Minnie Traction Engine - Fly Cutting

First of all a Happy New Year to everyone

Yet again I appeal for help.

I see in the "Bible" that there are several occasions that I have to Fly-Cut,. I have NEVER done this so ask for guidence:-

a.- Where to I get a Fly-cutter

b. What size do I need.

c. Any tips on how to do it. Or books I could learn from.

d. How hard is it to learn/do ?

As always any help is very greatly apreciated

Regards Malcolm Farrant

Of which “Bible” do you speak? It may help the accuracy of your expected answers.

What size machine? What size work?

No doubt the Bible is LC Masons book on building the Minnie.

I bought one of the sets of 3 flycutters quite early on when I started model engineering and they still get used a lot to this day, my large MT3 one seldom sees the light of day. So I would say go for those, available from several of the ME Suppliers such as ARC.

In this day and age I expect Youtube will show you all you need to know about flycutting and a whole lot more that you don't. It is quite easy to use a flycutter once you get the grind of the tool right.

I’m the opposite, I bought a fairly large MT3 Flycutter and have used it a lot. For some reason I bought a set of three small Flycutters and have never used them!

Easy enough to make, use a HSS knife tool as a cutter.

Milling with a decent diameter end mill should give results that are as good in terms of flatness, if not as good looking. If the mill is out of tram the end mill may give a stepped surface and the fly cutter a curved or angled one.

Edited By Neil Wyatt on 05/01/2018 17:50:45

I have a variety of milling cutters but get a better finish with a flycutter than any of the others. I use HSS with a rounded tip profile or a round carbide insert for harder stuff. As said the mill spindle must be perpendicular to the work or you won’t get a flat surface. I always reach for my Flycutter for squaring up stock.

Ideally the cutting diameter wants to allow the width to be cut in one pass, this will give the best flatness. The cut is intermittent so HSS is the better cutting edge as it is more forgiving of sudden shock during the cut. Having said that I have used a carbide lathe tool to good effect, RH one.

As Tubal Cain pointed out a multi-flute endmill, can remove metal at a much higher rate than a fly cutter.

Also, unless the mill is trammed absolutely perfectly either only the leading edge will cut or the trailing edge will cut.

The result is a concave surface.

Assuming the fly cutter cuts a path eight times wider than the end mill (say 80mm fly cutter against a 12mm end mill stepped over at 10mm per pass) the concavity of the end mill cut will be four times as great as any step left by the end mill.

The surface finish may look better than that left by the end mill, but in practice the Ra is unlikely to be significantly better and the overall flatness is likely to be worse.

The only real benefits from using a fly cutter are cosmetic.

Honest!

Neil

a.- Where do I get a Fly-cutter: Most vendors sell them. Try this one, the example is a set of 3 sizes that would cover most needs: HSS tool blanks are listed too.

b. What size do I need: Not critical. Ideally big enough to smooth the area that needs flattening in one pass.

c. Any tips on how to do it: Take light cuts only. Lubricate. Keep the tool sharp. Make sure it has clearance at the side and back. Calculate rpm as 10000 divided by the side to side sweep of the tool tip in mm

d. How hard is it to learn/do ? Not very. One or two experiments should be enough. Most likely mistake is putting the tool into the holder channel the wrong way - see clearance above!

Dave

And when you get it set right you end up with almost a hologram or damascused look.

I suspect the words 'Fly Cutter' as stated in LC Mason's book refers to the 'Between Centres' type Boring Bar which Malcolm is looking for?. It will be for machining the Curved faces of the Chimney Saddle, Cylinder Block and Motion Plate, probably Gunmetal. with a max radius of 1.5/16" (33mm-ish).

When I carried out these jobs, I made a Between Centres Bar out of 1.3/8" dia BMS and a 1/4" dia HSS round bit. Exactly as shown in his book on page 96 (Fig 42). Slowest Back Gear speed and finest feed to start.

The Chuck/MT retained Fly Cutter types would probably be best suited to producing flat surfaces due to lack of reach/clearance. But then I am making assumptions here.

.

Edited By Richard S2 on 05/01/2018 21:00:42

Absolutely true, but (a) how many people can get that* and (b) the only difference between flycutter and mill on that machine will be the type of pattern produced.

Neil

*Actually I've seen that pattern on the table of 'cheap imported drill presses' suggesting that the Chinese are very good at tramming their industrial-size mills

To you all ...Thank you so much for all your replies.

Alas I was not being very inteligent when I made my posting to the Forum

First of all I should have Spelt Mini correctly . I am making the Minnie Traction Engine, with castings fron A J Reeve.

The " Bible" I mentioned is L.C. Mason's Book "Scale Model Traction - Engine Building - Featuring Minnie.

It seems from the replies that infact it is not really a fly cutter I need. Richard S2 infact gave me the answers. It seemsn that Fly-Cutting is for Flat material whereas I am seeking to cut curves as I now realise are detailed in the book.....It seems at 80 I am still a vedry slow learner , but THANK YOU ALL

Very best wishes Malcolm Farrant

Malcolm, a fly cutter is a single point milling cutter, not always made for face cutting as described above. I have used one similar in shape to a boring bar as used in the lathe, but with the cutter(broken centre drill)ground to shape to cut a gear. The same cutter with a different shape tool is used to cut a 35 mm r grove in blocks of nylon for an agricultural machine I help build(we built 60+ of them).

Ian S C

Or their "Blanchard" grinding is so rough it looks like milling.