# Maximum tool stick out on a fly cutter



## ZombiWelder (Jul 6, 2018)

Howdy !
Gentlemen,  how much of 3/8 hss tool would let hang out a 2 1/2 fly cutter?  I got a 6x26 mill I'm hoping to make table extension out of aluminum slab I lucked out at the scrap yard. Hoping to flatten out 12" diameter in one go, I saw 3/8x8" hss on fleebay which would be long enough. The mill didn't vibrate a whole lot at 9" diameter cut but I didn't cut much out of caution. 
I briefly searched this question but did not find much. Any input is beyond appreciated! 
Best
Art.


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## Bob Korves (Jul 6, 2018)

I think that is far too much unsupported tool, and will tend to flex a lot causing intermittent cuts and other problems.  If you are just trying to make it pretty and don't care much about accurate sizing, more than standard stickout is possible, but a 12" cut on a 2 1/2" flycutter is way over the top in my book, even dangerously so.  If you throw a tool, sometimes it misses the operator...


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## ZombiWelder (Jul 7, 2018)

Bob Korves said:


> I think that is far too much unsupported tool, and will tend to flex a lot causing intermittent cuts and other problems.  If you are just trying to make it pretty and don't care much about accurate sizing, more than standard stickout is possible, but a 12" cut on a 2 1/2" flycutter is way over the top in my book, even dangerously so.  If you throw a tool, sometimes it misses the operator...


I'm not worried about pretty finish, I do want it as flat as a can reasonably get it, and repositioning the big slab accurately would be pain in the bacon. What would be maximum you'd suggest?  I'm thinking to super glue the hss  for extra friction and obviously super light cuts with a sharp tool.


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## ZombiWelder (Jul 7, 2018)

And what do you think of this kind of design 
Look at this on eBay http://www.ebay.com/itm/173368363466


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## Bob Korves (Jul 7, 2018)

ZombiWelder said:


> I'm not worried about pretty finish, I do want it as flat as a can reasonably get it, and repositioning the big slab accurately would be pain in the bacon. What would be maximum you'd suggest?  I'm thinking to super glue the hss  for extra friction and obviously super light cuts with a sharp tool.


The max I would try on your 2 1/2" flycutter is 6" total cut diameter, in general terms.  What kind of mill are you using?


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## Bob Korves (Jul 7, 2018)

ZombiWelder said:


> And what do you think of this kind of design
> Look at this on eBay http://www.ebay.com/itm/173368363466


I have not seen that specific configuration before, and it appears to be shop made.  The overall size of it compared to the shank size gives me pause, and I wonder how the shank is attached to the bar.  Still there are all kinds of fly cutters, which are simple tools.  Just never lose sight of the fact that they are inherently quite dangerous, but seem to be pretty safe with careful use and not pushing the envelope.  Machine tools in general are not inherently safe, they are inherently dangerous.  We try hard to keep from hurting ourselves...


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## ZombiWelder (Jul 7, 2018)

Bob Korves said:


> The max I would try on your 2 1/2" flycutter is 6" total cut diameter, in general terms.  What kind of mill are you using?


Its a Horror Freight 6X26 , I bought it used and maybe got a bit lucky: no voids in the casting,  or any other defects,  spindle runout is under .001.


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## ZombiWelder (Jul 7, 2018)

Thank you for the word of caution.  Yeah I was wondering about the attachment of that shank , it looks press fit or something . Me thinks with a welded 7/8 shank and carefull balancing that funky shop contraption could work, 12 in diameter,  250 rpm (lowest my mill would go )I'd be getting just about right 780ish SFPM , AmIright?


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## Downunder Bob (Jul 7, 2018)

ZombiWelder said:


> And what do you think of this kind of design
> Look at this on eBay http://www.ebay.com/itm/173368363466



That will do it, I like that it's symmetrical, it will be balanced while its spinning, you could even put two cutters in to make it quicker. something like this tool would be pretty easy to make at home.


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## Downunder Bob (Jul 7, 2018)

ZombiWelder said:


> Thank you for the word of caution.  Yeah I was wondering about the attachment of that shank , it looks press fit or something . Me thinks with a welded 7/8 shank and carefull balancing that funky shop contraption could work, 12 in diameter,  250 rpm (lowest my mill would go )I'd be getting just about right 780ish SFPM , AmIright?


About right, should be fine in Al.


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## Bob Korves (Jul 7, 2018)

ZombiWelder said:


> Its a Horror Freight 6X26 , I bought it used and maybe got a bit lucky: no voids in the casting,  or any other defects,  spindle runout is under .001.


With a mill that light, balance becomes more important, actually balance and eccentric weight combined.   You don't want it to walk off the table...  or damage the mill


ZombiWelder said:


> Yeah I was wondering about the attachment of that shank , it looks press fit or something .


My first impression was that it is threaded on, which might be a problem if it unscrews.


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## Downunder Bob (Jul 7, 2018)

It looks like a handy tool, not sure if shaft is screwed on or not. I always weld them on. I've made a few like it in the past, easily balanced with the extra holes. and no reason why you couldn't put more holes and increase diameter. A simple way to improve balance is to drill and tap a longitudinal hole through the body and put a grub screw in the light end winding the screw in and out will fine tune the balance.


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## P. Waller (Jul 7, 2018)

Do what works, if something does not work you will not do it again. 

This is called experience.


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## higgite (Jul 7, 2018)

P. Waller said:


> Do what works, if something does not work you will not do it again.
> 
> This is called experience.


Sometimes it's called history repeating itself. 
Can be good. Can be bad. Research is your friend. That's what the forum is for.

Tom


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## P. Waller (Jul 7, 2018)

higgite said:


> Sometimes it's called history repeating itself.
> Can be good. Can be bad. Research is your friend. That's what the forum is for.
> 
> Tom


Such work may be done several ways, facing it with a smaller diameter tool will leave tooling marks that many find objectionable, doing it very slowly with a large enough tool will not.

History tells us that the prefered method is to rough mill it then grind to finished size and surface finish. If I would have recommended this method many would have remarked that many home shops do not have the equipment for this and sending the part to a grinding shop would be costly.

My point being that if you do not try it you will not know if it can be done, the worst that can happen is that you scrap the first one. If it were customer supplied material and you can not easily replace one part then by all means go the traditional route that will surely work.

If a hobby project stretch your legs and have at it and see if it works, if no one tried a different approach to a problem you would be riding a horse to work everyday


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## Downunder Bob (Jul 8, 2018)

I would go for the fly cutter, pretty easy to make your own, have a look at this one for an idea. www.ebay.com/itm/173368363466  very easy to balance which is important.


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## Downunder Bob (Jul 8, 2018)

P. Waller said:


> Such work may be done several ways, facing it with a smaller diameter tool will leave tooling marks that many find objectionable, doing it very slowly with a large enough tool will not.
> 
> History tells us that the prefered method is to rough mill it then grind to finished size and surface finish. If I would have recommended this method many would have remarked that many home shops do not have the equipment for this and sending the part to a grinding shop would be costly.
> 
> ...


More like walking, and not to work, but hunting and gathering.


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## markba633csi (Jul 8, 2018)

Be aware that a large flycutter will magnify the runout of your machine spindle- if your machine has a quill be sure to lock it tight before milling
Personally on a machine like yours I wouldn't go bigger than about a  3" cutter (6" swath) in aluminum.  Smaller still for steel.


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## Bob Korves (Jul 8, 2018)

higgite said:


> Sometimes it's called history repeating itself.
> Can be good. Can be bad. Research is your friend. That's what the forum is for.
> 
> Tom


Sometimes it's called maimed or dead.  Pushing the envelope is great macho fun until we find the limits, then it's game over -- sometimes permanently.


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## markba633csi (Jul 8, 2018)

"Jaws" theme Da Da Da Da


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## Ken from ontario (Jul 8, 2018)

markba633csi said:


> "Jaws" theme Da Da Da Da


We need a bigger mill.


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## P. Waller (Jul 8, 2018)

Bob Korves said:


> Sometimes it's called maimed or dead.  Pushing the envelope is great macho fun until we find the limits, then it's game over -- sometimes permanently.


It would be difficult to injure oneself with such a small machine, if it has a 40,000 RPM capable spindle this is a different kettle of fish, no one would spin an unbalanced tool that large at that speed. If you spin a large fly cutter start at the slowest possible spindle speed and increase it if possible.
If it does not work at all you will have to go a different route, rough mill then finish by grinding. There is almost certainly a shop near you that does Blanchard type grinding.


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## mikey (Jul 8, 2018)

Art, you just need to flatten that piece of aluminum, right? What is the objection to making overlapping passes if that makes it flat? I ask because a flycutter normally uses nominal sized cutting tools, which means you will have about 1-1/2 to 2" of a 3" long, 3/8" tool bit sticking out. This gives you a cutting diameter of about 3-4", which is about the max you can expect. Using an 8" long tool might give you enough extension to span 12" but there may be enough resonance to make the finish/flatness a problem. 

The cutting forces you experience depends greatly on how your tool is ground and I hope you're pretty good at tool grinding if you go for that long a tool. 

Another option may be something like a Pinnacle Flycutter (https://www.pinnacleflycutter.com/) or maybe a B52 Flycutter (http://www.kristitool.com/shop/b-52-fly-cutter/). Both will do 12" at a go for a price.

Personally, I would do overlapping passes to get it flat and live with the pattern.


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## stupoty (Jul 9, 2018)

mikey said:


> Using an 8" long tool might give you enough extension to span 12" but there may be enough resonance to make the finish/flatness a problem.



Yea your probably much better to use narrower  passes which are smaller as the resonance will probably give an un even surface unless you run at a ridiculously slow rpm.

you could use fine abrasive paper spray mounted to glass after machining to get the last thou or 2 of total flatness.

like that tom does sometimes.  



  (he's using a sacrificial surface plate but glass is also a good thing to use)

starts sanding about 2:40

stu


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## Downunder Bob (Jul 9, 2018)

You can spin a fairly large fly cutter as long as you balance it. balance is always the key to spinning large diameter objects. It's also important that the cutter and its extensions are rigid. Your only problem then with a large diameter is to get the speed low enough. Small machines often won't go that slow.


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## Mitch Alsup (Jul 9, 2018)

stupoty said:


> Yea your probably much better to use narrower  passes which are smaller as the resonance will probably give an un even surface unless you run at a ridiculously slow rpm.
> 
> you could use fine abrasive paper spray mounted to glass after machining to get the last thou or 2 of total flatness.
> 
> like that tom does sometimes.



Tom is generally going for "Optically flat" or better than 1 micron.


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## stupoty (Jul 9, 2018)

Mitch Alsup said:


> Tom is generally going for "Optically flat" or better than 1 micron.



Yeah , when he's says flat he means really really really flat. 

But the sand paper thing he recons gets you to a couple of 10th's so for most purposes for a milling table thats probably flat enough for the majority of work.

Stu


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## P. Waller (Jul 9, 2018)

Downunder Bob said:


> You can spin a fairly large fly cutter as long as you balance it. balance is always the key to spinning large diameter objects. It's also important that the cutter and its extensions are rigid. Your only problem then with a large diameter is to get the speed low enough. Small machines often won't go that slow.


Correct
100 FPM is 32 RPMs at 12", I suspect that the machine will not go that slowly.


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## tomw (Jul 9, 2018)

This reply may not be necessary, but:

If the flycutter radius was, say, 4", at an rpm of 800, then the tip of the tool is moving approximately 20 mph. If things go **** up, you have a small but surprising problem that will be OK if you are wearing safety glasses. At an 8" radius, the tip would be moving at 38 mph. If the piece that is flying around has enough mass (say 100 grams), your safety glasses are probably in trouble.

Assuming my math is correct....


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## Mitch Alsup (Jul 9, 2018)

stupoty said:


> Yeah , when he's says flat he means really really really flat.



And then there is reference flat (1/20th wave of 550nm light or .01 micron). This becomes "difficult" on 20"+ optical flats.....


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## Larry42 (Jul 9, 2018)

Seems like you could make a disc type fly cutter with minimal tool stick out. It would probably run smooth enough at your slowest speed. If it is a bit out of balance just add weights until it smooths out. That is a lot of swing for that little mill! I'd go for multiple passes. The setup time is probably less than all the fooling around with giant fly cutters.


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## P. Waller (Jul 9, 2018)

tomw said:


> This reply may not be necessary, but:
> 
> If the flycutter radius was, say, 4", at an rpm of 800, then the tip of the tool is moving approximately 20 mph. If things go **** up, you have a small but surprising problem that will be OK if you are wearing safety glasses. At an 8" radius, the tip would be moving at 38 mph. If the piece that is flying around has enough mass (say 100 grams), your safety glasses are probably in trouble.
> 
> Assuming my math is correct....


A tool at 8" diameter at 800 RPMs would be cutting  at 1600+ FPM, this is well beyond what a high speed steel tool will do in ideal cutting conditions.
If the conditions are not ideal all bets are off, I would not exceed 200 FPM for such work in aluminum with HSS tooling.

However the OP may get away with dusting it off at that speed, say a .001" cut for a finish pass, you will not know until you try it. The worst that can happen is that you have to make another, stock aluminum shapes are cheap and easily sourced.

I will run aluminum parts in a lathe at 1200 SFM with carbide tooling in ideal cutting conditions, a large flycutter  with HSS tooling is Not Ideal.


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## Larry42 (Jul 9, 2018)

"250 rpm (lowest my mill would go)"
250*Pi*12"/12=785.39816339744830961566084581988'/min. For a 12" dia. cut.


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## P. Waller (Jul 10, 2018)

Larry42 said:


> "250 rpm (lowest my mill would go)"
> 250*Pi*12"/12=785.39816339744830961566084581988'/min. For a 12" dia. cut.


Way to fast for such a tool, In order to make this work I would use less then 40 RPMs, as I mentioned  you may be able to dust it off and have a satisfactory surface with a very shallow finish pass, this will work in some aluminum alloys but not all.

As many would ask, What Is The Proper Way To Do This job, the short answer is rough mill to around .005" per side big and grind it to finished size.
The long answer is try a whacking great flycutter and see if it works, if not you have only lost a cheap piece of stock material, if it is still within the  range of thickness required THEN grind it.
We did a job 2 years ago, 1 1/2" aluminum round bar cut 1 1/2"+long, all the blanks were cut in a bandsaw using a 1/16" wide blade.
12,000 parts, do the math and figure out how much stock went into the saw (-:

The purchasing agent came out into the shop and said that we were short 60' of stock and I told her that I knew exactly where it was, funny stuff


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## ZombiWelder (Jul 11, 2018)

Thanks a bunch gentlemen!   I think I'm gonna roll with Downunder Bob here. After watching everything Chris from Clickspring posted on YouTube a have a lot of faith in Australian machinists)  in all seriousness I happen to have some 1 1/2 square steel stock which would do OK I believe with 7/8 welded shank and 3/8 boring bar with carbide inserts.  People were asking why I don't want to do two passes : my table is 6x26,  the stock will be 12" x 30" x 1 3/4" aluminum that will be bolted to the ways so repositioning it accurately would be straight PITA !! I'm gonna use some strategic shimming and check to make sure that I'm not twisting the slab by bolting it. The table extension will allow me to pretend it's a big boy mill and   hold down large stock. Once I get to it  I'll either post a beautifully machined piece, or my shop mates will post a picture of my disfigured body as a lesson for everyone!


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