Choosing a boring head

[Bill PhinnParticipant @billphinn90025]

In connection with my recent thread on needle roller bearings, I feel the need for a boring head for my mill. The initial task I intend to use it on looks very simple: taking out the ID of an oilite bushing from 25 to 26mm.

Could anyone advise me on the pros and cons of two commonly available boring head sets, which seem to offer similar diameters of cut but are supplied with a very different range of cutters? They are sold by more than one supplier but I have linked to the Arc ones for simplicity:

**LINK**

**LINK**

I see that a common theme in this useful thread and elsewhere is the need to regrind the tips of the off-the-peg cutters before use.

Given this need for an initial grind and the need, presumably, for the grind geometry to vary slightly depending on the job being bored, could anyone point me to a source of information on achieving good grinds for boring bars specifically?

Lastly, what choice of grinding wheels would be suitable for grinding the brazed-on carbide-tipped boring tools?

Many thanks.

Edited By Bill Phinn on 25/08/2021 22:13:38

[Bill PhinnParticipant @billphinn90025]

[EmgeeParticipant @emgee]

Green grit wheel for grinding carbide, or you can use a diamond impregnated wheel for a good finish.

Emgee

[JasonBModerator @jasonb]

Having used the one in the second link I found that just a quick rub on a diamond slip was all that was needed.

You will probably need to grind one if doing very small holes >10mm or external faces in which case the green grit wheel will be needed.

If you don't want to go the green wheel route then a simple holder to take HSS bits is easy to make then they can be sharpened on a normal wheel. You get two of this type of holder in the 63mm head set so would not need to invest in anything extra to sharpen the bits for them.

Lastly any reason you can't bore the bearing in the lathe?

[DC31kParticipant @dc31k]

As you are buying for one specific job initially, it is worth assessing the tools against the requirements of that job.

All the Oilite literature recommends razor sharp tooling for single point cutting of its material.

You have to ask yourself if you will be able to fulfill this requirement by hand-grinding and lapping the supplied carbide bars, which are of unknown composition.

It is much easier to produce a razor sharp HSS tool than a carbide one.

As the heads take 12mm shank tooling, a standard 12mm dia. carbide-tipped lathe boring bar would fit (with some length reduction) and this gives you option of off-the-shelf razor-sharp tips designed for aluminium. You would need to check the minimum hole size a 12mm bar will enter.

The bush hole is 25mm dia. and the supplied HSS bit holders with the 62mm dia. head are 18mm dia. This means there can only be 7mm projection of the round toolbit (and you have to start with the head adjusted 'behind centre&#39. Are you able to grind the necessary cutting geometry onto a 6mm dia. toolbit within this space? A little more length might be available if some of the grind is inside the bar, but this will reduce the effectiveness of the bit clamping screw.

My conclusion is that either head you show will do the job, but make or buy or adapt a boring bar that will work for the job you are doing. Send all the supplied tooling to a drawer for future use.

[Andrew EntwistleParticipant @andrewentwistle]

You may be interested in this type of 12mm shank carbide insert boring bar to fit these boring heads, available in a variety of lengths. The TBGH Inserts are almost as sharp as CCGT types for aluminium/stainless.

Andrew.

[John HaineParticipant @johnhaine32865]

I have 2 boring heads. One is the generic sort shown in your second link which is OK but adjusting the radius as you get to final size is a bit of a lottery. It takes 12mm shank cutters. The other is an Arrand which takes 8mm cutters and is very much nicer and more precise but Arrand no longer exist AFAIK. I managed to get a set of HSS bits with 8mm shank at a show, I think from RDG but they no longer list them. But ARC list a 30mm od head that takes 6mm cutters and also sell 6mm od HSS tools, so maybe that would meet your needs? Max bored hole size is 52 mm.

Or you might find a much higher quality head used on eBay?

[Mike HurleyParticipant @mikehurley60381]

I've had one of the second link types (black body) for years, cant remember who it was supplied by now. It's always been fine, although I did chip the ends of most of the boring bars – don't know if this was just a dodgy batch of carbide tips – I use carbide tooling fairly often so don't think it was my use of them causing the issue.

If you've never used one of these before, as with most things, there are a few little wrinkles to be aware of to get good reliable results.

1. When the boring bar are in the vertical mounting holes, make sure the tip is in line with the direction of travel of the slide in the body – otherwise the adjustment ' scale ' will not result in accurate results.

2. if like mine it has 3 grub screws in the sliding gib, I find the best results are to use the outer 2 to set the degree of tightness of the gib slide and only use the centre one to lock the head after setting. Others may disagree, but I find this works reliably for me.

otherwise much the normal rules about feed and speed with different materials apply.

Regards, Mike

 

Edited By Mike Hurley on 26/08/2021 10:14:32 Dodgy spelling

Edited By Mike Hurley on 26/08/2021 10:19:25

[JasonBModerator @jasonb]

Though you may need to run slower than the cutter/material speed as the head can become unbalanced depending on where it is set and size of too if you want to avoid excessive vibrationl.

Edited By JasonB on 26/08/2021 10:18:23

[bernard towersParticipant @bernardtowers37738]

Just done a couple of toe bearing bushes for Chevy small block, used polished carbide tips which gave fantastic finish. Oilite from bearing boys as they are only round the corner from me.

[Bill PhinnParticipant @billphinn90025]

Thanks for all the replies.

I think I'm leaning towards a set that includes an HSS cutter and/or holders, as the 62mm one does. Knowing my luck, I suspect the 30mm one John mentions might end up being that bit too small for the next job that comes along. Being able to use carbide insert boring bars like the one Andrew mentions would be an attractive addition/alternative to brazed-on carbide.

Jason, I can't do it on a lathe because I haven't got one, unless you count a wood lathe, which I have successfully done a bit of hand turning of brass knobs/thumb screws etc. and thread cutting on; boring accurate inside diameters on bushings with a hand-held tool slung over the banjo is another matter; don't ask me how I know. It's not money that's the obstacle to me getting set up with a decent lathe; it's available workshop time, which I have very little of.

With regard to the two different sorts of HSS cutters in the 62mm set, can anyone tell me when you would use the two insert ones and when you would use the one shaped like a comma?

Posted by DC31k on 26/08/2021 07:01:24:

The bush hole is 25mm dia. and the supplied HSS bit holders with the 62mm dia. head are 18mm dia. This means there can only be 7mm projection of the round toolbit (and you have to start with the head adjusted 'behind centre'. Are you able to grind the necessary cutting geometry onto a 6mm dia. toolbit within this space?

I couldn't say at present because I don't know what the necessary cutting geometry is, but if someone would be good enough to answer one of my initial questions: "could anyone point me to a source of information on achieving good grinds for boring bars specifically?" I might be in a better position to do so.

 

Edited By Bill Phinn on 26/08/2021 16:51:35

[duncan webster 1Participant @duncanwebster1]

Posted by DC31k on 26/08/2021 07:01:24:

………

It is much easier to produce a razor sharp HSS tool than a carbide one.

……..

For razor sharp high carbon steel (ie silver steel) is even better, but you have to keep the speed down to avoid spoiling the hardness. Not a problem I suggest with a small boring job on Oilite

[JasonBModerator @jasonb]

Posted by Bill Phinn on 26/08/2021 16:50:05:

With regard to the two different sorts of HSS cutters in the 62mm set, can anyone tell me when you would use the two insert ones and when you would use the one shaped like a comma?

That would be for smaller holes, looks like it would go down to about 12mm dia and you could use it upto about 20-25mm at which point the ones that hold a bit will fit down the hole.

I mostly use holders that take the triangular inserts too.

[Bill PhinnParticipant @billphinn90025]

Thanks for the further replies. I'm beginning to get the picture.

Jason, can I take it I could make the HSS bits for the 62mm type from 6mm drill blanks, which I have a couple of?

The only vids I've found that go into any detail on grinding/honing are the following by two different "Stevens":

If anyone would like to add some comments of their own, that would be helpful.

[JasonBModerator @jasonb]

I've never used a drill blank but assuming they are hard HSS all the way through then you could use that. Old milling cutter shanks work well as do broken ctr drills, they are what I use..

I'm not sure what the point about" can you grind a cutter in the space" was about. Firstly the cutters are held at 45degrees so more like 10mm projecting and 25mm within the body. Secondly if the problem was holding a short bit of HSS and not burning your fingers then a scrap of bar drilled 6mm down its end and a grub screw at the side to hold the cutter will make for easy grinding (see the Princess Royal thread) I'd also have it so the holder is approx central to the hole to start with as it will make it easier for first time use to see what's going on plus it keeps tool overhang down.

You can also easily make your own holders, 12mm bar cross drilled for a HSS bit and a grub or cap head screw up from the end is all that s needed and may be easier to get the geometry of the tool right as it's square on rather than at 45deg

The tool bit is not unlike a lathe tool or boring bit you would use in a lathe, just watch the back does not rub on small diameters (again see the boring bar discussion in the Princess Royal Thread page 16/17)

 

Edited By JasonB on 27/08/2021 08:15:53

[JasonBModerator @jasonb]

[DC31kParticipant @dc31k]

The point about the grinding was his specific requirement of a 25mm starting bore, an 18mm dia. bar and a 6mm dia. toolbit.

If the bar is 18mm dia. and centred as shown in the plan, the annular space is 3.5mm. The grind on the cutter shown looks to be roughly half of that, 2mm in plan. I do not know how easy that is, hence the question. Drawing it out as you have done is the way to see, and as you say, presenting the bar at 45 degrees gives more space. Maybe some dimensions on the toolbit would allow assessment of practicality.

Also, if necessary, the bar does not need to be concentric with the hole. It could move to the right to give more space.

[Clive Brown 1Participant @clivebrown1]

If the OP wants to save £100+ on a boring head then Harold Hall has a design and build article on his website.

link

The instructions for making it are very clear and the cost of materials is negligible.

Here's mine. It's intended to be held in an ER collet The boring tool is made from silver steel.

[Clive FosterParticipant @clivefoster55965]

Lovely drawing from Jason (as usual).

This may help with some basic dimensions and angles for clearance. Obvious overkill in the size range.

Red face department. Who cocked up a bore yesterday 'cos he didn't check! Yep, moi!

Clive

[JasonBModerator @jasonb]

Posted by DC31k on 27/08/2021 10:09:07:

Maybe some dimensions on the toolbit would allow assessment of practicality.

The dark blue line is the distance from the tip to the extent of the grinding shown in light blue and measures 5mm. As the drawing is to scale there is another 4mm or so of unground shank sticking out so it could have been ground back further without issue. I made the toolbit 32mm long, this being 1/3rd of a 100mm x 6mm dia blank toolbit with cutting allowance so you could get 3 different shape cutters from one blank

[Bill PhinnParticipant @billphinn90025]

Many thanks for the further replies and illustrations – very helpful.

So, if I've understood things right, for my particular job (bore of 25mm, and 6mm bit held at 45 degrees), the relief (should that be "rake"?) on face 1 should be about 65°, on each face 2 it will be about 10°, the compound angle at the point is 90°, and face 3 is at right angles to the shank and about half its thickness?

Yes, Jason, the drill blanks I have are Sherwood HSS, but I might also get one of the 100mm blanks when I buy the boring head.

 

Edited By Bill Phinn on 27/08/2021 18:29:08

[JasonBModerator @jasonb]

Are you sitting comfortably?

If I were grinding this I would first do the grind that forms the near vertical forward face. Although this needs a slight angle it would be best done simply grinding to half diameter and then rotating the blank approx 5 degrees for the subsequent grinding. This is what it would then look like when viewed from the end, face 3 in your annotated pic is not critical nor is the fillet but that is likely to be left by your grinder.

Next will be the grind that forms the bottom edge of the tool, this is ground at 45degrees to the tools axis and also given 5 degrees of clearance by tilting the grinding rest downwards by that amount.

The final cut is the the other near vertical face, this is ground at 40 degrees to the tool axis so that it does not rub on the cut face and with a steeper clearance of 10 degreed minimum so the back edge does not rub

See angles marked on grinder table in first photo and then more tilt of th etable

Looking at the back of the tool you will have the 2nd & 3rd grind meeting at an 85degree angle and the two clearance angles will also show.

As I said face 3 is not critical and could just as easily be ground like this

None of the angles are set in stone so a bit either way won't hurt, the main thing to watch is that the back of the tool does not rub and you are clear where the red arrow points, as hole sizes get smaller you will need to alter the grind and make the 10deg steeper to maintain clearance or even grind a curved surface

[Bill PhinnParticipant @billphinn90025]

Many thanks indeed!

You were right to ask if I was sitting comfortably. I needed to be.

I can't deny I also ran your sketches etc. past my better half, who instinctively understands geometrical stuff much better than I do and, unlike me, can draw and easily visualize how things will look from different angles.

I've started the grind on an old drill bit. I'm not too confident I'll hit quite the right angles freehanding it on the grinder, but I might cheat slightly on the finished item and use my crocker-type graver honing jig to set the side angles more precisely after roughing them on the grinder.

I'm beginning to wonder now whether I'm getting a boring head primarily in order to complete a particular job or in order to test and improve my ability to grind and hone single point cutting tools. The second objective now seems the more important of the two.

[JasonBModerator @jasonb]

What are you intending to do about holding the Oilite bush for machining?

[Bill PhinnParticipant @billphinn90025]

Like in the photo, or possibly with a vee block front and back and with the bushing raised up slightly on parallels to bring it level with the top of the vee block[s].

One concern I have is whether I can hold the bushing firmly enough without the vice jaws squeezing it out of round slightly. I intend to take very light cuts.

I'm assuming edge-finding for boring is typically done with a DTI, not a mechanical edge finder/wobbler.

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