Pm727m and face milling

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What about the shars 2" 75degree indexable facemill? Has a 15 degree lead angle? I am having a hard time figuring out if this will put more axial load or radial load on the SPINDLE....????
 
I have some single-insert end mills that use a TPG. Like buffalo21 says, they seem a little high impact on the machine. Why is the Sherline approach better? I know the inserts are different but they seem similar in the lack of positive rake.
 
Also. What about using one of these generic face mills with just a single insert, to avoid any issue of height variation between inserts?
 
mikey said:
I've also experienced the swirl or lack of a smooth mirror-like surface with fly cutters and have pondered why this is. In my mind, the answer is multifactorial, and since this is coming from MY mind it is naturally suspect. However, this is what I think.
  • Fly cutting is not a finishing process. The intent is to obtain a truly flat and accurate surface, which fly cutting does quite well. If you want a finely finished surface, buy a surface grinder or go at it by hand.
  • Tool geometry matters because like all machining processes, fly cutting produces cutting forces. Accordingly, we have to use the right insert in the right way. You are using a turning tool and twirling it around, which that insert was not designed to do. Does it work? Of course it does, but are the right edges or surfaces making contact so that the insert works as it should? This is why I suggested that angling your SCLCL tool might not be a good idea because you are then cutting with the nose radius and that greatly increases radial cutting forces and may produce unpredictable or suboptimal results. In contrast, the Superfly has a fixed geometry; you cannot alter the angle of the tool and the angle puts the insert at the desired geometry. The insert is commonly used in face mills so it is optimized to cut with the surface of the insert that makes contact with the work. The insert is a high positive rake insert that I think is intended to reduce tangential cutting forces, which is one reason why the Superfly works well on low HP mills. Bottom line on this is that the tool designers of the Superfly knew what they were doing. Even when taking deep cuts, the Superfly works. On light cuts, the user has to understand that there is a minimal effective cut and that is typically going to be the nose radius plus about a 0.005" or so. Too light a cut and the insert will deflect and you have chatter.
  • Tram is always an issue. I would guess that most mills are trammed well enough to function quite well but when fly cutting we are looking at the effect of minute amounts of tram being off. We're talking in the sub-thou range of off. So why does the pattern seem to change when we feed from different directions? I think this is the effect of climb vs conventional milling, and going in a climb direction will typically produce a better finish. I see this effect with my Superfly on my RF-31. I see less of an impact on my Sherline with the Sherline flycutter because that mill is trammed within an inch of its life but I still try to take finish cuts in a climb direction when finish matters.
  • Then there are centripetal forces and how they interact with cutting forces. This one is complicated and I still haven't figured out how to visualize how they interact. In my research, I haven't found anything to suggest anyone else knows, either. This is an important topic because it also applies to boring on the mill. I can bore and I can fly cut but do I honestly understand how the cutting forces are interacting? Nope, I don't. The reason this matters is because I think the finishes could be greatly improved with fly cutting if we could get a handle on this. Someday I hope to understand it, or at least hear it from someone who is a lot smarter than me.
A final note on why I think the Sherline fly cutter is an outstanding tool. As mentioned, it is essentially a singe insert tiny face mill. The insert is fixed and mounted in a solid chuck of steel. The insert is not hanging out there at the end of a flexing arm like the typical fly cutter is. Centripetal forces are there but they are minimal. Accordingly, you can take relatively huge cuts with this tool and it will cut well. Because the geometry is fixed and is so solidly supported, the finish is much better with this tool as opposed to more conventionally designed fly cutters. It will put a finish on aluminum that will frost your eyeballs, at least with the unaided eye. Under magnification, you will still see the radial marks of a typical insert but they are much finer than with most inserts. I may seem to make a big deal about this little Sherline tool but I have over 30 years of experience with it and have come to understand why and how it works. Sherline found a way to orient the insert so that it cuts well with one edge oriented vertically (so it can cut to a shoulder); it cuts with the side edge primarily and with light cuts, with the nose radius. However, since the nose radius is very nearly in line with the spindle and it has a mass of steel behind it, deflection is pretty well controlled and that allows a Sherline fly cutter to take lighter cuts and still be fairly accurate when doing so.

Sherline finally woke up and made this tool with a straight shank. This allows us to hold it in a collet instead of a MT1 adapter. This is such a good idea that I'm sure it will sell much better as more people discover this tool. I used mine in a adapter and it worked well but of course, it never dawned on me to just turn the stupid shank down so it didn't have a taper ... Duh! Still, turning it down would have resulted in a much reduced shank diameter so I just decided to buy one with a straight 1/2" shank and will now be happy.

Okay, I'm sure I'll have other thoughts but off the top of my head, this is what I think.
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Okay, thanks Mike. Typically thorough response I hoped I'd hear from you. I'll need to study your response in detail, but tonight my brain is just toast. It's almost 9:00 PM my time, and I just got in from helping a friend RE-bale about a thousand bales of wheat straw that were bailed incorrectly - AND we were trying to beat a rain storm. (What a job, but we won!) I'll need to sleep on this, but I fully appreciate your superior knowledge on this subject.

Your first comment about fly cutting hits home with why I'm interested in picking your brain: "Fly cutting is not a finishing process. The intent is to obtain a truly flat and accurate surface, which fly cutting does quite well..." That observation removes quite a bit of uncertainty on my part. I am, indeed, getting a flat surface (that's a good thing); and apparently, the finish that I'm getting is fairly consistent with results on the videos I've seen (that, too, is a good thing). I need to study the rest of your response tomorrow. There's a very good chance that you may yet convince me to fork over the dough and get a Superfly. But not tonight. See how easy it is to tempt neophytes to spend their money?

Regards, and thanks for your typically thorough response. I'd be willing to bet I'm not the only reader who gets an education from your answer.

Regards,
Terry
 
jwmelvin said:
I have some single-insert end mills that use a TPG. Like buffalo21 says, they seem a little high impact on the machine. Why is the Sherline approach better? I know the inserts are different but they seem similar in the lack of positive rake.
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I don't know if it is better. For all I know, it isn't. I just found this tool listed on MSC. 3" fly cutter with an R8 shank that uses TPG inserts. It is essentially a single insert face mill.
 
You guy's are late to the party, look Mikey's been here. :)
 
I have this insert, and a silver insert which is for what, it's not noted on the ziploc?
 
Okay, mikey. You have me convinced to go for the Superfly cutter.

I have the MicroMark HSS steel flycutter, but I haven't been happy with it. I can't get a good finish and I can only take baby cuts. It takes me forever to square up and dimension stock. I probably have the cutter ground incorrectly, but I feel I'll never be able to take decent DOC and feed rates with it.

So, the Superfly will be okay on my PM25?
 
I think it will work fine. This fly cutter is intended for use on low HP mills. I recall they tested it on the Tormach 440 model and it kicked butt. My RF-31 currently has only a 1HP Baldor motor on it and it can really hog off material. Granted, the Tormach is a 600# machine and mine is close to that so I'm not sure how a 300# mill will handle it but it cuts with so little force that I really think it should work fine for you ... I think. I know @higgite has one but I cannot recall which mill he has. Maybe he'll give us an opinion.

Give it a try and let us know how it works out for you.
 
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