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Maximum tool stick out on a fly cutter

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ZombiWelder

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#1
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.
 

Bob Korves

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#2
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... :eek 2:
 

ZombiWelder

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#3
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... :eek 2:
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.
 

Bob Korves

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#5
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?
 

Bob Korves

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#6
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...
 

ZombiWelder

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#7
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.
 

ZombiWelder

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#8
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?
 

Downunder Bob

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#9

Downunder Bob

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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.
 

Bob Korves

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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
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.
 

Downunder Bob

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#12
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.
 

P. Waller

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#13
Do what works, if something does not work you will not do it again.

This is called experience.
 

higgite

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#14
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
 

P. Waller

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#15
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
 

Downunder Bob

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#16
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.
 

Downunder Bob

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#17
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
More like walking, and not to work, but hunting and gathering.
 

markba633csi

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#18
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.
 

Bob Korves

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#19
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.
 

markba633csi

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#20
"Jaws" theme Da Da Da Da
 

P. Waller

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#22
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.
 

mikey

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#23
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.
 

stupoty

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#24
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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#25
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.
 

Mitch Alsup

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#26
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.
 

stupoty

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#27
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
 

P. Waller

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#28
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.
 

tomw

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#29
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....
 

Mitch Alsup

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#30
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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