[SEL] Maching blank pistons
Ed Stoller
edstoller at earthlink.net
Mon Apr 22 05:53:25 PDT 2013
How about this.
D:\EDS2010\Blacksmith_Mch\TurningPiston_files\TurningPiston.htm. I think I
lost the link for it.
Ed Stoller
New Fairfield, CT, USA
www.enginesandmagnets.com
----- Original Message -----
From: "Peter Lowe" <plowe at exemail.com.au>
To: "ATIS" <sel at lists.stationary-engine.com>; "Oldengine.org"
<stationary-engine at oldengine.org>
Sent: Monday, April 22, 2013 7:36 AM
Subject: [SEL] Maching blank pistons
> Do we have any members who have a web site that shows the steps for
> machining blank pistons and making rings?
>
>
> Regards
> Peter Lowe
> R&V Engine Registrar
> http://www.oldengine.org/members/plowe/rv-engines/rvpage.htm
> Australia
> _______________________________________________
> SEL mailing list
> SEL at lists.stationary-engine.com
> http://www.stationary-engine.com/mailman/listinfo/sel
>
-------------- next part --------------
Piston machining sequence for the 1 1/2HP (3-1/4" bore) Herc/Econ piston
castings
Click on thumbnails to see larger images
Step #1. Using a grinder remove the core flashing from the inside
bottom edge of the piston skirt.
Step #2, mount a 4 jaw chuck in your lathe and loosely chuck up the
piston blank. Rough center the ID of the skirt using a large cone
center in the tail stock.
Step #3, fabricate an "L" shaped piece from 5/16" or 3/8" round stock.
The leg on the "L" should be about an 1" to an 1 1/4 long. This will
be used to indicate the inside of the casting up behind the bosses, in
the ring groove area. Hold the "L" tool in a tool holder in the
carriage.
[1] [P3230001_small.jpg] Here the 4 jaw chuck is seen holding the
piston casting. Leave about a 1/2" of space between the chuck jaws and
the edge of the casting (for later step).
Step #4, run the carriage & tool into the area between the top of the
boss and underside of the crown, being sure to avoid the rib over the
boss. At this point it is a matter of running the carriage out until
you hear the tool just make contact with the inside of the casting
(lathe in neutral rocking the chuck). Run the carriage in (so not to
hit the rib with the "L" tool) and rotate the chuck 180°. Run the
carriage back out until you just hear contact. Make adjustments to the
chuck jaws until that set of jaws is within a few thou of being
centered. Do the exact same with the other set of jaws.
Step #5, bring the carriage out to the skirt area of the piston about
3/4" in. Repeat Step #4 , but instead of moving the chuck jaws just tap
the piston to get this area "dialed" in.
Step #6, repeat Step #4 until the ID of the piston under the ring
groove area is running concentric within a few thou. These first steps
will be time consuming but ultimately will assure your cast part is not
ruined due to an off center core. This is the nature of casting. Cores
will always be off center from the pattern due to the huge floating
loads imposed by the combination of dense molten metal and light core
sand. I've seen the cores rise as little as .025 and as much as .180
off center. The patterns are correct, but core float is simply a fact
of foundry work. It is the hobbyist's responsibility to "dial" the ID
in true to prevent cut thru by the ring grooves. Credit will not be
issued for ring grooves that are cut thru that are the result of
failure to "dial" in the ID of the core area.
__________________________________________________________________
[2][P3230002_small.jpg] Here the OD has been rough turned just to make
the cast surface smooth.
Step #7 is to turn the bottom edge of the skirt to be exactly 4" away
from the crown. You can see the scale used to determine the 4" mark.
Make sure your scale is on the bottom of the flat crown and not on the
rib under the crown or in the radius transitioning to the rib. A scaled
4" like you see here is good enough.
__________________________________________________________________
[3][P3230004_small.jpg] Turning the inside diameter of the skirt.
Step #8 is to bore the ID of the skirt ring to 2.875 diameter.
__________________________________________________________________
[4][P3230005_small.jpg] The chamfer is being turned to provide for
clearance for the swing of the connecting rod.
Step #9 is to add the 1/8" x 45° chamfer.
__________________________________________________________________
[5][P3230007_small.jpg] The piston has been turned to the final
diameter. (.003 less than the bore of the engine)
Step #10, turn the OD of the piston to the final diameter. Do not turn
the diameter steps that compensate for crown swell. That will be done
later. In this step the entire length of the piston will be turned to
the correct clearance for the bore at the skirt diameter. See the chart
for the correct skirt clearance.
__________________________________________________________________
[6][P3230003_small.jpg] Establishing the top of the piston.
Step #11, touching off the right side (bottom of skirt), and accounting
for parting tool width, bring the tool over to make the piston over all
length 4.234". Bring the parting tool in at least a 1/2" to establish
the top of the piston. Don't cut into the chucking button yet.
__________________________________________________________________
[7][P3230008_small.jpg] The 3 ring grooves are being turned. The are to
be cut 5/32 deep (.156). Piston rings are to be .125 thick.
Step #12, is cutting the piston ring grooves. Using a parting tool (.20
wide) touch the right side of the piston (bottom of skirt) and set your
DRO. Bring the carriage left until the 3.875 mark. This is the location
of the left side of the top ring groove. Turn slow and plunge carefully
and slowly to cut the first ring groove. Zero your DRO just as you
touch the surface and go in .156 per side. (.3125 diameter read out)
Now move the tool right to the 3.437 location and cut the second ring
groove.
And finally move the tool right to the 3.000 location and cut the
bottom ring groove.
__________________________________________________________________
(No picture)
Step #13, consulting the chart, cut the ring land between the oil ring
and the middle ring (-.007 less than diameter of skirt)
Then cut the ring land between the middle ring and the top ring (-.009
less than diameter of skirt)
And finally cut the ring land at the top. (-.013 less than diameter of
skirt)
__________________________________________________________________
Step #14
Remove the piston and cut the chucking button off with a hack saw or
power abrasive saw about an 1/8" away from the crown.
__________________________________________________________________
[8][P3230009_small.jpg] Facing the crown after removing the chucking
button.
Step #15, chuck the piston the other direction and carefully turn the
remains of the chucking button with the portion of the piston already
faced in Step #11.'
You have finished the turning operation!
__________________________________________________________________
References
1. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230001.jpg
2. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230002.jpg
3. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230004.jpg
4. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230005.jpg
5. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230007.jpg
6. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230003.jpg
7. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230008.jpg
8. http://www.oldengine.org/members/holland/images/PistonMachiningSteps/P3230009.jpg
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