Boring bar mounting

I’ve recently bought 6mm and 7mm boring bars for CCMT style inserts and wondered how folks mounts them. I need to jack them up to get on centre in my four way toolpost so to avoid using any packing I thought of making a block for each of them. Just wondered if anyone has done anything similar. The bars are rounded with flat top and bottom.

Vic,

How's this for an idea?

On the basis your tool holder can accomodate 1/2"-12mm tooling, take a piece of square bar, of sufficient length to accomodate your boring bar. Drill through the centre lengthwise 6-7 mm to take your boring bar. Drill and tap for say M3 grub screws to hold the boring bar in place, then secure in tool holder. Just make sure the grub screws are not aligned with the tool holder securing screws....

With at least one threading bar, dia ~9mm IIRC, that I bought the cutting tip was exactly on centre line if the bar was held in a collet, which meant that I could easily use it for thread milling. If the same is true of boring bars (and they're nearly identical) then a hole bored on lathe centre line should do the job nicely. So clamp a lump of steel in the 4way TP and drill/ream it from the headstock. I have a couple of large diameter home made boring bard to take TC inserts as well, with a separate block that bolted to the topslide bored out on centreline.

Thanks John, that was one of my thoughts. The only problem is I may not have the height to accommodate the clamp screws. My toolpost easily takes 1/2 shanks so I’ll have to take some careful measurements.

Interesting idea there John, I’ll have to have a think about that and check my stock bins!

Vic, the clamping screws need only be short enough to go thru' the "wall thickness" of the bored square bar, better if they dont protrude or are proud of the surface...M3 x 3 grubs? Or else if the hole was reamed to suit the boring bar o/d, and then s,it saw the length, the tp holder clamp screws could double up to hold and compress the bar holder...no need for extra screws..

JH's suggestion is a variation on the theme...same result, different way of achieving.

Edited By John Rudd on 22/10/2018 19:24:57

Boring bars are not hard steel and mark easily when clamped by screws acting directly on the surface. Since it is good practice to only have them protruding just enough they are frequently repositioned and the surface can get chewed up. A clamping system that avoids direct contact by rotating screws should be used. If you drill a block and slot one side then the tool post clamping screws will squeeze the block to clamp the bar and keep the bar in good condition. The clamping block can be cleaned up or replaced as it becomes necessary.

Martin C

I made a similar holder for a small Sandvik boring bar. In my case, the holder was round but the priciple is the same. The boring bar is a tight sliding fit in the holder and if I remember correctly the bar had a chamfer on the rear end. I cross-drilled the holder at an angle of 5° or so and Loctited a silver steel pin through it. This ensures that the tip is presented to the work at the correct cutting angle. ( Make sure youre get the angle of rotation the right way round. ) There is a small allen head screw securing the bar in the holder and a flat milled along the top where the toolpost bolts bear upon it. End result:

John

Edited By John Hinkley on 22/10/2018 19:48:28

Or you can get square holders like these. They have a slot on one side that allows the bar to be clamped.

I've got a couple of 5/16" and 3/8" diameter boring bars that take 1/8" and 3/16" square-section HSS bits. They have a straight transverse location at one end and a 45 deg angled one at t'other, and a slotted square-section sleeve of the sort Martin describes to mount them at whatever protrusion length will cut the required bore depth.

You can adjust cutting rake to some extent by rotating the bar in the sleeve, and when you clamp it it's held tight.

I've so far (about 18 years) always used the angled bit location, since that way the bit clears the bore or bottoms out before the bar does.

By taking off the sleeve and fitting a long bit you can stick it in the chuck and use it as a handy flycutter, too.

These two do all the boring and flycutting I've ever needed. I've had to replace one that I damaged a long time ago by severe overtightening, but apart from that I can't see me wanting anything else.

A good example in 16mm size is Ebay Item 302924490432 .

I didn't know they were available to buy! Just seemed like a good idea.

Martin C

Nice find Dave, shame they don’t do a 7mm.

There is an AliExpress pic of one on ‘goggle’ images....

I just use packing strips under the boring bar. A few bits of 1/8" x 1/2" steel flat bar are handy so you don't end up with fiddly stacks of too many thin shims. With the larger diameter boring bars, if I run out of " head room" to raise the boring bar high enough in the rather narrow slot in the standard Myford 4-way toolpost I stick a pair of the above size packing strips between the toolpost and topslide, thus lifting the whole toolpost up by 1/8".

Good quality boring bars are made of stout enough steel that they don't scar up from the clamping screws. I have also domed the ends of my clamping screws slightly and this helps.

I need to replace 3 of them Sandviks for internal O ring grooves. They cut really well but dont like the price of them for just hss.
Beauty of that design is you can change a cutter over and retain zero though i do use two Sandvik holders.

Posted by Jon on 22/10/2018 22:40:47:

I need to replace 3 of them Sandviks for internal O ring grooves. They cut really well but dont like the price of them for just hss.

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I must have been lucky and got the last of some NOS or similar. Just looked it up and I paid £12.45 in 2016 for it. As you say, it cuts exceedingly well and retains its edge. I suspect O-ring groove tools might be a little more expensive, though.

John

As I don't have a quick-change toolpost, just a four-way, I made a dedicated post for boring bars. It is simply a lump of cast iron, bored and reamed in situ. There's a 1/2" hole and an 8mm hole to suit the bars I use. The securing screws are offset and and push against a bevelled pad (cotter?) that bears on the bar.

I use holders similar to the Arc ones illustrated above in my 4 way tool post for my round shanked boring bars, excepting one that sits on a little V block.

Ian S C

Did just what you are suggesting, cut a rebate in a bit of 1/2" square bar, so that theoretically the tip would be on centre height. The flat on the boring bar sits on the rebate, and the clamp screws operate on the top flat.

Almost all of my tools go into the Fourway Toolpost in this way, to minimise shimming.

If you are worried about marking the bar, just put a bit of steel on the top, to take the clamp screws.

Have worked like this for years!

Howard