# DIY Flycutter with 3/4" Shank



## Xyphota (Sep 19, 2022)

I made a fly-cutter. It seems fly-cutters are generally considered dust-collectors because of face mills, and I do plan on purchasing a 2-3" face mill. I figured if I was going to make a fly-cutter, why not potentially give it some utility over a face mill and make it extra large? I think I can sweep about 6" with this.

I tackled the project without a drawing and sort of just made it up as I went. The left-handedness was totally planned from the beginning and definitely not an accident.


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## trlvn (Sep 20, 2022)

So I've been playing at grinding a cutter for my flycutter.  It appears you are using a massive piece of HSS for yours?  What kind of geometry did you use?  Mine has roughly 7 degree clearance angles on the underneath and end.  The side and back rakes are about 13 degrees each.  Approximately a 1/32" radius or maybe a little less.

As a first test, I used a piece of H13 steel (courtesy of @Canadium ) which is pretty hard and tough stuff.  The finish is poor, however.  (Click on the picture to zoom.)






I think I had the feed rate too high for the RPM the cutter was running.  Ran out of time yesterday to try different combinations.

Incidentally, I believe my tool blank is cast alloy (like Stellite or Tatung G).  The piece was unmarked but came with some other Stellite pieces.  It is non-magnetic like other cast alloys.  Cast alloy can stand up to more heat than HSS and so can be run up to 2X as fast.  It is also quite impact resistant.  I think both of these things should make it really good for a fly cutter bit.  

OTOH, it is unbelievably tough to grind.  You are not supposed to dunk it in water to cool it while grinding.  Apparently temperature shocks can make cast alloys brittle.  I found I could grind for a minute or so (coarse wheel on 6 inch grinder) and then it would be too hot to hold.  I had to leave it for 5 minutes on a cast iron surface while it cooled.  Rinse and repeat.  

Craig


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## PaulL (Sep 20, 2022)

Xyphota said:


> The left-handedness was totally planned from the beginning and definitely not an accident.


Nope, I didn't do that either ;-)


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## Xyphota (Sep 20, 2022)

@Craig I am using a very large piece of HSS as I figured the extra stiffness would benefit the larger span. I was keen to throw it in the mill and I had little time to complete the grinding yesterday so I just left the rank angle neutral. But the rake angle especially I believe is a function of the material you are cutting, so I'm not sure if your setup would benefit from more or less rake. I also think my nose radius is a bit larger, maybe 1/16"? 

It looks like your table might be moving too far between cutter rotations. The first thing I would try is just moving the table half as fast. (Potentially 25% as fast if you are also going to be slowing the RPM down). Increasing the nose radius so the cutter is removing a wider chip should also improve your surface quality but I think this also increases cutter forces so if your are close to the horsepower limits of your machine, this might not be an option.


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## trlvn (Sep 20, 2022)

@Xyphota I think you are right.  I slowed down the feed so somewhere between 1 and 2 inches per minute (the DRO will display feed rate but it jumps between whole numbers).






I think I will try increasing the nose radius a bit.  I'm only taking off 8 - 10 thous for testing.  The cutter "thumps" but the machine doesn't seem to be working hard.

For you guys with a 1.5 HP mill/drill, how deep a pass will your machine take when roughing?

Craig


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## Degen (Sep 23, 2022)

trlvn said:


> @Xyphota I think you are right.  I slowed down the feed so somewhere between 1 and 2 inches per minute (the DRO will display feed rate but it jumps between whole numbers).
> 
> View attachment 26668
> 
> ...


I have a little more HP (2hp) , it really comes down to number of cutting edges, diameter, feed, rpm, cooling and cutter material (carbide is the way to go is you want to get aggressive).

I can't stress cooling enough, the biggest issue is cutters getting hot, be it HS or Carbide.  I am a big fan of flood cooling even if it makes a (big) mess.  I use Microchip from KBC and find that my bits have a long life.


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## Dabbler (Sep 23, 2022)

on my 2HP mill I still only take 5-6 thous per pass with my fly cutter.


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## cuslog (Sep 23, 2022)

I "try" to keep it to just .001 or .002" per pass.
I learned the hard way - I hammered out the keyway of the motor shaft on my knee mill taking cuts too aggressive (up to .010") with a fly cutter - nearly sheared the key in half. The key is replaced easily enough but the motor shaft keyway hammered out is much more difficult to repair.


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## thestelster (Sep 24, 2022)

Xyphota said:


> I made a fly-cutter. It seems fly-cutters are generally considered dust-collectors because of face mills, and I do plan on purchasing a 2-3" face mill. I figured if I was going to make a fly-cutter, why not potentially give it some utility over a face mill and make it extra large? I think I can sweep about 6" with this.
> 
> I tackled the project without a drawing and sort of just made it up as I went. The left-handedness was totally planned from the beginning and definitely not an accident.


Nice work!  I know you were just experimenting,  but may I suggest cutting so the table is moving along the x-axis, and the cutter is cutting towards the fixed jaw of your vice.  Also, this way you can decrease the sweep diameter, so that you can increase your rotational speed.


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## trlvn (Sep 24, 2022)

Dabbler said:


> on my 2HP mill I still only take 5-6 thous per pass with my fly cutter.





cuslog said:


> I "try" to keep it to just .001 or .002" per pass.
> I learned the hard way - I hammered out the keyway of the motor shaft on my knee mill taking cuts too aggressive (up to .010") with a fly cutter - nearly sheared the key in half. The key is replaced easily enough but the motor shaft keyway hammered out is much more difficult to repair.



@Dabbler Are you also concerned about the interrupted cuts causing damage?  

I've just got my fly cutter working this week.  As I mentioned, I've ground a piece of cast alloy steel since it is supposed to take twice the heat of HSS and handle shock loads well.  Since my first test, I've increased the cutting edge radius and I think I could increase it some more.  For testing, I've been taking up to 0.015" DOC in H13 steel.  With about 2.7" radius, at 285 RPM, I was getting thin curly chips with no colour.  It does 'thump' when the cutter engages but I found that was reduced if I lightly filed the edges of the workpiece first (basically just deburred the edges).

Since my little 10 inch lathe will happily take a 0.030 DOC in steel, I figured that since the mill-drill has roughly twice the horsepower should have no problem with what I was asking.  Am I deluded?

In steel, how deep a cut will you take with a carbide face mill?  I take it that is what you would use to really reduce a larger piece of stock?

Craig


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## cuslog (Sep 24, 2022)

Should maybe clarify my comments a bit:
The DIY fly cutter I made was hitting the (mild steel) work piece "square" in a kind of "chopping" motion on a 6" wide cut x .010" deep. I won't do that again. I now have a 2.5" wide face mill that I will take up to .025" DOC but the inserts are sloped / angled such that they are "slicing" the material rather than "chopping". Just "feels" much easier on the machine


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## thestelster (Sep 24, 2022)

trlvn said:


> @Dabbler Are you also concerned about the interrupted cuts causing damage?
> 
> I've just got my fly cutter working this week.  As I mentioned, I've ground a piece of cast alloy steel since it is supposed to take twice the heat of HSS and handle shock loads well.  Since my first test, I've increased the cutting edge radius and I think I could increase it some more.  For testing, I've been taking up to 0.015" DOC in H13 steel.  With about 2.7" radius, at 285 RPM, I was getting thin curly chips with no colour.  It does 'thump' when the cutter engages but I found that was reduced if I lightly filed the edges of the workpiece first (basically just deburred the edges).
> 
> ...


Hi Craig, I checked on an app that I have, FSWizard, and for HSS cutter, 5.4" diameter, on tool steel, with a depth of cut of 0.015, it indicates a spindle speed of 68rpm @.47in/min.


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## Degen (Sep 24, 2022)

trlvn said:


> @Xyphota I think you are right.  I slowed down the feed so somewhere between 1 and 2 inches per minute (the DRO will display feed rate but it jumps between whole numbers).
> 
> View attachment 26668
> 
> ...


One other thing looking at your cut, you head needs a little more tramming to get it true.  Took me a while to figure this out and it resulted in better cuts.  Note on have cuts smaller machines (including mine even though it is a small knee mill) tend to drift from proper alignment because of loading during feeds

I am going to be installing an adjustable link between the head and column to increase the stability of the head.

Awareness lets one mitigate negative effects.


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## Dabbler (Sep 24, 2022)

trlvn said:


> re you also concerned about the interrupted cuts causing damage?


I use 1/4" cheap HSS blanks ground to a neutral rake tool.  I never hit the work at 90 degrees with the cutter.  Where it encounters the work should be around 30-45 degrees.


trlvn said:


> since the mill-drill has roughly twice the horsepower


Horsepower doesn't enter into it.  a fly cutter is a fairly flimsy tool...  Even the suburban tool 1000$ fly cutter can only take shallow cuts.  You use a fly cutter for a nice finish, , and flat up to the tram of your mill. My machines are pretty heavy and they still get a poor finish after about .005 DOC.


trlvn said:


> ow deep a cut will you take with a carbide face mill


I have a 3/4" face mill and  a 1 1/2 inch face mill.  I take shallow cuts on those too - they are both offshore cheapoes and I don't need to push a big chip anyway.

If I had a Sandvik 4" face mill, it would be pushing the limits of my R8 spindle, but I think I could take about .020 - .040 DOC at about 1200RPM with a slow feed.  An ISO40 spindle could take more, with slightly faster feed rate.


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## trlvn (Sep 24, 2022)

thestelster said:


> Hi Craig, I checked on an app that I have, FSWizard, and for HSS cutter, 5.4" diameter, on tool steel, with a depth of cut of 0.015, it indicates a spindle speed of 68rpm @.47in/min.


Argh, I wrote 2.7" radius but actually meant 2.7" diameter!

The LittleMachineShop calculator gives 127 RPM for milling 2.7" diameter Alloy Steel so I doubled that for a Cast Alloy tool.  And then bumped up the speed a little.  On Youtube, both Tom's Techniques and Oxtools (Tom Lipton) seem to run faster than what would otherwise be calculated.  For example, on Tom's Techniques, he calculated that 177 RPM was appropriate...and then used 250 RPM with basically no explanation.  He did take a 15 thou DOC on steel, as well.

I should mention that my cast alloy tool bit has side and back rake so it cuts with somewhat of a slicing action.  When I got the fly cutter (used), it had a cemented carbide cutter in it.  No back or side rake and it really thumps when it cuts.  

BTW, I 'painted' cutting oil on the surface of the workpiece.  Tom's Techniques did not do that for the steel he was cutting.  I figured it couldn't hurt and might help keep the heat down.

Craig


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## trlvn (Sep 24, 2022)

Degen said:


> One other thing looking at your cut, you head needs a little more tramming to get it true.  Took me a while to figure this out and it resulted in better cuts.  Note on have cuts smaller machines (including mine even though it is a small knee mill) tend to drift from proper alignment because of loading during feeds
> 
> I am going to be installing an adjustable link between the head and column to increase the stability of the head.
> 
> Awareness lets one mitigate negative effects.


I agree.  I think my fore-and-aft is set pretty well but the left-right could be improved.  With my RF-30 style machine, though, getting that really accurate is...tedious.  Really tedious.  One day, I'll have another go at it.

Loading is definitely an issue too.  While attempting to tram the machine, I found that I could lift the head at least a thou with little effort.  A honking big mill is just not in the cards, though, so I'll live with that.  

Craig
(So far, the most frequent and troublesome problems with my tools would have to be attributed to the operator!)


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## Degen (Sep 24, 2022)

trlvn said:


> I agree.  I think my fore-and-aft is set pretty well but the left-right could be improved.  With my RF-30 style machine, though, getting that really accurate is...tedious.  Really tedious.  One day, I'll have another go at it.
> 
> Loading is definitely an issue too.  While attempting to tram the machine, I found that I could lift the head at least a thou with little effort.  A honking big mill is just not in the cards, though, so I'll live with that.
> 
> ...


Now if the machines could only get rid of error prone operators......


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