# Boring bar to fly cutter



## Alberto-sp (Aug 19, 2022)

Hello. I have a boring head and I want to use it as a fly cutter in this way





I would use this boring bar but the base of the boring head touch the piece I want to face  (sorry my english if this doesn´t make sense)





So I´m going to bend it in this way (putting it red hot)





The angles before the bending are these



 



I supose the 14º angle is OK, but th 5º how much can  it go bigger (obtuse, open)? Because the more I´ll bend the boring bar, the more obtuse it will be than angle.

Thank you


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## mmcmdl (Aug 19, 2022)

Why ? A 6" flycutter ? You won't have support to cut anything other than possibly plastic and I'm hoping you have a drawbar for the TS .


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## Alberto-sp (Aug 19, 2022)

Thanks for your answer.

I'll cut it. I wont keep it so long

What is TS?


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## Winegrower (Aug 19, 2022)

I think it’s worth messing around with stuff like this just for the learning experience.   You are going to know a lot about both boring bars and fly cutters when you get through with this.


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## Alberto-sp (Aug 19, 2022)

Nooo I prefer to know before having the boring bar encrusted in my cranium


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## extropic (Aug 19, 2022)

The 5° is OK for light cuts. The lower the angle, the more of the insert is into the cut meaning higher cutting forces.
The 14° worries me because that implies it's a Negative rake bar/insert.
I'm assuming you have a relatively light hobby mill so I would suggest a positive rake bar/insert to keep the cutting forces lower than negative rake.

TS = Tail Stock


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## Alberto-sp (Aug 19, 2022)

Thanks for your answer

So if I bent the draw bar the 5° angle will became for example 7 or 8° and the cutting forces will be softer right?

And yes I have a 750watts mini mill. 

I can reduce the 14° angle if is good for the purpose.

And I thought ts stands for tailstock but I wasn't sure because I din't see the connection with the milling machine


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## extropic (Aug 19, 2022)

Alberto-sp said:


> Thanks for your answer
> 
> So if I bent the draw bar the 5° angle will became for example 7 or 8° and the cutting forces will be softer right?
> 
> ...


I think you're missing the main point regarding the difference between positive rake and negative rake inserts.

Start a new thread to discuss the significance if you like.

I think you are wasting your time and money, but that's up to you and why they call it a hobby.
The interrupted cuts, typical of when using a fly cutter, will be hard on the boring head.
I think you're staring with the wrong kind of bar/insert.

Look at these accessories:









						BORING HEAD ACCESSORIES | mesatool
					






					www.mesatool.com


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## extropic (Aug 19, 2022)

Alberto-sp said:


> So if I bent the draw bar the 5° angle will became for example 7 or 8° and the cutting forces will be softer right?


Less insert edge in the cut = lower cutting forced (all other factors being equal).



Alberto-sp said:


> I can reduce the 14° angle if is good for the purpose.


Based on the flat on the shank, I assume the 14° angle is compatible with the intended insert geometry. If you change the 14°, what insert are you going to use?


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## mmcmdl (Aug 20, 2022)

I was actually referring to the Taper Shank of the holder in my above post .  Fly cutting with that long and weak of a tool might cause a few issues . A fly cutter is a cheap and readily available tool to acquire .


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## chip maker (Aug 20, 2022)

I think that the OP is just trying to use what he or she has on hand to make a usable tool for what ever part they are making. As this site implies most are just Hobby machinists we are not all flush with money that we can just go out and buy that perfect tool to get the job done. Many are probably on a fixed income and still wanting to have a hobby to keep them busy just the material now days takes alot out of the budget. It is nice that some people on this site try to keep that in context when they offer help. I only have a small 9 x 20 lathe and mini mill and have made many parts and tooling with both but it does take a bit longer and slower. I'm sure it would be great to just go buy any tooling needed  but not always possible. When you see some of the shops some have they are much larger and better equipped than any home hobby shop. Thanks to all who are willing to still help the Hobby Machinist.


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## mmcmdl (Aug 20, 2022)

Safety should ALWAYS be the number one concern regardless of the machines / tools we own . We try to stress this on this site , at home and in the workplace . Using a boring head with a tapered shank to fly cut is pushing the limit . If the interrupted cut pulled that taper shank out of the machine or un-screwed while running all holy heii would break loose . If the shank had a drawbar holding it in , it may be a different and safer operation , but still , not the correct tool for the job . We all do things to get by with what we have . Sometimes it works out and other times it doesn't , so we have to  consider the " what ifs " if they do in fact happen .


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## Liljoebrshooter (Aug 20, 2022)

Its also a right hand boring bar so it will just unscrew the head off the arbor.
You would need a left hand to work.
Joe


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## erikmannie (Aug 20, 2022)

extropic said:


> Less insert edge in the cut = lower cutting forces (all other factors being equal).
> 
> …



^^^^ I found this sentence to be very illuminating! 

I knew this with regard to depths of cut, but I had never thought about it for cutting tool rake. Thanks for the insight, @extropic.

Regarding the topic of the thread, I wonder if the OP’s idea could also be used for trepanning on a milling machine. I have never even thought about trepanning on a milling machine.

For the OP’s project, my initial reaction was that the setup would not be rigid enough, but taking lighter cuts (as you do with a fly cutter, anyway) + extra spring passes would compensate for this.

Also, kudos to the OP for thinking outside the box.


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## tq60 (Aug 20, 2022)

Stop...

The mill does not have the ability to be effective at that distance unless making plastic plates.

Other than power and rigidity the table is just too small.

To use as fly cutter configure as normal boring head and adjust for hole at large diameter.

It will act as a fly cutter more within limits of machine.

This is using tooling creatively.

Fly cutters are cheap, also easy to make.

Better to make one from cheap materials than to ruin expensive materials to improper use of something else.

Fly cutter would be cheaper than the ruined boring bar.

Sent from my SM-G781V using Tapatalk


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## erikmannie (Aug 20, 2022)

tq60 said:


> Stop...
> 
> The mill does not have the ability to be effective at that distance unless making plastic plates.
> 
> ...



I always ask myself “What is the weakest link here?”. In other words, if things go wrong, what will fail? If the weak link is the gears in a gearhead lathe, I will not use that setup. If the weak link is belt slippage, I will start out with a really small depth of cut. If even light cuts cause the belt to slip, I will almost certainly start looking for a different plan.

In the case of the OP, I think the weak link is the deflection of the boring bar. I have tried cutting operations on steel in which there is way too much tool stickout whereupon I failed to be able to execute the cut. The cutting tool would either break (e.g. a parting tool) or the boring bar would deflect & skate over the workpiece.

I have boring heads, but I have not yet had occasion “to use the side hole”. If ever I do so, I would take lighter cuts, extra spring passes, the best quality of inserts on hand, & a solid carbide boring bar if I had one in that sized shank.


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## benmychree (Aug 20, 2022)

The boring head would take a beating, could be ruined.


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## Alberto-sp (Aug 21, 2022)

First of all, I really apreciate all your help and the time you are spending with all your explanations. And as allways, I have learned a lot.

*chip maker* has described me perfectly, but *mmcmdl *is right too. And reading him I got the same conclusion as *Liljoebrshooter*. To use this boring bar the rotation of the spindle could loose the drawbar, so I won´t be able to take advantege of this boring bar. I´ll buy something like this.​​https://www.mesatool.com/product-page/2-boring-head-attachment-w-ccmt​​it seems solid, and the correct tool for that job.​
Thank you again!


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