Fly cutting setup for flathead

I need to figure out a work holding setup to fly cut the deck of a set of flatheads for my '46 Indian Chief motorcycle. How is this typically done? I don't have any experience machining heads.

I was planning on machining the heads with a Deckel FP-1. Any advice is appreciated- thank you in advance.

You can use, one short steel rod and two screw jacks in the head bolt face areas, with a mill clamp at each support location, outside of the face area.
Three supports is easy to level.

Thank you donie, I'll give it a try. I was concerned that the metal was so thin that clamping downward around the perimeter may warp the head.

Why do you want to cut them? Fixturing will be tough. If they are warped or just not sealing try gluing sandpaper to a flat surface ( old surface plate is ideal) and rub them in a figure 8 pattern until they clean up. If you are trying to raise the compression ratio I wouldn't recommend that with todays gasolines.
Oh and I am green with envy. Love those Indians

td- I'm not trying to raise the compression ratio. One of the heads is grooved deeply on the mating surface, so it will take some milling to resurface. Does a flathead require a very smooth surface, or does it need some imperfection to bite the gasket?

Oh and please don't do anything that might result in a "How can I weld these fins on this Indian head" thread. If you just have to machine them mount them in a block of beeswax and surface grind them. Much less cutting force and no damage from fixturing. I'm sure I don't have to tell you that pristine heads like the one shown are not so common.

Beeswax is an interesting idea. I don't have a surface grinder, so I guess I could tent my mill and chuck a cup grinding wheel. I'm not intending a thread on how to restore motorcycles.

I haven't found any information on how to machine a flathead, nor have I heard of grinding an aluminum head. There are a few machine shops that advertise that they flycut heads, so I thought it was the preferred method and correct surface finish.

neilert said:

Does a flathead require a very smooth surface, or does it need some imperfection to bite the gasket?

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There's much debate among engine builders about that. For your motor, either will work fine. I prefer as smooth as possible on aluminum.

tdmidget is giving you good advice on methods. I'd avoid clamping because those fins are so easy to break, and the head can be distorted during clamping, giving an uneven surface after you release it.

On a head like that I would support like Donnie said from the head bolt bosses. But I would make a bolt to go thru the spark plug hole for a hold down. This puts the clamping force inside the supports for less distortion.

For the bolt, take a 3/8 SHCS and bend the socket head end 110 degrees about 3/4" from the head end. This is so the head of the screw will tighten up in the chamber away from the spark plug threads.

There are many ways to hold down the threaded end of the screw. One of the simplist is to use a piece about 1/2 x 2 x 6 flat stock. Drill a 9/16" hole about 1/2" away from one end. Place the stock over the screw, then the ball of a Chevy rocker arm, and then a nut. Then you use a standard strap clamp somewhere on your flat stock to hold it down. It doesn't take much to hold down a head for a .005 fly cut. If you don't care for the stability of the set-up, use 3 toe clamps on risers to snug against the fins for a safety. The toe clamps shouldn't be tightened, just snugged.

Thanks everyone for the advice. I'll start hand sanding on a granite plate and see how it goes. If I can't remove the groove, I'll try the beeswax.

gbent- that sounds like a very stable setup, using the spark plug hole. The head has a bronze insert that I will replace, so the threads may be messed up and it wouldn't hurt anything. I may try this setup as well as beeswax for some extra clamp load distribution if it needs to be milled rather than sanded.

Holding an Indian head for milling

I prefer to cast stuff like this into a box with plaster of Paris...It's a lot more rigid than wax and can be removed reasonably easily if you pre-spray the part with a release agent.
If you stick the head to a board flat side down (use wax or Plasticene), you can build a simple frame to box in the head, and then just pour the plaster around it until it's covered. (Plug the through holes with Plasticene first!!)
If you make the box sidewalls out of something like hot rolled MS and tack weld it, you can use the edges of the box to clamp on when you flip the head over and remove the board.
If you want to reduce your work removing the plaster afterward, fill up most of the web spaces in the head with Plasticene too; you need relatively little plaster to hold the head in place against flycutting forces.
When you're done, break the tacks, and remove the plaster and the Plasticene.
Cheers

Marcus
www.implant-mechanix.com

Perhaps a person could hold something like that by the holes. Drill a 3 hole pattern in a piece of plate, the 3 holes matching some three holes in the head (facing up). Make three standoffs to sit against the spot faces on the head so that the thing sits level.

Take three allen capscrews that are small enough that the head will fit in the holes in the head. Machine a 60° angle on the underside of the capscrew heads. Make 3 small bushings that are a close fit in the head holes, centerdrilled in one end to match the modified capscrews. Split the bushings with a hacksaw (or better ).

Fasten the head to the plate with the standoffs, capscrews and bushings. Clamp the plate to the mill table, and shim it if required to perfect the level.

neilert, I have done a least a hundred sets of flatheads. Sure you can sink them in concrete, Bees wax, duck butter if you wish.
One would have to be an idiot to clamp them hard enough to break or even warp them enough to cause a problem.
If that be the case, then get elaborate.

neilert, I'm the biggest idiot in this thread. I can offer no practical advice *except* practice on something else. Neighbor kids go cart comes to mind

Bone simple. Grab them in a four jaw chuck and face them off in a lathe. Done a zillion flatheads and OHV head in a lathe.

If you don't have a lathe flycutting may be the way to go. Here a four jaw chuck is still the way to go. The chuck does have to be big enough to "swalllow" the finned portion so you can grapb the solid part. Don't jaw it too firmly. Some heads will redily distort.

Forrest Addy said:

Bone simple. Grab them in a four jaw chuck and face them off in a lathe. Done a zillion flatheads and OHV head in a lathe.

If you don't have a lathe flycutting may be the way to go. Here a four jaw chuck is still the way to go. The chuck does have to be big enough to "swalllow" the finned portion so you can grapb the solid part. Don't jaw it too firmly. Some heads will redily distort.

Click to expand...

That's how I do flat heads, its easy to do. I made 3 aluminum spacers that I bolt on the heads through the head bolt holes. this holds the head true while you tighten up the jaws. I then remove the 3 bolts, the spacers are trapped between the chuck and head by the fins.

Huge waste of time trying to deal with a head in a lathe chuck, and far to risky.
This thread has become funny to me, but, then again, I make money on this stuff and plenty of it.
Oh well, after 41 years of doing it, I get set in my ways, making money that is.
Just so happens, I have a set of Kmodel heads for an engine I am doing, so I walked out to my little home antique engine build shop, and whipped out a set of heads in 38minutes.

The machine is a vintage Moore jigbore. The flathead "Kmodel Harley Davidson" is sitting on a Gorton 15" rotary table, that I like to use for general work to preserve the Moores table.
So, as can be seen in this photo, the head is perched on two screw jacks in front and a steel pin at the rear with clamps at those locations.
Note the short handle wrench to prevent over tightening the clamps, and the level for setting the head true.
The clamps are tightened just enough, so as the head can not be pulled out with two hands. You see, very light cuts are taken, in this case .005" cleaned them up in one cut.
The tool is carbide, and very sharp with a rather small nose radius, in a Moore fly cut head.
Like this-
http://s170.photobucket.com/albums/u265/donsmonarch10ee/?action=view&current=Kmodelflathead001.jpg

The finished head-
http://s170.photobucket.com/albums/u265/donsmonarch10ee/?action=view&current=Kmodelflathead002.jpg

It may be of interest to note, that Kmodel heads use no gasket. The recommended seal is a thin layer of aluminum paint, so the heads and cylinder tops need to be pretty flat.
I should add that, I used a lube made of Bees Wax thinned to a grease with Sunnen hone oil, this was smeared on to the heads surface to prevent the rather crappy old aluminum from welding to the cutter, and was cut at 825 rpms.

Now, wasnt it nice of me to actually show something? That is, Rather then just blowing bubbles with others. And, no warp, WOW!

Donie, this is exactly what I needed. I'll post some photos of my setup also when I face the heads.

I'll make the thread even funnier.Use JB Weld.Used it on an Onan flat head years ago.Still running to this day.