Mill Boring Simplified.

[dapoling]

I have seen many times with some having trouble with boring and having them repeat.

We must respect the influences upon bores when prepping holes for boring and during the final bore as well.

I have been able to consistently produce bores with in .0002-.0003 in roundness and size for requirements of +/-.0005 and can be used effectively for bores with larger tolerances as well, thus these bores do not need to be honed unless the customers requires it.

1. Clamping pressure is usually the major culprit in out of round bores thus find them oversized when removed from the machine.
2. Ensure a close tolerance bore is done at the end of the process.
3. Unclamp and re-clamp using a torque wrench. **
4. Rough and finish the bore to .005-.01 undersize before boring.
5. If you have a tight true positioning call out then use a G60 in older machines or machines that are a little sloppy will help greatly in locating your bore even when you have to change out inserts and reset.
6. Feeds and Speeds, I uses .0025 per rev and usually never went above 750 rpm.
7. Use a fine bore cycle G98G85R.1Z-1.F2.L2 Start with an L2 and add another repeat when the bore size starts shrinking up, adjust up to L5 and then replace the insert and set back to L2 again. (this will reduce adjustments of the boring head and replacing inserts)
8. Use a bore or air gage to check for size and roundness and again after being unclamped to ensure your clamping pressure is good.


** When clamping with a vise, use a torque wrench and set to the lightest setting that will hold the part. (Note many will say that they can repeat clamping pressure by many methods by experience and even using 1, 2 or 3 fingers or even marking the vise.
Run your own test with a torque wrench and see.

[Geof]

Originally Posted by dapoling ....** When clamping with a vise, use a torque wrench and set to the lightest setting that will hold the part. (Note many will say that they can repeat clamping pressure by many methods by experience and even using 1, 2 or 3 fingers or even marking the vise. Run your own test with a torque wrench and see.

This is a very good point. It is difficult to the point of impossible to do it just by feel. And even with a torque wrench I have encountered operators who go right past the click and over-tighten.

I found the whrench and gauge in the picture at Westec a few years back; called THE REPEATER. The gauge has a one square inch piston so the psi reading equates directly to clamping force in pounds; the wrench has a slip clutch that just spins once the set torque is reached. Very repeatable and pretty well impossible to overtighten the vise.

[Oldmanandhistoy]

Originally Posted by Geof Very repeatable and pretty well impossible to overtighten the vise.

Hi,

One of my biggest faults is my compulsion to over tighten everything and the answer sees obvious to just use a torque wrench. Then the questions is how tight is tight enough? The thought of hurling a chunk of steel across the workshop just because I didn’t tighten my vice enough does not appeal to me.

So how tight is tight enough? Not an easy if not impossible question to answer as it depends greatly on type of jaws and clamping area amongst other things.

John

[dapoling]

Originally Posted by Oldmanandhistoy Hi, One of my biggest faults is my compulsion to over tighten everything and the answer sees obvious to just use a torque wrench. Then the questions is how tight is tight enough? The thought of hurling a chunk of steel across the workshop just because I didn’t tighten my vice enough does not appeal to me. So how tight is tight enough? Not an easy if not impossible question to answer as it depends greatly on type of jaws and clamping area amongst other things. John

John good question I find that I start with 60 Inch Lbs to begin with (this will vary with type and amount of material) and I do it as a unclamp and reclamp just before boring removing .005-.01 of material.
To verify if this while the material in still in the vise after being bored use a bore gage to measure run out at 90 degrees of each other and note what out of roundness you have, release the part and check again and you will have an idea of the amount of movement has occurred.

If it is greater then you want the lighten the clamping pressure if you feel the part is not being held well enough then tighten and recheck the part again.

Geof nice tool there as it seem that would have an affordable price and adequate accuracy.