View Full Version : Fly Cutter

05-18-2008, 07:04 PM
I’m new to milling machines as well as the forum, with some dabbling with lathe work. I’ve been experimenting with a milling machine using different tools and materials to take different cuts. I have no formal training in any of this so if the descriptions of my “technique” show utter ignorance constructive criticism is most welcome.
Using a fly cutter with a cemented carbide lathe tool to “face off” the top of some 3” mild carbon steel flat stock, as the work passes beneath the tool to the point where the tool come around to the trailing edge where I hoped it would just pass over, it instead take more metal off.
This is not what I expected. What does this indicate and how do I correct it?



05-18-2008, 07:14 PM
In general, it shows your mill head is out of tram. That means it is tilted relative to the plane of the table. So you can imagine the arc of the cutter is then not parallel to the table. Need to know a little more about your mill to suggest how to tram it.

Got a picture and model of it?



05-18-2008, 08:40 PM
Thanks for your response, Bob,
Don't have a picture but the machine is a Jet Mill/Drill Model JMD-18PF about 10-12 years old. I have the Operator's Manual but it is lean on useful information. The machine is very similar to this (http://industrial.jettools.com/Products.aspx?nav=ByPart&ClassID=333020&Part=350020) but without the DRO.

Thanks for any help you can provide.


05-18-2008, 08:49 PM
If yours is like the Jet then the head looks to be fixed. You can find out if your head is out by sweeping in the head with a dial indicator. If it's out you have a serious problem.

On the other hand, flycutters most always cut on the back side of the cut but only slightly. The reason, most the time, is the pressure of the leading cut compaired to the pressure on the back side cut and the looseness of the machine. Even a new machine will make a touch cut that leaves a texture to the surface without taking metal off.

05-18-2008, 09:04 PM
Not especially a serious problem, you can still tram it, you just have to do it where the column meets the base...and it just becomes more difficult. Do the trig to figure out how much you need to adjust or shim, then hope for the best, I'm sure there are lots of guys that have mill drills that can help you.

Ohio Farmer
05-18-2008, 09:07 PM
I agree with the suggestions above but that may or may not be what's wrong. Flycutting is a weak procedure especially if you have a lot of tool hanging out of your holder. How much are ya trying to take off in a pass? If it takes another bite after passing will it do it if you feed from the opposite side say from left to right instead of right to left. Does it do this with a regular end mill?

05-18-2008, 09:10 PM
You can find out if your head is out by sweeping in the head with a dial indicator...

On the other hand, flycutters most always cut on the back side of the cut but only slightly...

Thanks Carld.

Could you please explain the procedure for "sweeping in the head"?

The amount of material removed in this case amounts to .002 or .003 of an inch. Acceptable or is that way too much?



05-18-2008, 09:23 PM
Way too much.


That gives the "basic procedure"

05-18-2008, 10:13 PM
The amount of material removed in this case amounts to .002 or .003 of an inch. Acceptable or is that way too much?

depends on the mill. I was taking 50 thou off mild steel today, .002 - .003 is super light, almost too light.

the head may be out of tram, but a cross hatch pattern is expected of a properly trammed mill when fly cutting. Rigidity of the machine comes into play, but basically you'll get this with almost any mill....when it takes its cut the tool is forced upwards away from the work such there is still some interference between tool and and work left after the cut hence the cut surface is slightly proud of the plane the tool tip is traveling in...its cutting or rubbing a bit as the cutter passes through the back half circle. clear as mud?

....oh i get it, 2 or 3 three thou on the back stroke, sounds like too much. try cutting in the other direction, if its tram that's the problem, you should not get this second cut in both directions

05-18-2008, 11:01 PM
Toker got his round column mill trammed. Somebody may have the link or you can track it down. He built a jacking screw arrangement that was nice.

You should do the indicator sweep to be sure it's out of tram though.



05-18-2008, 11:39 PM
I have not seen where you might have stated, how much you were trying to take off in each pass or what the circumference of your flycutter is. Generally my first thought would be as with the rest of the group on "you are probably out of tram", but I also believe that if you are taking .050 off with each pass and your flycutter has a radius of 3" then you will not keep a round column mill trammed. Please explain in more detail what you are doing and check your tram also. Good luck Jay

05-20-2008, 01:40 PM
Thanks to everyone for the helpful replies.
Yes, indeed the mill is out of tram. Perfromed the "sweeping the head" procedure (http://www.gadgetbuilder.com/MillTram.html) and when measuring 4 1/2" to the left and to the right of the spindle along the X axis it went from -.010 to +.007. This readily explains why the 3 1/2' cutter was taking a second cut in the back half of the cut in one direction but not the other. It is also out along the Y axis, but jut barely.
This milling machine sits largely unused at my place of employment. Will not have the time to shim the column until maybe next week. I will post back with results.

Thanks again for the help.


05-31-2008, 04:54 AM
To close out the thread...

I followed the procedure and after several attempts using brass shims got it damn near spot on. Less then .001 difference all the way around. Makes for quite an improvment.

Thanks for the help.


Paul Alciatore
05-31-2008, 05:31 PM
I think most of the import mills are like this. The one I have at work was off by perhaps +/- 0.005. They don't call DIY kits for nothing.

You have to be careful doing this. DO NOT remove any of the screws, just make them all a turn or so loose and tilt the column slightly to work. Had to remove a ton of putty to get at the joint between base and column. Carefully cleaned between them with solvent soaked rags over a putty knife. Then add the shims and retighten. You should use a torque wrench to get them all even. Repeat above as needed. When you are within a few tenths, a bit of extra torque on one or two of the bolts can bring it closer. But your table is probably not that good. Mine was about +/-0.0007" so getting less than that was about impossible.

Good work on yours.