Author Topic: turning between offset centres  (Read 1122 times)

Offline Ratchap

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turning between offset centres
« on: January 06, 2019, 11:02:50 AM »
morning all  I have come accross an article on making a 2 cylinder steam engine with  a rotary valve that uses  no castings.I have no idea where it came from  its just called RoataryValveEngine.PDF. I plan on having a go at it
but to make the crankshaft it says the cranks is made  from 1 " dia 4 inch long cold rolled steel that is mounted in one pair of off set centres could some one please point me to  how this is done

happy new year all Nigel
what do you mean it wont fit  Get a bigger hammer

Offline Florian Eberhard

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Re: turning between offset centres
« Reply #1 on: January 06, 2019, 11:15:27 AM »
Hey Nigel

The "offset centres" refers to the center holes which are drilled off center. (but the same amount on each end of the bar). So if you take these center holes between centres on your lathe, you can machine the crankpin since those offset center holes are drillet to be the center of the crankpin.

Now there are different approaches on how to machine a crankshaft from barstock and as one piece - but I guess this can be found in the forum. (for example have a look at a building thread of Geroge (gbritnell)

Florian

Offline fumopuc

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Re: turning between offset centres
« Reply #2 on: January 06, 2019, 12:02:18 PM »
Hi Nigel,
may be this will help you to imagine the process.
http://www.modelenginemaker.com/index.php/topic,7395.msg173109.html#msg173109

Kind Regards
Achim

Offline Ratchap

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Re: turning between offset centres
« Reply #3 on: January 06, 2019, 12:45:16 PM »
many thanks guys  it now makes  sense  i need a lathe dog and drive plate
I knew some one would come through  with the way to  do it

Nigel
what do you mean it wont fit  Get a bigger hammer

Offline chucketn

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Re: turning between offset centres
« Reply #4 on: January 06, 2019, 01:07:33 PM »

Online steamer

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Re: turning between offset centres
« Reply #5 on: January 06, 2019, 02:39:34 PM »
many thanks guys  it now makes  sense  i need a lathe dog and drive plate
I knew some one would come through  with the way to  do it

Nigel

Hey Nigel, there are many ways to set up on centers.    The center could be a piece of stock held in a chuck with the 60 point turned "insitu".   To drive the piece you could use a bolt sticking out from the end of the part bearing on one of the chuck jaws.  My point being, before you spend money on tooling, talk to us and maybe we can get come up with a set up based on what you have.

What lathe do you have?

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Online steamer

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Re: turning between offset centres
« Reply #6 on: January 06, 2019, 03:40:01 PM »
Heres a double throw crank between centers on my lathe   Notice the use of the 3 jaw chuck with a piece of stock turned "Insitu" for the center.

Dave

"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Ratchap

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what do you mean it wont fit  Get a bigger hammer

Offline Ratchap

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Re: turning between offset centres
« Reply #8 on: January 06, 2019, 04:02:08 PM »

[/quote]

Hey Nigel, there are many ways to set up on centers.    The center could be a piece of stock held in a chuck with the 60 point turned "insitu".   To drive the piece you could use a bolt sticking out from the end of the part bearing on one of the chuck jaws.  My point being, before you spend money on tooling, talk to us and maybe we can get come up with a set up based on what you have.

What lathe do you have?

Dave
[/quote]

Cheers Dave  i   have  seen  various  ways  of  DIY  driving  but being a H&S manager    i am more inclined too increase  my tooling  supply.  I have a Generic Chinese mini lathe , its been stripped down cleaned  scraped honed polished  to within 0.025mm of its life  lolso far i  have added  a tailstock  DRO  and  QCTP with home made locking lever  and a tachometer
what do you mean it wont fit  Get a bigger hammer

Online steamer

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Re: turning between offset centres
« Reply #9 on: January 06, 2019, 04:16:58 PM »


Hey Nigel, there are many ways to set up on centers.    The center could be a piece of stock held in a chuck with the 60 point turned "insitu".   To drive the piece you could use a bolt sticking out from the end of the part bearing on one of the chuck jaws.  My point being, before you spend money on tooling, talk to us and maybe we can get come up with a set up based on what you have.

What lathe do you have?

Dave
[/quote]

Cheers Dave  i   have  seen  various  ways  of  DIY  driving  but being a H&S manager    i am more inclined too increase  my tooling  supply.  I have a Generic Chinese mini lathe , its been stripped down cleaned  scraped honed polished  to within 0.025mm of its life  lolso far i  have added  a tailstock  DRO  and  QCTP with home made locking lever  and a tachometer
[/quote]

H&S for between centers regardless is really about the same as for any lathe.    All the same safety precautions apply.     Safety is an attitude,

Same set up with drive dog and center

Why two set ups?    I didn't have a soft dead center, that I could true up.   That allowed a small amount of error to exist in the work.   That said, I changed the set up to a 3 jaw with a piece of tool steel in the chuck that I machined to a 60 degree point, like a standard soft dead center, and drove it off one of the jaws with the dog.

Dave


   
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline Lew Hartswick

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Re: turning between offset centres
« Reply #10 on: January 08, 2019, 01:25:19 PM »
How do you take a piece of round stock and get the two sets of  center holes aligned ???   I see for a rectangular piece it's no problem.
   ...lew...

Offline Mcgyver

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Re: turning between offset centres
« Reply #11 on: January 08, 2019, 06:03:00 PM »
How do you take a piece of round stock and get the two sets of  center holes aligned ???   I see for a rectangular piece it's no problem.
   ...lew...

clamp it to a rectangular piece - V block, block, even a vise if its the sort that be mounted on its side.  indicate to centre the dia, offset, centre drill, flip 180 and repeat.  It can also be via manual layout with V blocks, centre punching and drilling in the drill press
« Last Edit: January 09, 2019, 03:00:54 AM by Mcgyver »