Boring bar set up

I had my first go at boring today. It went ok but I've no idea if my set up was ok. The boring bar I have is round. What angle should the insert be set at, should the top of the insert be horizontal? It needed a lot of packing to get it to centre line. Is this ok or am I missing something?

Angle of the tip will really depend on the smallest diameter you will be boring as the edge of the tool needs to clear the inside of the hole. So for finishing a 50mm hole it could be set flat, a 20mm hole would need the insert pointing downwards. In all cases the corner of the tip that makes contact is set to ctr height.

Not a good idea to hold the tool like you have either use a tool holder with a Vee bottom, one for holding round tools or get a bit of square bar and ream a hole to match cutter shank down the length of it, slit one side so that when held in a standard tool holder the square will close down onto the round bar shank.

I think you may not be adjusting the centre height by the adjustment on the holder? The advantage of the square holder Jason describes is that the cutter angle will stay-put in the square holder, if the holder is a good fit, when removed from the tool holder.

From the photo's I would guess that you have been unlucky to get a boring bar with a round shank. If that is so, then the normal angle of the insert should be tilted down about 7 degrees, with the tip at or slightly above the spindle centre line, (+0.010" /+ 0.25mm would be fine for that size of bar). Most of the bars on the market have flats which preset the angle of dip for the insert.

It looks a bit odd having to pack a toolholder as the whole point of a QCTP is to be able to adjust the height, perhaps it could do with a pad under the toolpost to raise it a bit so that it can function as it is supposed to. I thought it might be worth adding images of the items discussed thus far:-

Top left is a toolholder designed for round boring bars with a V groove at the bottom (also available for the Aloris style toolpost) . Top right is the split sleeve to take a round boring bar. Bottom left another style of holder for larger boring bars. Bottom right sketch showing the common down angle for boring bar mounting which provides the front clearance.

John

Even if you do have to pack your tool up rather than a whole stack of thin packing use a mix of sizes so you reduce the total number eg replace 3 or 4 of those hack saw blades with a bit of 1/8" or 3mm flat bar.

The fact the knurled adjusting wheel on your tool holder is down to it's max suggests the tool post is too small or as John says needs packing up.

This pic shows how the angle of tilt gets less as the bar diameter and therefor minimum hole size increases

And this some of the square holders with bars, you could drill the hole offset to thetop which would also put the bar higher in the tool holder.

The whole point of a QCTP is to able to adjust the height.

Is it? Really? Wouldn't that be called a Height Adjustable Tool Holder?

The point of a QCTP is to make swapping tools as quick and easy as possible. That proves to be very useful(essential really) when even a simple part can need 3 tools to produce its features.

The height adjustment is a bonus from how most designs achieve that speed.

Yes, quite so. It's nice to know someone read that which I wrote earlier Perhaps I should have said - The whole point of a QCTP is to allow easy swapping of tools and as a tertiary adjunct (sorry I've been watching Star Trek Voyager again!) allows for the tool height to be easily set without resorting to packing.

John

Ah - Seven of Nine!

Me Too

Regards,

IanT

Thanks for all the input. I think in going to have a go at making a sleeve out of square stock. It will allow me to raise it up so get rid of the packing. I also like the idea of adjusting the angle of attack to squeeze it into smaller holes. Would I be able to secure it with some grub screws rather than slitting the whole block?

Yes, you could secure the bar with grub screws but the slit is much better. It is only a matter of a few strokes with a hacksaw, nothing too precise. The slot ensures that when clamped up maximum pressure is transferred from the tool holder screws to the boring bar preventing any chance of rotation when in use. Grub-screws provide only 2 or 3 point contacts.

This is one I made many years ago from a bit of 1/2" square BMS bar to take a 3/8" boring bar. The slot is just hacksawed. The only tricky bit is setting the bar to run true in the 4-jaw chuck.

John

Edit: Add photo

Edited By Journeyman on 31/10/2021 15:29:33

As parallelism ir more critical than concentricity for that type of holder, it may be easier to use the bench-drill or mill to form the hole from a carefully marked-out centre-spot.

Clamp the bar vertically in a V-block or Keets Angle-plate and clamp that to the machine table, ensuring the hole will go though into a slot or central hole of the table.

Or the old dodge - hold the square bar in a temporary split-collet made from round bar, gripped in the 3-jaw chuck with the split half-way between two jaws.

If one is unable to make the hole perfectly in line with the holder, there is always the opportunity to correct this afterwards - as long as there is sufficient material to make that/those corrections and the operator has a sufficiently long straight rod which will fit through the hole (and probably a milling machine).