Guidelines for Boring Tool Grinding

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Russ Hanscom
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Re: Guidelines for Boring Tool Grinding

Post by Russ Hanscom »

Got any sheet lead? A bit of sheet lead and a worm gear hose clamp to hold it should help.
pete
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Re: Guidelines for Boring Tool Grinding

Post by pete »

Almost anything other than the same metal the part is made from will work. Boring a couple of short pieces of screwed together pine or fir 2" x 4"s to the same I.D. as the parts O.D. remove maybe .100" off each joining face of the wood and use wood screws to clamp each half to the part would be more than enough to change the vibration frequency range. All your really doing is using a more vibration resistant or deadened material to prevent or help absorb those vibrations. Use a turned slightly tapered wooden plug wedged in the parts bore to turn it's O.D.

Unless your current chucks are set up to use bolt on soft jaws I don't know of any fast, easy way to get a set of probably aluminum insert jaws clamped securely enough to the chucks hardened jaws without getting a lot more complex than the job is worth. Since you know your ID/OD part dimensions, then check a few metal supplier websites for heavy wall pipe. Here's an overview of what's available. https://www.atc-mechanical.com/tube-pip ... -overview/ I've no idea if any off the shelf heavy wall pipe will fit your part parameters though.
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NP317
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Re: Guidelines for Boring Tool Grinding

Post by NP317 »

For ringing cylinders wrap them in...Duct Tape!!!
Who wudda thought...
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Bill Shields
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Re: Guidelines for Boring Tool Grinding

Post by Bill Shields »

Rubber bands..load up the od with rubber bands

I have put a board across the ways with a pair of spring loaded urethane wheels to 'stay in contact' with the sleeve. Not a lot of pressure. Just enough to keep it from ringing.

Assuming that you do not have a steady rest large enough to handle the part.
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atunguyd
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Re: Guidelines for Boring Tool Grinding

Post by atunguyd »

There is a great write up on grinding of boring bars on Harold's website here :
http://homews.co.uk/page138.html

No, not the Harold from this website, but I suspect this might be his machining doppelganger from the UK

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Harold_V
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Re: Guidelines for Boring Tool Grinding

Post by Harold_V »

mcman56 wrote: Thu Dec 30, 2021 6:59 pm Is there a better way to go about machining a large thin ring from bar?
Yes. Start with solid material, keep it chucked short, and bore/turn only deep enough to allow parting off the desired length ring. The solid mass behind the short sleeve will help dampen chatter and will eliminate any distortion you would achieve in chucking with tube.
Can you buy soft jaws for all chucks or is there DIY method for soft jaws?
Generally only for chucks with master jaws. Two piece jaws, in other words. If you don't have them, it's a lot of work to make soft jaws that would function, and they likely wouldn't do you much good unless they were pretty much full pie jaws. Thin items distort all too easily if they aren't fully support, thus the need for full pie jaws.
I'm looking for a 72 x 80 x 19mm ring.... although should be able to marrow a wider one.
I often make rubber cutters from mild steel, which works just fine if you need just one or two items. They demand a thin wall, much thinner than the wall you're attempting (often no more than ten thou). I have made cutters such as this in lengths similar to that you're trying to achieve, and in various diameters, some several inches. It can be done.

You must experiment with tool geometry if you hope to conquer this task. Start with solid material, and rough both inside and outside until you have about .010"/015" left to remove. Cut inside and outside alternately, to keep distortion at a minimum. Try to keep chatter out of the roughing cuts, so it doesn't influence the finish cuts. Those (the finish cuts) should be made with an extremely sharp tool with minimal tip radius. Stone a miniscule radius on the cutting edge, starting with sharp geometry. Then you'll have to use the finest possible feed. Make sure the tool has POSITIVE rake. Zero to negative will be a huge disadvantage in that it increases cutting pressure beyond reason. Keep the cut wet with cutting oil. Slow the spindle to the slowest possible setting if chatter is an ongoing problem, but don't fail to try to dampen any chatter that may arise. Don't let it start, as once the pattern is generated it's difficult to remove.

You can do it. It's done quite often by others.

H
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mcman56
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Re: Guidelines for Boring Tool Grinding

Post by mcman56 »

I was experimenting with different geometry and getting frustrated. I then moved on to minimal sticking out of the material in the chuck and minimal depth. I'm now getting acceptable results. The finish is OK but I'm not sure to what to expect. I usually work with aluminium so my expectations for a shiny finish may be too much. It is 8620 steel. I did try parting off with a 1/8" wide tool and the chatter was instantly massive. I went to the band saw. What do people mean by tightening down the gibs? Do you tighten down until you get a bunch of drag?
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Harold_V
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Re: Guidelines for Boring Tool Grinding

Post by Harold_V »

Gibs are best tightened until they're snug on the ends of travel. The center of travel will most likely be loose, depending on the miles that the machine has logged.

I hand grind parting tools, so it's common to have one that is quite narrow, which should eliminate any issues with parting. One ground 1/16" wide is acceptable and should eliminate chatter issues and it's quite useful for generating O ring and snap ring grooves. Width of cut can be controlled with the use of a long travel indicator.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
pete
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Re: Guidelines for Boring Tool Grinding

Post by pete »

Not all lathes have the design to even use the method, but one of the more common work around's on lighter and less rigid lathes is to use a rear mounted cut off tool with the tool mounted upside down and the spindle turning in the conventional counter clock wise direction. It can work a lot better because the cutting forces then lift the cross slide up against the male dovetail and that then removes all the clearance so it then makes the assembly much more rigid. A very minor side benefit might be it slightly helps with chip removal using gravity when cutting off, but I have doubts that really makes much difference. Over tightening the gib can also help remove that required clearance and stiffen up the cross slide assembly to remove that chatter if it's happening. But it also adds a whole lot of extra wear on the feed screw, nut and the dovetails so it wouldn't be advisable to keep the gib adjusted like that. It's really only meant as a temporary measure.

Chatter can be caused by the material, cutting tool shape and/or unsupported extension and even the lathes own harmonics, but also by more clearance than the minimum. And a wide tools cutting edge will almost always be easier to have it start to chatter than a narrower one. When was the last time you removed the cross slide on your lathe for a proper cleaning and adjustments? Most use manuals don't emphasize doing so enough, but it's standard maintenance. A clean properly lubed slide can be adjusted much tighter than a filthy one full of chips and old congealed oil. If the cross slide nut is adjustable, that's the time to do so as well. Excess clearance in that nut is another possible cause of that chatter when trying to do cut off operations. But again adjusting the nut is the same as the gib, a bit too tight causes excess wear. George Thomas in one of his books recommended adjusting slides to how they feel moving it back and forth by hand and without the screw installed. It might take a few minutes longer, but I've found his method to be easier and more sensitive to do the fine adjustments that way.
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