Author Topic: Pistons from plate  (Read 9812 times)

Offline Captain Jerry

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Pistons from plate
« on: June 08, 2011, 11:16:09 PM »
I have only recently joined this forum and have spent the last few days reading as a way of avoiding the reality that my present project is driving me nutty.  It has been reinvigorating, seeing all the ways that experienced shop pros get things done in amazingly simple ways.  Any one can make it look hard.  A real pro can make it look easy.  By putting as many of these invaluable tips as possible in my head, some of it pops out when it is needed.  This method of making pistons is certainly the result of combining other peoples methods and reaching a different end.  

I don't have much aluminum bar stock so when I needed to make some pistons, I started with a piece of 1/2" thick plate about 2" x 2".  Lacking a power hacksaw or bandsaw, I chopped it into small chunks about 7/8" x 7/8" x 1/2" using my table saw.  No pictures of the process but here is the result.



Each piece has been marked and a 1/4" dia x 1/4" deep hole drilled in the center of one face.  This face will become the bottom of the piston and the final machining of this face will be determined by your specs.  For now, it will be used to position the blank on the lathe.

A piece of 1/4" dia rod is set up in the 3 jaw chuck with about 1/2" protruding from the jaws with the jaws only barely tight.  Over this is placed a small square of hardwood about 1" square and 1/4" thick with a 1/4" hole in the center.  I used Red Oak that is readily available at home building supply stores in the U.S.



One of the aluminum piston blanks is fitted over the rod to position it and the tailstock with live center is brought up to bear on the unmarked face. A fair amount of force is used to press the blank against the hardwood.  Now the 3 jaw can be snugged up but it doesn't need to be very tight. The grip is provided by the friction of the aluminum against the hardwood face.  



This is an adaptation of the method that was shown by Bogstandard in his post on making a flywheel.  By using the hardwood face, it is possible to turn diameters less than the face of the chuck jaws without hitting the jaws with the tool. The cut continues past the end of the workpiece, into the wood. I think it provides a better friction grip than two sided tape and leaves no residue to be cleaned off afterward and can be used for multiple pieces as done here.

This operation is working very close to the chuck so be very careful to check for clearances.  I recommend manual advance of the cut for two reasons. First is the very close proximity of the chuck and second is the possibility of the workpiece slipping on the wooden face.  This is not a problem if you are advancing the cut manually but it using power feed, bad things will happen before you can stop it.

On this job friction is more than adequate.  In fact, the workpiece will go from square to full round in one pass.  Watch this video.



Repeat the above six times and this is the result:



By making the cut in one pass, without moving the crossfeed, all six pieces come out to the same dimension with a high degree of precision.  The diameter is greater than the required finished part but the dimension is not critical.

One of the pieces is then returned to the lathe or the last piece is just left in the lathe.  

Then, using whatever method you prefer, sneak up on the final dimension carefully and the lock the crossfeed to maintain that final depth of cut.  One piece done.
Replace it with one of the other oversize pieces and turn it to final diameter in one pass.  Second piece done.  Repeat four more times.  Six pieces done.  If your tool is sharp and your lathe at all rigid, since you did not change the depth of cut you should have six pieces to the same diameter within .0005"



The pistons in the last photo have a step turned after all six had been turned to the finished diameter.  This is peculiar to my project and the concentricity of the step is less critical so I had no problem removing and mounting to the wooden chuck.  My pistons will have a ball joint instead of a wrist pin so your on your own from here.

The 1/2" thickness was all i needed for my project but I would be comfortable using this method with 1" or more of thickness.

It works for me.  I hope it helps you.

Jerry


« Last Edit: June 09, 2011, 12:22:38 AM by Captain Jerry »

Offline Stilldrillin

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Re: Pistons from plate
« Reply #1 on: August 08, 2011, 03:45:45 AM »
Hi Jerry.
Never thought of using wood as a drive medium!  :doh:

I have lots of pieces of thin ply to play/ experiment with. Thanks!  :thumbup:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline Stilldrillin

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Re: Pistons from plate
« Reply #2 on: August 10, 2011, 02:02:27 AM »
Piece of mdf........




Spot on!  :thumbup:



David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline sbwhart

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Re: Pistons from plate
« Reply #3 on: August 10, 2011, 02:24:58 AM »
Thats a neat idea using the wood for the friction drive, that ones filed away in the memory bank.

 :thumbup:

Thanks for sharing.  :wave:

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline dickda1

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Re: Pistons from plate
« Reply #4 on: August 10, 2011, 12:49:07 PM »
Great idea with the wood plate.  I definitely need to remember this one.
-Dick
sunny (mostly) San Francisco, land of looney people, sane politics and occasional earthquakes.
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Offline CallMeAl

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Re: Pistons from plate
« Reply #5 on: August 11, 2011, 11:25:39 PM »
This is a good idea! I hope I can remember it long enough to use it.
I skin cats my own way!

Offline John Stevenson

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Re: Pistons from plate
« Reply #6 on: August 12, 2011, 03:33:06 AM »
To save putting a lot of strain on the point of the centre and / or marking the work, stick a small ball race in between the centre and the work.
Helps spread the load and also allows you to use a thinner normal dead centre so you can get closer in.

John S.
John Stevenson

Offline Stilldrillin

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Re: Pistons from plate
« Reply #7 on: August 12, 2011, 04:01:13 AM »
To save putting a lot of strain on the point of the centre and / or marking the work, stick a small ball race in between the centre and the work.
Helps spread the load and also allows you to use a thinner normal dead centre so you can get closer in.

John S.

Nice one John!  :clap:

I centre drilled a bolt head. Then sawed it off, and dish faced it....... :thumbup:



David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline PekkaNF

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Re: Pistons from plate
« Reply #8 on: August 12, 2011, 08:12:47 AM »
Stilldrill, very nice chuck guard you have on the last picture. How it is swung and lockked? I had plastic one, that had a miserable single poxy screw. Needles to say it failled to protect anything and broke away when back of my hand met it :lol:

Pekka

Offline Stilldrillin

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Re: Pistons from plate
« Reply #9 on: August 12, 2011, 12:17:52 PM »
Stilldrill, very nice chuck guard you have on the last picture. How it is swung and lockked? I had plastic one, that had a miserable single poxy screw. Needles to say it failled to protect anything and broke away when back of my hand met it :lol:

Pekka

Hi Pekka. Thank you! 

It is fastened on to the original clamp blocks, as a direct replacement to the original perspex "guard".........

Sorry, I do not have a clear photo handy. But I could take more later, if you need any.  :thumbup:




David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline dickda1

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Re: Pistons from plate
« Reply #10 on: August 14, 2011, 03:18:22 PM »
Yes please - pics of the guard would be greatly appreciated.
-Dick
sunny (mostly) San Francisco, land of looney people, sane politics and occasional earthquakes.
Skype: VladTheChemist

Offline Stilldrillin

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Re: Pistons from plate
« Reply #11 on: August 15, 2011, 04:26:38 AM »
Here yer go Dick! 

Chester Conquest mini lathe.

1/8" alloy chequer plate. Formed to clear my largest chuck's jaws. Held with the original guard's screws......




Original clamps. On the original, (disconnected) safety switch, shaft........








Works for me!  :thumbup:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!

Offline Kinkajou

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Re: Pistons from plate
« Reply #12 on: October 21, 2011, 08:08:43 PM »
There is great info on this thread!!