Made a tool today

[Evan]

Here's a pic of the tool geometry. The arrow indicates the cutting direction.



Here is the idea that YOD gave me. My wife gave me a small present the other day, a Valenite ceramic insert that was very old NOS and never likely to sell. I figured if I was going to put something on the end of the bar to prevent it from coming out under power it might as well be useful. All I have to do is to loosen the setscrew and rotate the bar 180 to bring either cutter into play. A ceramic insert is the perfect match for the high SFM that a fly cutter operates at.

[BadDog]

I like it. As shown, it's much better balanced than most. It also makes for a much simpler bit profile by mounting 90*, and could be used to trepan things (though lacking in fine adjustment).

[BadDog]

I wouldn't think that ceramic insert would like the interupted cuts typical of a fly cutter.

[Evan]

I'll find out. I only intend, as I said earlier, to use it for fine finishing cuts. It isn't going to be a scale breaker.

I'm pretty sure it is a silicon nitride insert, Valenite grade Q6. According to them:

Specifically recommended for operations ranging from heavy roughing to finishing of cast iron. Suitable for high speeds, heavy feeds, and interrupted cuts.

[andy_b]

Evan,

nice job (as usual). one question i have is there appears to be a hole parallel to the mounting shaft on the topside of the cutter body. what is that hole for, or was it just something in the piece of scrap you used.

also, you mentioned the set screw that holds the cutter bar in goes into a cup drilled in the bar. does that mean you can only set it at one diameter (until you drill more cups), or am i misinterpreting what you mean? could you post a photo of the individual pieces?

thanks,

andy b.

[Evan]

That hole was pre-existing in the scrap stainless steel shaft I used. I don't intend to change the position of the bar from the perfectly balanced position it is at. If I need a different length I will make another bar, also balanced. I can't see getting as good a finish with an unbalanced bar.

I'll take it apart later today or this evening. I have to go to town to buy some supplies and will be off line for most of the day.

[rotate]

Evan,

What's the cost and machineability of 7075 T-6 compare to the 6061? I may be interested in using that for future projects.

7075 may be slightly harder than mild steel, but I was told that alloying any metal does not significantly impact its modulus of elasticity (stiffness), so I'm guessing that you have to choose your application carefully. Your comment would be appreciated.

[comerrm]

This tool is giving me some ideas. I currently have a John Deere M 2 cylinder engine getting bored over and the crank ground. The machinist doing it for me said the block deck was cupped (concave) about .004 and he cleaned it up. I did not bring the cylinder head to him as I was hoping to do the valve work myself. I was wondering if a heavier version of this tool could be used to deck the head (only 5 thou at the most) on my round-ram bridgeport. Is this a decent way of going about it or should I fork over another $75 to have him do it? Eventually I would like to start doing this kind of work myself, once I aquire some more tooling and maybe a larger machine as I have plenty more 2 cylinders to fix up.
- Robert Comer

[lazlo]

Originally Posted by rotate

What's the cost and machineability of 7075 T-6 compare to the 6061?

7075 is about twice the price of 6061. I've machined a bunch of 7075-T651 and Fortal (which is basically the same stuff) and it machines beautifully. It can get a little gummy in the center if you have a thick section.

7075 may be slightly harder than mild steel, but I was told that alloying any metal does not significantly impact its modulus of elasticity (stiffness), so I'm guessing that you have to choose your application carefully.

7075 has 1/3 the stiffness of steel: 10.4 versus 30 x 10^6 psi. It's slightly stiffer than 6061-T6, which is 10.0 x 10^6 psi.

7075 is slightly harder than mild steel: 150 Brinell versus 135 Brinell for 1018. But it's a lot harder than 6061, which is around 95 Brinell.

[Evan]

To add to what Robert said 7075 and to a lesser degree 2024 have a tendency to grab the tool when drilling. You can get in real trouble if you drill close to final size and then try to run a slightly bigger bit through. It may just decide to seize so tight that the only way to remove it is to cut it out. Other than that machining 7075 is more like a cross between brass and steel with the excellent machinability of hard aluminum alloys thrown in. The grabbiness is due to the copper content and it also has enough silicon to dull HSS bits faster than you would expect. It has no trace of gumminess and cuts exceptionally uniformly and clean with no burrs.

I forgot to say that don't try bending it and it is considered to be unweldable except for some types of spot welding.