How critical is precision while flycutting?
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From: The Confederacy
How critical is precision while flycutting? Say if you were going to flycut your intakes .080 and your exhaust .050, what would be an exceptable range or error be before you started to run into problems with compression ratio? Also, if they were off enough... could you possibly throw the "balance" of your rotating assy off? For example, say that one intake was cut .070 and another was .090. It seems like it would be almost impossible to make them all exactly the same 
Originally Posted by badls1
i would measure the depth, to make sure they are all about the same
What I am doing is setting the collar 0.090 above the guide (with no seals) with feeler guages and then cutting until 0.010 no longer fits between the collar and the guide. I find it is a waste of time to try to "spark it out" when cutting. You can't use a depth mike to measure the depth since the notch is not flat. You can't use most verniers because the probe has a square end. I have been laying 0.080 worth of feeler guages in the notch and trying to sense the match between them and the deck of the piston with a finger nail. So far it takes two or three tries to get close, but I can only guess at what "close" is. I think you can feel a couple thou difference with a nail, but don't really know.
I think you can use geometry to figure the volume of the slice, but I haven't tried yet. I don't think that +/- 0.005 will hurt balance or compression, but can't prove it yet.
BTW, PP LQ9 heads going on ...
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From: The Confederacy
Originally Posted by critter
That does not seem to be an easy task. I am in the middle of cutting and am having the same problems/questions as Gomer, including what does "about the same" mean?
What I am doing is setting the collar 0.090 above the guide (with no seals) with feeler guages and then cutting until 0.010 no longer fits between the collar and the guide. I find it is a waste of time to try to "spark it out" when cutting. You can't use a depth mike to measure the depth since the notch is not flat. You can't use most verniers because the probe has a square end. I have been laying 0.080 worth of feeler guages in the notch and trying to sense the match between them and the deck of the piston with a finger nail. So far it takes two or three tries to get close, but I can only guess at what "close" is. I think you can feel a couple thou difference with a nail, but don't really know.
I think you can use geometry to figure the volume of the slice, but I haven't tried yet. I don't think that +/- 0.005 will hurt balance or compression, but can't prove it yet.
BTW, PP LQ9 heads going on ...
What I am doing is setting the collar 0.090 above the guide (with no seals) with feeler guages and then cutting until 0.010 no longer fits between the collar and the guide. I find it is a waste of time to try to "spark it out" when cutting. You can't use a depth mike to measure the depth since the notch is not flat. You can't use most verniers because the probe has a square end. I have been laying 0.080 worth of feeler guages in the notch and trying to sense the match between them and the deck of the piston with a finger nail. So far it takes two or three tries to get close, but I can only guess at what "close" is. I think you can feel a couple thou difference with a nail, but don't really know.
I think you can use geometry to figure the volume of the slice, but I haven't tried yet. I don't think that +/- 0.005 will hurt balance or compression, but can't prove it yet.
BTW, PP LQ9 heads going on ...
Originally Posted by gomer
I used a set of digital calipers and several other methods and finally gave up. I guess I took that head and fly cutting tool on and off the car over 100 times this past weekend. I think my deepest cut was a little over .095 and my "shallowest" was around .080.
I guess if the damn thing slings apart, I'll build a replacement using pistons with real valve reliefs in them. I WILL NEVER FLYCUT ANOTHER PISTON AGAIN AS LONG AS I LIVE
I have felt that thought trying to sneak into my head but having spent the money for the cutters, I quick force it out 
Teching In
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grind the tip of the calipers down so that it isnt so thick, then you can get a pretty accurate reading by measuring the back of the valve relief. If you want to know how much your cutting each time, throw them feeler gauges down ,and put a dial indicator with a mag base on top of the retainer , and measure it each time. I would figure 0.010 is acceptable for what your trying to do, its not like you got a piston vise, and a mill, etc.
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Originally Posted by DaleMX
I would guess that the degree of variance could be determined by measuring the length of the cut instead of trying to measure the depth.
Good luck!
Dale
Good luck!
Dale
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