Fly Cutters & Machine wear

EmilioG

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I read recently that the use of fly cutters on a mill can take a toll on the machines spindle/bearings and general wear & tear.
Is this correct and is it better to use a face mill or shell mill on a milling machine?
And with fly cutters, are insert tool fly cutters better than lathe bit fly cutters?

Can you square up stock just using a large end mill? If so, how large of an end mill in comparison to size of the stock?
 
Hi Emilio,
the interrupted cutting at deep depths will certainly shorten the life of any mill.
also the materials being cut also have a huge effect on the machine too.
maintenance and machine wear will also be factors.

i use a face mill until i need a fly cutter

i use large endmills to square up parts all the time.
you always want the minimum stick out on your endmills to keep them rigid.
i generally use an endmill size larger than the stock, if it that is possible
you can use small endmills for squaring- but they break easier if you mess up
i take light cuts when squaring until i get a feel for how the cutter is working in that material
i use multi flute cutters with steel when possible and use 2 flute endmills in softer materials
if you can get roughing endmills, they use up a little less HP than finishing bits for moderate to heavy cutting.
you'll spin small endmills fast, and big endmills slow.

i hope the information is helpful
 
I think the interrupted cuts a fly cutter makes can possibly wear spindle bearings but in a hobby shop, I have to wonder how big a risk this is. How often do we really use this tool? Personally, I use a flycutter to square most parts at the start of a project and have done so for many years. I've noticed no appreciable wear in my spindle bearings but I admit that I'm just a simple hobby guy.

I used to use lathe tool bits in my flycutter but I quickly gave that up for inserted carbide tools. Sherline makes an inserted carbide flycutter that is basically a single flute face mill and I use it on my Sherline mill and my RF-31. Leaves a beautiful finish, can cut shoulders and the inserts last a long time. I also own a Tormach Superfly and it works well but it only comes out when I have a wide part to flycut. It, too, leaves a fairly good finish, can take decent cuts and requires little horsepower. The inserts have a very positive rake and they cut well, albeit at fairly high speeds.

Bottom line is that theoretically, interrupted cuts probably wear parts on a mill. On a hobby mill used by a hobby guy on hobby projects, probably not something I would lose sleep over. But this is just an opinion and a guess - I have no proof of this.
 
I contend you can do a better job of squaring a block with a smaller diameter endmill than a large diameter face mill.
Why?
Lets say that you have the head of the mill trammed square to 0.001 inch in 4 inches. I am just picking numbers to make the math work out and make a point.
Use a 4 inch diameter face mill to cut a 4 inch wide block and the top surface will be out of square by 0.001.
Now replace the face mill with a 1 inch endmill and face it with 4 passes. Each pass is out of square by 0.00025 inches The surface a series of triangles 1 inch wide and 0.00025 high.
Use a 1/2 inch endmill and the error gets smaller still.
 
However... If you were to sweep the face in both x and y directions wouldn't the error come out pretty much the same?
Mark
 
The only fly cutter that I think would hasten wear is those new super cutters that cut wider then 3-4" . If you make the fly cutter with vertical slots and use two or four tool bits it shouldn't ever make it wear more then using a boring head.
 
So, for squaring blocks, use an end mill that is about 1/2 that of the block that is being squared?
 
So, for squaring blocks, use an end mill that is about 1/2 that of the block that is being squared?
No, use whatever tool will do the work the fastest way possible, think Metal Removal Rate.
If you require a very high degree of accuracy and surface finish at all times simply grind everything that you do after rough machining in lathes and mills, a cylindrical grinder will be your friend.
 
That would be nice. I have no plans to buy a surface grinder at this time., nor do I really need one.
I can live with a nice hand sanded finish after careful milling. But.... I was looking at the Tormach personal surface grinder.
Small footprint. It may fit in the corner of the shop I'm building. Who knows.

https://www.tormach.com/product_psg_612.html#docs
 
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