Fly Cutter RPMs, etc.

[devils4ever]

I see there are a lot of other fly cutter threads going on at the moment, but I don't want to hijack them. So, I'll post a new one here. (Hope this it the right thing to do!)

In any case, I bought a fly cutter (with HSS bit) with a R8 shank from Micro-Mark that I have just started to use on my PM-25MV mill. I'm trying to to determine the proper RPM for this. I know I don't want to go too high since it's not balanced like an end mill.

I see a lot of equations for determining RPMs based on SFM and diameter such as: RPM = SFM X 3.82 / D. But, on a manual mill, how do I determine SFM?

Thanks.

 

[John TV]

So I am one of the fellows asking the fly cutter questions but I think this is the formula you start with ( see pic) then adjust from there. So if calculated rpm is say 200 then you multiply that times chip load per tooth, say .002 and multiply that times number of flutes in your cutter, say 4.

So 200 x .002 x 4 = 1.6 inches per minute feed rate. Then adjust to machine, sound, experience ( which I don't have much of). If I'm wrong one of the folks with much more experience can correct me. Good luck.

Then for manual feed, practice hand revolutions say one per second and see how far table travels in one minute. Adjust from there, faster/ slower to approximate speed. Just a thought
Sent from my iPhone using Tapatalk

 

[benmychree]

On ordinary steel, cutting speed in FPM should be about 100 for HSS tools. In high school shop, we were taught to round off the 3.82 to 4 to simplify the math and be able to do it in your head, so take the cutting speed in FPM, multiply it by 4, and divide that product by the diameter of the moving part.

 

[devils4ever]

Okay, so for steel, I would use: RPM = SFPM X 4 / Dflycutter = (100 ft/min) * 4 / 4" = 100 rpm

I'm testing with 6061 Aluminum which I think is about 1000 ft/min? This gives (1000 ft/min) * 4 /4" = 1000 rpm.

For a fly cutter with one cutter edge: Feed = 1000 rpm * 0.002" * 1 = 2"/min

My mill advances 0.100" per revolution. So, (2"/min) / (0.100"/rev) = 20 rev/min.
(20 rev/min) * (1 min/60 sec) = 0.333 rev/sec. Or, 3 sec/rev.

Sound correct?

 

[mikey]

The cutting speed varies with the tool type. It will be 2-3 times higher if using carbide. For aluminum when cutting with carbide you will almost always be running at max speed unless your tool is a foot long.

 

[benmychree]

So far as feed is concerned, I pretty much go by feel and intuition; I do not use fly cutters, but rather face mills and shell end mills. The best thing to do is get a cutting speed/feed slide rule calculator, cutting tool companies give them away.

 

[MrWhoopee]

1000 sfm is appropriate for carbide in aluminum. 200-300 is much closer for HSS. Bookmark this table for a quick reference.

Cutting Speeds for Turning and Threading with HSS Tool Bits | Smithy - Detroit Machine Tools

MATERIAL STRAIGHT TURNING SPEED THREADING SPEED Feet Per

smithy.com

 

[benmychree]

1000 sfm is appropriate for carbide in aluminum. 200-300 is much closer for HSS. Bookmark this table for a quick reference.

Cutting Speeds for Turning and Threading with HSS Tool Bits | Smithy - Detroit Machine Tools

MATERIAL STRAIGHT TURNING SPEED THREADING SPEED Feet Per

smithy.com

Good practical data! That and a slide rule calculator, and you have a easy to use practical method of determining cutting speeds. and RPMs.

 

[higgite]

1000 sfm is appropriate for carbide in aluminum. 200-300 is much closer for HSS. Bookmark this table for a quick reference.

Cutting Speeds for Turning and Threading with HSS Tool Bits | Smithy - Detroit Machine Tools

MATERIAL STRAIGHT TURNING SPEED THREADING SPEED Feet Per

smithy.com

The Smithy tables give vastly different SFMs for milling aluminum vs turning aluminum with HSS cutters. For turning they say 200-300 SFM, but for milling they say 400-1000 SFM. Shouldn’t they be the same? Or at least close? For other metals they list, the SFMs aren’t exactly the same for turning vs milling, but they are in the same ballpark. Think Smithy made a typo or what?

Turning: https://smithy.com/machining-reference/lathe-turning/page/2
Milling: https://smithy.com/machining-reference/milling/page/12

Tom

 

[MrWhoopee]

The Smithy tables give vastly different SFMs for milling aluminum vs turning aluminum with HSS cutters. For turning they say 200-300 SFM, but for milling they say 400-1000 SFM. Shouldn’t they be the same? Or at least close? For other metals they list, the SFMs aren’t exactly the same for turning vs milling, but they are in the same ballpark. Think Smithy made a typo or what?

Turning: https://smithy.com/machining-reference/lathe-turning/page/2
Milling: https://smithy.com/machining-reference/milling/page/12

Tom

Yes, the speeds should be the same regardless. I have no idea why they even have two different charts. It's all about the the relative speed between metal and cutting tool. That speed for milling aluminum is too high.