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Fly Cutters & Machine wear

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EmilioG

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#1
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?
 

Ulma Doctor

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#2
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
 

mikey

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#3
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.
 

Asm109

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#4
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.
 

markba633csi

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#5
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
 

Silverbullet

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#7
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.
 

EmilioG

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#8
So, for squaring blocks, use an end mill that is about 1/2 that of the block that is being squared?
 

Wreck™Wreck

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#9
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.
 

EmilioG

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#10
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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