journals after you turn the crank (offset) journal.
There are other ways, but I find that way most interesting. Sort of hard to describe, but it does work.
Make sure your bar stock is large enough to accommodate the part. Turn the journals on both ends, true with each other. Leave a center section large enough to take care of the throw. Now make some tooling. Take a piece of round stock and bore a close fitting hole to slip up on your end journals. Bore this hole offset by the throw you want. You'll want to true up the od and faces. Make it long enough to saw in two, one for each end. Drill and tap some set screw holes to clamp on the end journals. They should be oversized by .100 or so for finishing, btw. Before you saw it in half, mill a flat along the side to give yourself something to indicate on to make sure your timing is right between the two pieces. One of the pieces should have a center drilled hole true the OD. If the throw versus the journal diameter gives an interference problem, make the journal hole shallow enough to leave drilling stock on one end of your tooling. These are called "catheads" in some circles.
Now when you have these two pieces clamped onto the journals, in time with each other, simply chuck and tailstock the fixture and the "lump" you left in the middle when you turned the journals will be running out by the throw amount. Turn this away and you have the crank journal. Go back and finish the end journals after you turn the crank (offset) journal.
There are other ways, but I find that way most interesting. Sort of hard to describe, but it does work.
- Joined
- Jan 22, 2011
- Messages
- 8,016
Right, Chris. A real crank grinder has an adjustable throw faceplate on the "tailstock" end of things. Then the throw is dialed in to match the headstock end.
- Joined
- Jan 26, 2011
- Messages
- 632
Copy and paste this to google it is a video of a guy machining a crank for a moped on a lathe. [video=youtube;taMV8CcszbE] www.youtube.com/watch?v=taMV8CcszbE [/video]
enjoy,
Paul
enjoy,
Paul
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