Fly Cutter

[jsmith]

Does anyone have advice or pictures to help make a fly cutter for skimming heads on a bridgeport mill.??

Thanks

[SWB]

If you are doing aluminum heads then you can get by with uncoated carbide cutters and making a fly-cutter for brazed tools is easy. Or you could use indexable cutters, like for use on a lathe. Either way it will work OK. For cast iron the only thing that really works well to my knowledge is CBN (turns fast and leaves a clean finish) which is about $200 an insert and you'll have to be more fancy about milling out a pocket in your flycutter, as well as effecting some kind of clamp for it. Otherwise it's a simple machining exercise and shouldn't be too hard.

SWB

[jsmith]

Do I need 2 cutters on it?

[SWB]

No, you could get away with only one. I know a guy who does that and his heads and blocks come out looking great, it's more of a time thing. With two you should be able to traverse faster than with only one.

SWB

[Greg]

I'll take some photos this afternoon. I made a hub up and used a (I think?) mazda diesel flywheel, just removed the ring gear and milled a slot to fit the cutter in.

I bolted the hub to the flywheel, then machined the R8 taper in the lathe.

I use one 3/8" round insert cutter, CBN for cast iron and PCD for aluminium. The CBN insert has so far lasted for 12 months with a lot of edge still left on it and the finish is as shiny as grinding but much flatter.

[jsmith]

could I simply remove the jacobs chuck from my spare R8 adaptor and mount some sort of flywheel onto that? Would this be strong enough or would it vibrate / shear?

[Greg]

I had one that I made to use on an adaptor but found that especially on cast iron it deflected a bit and the finish suffered. It worked fine on alloy heads.

The one I have now I made up one day from bits and pieces i had around. The flange that the flywheel bolts to is from a mini, its around 5 inches diameter and made of steel. I pressed a piece of steel bar into it and welded it on the bottom side. I turned a hub on the bottom to fit the flywheel I used. Then drilled the flywheel to the bolt holes on the flange and bolted it up with bolts and self locking nuts, you could also tap threads to bolt it together, I just used the original mini bolts.

I set the flywheel up in the lathe and machined the R8 taper on the shaft and drilled and tapped the drawbar bolt thread, then put it back in the mill and clamped a lathe tool to the bed and machined the outside and bottom of the flywheel.

Next I machined a slot and some threads for grub screws to hold the cutter in place.

Thats about it, I spin it at 750RPM for both cast iron and alloy, using CBN (cubic boron nitride) tips for cast and PCD (polycrystaline diamond) for alloy. I used to use carbide cutters, heaps cheaper to buy and work well, just dont last as well and you need to spin much slower on cast iron, about 150-200RPM, depending on the diameter of your flycutter, you also need to feed a lot slower.

I just fitted a new power feed unit to my mill and the difference is amazing, it has around 500in/lb torque compared to the original 100. It can maintain constant very slow feeds and the difference to the finish is amazing.

Below are some pics of the flycutter in the mill. Sorry for the slow reply, I did mean to post these pics up last week.

[jsmith]

Cheers Greg - much appreciated.

Do you have correct measurements of the R8 taper or shall I just measure it off existing tooling?

The cuter you are using, is that a lathe tool with a slot milled in the side for the bolt?

Do the grub screws have a positive location in the tool or are they just clamping it?

Thanks.

[Greg]

You're welcome, Thats a pretty readable drawing above of the R8 taper.

The tool in there is made for a robbi style mill, its help in by a M6x1 bolt, plus I use one of the grubscrews just to be safe. Originally i used the 2 grubscrews to clamp in a small lathe tool.

The cutter in there now uses a 3/8" round CBN or PCD insert.