calling all machinists!

[bikedude189]

i work at the machine shop at school and have access to a large cnc knee mill.
i want to disc my pistons to, IIRC, 21 or so cc's.

can anyone give me a repeatable and accurate way to mount each piston to the table? a way that i can repeat 6 times that will give me the same results within about .001"? also, how can i figure out how deep to go, without trial and error and cc'ing?

its been a while, but i want to start my stroker build again...

[Biggrnjeep97]

There are 100 ways to skin this cat, but id personally use a V block to hold the piston and a last word to indicate the wrist pin. Google "piston vise", thatll give you an idea or 2.
-Will

[Biggrnjeep97]

i work at the machine shop at school and have access to a large cnc knee mill.

How large we talkin? Series II Bridgeport? Kearney & Trecker boring mill? CNC or not, Id personally stay away from REAL BIG Mills and tiny end mills.
-Will

[bikedude189]

its a spuermax, which is about the size of a series II bridgeport, i think. something like a 18x16 inch xy range. i'm not familiar with this 'last word' of yours...

[Biggrnjeep97]

i'm not familiar with this 'last word' of yours...

Check this link out. If you dont have one yet, get one. Its probalbly one of the top 4 tools i use daily.
http://www.starrett.com/download/261_p146_149.pdf
-Will

[bikedude189]

ah, yeah, we have a bunch of those in the shop. just don't use them often.

i am thinking a plate with a bar that goes through the wrist pin holes (.002 clearance prob)and is held in place with a bolt on either side. then clamp the plate to the table and set my zero on the corner. maybe machine a groove for the piston skirt to sit in, what do you think?

[Jak Flash]

you need to use a 3 jaw chuck. and a stop for the wrist pin to control the rotation.

clamp the chuck down so it won't move and put in the piston. Once you pick up the center axis and top of that cylinder everytime you replace the piston the center etc is in the same location.

a way to know the amount of cc's you are cutting out. have someone on a cad station model the top of the piston and remove the dish of the desired volume.

you must then create the program with toolpathing software. that will code the cnc to cut in the amount out that you want it to.

Now you must get a piece of aluminum stock of the same diameter or larger than the piston to cut first. it will be much cheaper than ruining an expensive piston.

Good luck and take pics. Love to see how you make out.

[bikedude189]

i'm not sure we have a 3 jaw chuck that we can use on a mill table, and i'm not buying one out of my own pocket, the shop doesn't have money to buy one either. besides, i'm kind of leery about clamping to the surface of the piston, as they are coated (677cp) and don't want to risk ruining one.

i have made a cad model that's close to accurate (don't have a piston handy to measure) and will be writing G-code when i have the final dimensions.

since the cut doesn't have to be absolutely centered, as it has no mechanical interaction with anything (just gas pressure) i think i will try my self made piston jig described above, unless anyone has any suggestions, or reasons not to.

[Jak Flash]

There should be one.... do you have a manual lathe? there will be one on there.

Use brass shims to protect the piston every shop will have some. no need to squeeze very hard.

I also edited the post above. sorry you postred B4 I was done.

[YJason]

X2, on the 3 jaw chuck from a manual lathe and a set of brass shims. I used pc's of copper pipe about 1.25" long mashed flat when I was a machinist.

A better way would be to use a 3 jaw chuck and use a set of soft jaws bored out to the piston diameter.

Most MS's will have a indexing head with a 3 or 4 jaw chuck that could be clamped to the table also.

[bikedude189]

my shop has a whole grip of lathe chucks. didn't realize i could use them for a mill table. i know the big ones have 8 'legs' on the back of them and i think the little ones have a raised ring around the center around the screw threads that attach it to the spindle. how would i mount this securely to a mill table? suppose i could just clamp with even pressure, or bore out a piece of mdf to fit around the ring...

my problem isn't writing code or finding the correct cc's for a certain depth and toolpath, solidworks is helping me with that...
i'm just unsure how to secure the piston reliably. i think some v blocks and a 'last word' may be my best solution, i have a mill vice i can move to the cnc mill. and set up a stop for the lateral movement of it. then just align it rotationally each time.

it will probably be next semester before i can cut them, but i will definately get pics.

*edit* i knew i'd seen this idea somewhere... its for a sv650 piston, but same principles apply...

http://www.metricmotorcycles.com/images ... odPrep.JPG