# Critique my flycutting results



## chris.trotter (Feb 23, 2018)

A lovely present was in the mail when I got home - an R8 flycutter!  Got it cleaned up, ground the HSS blank, and took some test cuts.  I definitely need a power feed on the X-axis, haha!

*Some questions!!*
 - The chips/dust produced - what does that indicate?
 - When running this past about 200rpm, the entire machine goes into harmonic vibrations until about 700rpm? - normal for a flycutter on a small machine? (_I haven't bolted this to the counter yet_)
 - Other input/suggestions?

*Wooo*



*Result of two passes*
 - Center of cutter diameter was in line with the left side of this round stock. 
 - First pass, very light (_2-3 thou_).  Second pass, 5-6 thou.  
 - Very slow manual feed rate. (_uh.... 5 thou a second?  Maybe a bit less?_)
 - It took about 5-10m per pass (_my kingdom for a power feed!_)
 - About 200rpm spindle speed (_guessing - I have no RPM meter yet_)

The center of the blank has some ridging, but I suspect that's because I didn't get past the rough hacksawn surface.  The outer edge is perfectly flat.

During the cut, there was a kind of flat chip being produced and pushed forward, and the rest is just that dust you see.



*Cutter grind*
Based off this post's guidance: how-do-i-sharpen-hss-blanks-for-fly-cutting

I ground it in, then used a 'normal' diamond card to hone it as best I know how.  After watching the Tom's Techniques video on flycutting, I have some more grinding knowledge to apply for next time!


----------



## Billh50 (Feb 23, 2018)

It looks to me like you have that cutter sharpened wrong. It may be me but from the pics it looks like the cutting may be happening back from the end where there is not enough relief. I would have just sharpened the blank with a relieved radius.


----------



## chris.trotter (Feb 23, 2018)

Thanks Bill - I am sure it is in some way inaccurate.  Here's a very rough sketch of the basic idea:


 - Arrow shows direction cutter is spinning

I don't have an angle gauge, so it's all just by eye right now.  I will be trying something like this next:  Fly cutter geometry

What do dusty chips mean?


----------



## RandyM (Feb 23, 2018)

chris.trotter said:


> Thanks Bill - I am sure it is in some way inaccurate.  Here's a very rough sketch of the basic idea:
> 
> - Arrow shows direction cutter is spinning
> 
> ...



What is the material you are cutting?


----------



## chris.trotter (Feb 23, 2018)

Oh, sorry!  It's mild steel - I think 1018.


----------



## Billh50 (Feb 23, 2018)

here's a older post on fly cutter geometry.
https://www.hobby-machinist.com/threads/creating-a-fly-cutter-bit.9678/


----------



## chris.trotter (Feb 23, 2018)

Bill, that's excellent, thanks!  PDF was a good read - more fodder for my next attempt.


----------



## Eddyde (Feb 23, 2018)

Here is a photo of one I ground for my fly cutter, just a radius on the tip like Bill mentioned. In this picture I was using it vertically to mill a relief but it works horizontally just as well.


----------



## Billh50 (Feb 23, 2018)

This is what I usually do for a bit.


----------



## markba633csi (Feb 23, 2018)

The dust means it's rubbing not cutting- need to improve your tool geometry
Mark


----------



## chris.trotter (Feb 23, 2018)

markba633csi said:


> The dust means it's rubbing not cutting- need to improve your tool geometry
> Mark


Ah, perfect!  Thanks.


----------



## Silverbullet (Feb 23, 2018)

The angle of the dangle isn't angled enough lol . Ok it's just not cutting only on the tip it's rubbing ,, making the powder ,, if you grind the back of the angle off a bit it should be better. With a touch of coolant your finishes will get better.


----------



## MSD0 (Feb 23, 2018)

chris.trotter said:


> Thanks Bill - I am sure it is in some way inaccurate.  Here's a very rough sketch of the basic idea:
> View attachment 259334
> 
> - Arrow shows direction cutter is spinning
> ...


Your sketch looks right, but the tool looks like it’s upside down in the first picture. Maybe it’s just the pic (or my eyes).


----------



## chris.trotter (Feb 23, 2018)

Silverbullet said:


> The angle of the dangle isn't angled enough lol . Ok it's just not cutting only on the tip it's rubbing ,, making the powder ,, if you grind the back of the angle off a bit it should be better. With a touch of coolant your finishes will get better.


Coolant, good point!  I had brushed on some Tap Magic, as it's all that was handy at the moment.  Honestly, a lot of the geometry stuff is probably just wayyy off, and I need practice sharpening HSS.



MSD0 said:


> Your sketch looks right, but the tool looks like it’s upside down in the first picture. Maybe it’s just the pic (or my eyes).


The tool _is_ upside down.    Also it looks odd because you can't see the downward cant of the toolbit.


----------



## JR49 (Feb 23, 2018)

chris.trotter said:


> Other input/suggestions?


      chris.   When I'm grinding a bit for flycutting, I can never picture the shape and angle I need until I put it into the the flycutter and hold it facing down like it will be when machining.  
	

		
			
		

		
	




	

		
			
		

		
	
I took 2 of your pics and rotated them upside down and you can easily see that it is cutting at the lowest point (yellow circle and arrow) rather than the point you intended it to cut on (red).  At the yellow points it would probably cut fine but, as others have already said there is no relief.  not saying this is the perfect grind, but that will come with practice.  Billh50 showed an excellent grind.  Hope the upside down pics help.  JR49


----------



## chris.trotter (Feb 23, 2018)

Thanks JR49!  When actually mounted in the machine, the red part is the only part actually touching, but I suspect I haven't done enough relief, or really understand where the sharp edges need to be (thinking I probably dulled the bit rather than sharpening it when I ran over the diamond stone)


----------



## mikey (Feb 23, 2018)

chris.trotter said:


> ... but I suspect I haven't done enough relief, or really understand where the sharp edges need to be.



Take a good look at the tool that @Billh50 posted. It is basically a LH turning tool with a fairly large nose radius. The nose is where it cuts and the relief angles are under the cutting edges. Another option is to buy a brazed carbide LH turning tool and round the nose a bit and sharpen the carbide part. It works quite well and lasts a long time.


----------



## chris.trotter (Feb 23, 2018)

Thanks mikey.

Here's some interesting reading: https://www.cnccookbook.com/fly-cutter/


----------



## EmilioG (Feb 24, 2018)

Are there LH and RH cutting flycutters?


----------



## chris.trotter (Feb 24, 2018)

Until I wire up a reverse switch, my machine only spins clockwise.

Based on what others have said, my cutting face is vertical, it needs to be angled back - plus I need some radiusing.


----------



## Bob Korves (Feb 24, 2018)

EmilioG said:


> Are there LH and RH cutting flycutters?


Symmetrical fly cutters with horizontal tool slots work in both directions.  I have several.  Fly cutters are also fairly easily shop made in whatever direction you prefer.  Making a one off custom cutter for a particular job can be worthwhile, and it will likely also be used later on other and different jobs.  Can't have too many!


----------



## MrWhoopee (Feb 27, 2018)

I have a similar fly cutter. The head of mine is 2.5 diameter. Using 80 SFM cutting speed for 1018 and the tool sticks out 1/2 inch, 80 x 4/3.5=91 rpm. 
(cutting speed x 4/ diameter). While it won't contribute a lot to your cutter grinding skills, I recommend a brazed carbide tool for this application.
The higher rpm range gives better finishes, particularly in 1018.


----------



## chris.trotter (Feb 27, 2018)

I took another crack at this on Saturday, it did not go well, haha.

This was the first re-grind I attempted.  The second I did not get pictures of, but I tried to get it looking like the one BillH posted.  Both failed pretty badly.  Ran out of time, and I'm out of the country on business this week, but will give it another shot on the weekend.

I have a bunch of spare lathe tooling that I will see about putting in the flycutter, but my real problem is that the machine vibrates and generally goes bananas when you turn it past 1/4 speed.  (possibly due to it not being bolted to the countertop)

Dented but not daunted.


----------



## epanzella (Mar 4, 2018)

Based on your description of chips AND dust it sounds like part of the edge is cutting and another part is rubbing.  Seems like you're close but no cigar!


----------



## chris.trotter (Mar 15, 2018)

Round...3?

I found another view of cutting geometry online, tried it.  I think the key for my brain is to have a very clearly laid out grind geometry, those examples seem to serve me best.  This attempt cut wayyy smoother, but left an unpleasant surface finish.

Speed was low (_due to the size of my machine_), very low (200-400rpm?) speeds are the only ones that won't start resonating or vibrating the entire machine too much.  Feed rate was very slow, used oil to lubricate.  Chips looked much more like "normal" chips - did not notice any dust (_although maybe the oil absorbed it_?).






And here's the result:



Thoughts?


----------



## mikey (Mar 16, 2018)

Chris, go to post #9 and look at the bit that Bill showed you. This is a left hand turning tool shape that works well in a fly cutter. The shape of your cutter in post #25 is not going to work well. You must have relief angles under the side cutting edge and you need side and back rake as well as a decent nose radius. The tool in your post is just going to hammer at the work piece so yes, you can expect vibration because the tool is not cutting. 

Go here and look at this thread: https://www.hobby-machinist.com/threads/how-to-grind-a-hss-turning-tool.52581/. The tool in the article is a right hand tool. You need to grind a mirror image of that tool but the process is exactly the same. Stone a 1/32" nose radius on it and the tool will cut well for you.


----------



## chris.trotter (Mar 16, 2018)

Yeah, I feel like I might be coming across as obtuse - I looked and pondered at that pic, but my brain couldn't figure it out.  Will look at that post and try again today.


----------



## chris.trotter (Apr 2, 2018)

I have made two more attempts at this.  The first of these gave identical results - I think because the radius was too large, and the relief angles too shallow.  It ended up rubbing the cutting tip right off the tool.

The second (lol fourth) attempt I made the relief angles much steeper, and the cutting tip radius much smaller.  It did the same thing, ended up completely removing the cutting tip.

Fifth time's the charm?  lol.

@Billh50 would you be able to provide some more pictures of what you have in post #9?


----------



## MrWhoopee (Apr 2, 2018)

chris.trotter said:


> Speed was low (_due to the size of my machine_), very low (200-400rpm?) Thoughts?



Chris, what is the diameter of your fly cutter?
With a high speed cutting tool, 200 rpm would be appropriate for a cutter of approximately 1.50 diameter, at 400 rpm the cutter would need to be under 1 in. diameter. I think you're running too fast.


----------



## chris.trotter (Apr 2, 2018)

I read something somewhere (lol) that said HSS needs faster speeds (like 1500+rpm).  During my geometry tests, I try low and high speeds.

If by diameter you mean, the circle the cutting point turns around, I think it's something like 3-4".  Is this something I can look up in Machinery's Handbook?  (I have a copy, but have no experience in using it as a tool)


----------



## MrWhoopee (Apr 2, 2018)

chris.trotter said:


> I read something somewhere (lol) that said HSS needs faster speeds (like 1500+rpm).  During my geometry tests, I try low and high speeds.
> 
> If by diameter you mean, the circle the cutting point turns around, I think it's something like 3-4".  Is this something I can look up in Machinery's Handbook?  (I have a copy, but have no experience in using it as a tool)



Yes, the diameter of the circle that the cutting point turns. The appropriate rpm is determined by the diameter of the cutter, the larger the cutter, the lower the rpm must be. In my previous post, I gave an approximate formula for determining the correct rpm based upon the cutting speed of the material (in surface feet per minute) and the diameter of the cutter. The formula is:  Cutting speed (of material) x 4/diameter. This is for high speed steel cutters, carbide can be run 2-10 times as fast.

The cutting speed of C1018 steel is given as 80-100 sfm (surface feet per minute). 4x80=320/4 (diameter of cutter)=80 rpm.
You may find higher cutting speeds listed in different charts, I tend to be conservative to prolong cutter life.
This formula is used for any type of high speed cutter including lathe tools, drills etc. Memorize the formula. For quick reference, a 1 in. diameter drill should be run at 320 rpm, 1/2 in. at 640 and 1/4 in. at 1280. Remember these numbers and you will never be very far off.

I think your grind is fine, you're just running the cutter much too fast. As I suggested before, with a fly cutter of this diameter, you would be better served with a brazed carbide bit.


----------



## MrWhoopee (Apr 2, 2018)

In Machinery's Handbook, look up the section on Speeds and Feeds. There are tables of cutting speeds for all types of materials.


----------



## chris.trotter (Apr 2, 2018)

That's excellent, thanks.  Apologies for glossing over it earlier, and thanks for taking the time to respond.

I have a pile of brazed carbide lathe bits, will give it a try.  In my head I keep hearing "only use carbide if your machine can handle it" (_my understanding is that to effectively cut with carbide, you need horsepower and speed_), which is mentally blocking me from thinking it'll work well.


----------



## Billh50 (Apr 2, 2018)

Chris,
not sure if this will help. But it would be a couple days from now before I can get a photo of the one in my fly cutter as I just had chemo this morning.


----------



## chris.trotter (Apr 2, 2018)

Jeeeepers...hope the outlook is good for you.  You're a champ for posting at all!

Yup, that confirms that the geometry is correct, is what my latest attempt looked like, for the most part.  The top angle (clearance angle?) on mine was less aggressive, and the radius was much smaller, but the 'end' view looks almost exactly like it.

The radius I have read needs to be smaller (1/64, 1/32) for steel, and larger (1/16, 1/8) for aluminum - is that information in Machinery's Handbook, too?


----------



## Billh50 (Apr 2, 2018)

that seems good. i use the larger 1/8 for aluminum. For steel I start off with a 1/64 and end up going larger as I need to sharpen the tool bit.


----------



## chris.trotter (Apr 3, 2018)

You guys are awesome.  I re-ground the tool bit (attempted to give the face some more angle, too), stoned it, then gave this another shot using what I estimated to be ~80-100rpm.  It works!!  Still not a mirror finish or anything, but an order of magnitude better than my previous attempts.

I experimented with feed speeds, too.  Well, as best as one can using a mini-mill and no power feed.   

Speed did not appear to affect the visual quality, but it is semi-noticeably smoother when I was feeding it veerrrry slowly.  At the fastest I dared to go, the appearance was the same, but you can barely feel with your fingernail some ridges.  It did actually manage to bind up entirely for a second, but you could push it pretty fast, lots of "nice" chips coming off.  This was also a pretty thin cut, fwiw.  I'm still struggling with conversions, but ~2-3 thou probably?

So I guess the last question would be - is this an acceptable flycut appearance?  Anything else I can do to improve?


----------



## Billh50 (Apr 3, 2018)

That finish looks good. Different materials will give you a slightly different appearance also. Some will shine like a mirror and others may stay dull but look and feel good.


----------



## chris.trotter (Apr 3, 2018)

If I have time this week, I'll give the carbide a shot, too, just to see what happens.  Thanks again everyone!  I was so pleased after this, recharged me after the many failures.     Was a great lesson in perseverance.


----------



## MrWhoopee (Apr 3, 2018)

Looking much better. I'm guessing that the rigidity of your mill is the limiting factor for further improvement. Now try the carbide at about 500 rpm. Remember that a carbide will not hold up well if ground like HSS. I don't regrind brazed carbides, I use them as they come, but I've got a full-size BP copy and I'm lazy. YMMV

Thinking about this a little more, that's an awfully big fly cutter for a mini mill. I'd suggest getting one about half that size.


----------



## chris.trotter (Apr 3, 2018)

I have no real way of regrinding carbide anyways, but will try with what I have.  When I bought my lathe, while it's a bit of an ancient thing, it did come with a pile of tooling and accessories (like 70-80 hss/carbide toolbits).

The fly cutter was the only R-8 shank available from KBC, and it's definitely too big, haha.  The harmonic vibration kicks in around 300-400rpm and is rather violent.  Below that, runs nice and smooth.  Around 1500rpm it gets smooth again, lol.  I wonder if I can turn it down on the lathe...


----------



## MrWhoopee (Apr 3, 2018)

Go with a straight shank fly cutter in a collet. I got a little set of 3 with 1/2 in. shanks and use them much more than the big one. 
https://www.ebay.com/itm/SHARS-1-2-...778453?hash=item4ceb64fc55:g:VrsAAOSwD0lUbijC


----------



## chris.trotter (Apr 3, 2018)

Thanks MrWhoopee, will keep that in mind for future purchases.  Don't have any R8 collets at the moment, but looks like a 1/2" R8 collet & 3/4" or 1 1/8" body fly cutter only adds up to ~$30.  I'm happy with the finish even in this state, a lot of what I'm making for the time being will be simple stuff like clamps.  Once I get into stuff I want to make pretty, will pull the trigger.

I should also do a test on some aluminum...have yet to really cut anything Al on the mill yet.  Figured steel was a better practice medium, enforce good habits and whatnot.


----------



## chris.trotter (Apr 19, 2018)

Just wanted to say thanks again - did my first attempt of fly cutting aluminum last night, turned out beautiful!  (_well, to me_  )  Exact same tool I used for steel, slightly faster speeds, and dang I could feed way faster.  (_the weird coloured bands are due to fluorescent lights and the camera phone_)


----------



## Bob Korves (Apr 19, 2018)

chris.trotter said:


> Just wanted to say thanks again - did my first attempt of fly cutting aluminum last night, turned out beautiful! (_well, to me_ )


Looks really nice, Chris!


----------

