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using boring bar in Machturn
« on: February 08, 2008, 04:08:54 PM »
How do I setup a boring bar?  I have a QCTP and would like to do some internal countouring on a few parts. Do I just set it up as additional tool in the tool table? What things do I need to watch to make it work?

Offline jimpinder

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Re: using boring bar in Machturn
« Reply #1 on: February 09, 2008, 08:18:06 AM »
What I understand to be a boring bar is a  thickish bar, centered at both ends, that you set up between the centres of the lathe. There is a tool tip protruding from the bar (usually in the centre (lengthwise)). It is used for boring long cylinders, the work being mounted on the cross slide. The spindle turns the boring bar which passes through he cylinder and cuts the inside surface. The tool tip needs alteration after every pass.

I cannot see how you can do other than just bore cylinders with that, because the cross - slide is clamped in the X direction, and only moves in the Z direction.You cannot use the x-axis because the tool will foul the opposite wall of the cut cylinder. G Code is simple - cut to one end, wait for tool tip to be altered, cut to other end, wait etc etc,

If you are meaning a simple boring tool - i.e.held at one end in the tool post, which can bore out say an axle hole in a wheel, then yes - this is just another tool. You can use the offsets in the tool table (but remember they are the opposite (i.e. x is +)). You set it up as you would a normal cutting tool - end of work is Z0 and X0 is the lathe centre.
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Re: using boring bar in Machturn
« Reply #2 on: February 09, 2008, 08:30:11 AM »
Well the type I am refering to , are held in the tool post and the workpiece in the headstock. I think Chip helped me understand the procedure to do the tool offsets. Time will tell.

Offline jimpinder

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Re: using boring bar in Machturn
« Reply #3 on: February 09, 2008, 09:45:59 AM »
OK - it is very easy to over bore, because of the spring in the tool. Tend to set your finish diameter few thou below what it is you want until you have checked it.ALTERNATIVELY - work up to the finish diameter by making 2 or three small cuts to nullify the tool spring. A bit of a pain if you are only doing one, but if you are then making a few, once you have the finish diameter correct, let the machine rip.
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Offline Hood

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Re: using boring bar in Machturn
« Reply #4 on: February 09, 2008, 10:02:07 AM »
I dont have any experience with boring yet on my CNC lathe (need to make up holders) and I think my problems will be greater as I have front post for boring bars etc and rear turret for normal turning. However the reason I am posting is because I have done a lot of manual turning and have found (in my experience anyway) it is best not to tickle the metal with a boring bar, always have a good cut on it. Always use the largest diameter that you can, even if it means changing halfway through to go to the next size up. Use a small nose radius tip to help with chatter problems and never take a cut less than the nose radius, even for your final pass. Deflection can be a problem so also keep your bar as short as you can but if you work out your position from doing test runs at your finish pass depth you should be able to keep things accurate.
 As I said this is just my experience from manual turning so your own findings may be different.

Hood
Re: using boring bar in Machturn
« Reply #5 on: February 09, 2008, 10:59:06 AM »
Thanks for the tips guys, I have to bore a 3.0 inch deep bore so I imagine I am going to run into some flex in the boring bar. This is in cast acryilc stock so hopefully it will cut easier than say steel. I won't be able to give it a go until monday so I'll see how it goes.

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Re: using boring bar in Machturn
« Reply #6 on: February 09, 2008, 11:26:05 AM »
Cast acrylic shouldnt cause you many problems with deflection, well as long as you use a decent Dia boring bar. My main work is for fishing boats and because of this most of my work is in 316 stainless.
Hood

Offline DAlgie

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Re: using boring bar in Machturn
« Reply #7 on: February 09, 2008, 07:20:34 PM »
A 3" deep bore is a long way if it is a .5" diameter, but if it's a 3" diameter hole then it's very short. The point I'm making here is the bar diameter/ length of overhang ratio, always us as large of boring bar as you can fit in the pilot hole. Cast acrylic will be a problem if the swarf gets trapped in the hole, it will melt and cause problems. try to use a chip coiler, a chip breaker never really works because you can't take a big enough cut to make it work. A groove in the tool just behind the cutting edge will coil the chip up and it will come out cleaner from the hole. For metal a ton of coolant blasted into the hole helps to wash the chips out also.
     DaveA.