fly cutter ptoblems

I am trying to machine a cast iron valve face with a fly cutter . but it blunts very quickly , Iron files easily . Cutter is turning about 250 rpm , 1 1/2 radius . what am I doing wrong

Bit fast swinging a 3" diameter, should be about 85rpm with HSS cutter in iron but you may need to run a bit faster if the mill lacks power at low speed

Yes too fast I run my 32mm dai at 200 with no problems and long tool life so reduce speed or diameter of cut

I recently found I could use a small left-hand CCMT carbide insert tool in my morse-taper flycutter. Might help with cast iron?

I wondered about a carbide cutter , but would it stand up to an interrupted cut . Regrinding my HHS this morning and trying much lower speed

I use a 12mm round carbide insert in my fly cutter and it works fine.

You may find that a carbide tool chips, as they generally do not like interrupted cuts, a fly cutter reproduces that to quite an extreme degree.

That's a bit of a lazy cliche. There are many carbide inserts that are designed for interrupted cuts - for one thing, consider milling cutters that by definition spend their life doing interrupted cuts. For turning, there are both geometries and materials that are optimised for that application. Obviously you wouldn't expect to see a ground edge (finishing tool) used to rough out a casting. For that you tend to find the edges are less sharp and more robust.

Choosing an insert that is described as suitable for roughing milling of CI might be a start....

Murray

Edited By Muzzer on 06/03/2018 09:58:12

I was dressing EN3, but it worked fine. CCMT inserts are small and well-supported, and this may help.

Also depends on the form of the flycutter. I was using a 2MT flycutter from Arc, with one of their 8mm holders.

Hi Murray I agree, if you are going to research the most suitable insert of course it will work, but I suspect most hobby engineers will not have a suitable insert to hand but will use an insert designed for turning round stock, as most of those supplied to us are designed for. My point was, if you use a standard carbide insert do not be surprised if it chips.

The traditional formula for calculating RPM of either the job in the lathe or the outer edge of a milling cutter is

RPM = 4 x Cs/D

where Cs is the cutting speed in feet per minute. 100 for mild steel. 60 for cast iron. 200 for brass and ally.

D is the diameter of the job, or the milling cutter OD, in inches.

So you get 4 x 60 divided by 3, which gives as near as dammit to Jason's 85rpm. Just so you know how to work it out for future jobs.

The shortcut way is to divide 400 by the diameter in inches. Then for cast iron, halve the answer. For brass or ally, double it.

Edited By Hopper on 06/03/2018 11:22:30

I don't flycut CI often buy when I do a CCMT insert same as I use for turning works fine, I doubt any of you change inserts when turning square stock of an odd shaped item in the 4-jaw so no problem with interupted cuts.

You can also run carbide quite a bit faster

Jason, slight change of subject. But can you explain the cutting direction you are using here? It appears be towards the operator.

On my Myford I would have (maybe wrongly) passed the cross slide away from the operator so that loads are carried towards the bed? But my money is on you having rather more experience....

Cheers, Colin

I think it was a case of having to mount it that way round as I did not have the room to swing the flycutter clear of the work if it was mounted towards the front of the cross slide. Also with it in that position I had the most slide engaged in the dovetails.

The hole for end of the cylinder liner was also bored out at that setting.