surface finish flycutter or shell mill on lathe?

Hi all

I am trying to build a fingerplate 3" square x 7/8" from a piece of hot rolled steel following clip spring's example. However I dont have a rugged milling machine so its down to the 3 1/4" speed 10 lathe.

Im looking to get a reasonable surface finish from either a flycutter such as Myfordboys back plate cutter or an off the shelf carbide shell mill.

I will probably use the vertical slide, which solution might give a better finish?

https://www.youtube.com/watch?v=I-iVLgILSFY

https://www.youtube.com/watch?v=FgBM-JVRWgU

Is there any reason for not holding the part in the 4-jaw and just turning the six faces?

There were a number of recent posts about flycutters ( do. Search from the Google search facility via the homepage - not the one at the top of these pages). Whichever tool you use you must remember that using a vertical slide on a lathe will only let you get away with light cuts. Most carbide tools work better with a fairly heavy cut.

Practice on some scrap to see what would work best on your set-up.

Regards Mike

Hi Jason

I hadnt considered holding the work in the chuck because of the size and weight. the blank is approx 3.15" squared x 1" thick. I think I was a bit terrified of holding it in the 4 jaw and have never used a face plate.

Would I get a similar finish in the 4 jaw or face plate?

Just bear in mind that no reasonable quality lathe's cross-slide is set at exactly 90deg. to the longitudinal axis. It should be set to face very slightly concave. This is the reason there will be a light back-cut when using a fly-cutter to face-off a work-piece clamped to the vertical slide as it traverses the centre-line of the lathe.

Myford like you have should handle a square just over 3" without issue depends if there is much wear in the old girl.

I've certainly flycut on all my lathes in the past, don't think I have tried a face mill but if I did would use the sharper inserts meant for non ferrous metal to lessen the load.

You also need to consider how you would hold the block onto a vertical slide to machine the two flat 3 x 3 faces same would apply to a faceplate so 4-jaw is the easy option, probably have to use the outside jaws. The sides would not be so hard to hold for fly/face cutting I'd clamp them down to the cross slide with some packing to bring them upto ctr height

If you don't fancy any of that then clicksprings rubbing on a sheet of emery looks to give him a good finish.

I doubt you would have enough cross slide travel to worry about the trailing cut if flycutting might even be a problem just doing one face but not sure how far towards you the cross slide will go and what it's travel is.

Edited By JasonB on 03/08/2023 07:12:25

Like Jason, can't see that holding the work in a 4 jaw will cause any major problems.

Having a larger lathe than a ML7. (Think Chester Craftsman lookalike ) I prefer producing a flat surface by facing rather than using a face mil or flycutter.

The PCF produces a better finish than my hand feed can on the the mill.

Howard

Besides tooling and machine rigidity material quality is an important factor in getting a good finish.

Is your hot rolled steel to a proper specification from from an engineering materials supplier or just a lump from a steel stockholder primarily providing materials to the structural community. If its the latter you could be in for a nasty shock when trying to machine it.

If it is at all dubious odds are the only way you have a hope of getting a good finish is to turn it in a four jaw. If you have any offcuts experiment first.

Cautionary tale

Due to placing an order with brain disengaged I ended up with 9 metres of nominal 25 mm by 300 mm steel bar that is exceedingly difficult to cut and seriously hard work to get a decent finish on it. Cutting is an abrasive disk job and machining needs coolant, a respectably stiff machine and sharp high quality cutters able to run at a decent speed.

My shaper leaves a finish like a ploughed field and its not terribly impressed by a flycutter.

Fortunately I have ex-industrial machinery and can afford higher end HSS milling cutters for the Bridgeport but the finish quality barely makes it to "hafta do".

After a lot of work and creative language.

It does turn reasonably well given good inserts or super-sharp HSS and appropriate feed.

Seriously impressed by the Chronos Little Hogger milling cutter which comes close to a properly decent finish if pushed hard. Kills the inserts tho'. A bigger shell mill with Maydown inserts works OK ish.

Lord knows what the stuff is but it certainly isn't to the specification discussed when I ordered. Frankly I should have left it on the lorry when I saw the invoice had no specification numbers. Supporting my local(ish) small guy kept delivery costs down and I got 9 m for the price of 3 m delivered from more engineering focused folk but false economy in retrospect. Thats the second time I've ended up with crazy stuff from him so won't be buying there again.

Application is totally undemanding so I just wanted "steel". Bad mindset when spending over a months pension in one hit!

Clive

I'd face this type job in a lathe every time, provided, in this case, the 4-jaw is 5" or over. The tiny facing concavity is of no consequence for this project, in fact, as intended it will ensure no rock in the finished job. A further benefit is that if the workpiece is accurately centred in the chuck then the centre hole can be drilled and tapped in the same op.

Edited By Clive Brown 1 on 03/08/2023 09:53:15

Just when you need a shaper!