Bars for Boring Head

[adamcowmanParticipant @adamcowman]

How ya lads

Recently got myself a good quality boring head for my mill at a yard sale recently and want to get it setup.

it came with a load of toolbars that take hss toolbits but I want to get a set of bars with carbide inserts. Trouble is I can’t figure which bars to buy size wise. The seller told me the boring head took 3/4” tools, which makes sense cos it’s from the imperial era. But measuring the holes they all come out at around 18.6 – 18.7mm. So do I get standard 18mm bars or try find 3/4” ones. My tooling supplier can’t get me any 3/4” as he only stocks 18mm and 20mm.

I could modify the bars but that’s a hassle I’d rather avoid. Leaning towards buying 18mm bars that the head can clamp on the flat so should be no play/riggidity issues.
Im relatively new to machining so never used a boring head before and don’t want to spend money on the wrong tools.

Thanks.

[JasonBModerator @jasonb]

Well you could grind up a bit of Carbide and put that in your holders they won’t know the difference between HSS or Carbide. Old milling cutter shanks work well enough or just buy blanks.

Do you really need the bars to be that big? For a lot of work you could simply sleeve the bore down to 12mm or 1/2″ and then buy the insert holders made specifically for boring heads. I mostly use these

Have you actually tried something exactly 3/4″ in the holes, I expect they will fit.

[JohnFParticipant @johnf59703]

The sizes you quoted are odd ball !  3/4″ is 19.05mm so aim for 19mm or something you can turn down to 3/4″

It may help to know what make of boring head is it ? Plus a photo of what accessories you have with it.

John

[adamcowmanParticipant @adamcowman]

Ill try attach some pics here now. No brand on the head itself and only a part number on the box. The head itself is quite big compared to a modern one with 18mm holes.

Never thought to make a sleeve i suppose it would be the handiest thing to do really. Only picked it up yesterday so havent got to try much in it yet. The bars that came with it fit of cource but a 19mm drill bit i have doesnt the holes. 

[David George 1Participant @davidgeorge1]

I have Many diferent boring bars for my boring head. I have silver steel turned down to match the boring head which gives a more solid bar for large bored holes. These have holes drilled for HSS or carbide round bar with grub screws. Others have carbide tips brazed on to act like bought bars and to lengths which suit job in hand.

David

 

 

 

[FulmenParticipant @fulmen]

I just use small indexable boring bars from the lathe in a sleeve.

[Nigel Graham 2Participant @nigelgraham2]

Adam –

Aha! That looks very much the same as mine, apparently “made in France” for Colchester [Tools ??]!

I will examine mine and see what that might reveal…… I’ll try for diameters and any Part or Serial numbers, on it and its rather nice wooden box.

I’m not sure what the arbor taper is on yours. Mine is R8, to fit my Myford mill (also the standard for Bridgeport among many others).

[adamcowmanParticipant @adamcowman]

Please do  Nigel that would be a great help

Taper on mine is a iso40 taper but ive an R8 one to replace it for my bridgeport.

[David George 1Participant @davidgeorge1]

Hi Adam if you bought some 20mm diameter shank boring bars they are machinable on the location diameter. I would hold them in my four jaw chuck and using a dial indicator set them true and maybe some packing on the jaws, to ensure the cutting tip is not damaged, and with a centre in the end just turn them to match the diameter of the holder using possibly a carbide turning tool.

David

[JasonBModerator @jasonb]

Or just buy a 3/4″ one intended for the US market but as that is only likely to go down to about a 1″ hole you will still need something for the smaller holes. The smaller bars also don’t unbalance the head so much which means you can run the head faster though still they generally need to run below optimum cutting speed.

[Clive FosterParticipant @clivefoster55965]

Certainly looks like a French made Gamet boring head.

Enco in the USA sold a lot of these in three or four sizes so it may be worth a trawl around the Americentric sites for data.

General opinion seems to be that these are a solid, workday, piece of kit.

Clive

[Julie AnnParticipant @julieann]

While I use inserts extensively for turning, for boring heads I prefer to use HSS toolbits as they can be easily adjusted for clearance, and to reduce any chatter:

Unbalanced boring heads will not run fast enough to really benefit from using inserts.

Julie

[DC31kParticipant @dc31k]

FWIW, Gloster Tooling list a set of 3/4″ shank inserted boring bars (identical to the Glanze ones sold by Chronos, but larger shank).

[PeteParticipant @pete41194]

If your new to boring on a mill Adam maybe some of this will help. Given the rigidity of Bridgeport type mills, any boring head capable of using 3/4″ boring bars is getting up there for what’s actually usable. Unless you really are needing to bore very large and deep holes, I’d go with what others have said and use adapter sleeves to allow those smaller diameter boring bars to be used. There’s hardened and ground commercial sleeves available to do exactly that. But shop made unhardened steel sleeves would still be fine. Just make sure they have either a hole or slot in them so the boring heads set screw bears directly against the usual alignment flat the better made boring bars will already have.

I’d also very much agree with Julie Ann’s point about carbide and trying to spin any larger and unbalanced head at the speed where carbide provides the best surface finish. If you don’t already know and depending on your boring heads exact design. There’s numerous Youtube videos and forum posts either saying they do or trying to give user information to others that all three set screws should be used to lock the boring heads slide after an adjustment. That’s not how there designed to be used. The outer two set screws are only used to set the gib adjustment to a smooth but almost zero clearance fit. The center set screw is then used to fully lock the slide after an adjustment. You’ll also have to double check your heads dial markings. Some are set up to show the diameter change in the hole size any slide adjustment will produce, and some will show radius which will be half of what the actual hole size increase will be.

In my opinion a mill is seriously lacking in what it can really do without a good boring head. But there not quite as easy to reliably hit your expected dimensions as it seems. Boring is much like outside turning or boring on a lathe. Ideally you want to divide the remaining material to be taken off in at least 3 equal depths of cut while measuring the exact amount removed on the first two cuts. That allows you to compensate for any deflection in the tool or mill head. With that information, you should then be able to make the proper last adjustment with a high expectation of hitting the size you want. For anything highly precise like a slip or press fit for bearings, a lot is going to depend on what you have available to even reliably measure hole sizes. Some dedicated practice with decent telescoping gauges and a micrometer can usually get you within a couple of 10ths. Those cheaper off shore sets of telescoping gauges usually don’t work smoothly enough for those levels of accuracy without some work de-burring the internal slots and parts and checking for straightness of the telescoping parts. But to adjust the boring head to it’s final size on anything that critical, I generally don’t use the dial at all. Instead I’ll use a .0001″ or metric equivalent dial indicator or dti against the end of the boring heads slide that I’m going to be moving that slide towards. In that case the indicator will only display the amount of slide offset your adjusting to as a radius change, or half of what the finished hole size change will be. And if it were me, I’d definitely practice using your new boring head on scrap material first and trying to hit exact sizes before trying to do the same with real parts that might have a much higher value.

[adamcowmanParticipant @adamcowman]

Thanks to everyone for their input.

Like I say im relatively new to milling and have never used a boring head before, so while im learning I want to eliminate as many variables as possible.

For instance i just want to use carbide inserts, A: cos ive got loads for the lathe and B: trying to grind a good toolbit is a job in and of itself for a novice. Ill take it one step at a time and keep trying new techniques.

Ill probably buy a set of 1/2″ bars and sleeve them for now purely cos I cant get any 3/4″ ones here in Ireland. The head with 3/4″ holes probably wouldnt be my first choice but this just came up at extremely good money, and its also a facing head which may come in handy. id say will encounter some large bores in the future given what i work on.

[Julie AnnParticipant @julieann]

The case for the prosecution:

Dreadful chatter in the bores on my cylinder using a 25mm insert boring bar machined down to 22mm to fit the boring head. Nothing I tried in terms of feeds, speeds and different inserts made any difference to the chatter.

The case for the defence:

A much better finish on the liners using a similar boring setup but with a length of EN8 steel as a boring bar and a short length of round HSS for the tool.

On a positive note the chatter in the cylinder bores acted as a key for the Loctite used to hold the liners in place. The liner bores measure round and parallel to within a few tenths. The setup for boring the liners used a horizontal mill as a poor girls horizontal borer:

Grinding HSS toolbits is simple, just a few faces at angles none of which are critical. If there is an issue it’s easy to tweak the toolbit and see what happens. All my HSS turning and boring tools are ground freehand. Fancy kit to hold the toolbit at precise angles is not needed.

Julie

[Nigel Graham 2Participant @nigelgraham2]

Right, now I’ve managed to penetrate this forum’s digital defenses….

My boring-head is in a box branded merely “EMCO”… which doesn’t help much but does look the right box for it.

The head has a small circular label saying:

“GMT. Made in France for Gamet Products, Colchester”.

So not for the American market, at least not this specimen.

As for the boring-bar holes… all 0.500″ diameter.

 

Worry thee not about the curious diameters on thine.

Nor the replies trying to complicate a simple problem.

Just make a close-fitting, mild-steel sleeve of that 18.6mm o.d., bored or drilled and reamed to take readily-available, smaller diameter tooling.

OR:

Make a boring-bar that fits the head as it is, to take small (say, 6mm / 1/4″ dia) HSS bits. 

Far simpler, easier and quicker than trying to find 18-point-whatsit-mm tools that don’t exist, or trying to machine 3/4″ tools down so they don’t fit anything else; but I do wonder why that odd size. Perhaps the original manufacturers did supply their own tooling for it, at 18.6mm dia.

[JasonBModerator @jasonb]

It is not just speed, the other advantage of Carbide it it will cope better with any hardspots or impurities in a casting which would otherwise knock the edge straight off a HSS tool.

I also take advantage of the unused hole in the head to hold bits of 1/2″ material which helps counterbalance any offset of head and tool so you can run a bit faster without the mill jumping along the bench

[Julie AnnParticipant @julieann]

My mills won’t fit on a bench.

Julie

[PlasmaParticipant @plasma]

Lol Julie, what milling machines are you toting there?

I have a senior horizontal and a shaftsbury vertical jig borer. Enough for my meagre efforts though.

Mick

[Plasma]

On Plasma Said:

Lol Julie, what milling machines are you toting there?

Vertical mill is a Bridgeport Series 1. Even with it on the floor I am on tippy toes in order to reach the drawbar. Wearing heels is not really appropriate in the workshop. Also have an old A&S universal horizontal. At 3500lbs it would need a very strong bench, and I have no means of lifting it onto same.

Julie

[PeteParticipant @pete41194]

Depending on your available and open floor space Julie, building up a U shaped set of what are called Machine Tool Duckboards in North America across the front and on each side of your mill sounds like just what you need. In general there an assembled frame work of 2″ x 2″ wood with open spaces between each row for any swarf, although for gaining the extra height, I’ve also seen them built using common 2″ x 4″ construction grade lumber. There also much more comfortable to stand on for long periods of time than bare concrete. But they can be a tripping hazard until you get used to where they are.

My own BP clone is classed as a 3/4 sized or baby BP, so the draw bar is only 6″ – 8″ above eye level. That’s fortunate because I’d draw the line at having to wear heels to reach that draw bar. 🤣

[PlasmaParticipant @plasma]

The duck boarding is a good idea, I’m fortunate enough to be on the tall side so don’t need it.

Bear in mind the gaps in the planking would definitely trap high heels lol.

We seem to have strayed from a discussion on tooling.

Mick

[Julie Ann]

On Julie Ann Said:

While I use inserts extensively for turning, for boring heads I prefer to use HSS toolbits as they can be easily adjusted for clearance, and to reduce any chatter:

Unbalanced boring heads will not run fast enough to really benefit from using inserts.

Julie

You make some good points. If necessary you could always use part of an old broken carbide end mill in place of HSS if you needed to.

I have a tangential turning tool in which I use HSS but I do have a piece of carbide I can use if I need to turn anything hard with it.

[Vic]

On Vic Said:

….If necessary you could always use part of an old broken carbide end mill in place of HSS if you needed to.

Good point, I keep broken/worn carbide milling cutters as they have a recycling value. I had an agreement with a local industrial supplier of a £10 discount per kg of carbide.

Julie

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