Boring bar height setting

[Gordon]

My conclusion from all of this is that I have to make something which fits onto the bed of the lathe so that I have a consistent surface to index from. I have a QCTP so I have done some of the things suggested but there is no good surface on the lathe carriage to measure from so I guess that I will have to create a surface.

 

[Tom Clark]

After all the years that I have been doing this I should have figured out the proper way. Does anyone have a good method of setting the height of a boring bar? When setting tool height on OD the ruler method works well but that does not work on ID. I have made gages to set tool height relative to the compound but usually the boring bar is several inches away from the compound. I have tried making gages working from the bed but my South Bend has a flat on one side and a V on the other side so short of making a special piece to fit the bed I have not found a good way. Depending on the shape of the piece being bored I sometimes can use my caliper to measure from a known surface to the top of the cutter but that does not always work. There has to be a better way than just keep trying until it seems to be working.

You can put a round piece of metal in the lathe, then run the boring bar back past the piece and come at it from behind. Now, use your ruler (I use a popsickle stick) to set the height. You can now reposition the boring bar in front of your work piece and have at.

 

[krypto]

If you don't mind twisting the tool post around you can also mark the side of the tailstock quill at the lathe centerline. Mine came from the factory like that and it's very handy.

 

[pete]

There's obviously multiple methods of setting tool height, some either faster, easier or more accurate than others. I also use a combination of the OEM 4 way or a QCTP. There's quite a few fixed dimensions on a lathe that each owner ought to have written down. Even G. H. Thomas mentions there importance. I machined a couple of pieces of scrap bar stock once I had the measured dimensions from both my lathes flat surfaced cross slides to there head stocks C/L. But other areas can be used as well if your cross slide isn't already machined. Both those gauges are kept protected and safe from damage, I then bought a cheap off shore magnetic base and .001" reading dial indicator and added what's known as an Elephants Foot indicator tip. That enlarge flat tip makes finding the exact cutting tip height a whole lot easier on neutral or positive rake tools. It obviously couldn't be used with negative rake tools, but few at the hobby level would be using them. A heavy lump of steel bar stock and vertical rod to fit the snugs used with those magnetic indicator stands would do as well if you don't want to dedicate a magnetic base to this. I used those setting gauges I machined as my indicator zero point when switching between lathes or just as a quick recheck the indicator is in fact still zeroed. Most lathe tools work as well as there going to at that true spindle C/L. For whatever reason you happen to believe, boring bars may or may not in all conditions and materials. So I've found setting the tool point on them .003"- as much as .005" high will sometimes work better. Without a fairly accurate way to measure exactly where the actual tool point is, you can't easily duplicate where you want it. No doubt others will disagree with my method, but this has proven itself to work well for me, so I'm not about to change how I set my tool heights since its fairly quick, accurate enough, repeatable, and the forces involved are very light, it won't chip that delicate carbide tipped tooling.

Using a dead or live center in the tail stock as your tool point height position might only get you fairly close for the lathes in decent or highly used condition that most of us would be using. Even the best tool room lathes in the world will come with the tail stock C/L purposely set high by a few thou. A highly worn lathe will almost always show the tail stock quill pointing down by a little or a whole lot depending on the amount of wear it has. In general, and as long as its not excessive, that vertical misalignment has almost zero measurable effect on the part diameter when supported with the tail stock. Used to set your tool height it just might. And there's a great many off shore lathes where that tail stock quill is anything but correct or even close enough to be used to set that tool tip. I had one that was pointing up and over .009" high with just 2" of tail stock quill extension. In theory, the trick of using a machinist's scale and eyeballing its vertical alignment works well. Sometimes it does, I've also double checked it using that indicator and have seen a few thou variation at times. It could also crack or chip carbide if your not using a very light and gentle touch. And the larger the diameter of the shaft, chuck body or face plate rim your using that scale against, the less accurate it might be. And that's something that seems to be rarely even mentioned.

 

[Lloyd-ss]

.......................................... There's quite a few fixed dimensions on a lathe that each owner ought to have written down. Even G. H. Thomas mentions there importance...................................................

snip of the quote

Darn, now something else to feel guilty about. Sigh. Yes, that is true.

 

[krypto]

If an old war veteran lathe has tons of brewer's droop in the tailstock, you might as well use the scale trick for tool height anyways as the bed ways will certainly have up's and down's similar to a roller coaster. Since the tool height will change as it traverses the bed it's no use getting that fussy about it as the operator will simply have to deal with it if and when needed.

I've always used the initial tool height from a gauge as a starting point anyway. With a QCTP, it's easy enough to adjust the tool after a facing cut and that's plenty accurate. The only tools I've found that are really sensitive to height adjustments are carbide cut-off tools, you just have to learn the feel of the tool and adjust the tool height if the cut is taking too much pressure. The good news is that when adjusted they are trouble-free until you have to replace the tip, when may or may not require another height adjustment.

 

[Technical Ted]

I have a SB 15" and SB 13" lathes. I simply use my combination square measured from the flat way. For some operations i.e. taper boring, cutting grooves, etc. having the cutting tool exactly on center is more important, but for most simple boring, being right on center is not necessary. On small bores, a lot of times I find myself purposely raising the tool above center to give the tool enough clearance to fit in the hole. There are limitations of course, but you can cheat a little and still get good results...

Ted

 

[metalmangler]

I use a centre-height gauge I made 25 years ago, it's the first project in Geo. H. Thomas' "The Model Engineer's Workshop Manual". My version has three knife-edge holders, for use when placed on the lathe-ways, the saddle or the cross slide - in practice I find I rarely use it anywhere but on the lathe-ways. In fact it's just occurred to me, a mere 25 years later, that I could use a superfluous holder upside-down in another stand to set boring-tools . FYI the lathe is a Myford 254, with an early Myford QCTP.

 

[Gordon]

I made a piece to straddle the lathe V ways so that I have a consistent surface to work from. I just have to make a gauge to set the height between that surface and the lathe tool. For most things just measuring with my 6" rule is close enough but I will make a permanent gauge.