backlash on your boring head screw is immaterial as you are only travelling in one direction and usually whatever you put on the dial is doubled on the dia. what sort of accuracy are you after? a thou should be achievable. Why not make a shallow plug gauge that is stepped that you can insert after a cut to check where you are.

If the clamp screws are lightly nipped, any backlash should be taken out as the cutter is advanced. Once set, the clamp screws should be tightened more, to prevent the cutter backing itself off.

As final size is approached, it will be worth taking one or more spring cuts, without any alteration to the boring head. Check size after each cut if possible.

Howard

I have a small and a large boring head.  The large one was bought from one of the usual suspect suppliers and behaves just as you say.  The only way to make it work is to lock the slide tight for a cut, then bring the adjustment screw hard against the slide  before slacking off the gibs to advance the feed.  Getting a hole the right size is a lottery.

The small one cost a lot more and is an Arrand. Yet again, bought cheap, bought twice.

Bill

To make adjusting the boring head simpler and more accurate get one of these Erickson boring heads, each division adds 0.002mm to the diameter, may cost a bit more than others available but you only get what you pay for with tooling. This is a No.12 that uses 12mm diam tools, I also have a No.10 for 10mm tooling.

Emgee

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The GHT design has a separate lock screw which I find useful. It could be a possible addition to other designs.

It’s a fairly complex to explain question Bill, and there’s always more than one way to do anything. It also took me a very long time just to pick up the information I’ve manged to find and learn a few tricks of my own since it’s not all in any one place that I’ve found.

I’d guess all of these off shore heads were originally cloned from the American made Criterion DBL series of boring heads since they all seem to be the exact same design. And Criterion are pretty specific about only using the center locking screw to lock or unlock the adjustment slide. In fact they now have the other two gib adjustments temporarily covered today because so many won’t read the instructions. https://www.mscdirect.com/product/details/01066489 There’s no need and its actually improper and counter productive to use all three of those gib screws to lock the slide. And most of these cloned heads don’t have a very precise fit with how the collar on the feed screw fits the radial half slot in the head. Properly shimming that for a better and tighter but still a very slight clearance fit might also help. But like others have also said, backlash in the adjustment screw isn’t all that important.

Adjustable slide boring heads have been in common use for roughly 100 years and maybe a bit longer than that. Some were designed and used on jig borers to precision bore holes to under .0001″ /.00254 mm for size, straightness, roundness since at least the late 1920s to early 1930s. However they weren’t priced nor built like some of those Asian boring heads are today. High accuracy screw threads have world wide limit standards for both imperial and metric threads for size, allowable + – for thread flank angles, and much like lead screws on lathes, there accuracy and consistency of pitch. My Criterion heads I believe used finish ground feed screw threads and likely lapped nut threads for both operating smoothness and pitch accuracy. But, there is NO such thing as a perfect thread, Moore Tools in the US tried to produce feed screws and nuts to the accuracy they wanted for there jig borers and grinders. Yet no matter how much time, effort and funding they threw at the problem they failed and mostly due to thread pitch issues. They could and did measure the level of inaccuracy to low millionths of an inch, but they still couldn’t improve or fully eliminate their feed screw and nut inaccuracies. Well before DRO’s were invented, they instead used .0001″ indicators with 1″ travels and what were called high precision distance setting rods that came in sets of 1″ increments for any distance settings beyond the indicators travel limits for the tables X,Y position. Those rods were checked and certified to far better accuracy, but were still a bit like today’s micrometer setting rods. https://www.practicalmachinist.com/forum/threads/jig-bore-measuring-rods-use.428069/#post-4229749

If you want to hit a target dimension with any boring head, it starts with a properly trammed mill, a well built, repeatable, accurate boring and milling head, correct cutting tool angles for the material, and very sharp tools with the correct fine radius on the tool tip. Mill rigidity, spindle grinding, preload and bearing seats quality / accuracy are another big help as well as having built in powered spindle feeds since the holes bored surface finish affects your measurements accuracy as well. With all else being equal, HSS boring bars will usually deflect a fair bit less than carbide tipped, solid carbide will be much less than HSS, but it still depends a lot on the cutting tools shank diameter verses it’s unsupported length. Anything longer than about 3 X the tool diameter for HSS and roughly 5 X diameter for solid carbide might be pushing it a bit. So that depth of cut compensation is then even more important. Highly accurate measurements are just as important as the boring itself. And all of this requires the best methods and techniques you know. Most or maybe all of those cheaper telescoping gauge sets require checking that the telescoping parts are in fact really straight and 100% burr free on all the internal sufaces. If they aren’t, they start to create drag or even bind up, and inaccurate measurements are guaranteed. I own a set of Starrett’s I bought over 40 years ago that have always worked fine out of the box. I also don’t oil mine, instead I use dry graphite. Any oil could become sticky over some time and then start to affect the sensitivity of these types of telescoping gauges. Even then, I doubt I’d bet real money I could guarantee any hole size to much better than maybe .0002″-.0003″ with the metrology equipment I have right now. My mikes can measure and do better than that, but my telescoping gauges can’t. I also find that gently holding the micrometer in a micrometer vise and holding one end of the gauge against the mikes fixed anvil, sweeping the other end of the telescoping gauge past the moving anvil on the micrometer as I’m adjusting it until it just barely starts to drag on the face of that anvil is much more consistent for the measurements repeatable accuracy.

Accurate boring on a lathe or with a boring head in a mill are both the same, you still have to compensate for the inevitable tool and machine deflections. I always use what’s usually thought of as a 3 cut method. To simplify, lets say I’m getting roughly close to size, but my telescoping gauge says I’m exactly .030″ or for metric .9 mm under size. I still want and need that first initial measurement to be accurate, with that baseline, I’d then take 1/3rd or .010″ / .3 mm depth of cut. Then remeasure to see what a lathes boring bar or boring head took for a cut. Lets say it actually took a .009″ /.27 mm depth of cut due to that deflection issue. In either measurement system, that would still leave the hole .021″ /.63 mm under size. For the next cut, I’d probably chose to adjust the lathes cross slide or boring head to take .0105″ / .33 mm depth of cut. Remeasure, now you have a fairly good estimate of how much the tool cuts verses what the adjustment was to hit your last adjustment to very fine limits for the proper adjustment depth of cut. This is simplified with mostly round numbers to make it easier to visualize, but the method is still the same. Subtract the target hole size from your under size measurement, then divide that into 3 very close to equal cuts. If you don’t know the deflection variation of what the tool actually takes verses what you adjusted for, it’s extremely difficult to hit your size. Judging material types and how much experience you have boring to precision sizes are also a big help, and that really isn’t something that imo can be taught. Those spring cuts can help, but in my opinion, there more uncertain just how much they will remove. Multiple passes with roughly the same depth of cut and adjusting for any deflection your then seeing after each cut seems to be more predictable.

The dials on my own Criterion boring heads aren’t adjustable, so for at least the last 3 cuts, I’d do much the same as you do and use a dial indicator. Until I added my mills dro, using that magnetic base and indicator to measure the boring heads adjustment in my opinion took too much time and effort to set it up for measurement as I was adjusting the BH’s slide each time. I then started positioning the indicators base magnetically attached to the table with the indicator tip correctly squared, aligned and zeroed to the boring heads slide. Then I used two 123 blocks bolted down to the mills table, one touching the left side and one touching the rear face of the magnetic base. With those correctly positioned, it’s then fast and easy to slide the base against both of those 123 blocks and magnetically attach the base in the same spot on the mill table each time. Then all you really need to do is fine adjust the indicators zero for the next adjustment.

You do have to watch for any swarf getting into that area if the magnetic base is moved out of the way, but that’s nothing unusual. I always work and visualize much better with imperial measurements, luckily I ran across a fairly good deal for a brand new .0005″ Mitutoyo dial indicator quite a few years ago. So I normally use that as a direct reading method to .001″ for my boring head adjustments and predicted hole size. Although I also have indicators with far finer resolutions and accuracy, however the best only has .003″ of total measurement range. But single point boring isn’t anything as accurate as radial internal grinding would be, and can’t bore finished hole sizes close to that level of accuracy anyway. A .0001″ .002 mm reading indicator might be usable, but you still probably won’t know for sure which .0001″ or thousandth’s of a mm the hole size really is.

There pretty expensive for what they are, but I’ve also found these https://www.starrett.com/products/precision-measuring-tools/precision-hand-tools/fixed-gage-standards/taper-gages are pretty useful to get me fairly close for smaller bored holes that the telescoping gauges can’t do. Finding a very good condition used set in your area might be worthwhile? Holes still need to be properly de-burred before there used since there only a visual gauge. Hopefully all this will save you a bit of time trying to find what I had to over quite a few years.

On 3 April 2025 at 08:07 John Haine Said:

….Yet again, bought cheap, bought twice.

Only too true!

I never got on with my cheap Soba boring head. The slide, and tool, grubscrews were very poor quality. It was also impossible to bore accurate holes with any sort of consistency due to the sloppy fit of the adjustment screw and slide.

The only solution, for me at least, was to acquire decent boring heads. I now have a Wohlhaupter boring and facing head for the horizontal mill:

And a Kuroda boring and facing head for the vertical mill:

Both of these heads make it simple to bore to a few tenths, which is at the limit of my measurement capability.

The manuals for both the Wohlhaupter and the Kuroda state that the slide locking screw should always be used to lock the slide, except when making adjustments. In the picture of the Kuroda the slide lock is the knurled screw in the centre.

The ideal solution to the original problem is use a quality boring head. It also helps to use home ground HSS toolbits in my experience.

Julie

Certainly with the generic Boring Heads from the Far East, I second the general idea of keeping the gib screws fairly tight (and locking the slide), but not too tight as to cause stick slip as alluded to earlier.  However for me, the bigger issue is reading the dial and index mark that are slightly recessed into the head with questionable contrast.  I’ve pondered for a while, how to improve the contrast, but that’s still “work in process”.

With smaller and lighter mills the lathe may actually be the better choice. Unlike the larger machines they are unlikely to have a power feed on the quill and many won’t have a PF on the table so a more consistant feed on the lathe is likely to give a better finish than handfeeding with the quill. The lathe will also do the stepped hole as shown in Julie’s second photo.

I mostly use an insert holder in my heads for parallel cuts, the 9pc sets have mostly been ground for things like external cutting, chamfering or leaving a fillet at the end of the cut.

Many thanks for those extra details about each different head Julie.

I looked for a long time for one of the smaller Wohlhaupters without much success for condition, possible unknown internal damage and price. Since Wohlhaupter isn’t manufacturing them any more, used is the only option as you’d already know. I thought there were just too many unknowns without being able to try anything I was interested in first. So I finally bought a Narex VHU-36 B&F kit from MSC during a sale. If your interested, page 9 of this PDF has the operating instructions, and the parts exploded view on page 20. https://www.narexmte.cz/servis/Vhu_Instructions_complet_EN.pdf

My Bridgeport clone only has an R8 taper, so I felt anything larger than what I bought would be just too much. Things would be different if I also had a larger horizontal mill like yours with what looks to be a 40 taper, so what you bought for it seems to be a very good choice. And very smart to lay out and list the part numbers during that disassembly.

I really like the simple but well thought out design Narex uses for there replaceable tool shank attachment, but converted over to your UK pounds, even a R8 shank runs about 350 BP’s today. And so far I’ve never found any other company that produces them. I think there there tool shanks are completely over priced for what they are. And the heads have almost doubled in price since I bought mine. But they might be better in the UK than here. Since mine is the only B&F head I’ve ever used, I can’t compare how good it is to anything else, but it seems to have been really well designed, built and finish ground since there’s no detectable clearances at all.

I believe there’s a few far east B & F head clones, and Vertex did or still does make at least one or more sizes of them. For most with smaller bench top mills, then the smallest UPA 2 Wohlhaupter B & F head is the only one I know of that might not be too large and heavy.