Measuring increments on boring head

[Julie AnnParticipant @julieann]

Wolhuapter advertised a UPA1, but I’ve never seen one for sale. The UPA2 also seems to be rare, only seen one for sale. In contrast there seem to be a lot of the larger, UPA4/5/6, heads for sale.

Julie

[Bill PhinnParticipant @billphinn90025]

Many thanks for the further replies, and my apologies for not returning sooner.

Pete, your post is very useful.

Deflection is something I’ve been slowly acclimatising myself to on the lathe (and not just when boring), and clearly boring on the mill brings the same problem with it.

Your advice on how to creep up on a final dimension and on the use of 123 blocks as a guide for the mag base was particularly helpful.

Taper gauges aren’t something I have in my armoury, so I will have a look at getting those.

My telescoping gauges aren’t top quality but aren’t the cheapest of the cheap either (Kennedy). Your advice on how to look after them, get the best out of them and take measurements from them will be put to good use.

Julie, your information on the Wohlhaupter and Kuroda boring heads and the finer points of difference between them is very useful, to others as well as me, I’m sure.

Jason, you mention using insert boring bars on the mill. What inserts do you (or other people) recommend? I’d imagine it depends on the job, but I’m sure I’ve seen several different kinds in use on Youtube: e.g. CCMT, RCMT, TCMT.

I’ve only got one of the brazed carbide type of boring bars. I’ve not actually tried it yet. My first task was reducing the nominal 12mm diameter shank down to a size (i.e. actually 12mm) and state of roundness that would allow me to insert it into the boring head it came with.

On another note, I don’t know why the cheaper boring heads all seem to come with knurled cup point set screws to hold the bars into the head, when knurled cup points will chew up the surface of the shank and make extraction difficult.

Finally, how safe is it to run screwed-shank boring heads in reverse to cut ODs?

[JasonBModerator @jasonb]

My insert holders that I use in the boring head take TCMT or TCGT inserts. You can also see that they have a flat which not only saves them getting chewed up but also sets them at the correct position in the hole. I replaced the screws on mine with better ones once the hex holes started to split at the corners.

I ground a couple of the brazed inserts for doing external cuts rather than risk doing it in reverse. Does not take much – just grind the curved part of the head of the cutter flat.

[Bill PhinnParticipant @billphinn90025]

Thanks, Jason. Very useful info. Those insert holders are on the to-buy list.

Grinding specially to cut ODs clockwise seems the way to go rather than running in reverse.

I’ve already replaced all the screws on my boring head: flat-ended ones or dog point. I notice that the gib strip on my boring head has misshapen (certainly not round) pits in which a ball bearing sits. From the look of the marks on the originally fitted cup point screws the balls were not actually locating in the cups in two cases. The theory was good though.

[Bill Phinn]

On Bill Phinn Said:

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Finally, how safe is it to run screwed-shank boring heads in reverse to cut ODs?

Not at all in my experience…

[PeteParticipant @pete41194]

I hadn’t known Wohlhaupter also made a UPA1 sized B&F head Julie, thanks.

Understanding and learning to compensate for those inevitable tool and machine deflections is an important lesson Bill. I didn’t invent the explanation. But at the micro or nano level, everything really could be compared to being made of slightly more rigid levels of rubber. Even diamonds.

For my Criterion braised tip bars, they came with a surface ground Weldon flat to position the cutting tip at the correct orientation in the head once the set screw is tightened. For bars without that? I’d start by stoning off any burrs that are already present, then machine the set screws ends to a smooth and flat face, or put a reduced size step on it below the threads minor diameter. After that, use a very short piece of clearance sized brass rod between the boring bar shank and the end of the set screw to prevent further burrs. And if your gib isn’t flat, and it likely wasn’t even when brand new, your going to have a very tough time making any fine slide movements. Machine a new one that’s as thick as possible that still allows a few thou of adjustment, then hand lap it to a very good surface finish while still keeping it dead flat and parallel.

When I bought my first lower priced boring head, one bored trial hole was enough to take it apart for de-burring the internals and shimming that collar slot that helps move the slide. I then slowly spun the feed screw in my lathe while using some 1,000 grit sand paper to smooth and de-burr the whole thread. You don’t need or want to polish it, just smooth and de-burr it a bit. Flush the feed nut clean with some de-greaser because it almost for sure has grinding dust in it, then lightly relube with some proper way oil if you have it. Way oil helps to prevent what’s known as stick / slip which is pretty important on any machine tool slide. All of that made improvements with mine. Things may be better today, but the braised tip carbide boring bar set that came with mine were all sharpened poorly and completely wrong. And for any holes close to the bar diameter, they mostly rubbed on the side of the tool instead of cutting with the tip. Luckily I understood enough to figure out the issues over a bit of time, so I think I can relate pretty well to where you are right now.

You can also make your own mild steel boring bars to fit whatever bar shank size your head uses. As well as for use on your lathe. And then use economical round HSS or solid carbide tips. Good drawings are in this book, https://www.teepublishing.co.uk/books/in-your-workshop/model-engineers-workshop-manual/ And there’s no question Stefan is using the exact same book and drawings in this video about how to make them. https://www.youtube.com/watch?v=O9d_I0A4kzg And that same book has some logical thoughts about the importance of pinning set screw adjusted gibs in place that also might help. Any pointed or cup tips on the ends of the set screws, or those ball detents pressed into the gib surface change the gib adjustment the instant the slide starts to move because they act just like very tiny wedges in those dimples they created, or that are sometimes machined in the gib. That wedging action self tightens the gib and drastically changes how smooth any slide will operate no matter how carefully it’s adjusted. For logical reasons, a set screw type gib should only be allowed to be adjusted towards or away from the dovetail slide, and never move laterally or end to end on the slide at all. The more desirable taper gibs will always have a screw at each end to both lock the adjustment and also prevent any linear movement that would loosen or tighten the gib as the slide moves in either direction.

Depending on how clever you are and what taper shank / boring head you have, a clamped on collar and single screw through it and into the top of the boring head might work while running it in reverse? Because of the upper shape on my own boring heads, a simple stepped clamping ring could also work, it just depends on what you have. But in my opinion, running the head in reverse has a bit too much uncertainty, its safer and easier if you can make or buy the correct handed boring bars.

Selecting a slightly oversized left hand lathe boring bar or turning tool if you can’t find one with the correct shank size and turning it to fit your head could work just as well? You might need to buy more than one left hand tool though. Boring bar length verses how much the project really needs has a way of inviting chatter if there too long at all. In general ball park numbers, tool rigidity starts really dropping off once the extension outside of where it’s being held goes above 3 times the tool diameter for steel, and approximately 5-7 times the diameter for solid carbide. Young’s Modulus would be the search term to use if your interested. Lighter cuts can sometimes allow you to cheat those numbers a bit. Dropping the rpm and a faster feed rate can also help with that chatter (sometimes)

Making do with what you already have available has to be done by all of us sometimes. If what your project involves justifies it, I think I’d chose to just buy the correct left hand tool. And if your own boring head has that horizontal cross hole? That same left hand tool can be used in it to bore far larger holes than the bottom two tool positions allow. I bought a left hand tool for mine to do just that because that’s exactly what that cross hole is for.

In reality, most of the difference between the expensive telescoping gauges and the cheaper one’s is being dead straight for the telescoping tubing, a very close fit between those two tubes & there surface finish. Ensuring they slide together without a hint of binding anywhere, stoning and smoothing the sidewalls and bottom of the slot in the telescoping end, a good smooth surface on the locking tip, and stoning all burrs off to improve both the locking and smoothness of operation isn’t optional with the less expensive ones. I’d also spray degrease everything when I was done with that stoning. And polish the end tips of each gauge if it’s needed, some of the cheaper sets I’ve seen were very poorly finished. I think it’s well worth taking however many hrs it involves to do so. You can’t machine what you can’t measure to. It also needs to be understood how there positioned in the hole and then gently rocked out with the telescoping part partially locked to allow the telescoping end to move to what the hole size is. If your unsure of exactly how it’s done correctly, there’s many Youtube videos about it.

For some measuring tools, they really only need a hint of lubricating oil. Less than a single drop for much of it. For my Starrett hole guages, I don’t use any oil, just a bit of dry powdered graphite that seems to work better than any oil I’ve tried. And I think the graphite makes gauges like this slightly more sensitive since any liquid lubrication product requires it’s oil layer to be sheared as the parts move, graphite doesn’t.

That proper technique with these telescoping hole gauges is also not something that can be instantly mastered by anyone. You absolutely have to practice a lot to develop the correct technique and feel on something that already has a high precision and known hole size just to double check what both yourself and the tool can work to for repeatable accuracy every time. A few different sized ball or roller bearing bores might be useful for that practice? Even then, there can still a bit of uncertainty with the gauges position always being at the exact hole C/L. I never make less than 3 measurements on any hole I’m boring just to double check I am getting that repeatable size. And even then, I’ll sometimes I’ll get measurements that don’t always agree. So I think it takes that developed feel that can’t be taught or even described very well. And that’s something anyone has to learn on there own and then verify they’ve actually learned to do so with that practice.

Hole measurement or any measurement under .001″ or within low 10ths most definitely isn’t as easy as some might assume. And I can verify that after checking what both myself and my own metrology equipment can do against good gauge blocks. Your measuring equipment might be able to measure to a few 10ths, but which 10th is it for sure, and can the user and the techniques your using, or even the environment it’s being done in allow that as well? Steel expands or contracts by roughly 6 millionths of an inch per degree of temperature difference, per inch of size. Obviously most M.E. projects don’t require nearly that level of accuracy, but what happens if/when something comes up such as just press fitting a precision ball or roller bearing into the correctly sized hole? Fitting a lathes back plate to the spindle would be another. It’s much easier if you know with some degree of certainty that you and what your using can actually do so before you even start.

[DiogenesParticipant @diogenes]

For ‘every-day’ boring (in my metric head) I mostly use cut-down versions of the SCLCR bars I use in the lathe – it means I can use the same style/size tips for most everyday work and both bars and tips come in a useful range of grades / levels of competence..

In my cheap 50mm head I haven’t found the state of the gib etc. makes much practical difference, as you need to keep a reasonable amount of drag on it anyway.

 

[JasonBModerator @jasonb]

Same here I have never had those screws out the three were nipped up early on and have not been touched for about 15yrs couldnot say if there is a ball behind them or not. It was just the tool holding screws I replaced.

[Bill PhinnParticipant @billphinn90025]

Many thanks for the further replies, and particularly to Pete for his very detailed treatment of the subject and its pitfalls.

It’s hard to appreciate how an operation so apparently simple as making a straight-sided hole in metal can be such a technical matter until you actually start trying to make accurately sized holes yourself.

I’ve just watched the Stefan Gotteswinter video in Pete’s link.

Following Stefan’s pattern (actually George Thomas’, it seems) I would like to do another 45 degree boring bar holder that is shorter than the two that came with my 63mm boring head (the shorter of which is visible in my opening post).

The sort I mean is the one with a clearance hole down its length that uses a push rod with a 45 degree tip to lock the cutter. I’ve got a selection of long parabolic-flute drills that should help to reduce wander as the drill travels down the centre of the bar. I plan to make HSS cutting inserts ground to bore internally as well as externally. Then I will be able to do ODs without worrying about the boring head unscrewing from its shank.

The internal boring tool in my photo that I made from a 6mm end mill was ground according to Jason’s illustrated instructions published on the forum some time ago (2021). I believe the link to the thread containing his instructions is in the last post in the following thread: https://www.model-engineer.co.uk/forums/topic/looking-for-solution-to-incorrigibly-jumpy-needle-roller-bearings/.

However, the link appears no longer to work.

Anyway, the boring cutter I made some time ago following those instructions works very well indeed, as I’ve already stated, even if it is only bog standard HSS, not some version of HSS-Co, as recommended by Stefan. It does require fairly frequent re-honing though.

 

 

 

 

[JasonBModerator @jasonb]

It was interesting to see on this video that even the industrial size machines can benifit from using the **GT inserts that I tend to suggest for use on hobby mills. Curtis’s machines are certainly what I would class as big boys (and girls) toys. He also seems to be able to adjust his boring head OK and no locking of the central screw, just all three nipped up.

 

[PeteParticipant @pete41194]

I’d compare machining as being a bit similar to using a known recipe while cooking Bill. When you know for sure what should work, (technique, experience and knowledge) You can then get fairly repeatable results most times. When they aren’t working out how they should, then there’s usually only a few variables that could be tried. Poor surface finishes are or can be tougher problems to solve with longer boring bars and deeper holes. Part shape or in more special cases, thin part walls could make that chatter multiple times more likely as well. Cutting tip material, angles etc also plays a part.

Possibly there other reasons I’ve not run across yet, but poor surface finish showing those chatter marks is afaik mostly or maybe all related to the the machine tools, cutting tools, part shape, material etc, etc, and there natural frequency of vibration, or in more simple terms, there harmonics. And learning that the hard way cost me a set of spindle bearings I didn’t need. It’s a fairly complex subject, but understanding why it happens and that there’s many and variable causes is likely what most of us would really need for information. 80% – 90% of the time, changing the feed rate to a bit quicker, depth of cut change, lowering the rpm, or all of them usually helps a lot. For boring bars and longer extensions, sometimes solder wire or a wide elastic band tightly wrapped along and around the bars OD and taped in place could be enough. At that point, your using materials that are just about immune to harmonics and help absorb and / or change those natural frequencies that might be present to something that may work well enough.

And you can hear that harmonic ‘ringing’ on Curtis’s new shop made large blade type cutter in Jason’s link. I thought when he built it that he should have welded on some tapered and vertical stiffening ribs running from it’s OD and in to where that tool shank was bolted on. He didn’t because of how he wanted to machine both upwards and downwards facing surfaces in just one set up. So I think his design was correct for what he wanted. Gluing on some type of thin inert material over most of both faces of that tool could be enough to help, even thin sheet rubber might do it?

It could easily have been mentioned by others, but a few years ago, Oxtools on YT pointed out that he no longer locks the slide on his boring heads after an adjustment just like Curtis doesn’t seem to be doing. In ‘theory’ and when your adjusting the slide, all the feed screw and nut back lash is taken up in the correct direction, so the slide shouldn’t ever be able move backwards and slightly reduce your adjusted depth of cut. Boring head fit, finish, quality varies, or much smaller bores might have the head rotating at far higher rpms. It’s not impossible in a situation like that the slide could move outwards a tiny amount, maybe unlikely or maybe not? Either of those YT posters have forgotten more than I’ll ever know. But using that lock still makes me a lot more confident it’s not going to.

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